Method and device for determining defects and / or material characteristics of a workpiece

Abstract

The invention relates to a method for determining one or more defects (102) in a workpiece (104) and / or for determining at least one characteristic (K) of the material of the workpiece (104), having the following steps: - pressing an indentation element (112), in particular a first indentation element, into the surface (114) of the workpiece (104) with a static press-in force (Fs) in order to plastically deform the workpiece (104) by means of the indentation element (112) in order to produce a plastically deformed workpiece indentation (118); and / or - detecting the shape (124), in particular the three-dimensional shape (124), of the plastically deformed workpiece indentation (118); and / or - supplying the indentation element (112), in the pressed-in state, with an oscillating force (Fo), having a force amplitude and / or a force frequency, in addition to or alternatively to the static press-in force (Fs) during and / or after the step of pressing the indentation element (112) into the surface (114) of the workpiece (104). The invention also relates to a device (100) for determining one or more defects (102) in a workpiece (104) and / or for determining at least one characteristic (K) of the material of the workpiece (104).

Description

[0001] Method and device for determining defects and / or material parameters of a workpiece

[0002] The present invention relates to a method and a device for determining one or more defects in a workpiece and / or for determining at least one material characteristic of a material of the workpiece.

[0003] The methods and devices disclosed in the prior art for determining defects or material parameters in a workpiece are still expensive, time-consuming, and complex in sample production and process control. Quality assurance is therefore still complex, which often makes the use of certain components, e.g., those manufactured by 3D printing, uneconomical in highly safety-sensitive areas such as aviation.

[0004] Such devices and methods are already known from the state of the art.

[0005] Accordingly, DE 102011115519 A1 shows a generic method and a generic device.

[0006] The present invention is therefore based on the object of providing, in particular, a method and a device for determining one or more defects in a workpiece and / or for determining at least one material characteristic of a material of the workpiece, which are preferably more cost-effective, faster and easier to handle.

[0007] This object is achieved according to the invention by the features of independent claim 1. Advantageous developments of the invention are described in the dependent claims.

[0008] A method according to the invention can be configured and set up to determine one or more defects in a workpiece. Additionally or alternatively, the method according to the invention can be configured and set up to determine at least one material characteristic of a material of the workpiece and can comprise the following steps.

[0009] First, an indentation body can be pressed into a surface of the workpiece with a static indentation force to plastically deform the workpiece by means of the indentation body, thereby creating a plastically deformed workpiece indentation. The indentation body can, in particular, be a first indentation body.

[0010] Additionally or alternatively, the shape of the plastically deformed workpiece indentation can be recorded. The shape can, in particular, be a three-dimensional shape.

[0011] Additionally or alternatively, it can be provided that the pressing body in the pressed-in state is subjected to an oscillating force in addition to the static pressing force.

[0012] Furthermore, it may be conceivable that the oscillating force is applied to the indentation body in the indented state as an alternative to the static indentation force.

[0013] The application of the oscillating force to the indenter in the indented state in addition to or alternatively to the static indentation force can take place during the step of pressing the indenter into the surface of the workpiece.

[0014] Additionally or alternatively, the application of the oscillating force to the indentation body in the pressed-in state can be carried out in addition to or alternatively to the static indentation force after the step of pressing the indentation body into the surface of the workpiece.

[0015] The steps of detecting the shape and applying an oscillating force to the indenter in the indented state can be carried out independently of each other in time.

[0016] In other words, the step of detecting the shape can take place before the step of applying pressure to the indentation body or vice versa.

[0017] The oscillating force may have a force amplitude. Additionally or alternatively, the oscillating force may have a force frequency.

[0018] Defects in the workpiece can be surface defects and / or volume defects. Examples of surface defects include cracks, pores, scratches, extrusions or intrusions, and / or notches on the workpiece surface.

[0019] Volume defects, on the other hand, can be shrinkage cavities or other preferably internal hollow spaces or open spaces or structural inhomogeneities; gas bubbles; inclusions; cracks; notches and / or pores inside the workpiece.

[0020] A workpiece can be a ready-to-use component that can be set up and configured for immediate installation and use in a respective product.

[0021] An example could be a 3D-printed metal component for use in aviation.

[0022] Alternatively, the workpiece can also be a semi-finished product, which can be understood as a prefabricated raw material and starting workpiece or as a semi-finished product in its simplest form.

[0023] Alternatively, the workpiece can also be a sample made of the respective material specifically for the process described above.

[0024] A material parameter can be understood as a physical parameter by which the material can be characterized and quantified. Preferably, the material parameter can be a mechanical material parameter.

[0025] Examples of a mechanical material property can be one or more of the following material properties: Young's modulus, yield strength, proof strength, tensile strength, fatigue strength, yield stress, elongation at break, uniform elongation or hardness.

[0026] In its most general form, the material of the workpiece can be a ductile, preferably metallic, material that allows reproducible and defined plastic deformation (for example, with several indentation processes at different positions on the surface of the workpiece).

[0027] A material can be considered ductile if it can undergo permanent plastic deformation under shear stress before fracture or macroscopic separation. A material parameter that characterizes ductility is the elongation at break, which can preferably range from approximately 0.1% to approximately 30%.

[0028] Metals can preferably be aluminum, iron, titanium, or magnesium. Furthermore, it can be advantageous for the metals to be present in the form of metal alloys such as aluminum alloys, iron alloys such as steel or cast iron, titanium alloys, or magnesium alloys.

[0029] The following steel alloys should preferably be used: unalloyed steels, alloyed steels or stainless steels.

[0030] The steel alloys can be further divided into: structural steel, case-hardening steel, tempering steel, nitriding steel, tool steel, stainless steel or acid-resistant steel.

[0031] The indentation body may preferably be a component of an indentation element region of an indentation element, by means of which the indentation body can be pressed into a surface of the workpiece.

[0032] The indentation element and the indentation body can be designed as a one-piece indentation unit so that at the macroscopic level there is no separating surface between the indentation element and the indentation body.

[0033] Alternatively, the pressing element and pressing body can be designed in two parts, so that both the pressing element can have a separate pressing element body and the pressing body itself can have a separate body.

[0034] In this case, the indentation body can be held and secured by the indentation element. The securing can be detachable.

[0035] The indentation body is the portion of the indentation element that penetrates the surface of the workpiece and thus creates the workpiece indentation as described above. In other words, the indentation body can also be referred to as the indenter.

[0036] The indentation direction is preferably perpendicular to the surface of the workpiece. The indentation body can preferably have a conical shape, with a tip facing the workpiece surface in the indentation direction.

[0037] The tip of the indenter can advantageously be rounded. This minimizes mechanical stress peaks due to a notch effect in the resulting base of the workpiece indentation, allowing the process described above to be carried out more precisely.

[0038] Alternatively, the indenter may have a spherical shape, a pyramidal shape, or a tetrahedral shape.

