Method for constructing hole surface defect distribution curve for probabilistic damage tolerance evaluation

Abstract

The invention relates to a method for constructing a hole surface defect distribution curve for probabilistic damage tolerance evaluation. The method comprises the following steps: preparing a tested piece with a hole; performing a low-cycle fatigue test on the tested piece under different loading conditions to obtain the low-cycle fatigue life of the tested piece; deducing an equivalent initial defect size based on crack propagation analysis by using the loading condition and the low-cycle fatigue life of the tested piece as constraints; fitting the equivalent initial defect size according to extreme value distribution to obtain a defect size distribution curve; the defect size distribution curve is used for obtaining the defect occurrence rate through a probability damage tolerance evaluation example; and combining the defect size distribution curve and the defect occurrence rate to obtain the hole surface defect distribution curve.

Description

Technical Field

[0001] This disclosure relates to the field of aero-engines, and in particular to the damage tolerance risk assessment of surface machining and usage defects in life-limiting components of aero-engine rotors. Background Technology

[0002] Airworthiness regulations FAR 33.70, CCAR 33.70, and CS-E 515 all stipulate that appropriate damage tolerance assessments must be performed to determine potential failures due to defects in materials, manufacturing, and use within the approved lifespan of the part. In response to this, the FAA issued Advisory Circular AC33.70-2, introducing the concept of damage tolerance and requiring probabilistic damage tolerance assessments for machining and use defects at holes included in engine rotor components, as a supplement to existing safe-life methods.

[0003] The surface defect distribution curve of the hole is an essential input for this probabilistic damage tolerance assessment. Although the airworthiness regulation AC33.70-2 advisory circular provides a defect distribution curve for reference, this curve is not well applicable to all hole machining defects.

[0004] This disclosure addresses, but is not limited to, the many factors mentioned above. Summary of the Invention

[0005] To this end, this disclosure provides a method for constructing a hole surface defect distribution curve for probabilistic damage tolerance assessment of aero-engines. The method uses the same hole machining process as actual parts to prepare a test part (i.e., a hole simulation part) with holes. Fatigue testing is performed on the test part to determine its lifespan. Based on the fatigue life, the equivalent initial defect size is deduced, and a defect size distribution curve is fitted. Subsequently, a probabilistic system is used to determine the defect occurrence frequency, thereby enabling the establishment of a hole surface defect distribution curve without field service data to support engine airworthiness certification.

[0006] The method disclosed herein is based on low-cycle fatigue testing of the test piece at the current level of hole machining technology to back-calculate the initial defect size and then establish a defect distribution curve. It can acquire a sufficient amount of defect data in a short time, thereby enabling the establishment of a hole surface defect distribution curve without field service data. This can be used for hole surface defect probability damage tolerance assessment to support engine airworthiness certification.

[0007] This disclosed method breaks through the traditional approach of obtaining defect data only from production and in-service inspection processes. It proposes a novel method to establish defect distribution curves by acquiring defect data from fatigue tests of the tested simulated parts, thus solving the problem of not being able to obtain defect data from field in-service inspections during engine development. The method uses simulated parts with holes whose geometry and processing technology are consistent with actual parts. This reflects the current level of hole processing technology and comprehensively considers the influence of various factors such as hole geometry and materials. Furthermore, the tested simulated parts have short testing cycles, low testing costs, and readily obtain sufficient defect data. In this method, the crack propagation life calculated using the equivalent initial defect size represents the true fatigue life of the part, because the process of deducing the defect size based on fatigue life is consistent with the process of calculating the crack propagation life based on the initial defect. This method also determines the defect incidence rate by referring to the probabilistic damage tolerance assessment example in AC33.70-2 when no field service data is available, and enables rapid curve calibration iteration when field service data becomes available in the future.

[0008] Therefore, the method disclosed herein achieves the goal of probabilistic risk assessment in the absence of commercial engine service data, while obtaining a large amount of defect data and saving time and economic costs, thus supporting airworthiness certification.

