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

Abstract

The present invention relates to 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). Furthermore, the present invention relates to a 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).

Description

The present invention relates to a method and a device for determining one or more flaws in a workpiece and / or for determining at least one material characteristic variable of a material of the workpiece.The determination methods or devices disclosed in the prior art for defect determination or material characteristic variable determination of a workpiece are still expensive, long and complicated in sample production and in process control. Quality assurance is therefore still complicated, which frequently makes the use of certain components, for example produced by 3D printing, in areas which are very sensitive to safety, such as, for example, aviation, uneconomical.Devices and methods of this type are already known from the prior art.Accordingly, DE 1020111115519 A1 shows a method of the generic type and a device of the generic type.The present invention is therefore based on the object of providing in particular a method and a device for determining one or more flaws in a workpiece and / or for determining at least one material characteristic variable of a material of the workpiece, which are preferably less expensive, faster and easier to handle.This object is achieved according to the invention by the features of independent claim 1. Advantageous further developments of the invention are described in the dependent claims.A method according to the invention can be configured and set up for determining one or more flaws in a workpiece. Additionally or alternatively, the method according to the invention can be configured and set up for determining at least one material characteristic variable of a material of the workpiece and comprise the following steps.First, an impression of an impression body into a surface of the workpiece can be carried out with a static impression force for the plastic deformation of the workpiece by means of the impression body for generating a plastically deformed workpiece impression. The push-in body can be, in particular, a first push-in body.Additionally or alternatively, a determination of a shape of the plastically deformed workpiece impression can be made. The shape can be, in particular, a three-dimensional shape.Additionally or alternatively, it can be provided that an oscillating force is applied to the pressing-in body in the pressed-in state in addition to the static pressing-in force.Furthermore, it can be conceivable that the application of the oscillating force to the pressing-in body in the pressed-in state takes place alternatively to the static pressing-in force.The application of the oscillating force to the pressing-in body in the pressed-in state, in addition or alternatively to the static pressing-in force, can take place during the step of pressing-in the pressing-in body into the surface of the workpiece.Additionally or alternatively, the application of the oscillating force to the pressing-in body in the pressed-in state can be carried out additionally or alternatively to the static pressing-in force after the step of pressing the pressing-in body into the surface of the workpiece.The steps of detecting the shape and applying an oscillating force to the pressing-in body in the pressed-in state can take place independently of one another in time.In other words, the step of detecting the shape can take place before the step of applying pressure to the push-in body, or vice versa.The oscillating force may have a force amplitude. Additionally or alternatively, the oscillating force may have a force frequency.Defects of the workpiece can be surface defects and / or volume defects.Examples of surface defects can be cracks, pores, scratches, extrusions or intrusions and / or notches on the workpiece surface.Volume defects, on the other hand, can be voids or other preferably inner hollow or free spaces or microstructure inhomogeneities; gas bubbles; inclusions; cracks; notches and / or pores in the interior of the workpiece.A workpiece may be a ready-to-use component that may be configured and configured for immediate installation and use in a respective product.An example may be a metallic component made of 3D printing for aviation use.Alternatively, the workpiece can also be a semi-finished product which can be understood as a prefabricated raw material and a blank workpiece or as a semi-finished product in a simplest form.Alternatively, the workpiece can also be a sample made of the respective material specifically produced for the method described above.A material characteristic variable can be understood to mean a physical characteristic variable by means of which the material can be characterized and quantified. The material characteristic variable can preferably be a mechanical material characteristic variable.Examples of a mechanical material characteristic can be one or more of the following material characteristics: modulus of elasticity, yield strength, yield strength, tensile strength, vibration resistance, yield stress, elongation at break, uniform elongation or hardness.The material of the workpiece can be a ductile, preferably metallic, material in its most general shape, which permits reproducible and defined plastic deformation (for example in the case of a plurality of pressing-in processes at different positions on the surface of the workpiece).A material can be considered ductile if it can permanently plastically deform under shear stress before fracture or macroscopic separation.A material characteristic characterizing ductility is elongation at break, which may preferably be in a range from about 0.1% to about 30%.Metals can preferably be aluminum, iron, titanium or magnesium. Furthermore, it can be advantageously provided if the metals are present in the form of metal alloys such as aluminum alloys, iron alloys such as steel or cast iron, titanium alloys or magnesium alloys.The following steel alloys are preferably used: unalloyed steels, alloyed steels and stainless steels, respectively.The steel alloys can be further divided into: structural steel, mild steel, tempered steel, nitriding steel, tool steel, stainless steel and acid-resistant steel, respectively.The pressing body can preferably be a component of a pressing element region of a pressing element, by means of which the pressing body can be pressed into a surface of the workpiece.The pressing-in element and the pressing-in body can be formed as an integral pressing-in unit, so that there is no separating surface between the pressing-in element and the pressing-in body on a macroscopic level.Alternatively, the pressing-in element and the pressing-in body can be formed in two parts, so that both the pressing-in element can have a separate pressing-in element body and the pressing-in body itself can have a separate body.In this case, the pressing body may be accommodated and fixed by the pressing member. The fixing can be effected in a detachable manner.The depression body is that region of the engagement element which penetrates into the surface of the workpiece and thus generates the workpiece impression as described above. In other words, the push-in body can also be referred to as a penetration body.The pressing-in direction is preferably perpendicular to the surface of the workpiece.The pressing-in body may preferably have a conical shape, with a tip facing the workpiece surface in the pressing-in direction.The tip of the push-in body can advantageously be rounded. As a result, in the resulting cause of the workpiece impression, mechanical stress peaks as a result of a notch effect can be minimized, so that the method described above can proceed more precisely.Alternatively, the crush body may have a spherical shape or a pyramidal shape or a tetrahedral shape.The indenter may preferably be made of diamond. Natural diamonds or artificially produced diamonds may be conceivable here. Other suitable materials such as boron nitride may also be used.The shape of the workpiece impression can be detected optically or tactilely. Preferably, the capturing takes place optically by means of a white light interferometer method for generating the captured shape