CN117131729B - Integrity assessment method of structures containing composite cracks under compressive load - Google Patents

Abstract

The invention discloses a method for evaluating the integrity of a pressed load composite crack structure, which comprises the following steps: characterizing the geometric dimension and the defect dimension of the composite crack-containing structure; calculating limit loadP _L Buckling loadP _B Calculating line elasticity under different ballast loadsJIntegration ofJ _e ElastoplasticityJIntegration ofJ _ep And calculating the fracture load ratioL _r And buckling load ratioB _r The method comprises the steps of carrying out a first treatment on the surface of the By calculating cut-off lines of two failure assessment curvesL _r ^max AndB _r ^max establishing a fracture failure evaluation curve and a buckling failure evaluation curve; establishing a three-dimensional failure evaluation curve combining fracture failure and buckling failure; and calculating and evaluating the coordinates of the evaluation points. The invention combines fracture failure and buckling failure, is suitable for defect evaluation of a composite crack structure under pressure load, and expands the existing failure evaluationAnd (5) determining a method.

Description

Integrity assessment method of structures containing composite cracks under compressive load

Technical field

The invention belongs to fault diagnosis and health maintenance technology, and specifically relates to an integrity assessment method of a structure containing composite cracks under compressive load.

Background technique

As the backbone of the modern industrial system, high-end equipment manufacturing is a strategic emerging industry led by high and new technologies that determines the comprehensive competitiveness of the entire industrial chain. Among them, fault diagnosis and health maintenance technology, as an indispensable part of the nine types of key intelligent basic common technologies, plays a vital role in predicting equipment and structure failures and providing maintenance suggestions. The integrity assessment of defective structures belongs to health maintenance technology, which aims to provide health management strategies for equipment and engineering structures, optimize use and maintenance, and reduce maintenance costs. Under extreme conditions, various engineering structures and equipment such as pressure vessels and pressure pipelines will inevitably produce defects during the manufacturing and service processes. Therefore, the integrity assessment of structures containing defects plays an important role in ensuring the safe operation of equipment. For the integrity evaluation of defective structures, there are currently multiple methods to provide guarantees, including the COD curve method, the stress intensity factor method, the J criterion method, and the most commonly used failure assessment diagram method. The failure assessment diagram method is based on the principles of fracture mechanics and structural strength theory. It characterizes brittle fracture failure and ultimate load failure in the same two-dimensional coordinate system, so it is also called the double criterion method. Therefore, the traditional failure assessment diagram method only considers the fracture failure mode and does not consider the impact of buckling failure on the integrity evaluation of structures containing defects.

Patent CN115169115A "Method, Equipment and Storage Medium for Strain-Based Pipeline Girth Weld Failure Assessment Chart" introduces a strain-based pipeline girth weld failure assessment chart, which accurately represents the impact of weld strength matching on structural fracture; patent CN112287577A "Structural Integrity Assessment Method Incorporating Unified In-Plane and Out-of-Plane Constraints" proposes a failure assessment diagram based on unified constraint parameters to improve the assessment accuracy of the failure assessment diagram. The above patents all involve improvements to failure assessment diagrams, but no patent considers the impact of buckling failure of structures containing composite cracks under compressive load on defect assessment. Structures containing defects will not only suffer fracture failure, but also buckling failure, which depends on the geometric dimensions of the structure, defect size, material properties and loads. When buckling failure occurs in a structure containing defects, traditional fracture failure assessment diagrams are not applicable.

Contents of the invention

The present invention proposes an integrity assessment method for structures containing composite cracks under compressive load. This method is more traditional than the traditional failure assessment method based on fracture failure. It comprehensively considers the possible failure modes of structures containing composite cracks under compressive load and solves the problem. This method solves the problem that traditional fracture failure assessment diagrams are not applicable when buckling failure occurs in a structure containing defects, and can improve the accuracy of integrity assessment of structures containing surface cracks under compressive load.

The technical solution to realize the present invention is: a method for integrity assessment of cracked structures under compressive load. The steps are as follows:

Step S1: Characterize the geometric dimensions and defect sizes of the structure containing composite cracks to be evaluated, and determine the material properties of the structure containing composite cracks, and then proceed to step S2.

Step S2: Based on the geometric size, defect size and material properties, set the load form to compressive load, establish a finite element model of the structure containing composite cracks, and then determine the ultimate load _PL and buckling of the structure containing composite cracks through the finite element method Load P _B , and determine the fracture load ratio set L _r , the buckling load ratio set B _r and the fracture ratio set K _r under different load ratios, and then proceed to step S3.