[0009] According to a first aspect of this disclosure, a method for constructing a hole surface defect distribution curve for probabilistic damage tolerance assessment is provided, comprising: preparing a test piece having a hole; performing a low-cycle fatigue test on the test piece under different loading conditions to obtain a low-cycle fatigue life of the test piece; using the loading conditions and the low-cycle fatigue life of the test piece as constraints, deriving an equivalent initial defect size based on crack propagation analysis; fitting the equivalent initial defect size to an extreme value distribution to obtain a defect size distribution curve; using the defect size distribution curve to obtain a defect incidence rate through a probabilistic damage tolerance assessment example; and combining the defect size distribution curve and the defect incidence rate to obtain the hole surface defect distribution curve.

[0010] According to one embodiment, the loading conditions include a combination of stress and temperature.

[0011] According to another embodiment, the extreme value distribution is a Gumbel distribution or a Weibull distribution.

[0012] According to yet another embodiment, the formula for the probabilistic damage tolerance assessment example is as follows:

[0013] POF = 1 - (1 - P fd *S*P d / credit) n

[0014] Where POF represents the failure probability, P fd The conditional failure probability is calculated using probabilistic fracture mechanics based on the defect size distribution curve, where S represents the surface area of ​​the hole, and P represents the surface area of ​​the hole. d represents the defect occurrence rate, credit represents the hole processing confidence level, and n represents the number of holes.

[0015] According to another embodiment, using the defect size distribution curve to derive the defect occurrence rate through a probabilistic damage tolerance assessment example includes: using the hole surface defect distribution curve provided by airworthiness regulations to calculate the failure probability using the formula; and using the calculated failure probability and the obtained defect size distribution curve to extrapolate the defect occurrence rate using the formula.

[0016] According to another embodiment, the method further includes: obtaining the true failure probability from the field service data when field service data is available; and using the true failure probability and the obtained defect size distribution curve to calculate the defect occurrence rate through the formula.

[0017] According to yet another embodiment, the true failure probability is calculated as follows:

[0018]

[0019] According to another embodiment, the defect size distribution curve is in a coordinate system in which the horizontal axis represents the defect length and the vertical axis represents the cumulative probability of defect occurrence.

[0020] According to another embodiment, combining the defect size distribution curve and the defect occurrence rate to obtain the hole surface defect distribution curve includes: translating the defect size distribution curve so that the intersection of the defect size distribution curve and the vertical axis of the coordinate system is at point (0,1); and multiplying the translated defect size distribution curve by the defect occurrence rate to obtain the hole surface defect distribution curve.

[0021] According to yet another embodiment, the hole is prepared using the same machining process as the actual part.

[0022] According to yet another embodiment, the method further includes using the defect distribution curve on the hole surface to perform probabilistic damage tolerance assessment.

[0023] According to yet another embodiment, the probabilistic damage tolerance assessment also uses the geometric information, stress distribution, and material data of the part.

[0024] According to another embodiment, the test piece is a plurality of test pieces prepared using each of a plurality of different materials, and the obtained hole surface defect distribution curve includes a hole surface defect distribution curve for the test piece for each of the plurality of different materials and a hole surface defect distribution curve for all test pieces, wherein the most conservative curve among these hole surface defect distribution curves is selected as the aforementioned hole surface defect distribution curve.

[0025] The aspects generally include, as substantially as described herein with reference to the accompanying drawings and as explained by the drawings, methods, apparatus, systems, computer program products, and processing systems.

[0026] The foregoing has broadly outlined the features and technical advantages of the examples according to this disclosure so that the following detailed description may be better understood. Additional features and advantages will be described thereafter. The disclosed concepts and specific examples can be readily used as the basis for modifying or designing other structures for implementing the same purposes as this disclosure. Such equivalent constructions do not depart from the scope of the appended claims. The characteristics of the concepts disclosed herein, in both their organization and manner of operation, and their associated advantages, will be better understood by considering the following description in conjunction with the accompanying drawings. Each drawing is provided for illustrative and descriptive purposes and does not define any limitation on the claims. Attached Figure Description

[0027] To gain a more detailed understanding of the features described above in this disclosure, reference can be made to various aspects of the above-briefly summarized content, some of which are illustrated in the accompanying drawings. However, it should be noted that the drawings illustrate only certain typical aspects of this disclosure and should not be considered as limiting its scope, as other equivalent aspects are permissible in this description. Identical reference numerals in different drawings may identify the same or similar elements.