[0039] The indenter is preferably made of diamond. Natural or synthetic diamonds are conceivable. Other suitable materials such as boron nitride can also be used.

[0040] The shape of the workpiece indentation can be captured optically or tactilely. Preferably, the capture is performed optically using a white-light interferometer method to generate the captured shape or three-dimensional shape.

[0041] This captured shape or three-dimensional shape can then be transferred to an evaluation device for further processing.

[0042] The static indentation force can have a force vector only in the indentation direction and a force magnitude which is transmitted to the indentation element by means of a force generator and by means of which the indentation body is then pressed into the surface of the workpiece.

[0043] The force vector of the indentation force should be aligned orthogonally to the surface of the workpiece, as should the longitudinal axis of the indentation element and the indentation body.

[0044] When the force is applied, a movement along the longitudinal axis of the indentation element or indentation body occurs, but this movement is so slow that it can still be described as a quasi-static force application to create the workpiece indentation. The oscillating indentation force can have a force vector in and against the indentation direction and a force magnitude that changes periodically over time, for example, in the form of a sine or cosine function.

[0045] The amount of force can be periodically modulated in terms of force frequency and / or force amplitude.

[0046] The combination of the indentation process (with the static indentation force) to generate the plastically deformed workpiece indentation and the application of an oscillating force to the indentation body in the indented state ensures a significantly accelerated analysis of several testing methods relevant to component quality.

[0047] In addition, due to the speed of the determination method explained above, a larger number of components (for example in series production) can also be assessed.

[0048] In addition, the detected shape of the plastically deformed workpiece indentation can be compared with a simulated shape of a plastically deformed workpiece indentation according to a material deformation model of the workpiece.

[0049] The detected shape may in particular be a detected three-dimensional shape, whereas the simulated shape may in particular be a simulated three-dimensional shape.

[0050] Following the comparison, at least one material characteristic of the material of the workpiece can be determined from the comparison.

[0051] The simulated shape of the plastically deformed workpiece indentation is based on a so-called flow curve of the material, whereby the flow curve is mathematically defined by several material input parameters (to characterize the plastic material behavior).

[0052] The flow curve, together with the real boundary conditions of the previous step of indenting the indenter (such as static indentation force, indentation depth, and the shape and geometry of the indenter), is processed in a finite element simulation (according to the material deformation model), from which the simulated shape of the plastically deformed workpiece indentation is calculated. This finite element simulation can be stored as a corresponding software application on a storage unit of the evaluation device and executed by a processing unit of the evaluation device.

[0053] By varying the material input parameters, the evaluation device can iteratively minimize the difference between the simulated shape of the plastically deformed workpiece indentation and the actually recorded shape of the plastically deformed workpiece indentation (objective function) using an optimization algorithm using the sum of squares method.

[0054] The optimization algorithm ends when the objective function converges and falls below a defined limit.

[0055] This limit value can preferably be approximately 5% deviation for three-dimensional simulation and approximately 3% deviation for two-dimensional simulation.

[0056] The flow curve calculated by convergence (with the final calculated material input parameters) can be converted into a technical stress-strain curve and from this the following comparative parameters can be determined based on the tensile test:

[0057] - Comparative yield strength R p o,2',

[0058] - Comparative tensile strength R m;

[0059] - hardening behavior; and / or

[0060] - qualitative determination of ductility for specific materials.

[0061] As explained above, the method can also be used to determine one or more defects in the workpiece.

[0062] First, the indenter body is subjected to the oscillating force in the pressed-in state to excite the oscillation of the workpiece.

[0063] The oscillation excitation is preferably provided by an oscillation generator, so that the workpiece begins to oscillate at a natural frequency and amplitude as a type of oscillation response. The oscillation generator can be designed as an ultrasonic or piezoelectric generator.

[0064] Subsequently, an oscillation response of the workpiece can be recorded in response to the oscillation excitation of the workpiece.

[0065] This detection can preferably be carried out with an oscillation detection device, which can also be connected to the evaluation device for evaluating the detected oscillation responses.

[0066] The oscillation detection device may, for example, comprise a piezo-based acceleration or speed sensor.

[0067] Since the workpiece shape and the workpiece material in particular have a great influence on the workpiece natural frequency and the workpiece natural amplitude, each individual workpiece can give a corresponding individual oscillation response to the oscillation excitation.

[0068] A workpiece for the defect detection process can preferably be a finished, ready-to-use component. An example of such a component could be a series-produced part.

[0069] The recorded oscillation response can then be used to determine one or more defects in the workpiece.

[0070] In addition to the workpiece shape and the workpiece material, the defects in the workpiece can have a major influence on the workpiece natural frequency or its natural frequency response and the workpiece natural amplitude or its natural amplitude response.

[0071] In this respect, a correspondingly individually recorded oscillation response can be recorded for each individual workpiece, depending on the defects present in the workpiece or in the case of no defects. The determining step preferably comprises comparing the recorded oscillation response with a tolerance range based on a target oscillation response of a workpiece.

[0072] The target oscillation response can preferably be a recorded oscillation response of a workpiece of the same construction with the same material and without any defects present in the workpiece and can be stored in the evaluation device.

[0073] To verify that there are no defects in this component, this component can be tested using one or more additional testing methods (such as an X-ray or ultrasonic testing method) before its oscillation response can be stored as the target oscillation response.

[0074] In particular, the tolerance range has a lower threshold value of a desired natural frequency response and / or desired natural amplitude response.

[0075] Additionally or alternatively, the tolerance range may include an upper threshold value of a desired natural frequency response and / or desired natural amplitude response.

[0076] Thus, a recorded actual natural frequency response of the recorded oscillation response may lie within this tolerance range.

[0077] Additionally or alternatively, a recorded actual natural amplitude response of the recorded oscillation response may also lie within this tolerance range.

[0078] The indentation body can be pressed in, in particular, with a proportional static indentation force.

[0079] This proportional static indentation force can correspond to a percentage static force component of a maximum static indentation force, whereby the percentage static force component corresponds in particular to approximately 60% of the maximum static indentation force.

[0080] More preferably, the percentage static force corresponds to approximately 70% of the maximum static indentation force. Particularly preferably, the percentage static force corresponds to approximately 80% of the maximum static indentation force.

[0081] The reduction of the static indentation force to the percentage static force component of approximately 80% is due to the fact that the additional force amplitude from the oscillation excitation should not further plastically deform the material within the workpiece indentation.

[0082] Nevertheless, the static force component should be selected as high as possible to ensure the best possible contact between the indenter and the workpiece impression, thus enabling reliable oscillation excitation.

[0083] After the oscillation excitation has been completed, the same workpiece indentation can be plastically deformed using 100% of the maximum static indentation force.

[0084] Subsequently, as described above, the mechanical comparative parameters can be determined in accordance with the tensile test.