or three-dimensional shape.This detected shape or three-dimensional shape can be transmitted to an evaluation device for further processing.The static pressing-in force can have a force vector only in the pressing-in direction and a force amount which is transmitted to the pressing-in element by means of a force generator and by means of which the pressing-in body is then pressed into the surface of the workpiece.The force vector of the pressing-in force should be oriented orthogonally to the surface of the workpiece, like the longitudinal axis of the pressing-in element and of the pressing-in body.When the force is applied, a movement along the longitudinal axis of the pressing element or the pressing body does indeed occur, wherein the movement is however so slow that a quasistatic force application for generating the workpiece impression can still be spoken of.The oscillating pressing-in force can have a force vector in and counter to the pressing-in direction and have a force amount which changes periodically over time, for example in the form of a sine or cosine function.The amount of force may be periodically modulated in terms of force frequency and / or force amplitude.The combination of the pressing-in method (with the static pressing-in force) for generating the plastically deformed workpiece impression and the application of an oscillating force to the pressing-in body in the pressed-in state ensures a significantly accelerated analysis of a plurality of test methods relevant to the component quality.In addition, due to the speed of the above-explained determination method, a larger number (for example, in series production) of components can also be evaluated.In addition, a comparison of the detected shape of the plastically deformed workpiece impression with a simulated shape of a plastically deformed workpiece impression can be made according to a material deformation model of the workpiece.The detected shape can be in particular a detected three-dimensional shape, whereas the simulated shape can be in particular a simulated three-dimensional shape.Following the comparison, the at least one material characteristic variable of the material of the workpiece can be determined from the comparison.The simulated shape of the plastically deformed workpiece impression is based on a so-called flow curve of the material, wherein the flow curve is mathematically defined by a plurality of material input parameters (for characterizing the plastic material behavior).The flow curve is processed together with the real boundary conditions of the previously performed step of pressing in the pressing body (such as static pressing-in force, pressing-in depth and shape and geometry of the pressing body) in a finite element simulation (according to the material deformation model), from which the simulated shape of the plastically deformed workpiece impression is calculated.This finite element simulation can be stored as a corresponding software application on a memory unit of the evaluation device and can be executed by a processing unit of the evaluation device.By varying the material input parameters, the evaluation device can iteratively minimize the difference between the simulated shape of the plastically deformed workpiece impression and the actually detected shape of the plastically deformed workpiece impression (target function) by means of an optimization algorithm according to the method of the sum of the squares of errors.The optimization algorithm ends when the target function converges and falls below a defined limit value.This limit value can preferably lie at about 5% deviation in the case of a three-dimensional simulation and preferably at about 3% deviation in the case of a two-dimensional simulation.The flow curve calculated by convergence (with the finally calculated material input parameters) can be converted into a technical stress-strain curve and from this the following comparative characteristics can be determined on the basis of the tensile test:- Comparative yield point R p0,2;Comparative tensile strength R m;solidification behavior; and / orqualitative determination of ductility for certain materials.As explained above, the method can also be used for determining one or more defects in the workpiece.In this case, the impact of the pressing-in body in the pressed-in state with the oscillating force for excitation of oscillations of the workpiece is initially carried out.The oscillation excitation is preferably performed by an oscillation generator so that the workpiece starts oscillating with a natural frequency and with a natural amplitude as a kind of oscillation response. The oscillation generator can be designed as an ultrasonic or piezoelectric generator.Subsequently, a detection of an oscillation response of the workpiece can be effected in response to the oscillation excitation of the workpiece.This detection can preferably be carried out with an oscillation detection device, which can likewise be connected to the evaluation device for evaluating the detected oscillation responses.The oscillation detection device can have, for example, a piezo-based acceleration or speed sensor.In particular, since the workpiece shape and the material of the workpiece have a large influence on the workpiece natural frequency and the workpiece intrinsic amplitude, each individual workpiece can give a corresponding individual oscillation response to the oscillation excitation.A workpiece for the method of defect determination can preferably be a completely produced component ready for use. An example of such a component could be a series component.From the detected oscillation response, a determination of the one or more flaws in the workpiece can then be made.In addition to the workpiece shape and the material of the workpiece, the defects of the workpiece can have a great influence on the workpiece natural frequency or its natural frequency response and the workpiece intrinsic amplitude or its intrinsic amplitude response.In this respect, for each individual workpiece, a correspondingly individually detected oscillation response can be detected depending on the flaws present in the workpiece or in the case of no flaws.The step of determining preferably comprises comparing the detected oscillation response with a tolerance range starting from a desired oscillation response of a workpiece.The desired oscillation response can preferably be a recorded oscillation response of a workpiece of identical construction with the same material with no defects present in the workpiece and be stored in the evaluation device.To check that no defects are present in this component, this component can be checked by one or more further test methods (such as a Röentgen or ultrasonic test method) before its oscillation response can be stored as a setpoint oscillation response.In particular, the tolerance range has a lower threshold value of a setpoint natural frequency response and / or setpoint natural amplitude response.Additionally or alternatively, the tolerance range can have an upper threshold value of a setpoint natural frequency response and / or setpoint natural amplitude response.Thus, a detected actual natural frequency response of the detected oscillation response may be in this tolerance range.Additionally or alternatively, a detected actual self-amplitude response of the detected oscillation response may also lie in this tolerance range.The pressing-in body can be pressed in in particular with a proportional static pressing-in force.This proportional static pressing-in force can correspond to a percentage static force component of a maximum static pressing-in force, wherein the percentage static force component corresponds in particular to approximately 60% of the maximum static pressing-in force.More preferably, the percentage static force component corresponds to approximately 70% of the maximum static pressing-in force.Particularly preferably, the percentage static force component corresponds to approximately 80% of the maximum static pressing-in force.The reduction of the static pressing-in force to the percentage static force component of approximately 80% has the background that the additional force amplitude from the oscillation excitation should no longer plastically deform the material within the workpiece impression.Nevertheless, the