JP2001272318A - 3D automatic crack growth analysis system - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To provide a three-dimensional automatic crack growth analysis system for a structure capable of re-creating a structural model without manual intervention. SOLUTION: In a three-dimensional automatic crack growth analysis system for three-dimensionally analyzing crack growth of a welded structure, (a)
Structural model generating means 1 for arranging nodes and generating a structural model for finite element analysis based on information on each member, information on joining with other members, and information on cracks
And (b) a finite element analysis means 2 for performing a finite element analysis to calculate a fracture mechanics parameter when a predetermined load is applied to the structural model, and (c) defining in advance using the calculation results A three-dimensional automatic crack growth analysis system for a structure, comprising: a crack growth control means 3 for calculating a growth direction and a growth amount of a crack according to a certain crack growth rule and updating information on the crack.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a three-dimensional analysis of crack propagation in a welded structure comprising a plurality of members.
One-dimensional automatic crack growth analysis system.

[0002]

2. Description of the Related Art With respect to a crack having a simple shape, there are two basic types.
With the aid of the formulation of two-dimensional cracks (semi-elliptical cracks that define the width and depth of cracks), the relationship between the number of applied loads and the amount of crack propagation can be estimated with a simple program It is.

In order to carry out a precise crack growth analysis in which the crack shape is complex and it is necessary to consider stress redistribution due to the crack growth, a structural model is created for each step of the crack growth and a finite The K value and the J value of the fracture mechanics parameters are calculated by the element method program. Crack growth analysis is performed using the results to estimate the direction and amount of crack growth.

[0004] Specifically, it is as shown in FIG. First, a structural model is created in step S21,
A load model is created separately in step S22. In step S23, a finite element analysis is performed using the structural model and the load model, and a fracture mechanics parameter (J value) is calculated in step S24 from the analysis result.

[0005] Using this calculation result, crack growth analysis is performed in step S25, and the presence or absence of crack growth is determined in step S26. If there is no crack growth (if less than a predetermined value), a series of processing is ended. If the result of the determination is that there is crack growth, the structural model is updated in step S27. Based on the updated structural model, the processing from the step S23 finite element method analysis to the step S26 determination is repeated.

There is also a method in which a three-dimensional structural model is generated by preparing in advance a structural part model (crack block) including a crack shape and incorporating it in an overall analysis model of the structure. In this case as well, the fracture mechanics parameters are obtained by a general-purpose finite element method analysis program, and the direction and amount of crack propagation are calculated using the obtained parameters. This is a three-dimensional automatic crack propagation analysis system that automatically updates the node distribution before crack propagation in a crack block to a new node distribution after crack propagation based on the calculation results.

This method is specifically shown in FIG. First, structural data not including a crack is created in step S31, and a crack block is created separately in step S32, and a load model is created in step S33. In step S34, a crack block is incorporated into the structure data. In step S35, a finite element analysis is performed using the structural data and the load data, and a fracture mechanics parameter (J value) is calculated in step S36 from the analysis result.

Using this calculation result, a crack growth analysis is performed in step S37, and a crack growth amount and a crack growth direction are obtained in step S38. In step S39, the control variables (various parameters related to crack growth) and the limit values are determined. If the control variable exceeds the limit value, the series of processes is terminated. Otherwise, the crack information is updated, and the process from the creation of the crack block in step S32 to the determination in step S39 is repeated.

[0009] Japanese Patent Application Laid-Open No. Hei 8-1144531 proposes a method for estimating, by calculation, the amount of wall thickness reduction or remaining life of a water wall tube of a boiler for thermal power generation due to generation of fatigue cracks from corrosion pits. Have been. According to this technique, the depth of a corrosion pit when the stress intensity factor at the bottom of the corrosion pit reaches the limit value for the occurrence of fatigue cracks is determined from the corrosion pit growth rule. Further, the total depth is obtained by calculating the growth depth of the fatigue crack generated by the application of stress by the Paris-type equation of integral type. Hereinafter, by repeating such calculations, the amount of reduction in wall thickness or the remaining life of the water wall pipe is obtained.

[0010]

However, these prior arts have the following problems. First, in the case of using a calculation for a crack having a simple shape or a calculation based on a formulation in which the crack is replaced with a crack having a simple shape, there is a limitation that a crack model that can be supported is limited, and it is not possible to determine the propagation direction of the crack. For example, Japanese Unexamined Patent Publication No.
In the technique disclosed in Japanese Patent Publication No. 31-301, the depth of growth of a fatigue crack is determined by a mathematical formula. However, the direction of growth of the crack is premised on the thickness direction of the plate, and no consideration is given to the growth in the plane of the plate.