[0085] The previously described oscillation excitation of the workpiece is used in particular to determine one or more defects in the workpiece.

[0086] This oscillation excitation of the workpiece can also be carried out on several workpiece indentations at several positions in the surface of the workpiece.

[0087] Additionally or alternatively, an oscillation excitation of the workpiece can be carried out to determine at least one further material characteristic of the material of the workpiece in accordance with the Wöhler test.

[0088] This additional material parameter can indicate a fatigue characteristic of the material of the workpiece, for example in the form of an indication of fatigue strength.

[0089] The procedure is as follows:

[0090] The starting point is the workpiece indentation or indentations created (in the above-explained determination of the comparison parameters by, in particular, the first indentation body) in the surface of the workpiece. In other words, several plastically deformed workpiece indentations can be created in a surface of the workpiece using the first indentation body.

[0091] Thus, an automatic exchange of the first indentation body and provision of a second indentation body takes place after the step of pressing the first indentation body into the surface of the workpiece.

[0092] For this purpose, the complete pressing element can preferably be replaced accordingly, because the pressing body and pressing element usually form an inseparable unit.

[0093] Additionally or alternatively, the replacement can also be done manually.

[0094] The second pressing body may preferably have a pressing surface in which one or more recesses are provided.

[0095] Without the recess(es), the workpiece indentation is essentially (i.e., apart from mechanical residual stresses) in a state of compressive stress, which is caused by the contact of the indentation surface with the workpiece indentation under an indentation force.

[0096] However, only the compressive stress state is less suitable for carrying out a method for determining a fatigue characteristic due to its low material-damaging effect.

[0097] In this respect, a tensile stress state should be achieved at least partially in the workpiece impression, which can be achieved by one or more recesses.

[0098] Assuming a conical indenter without a recess, the compressive stress state is created in the workpiece indentation by transferring the indentation force across the indentation surface as a normal force.

[0099] However, if the indentation surface of the conical indentation body has a recess (which preferably extends on the lateral surface along a connecting line from the tip to the base of the cone), tensile stresses can be generated in the region of the recess in the circumferential direction of the conical workpiece indentation.

[0100] Since the tensile stress state within the workpiece indentation does not exactly correlate with that from a conventional tensile test, correction values ​​can be determined if necessary, for example by comparing the tensile stress state in the workpiece indentation with that from a conventional tensile test.

[0101] As a result, the second indentation body can be moved into the workpiece indentation previously plastically deformed by the first indentation body until contact is established between the second indentation body and the workpiece indentation.

[0102] The pressing of the second indentation body into the workpiece impression is preferably carried out with a static pressing force for elastic deformation of the workpiece impression by means of the second indentation body.

[0103] This step serves to set an elastic mean stress or prestress based on the Wöhler test to generate a static elastic stress level so that the workpiece indentation is elastically prestressed.

[0104] If there are several workpiece indentations, a different defined elastic stress level can be generated for each workpiece indentation so that the respective workpiece indentation is elastically prestressed.

[0105] The defined elastic stress level for the respective workpiece indentation can be determined from the previously determined comparison parameters using the material simulation model and adjusted accordingly using the respective static indentation force.

[0106] The static indentation force can therefore preferably be varied by means of several static force values.

[0107] Additionally or alternatively, the oscillating force can be varied by means of several force amplitudes and / or several force frequencies.

[0108] Subsequently, the second indentation body is preferably subjected to an oscillating force having a force amplitude in addition to the static indentation force for oscillating elastic deformation of the workpiece indentation. Additionally or alternatively, the oscillating force can have a force frequency.

[0109] If there are multiple workpiece impressions, you can proceed as follows:

[0110] The second indentation body can first be pressed into a first workpiece impression with a first static indentation force

[0111] Additionally or alternatively, the second indentation body in the indented state can be subjected to a first oscillating force having a first force amplitude and / or a first force frequency in addition to the first static indentation force.

[0112] Accordingly, the second indentation body can be pressed into a second workpiece indentation with a second static indentation force.

[0113] Additionally or alternatively, the second indentation body in the indented state can be subjected to a second oscillating force having a second force amplitude and / or a second force frequency in addition to the second static indentation force.

[0114] If more than two workpiece impressions are made, the static indentation force and / or the oscillating force can be varied step by step for each subsequent workpiece impression.

[0115] By means of the force amplitude, in accordance with the Wöhler test, the nominal stress amplitude S a be recreated.

[0116] On the other hand, the force frequency can be used to preferably influence the test time and, in addition, taking the test time into account, the so-called number of oscillation cycles (i.e. the actual number of force oscillations generated) can be determined, as explained below.

[0117] The static indentation force can be initially measured and compared with a static target indentation force. Additionally or alternatively, the oscillating force, including its force amplitude and / or force frequency, can be measured and compared with an oscillating target force, including its target force amplitude and / or force frequency.

[0118] The static target indentation force or the oscillating target force for the respective workpiece indentation can also be determined from the previously determined comparison parameters using the material simulation model.

[0119] If the comparison shows that the measured static indentation force or the measured oscillating force is outside a defined tolerance range based on the static target indentation force or the oscillating target force, it can be concluded that the material has failed within the workpiece indentation.

[0120] The failure of the material within the workpiece indentation can occur in the form of material breakout or material erosion, crack formation or other damaging deformation.

[0121] Consequently, by means of this comparison, at least one fatigue characteristic of the material of the workpiece in the workpiece indentation can be determined.

[0122] The fatigue characteristic can be determined in particular in the form of a maximum number of fatigue cycles.

[0123] This maximum number of cycles can then be compared with the correspondingly recorded static indentation force or the recorded oscillating force or the resulting nominal stress amplitude S a linked to a data pair and entered as a measuring point in a Wöhler diagram.

[0124] By varying the static indentation force or the recorded oscillating force (at the different workpiece indentations), a wide variety of nominal voltage amplitudes S a are set and the resulting maximum number of cycles are determined and entered as measuring points in the Wöhler diagram

[0125] Furthermore, the present invention relates to a device for determining one or more defects in a workpiece and / or for determining at least one material characteristic of a material of the workpiece, preferably comprising: - a workpiece holder for receiving and / or fixing the workpiece;

[0126] - an indentation element comprising an indentation element region having an indentation body for indentation into a surface of the workpiece;

[0127] - a force generator, which is mechanically coupled to the workpiece holder and / or the indentation element, for generating a static indentation force for indenting the indentation body into a surface of the workpiece for plastically deforming the workpiece by means of the indentation body to generate a plastically deformed workpiece indentation; and

[0128] - an oscillation generator which is mechanically coupled to the workpiece holder and / or the indentation element, for generating an oscillating force having a force amplitude and / or a force frequency in addition to or alternatively to the static indentation force in the indented state of the indentation body.