static force component should be selected as high as possible, so that the best possible contact of the pressing body with the workpiece impression is produced and thus a reliable oscillation excitation is possible.After the oscillation excitation has been concluded, the same workpiece impression can be plastically deformed by means of 100% of the maximum static pressing-in force.Subsequently, as described above, the mechanical comparison characteristics can be determined on the basis of the tensile test.The above-described excitation of oscillations of the workpiece serves in particular for the determination of one or more flaws in the workpiece.This oscillation excitation of the workpiece can also be performed at multiple workpiece impressions at multiple positions in the surface of the workpiece.Additionally or alternatively, an oscillation excitation of the workpiece can be carried out in order to determine at least one further material characteristic variable of the material of the workpiece on the basis of the Wöhler test.This further material characteristic variable can characterize a fatigue characteristic value of the material of the workpiece, for example in the form of specifying a vibration resistance.To this end, the method proceeds as follows:The starting point is the generated workpiece impression or the generated workpiece impressions (in the above-explained determination of the comparison characteristic values by in particular the first impression body) in the surface of the workpiece.In other words, by means of the first impression body, a plurality of plastically deformed workpiece impressions can be produced in a surface of the workpiece.Thus, an automatic replacement of the first press-in body and provision of a second press-in body takes place after the step of pressing the first press-in body into the surface of the workpiece.For this purpose, the complete press-in element can preferably be replaced accordingly, because the press-in body and the press-in element generally form an indivisible unit.Additionally or alternatively, the replacement can also be carried out manually.The second pressing body can preferably have a pressing surface in which one or more recesses are introduced.Without the cutout / s, a compressive stress state is present in the workpiece impression essentially (i.e. apart from mechanical internal stresses), which is produced by the contact of the impression surface with the workpiece impression in the event of an impression force.However, only the compressive stress state is less well suited for carrying out a method for determining a fatigue characteristic value because of its low material-damaging effect.In this respect, a tensile stress state in the workpiece impression should be achieved at least partially, which can be achieved by the one or more recesses.Assuming a cone-shaped depression body without a recess, the compressive stress state is established in the workpiece impression by transmitting the depression force via the depression surface as a normal force.However, if the pressing surface of the conical pressing body has a recess (which preferably extends on the lateral surface along a connecting line from the tip to the base surface of the cone), tensile stresses can be generated in the circumferential direction of the conical workpiece impression in the region of the recess.Since the tensile stress state within the workpiece impression does not correlate exactly 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 impression with that from a conventional tensile test.Consequently, the second pressing body can be moved into the workpiece impression that was previously plastically deformed by the first pressing body until a contact is produced between the second pressing body and the workpiece impression.The pressing of the second pressing 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 pressing body.This step serves for setting an elastic medium tension or prestress in a manner based on the Wehler test in order to generate a static elastic tension level, so that the workpiece impression is elastically prestressed.If a plurality of workpiece impressions are present, a different defined elastic stress level can be generated for each workpiece impression, such that the respective workpiece impression is elastically prestressed.The defined elastic stress level for the respective workpiece impression can be determined from the previously determined comparison characteristic values by means of the material simulation model and can be adjusted accordingly via the respective static pressing-in force.The static pressing-in force can therefore preferably be varied by means of a plurality of static force values.Additionally or alternatively, the oscillating force can be variable by means of a plurality of force amplitudes and / or a plurality of force frequencies.Subsequently, the second pressing body is preferably acted upon with an oscillating force having a force amplitude in addition to the static pressing force for oscillating elastic deformation of the workpiece impression. Additionally or alternatively, the oscillating force may have a force frequency.In the case of a plurality of workpiece impressions, the following procedure can be adopted:The second pressing-in body can first be pressed into a first workpiece impression with a first static pressing-in forceAdditionally or alternatively, the second pressing-in body can be acted upon in the pressed-in state with a first oscillating force having a first force amplitude and / or a first force frequency in addition to the first static pressing-in force.Accordingly, the second pressing-in body can be pressed into a second workpiece impression with a second static pressing-in force.Additionally or alternatively, the second pressing-in body can be acted upon in the pressed-in state with a second oscillating force having a second force amplitude and / or a second force frequency in addition to the second static pressing-in force.In the case of more than two workpiece impressions, the static impression force and / or the oscillating force can be varied step by step for each further workpiece impression.By means of the force amplitude, the rated voltage amplitude S a can be simulated in particular on the basis of the Wehler test.By contrast, the test time can preferably be influenced with the force frequency and, in addition, the so-called oscillation play count (i.e. the actual number of force oscillations generated) can be determined taking into account the test time, as will be explained below.The static pressing-in force can be initially detected and compared with a static desired pressing-in force.Additionally or alternatively, the oscillating force having its force amplitude and / or its force frequency can be detected and compared with an oscillating desired force having its desired force amplitude and / or its desired force frequency.The static setpoint pressing-in force or the oscillating setpoint force for the respective workpiece impression can likewise be determined from the previously determined comparison characteristic values by means of the material simulation model.If the comparison reveals that the detected static pressing-in force or the detected oscillating force lies outside a defined tolerance range starting from the static setpoint pressing-in force or the oscillating setpoint force, it is possible to infer a failure of the material within the workpiece impression.The failure of the material within the workpiece impression can take place in the form of a material break-out or a material erosion, a crack formation or another damaging deformation.Consequently, by means of this comparison, at least one fatigue characteristic value of the material of the workpiece in the workpiece impression can be determined.The fatigue characteristic value can be determined in particular in the form of a maximum vibration play number.This maximum vibration cycle number can then be linked in a to a data pair with the correspondingly detected static pressing-in force or the detected oscillating force or the nominal voltage amplitude S resulting therefrom and entered as a measurement point in a Wehler diagram.By varying the static pressing-in force or the detected oscillating force (at the different workpiece pressings), the most varied