[0028] Figure 1 This is a flowchart illustrating a method for constructing a hole surface defect distribution curve for probabilistic damage tolerance assessment according to an example embodiment of the present disclosure;

[0029] Figure 2 A schematic diagram is shown illustrating the derivation of the equivalent initial defect size based on crack propagation analysis according to an example embodiment of the present disclosure;

[0030] Figure 3 A schematic diagram is shown of a defect size distribution curve obtained by fitting a Weibull distribution according to an example embodiment of the present disclosure;

[0031] Figure 4 A schematic diagram of a hole surface defect distribution curve according to an example embodiment of the present disclosure is shown;

[0032] Figure 5 A schematic diagram is shown illustrating a plurality of defect size distribution curves obtained by fitting a Weibull distribution according to an example of this disclosure;

[0033] Figure 6 A schematic diagram of the stress distribution contour plot and calculation location of the calculated section is shown when calibrating a probabilistic damage tolerance assessment system using the AC33.70-2 example according to an example of this disclosure;

[0034] Figure 7 An example of the respective corresponding to this disclosure is shown. Figure 5 A schematic diagram of the defect distribution curves on the surface of multiple holes, showing the distribution curves of various defect sizes.

[0035] Figure 8 A schematic diagram showing the stress distribution and calculation location of a section for probabilistic damage tolerance assessment of a turbine disk bolt hole, according to an example of this disclosure; and

[0036] Figure 9 A schematic diagram is shown of the probability damage tolerance assessment results of a certain type of turbine disk bolt hole using different EIFS defect distribution curves according to an example of this disclosure. Detailed Implementation

[0037] Terminology Explanation:

[0038] Rotor life-limiting components: Rotor parts whose primary failure may lead to harmful consequences for the engine.

[0039] Probabilistic damage tolerance: An element of life management that identifies potential defects caused by materials, processing, or use, and assesses the potential for such defects to reduce the structural integrity of parts through fracture mechanics, process control, and nondestructive testing, as a complement to existing safe life methods.

[0040] Hole surface defect distribution curve: The machining defect distribution curve of the circular hole of the rotor is a key input for probabilistic damage tolerance assessment, which expresses the statistical defect information in the form of defect size distribution and defect occurrence frequency.

[0041] The inventors recognized that probabilistic damage tolerance assessment requires inputting component geometry, defect distribution curves, stress and temperature distributions, load spectra, material data, non-destructive testing detection probabilities, inspection intervals, etc., before assessing failure risk using probabilistic fracture mechanics. The hole surface defect distribution curve, as one of the defect distribution curves, is an indispensable key input for this probabilistic damage tolerance assessment, representing the defect size distribution and defect occurrence frequency, reflecting the hole machining level. The defect distribution curves provided in Advisory Circular AC33.70-2 are statistics on wheel disc hole machining defects from foreign engine service failures and in-service inspections detected between approximately 1970 and 2004. This only reflects the hole machining level of foreign suppliers decades ago, and AC33.70-2 does not provide a method for establishing defect distribution curves. Considering the improvements in machining equipment, processes, and non-destructive testing capabilities over the decades, as well as further advancements in industrial development leading to smaller defect sizes and lower detection rates, continuing to use the defect distribution curves in AC33.70-2 for damage tolerance assessment would sacrifice the economic efficiency of some rotor life-limiting components and increase design iterations. Therefore, it is necessary to construct a new defect distribution curve for the pore surface.

[0042] The inventors also recognized that domestically produced commercial aero engines are in the development stage and have no field service experience, so it is impossible to capture defect data from the field. Under these circumstances, it is impossible to establish a hole surface defect distribution curve based on field service data.