[0129] All structural and functional features associated with the previously described method and embodiments thereof may also be included in the device, either alone or in combination, and the associated properties, configurations, and advantages may also be included and achieved accordingly.

[0130] Furthermore, the device may be configured to carry out the method described herein, and the method described herein may be configured to be executable by means of the device described above.

[0131] The workpiece holder can be configured, in particular, for releasably receiving and / or securing the workpiece. For this purpose, the workpiece holder can have one or more positive and / or non-positive receiving and / or securing elements for receiving and securing the workpiece.

[0132] The pressing element and the pressing body can be designed as a one-piece pressing unit so that at the macroscopic level there is no separating surface between the pressing element and the pressing body.

[0133] Alternatively, the pressing element and pressing body can be formed in two parts, so that both the pressing element and the pressing body itself can have a separate pressing element body. In this case, the pressing body can be accommodated and secured by the pressing element. The securing can be detachable. The mechanical coupling of the force generator with the workpiece holder and / or the pressing element can be understood as a direct mechanical coupling.

[0134] In other words, there can be direct mechanical contact between the force generator and the workpiece holder and / or the pressing element for direct force transmission.

[0135] Alternatively, the mechanical coupling of the force generator with the workpiece holder and / or the indentation element can be understood as an indirect mechanical coupling.

[0136] In other words, an indirect mechanical coupling (e.g. via another intermediate component) can exist between the force generator and the workpiece holder and / or the pressing element for indirect force transmission.

[0137] Furthermore, it can be provided that the force generator is only mechanically coupled to the pressing element for transmitting the static pressing force to the pressing element.

[0138] Additionally or alternatively, the oscillation generator can be mechanically coupled to the pressing element to transmit the oscillating force to the pressing element.

[0139] The mechanical coupling of the oscillation generator with the pressing element can in particular be carried out directly, whereas the mechanical coupling of the force generator with the pressing element can preferably be carried out indirectly.

[0140] In particular, an elastic spring element can be arranged between the force generator and the pressing element. The spring element can preferably be designed as a compression spring element.

[0141] The spring element can be used to transmit the generated pressing force from the force generator to the pressing element.

[0142] The spring element can also be made of fiberglass or another suitable composite material. Furthermore, the spring element can be used to achieve oscillatory decoupling between the oscillation generator and the force generator, which is particularly gentle on the force generator and its support structure.

[0143] In this context, the natural frequency and / or natural amplitude of the elastic spring element may differ from the force amplitude and / or force frequency of the oscillating force from the oscillation generator. This difference can be expressed, for example, as a mathematical relationship.

[0144] This difference can be within a maximum of 5%, a maximum of 10%, a maximum of 20%, a maximum of 30%, a maximum of 40%, a maximum of 50%, a maximum of 60%, a maximum of 70%, a maximum of 80%, or a maximum of 100%. A difference of several hundred percent is also conceivable.

[0145] Further preferred features and / or advantages of the present invention are the subject of the following description and the drawings of exemplary embodiments.

[0146] The drawings show:

[0147] Fig. 1 is a schematic representation of a device according to an exemplary embodiment of the present invention;

[0148] Fig. 2 is a further schematic representation of the device according to Fig. 1 for carrying out a method according to an exemplary embodiment of the present invention;

[0149] Fig. 3 is a further schematic representation of the device according to Fig. 1 for carrying out the method according to Fig. 2;

[0150] Fig. 4 is a schematic partial sectional view in plan view of an indentation body of the device according to Fig. 1 for carrying out a method according to a further exemplary embodiment of the present invention; and Fig. 5 is a schematic representation of a stress-strain diagram for illustrating one or more material properties determined according to the method according to Fig. 4.

[0151] Identical or functionally equivalent elements or devices are provided with the same reference numerals in all figures.

[0152] Fig. 1 shows a schematic representation of a device 100 according to an exemplary embodiment of the present invention.

[0153] The device 100 for determining one or more defects 102 (shown in Fig. 3) in a workpiece 104 and for determining at least one material characteristic K of a material of the workpiece 104 comprises a workpiece holder 106 for receiving and securing the workpiece 104.

[0154] The material of the workpiece 104 can be a ductile metallic material that allows reproducible and defined plastic deformation.

[0155] A material can be considered ductile if it can undergo permanent plastic deformation under shear stress before fracture or macroscopic separation occurs.

[0156] A material parameter K, which characterizes the ductility, is the elongation at break, which can preferably be in a range from approx. 0.1% to approx. 30%.

[0157] Metals can preferably be aluminum, iron, titanium, or magnesium. Furthermore, it can be advantageous for metals to be present in the form of metal alloys such as aluminum alloys, iron alloys such as steel or cast iron, titanium alloys, or magnesium alloys.

[0158] The following steel alloys should preferably be used: unalloyed steels, alloyed steels or stainless steels.

[0159] The steel alloys can be further divided into: structural steel, case-hardening steel, tempering steel, nitriding steel, tool steel, stainless steel, and acid-resistant steel. The workpiece holder 106 is designed to releasably hold and secure the workpiece 104.

[0160] For this purpose, the workpiece holder 106 can have one or more positive and / or non-positive receiving and / or fixing elements for receiving or fixing the workpiece 104.

[0161] The workpiece 104 is shown only schematically in Fig. 1.

[0162] In the case of determining one or more defects 102, the workpiece 104 can preferably be a finished and ready-to-use component. One example could be a 3D-printed metallic component for use in aviation.

[0163] The device 100 further comprises an indentation element 108 having an indentation element region 110 arranged at a free end of the indentation element 108.

[0164] The pressing element 108 is designed as an elongated, circular-cylindrical component, ie it has a substantially greater extension along its longitudinal axis than in its transverse direction aligned therewith.

[0165] The indentation element region 110 further comprises an indentation body 112 for indentation into a surface 114 of the workpiece 104.

[0166] An indentation direction of the indentation body 112 extends perpendicular to the surface 114 of the workpiece 104.

[0167] According to Fig. 1, the indentation body 112 has a conical shape which is oriented such that its conical tip faces the workpiece holder 106 in the indentation direction.

[0168] The pressing element 108 and the pressing body 112 can be formed as a one-piece pressing unit, so that at the macroscopic level there is no separating surface between the pressing element 108 and the pressing body 112. Consequently, the pressing element 108 and the pressing body 112 can be made of the same material. Alternatively, the pressing element 108 and the pressing body 112 can be formed in two parts, so that both the pressing element 108 can have a separate pressing element body and the pressing body 112 itself can have a separate body.

[0169] In this case, the indentation body can be held and secured by the indentation element. The securing can be detachable.

[0170] The indenter body can preferably be made of diamond, although other suitable materials such as boron nitride may also be conceivable.

[0171] The device 100 comprises a force generator 116 for generating a static indentation force Fs for indenting the indentation body 112 into a surface 114 of the workpiece 104 for plastically deforming the workpiece 104 by means of the indentation body 112 to generate a plastically deformed workpiece indentation 118 (see Fig. 4).