nominal voltage amplitudes S a can be set and the maximum oscillation play numbers resulting therefrom can be determined and entered accordingly as measurement points in the Wehler diagramFurthermore, the present invention relates to a device for determining one or more flaws in a workpiece and / or for determining at least one material characteristic of a material of the workpiece, preferably comprising:a workpiece receptacle for receiving and / or securing the workpiece;a pressing member comprising a pressing member portion having a pressing body for pressing into a surface of the workpiece;a force generator, which is mechanically coupled to the workpiece receptacle and / or the pressing element, for generating a static pressing force for pressing the pressing body into a surface of the workpiece for the plastic deformation of the workpiece by means of the pressing body for generating a plastically deformed workpiece impression; andan oscillation generator, which is mechanically coupled to the workpiece holder and / or the pressing element, for generating an oscillating force having a force amplitude and / or a force frequency in addition or alternatively to the static pressing force in the pressed-in state of the pressing body.All structural and functional features associated with the method and embodiments described above may also be included in the device, either alone or in combination, and the associated characteristics, configurations, and advantages may likewise be included and achieved accordingly.In addition, the apparatus 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 apparatus described above.The workpiece receptacle can be configured in particular for the detachable receiving and / or fixing of the workpiece. For this purpose, the workpiece holder can have one or more positively and / or non-positively locking holding and / or securing elements for holding and securing the workpiece.The pressing-in element and the pressing-in body can be formed as an integral pressing-in unit, so that there is no separating surface between the pressing-in element and the pressing-in body on a macroscopic level.Alternatively, the pressing-in element and the pressing-in body can be formed in two parts, so that both the pressing-in element can have a separate pressing-in element body and the pressing-in body itself can have a separate body. In this case, the pressing body may be accommodated and fixed by the pressing member. The fixing can be effected in a detachable manner.The mechanical coupling of the force generator to the workpiece receptacle and / or the pressing-in element can be understood as a direct mechanical coupling.In other words, there can be a direct mechanical contact between the force generator and the workpiece receptacle and / or the pressing element for the direct force transmission.Alternatively, the mechanical coupling of the force generator to the workpiece receptacle and / or the pressing element can be understood as an indirect mechanical coupling.In other words, there can be an indirect mechanical coupling (e.g. via a further intermediate component) between the force generator and the workpiece receptacle and / or the pressing element for indirect force transmission.Furthermore, it can be provided that the force generator is mechanically coupled only to the pressing element for transmitting the static pressing force to the pressing element.Additionally or alternatively, the oscillation generator may be mechanically coupled to the pressing element for transmitting the oscillating force to the pressing element.The mechanical coupling of the oscillation generator to the pressing element can be effected in particular directly, whereas the mechanical coupling of the force generator to the pressing element can be effected preferably indirectly.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.The spring element can serve for transmitting the generated pressing-in force from the force generator to the pressing-in element.In addition, the spring element can be made of fiberglass or of another composite material suitable for this purpose.In addition, by means of the spring element, an oscillating decoupling between the oscillation generator and the force generator can be achieved, which is in particular material-saving for the force generator and its holding structure.In this context, a natural frequency and / or a 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.This difference can be in the range of 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 100% may also be conceivable.Further preferred features and / or advantages of the present invention are the subject matter of the following description and the graphical representation of exemplary embodiments.In the drawings, there are shown: FIG. 1 is a schematic diagram of an apparatus according to an exemplary embodiment of the present invention; FIG. 2 shows a further schematic illustration of the apparatus according to FIG. 1 for carrying out a method according to an exemplary embodiment of the present invention; FIG. 3 shows a further schematic illustration of the apparatus according to FIG. 1 for carrying out the method according to FIG. 2 ; FIG. 4 shows a schematic partial sectional illustration in a plan view of an impression 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 shows a schematic illustration of a stress-strain diagram for illustrating one or more material characteristics determined according to the method according to FIG. 4.Identical or functionally equivalent elements or devices are provided with the same reference numerals in all figures.FIG. 1 shows a schematic representation of an apparatus 100 according to an exemplary embodiment of the present invention.The device 100 for determining one or more flaws 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 receptacle 106 for receiving and fixing the workpiece 104.The material of the workpiece 104 can be a ductile metallic material that allows reproducible and defined plastic deformation.A material can be considered ductile if it can permanently plastically deform under shear stress before fracture or macroscopic separation.A material characteristic K characterizing the ductility is the elongation at break, which can preferably be in a range from about 0.1% to about 30%.Metals can preferably be aluminum, iron, titanium or magnesium. Furthermore, it can be advantageously provided if metals are present in the form of metal alloys such as aluminum alloys, iron alloys such as steel or cast iron, titanium alloys or magnesium alloys.The following steel alloys are preferably used: unalloyed steels, alloyed steels and stainless steels, respectively.The steel alloys can be further divided into: structural steel, mild steel, tempered steel, nitriding steel, tool steel, stainless steel, acid-resistant steel.The workpiece receptacle 106 is configured for releasably receiving and securing the workpiece 104.For this purpose, the workpiece holder 106 can have one or more positively and / or non-positively locking holding and / or securing elements for holding or securing the workpiece 104.The workpiece 104 is only schematically shown in FIG. 1.In the case of the determination of one or more flaws 102, the workpiece 104 can preferably be a completely produced component ready for use. An example may be a metallic component made of 3D printing for aviation use.The device 100 further comprises a pressing element 108 with a pressing element region 110 arranged at a free end of the pressing element 108.The pressing-in element 108 is designed as an elongate, circular-cylindrical component, i.e. it has a substantially greater extent along its longitudinal axis than in its transverse direction aligned with it.The pressing element region 110 further comprises a pressing body 112 for pressing into a surface 114 of the workpiece 104.A direction of depression of the depression body 112 extends perpendicularly to the surface 114 of the workpiece 104.According to FIG. 1, the pressing-in body 112 has a conical shape which is oriented such that its cone tip faces the workpiece receptacle 106 in the pressing-in direction.The pressing-in element 108 and the pressing-in body 112 can be formed as an integral pressing-in unit, so that there is no separating surface between the pressing-in element 108 and the pressing-in body 112 on a macroscopic level. Consequently, the push-in element 108 and the push-in body 112 can be produced from the same material.Alternatively, the pressing-in element 108 and the pressing-in body 112 can be formed in two parts, so that both the pressing-in element 108 can have a separate pressing-in element body and the pressing-in body 112 itself can have a separate body.In this case, the pressing body may be accommodated and fixed by the pressing member. The fixing can be effected in a detachable manner.The impression body can preferably be made of diamond, wherein other suitable materials such as boron nitride can also be conceivable.The device 100 comprises a force generator 116 for generating a static pressing force Fs for pressing the pressing body 112 into a surface 114 of the workpiece 104 for plastically deforming the workpiece 104 by means of the pressing body 112 for generating a plastically deformed workpiece impression 118 (cf. FIG. 4 ).