Step S3: Based on L _r , B _r and K _r , and with reference to the GB/T 19624-2019 specification, establish a failure assessment curve for the structure containing composite cracks, including a failure assessment curve based on fracture failure and a failure assessment curve based on buckling failure.

The failure evaluation curve expression f(L _r ) based on fracture failure is as follows:

f(L _r )＝K _r , L _r ≤L _r ^max

The failure evaluation curve expression f( _Br ) based on buckling failure is as follows:

f(B _r )＝K _r , B _r ≤ B _r ^max

Among them, L _r ^max is the cut-off line value of the failure assessment curve based on fracture failure, and B _r ^max is the cut-off line value of the failure assessment curve based on buckling failure.

Go to step S4.

Step S4: Construct the above three-dimensional failure assessment curve of the structure containing composite cracks based on the failure assessment curve of the structure containing composite cracks, as follows:

S41. Establish a three-dimensional failure assessment curve expression f (L _r , B _r ):

f(L _r ,B _r )=K _r

S42. Draw a three-dimensional failure assessment curve:

In the three-dimensional failure assessment curve of a structure containing composite cracks, L _r , B _r , and K _r respectively represent the X-axis, Y-axis, and Z-axis. The projection line of the three-dimensional failure assessment curve in the L _r -K _r plane is the fracture failure. Evaluation curve, the projection line in the B _r -K _r plane is the buckling failure evaluation curve. Then the cut-off line of the fracture failure assessment curve and the cut-off line of the buckling failure assessment curve are respectively projected onto the three-dimensional failure assessment curve, forming two cut-off lines of the three-dimensional failure assessment curve, and then the three-dimensional failure assessment curve is obtained.

Go to step S5.

Step S5: Apply a certain compressive load F to the structure containing composite cracks. The coordinates of the evaluation point under the current working condition are (L _r ^* , B _r ^* , K _r ^* ), as follows:

Among them, L _r ^* represents the position of the evaluation point on the X axis, B _r ^* represents the position of the evaluation point on the Y axis, and K _r ^* represents the position of the evaluation point on the Z axis. F is a certain compressive load applied to the structure containing composite cracks. K is the crack tip stress intensity factor. K _c is the material fracture toughness.

Go to step S6.

Step S6: Determine the positional relationship between the projection point of the evaluation point in the L _r -K _r plane and the fracture failure evaluation curve, and the positional relationship between the projection point of the evaluation point in the B _r -K _r plane and the buckling failure evaluation curve. Safety assessment of structures containing composite cracks:

When the projection point of the evaluation point coordinates (L _r ^* , B _r ^* , K _r ^* ) falls within the area enclosed by the respective failure evaluation curve, cut-off line and coordinate axis, it indicates that the structure containing composite cracks is under the compressive load F It is safe under load, and the structure containing composite cracks will not suffer from fracture failure or buckling failure.

When the projection point of the evaluation point coordinates (L _r ^* , B _r ^* , K _r ^* ) falls outside the buckling failure evaluation curve and its cut-off line, and falls within the fracture failure curve and its cut-off line, it indicates that there is a composite crack. Buckling failure of the structure occurs.

When the projection point of the evaluation point coordinates (L _r ^* , B _r ^* , K _r ^* ) falls outside the fracture failure evaluation curve and its cut-off line, and simultaneously falls within the buckling failure curve and its cut-off line, it indicates that there is a composite crack. The structure breaks and fails.

Compared with the prior art, the significant advantages of the present invention are:

(1) Consider the buckling failure of a structure containing composite cracks under compressive load. Therefore, based on the existing fracture failure evaluation curve, a buckling failure evaluation curve was established by considering the buckling failure mode of the structure containing composite cracks under compressive load. It comprehensively incorporates the possible failure modes of the assessment structure, which is more reasonable and accurate compared with the fracture failure assessment mode.

(2) A buckling failure evaluation curve corresponding to the traditional fracture failure evaluation curve was established.

(3) The failure assessment chart is a three-dimensional failure assessment chart that combines the fracture failure assessment curve with the buckling failure assessment curve, which can more intuitively determine the failure mode of a structure containing composite cracks.

Description of the drawings

Figure 1 is a schematic diagram of the fracture failure evaluation curve and the buckling failure evaluation curve in the present invention.