[0172] The force generator 116 may include one or more hydraulic cylinders and / or one or more electro-mechanical force generators (such as a spindle driven by an electric motor) for generating the static indentation force Fs.

[0173] Force generator 116 is indirectly mechanically coupled to the pressing element 108 for the indirect transmission of the static pressing force Fs to the pressing element 108.

[0174] This is because an elastic spring element 122 is arranged between the force generator 116 and the pressing element 108, so that the transmission of the static pressing force Fs to the pressing element 108 takes place indirectly via the spring element 122.

[0175] The spring element 122 comprises a compression coil spring and can be made of fiberglass or another suitable composite material

[0176] Additionally or alternatively, the force generator 116 may be mechanically coupled to the workpiece holder 106 (not shown in Fig. 1).

[0177] The device 100 further comprises an oscillation generator 120 for generating an oscillating force Fo having a force amplitude and a force frequency in addition to the static indentation force Fs in the indented state of the indentation body 112. The oscillation generator can be designed as an ultrasonic or piezoelectric generator.

[0178] A natural frequency and a natural amplitude of the elastic spring element 122 differ from the force amplitude and force frequency of the oscillating force Fo.

[0179] The oscillation generator 120 is mechanically coupled directly to the pressing element 108 for transmitting the oscillating force Fo to the pressing element 108.

[0180] Additionally or alternatively, the oscillation generator 120 may also be mechanically coupled to the workpiece holder 106 (not shown in Fig. 1).

[0181] The device 100 further comprises an oscillation detection device 132 for detecting the force amplitude and force frequency of the oscillating force Fo and an oscillation response of the workpiece 104.

[0182] This oscillation detection device 132 may, for example, comprise a piezo-based acceleration or speed sensor.

[0183] The oscillation detection device 132 is part of the workpiece holder 106.

[0184] Alternatively, the oscillation detection device 132 may be part of the oscillation generator 120.

[0185] The device 100 further comprises a force detection device 134 for detecting the static indentation force Fs. The force detection device 134 is a component of the force generator 116.

[0186] Furthermore, the device 100 comprises a shape detection device 136 for detecting a three-dimensional shape of the workpiece indentation 118 (see Fig. 4). For this purpose, the shape detection device 136 has a white light interferometer.

[0187] Furthermore, the device 100 comprises a central evaluation device 138, which has a memory device for storing control and / or regulation algorithms, evaluation algorithms, simulation algorithms, and / or determination algorithms, which are executed by a processing unit. The central evaluation device 138 is connected to the oscillation detection device 132, the force detection device 134, and the shape detection device 136 via corresponding signal lines 142 for processing and evaluating the data acquired by these devices 132, 134, and 136.

[0188] Furthermore, the central evaluation device 138 is connected to the force generator 116 and the oscillation generator 120 via corresponding signal lines 142.

[0189] By executing the control and / or regulation algorithms, the central evaluation device 138 can be configured to control or regulate the force generator 116 and the oscillation generator 120. The oscillation generator 120 can be configured as an ultrasonic or piezoelectric generator.

[0190] The device 100 described above may further be surrounded by a noise protection device (not shown in Fig. 1) to dampen the noise emissions generated during oscillation excitation.

[0191] The noise protection device can preferably be constructed as a noise protection capsule.

[0192] Fig. 2 shows a further schematic representation of the device according to Fig. 1 for carrying out a method according to an exemplary embodiment of the invention.

[0193] The device 100 according to Fig. 2 basically has the same or equivalent or corresponding structural and / or functional features as the device 100 according to Fig. 1.

[0194] The device described in Fig. 1 is configured to carry out the method described below.

[0195] The method is configured to determine one or more defects 102 in a workpiece 104.

[0196] In addition, the method is configured to determine at least one material characteristic K of a material of the workpiece 104. In its most general form, the method comprises the following steps:

[0197] First, the first indentation body 112 is pressed into the surface 114 of the workpiece 104 with the static indentation force Fs to plastically deform the workpiece 104 by means of the indentation body 112 to produce a plastically deformed workpiece indentation 118.

[0198] The static indentation force Fs is generated by the force generator 116 and transmitted to the indentation body 112 via the spring element 122 and the indentation element 108.

[0199] In addition, the static indentation force Fs is detected in real time by the force detection device 134 and transmitted to the evaluation device 138 for further processing.

[0200] A three-dimensional shape 124 of the plastically deformed workpiece impression 118 is then recorded.

[0201] The three-dimensional shape 124 is detected by means of the shape detection device 136, which also transmits detection data on the detected three-dimensional shape 124 to the evaluation device 138 in real time.

[0202] In addition, the indentation body 112 is subjected in the indented state to an oscillating force Fo having a force amplitude and a force frequency in addition to the static indentation force Fs after the step of pressing the indentation body 112 into the surface 114 of the workpiece 104.

[0203] The steps of detecting the three-dimensional shape 124 and applying an oscillating force to the indentation body 112 in the indented state can be carried out independently of one another in time.

[0204] In other words, the step of detecting the three-dimensional shape 124 can occur before the step of applying pressure to the indentation body 112 or vice versa.

[0205] In the event that the step of detecting the three-dimensional shape 124 occurs after the step of applying pressure to the indentation body 112, the method proceeds as follows: The indentation body 112 is first pressed in with a proportional static indentation force Fs, which corresponds to a percentage static force component of a maximum static indentation force Fs.

[0206] The maximum static indentation force Fs can be regarded as the indentation force that enables the most suitable workpiece indentation 118 in terms of shape, size, penetration depth and required static indentation force Fs, depending on the material of the workpiece 104.

[0207] The percentage static force corresponds to approximately 80% of the maximum static indentation force Fs.

[0208] Alternatively, the percentage of static force can correspond to approximately 60% or approximately 70% of the maximum static indentation force.

[0209] The reduction of the static indentation force Fs to the percentage static force component of approximately 80% of the maximum static indentation force is due to the fact that the additional force amplitude from the oscillating force Fo should not further plastically deform the material within the workpiece indentation 118.

[0210] Nevertheless, the static force component should be selected as high as possible to ensure the best possible contact between the indenter and the workpiece impression, thus enabling a reliable force introduction into the workpiece.

[0211] According to Fig. 2, the application of the oscillating force Fo to the indentation body 112 in the pressed-in state can be seen for oscillating the workpiece 104 (see the double arrow shown at the oscillation generator 120).

[0212] The oscillation excitation occurs by introducing the oscillating force Fo into the workpiece 104, so that the workpiece 104 begins to oscillate with a natural frequency and with a natural amplitude in the form of an oscillation response.

[0213] The oscillation response of the workpiece 104 can then be detected in response to the oscillation excitation of the workpiece 104 by means of the oscillation detection device 132. The detected oscillation responses of the workpiece 104 are then transmitted to the evaluation device 138 for further processing or evaluation of the detected oscillation responses.