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 crush force Fs.Force generator 116 is indirectly mechanically coupled to the push-in member 108 for indirectly transmitting the static push-in force Fs to the push-in member 108.This is because an elastic spring element 122 is arranged between the force generator 116 and the pressing element 108, so that the static pressing force Fs is transmitted to the pressing element 108 indirectly via the spring element 122.The spring element 122 comprises a compression coil spring and can be made of fiberglass or another suitable composite material for this purposeAdditionally or alternatively, the force generator 116 may be mechanically coupled to the workpiece receiver 106 (not shown in FIG. 1 ).The apparatus 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 pressing-in force Fs in the pressed-in state of the pressing-in body 112. The oscillation generator can be designed as an ultrasonic or piezoelectric generator.A natural frequency and a natural amplitude of the elastic spring member 122 are different from the force amplitude and force frequency of the oscillating force Fo.The oscillation generator 120 is directly mechanically coupled to the pressing member 108 for transmitting the oscillating force Fo to the pressing member 108.Additionally or alternatively, the oscillation generator 120 may also be mechanically coupled to the workpiece receptacle 106 (not shown in FIG. 1 ).The apparatus 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.This oscillation detection device 132 can have, for example, a piezo-based acceleration or speed sensor.The oscillation detection device 132 is a component of the workpiece receptacle 106.Alternatively, the oscillation detection device 132 may be a component of the oscillation generator 120.The device 100 further comprises a force detection device 134 for detecting the static pressing-in force Fs. The force detection device 134 is a component of the force generator 116.Furthermore, the device 100 comprises a shape detection device 136 for detecting a three-dimensional shape of the workpiece impression 118 (cf. FIG. 4 ). For this purpose, the shape detection device 136 has a white light interferometer.Moreover, the device 100 comprises a central evaluation device 138, which comprises a storage 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 detected by these devices 132, 134, 136.Furthermore, the central evaluation device 138 is connected to the force generator 116 and the oscillation generator 120 via corresponding signal lines 142.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 constructed as an ultrasonic or piezoelectric generator.The device 100 described above can furthermore be surrounded by a noise protection device (not shown in FIG. 1 ) for damping the noise emissions produced during the oscillation excitation.The noise protection device can preferably be constructed as a noise protection capsule.FIG. 2 shows a further schematic illustration of the apparatus according to FIG. 1 for carrying out a method according to an exemplary embodiment of the invention.The device 100 according to FIG. 2 fundamentally has the same or equivalent or corresponding structural and / or functional features as the device 100 according to FIG. 1.The apparatus described in FIG. 1 is configured to perform the method described below.The method is configured to determine one or more imperfections 102 in a workpiece 104.In addition, the method is configured for determining at least one material characteristic variable K of a material of the workpiece 104.In its most general form, the method comprises the following steps:First, the first pressing body 112 is pressed into the surface 114 of the workpiece 104 with the static pressing force Fs for plastically deforming the workpiece 104 by means of the pressing body 112 for generating a plastically deformed workpiece impression 118.The static pressing force Fs is generated by the force generator 116 and transmitted to the pressing body 112 via the spring member 122 and the pressing member 108.In addition, the static pressing-in force Fs is detected by the force detection device 134 in real time and transmitted to the evaluation device 138 for further processing.A three-dimensional shape 124 of the plastically deformed workpiece impression 118 is then detected.The three-dimensional shape 124 is detected by means of the shape detection device 136, which likewise transmits detection data relating to the detected three-dimensional shape 124 to the evaluation device 138 in real time.In addition, an oscillating force Fo having a force amplitude and a force frequency in addition to the static pressing force Fs is applied to the pressing body 112 in the pressed state after the step of pressing the pressing body 112 into the surface 114 of the workpiece 104.The steps of detecting the three-dimensional shape 124 and applying an oscillating force to the pressing-in body 112 in the pressed-in state can take place independently of one another in time.In other words, the step of detecting the three-dimensional shape 124 may be performed before the step of applying pressure to the push-in body 112, or vice versa.In the case that the step of detecting the three-dimensional shape 124 is performed after the step of applying pressure to the pressing body 112, the method proceeds as follows:The pressing body 112 is first pressed with a percentage static pressing force Fs corresponding to a percentage static force percentage of a maximum static pressing force Fs.The maximum static pressing-in force Fs can be considered as the pressing-in force which, depending on the material of the workpiece 104, enables the most suitable workpiece impression 118 with regard to shape, size, penetration depth and required static pressing-in force Fs.The percentage static force corresponds to about 80% of the maximum static pressing-in force Fs.Alternatively, the percentage static force fraction may correspond to about 60% or about 70% of the maximum static pressing-in force.The reduction of the static pressing-in force Fs to the percentage static force component of approximately 80% of the maximum static pressing-in force has the background that the additional force amplitude from the oscillating force Fo should no longer plastically deform the material within the workpiece impression 118.Nevertheless, the static force component should be selected as high as possible, so that the best possible contact of the pressing-in body with the workpiece impression is produced and thus a reliable introduction of force into the workpiece is possible.According to FIG. 2, the application of the oscillating force Fo for excitation of oscillation of the workpiece 104 to the pressing-in body 112 in the pressed-in state is recognizable (see the illustrated double arrow in the oscillation generator 120).The oscillation excitation is performed by applying the oscillating force Fo to the workpiece 104 so that the workpiece 104 starts oscillating at a natural frequency and an intrinsic amplitude in the form of an oscillation response.Thereafter, the oscillation response of the workpiece 104 in response to the oscillation excitation of the workpiece 104 can be detected 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.Since the workpiece shape and material of the workpiece 104 have a large influence on the natural frequency