[0043] To this end, this disclosure provides a method for constructing a hole surface defect distribution curve for probabilistic damage tolerance assessment of aero-engines. The method uses the same hole machining process as actual parts to prepare a test part (i.e., a hole simulation part) with holes. Fatigue testing is performed on the test part to determine its lifespan. Based on the fatigue life, the equivalent initial defect size is deduced, and a defect size distribution curve is fitted. Subsequently, a probabilistic system is used to determine the defect occurrence frequency, thereby enabling the establishment of a hole surface defect distribution curve without field service data to support engine airworthiness certification.

[0044] The method disclosed herein is based on low-cycle fatigue testing of the test piece at the current level of hole machining technology to back-calculate the initial defect size and then establish a defect distribution curve. It can acquire a sufficient amount of defect data in a short time, thereby enabling the establishment of a hole surface defect distribution curve without field service data. This can be used for hole surface defect probability damage tolerance assessment to support engine airworthiness certification.

[0045] The method disclosed herein breaks through the traditional approach of obtaining defect data only from production and in-service inspection processes. It proposes a novel method to obtain defect data from fatigue tests of the tested simulated parts to establish defect distribution curves, thereby solving the problem that defect data cannot be obtained from field in-service inspections during the engine development stage.

[0046] The method disclosed herein uses a simulated hole with the same geometry and machining process as the actual part, reflecting the current state of hole machining technology and comprehensively considering the influence of various factors such as hole geometry and material. Furthermore, the simulated hole has a short testing cycle, low testing cost, and readily obtains sufficient defect data. In this method, the crack propagation life calculated using the equivalent initial defect size represents the true fatigue life of the part, because the defect size deduction process based on fatigue life is consistent with the crack propagation life calculation process based on initial defects. This method also determines the defect incidence rate by referring to the probabilistic damage tolerance assessment example in AC33.70-2 when no field service data is available, and enables rapid curve calibration iteration when field service data becomes available in the future.

[0047] Furthermore, field service data (i.e., failures of parts during actual service, such as fractures or cracks) are extremely rare, making it difficult to accumulate sufficient data in a short period. Therefore, the method disclosed herein achieves the goal of probabilistic risk assessment in the absence of commercial engine service data, obtaining a large amount of defect data while saving time and economic costs, thus supporting airworthiness certification.

[0048] The detailed description that follows, taken in conjunction with the accompanying drawings, is intended as a description of various configurations and is not intended to represent the only configurations in which the concepts described herein can be practiced. This detailed description includes specific details to provide a thorough understanding of the various concepts. However, it will be apparent to those skilled in the art that these concepts can be practiced without these specific details.

[0049] The following is for reference. Figure 1 The document illustrates a flowchart of a method 100 for constructing a hole surface defect distribution curve for probabilistic damage tolerance assessment according to an example embodiment of the present disclosure.

[0050] As shown in the figure, method 100 may include, within block 110, the preparation of a test piece with holes. In one embodiment of this disclosure, method 100 may select rotor life-limiting component holes of different materials and geometries to design a test piece with holes (also referred to as a hole simulation component), wherein these holes are prepared using the same hole processing technology as the actual part.

[0051] Next, in block 120, method 100 may include performing low-cycle fatigue tests on the test piece under different loading conditions to obtain the low-cycle fatigue life of the test piece. In one embodiment of this disclosure, the loading conditions may include a combination of stress and temperature. According to this embodiment, the low-cycle fatigue life of each test piece can be obtained by performing multiple sets of grouped low-cycle fatigue tests under different stresses and temperatures on each test piece.

[0052] In one embodiment of this disclosure, method 100 may prepare multiple test pieces and perform low-cycle fatigue tests on these test pieces respectively to collect sufficient test data (such as the low-cycle fatigue life of the test pieces).

[0053] Method 100 may further include, in block 130, using loading conditions and the low-cycle fatigue life of the test piece as constraints, deriving the equivalent initial defect size (EIFS) based on crack propagation analysis. Those skilled in the art will understand that crack propagation is a dynamic process of crack nucleation and growth in a material under the influence of external factors. The crack propagation analysis employed in Method 100 is a commonly used analytical method in the field of studying how cracks propagate, and will not be elaborated upon here. However, as mentioned above, the use of crack propagation analysis in Method 100 is not for studying how cracks will undergo stages such as nucleation, steady-state propagation, and unstable propagation, but rather for reversing the initial crack size.