[0214] Since the workpiece shape and the material of the workpiece 104 have a great influence on the natural frequency and the natural amplitude, each individual workpiece 104 can give a corresponding individual oscillation response to the oscillation excitation.

[0215] From the detected oscillation response, the evaluation device 138 can then be used to determine the one or more defects! 02 in the workpiece 104.

[0216] In addition to the workpiece shape and material, defects in the workpiece 104 can have an influence on the oscillation response.

[0217] In this respect, for each individual workpiece 104, a correspondingly individually recorded oscillation response can be recorded, depending on the defects 102 present or not present in the workpiece 104, and stored in the evaluation device 138.

[0218] The step of determining the one or more defects 102 further comprises comparing the detected oscillation response with a tolerance range based on a desired oscillation response of a workpiece 104.

[0219] If the detected oscillation response is within the tolerance range, the workpiece 104 has no defects, whereas defects are present if the detected oscillation response is outside the tolerance range.

[0220] The target oscillation response can be a recorded oscillation response (i.e., a natural frequency and a natural amplitude) of an identical workpiece 104 made of the same material with no defects 102 present in the workpiece and can be stored in the evaluation device 138. Alternatively, the target oscillation response can be a simulated oscillation response of the identical workpiece made of the same material.

[0221] To verify that no defects are present in this identical workpiece 104, this workpiece 104 can be tested by one or more testing methods (such as an X-ray or ultrasonic testing method) before its target oscillation response is stored in the evaluation device 138 for comparison.

[0222] The tolerance range has a lower threshold value and an upper threshold value of a desired natural frequency response and / or desired natural amplitude response, within which a detected actual natural frequency response and a detected actual natural amplitude response of the detected oscillation response may lie.

[0223] Fig. 2 shows such a workpiece 104 which has no defects and was checked by means of the previously described method for determining one or more defects 102 by means of oscillation excitation.

[0224] The previously described method was described for a single workpiece indentation 118, although this method can of course also be applied to multiple workpiece indentations 118 (not shown in Fig. 2).

[0225] After the oscillation excitation for determining one or more defects 102 has been completed, the same workpiece indentation 118 can now be plastically deformed by means of the indentation body 112 using the maximum static indentation force Fs.

[0226] The workpiece indentation 118 can, of course, also be plastically deformed directly in an indentation process by means of the maximum static indentation force Fs without prior oscillation excitation in order to determine one or more defects 102.

[0227] The indentation body 112 is then moved out of the workpiece indentation 118 again, so that the three-dimensional shape 124 of the plastically deformed workpiece indentation 118 is subsequently recorded.

[0228] As explained above, the three-dimensional shape 124 is detected by means of the shape detection device 136, which transmits the shape detection data relating to the detected three-dimensional shape 124 to the evaluation device 138 in real time.

[0229] By means of the evaluation device 138, the detected three-dimensional shape 124 of the plastically deformed workpiece indentation 118 is then compared with a simulated three-dimensional shape of a plastically deformed workpiece indentation according to a material deformation model of the material 104.

[0230] From the comparison, at least one material characteristic K of the material of the workpiece 104 is determined.

[0231] The material deformation model of the workpiece 104 is stored in the storage device of the evaluation device 138, whereby the comparison proceeds as follows:

[0232] The simulated three-dimensional shape of the plastically deformed workpiece indentation is based on a so-called flow curve of the respective material, whereby the flow curve is mathematically defined by several material input parameters (to characterize the plastic material behavior).

[0233] The flow curve is implemented together with the real boundary conditions of the previous indentation process of the indentation body 112 (such as static indentation force, indentation depth as well as shape and geometry of the indentation body) in a finite element simulation (according to the material deformation model), resulting in a first simulated shape of the plastically deformed workpiece indentation.

[0234] This finite element simulation can be stored as a corresponding software application on the storage device of the evaluation device 138 and executed by the processing device of the evaluation device 138.

[0235] By varying the material input parameters of the flow curve, the processing device can iteratively minimize an objective function defined as the difference between the simulated shape and the actually recorded shape of the plastically deformed workpiece indentation 118 using an optimization algorithm according to the sum of squares method.

[0236] The optimization algorithm ends when the objective function converges and falls below a defined limit.

[0237] This limit value should preferably be approximately 5% deviation for three-dimensional simulations and approximately 3% deviation for two-dimensional simulations. The flow curve calculated by convergence (with the final calculated material input parameters) can be converted into a technical stress-strain curve, from which the following material parameters K can be determined in the form of comparative values ​​based on tensile testing:

[0238] - comparative proof stress Rpo,2 from the determination method;

[0239] - Comparative tensile strength R m from the determination procedure;

[0240] - hardening behavior; and / or

[0241] - qualitative determination of ductility for specific materials.

[0242] Fig. 3 shows a further schematic representation of the device according to Fig. 1 for carrying out the method according to Fig. 2.

[0243] The device 100 according to Fig. 3 basically has the same or equivalent or corresponding structural and / or functional features as the device 100 according to Fig. 1.

[0244] In contrast to Fig. 2, in which the workpiece 104 was tested without defects, the workpiece 104 according to Fig. 3 has defects.

[0245] Consequently, the detected oscillation response of the workpiece 104 (described in Fig. 2) is outside the tolerance range, which is graphically represented by an atypical oscillation response on a display device 140 of the evaluation device 138.

[0246] In contrast, a typical or normal oscillation excitation is carried out by the oscillation generator 120 (represented by the point-symmetric course of the

[0247] oscillation excitation).

[0248] Fig. 4 shows a schematic partial sectional view in a plan view of a second indentation body 126 of the device 100 according to Fig. 1 for carrying out a method according to a further exemplary embodiment of the present invention.

[0249] As can be seen in Fig. 4, the indentation body 126 does not correspond to the first indentation body 112 from Figs. 1 to 3. The oscillation excitation of the workpiece 104 described above according to Figs. 2 and 3 serves to determine one or more defects in the workpiece 104.

[0250] In addition, an oscillation excitation of the workpiece 104 can be carried out to determine at least one further material characteristic K of the material of the workpiece 104 in accordance with the Wöhler test.

[0251] For this purpose, the first indentation body 112 is replaced and a second indentation body 126 is provided after the step of pressing the first indentation body 112 into the surface 114 of the workpiece 104 with the maximum static indentation force Fs.

[0252] The replacement of the first indentation body 112 can be done manually and / or automatically.

[0253] The first indentation body 112 and the second indentation body 126 both have the same conical shape.

[0254] The pressing element and the pressing element region (not shown in Fig. 4) of the second pressing body 126 are also the same as the pressing element 108 and the pressing element region 110 of the first pressing body 112.

[0255] The resulting workpiece indentation 118 below the second indentation body 126 can be seen in Fig. 4.