and the natural amplitude, each individual workpiece 104 can give a corresponding individual oscillation response to the oscillation excitation.From the detected oscillation response, a determination of the one or more flaws 102 in the workpiece 104 can then be made by means of the evaluation device 138.In addition to the workpiece shape or shape and the material of the workpiece, defects of the workpiece 104 can have an influence on the oscillation response.In this respect, for each individual workpiece 104, a correspondingly individually detected oscillation response can be detected as a function of the flaws 102 present or absent in the workpiece 104 and stored in the evaluation device 138.The step of determining the one or more flaws 102 additionally comprises a comparison of the detected oscillation response with a tolerance range starting from a desired oscillation response of a workpiece 104.If the detected oscillation response is within the tolerance range, the workpiece 104 does not have any defects, whereas defects are present if the detected oscillation response is outside the tolerance range.The setpoint oscillation response can be a recorded oscillation response (i.e. a natural frequency and a natural amplitude) of a workpiece 104 of identical construction with the same material with no defects 102 present in the workpiece and can be stored in the evaluation device 138. Alternatively, the desired oscillation response can be a simulated oscillation response of the identically constructed workpiece with the same material.In order to check that no flaws are present in this identically constructed workpiece 104, this workpiece 104 can be checked by one or more test methods (such as a Roentgen or ultrasonic test method) before its desired oscillation response is stored in the evaluation device 138 for the purposes of matching.The tolerance range has a lower threshold value and an upper threshold value of a setpoint natural frequency response and / or setpoint natural amplitude response, in which a detected actual natural frequency response and a detected actual natural amplitude response of the detected oscillation response may lie.FIG. 2 shows a workpiece 104 of this type which has no defects and has been checked by means of the previously described method for determining one or more defects 102 by means of oscillation excitation.The method described above has been described for a single workpiece impression 118, wherein this method can naturally also be applied to a plurality of workpiece impressions 118 (not illustrated in FIG. 2 ).After the oscillation excitation for determining one or more flaws 102 has been completed, the same workpiece impression 118 can now be plastically deformed by means of the maximum static pressing-in force Fs by means of the pressing-in body 112.The workpiece impression 118 can naturally also be plastically deformed without previously performed oscillation excitation for determining one or more flaws 102 directly in a pressing-in process by means of the maximum static pressing-in force Fs.The pressing body 112 is then moved out of the workpiece impression 118 again, so that the three-dimensional shape 124 of the plastically deformed workpiece impression 118 is subsequently detected.As explained above, the three-dimensional shape 124 is acquired by means of the shape acquisition device 136, which transmits the shape acquisition data relating to the acquired three-dimensional shape 124 to the evaluation device 138 in real time.The evaluation device 138 then compares the captured three-dimensional shape 124 of the plastically deformed workpiece impression 118 with a simulated three-dimensional shape of a plastically deformed workpiece impression according to a material deformation model of the material 104.From the comparison, the at least one material characteristic variable K of the material of the workpiece 104 is determined.The material deformation model of the workpiece 104 is stored in the memory device of the evaluation device 138, wherein the comparison takes place as follows:The simulated three-dimensional shape of the plastically deformed workpiece impression is based on a so-called flow curve of the respective material, wherein the flow curve is mathematically defined by a plurality of material input parameters (for characterizing the plastic material behavior).The flow curve is implemented together with the real boundary conditions of the previously performed pressing-in process of the pressing-in body 112 (such as static pressing-in force, pressing-in depth and shape and geometry of the pressing-in body) in a finite element simulation (according to the material deformation model), from which a first simulated shape of the plastically deformed workpiece impression arises.This finite element simulation can be stored as a corresponding software application on the memory device of the evaluation device 138 and can be executed by the processing device of the evaluation device 138.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 detected shape of the plastically deformed workpiece impression 118 by means of an optimization algorithm according to the method of the sum of the squares of errors.The optimization algorithm ends when the target function converges and falls below a defined limit value.This limit value can preferably lie at about 5% deviation in the case of a three-dimensional simulation and preferably at about 3% deviation in the case of a two-dimensional simulation.The flow curve calculated by convergence (with the finally calculated material input parameters) can be converted into a technical stress-strain curve and from this the following material characteristics K can be determined in the form of comparison characteristic values based on the tensile test:comparison yield point R p0,2 from the determination method;comparative tensile strength R m from the determination method;solidification behavior; and / orqualitative determination of ductility for certain materials.FIG. 3 shows a further schematic illustration of the apparatus according to FIG. 1 for carrying out the method according to FIG. 2.The device 100 according to FIG. 3 fundamentally has the same or equivalent or corresponding structural and / or functional features as the device 100 according to FIG. 1.In contrast to FIG. 2, in which the workpiece 104 without defects has been tested, the workpiece 104 according to FIG. 3 has defects.Consequently, the detected oscillation response of the workpiece 104 (described in FIG. 2 ) lies outside the tolerance range, which is graphically represented by an atypical oscillation response on a display device 140 of the evaluation device 138.In contrast, a typical or normal oscillation excitation takes place by the oscillation generator 120 (illustrated by the point-symmetrical profile of the oscillation excitation).FIG. 4 shows a schematic partial sectional illustration in a plan view of a second depression body 126 of the apparatus 100 according to FIG. 1 for carrying out a method according to a further exemplary embodiment of the present invention.As can be seen in FIG. 4, the depression body 126 does not correspond to the first depression body 112 from FIGS. 1 to 3.The excitation of oscillations of the workpiece 104 described above according to FIGS. 2 and 3 serves to determine one or more flaws in the workpiece 104.In addition, an oscillation excitation of the workpiece 104 can be carried out in order to determine at least one further material characteristic variable K of the material of the workpiece 104 on the basis of the Wehler test.For this purpose, the first pressing body 112 is replaced and a second pressing body 126 is provided after the step of pressing the first pressing body 112 into the surface 114 of the workpiece 104 with the maximum static pressing force Fs.The first pressing-in body 112 can be exchanged manually and / or automatically.The first pressing body 112 and the second pressing body 126 both have the same cone shape.The pushing-in member and pushing-in member portion (not shown in FIG. 4 ) of the second pushing-in body 126 are also the same as the pushing-in member 108 and pushing-in member portion 110 of the first pushing-in body 112.The workpiece impression 118 produced thereby below the second impression body 126 can be seen in FIG. 4.In contrast to the first