METHOD FOR THE PREDICTION OF FATIGUE LIFE FOR WELDED STRUCTURES

• US 20120259593A1
• Filed: 04/07/2011
• Published: 10/11/2012
• Est. Priority Date: 04/07/2011
• Status: Abandoned Application

• Current Assignee: Deere & Company
• Original Assignee: Deere & Company
• Inventors: El-Zein, Mohamad S., Goyal, Rakesh K., Glinka, Grzegorz
• Application Number:
  US13/082,195
• Publication Number:
  US 20120259593A1
• Time in Patent Office: Days
• US Class Current: 703/1
• CPC Class Codes: G06F 2119/04 Ageing analysis or optimisation against ageing
• CPC Class Codes: G06F 30/23 using finite element methods [FEM] or finite difference methods [FDM]

Abstract

A method of determining the fatigue life of a welded structure, including the steps of: creating a 3D coarse mesh model of the welded structure to be analyzed; analyzing the coarse mesh model using an FEA model to generate FEA data; identifying a critical stress location on the coarse mesh model having a through thickness stress distribution, based on the FEA data; post processing the FEA data in the middle portion of the through thickness stress distribution while excluding the through thickness stress distribution near the edges of the identified critical stress location to determine a peak stress; and determining a fatigue life of the welded structure at the identified critical stress location, dependent on the determined peak stress.

Claims

1. A method of determining the fatigue life of a welded structure, said method comprising the steps of:

creating a three-dimensional (3D) coarse mesh model of the welded structure to be analyzed;

analyzing the coarse mesh model using a finite element analysis (FEA) model to generate FEA data;

identifying a critical stress location on the coarse mesh model having a through thickness stress distribution, based on the FEA data;

post processing the FEA data in the middle portion of the through thickness stress distribution while excluding the through thickness stress distribution near the edges of the identified critical stress location to determine a peak stress; and

determining a fatigue life of the welded structure at the identified critical stress location, dependent on the determined peak stress.

2. The method of determining a fatigue life of a welded structure of claim 1, wherein said post processing step includes determining a through thickness stress distribution in the middle approximate one half thickness of the of the coarse mesh model at the identified critical stress location.

3. The method of determining a fatigue life of a welded structure of claim 2, wherein the through thickness stress distribution in a middle approximate one half thickness of the coarse mesh model is used to calculate a bending moment M_c from the middle approximate one half thickness.

4. The method of determining a fatigue life of a welded structure of claim 3, wherein the through thickness stress distribution in the middle approximate one half thickness is independent of a mesh size of a 3D mesh model used in the FEA analysis.

5. The method of determining a fatigue life of a welded structure of claim 3, wherein the bending moment M_c is calculated using the mathematical expression:

6. The method of determining a fatigue life of a welded structure of claim 3, wherein said post processing step includes calculating a total bending moment M_b at the identified critical stress location, dependent on the bending moment M_c.

7. The method of determining a fatigue life of a welded structure of claim 6, wherein the total bending moment M_b is calculated using the mathematical expression:

M_b=10*M_c.

8. The method of determining a fatigue life of a welded structure of claim 1, wherein the welded structure includes a weld having a weld toe angle and a weld toe radius, and the critical stress location is identified by extracting a normal stress component which is normal to a weld toe line within the welded structure.

9. The method of determining a fatigue life of a welded structure of claim 1, wherein the 3D coarse mesh model is defined by a minimum of four linear order elements through the through thickness of the welded structure.

10. The method of determining a fatigue life of a welded structure of claim 1, wherein said post processing step includes calculating a membrane stress (σ

_hs^m) at the identified critical stress location.

11. The method of determining a fatigue life of a welded structure of claim 10, wherein said membrane stress (σ

_hs^m) is calculated using the mathematical expression;

12. The method of determining a fatigue life of a welded structure of claim 10, wherein said post processing step includes calculating a middle half-thickness bending moment (M_c) at the identified critical stress location.