Figure 2 is a schematic diagram of a three-dimensional failure assessment diagram combining the fracture failure assessment curve and the buckling failure assessment curve in the present invention.

Figure 3 is a schematic diagram of the buckling failure occurring when the coordinates of the assessment points are put into a three-dimensional failure assessment diagram for assessment.

Figure 4 is a schematic diagram of the assessment point coordinates being put into a three-dimensional failure assessment diagram for assessment, and fracture failure occurs.

Figure 5 is a schematic diagram illustrating the geometry and crack size of a plate containing composite surface cracks under compressive load according to an embodiment of the present invention.

Figure 6 is a finite element model and crack front grid distribution diagram of a plate containing composite surface cracks under compressive load according to an embodiment of the present invention.

Figure 7 is a three-dimensional failure assessment result diagram according to an embodiment of the present invention.

Figure 8 is a flow chart of the integrity assessment method of a structure containing composite cracks under compressive load according to the present invention.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

It should be noted that all directional indications (such as up, down, left, right, front, back...) in the embodiment of the present invention are only used to explain the relationship between components in a specific posture (as shown in the drawings). Relative positional relationship, movement conditions, etc., if the specific posture changes, the directional indication will also change accordingly.

In addition, the technical solutions between the various embodiments of the present invention can be combined with each other, but it must be based on what a person of ordinary skill in the art can implement. When the combination of technical solutions is contradictory or cannot be realized, it should be considered that such a combination of technical solutions is possible. It does not exist and is not within the protection scope required by the present invention.

The specific implementation, as well as the technical difficulties and invention points of this invention will be further introduced below based on this design example.

Combined with Figures 1 to 8, a method for integrity assessment of structures containing composite cracks under compressive load is provided. The steps are as follows:

Step S1: Characterize the geometric dimensions and defect sizes of the structure containing composite cracks to be evaluated with reference to GB/T 19624-2019, and determine the material properties of the structure containing composite cracks. The defect size includes surface crack depth a, crack semi-major axis c, and composite surface crack inclination angle β. Material properties include elastic modulus E, crack surface friction coefficient μ, Poisson’s ratio υ, yield strength σ _s and tensile strength σ _b .

Go to step S2.

Step S2: Based on the geometric size, defect size and material properties, set the load form to compressive load, establish a finite element model of the structure containing composite cracks, and then determine the ultimate load _PL and buckling of the structure containing composite cracks through the finite element method Load P _B , and determine the fracture load ratio set L _r , the buckling load ratio set B _r and the fracture ratio set K _r under different load ratios:

Among them, P is the different compressive loads applied to the structure containing composite cracks; J _e is the linear elastic J integral, and J _ep is the elastic plastic J integral.

Go to step S3.

Step S3: Under compressive load, buckling failure of the structure may occur, which depends on the geometric size, defect size, material properties and load of the structure containing composite cracks. For example, when the thickness of a plate structure containing composite cracks decreases or the size of defects increases, the possibility of buckling failure of the plate structure containing composite cracks increases. At this time, there is no reasonable basis for using the traditional fracture failure assessment chart for assessment, and a buckling failure assessment chart needs to be established to meet the assessment needs. According to L _r , B _r and K _r , with reference to the GB/T19624-2019 specification, the failure assessment curve in the failure assessment diagram of the structure containing composite cracks is established, including a failure assessment curve based on fracture failure and a failure assessment curve based on buckling failure ( As shown in Figure 1).

The failure evaluation curve expression f(L _r ) based on fracture failure is as follows:

f(L _r )＝K _r , L _r ≤L _r ^max

When establishing the buckling failure evaluation curve, the fracture load ratio L _r in the traditional failure evaluation curve is changed to the buckling load ratio B _r , and the two share the fracture ratio K _r .

The failure evaluation curve expression f( _Br ) based on buckling failure is as follows:

f(B _r )＝K _r , B _r ≤ B _r ^max

Among them, L _r ^max is the cut-off line value of the failure assessment curve based on fracture failure, and B _r ^max is the cut-off line value of the failure assessment curve based on buckling failure.

Among them, σ _b is the tensile strength of the material; σ _s is the yield strength of the material.

Go to step S4.