indenter 112, however, the second indenter 126 has an indenter surface 128 in which a recess 130 is made.The recess extends on a lateral surface or the pressing surface 128 along a straight connecting line from the tip to the base surface of the cone, the incision of which through the recess 130 can be seen in FIG. 4.Alternatively, a plurality of recesses 130 can also be made in the second pressing-in body 126.In order to determine the at least one further material characteristic variable K of the material of the workpiece 104 in a manner based on the Wehler test, the method or the device 100 executing this method takes place as follows:First, the second pressing body 126 is moved into the workpiece impression 118 that was previously plastically deformed by the first pressing body 112 until a contact is established between the second pressing body 126 and the workpiece impression 118.The second pressing body 126 is now pressed into the workpiece impression 118 with a static pressing force Fs for elastic deformation of the workpiece impression 118 by means of the second pressing body 126.This step serves to set an elastic medium or prestress in a manner based on the Wehler test in order to generate a static and elastic state of tension in the workpiece impression 118.The defined elastic stress level for the respective workpiece impression can be determined from the previously determined comparison characteristic values (cf. FIG. 3 ) by means of the material simulation model and can be adjusted accordingly via the static pressing-in force Fs.Without the cutout 130, compressive stresses σ p would be present in the workpiece impression 118 (apart from mechanical internal stresses as a result of the plastic deformation), which compressive stresses σ arise as a result of the contact of the homogeneous impression surface with the workpiece impression 118 at a certain impression force.However, only the compressive stress state is less suitable for carrying out a method based on the Wehler test because of its low material-damaging effect.In this respect, a tension state should be achieved in which tensile stresses σ z are also achieved in the workpiece impression 118, which is achieved by the cutout 130, since the material bulges minimally into the cutout 130 through the latter and is thus loaded in tension in the circumferential direction (indicated by the arrow).Consequently, the second pressing body 126 is applied with an oscillating force Fo having a force amplitude and a force frequency in addition to the static pressing force Fs for oscillating elastic deformation of the workpiece impression 118.By means of the force amplitude, the rated voltage amplitude S a can be simulated in the workpiece impression 118 in particular on the basis of the Wehler test.By contrast, the test time can be influenced with the force frequency and, in addition, the so-called oscillation play count (i.e. the actual number of generated force oscillations until fatigue) can be determined taking into account the test time, as will be explained below.For this purpose, static pressing-in force Fs is detected by means of force detection device 134, and oscillating force Fo having its force amplitude and its force frequency is detected by means of oscillation detection device 132 and transferred to evaluation device 138.The force detection device 134 can additionally or alternatively be used to detect the depth of depression of the second indenter 126.The evaluation device 138 compares the detected static pressing-in force Fs with a static desired pressing-in force and the detected oscillating force Fo with a desired oscillating force having its desired force amplitude and its desired force frequency.The static setpoint pressing-in force or the oscillating setpoint force for the respective workpiece impression can likewise be determined from the previously determined comparison characteristic values by means of the material simulation model.If the comparison reveals that the detected static pressing-in force or the detected oscillating force lie outside a defined tolerance range for the static setpoint pressing-in force or the oscillating setpoint force, it is possible to infer a failure of the material within the workpiece impression. The same applies to the detected depression depth.The failure of the material within the workpiece impression 118 can take place in the form of a material break-out or a material erosion, a crack formation or another material-separating deformation.Consequently, 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 impression 118. The fatigue characteristic value can be determined in particular in the form of a maximum vibration play number N.This maximum oscillation play count N can then be linked in a to the correspondingly detected static pressing force Fs or the detected oscillating force and the resulting rated voltage amplitude S to form a data pair and entered as a measurement point in a Wehler diagram.The previously described procedure of the method relates to an individual workpiece impression 118 and its elastic prestress and application of a swelling tensile stress.In the case of a plurality of workpiece impressions 118, a different defined elastic stress level can be generated for each workpiece impression 118, with the result that the respective workpiece impression 118 is elastically prestressed.Consequently, the static pressing-in force Fs can be varied by means of a plurality of static force values and the oscillating force Fo can be varied by means of a plurality of force amplitudes and a plurality of force frequencies.For this purpose, firstly a plurality of plastically deformed workpiece impressions 118 are produced in a surface 114 of the workpiece 104 by means of the first impression body 112Subsequently, the second pressing-in body 126 is pressed into a first workpiece impression 118 with a first static pressing-in force Fs 1 and, in the pressed-in state, is acted upon with a first oscillating force Fo 1 having a first force amplitude and a first force frequency in addition to the first static pressing-in force Fs 1.Accordingly, the second pressing-in body 126 is pressed into a second workpiece impression 118 with a second static pressing-in force Fs 2 and, in the pressed-in state, is acted upon with a second oscillating force Fo having a second force amplitude and a second force frequency in addition to the second static pressing-in force Fs 2.If there are more than two workpiece impressions 118, the static impression force Fs and the oscillating force Fo can be correspondingly varied for each further workpiece impression 118 and the procedure can be as described above.This maximum oscillation play count N determined per workpiece impression 118 can then be linked in a with the correspondingly detected static pressing force or the detected oscillating force or the nominal voltage amplitude S resulting therefrom to form a respective data pair and entered as further measurement points in a Wöhler diagram.FIG. 5 shows a schematic illustration of a stress-strain diagram for illustrating one or more material characteristics determined according to the method according to FIG. 4.This shows, by way of example, the variation of three different elastic tensile prestresses σ1, σ2and σ3along the Hook straight line with subsequent application of an elastic swelling tensile stress in addition to the elastic tensile prestresses σ1, σ2and σ3.As explained in FIG. 4, these elastic tensile prestresses can be generated by the second pressing body 126 being pressed into three different workpiece impressions 118 with three different static pressing forces Fs.Accordingly, as illustrated in FIG. 4, the elastically swelling tensile stresses can be generated by applying three different oscillating pressing forces Fo to the second pressing body 126 in three different workpiece presses 118.The kink at the end of the respective three temporal progression curves of the sum of elastic tensile prestress and elastically swelling tensile stress corresponds to the running time until material fatigue occurs, which can be determined by means of the respectively detected static pressing-in force Fs or pressing-in depth (as explained in FIG. 4 ).By knowing the running time, the material parameter K can then be determined in the form of the maximum vibration cycle number N (marked n in FIG. 5 in the form of n1, n2and n3) of the respective tensile prestresses σ1, σ2and σ3.List of reference characters100 Device 102 defect 104 workpiece 106 workpiece holder 108 pressing element 110 pressing element region 112 first pressing body 114 surface of the workpiece 116 force generator 118 workpiece impression 120 oscillation generator 122 elastic spring element 124 shape of the workpiece impression 126 second pressing body 128 pressing surface 130 recess 132 oscillation detection device 134 force detection device 136 shape detection device 138 central evaluation device 140 display device 142 signal line Fs static pressing force Fs 1 first static pressing force Fs 2 second static pressing force Fo oscillating force Fo 1 first oscillating force Fo 2 second oscillating force K material characteristic variable N number of oscillation clearances σ p compressive stress σ z tensile stressReferences included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedDE1020111115519 A1