13. The method of determining a fatigue life of a welded structure of claim 12, wherein the middle half-thickness bending moment (M_c) is calculated using the mathematical expression:

14. The method of determining a fatigue life of a welded structure of claim 12, wherein said post processing step includes calculating a total bending moment (M_b) at the identified critical stress location.

15. The method of determining a fatigue life of a welded structure of claim 14, wherein the total bending moment (M_b) is calculated using the mathematical expression:

M_b=10*M_c.

16. The method of determining a fatigue life of a welded structure of claim 14, wherein said post processing step includes calculating a bending stress (σ

_hs^b) at the identified critical stress location.

17. The method of determining a fatigue life of a welded structure of claim 16, wherein the bending stress (σ

_hs^b) is calculated using the mathematical expression;

18. The method of determining a fatigue life of a welded structure of claim 16, wherein said post processing step includes empirically determining a membrane stress concentration factor K_t,hs^m and a bending stress concentration factor K_t,hs^b, dependent upon a geometry of the welded structure.

19. The method of determining a fatigue life of a welded structure of claim 18, wherein the membrane stress concentration factor K_t,hs^m and the bending stress concentration factor K_t,hs^b are each based upon a statistical determination of measured data for a fabrication site of the welded structure.

20. The method of determining a fatigue life of a welded structure of claim 19, wherein the measured data includes a weld toe angle and weld toe radius.

21. The method of determining a fatigue life of a welded structure of claim 20, wherein the empirically determined data requires input of the measured data.

22. The method of determining a fatigue life of a welded structure of claim 19, wherein the welded structure is a symmetric butt weld, and the membrane stress concentration factor K_t,hs^m is calculated using the mathematical expression:

23. The method of determining a fatigue life of a welded structure of claim 19, wherein the welded structure is a symmetric fillet weld, and the membrane stress concentration factor K_t,hs^m is calculated using the mathematical expression:

24. The method of determining a fatigue life of a welded structure of claim 19, wherein the welded structure is a non-symmetric fillet weld, and the membrane stress concentration factor K_t,hs^m is calculated using the mathematical expression:

25. The method of determining a fatigue life of a welded structure of claim 19, wherein said post processing step includes determining a peak stress (σ

_peak) at the critical stress location, dependent on the membrane stress concentration factor K_t,hs^m and the bending stress concentration factor K_t,hs^b.

26. The method of determining a fatigue life of a welded structure of claim 25, wherein the peak stress (σ

_peak) is calculated using the mathematical expression;

σ

_peak=σ

_hs^m×

K_t,hs^m+σ

_hs×

K_t,hs^b.

27. The method of determining a fatigue life of a welded structure of claim 25, wherein said determined fatigue life is dependent on the peak stress (σ

_peak).

28. A computer-based method of determining the fatigue life of a welded structure using a computer having at least one processor and at least one memory, said method comprising the following steps which are each sequentially carried out within the computer:

creating a three-dimensional (3D) coarse mesh model of the welded structure to be analyzed;

analyzing the coarse mesh model using a finite element analysis (FEA) model to generate FEA data;

identifying a critical stress location on the coarse mesh model having a through thickness stress distribution, based on the FEA data;

post processing the FEA data in the middle portion of the through thickness stress distribution while excluding the through thickness stress distribution near the edges of the identified critical stress location to determine a peak stress; and

determining a fatigue life of the welded structure at the identified critical stress location, dependent on the determined peak stress.

29. The computer-based method of determining the fatigue life of a welded structure of claim 28, wherein the 3D coarse mesh model is stored within the at least one memory of the computer.

30. The computer-based method of determining the fatigue life of a welded structure of claim 28, wherein the FEA data is stored within the at least one memory of the computer.

31. The computer-based method of determining the fatigue life of a welded structure of claim 28, wherein the FEA model provides instructions to the processor to generate the FEA data.