Numerical and experimental investigations of effects of residual stresses on crack behavior in Aluminum 6082-T6

Abstract

In the structural integrity assessment, residual stresses play an important role. The residual stresses affect both the crack driving forces and the crack-tip constraint. To investigate the interaction of residual stresses with mechanical loading during the onset of crack growth in Aluminum 6082-T6, modified single edge-notched bending specimens were used. Aluminum 6082 has the highest strength of the 6000 series alloys with excellent corrosion resistance. A residual stress field was created in the specimens by pre-loading. To accurately quantify the residual stress field created during this test procedure, the strains were measured during loading and unloading and compared with finite element results. After the introduction of the residual stress field, the specimens were tested under three-point bending to determine the load versus displacement behavior and fracture toughness. Also, a post-processor for finite element calculation was developed to enable determination of the J-integral values for the specimens having residual stresses. The constraint parameters Q and R were calculated at the crack-tip to describe the stress field in this region. The parameter Q is used to characterize the loading and geometry constraint, and the parameter R is used for characterizing the crack-tip constraint due to residual stresses. It is observed that tensile residual stresses around the crack-tip increase the crack-tip constraint and decrease the fracture toughness of the bodies. By increasing the external load, the constraint parameter R goes toward zero and the effects of residual stresses on the crack growth resistance become negligible.

Keywords

Residual stresses fracture toughness

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References

Ainsworth

Sharples

Smith

. Effects of residual stresses on fracture behaviour—experimental results and assessment methods. J Strain Anal 2000; 35: 307–316.

Mahmoudi AH, Aird C, Truman CE, et al. Generating well defined residual stresses in laboratory specimens. In: Proceedings of the ASME pressure vessels and piping conference, Vol. 6, Vancouver, BC, Canada, 23–27 July 2006, pp.631–639. New York: ASME.

Hossain

Daymond

Truman

. Prediction and measurement of residual stresses in stainless steel spheres. J Mater Sci Eng 2004; 373: 339–349.

Hossain

Truman

Smith

. Creating highly triaxial residual stresses in a type 316h stainless steel. J Mech Sci 2006; 48(3): 235–243.

Mirzaee-Sisan

Truman

Smith

. Interaction of residual stress with mechanical loading in a ferritic steel. J Eng Fract Mech 2007; 74: 2864–2880.

Mirzaee-Sisan

Truman

Smith

. Interaction of residual stress with mechanical loading in an austenitic stainless steel. J Fatigue Fract Eng Mater Struct 2008; 31: 223–233.

Harris CP, Bowen P and Knott JF. Warm pre-stressing of blunt notches. In: Proceedings of fracture control of engineering structures conference, Vol. 1, Amsterdam, The Netherlands, 15–20 June 1986, pp.335–350. UK: Engineering Materials Advisory Services Ltd.

Cotton C. A candidate test-piece to investigate creep crack growth in a residual stress field. MSc Thesis, University of Sheffield, 1977.

Turski M. High temperature creep cavitation cracking under the action of residual stress in 316h stainless steel. PhD Thesis, University of Manchester, 2004.

10.

Rice

. A path independent integral and the approximate analysis of strain concentration by notches and cracks. J Appl Mech 1968; 35: 379–386.

11.

Shih

Moran

Nakamura

. Energy release rate along a three-dimensional crack front in a thermally stressed body. J Fract 1985; 30(2): 79–102.

12.

Hou

Pan

. A fracture parameter for welded structures with residual stresses. J Comput Mech 1998; 22(3): 281–288.

13.

Pavier

Poussard

CGC

Smith

. Effect of residual stress around cold worked holes on fracture under superimposed mechanical load. J Eng Fract Mech 1999; 63: 751–773.

14.

Lei

. J-integral evaluation for cases involving non-proportional stressing. J Eng Fract Mech 2005; 72: 577–596.

15.

Beardsmore DW and Sherry AH. Allowance for residual stresses and material interfaces when calculating J in and close to welded joints. In: ASME pressure vessels and piping conference, OH, USA, 20–24 July 2003, pp. 11–21. New York: ASME.

16.

Råde

Westergren

. Mathematics handbook for science and engineering. Berlin: Springer Publication, 1988.

17.

Anderson

. Fracture mechanics: fundamentals and applications. Texas: CRC Press, 2005.

18.

O’Dowd

Shih

. Family of crack-tip fields characterized by a triaxiality parameter, Part-I: Structure of fields. J Mech Phys Solids 1991; 39: 989–1015.

19.

Liu

Zhang

Nyhus

. Residual stress induced crack-tip constraint. J Eng Fract Mech 2008; 75: 4151–4166.

20.

Ren

Zhang

Nyhus

. Effect of residual stresses on the crack-tip constraint in a modified boundary layer model. J Solids Struct 2009; 46: 2629–2641.

21.

Standard test method for measurement of fracture toughness, 2007, ASTM-E 1820-06.

22.

Standard test methods for tension testing of metallic materials, 2008, ASTM-E8.

23.

Lei

O’Dowd

Webster

. Fracture mechanics analysis of a crack in a residual stress field. J Fract 2000; 106: 195–216.

24.

Sattari-Far

Dillstrom

. Local limit load solutions for surface cracks in plates and cylinders using finite element analysis. Sweden: Det Norske Veritas, 2003.

25.

ABAQUS/standard users manual, 1996, Version 5.6.

26.

Assessment of the integrity of structures containing defects, 2006, R6 rev.4, British Energy Generation Ltd.

27.

Shih

Needleman

. Fully plastic crack problems, Parts I and II. ASME J Appl Mech 1984; 51: 48–64.

28.

Kumar V, German MD and Shih CF. An engineering approach for elastic-plastic fracture analysis. Research project 1237-1, Topical Report, Electric Power Research Institute, July 1981.

29.

Sattari-Far I. Solutions of constraint parameters Q, Qm and H in different cracked geometries. Report No. SINTAP/SAQ/08, SAQ Kontroll AB, 1998, Stockholm, Sweden, 1998.

30.

Dodds

Shih

Anderson

. Continuum and micromechanics treatment of constraint in fracture. J Fract 1993; 64: 101–133.