[0004]

Claims

Method for determining one or more flaws (102) in a workpiece (104) and / or for determining at least one material characteristic variable (K) of a material of the workpiece (104), comprising the following steps: - pressing an, in particular first, pressing body (112) into a surface (114) of the workpiece (104) with a static pressing force (Fs) for the plastic deformation of the workpiece (104) by means of the pressing body (112) for generating a plastically deformed workpiece impression (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 push-in body (112) in the pushed-in state, in addition or alternatively to the static push-in force (Fs), during the step and / or after the step of pushing the push-in body (112) into the surface (114) of the workpiece (104).Method according to Claim 1, characterized by - a comparison of the captured shape (124), in particular of the captured three-dimensional shape (124), of the plastically deformed workpiece impression (118) with a simulated shape, in particular of a simulated three-dimensional shape, of a plastically deformed workpiece impression (118) according to a material deformation model of the workpiece (104); and - a determination of the at least one material characteristic variable (K) of the material of the workpiece (104) from the comparison.Method according to Claim 1 or Claim 2, characterized by - the application of the oscillating force (Fo) for oscillating excitation of the workpiece (104) to the depression body (112) in the pressed state; - a detection of an oscillation response of the workpiece (104) in response to the oscillation excitation of the workpiece (104); and - a determination of the one or more flaws (102) in the workpiece (104) from the detected oscillation response.Method according to Claim 3, characterized in that the step of determining comprises comparing the detected oscillation response with a tolerance range starting from a setpoint 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 setpoint natural frequency response and / or setpoint intrinsic amplitude response, in which a detected actual natural frequency response and / or a detected actual intrinsic amplitude response of the detected oscillation response may lie.Method according to one of the preceding claims, characterized in that the pressing-in body (112) is / is pressed in with a proportional static pressing-in force (Fs) which corresponds to a percentage static force fraction of a maximum static pressing-in force (Fs), wherein the percentage static force fraction corresponds to approximately 60%, preferably approximately 70%, and particularly preferably approximately 80% of the maximum static pressing-in force (Fs).Method according to one of the preceding claims, characterized bya manual and / or automatic replacement of the first press-in body (112) and provision of a second press-in body (126) after the step of pressing the first press-in body (112) into the surface (114) of the workpiece (104), wherein the second press-in body (126) has a press-in surface (128) in which one or more recesses (130) is / are introduced.Method according to Claim 5 or Claim 6, characterized bya movement of the second impression body (126) into the workpiece impression (118) which has previously been plastically deformed by the first impression body (112) until a contact is produced between the second impression body (126) and the workpiece impression (118).Method according to Claim 7, characterized by - pressing the second pressing body (126) into the workpiece impression (118) with a static pressing force (Fs) for the elastic deformation of the workpiece impression (118) by means of the second pressing body (126); and - applying to the second pressing body (126) an oscillating force (Fo) having a force amplitude and / or a force frequency in addition to the static pressing force (Fs) for the oscillating elastic deformation of the workpiece impression (118).Method according to claim 8, characterised in that the static pressing-in force (Fs) and / or the oscillating force (Fo) having its force amplitude and / or its force frequency are / is detected and compared with a static desired pressing-in force and / or with an oscillating desired force having its desired force amplitude and / or its desired force frequency.Method according to Claim 9, characterized in that at least one fatigue characteristic value of the material of the workpiece (104) in the workpiece impression (118), in particular in the form of a maximum vibration play number (N), is determined by means of this comparison.Method according to one of Claims 8 to 10, characterized in that the static pressing-in force (Fs) can be varied by means of a plurality of static force values and / or the oscillating force (Fo) can / is varied by means of a plurality of force amplitudes and / or a plurality of force frequencies.Method according to Claim 11, characterized in that - a plurality of plastically deformed workpiece impressions (118) are produced in a surface (114) of the workpiece (104) by means of the first impression body (112); - the second impression body (126) is pressed into a first workpiece impression (118) with a first static impression force (Fs1) and / or, in the pressed-in state, is acted upon by a first oscillating force (Fo1) having a first force amplitude and / or a first force frequency in addition to the first static impression force (Fs1); and - the second pressing-in body (126) is pressed into a second workpiece impression (118) with a second static pressing-in force (Fs2) and / or, in the pressed-in state, is acted upon with a second oscillating force (Fo) having a second force amplitude and / or a second force frequency in addition to the second static pressing-in force (Fs2).Device (100) for determining one or more flaws (102) in a workpiece (104) and / or for determining at least one material characteristic variable (K) of a material of the workpiece (104), comprising: - a workpiece receptacle (106) for receiving and / or fixing the workpiece (104); - a pressing element (108) comprising a pressing element region (110), which has a pressing body (112) for pressing into a surface (114) of the workpiece (104); a force generator (116), which is mechanically coupled to the workpiece receptacle (106) and / or the pressing element (108), for generating a static pressing force (Fs) for pressing the pressing body (112) into a surface (114) of the workpiece (104) for plastically deforming the workpiece (104) by means of the pressing body (112) for generating a plastically deformed workpiece impression (118); and an oscillation generator (120), which is mechanically coupled to the workpiece receptacle (106) and / or the pressing element (108), for generating an oscillating force (Fo) having a force amplitude and / or a force frequency in addition or alternatively to the static pressing force (Fs) in the pressed state of the pressing body (112).Device (100) according to claim 13, characterised 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).Device (100) according to claim 14, characterised in that a natural frequency and / or a natural amplitude of the elastic spring element (122) differ / differs from the force amplitude and / or force frequency of the oscillating force (Fo).

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