On the other hand, in the method of estimating the direction and amount of crack propagation by performing crack propagation analysis from the analysis results of the finite element method, different sizes of cracks are used for finite element analysis after crack propagation. It is necessary to create several cases of the structural model. Therefore, this method spends a lot of time and money on creating a structural model. In particular, the crack tip is the center of stress concentration, and the element division needs to be finer than other parts. Therefore, it can be said that it is actually not easy but difficult to create a structural model so as to ensure sufficient analysis accuracy.

Regarding element division in the finite element method analysis, there is no problem if the direction of crack propagation is known in advance by a two-dimensional automatic crack propagation analysis system, but if a structure in which this direction of propagation is not determined is handled, It is necessary to perform element division many times. There is no problem with the three-dimensional automatic crack growth analysis system if the crack growth is within the range of the specified crack block. However, if the crack grows beyond the range of the crack block, the input structural model Need to be recreated. In this case, it is necessary to manually divide elements other than the crack block.

The present invention solves the above-mentioned problems of the prior art, and makes it possible to carry out crack growth analysis without manually and without spending time and money to recreate a structural model. It is an object of the present invention to provide a three-dimensional automatic crack growth analysis system for a structure.

[0014]

The above object is achieved by the following invention. The present invention relates to a three-dimensional automatic crack growth analysis system for three-dimensionally analyzing the growth of a crack in a welded structure composed of a plurality of members, wherein (a) information on each member, joining information with other members, and cracks Model generating means for generating a structural model for finite element analysis by arranging nodes based on the information about (b), and performing a finite element analysis and performing destruction when a predetermined load is applied to this structural model Finite element analysis means for calculating mechanical parameters, and (c) crack growth control means for calculating the direction and amount of growth of the crack according to a crack growth rule defined in advance using the calculation results and updating information about the crack And a three-dimensional automatic crack growth analysis system for a structure, comprising:

According to the system of the present invention, a model of a structure including a crack as an element is created in a computer by inputting information of a crack together with information of a member of the structure, and the progress of the crack is analyzed by finite element analysis. To analyze. The main components of this system are a structural model generation means for generating a structural model for analysis, a finite element analysis means for calculating fracture mechanics parameters, and a crack growth control means for calculating the direction and amount of crack growth. The respective processing contents will be described below.

[0016] The structural model generation means generates a structural model by arranging nodes for finite element analysis based on the member information, the joint information, and the crack information. At this time, crack information at the crack tip is added, and a model including members, joints, and cracks is obtained. Nodes are arranged in this model to generate a structural model for finite element analysis.

The finite element analysis means performs a finite element analysis using the structural model. Here, the fracture mechanics parameters are calculated when a predetermined load is applied.

The crack growth control means calculates the direction and amount of growth of the crack using the calculation results of the fracture mechanics parameters. Here, the user defines a crack growth rule in advance, and calculates the presence or absence of crack growth and its size and direction from the fracture mechanics parameters based on the rule. The information about the crack is updated based on the obtained calculation result.

The structural model generating means updates the nodes from the updated crack information, and the finite element analysis means performs finite element analysis based on the updated crack information, and the crack growth control means calculates the direction and amount of growth of the crack. The system of the present invention can automatically perform a crack growth analysis of a structure by repeating these processes. As described above, since the structural model is sequentially updated based on the result of the automatic analysis of the crack, the accuracy of the finite element analysis around the crack is greatly improved, and the analysis accuracy of the entire structure is also improved.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In practicing the present invention, a model of a structure is created, that is, a structure is defined by a structure model generating means. In this definition, first, a model of a structure is created in a computer, and further, crack information is added. At this time, for a member in contact with the crack, that is, a member in which a part of the boundary surface is a crack, joint information with the crack is provided together with joint information with another member. The positional relationship between the members and the cracks is determined based on the respective pieces of joining information.

Thereafter, the model of the structure is divided into elements (mesh) for finite element analysis. here,
The crack tip may be specially divided from the viewpoint of improving the accuracy of the finite element analysis, and the other portions may be divided based on the joining information of the members, that is, by dividing the interface of the element with the joining surface. In this way, the structural model generating means generates a structural model in which elements are divided for finite element analysis.

Next, the finite element analysis means performs a finite element analysis on the obtained structural model. In this case, the finite element analysis is performed when a predetermined load is applied,
The load data for each element may be stored as member information, taken out as needed, and applied to each element. The finite element analysis means calculates a fracture mechanics parameter such as a J value based on the analysis result.

Finally, the crack growth control means takes in the results of the finite element analysis and calculates the amount and direction of growth of the crack. At this time, the numerical values representing the state of growth of these cracks are calculated using a separately defined crack growth rule. Here, the crack growth rule may be determined beforehand by examining the relationship between the fracture mechanics parameter and the state of crack growth by an experiment or the like and checking a certain safety coefficient. From the calculation results, the positions and dimensions of the crack and the joining line are updated.