[0054] In yet another embodiment of this disclosure, in crack propagation analysis, the low-cycle fatigue life of the test piece is considered as the crack propagation life, and the equivalent initial defect size is equivalent to the crack size that begins to propagate in the first stress cycle. (See reference...) Figure 2 This illustrates a schematic diagram of deriving the equivalent initial defect size based on crack propagation analysis according to an example embodiment of the present disclosure. Figure 2 As shown, the vertical axis represents the defect length, and the horizontal axis represents the life (i.e., based on crack propagation life). After obtaining the low-cycle fatigue life N of the test piece (which can be expressed as the number of cycles in the low-cycle fatigue test), it can be... Figure 2 The curve shown is based on the EIFS curve obtained from crack propagation analysis, which is dependent on N, and the EIFS can be conveniently calculated.

[0055] Continue to refer to Figure 1 Method 100 may include, in block 140, fitting an equivalent initial defect size to an extreme value distribution to obtain a defect size distribution curve. In one embodiment of this disclosure, the extreme value distribution may be a Gumbel distribution or a Weibull distribution. (See reference...) Figure 3 This illustrates a schematic diagram of a defect size distribution curve obtained by fitting a Weibull distribution according to an example embodiment of the present disclosure. Figure 3 In the example curve shown, the horizontal axis of the coordinate system represents the defect length, and the vertical axis represents the cumulative probability of defect occurrence. It will become clear that... Figure 3 The curves shown only represent the defect size distribution and do not take into account the defect incidence rate.

[0056] Continue to refer to Figure 1 Method 100 may include in box 150, using a defect size distribution curve to derive the defect occurrence rate through a probabilistic damage tolerance assessment example.

[0057] In one embodiment of this disclosure, the formula for the probabilistic damage tolerance assessment example is as follows:

[0058] POF = 1 - (1 - P fd *S*P d / credit) n (1)

[0059] Where POF represents the failure probability, P fd The conditional failure probability is calculated using probabilistic fracture mechanics based on the defect size distribution curve, where S represents the surface area of ​​the hole, and P represents the surface area of ​​the hole. d represents the defect occurrence rate, credit represents the hole processing confidence level, and n represents the number of holes.

[0060] Further according to this embodiment, using the defect size distribution curve to derive the defect occurrence rate through a probability damage tolerance assessment example may include: using the hole surface defect distribution curve provided by airworthiness regulations (e.g., AC33.70-2) to calculate the failure probability using Formula 1; and using the calculated failure probability and the obtained defect size distribution curve to deduce the defect occurrence rate using Formula 1.

[0061] For example, Method 100 may first use the hole surface defect distribution curve provided by airworthiness regulations (e.g., AC33.70-2) to derive the defect size distribution curve and defect incidence rate. Then, using the derived defect size distribution curve, a first conditional failure probability is calculated through probabilistic fracture mechanics. Subsequently, the hole surface area, hole machining confidence level, number of holes, the calculated first conditional failure probability, and the derived defect incidence rate are substituted into Formula 1 to calculate the failure probability. Next, Method 100 may use the defect size distribution curve obtained in block 140 to calculate a second conditional failure probability through probabilistic fracture mechanics, and substitute the hole surface area, hole machining confidence level, number of holes, the calculated failure probability, and the second conditional failure probability into Formula 1 to calculate the defect incidence rate.

[0062] Finally, in box 160, method 100 may include combining a defect size distribution curve and a defect occurrence rate to obtain a hole surface defect distribution curve.

[0063] In one embodiment of this disclosure, combined with Figure 3 To obtain the hole surface defect distribution curve by combining the defect size distribution curve and the defect occurrence rate, the following methods can be used: translating the defect size distribution curve so that its intersection with the vertical axis of the coordinate system is at point (0,1); and multiplying the translated defect size distribution curve by the defect occurrence rate to obtain the hole surface defect distribution curve. For example... Figure 3As shown, the horizontal axis of the coordinate system represents the defect length, and the vertical axis represents the cumulative probability of defect occurrence. The curve translation described above is equivalent to a normalization operation, which can then be combined with the defect occurrence rate to obtain the desired defect distribution curve on the hole surface.