Step S4: Construct the above three-dimensional failure assessment curve of the structure containing composite cracks based on the failure assessment curve of the structure containing composite cracks (as shown in Figure 2), the details are as follows:

S41. Establish a three-dimensional failure assessment curve expression f (L _r , B _r ):

f(L _r ,B _r )=K _r

S42. Draw a three-dimensional failure assessment curve:

In the three-dimensional failure assessment curve of a structure containing composite cracks, L _r , B _r , and K _r respectively represent the X-axis, Y-axis, and Z-axis. The projection line of the three-dimensional failure assessment curve in the L _r -K _r plane is the fracture. Failure assessment curve, the projection line in the B _r -K _r plane is the buckling failure assessment curve; then the cut-off line of the fracture failure assessment curve and the cut-off line of the buckling failure assessment curve are respectively projected onto the three-dimensional failure assessment curve to form a three-dimensional failure The two cut-off lines of the evaluation curve are then used to obtain a three-dimensional failure evaluation curve.

Go to step S5.

Step S5: Apply a certain compressive load F to the structure containing composite cracks. The coordinates of the evaluation point under the current working condition are (L _r ^* , B _r ^* , K _r ^* ), as follows:

Among them, L _r ^* represents the position of the evaluation point on the X axis, B _r ^* represents the position of the evaluation point on the Y axis, K _r ^* represents the position of the evaluation point on the Z axis, and K is calculated by the finite element method. Crack tip stress intensity factor, K _c is the material fracture toughness.

The material fracture toughness K _c is as follows:

Among them, E is the elastic modulus of the material, υ is the Poisson's ratio of the material, and J _IC is the ductile fracture toughness of the material.

For the stress intensity factor K at the crack tip, the stress intensity factor value at the crack front is selected. Since the structure containing composite cracks is subject to compressive load, the type I stress intensity factor K _I is 0. The stress intensity factor takes the value of type II stress intensity factor K _II and type III stress intensity factor K _III at the crack front. _JIC is the ductile fracture toughness of the material, which can be obtained through experiments or standards.

Go to step S6.

Step S6: Determine the positional relationship between the projection point of the evaluation point in the L _r -K _r plane and the fracture failure evaluation curve, and the positional relationship between the projection point of the evaluation point in the B _r -K _r plane and the buckling failure evaluation curve. Safety assessment of structures containing composite cracks:

When the projection point of the evaluation point coordinates (L _r ^* , B _r ^* , K _r ^* ) falls within the area enclosed by the respective failure evaluation curve, cut-off line and coordinate axis, it indicates that the structure containing composite cracks is under the compressive load F It is safe under load, and the structure containing composite cracks will not suffer from fracture failure or buckling failure.

When the projection point of the evaluation point coordinates (L _r ^* , B _r ^* , K _r ^* ) falls outside the buckling failure evaluation curve and its cut-off line, and falls within the fracture failure curve and its cut-off line, it indicates that there is a composite crack. The structure suffered buckling failure (as shown in Figure 3).

When the projection point of the evaluation point coordinates (L _r ^* , B _r ^* , K _r ^* ) falls outside the fracture failure evaluation curve and its cut-off line, and simultaneously falls within the buckling failure curve and its cut-off line, it indicates that there is a composite crack. The structure fractured and failed (as shown in Figure 4).

Example

In this embodiment, the structure containing composite cracks to be evaluated is a plate, and its material is TA2 industrial pure titanium, with an elastic modulus E=113161.41MPa and a Poisson's ratio υ=0.348. Yield strength σ _s =418.23MPa, tensile strength σ _b =500.18MPa. The size of the set containing composite cracked plates is t=10mm, and the width is 2W=200mm. The size of the composite surface crack is a=4mm, c=20mm (a/c=0.2, a/t=0.4, inclination angle β=45°, t is the plate thickness), the friction coefficient μ of the crack surface is 0.3, in the cracked plate A compressive load of F=300MPa is applied to the upper and lower ends.

Step S1: Clarify the geometric dimensions of the structure to be evaluated (plate thickness t = 10mm and plate width 2W = 200mm), defect size (complex surface crack depth a = 4mm, crack semi-major axis c = 20mm, crack inclination angle β = 45° ) (shown in Figure 5) and material properties (elastic modulus E=113161.41MPa and Poisson’s ratio υ=0.348).

Step S2: Use the finite element method to calculate (as shown in Figure 6) the plastic limit load P _L =370.441MPa and the buckling load P _B =297.558MPa of the plate containing composite surface cracks under compressive load; determine the fracture by applying different loads P The values of the load ratio set L _r and the buckling load ratio B _r ; by applying different loads P, the finite element method is used to obtain the ratio J _e /J _ep of the elastic J integral J _e and the elastic-plastic J integral J _ep under different loads, and then Determine the fracture ratio set K _r value.

