Interaction of plastic zone, pores, and stress ratio with fatigue crack growth of sintered stainless steel

Abstract

The relationships between plastic zone, pores, fatigue crack growth rate (da/dN), and fracture mechanics parameters of metal injection molding (MIM) 316L stainless steel at various stress ratios (R = 0.1 and 0.4) are investigated in the present work. Using two-dimensional (2D) plane strain finite element analysis (FEA), the stress intensity factor and cyclic-plastic zone at crack tip are evaluated. The slow-growth da/dN at near-threshold regime is in brittle manner, and can be characterized by maximum stress intensity factor (K max ). While, the mid-growth da/dN at Paris regime is in ductile manner, and can be characterized by stress intensity factor range ( K). As a fracture mechanics parameter that combines K max and K, the K* successfully characterizes the stress ratio effect on FCG rate at near-threshold and Paris regimes. The transition from slow-growth da/dN to mid-growth da/dN occurs when the cyclic-plastic zone at crack tip coalesces with pore. The appearances of fracture surfaces at near-threshold and Paris regimes are in good agreement with the FEA results.

On the fatigue crack growth behaviour of selective laser melting fabricated Inconel 625: Effects of build orientation and stress ratio

“…The FCG data for the 7175‐T451 aluminium alloy at stress ratios of 0.05 and 0.70 was obtained from Garcia, and the sample used was a SENT specimen with a thickness of 12.7 mm and a width of 50.8 mm . Noraphaiphipaksa et al performed detailed studies of the effect of stress ratio (0.1 and 0.4) on FCG in SENB specimens of metal injection moulding (MIM) 316 L stainless steel, with thickness of 5 mm and width of 10 mm. Zhao used CT specimens with a 12.7‐mm‐thick SLM Ti6Al4V alloy to perform an FCG test, with a stress ratio of 0.1 and 0.5.…”

“…The FCG rate points of 7075‐T7451 aluminium alloy (SENT specimens), MIM 316 L stainless steel (SENB specimens), SLM Ti6Al4V alloy (CT specimens) and Al‐mg‐Si alloy (M(T) specimen) were associated with (a) SIF range, Δ K and (B) effective driving force factor range, Δ κ # [Colour figure can be viewed at wileyonlinelibrary.com]…”