[0064] refer to Figure 4 This illustrates a schematic diagram of the surface defect distribution curve of a hole according to an example embodiment of the present disclosure. As can be seen, Figure 4 The example curve shown has its vertical axis representing the number of defects per unit area (in this example, per square inch), and its horizontal axis representing the length of defects (in inches in this example). It will be understood that the units for area and length can be any suitable units, which will not be elaborated upon here.

[0065] In yet another embodiment of this disclosure, method 100 may optionally include using a hole surface defect distribution curve to perform probabilistic damage tolerance assessment. It will be understood that probabilistic damage tolerance assessment also utilizes part geometry, stress distribution, material data, etc., which will not be elaborated upon here.

[0066] In a preferred embodiment of this disclosure, when field service data becomes available in the future, method 100 can update the obtained hole surface defect distribution curve. For example, method 100 may include obtaining the true failure probability from the field service data when available; and using the true failure probability and the obtained defect size distribution curve to calculate the defect incidence rate using Formula 1. Thus, this defect incidence rate will be the true defect incidence rate that conforms to the actual data at that time. Therefore, method 100 can combine the defect size distribution curve and the true defect incidence rate at block 160 to obtain the updated hole surface defect distribution curve.

[0067] According to this embodiment, the true failure probability can be calculated as follows:

[0068]

[0069] For example, when field service data on engine failure / crack detection exists, the defect incidence rate can be corrected based on this actual field service data, as shown in the calculation principle above. Therefore, by statistically analyzing the number of holes on a part, the number of times the part fails / cracks are detected in service, and the total number of times the part has been in service, the probability of field failure or crack detection, i.e., the actual failure probability, can be determined.

[0070] In a preferred embodiment of this disclosure, the test piece may include multiple test pieces prepared using each of a variety of different materials, and the obtained hole surface defect distribution curve includes hole surface defect distribution curves for test pieces made of each of the various different materials and a hole surface defect distribution curve for all test pieces, wherein the most conservative curve among these hole surface defect distribution curves is selected as the final hole surface defect distribution curve.

[0071] In another preferred embodiment of this disclosure, when the experimental sample size is insufficient or the fitting parameters of the equivalent initial defect size curve are not stable due to factors such as different materials, hole geometry, and processing positions, the probability damage tolerance assessment results of the real part structure can be used to help select the most conservative defect distribution curve.

[0072] The following specific example further illustrates the method of this disclosure:

[0073] (1) The equivalent initial defect size was deduced from the fatigue life of the perforated test specimen prepared using TC4 and IN718 materials, and a series of defect size distribution curves were obtained by fitting different materials, such as Figure 5 As shown. Figure 5 A schematic diagram is shown illustrating a method for fitting multiple defect size distribution curves using a Weibull distribution according to an example of this disclosure. Figure 5 As shown, curve 1 represents the defect size distribution curve of the hole surface defects for parts made of all materials; curve 2 represents the defect size distribution curve of the hole surface defects for parts made of TC4 material; and curve 3 represents the defect size distribution curve of the hole surface defects for parts made of IN718 material. It will be understood that any other suitable material can be used as a substitute or supplement to the two materials mentioned above, which will not be elaborated upon here.

[0074] (2) Use the examples provided in AC33.70-2 to calibrate the probabilistic damage tolerance assessment system. Input the part's geometry, load, material data, defect distribution curve, eddy current testing POD curve, defect numerator, and inspection strategy into the probabilistic damage tolerance assessment system. The stress distribution and calculation location are as follows: Figure 6 As shown, locations 1# and 2# are calculated as surface cracks of type SC18, while locations 3# and 4# are calculated as corner cracks of type CC08. A probabilistic damage tolerance assessment is performed on this example, and the highest failure probability among these four locations is taken as the failure risk for that hole. In this example, the probabilistic damage tolerance assessment system uses the Monte Carlo method to calculate the failure probability. The location with the highest failure probability within a 20,000-hour service life is location 2#, with a failure probability of 2.616E-4 without in-service inspection. Within the acceptable failure risk range of AC33.70-2 service life, the probabilistic damage tolerance system is calibrated.