Step S3: Based on L _r , B _r and K _r , and with reference to the GB/T 19624-2019 specification, establish a failure assessment curve for the structure containing composite cracks, including a failure assessment curve based on fracture failure and a failure assessment curve based on buckling failure; calculation The cut-off line is obtained as L _r ^max (B _r ^max ) = 1.1.

Step S4: Construct the above three-dimensional failure assessment curve of the structure containing composite cracks based on the failure assessment curve of the structure containing composite cracks, as follows:

S41. Establish a three-dimensional failure assessment curve expression f (L _r , B _r ):

f(L _r ,B _r )=K _r

S42. Draw a three-dimensional failure assessment curve:

In the three-dimensional failure assessment curve of a structure containing composite cracks, L _r , B _r , and K _r respectively represent the X-axis, Y-axis, and Z-axis. The projection line of the three-dimensional failure assessment curve in the L _r -K _r plane is the fracture failure. Assessment curve, the projection line in the B _r -K _r plane is the buckling failure assessment curve; then the fracture failure assessment curve cut-off line and the buckling failure assessment curve cut-off line are respectively projected onto the three-dimensional failure assessment curve to form the three-dimensional failure assessment curve. Two cut-off lines are drawn, and a three-dimensional failure assessment curve is obtained.

Step S5: Apply a certain compressive load F to the structure containing composite cracks. The coordinates of the evaluation point under the current working condition are (L _r ^* , B _r ^* , K _r ^* ), as follows:

The finite element method is used to calculate the stress intensity factor value at the deepest point of the crack front. Obtain the ductile fracture toughness J _IC =182.76KJ·m ^-2 of the material through experiments or standards, and calculate the fracture toughness of the material/>

Step S6: The projection points of the evaluation point coordinates (L _r ^* , B _r ^* , K _r ^* ) fall within the three-dimensional area enclosed by the respective failure evaluation curves, cut-off lines and coordinate axes, indicating that the cracked plate is under compressive load F = It is safe under 300MPa, and no strength failure or buckling failure occurred in the cracked plate (as shown in Figure 7).

Claims (7)

1. The method for evaluating the integrity of the composite crack-containing structure under the action of the ballast load is characterized by comprising the following steps:

step S1: characterizing the geometric dimension and the defect dimension of the structure containing the composite cracks to be evaluated, determining the material properties of the structure containing the composite cracks, and turning to the step S2;

step S2: according to the geometric dimension, the defect dimension and the material property, the load form is set as the compressive load, a finite element model containing the composite crack structure is established, and the limit load P containing the composite crack structure is determined by a finite element method _L And buckling load P _B And determining a set L of breaking load ratios at different load ratios _r Buckling load ratio set B _r Fracture ratio set K _r Step S3 is carried out;

step S3: according to L _r 、B _r And K _r Establishing a failure evaluation curve containing a composite crack structure according to GB/T19624-2019 specification, wherein the failure evaluation curve comprises a failure evaluation curve based on fracture failure and a failure evaluation curve based on buckling failure;

failure assessment Curve expression f (L) _r ) The following are provided:

f(L _r )＝K _r ，L _r ≤L _r ^max

failure assessment Curve expression f (B) based on buckling failure _r ) The following are provided:

f(B _r )＝K _r ，B _r ≤B _r ^max

wherein L is _r ^max To evaluate the curve cut-off line value for failure based on fracture failure, B _r ^max Evaluating a curve cutoff value for a failure based on a buckling failure;

turning to step S4;

step S4: constructing the three-dimensional failure evaluation curve containing the composite crack structure according to the failure evaluation curve containing the composite crack structure, wherein the three-dimensional failure evaluation curve containing the composite crack structure is specifically as follows:

s41, establishing a three-dimensional failure evaluation curve expression f (L) _r ,B _r )：

f(L _r ,B _r )＝K _r

S42, drawing a three-dimensional failure evaluation curve:

in the three-dimensional failure evaluation curve containing the composite crack structure, L _r 、B _r 、K _r Respectively are provided withCorresponding to the X axis, the Y axis and the Z axis, the three-dimensional failure evaluation curve is in L _r -K _r The projection line in the plane is the fracture failure evaluation curve, at B _r -K _r The projection line in the plane is a buckling failure evaluation curve; respectively projecting the breaking failure evaluation curve cut-off line and the buckling failure evaluation curve cut-off line onto the three-dimensional failure evaluation curve to form two cut-off lines of the three-dimensional failure evaluation curve, thereby obtaining the three-dimensional failure evaluation curve;

turning to step S5;

step S5: applying a certain compressive load F to the structure containing the composite cracks, wherein the coordinate of the evaluation point under the current working condition is (L _r ^* ,B _r ^* ,K _r ^* ) The method is characterized by comprising the following steps:

wherein L is _r ^* Represents the position of the evaluation point on the X-axis, B _r ^* Represents the position of the evaluation point on the Y-axis, K _r ^* Representing the position of the evaluation point on the Z axis; f is a certain ballast load applied to the structure containing the composite cracks; k is a crack tip stress intensity factor; k (K) _c Fracture toughness of the material;

turning to step S6;

step S6: judging that the evaluation point is at L _r -K _r Positional relationship between projected points in plane and fracture failure evaluation curve, and evaluation point in B _r -K _r And (3) carrying out safety assessment on the structure containing the composite cracks by the position relation between the projection points in the plane and the buckling failure assessment curve:

when evaluating the point coordinates (L _r ^* ,B _r ^* ,K _r ^* ) When the projection points of the composite crack structure fall in the area surrounded by the failure evaluation curve, the cut-off line and the coordinate axis, the composite crack structure is safe under the action of the ballast load F, and the composite crack structure does not generate fracture failure or buckling failure;

when evaluating the point coordinates (L _r ^* ,B _r ^* ,K _r ^* ) The projection points of the (a) fall outside the buckling failure evaluation curve and the cut-off line thereof, and fall inside the fracture failure curve and the cut-off line thereof, so that the buckling failure of the composite crack-containing structure is indicated;

when evaluating the point coordinates (L _r ^* ,B _r ^* ,K _r ^* ) The projection points of the composite crack structure are located outside the fracture failure evaluation curve and the cut-off line thereof, and the projection points of the composite crack structure are located in the buckling failure curve and the cut-off line thereof at the same time, so that the composite crack structure is indicated to have fracture failure.

2. The method for evaluating the integrity of a composite crack-containing structure under a compressive load according to claim 1, wherein in step S1, the geometric dimensions and the defect dimensions of the composite crack-containing structure to be evaluated are measured and characterized, and the material properties of the composite crack-containing structure are determined, specifically as follows:

performing defect size characterization on the composite crack by referring to GB/T19624-2019;

the defect size comprises a surface crack depth a, a crack semi-long axis c and a composite surface crack inclination angle beta, and the material properties comprise an elastic modulus E, a crack surface friction coefficient mu, a Poisson ratio upsilon and a yield strength sigma _s And tensile strength sigma _b 。

3. The method for evaluating the structural integrity of a composite crack-containing structure under a compressive load according to claim 1, wherein in step S2,

wherein P is different ballast loads applied to the composite crack-containing structure; j (J) _e Is the linear elasticity J integral, J _ep Is the elastoplastic J integral.

4. The method for evaluating the structural integrity of a composite crack-containing structure under a compressive load as set forth in claim 1, wherein in step S3, the cutoff value L of the failure evaluation curve based on fracture failure is set _r ^max And a cutoff value B of a failure assessment curve based on buckling failure _r ^max Is defined as

Wherein sigma _b Is the tensile strength of the material; sigma (sigma) _s Is the yield strength of the material.

5. The method for evaluating the structural integrity of a composite crack under a compressive load according to claim 1, wherein in step S5, the crack tip stress intensity factor K is calculated by a finite element method;

fracture toughness K of material _c The following are provided:

wherein E is the elastic modulus of the material, v is the Poisson's ratio of the material, J _IC Is ductile fracture toughness of the material.

6. The method of claim 5, wherein the crack tip stress intensity factor K is selected from the group consisting of stress intensity factor values of crack fronts, and I-type stress intensity factor K due to the compressive loading of the composite crack structure _I Is 0; the stress intensity factor takes the II type stress intensity factor K of the crack front _II And type III stress intensity factor K _III Values.

7. The method for evaluating the structural integrity of a composite crack-containing structure under a compressive load as set forth in claim 5, wherein J _IC Is the ductile fracture toughness of the material, and can be obtained through experiments or standards.