Effects of laser shock processing on high cycle fatigue crack growth rate and fracture toughness of aluminium alloy 6082-T651

Abstract

The effects of laser shock processing without protective coating on high-cycle fatigue crack growth and fracture toughness were investigated. Laser shock peening treatment was performed on compact tension specimens from both sides perpendicular to the crack growth direction, followed by subsequent grinding. Fatigue crack growth tests were performed at frequencies between 116 and 146 Hz, at R=0.1 and a constant stress intensity range during the fatigue crack initiation phase and K-decreasing test. A lower number of cycles was required to initiate a fatigue precrack, and faster fatigue crack growth was found in tensile residual stress field of LSP-treated specimens. The crack growth threshold decreased by 60 % after LSP treatment. The fracture toughness decreased by 28-33 % after LSP treatment. The fatigue-to-ductile transition boundary on fractographic surfaces show linear fatigue crack fronts in nontreated specimens and curves after LSP treatment.

Effects of laser shock peening on the microstructure and fatigue crack propagation behaviour of thin AA2024 specimens

“…The retardation effect of LSP on the FCP rate was attributed to high compressive residual stresses, which were generated in 2 mm-thick AA2024 sheets. Bergant et al (2016) [1] observed an inferior FCP behaviour of 10 mm-thick 6082-T651 C(T) specimens with LSP compared to that of BM specimens. The reason was probable in the unoptimised LSP process, which resulted in higher surface roughness without introducing noticeable compressive residual stresses in the investigated material.…”

Fatigue Life Behavior of Laser Shock Peened Duplex Stainless Steel with Different Samples Geometry

“…Further, the effects on chemical composition after LSP and geometric [17] analyzed the effect of pulse density on low cycle fatigue in super-ferritic stainless steel and it is observed that the LSP causes thermal effects on the surface microstructure, generating intergranular corrosion, which decreases the fatigue life of this alloy. Bergant et al [18] founded that the LSP increases fatigue crack growth rate in 6082-T651 Al alloy due the equilibrium tensile stresses in the center of specimen and notches edge as explained by Correa et al [5,7] through MEF simulation. Granados-Alejo et al [19] analyzed the effect of samples thickness in 2205 DSS, in which it is observed that in thinner samples, higher fatigue life is obtained by LSP.…”

Fatigue Life Extension of AA2024 Specimens and Integral Structures by Laser Shock Peening

“…The results clearly demonstrated that LSP can be used as an effective surface treatment technique for reducing or suppressing fatigue crack growth in aluminium alloys. However, application of a not optimised LSP process can produce high surface roughness without introducing noticeable compressive residual stresses [10]. In this case, LSP can reduce the fatigue life of critical components and structures.…”