[0075] (3) Construct a defect distribution curve that considers the defect occurrence rate. Using the failure probability of 2.616E-4 as the failure probability, replace the defect distribution curve in the calibration example with the EIFS defect size distribution curve fitted in (1), without changing other input items. After multiple iterations of calculation by the probability damage tolerance assessment system, the defect occurrence rate P corresponding to each defect size distribution curve can be determined. d Combining the defect occurrence rate with the defect size distribution curve yields a defect distribution curve that simultaneously considers both defect frequency and distribution shape, such as... Figure 7 As shown. Figure 7 An example of the respective corresponding to this disclosure is shown. Figure 5 A schematic diagram of the defect distribution curves on the surface of multiple holes, showing the distribution curves of various defect sizes. (See attached diagram.) Figure 7 As shown, curve 1 represents the distribution curve of hole surface defects for parts made of all materials; curve 2 represents the distribution curve of hole surface defects for parts made of TC4 material; and curve 3 represents the distribution curve of hole surface defects for parts made of IN718 material.

[0076] (4) Select the defect distribution curve based on the probability damage tolerance assessment results of the hole surface defects of the actual part. Select the actual structure of the part, and input the geometric information, stress distribution, material data, and the defect occurrence rate and hole surface defect distribution curve obtained in (3) into the probability damage tolerance assessment system to assess the failure risk of the actual part. Taking the bolt hole of a certain type of turbine disk as an example, the probability damage tolerance assessment is carried out. The input stress, temperature distribution and calculation location are as follows: Figure 8 As shown, the defect size distribution curve is as follows: Figure 5 As shown, the failure probability curve corresponding to the number of cycles is as follows: Figure 9 As shown, curve 1, which has the most conservative risk assessment result (i.e., the risk of the assessment result of this curve is the highest compared to the assessment results of other curves), is selected as the final hole surface defect distribution curve.

[0077] This invention starts with fatigue testing of a simulated component with holes, representing the current level of hole machining technology. It uses fatigue life to inversely deduce the equivalent initial defect size to establish an EIFS defect size distribution curve. Then, by referring to the AC33.70-2 case or the field failure risk of other engine models, it uses a probabilistic damage tolerance assessment system to iteratively determine the defect incidence rate. This achieves the goal of probabilistic damage tolerance risk assessment in the absence of commercial engine service data. It obtains a large number of data points while saving time and economic costs, and supports airworthiness certification.

[0078] It will be understood that the methods disclosed herein can be applied to fields other than aero-engines for evaluating the lifespan of perforated parts.

[0079] In this disclosure, the terms "engine" and "aircraft engine" are used interchangeably.

[0080] The above detailed description includes references to the accompanying drawings, which form part of the detailed description. The drawings illustrate specific embodiments that can be practiced by way of illustration. These embodiments are also referred to herein as “examples.” Such examples may include elements other than those shown or described. However, examples including the shown or described elements are also contemplated. Furthermore, examples of any combination or arrangement of those elements shown or described are contemplated, or with reference to specific examples (or one or more aspects thereof) shown or described herein, or with reference to other examples (or one or more aspects thereof) shown or described herein.

[0081] In the appended claims, the terms “comprising” and “including” are open-ended, meaning that a system, apparatus, article of manufacture, or process containing elements other than those listed after such terms in a claim is still considered to fall within the scope of that claim. Furthermore, in the appended claims, the terms “first,” “second,” and “third,” etc., are used merely as designations and are not intended to indicate a numerical order of their contents.

[0082] Furthermore, the order of operations described in this specification is exemplary. In alternative embodiments, the operations may be performed in a different order than that shown in the accompanying drawings, and the operations may be combined into a single operation or broken down into more operations.