[0256] In contrast to the first indenter 112, however, the second indenter 126 has an indentation surface 128 in which a recess 130 is formed.

[0257] The recess extends on a lateral surface or the indentation surface 128 along a straight connecting line from the tip to the base of the cone, the incision of which can be seen through the recess 130 in Fig. 4.

[0258] Alternatively, a plurality of recesses 130 may also be incorporated into the second indentation body 126. To determine the at least one further material characteristic K of the material of the workpiece 104 based on the Wöhler test, the method or the device 100 executing this method proceeds as follows:

[0259] First, the second indentation body 126 is moved into the workpiece indentation 118 previously plastically deformed by the first indentation body 112 until contact is established between the second indentation body 126 and the workpiece indentation 118.

[0260] The second indentation body 126 is now pressed into the workpiece indentation 118 with a static indentation force Fs for elastic deformation of the workpiece indentation 118 by means of the second indentation body 126.

[0261] This step serves to set an elastic mean or prestress based on the Wöhler test to generate a static and elastic stress state in the workpiece indentation 118.

[0262] The defined elastic stress level for the respective workpiece indentation can be determined from the previously determined comparison parameters (see Fig. 3) using the material simulation model and adjusted accordingly via the static indentation force Fs.

[0263] Without the recess 130, the workpiece indentation 118 would essentially contain compressive stresses (apart from mechanical residual stresses due to plastic deformation). p which are caused by the contact of the homogeneous indentation surface with the workpiece indentation 118 at a certain indentation force.

[0264] However, only the compressive stress state is less suitable for carrying out a procedure based on the Wöhler test due to its low material-damaging effect.

[0265] In this respect, a stress state should be achieved in which tensile stresses o zin the workpiece indentation 118, which is achieved by the recess 130, since the material bulges minimally into the recess 130 and is thus subjected to tensile stress in the circumferential direction (indicated by the arrow). Consequently, the second indentation body 126 is subjected to an oscillating force Fo having a force amplitude and a force frequency in addition to the static indentation force Fs for the oscillating elastic deformation of the workpiece indentation 118.

[0266] By means of the force amplitude, in accordance with the Wöhler test in the workpiece indentation 118, in particular the nominal stress amplitude S a be recreated.

[0267] On the other hand, the test time can be influenced by the force frequency and, in addition, the so-called number of cycles (i.e. the actual number of force oscillations generated until fatigue) can be determined taking the test time into account, as explained below.

[0268] For this purpose, the static indentation force Fs is detected by means of the force detection device 134 and the oscillating force Fo, having its force amplitude and its force frequency, is detected by means of the oscillation detection device 132 and transferred to the evaluation device 138.

[0269] The force detection device 134 can additionally or alternatively detect the indentation depth of the second indenter 126.

[0270] Using the evaluation device 138, the detected static indentation force Fs is compared with a static target indentation force and the detected oscillating force Fo is compared with an oscillating target force having its target force amplitude and its target force frequency.

[0271] The static target indentation force or the oscillating target force for the respective workpiece indentation can also be determined from the previously determined comparison parameters using the material simulation model.

[0272] If the comparison shows that the measured static indentation force or the measured oscillating force lie outside a defined tolerance range for the static target indentation force or the oscillating target force, it can be concluded that the material has failed within the workpiece indentation. The same applies to the measured indentation depth. Failure of the material within the workpiece indentation 118 can occur in the form of material breakout or material erosion, crack formation, or other deformation that separates the material.

[0273] Accordingly, by means of this comparison, the at least one material characteristic value K can be determined in the form of at least one fatigue characteristic value of the material of the workpiece in the workpiece indentation 118. The fatigue characteristic value can be determined in particular in the form of a maximum number of fatigue cycles N.

[0274] This maximum number of cycles N can then be compared with the correspondingly recorded static indentation force Fs or the recorded oscillating force and the resulting nominal stress amplitude S a linked to a data pair and entered as a measuring point in a Wöhler diagram.

[0275] The procedure of the method described above refers to a single workpiece indentation 118 and its elastic prestressing and application of a pulsating tensile stress.

[0276] If there are several workpiece indentations 118, a different defined elastic stress level can be generated for each workpiece indentation 118, so that the respective workpiece indentation 118 is elastically prestressed.

[0277] Consequently, the static indentation force Fs can be varied using several static force values ​​and the oscillating force Fo can be varied using several force amplitudes and several force frequencies.

[0278] For this purpose, a plurality of plastically deformed workpiece impressions 118 are first produced in a surface 114 of the workpiece 104 by means of the first indentation body 112.

[0279] Subsequently, the second indentation body 126 is pressed into a first workpiece indentation 118 with a first static indentation force Fs1 and, in the indented state, is subjected to a first oscillating force Fo1 having a first force amplitude and a first force frequency in addition to the first static indentation force Fs1.

[0280] Accordingly, the second indentation body 126 is provided with a second static

[0281] Indentation force Fs2 is pressed into a second workpiece impression 118 and, in the pressed-in state, is subjected to a second oscillating force Fo having a second force amplitude and a second force frequency in addition to the second static indentation force Fs2.

[0282] If there are more than two workpiece impressions 118, the static impression force Fs and the oscillating force Fo can be varied accordingly for each additional workpiece impression 118 and the procedure can be as described above.

[0283] This maximum number of cycles N determined per workpiece indentation 118 can then be compared with the correspondingly recorded static indentation force or the recorded oscillating force or the resulting nominal stress amplitude S a linked to a respective data pair and entered as additional measuring points in a Wöhler diagram.

[0284] Fig. 5 shows a schematic representation of a stress-strain diagram to illustrate one or more material properties determined according to the method according to Fig. 4.

[0285] This shows, as an example, the variation of three different elastic tensile prestresses o1, o2 and o3 along the hook' straight line with the subsequent application of an elastic swelling tensile stress in addition to the elastic tensile prestresses o1, o2 and o3.

[0286] These elastic tensile prestresses can be generated according to the explanation in Fig. 4 by pressing the second pressing body 126 into three different workpiece impressions 118 with three different static pressing forces Fs.

[0287] Accordingly, the elastically swelling tensile stresses can be generated according to the explanation in Fig. 4 by applying three different oscillating indentation forces Fo to the second indentation body 126 in three different workpiece indentations 118.

[0288] The kink at the end of the three respective time curves of the sum of elastic tensile prestress and elastically pulsating tensile stress corresponds to the time until material fatigue occurs, which can be determined using the respectively recorded static indentation force Fs or indentation depth (as explained in Fig. 4). Knowing the time, the material parameter K can then be determined in the form of the maximum number of fatigue cycles N (indicated in Fig. 5 by n in the form of n1, n2, and n3) of the respective tensile prestresses o1, o2, and o3.

