Residual stress induced tension-compression asymmetry of gradient nanograined copper

Abstract

The residual stress significantly influences the cyclic stress response of the hierarchical nanostructured materials. An obvious tension-compression asymmetry with minimum stress in compression larger than maximum stress in tension was observed in gradient nanograined (GNG) Cu under straincontrolled high-cycle fatigue tests, which gradually diminished with increasing cycles or after being annealed at a low temperature. The observed asymmetric response is primarily induced by the presence of the residual compressive stress in the GNG surface layer. The longer fatigue life can be achieved in GNG Cu with a higher residual stress, compared to that of annealed GNG Cu. IMPACT STATEMENT Obvious tension-compression asymmetry was observed in cyclically deformed gradient nanograined Cu under strain control, caused by the residual compressive stress in the GNG surface layer.

Effect of Volume Fraction of Gradient Nanograined Layer on Low‐Cycle Fatigue Behavior of Cu

“…The process of SMGT, like other surface treatment methods, such as deep rolling and shot peening, can also induce a residual compressive stress in the GNG surface layer, due to an inhomogeneous plastic deformation in grains or between grains . Previous study indicated that residual stress can improve the high‐cycle fatigue life of GNG/CG Cu due to the suppressed initiation and propagation of cracks in the tension side .…”

“…[36] Previous study indicated that residual stress can improve the high-cycle fatigue life of GNG/CG Cu due to the suppressed initiation and propagation of cracks in the tension side. [36] However, a few studies have demonstrated largeamplitude cyclic straining in low-cycle fatigue tests will induce microstructure recovery/grain coarsening and the rapid release of residual stress in the GNG layer in very short initial cycles. [15,33,37] For instance, the residual stresses of gradient nanostructured 316L stainless steel can be rapidly released after fatigue to only 6%N f at Δε t /2 ¼ 0.4%.…”

“…[17] Combining with the present results, it can be concluded that the superior all-round fatigue performance with longer fatigue life in low-cycle regime and enhanced fatigue endurance limits in high-cycle regime can be achieved in GNG/CG metals, distinct from the trend of trade-off of high-cycle and low-cycle fatigue properties for conventional metals with homogeneous nanostructures, i.e., a high fatigue limit but a much shortened fatigue life. [1,7] The process of SMGT, like other surface treatment methods, such as deep rolling and shot peening, [33][34][35][36] can also induce a residual compressive stress in the GNG surface layer, due to an inhomogeneous plastic deformation in grains or between grains. [36] Previous study indicated that residual stress can improve the high-cycle fatigue life of GNG/CG Cu due to the suppressed initiation and propagation of cracks in the tension side.…”

“…[1,7] The process of SMGT, like other surface treatment methods, such as deep rolling and shot peening, [33][34][35][36] can also induce a residual compressive stress in the GNG surface layer, due to an inhomogeneous plastic deformation in grains or between grains. [36] Previous study indicated that residual stress can improve the high-cycle fatigue life of GNG/CG Cu due to the suppressed initiation and propagation of cracks in the tension side. [36] However, a few studies have demonstrated largeamplitude cyclic straining in low-cycle fatigue tests will induce microstructure recovery/grain coarsening and the rapid release of residual stress in the GNG layer in very short initial cycles.…”

Residual stress provides significant strengthening and ductility in gradient structured materials

“…For example, it has been recently reported that gradient-structured metals produced by surface mechanical attrition treatment (SMAT) possess superior strength and ductility [14,15,18]. SMAT is expected to produce CRS in the sample sub-surface layers [2,6,7,19]. However, due to the above belief, the CRS was not considered in explaining the mechanical behavior of these gradient materials.…”