[0083] The above description is intended to be illustrative and not restrictive. For example, the examples described above (or one or more aspects thereof) may be used in conjunction with other embodiments. Other embodiments may be used by those skilled in the art after reviewing the above description. The abstract allows the reader to quickly determine the nature of this technical disclosure. This abstract is submitted and it is understood that it is not intended to interpret or limit the scope or meaning of the claims. Furthermore, in the above detailed description, various features may be grouped together to make this disclosure flow smoothly. However, the claims may not state every feature disclosed herein, as embodiments may characterize a subset of said features. Furthermore, embodiments may include fewer features than those disclosed in a particular example. Therefore, the appended claims are thus incorporated into the detailed description, with each claim existing independently as a separate embodiment. The scope of the embodiments disclosed herein should be determined by reference to the full scope of the appended claims and equivalents of such claims.

Claims

1. A method for constructing a hole surface defect distribution curve for probabilistic damage tolerance assessment, comprising: Prepare a test piece with holes; The test piece was subjected to low-cycle fatigue tests under different loading conditions to obtain its low-cycle fatigue life. Using the loading conditions and the low cyclic fatigue life of the test piece as constraints, the equivalent initial defect size is derived based on crack propagation analysis. The equivalent initial defect size is fitted according to the extreme value distribution to obtain the defect size distribution curve; The defect occurrence rate is derived using the aforementioned defect size distribution curve through probabilistic damage tolerance assessment examples; and The defect size distribution curve and the defect occurrence rate are combined to obtain the defect distribution curve of the hole surface.

2. The method according to claim 1, characterized in that, The loading conditions include a combination of stress and temperature.

3. The method according to claim 1, characterized in that, The extreme value distribution is either a Gumbel distribution or a Weibull distribution.

4. The method according to claim 1, characterized in that, The formula for the probabilistic damage tolerance assessment example is as follows: POF=1-(1-P fd *S*P d / credit) n Where POF represents the failure probability, P fd The conditional failure probability is calculated using probabilistic fracture mechanics based on the defect size distribution curve, where S represents the surface area of ​​the hole, and P represents the surface area of ​​the hole. d represents the defect occurrence rate, credit represents the hole processing confidence level, and n represents the number of holes.

5. The method according to claim 4, characterized in that, The defect occurrence rate is derived using the aforementioned defect size distribution curve through a probabilistic damage tolerance assessment example, including: The failure probability is calculated using the formula based on the hole surface defect distribution curves provided by airworthiness regulations; and The failure probability and the obtained defect size distribution curve are used to deduce the defect occurrence rate using the formula.

6. The method according to claim 4, characterized in that, Also includes: When field service data is available, the actual failure probability can be obtained from the field service data. as well as The defect occurrence rate is calculated using the actual failure probability and the obtained defect size distribution curve through the formula.

7. The method according to claim 6, characterized in that, The actual failure probability is calculated as follows:

8. The method according to claim 1, characterized in that, The defect size distribution curve is in the following coordinate system: the horizontal axis of the coordinate system represents the defect length, and the vertical axis of the coordinate system represents the cumulative probability of defect occurrence.

9. The method according to claim 8, characterized in that, The defect size distribution curve and the defect occurrence rate are combined to obtain the hole surface defect distribution curve, which includes: Translate the defect size distribution curve so that the intersection of the defect size distribution curve and the vertical axis of the coordinate system is at point (0,1); and The defect distribution curve on the hole surface is obtained by multiplying the translated defect size distribution curve by the defect occurrence rate.

10. The method according to claim 1, characterized in that, The holes are fabricated using the same machining process as the actual parts.

11. The method according to claim 1, characterized in that, It also includes using the surface defect distribution curve of the hole to perform probabilistic damage tolerance assessment.

12. The method according to claim 11, characterized in that, The probabilistic damage tolerance assessment also uses the part's geometry, stress distribution, and material data.

13. The method according to claim 1, characterized in that, The test piece includes multiple test pieces prepared using each of a variety of different materials, and the obtained hole surface defect distribution curves include hole surface defect distribution curves for test pieces made of each of the variety of different materials and a hole surface defect distribution curve for all test pieces, wherein the most conservative curve among these hole surface defect distribution curves is selected as the hole surface defect distribution curve.

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