[0289] List of reference symbols

[0290] 100 Device 102 Defect

[0291] 104 Workpiece 106 Workpiece holder

[0292] 108 Indentation element 110 Indentation element area 112 First indentation body

[0293] 114 Surface of the workpiece 116 Force generator

[0294] 118 Workpiece impression 120 Oscillation generator 122 Elastic spring element

[0295] 124 Shape of the workpiece indentation 126 Second indentation body 128 Indentation surface 130 Recess 132 Oscillation detection device

[0296] 134 Force detection device 136 Shape detection device 138 Central evaluation device 140 Display device 142 Signal line

[0297] Fs static indentation force Fs1 first static indentation force

[0298] Fs2 second static indentation force Fo oscillating force

[0299] Fo1 first oscillating force Fo2 second oscillating force K material parameter

[0300] N Number of cycles o P Compressive stress a z Tensile stress

Claims

Patent claims 1. A method for determining one or more defects (102) in a workpiece (104) and / or for determining at least one material characteristic (K) of a material of the workpiece (104), comprising the following steps: - pressing a, in particular first, indentation body (112) into a surface (114) of the workpiece (104) with a static indentation force (Fs) for plastically deforming the workpiece (104) by means of the indentation body (112) to produce a plastically deformed workpiece indentation (118); and / or - detecting a shape (124), in particular a three-dimensional shape (124), of the plastically deformed workpiece impression (118); and / or - applying an oscillating force (Fo) having a force amplitude and / or a force frequency to the indentation body (112) in the indented state in addition to or alternatively to the static indentation force (Fs) during the step and / or after the step of indenting the indentation body (112) into the surface (114) of the workpiece (104).

2. Method according to claim 1, characterized by - comparing the detected shape (124), in particular the detected three-dimensional shape (124), of the plastically deformed workpiece impression (118) with a simulated shape, in particular a simulated three-dimensional shape, of a plastically deformed workpiece impression (118) according to a material deformation model of the workpiece (104); and - determining the at least one material characteristic (K) of the material of the workpiece (104) from the comparison.

3. Method according to claim 1 or claim 2, characterized by - applying the oscillating force (Fo) to the indentation body (112) in the indented state to excite oscillation of the workpiece (104); - detecting an oscillation response of the workpiece (104) in response to the oscillation excitation of the workpiece (104); and - determining the one or more defects (102) in the workpiece (104) from the detected oscillation response.

4. Method according to claim 3, characterized in that the step of determining comprises comparing the detected oscillation response with a tolerance range based on a desired oscillation response of a workpiece (104), wherein in particular the tolerance range has a lower threshold value and / or an upper threshold value of a desired natural frequency response and / or desired natural amplitude response, within which a detected actual natural frequency response and / or a detected actual natural amplitude response of the detected oscillation response may lie.

5. Method according to one of the preceding claims, characterized in that the indentation body (112) is / is pressed in with a proportional static indentation force (Fs) which corresponds to a percentage static force component of a maximum static indentation force (Fs), wherein the percentage static force component corresponds to approximately 60%, preferably approximately 70% and particularly preferably approximately 80% of the maximum static indentation force (Fs).

6. Method according to one of the preceding claims, characterized by a manual and / or automatic exchange of the first indentation body (112) and provision of a second indentation body (126) after the step of indenting the first indentation body (112) into the surface (114) of the workpiece (104), wherein the second indentation body (126) has an indentation surface (128) in which one or more recesses (130) are introduced.

7. Method according to claim 5 or claim 6, characterized by moving the second indentation body (126) into the workpiece indentation (118) previously plastically deformed by the first indentation body (112) until contact is established between the second indentation body (126) and the workpiece indentation (118).

8. Method according to claim 7, characterized by - pressing the second indentation body (126) into the workpiece indentation (118) with a static indentation force (Fs) for elastically deforming the workpiece indentation (118) by means of the second indentation body (126); and - applying an oscillating force (Fo) to the second indentation body (126) having a force amplitude and / or a force frequency in addition to the static indentation force (Fs) for the oscillating elastic deformation of the workpiece indentation (118).

9. Method according to claim 8, characterized in that the static indentation force (Fs) and / or the oscillating force (Fo) having its force amplitude and / or its force frequency are / is recorded and are / is compared with a static target indentation force and / or with an oscillating target force having its target force amplitude and / or its target force frequency.

10. The method according to claim 9, characterized in that by means of this comparison at least one fatigue characteristic value of the material of the workpiece (104) in the workpiece impression (118) is determined, in particular in the form of a maximum number of fatigue cycles (N).

11. Method according to one of claims 8 to 10, characterized in that the static indentation force (Fs) can be varied by means of several static force values ​​and / or the oscillating force (Fo) can be varied by means of several force amplitudes and / or several force frequencies.

12. Method according to claim 11, characterized in that - by means of the first indentation body (112) a plurality of plastically deformed workpiece indentations (118) are produced in a surface (114) of the workpiece (104); - the second indentation body (126) is pressed into a first workpiece indentation (118) with a first static indentation force (Fs1) and / or, in the indented state, is subjected to a first oscillating force (Fo1) having a first force amplitude and / or a first force frequency in addition to the first static indentation force (Fs1); and - the second indentation body (126) is pressed into a second workpiece indentation (118) with a second static indentation force (Fs2) and / or in the indented state is subjected to a second oscillating force (Fo) having a second force amplitude and / or a second force frequency in addition to the second static indentation force (Fs2).

13. Device (100) for determining one or more defects (102) in a workpiece (104) and / or for determining at least one material characteristic (K) of a material of the workpiece (104), comprising: - a workpiece holder (106) for receiving and / or fixing the workpiece (104); - an indentation element (108) comprising an indentation element region (110) having an indentation body (112) for indentation into a surface (114) of the workpiece (104); - a force generator (116) mechanically coupled to the workpiece holder (106) and / or the indentation element (108) for generating a static indentation force (Fs) for indenting the indentation body (112) into a surface (114) of the workpiece (104) for plastically deforming the workpiece (104) by means of the indentation body (112) to generate a plastically deformed workpiece indentation (118); and - an oscillation generator (120) which is mechanically coupled to the workpiece holder (106) and / or the indentation element (108), for generating an oscillating force (Fo) having a force amplitude and / or a force frequency in addition to or alternatively to the static indentation force (Fs) in the indented state of the indentation body (112).

14. Device (100) according to claim 13, characterized in that the force generator (116) and / or the oscillation generator (120) are / is mechanically coupled to the pressing element (108) for transmitting the static pressing force (Fs) and / or the oscillating force (Fo) to the pressing element (108), wherein in particular an elastic spring element (122) is arranged between the force generator (116) and the pressing element (108).

15. Device (100) according to claim 14, characterized in that a natural frequency and / or a natural amplitude of the elastic spring element (122) differs / differs from the force amplitude and / or force frequency of the oscillating force (Fo).

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