After that, if the number of load cycles or the amount of crack growth is less than the set upper limit, the crack growth control means updates the crack information after the crack growth and transmits the updated crack information to the structural model generating means. Repeat a series of processing. If the upper limit has been reached, a series of processing ends.

In carrying out these processes, a system can be easily constructed by applying a programming method using an object-oriented language. In particular, when creating subsystems corresponding to the individual means described above, at least a part related to a model of a structure is preferably created using an object-oriented programming language. In this case, the member information, the joint information, and the crack information can also be defined in the form of objects, respectively, so that registration and updating of individual information can be easily performed. Hereinafter, an embodiment using an object-oriented technique will be described.

A member object constituting a structure has information on itself such as a position, a dimension, and a plate thickness. For example, "I am a member and the position is (x,
(y, z coordinates), the plate thickness is XX mm, and the material is XX ". In addition, the joining information at the joining portion between the members is such that “members in contact with this joining line are XX and Δ
△, the length of the joining line is XX mm, the welding method of the members is XX
Is information. In addition to this, the crack information at the crack tip is as follows: "I am the crack tip, the members in contact with the crack are XX and ○, and the length of the crack joining line is は
○ mm ”.

FIG. 1 is a flowchart showing an example of the flow of processing in this system. First, member information, joint information, and crack information are prepared in the structural model generating means 1. In step S11, a model of the structure is created using these pieces of information. In step S12, nodes are arranged on the basis of the joining line information between members, and they are connected by a method known as a front method, thereby automatically dividing the element as a structural model of the finite element method. At that time, the element is divided into arcs around the crack tip up to a certain distance from the crack tip.

Next, in step S13, the obtained structural model is stored as structural data, and in step S14, load data corresponding to these structural data is stored. In this example, the load data is stored as part of the member information, and the load data stored as the member information is used as the element division is changed for each crack propagation.

In the finite element analysis means 2, step S15
Then, a load is applied to these structural models to perform a finite element analysis. A fracture mechanics parameter (J value) is calculated from the analysis result in step S16.

The crack growth control means 3 fetches this calculation result, performs a crack growth analysis in step S17, and calculates the amount and direction of crack growth using a crack growth rule defined by the user. In step S18, the state of crack propagation is determined from the amount and direction of crack propagation. As a result, if the number of load cycles or the amount of crack propagation has reached the set upper limit, a series of processing is ended.

If the determination result does not reach these upper limits, in step S19, the crack information is updated based on the crack growth analysis result (step S17), in particular, the crack joining line is updated. Thereafter, based on the updated member information, joining information, and crack information, step S11 is performed.
A series of processing is repeated from (structural model creation). In this way, the crack growth control means 3 controls the entire three-dimensional crack growth automatic analysis system using the number of load cycles and the amount of crack growth set by the user as control data.

[0032]

According to the present invention, a structural model including crack information together with member information is automatically generated by structural model generating means, and fracture mechanics parameters are calculated by finite element analysis.
Based on this, the direction and amount of crack propagation are automatically analyzed.
At this time, since the structural model is sequentially updated based on the results of the automatic analysis of the crack, the operation of creating the structural model is automated, and the accuracy of the finite element analysis around the crack is greatly improved. As a result, the automatic crack growth analysis of the structure can be quickly performed without manual intervention.

[Brief description of the drawings]

FIG. 1 is a flowchart showing an example of an embodiment of the present invention.

FIG. 2 is a flowchart showing an example of a crack growth analysis according to the related art.

FIG. 3 is a flowchart showing an example of crack propagation analysis according to another conventional technique.

[Explanation of symbols]

 1 Structural model generation means 2 Finite element analysis means 3 Crack growth control means

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Kazuhiro Aoyama 7-3-1 Hongo, Bunkyo-ku, Tokyo F-term in the Faculty of Engineering, Tokyo University 2G024 AD34 BA12 BA17 BA21 CA02 CA04 DA01 FA06 2G061 BA03 DA12

Claims (1)

[Claims] 1. A three-dimensional automatic crack growth analysis system for three-dimensionally analyzing the growth of a crack in a welded structure composed of a plurality of members, comprising: (a) information on each member and information on joining with other members; Based on information about the crack, a structural model generating means for generating a structural model for finite element analysis by arranging nodes, and (b) performing a finite element analysis on a case where a predetermined load is applied to this structural model. Finite element analysis means for calculating fracture mechanics parameters, and (c) crack growth control for calculating the direction and amount of crack growth based on a crack growth rule defined in advance using the calculation results and updating information about the crack Means for analyzing a three-dimensional automatic crack growth analysis of a structure.