Cyclic Stress Response Behavior of Near β Titanium Alloy and Deformation Mechanism Associated with Precipitated Phase

The cyclic stress response behavior of Ti-3Al-8V-6Cr-4Mo-4Zr alloy with three different microstructures has been systematically studied. The cyclic stress response was highly related to the applied strain amplitude and precipitated phase. At low strain amplitude, the plastic deformation was mainly restricted to soft α phase, and a significant cyclic saturation stage was shown until fracture for all three alloys. At high strain amplitude, three alloys all displayed an initial striking cyclic softening. However, the softening mechanism was obviously difference. Interestingly, a significant cyclic saturation stage was noticed after an initial cyclic softening for alloy aging for 12 h, which could be attributed to the deformation of {332}<113> twin and precipitation of α″ martensite.

Effects of mean strain and tensile pre-strain on torsional fatigue behaviours of duplex stainless steel SAF2205

Effects of mean strain and tensile pre-strain were investigated on the torsional fatigue behaviours of duplex stainless steel SAF2205. Two equivalent strain amplitudes (0.5%,0.7 %), three strain ratios (-1, - 0.5, -0.25) and 5% tensile pre-strain were chosen. Results indicated that the mean strain had no distinct influences on the torsional fatigue behaviours in terms of cyclic stress reponse and fatigue life while tensile pre-straining made a significant increase in cyclic stress response which was mainly attributed to the cross hardening derived from the loading sequence of monotonic tension preceding to cyclic torsion and led to a reduction in fatigue life. The failure mechanisms were revealed by scanning electron microscope characterized by microcracks initiation at the extrusions in ferrite and phase boundary inhibited further propagation. Additionally, the fractography of all fatigued specimens revealed a quasi-cleavage brittle mode with features of distinct tearing ridges and cleavage facets.

Cyclic Stress Response and Fracture Behaviors of Alloy 617 Base Metal and Weld Joints under LCF Loading

Cyclic stress response and fracture behaviors of Alloy 617 base metal (BM) and Alloy 617 weld joints (WJ) are investigated under strain controlled low cycle fatigue (LCF) loading. Axial fully reversed total-strain controlled tests have been conducted at room temperature with total strain ranges of 0.6, 0.9, 1.2, and 1.5%. At the all testing conditions, weld joint specimens have shown higher peak stresses than the base metal specimens, whereas the plastic strain accumulation of the base metal specimens is comparatively higher than those of the weld joint specimens. The cyclic stress response behavior of both base metal and weld joint specimens revealed initial cyclic hardening during first small number of cycles followed by progressive softening to failure. Higher strain amplitudes decreased the fatigue lives for both base metal and weld joint specimens; subsequently weld joint specimens had lower fatigue resistances relative to base metal specimens. Furthermore, the cracking in weld joint specimens initiated in the weld metal (WM) region. The crack initiation and propagation showed transgranular mode for both base metal and weld joint specimens; especially weld joint specimens showed a wedge type crack initiation about 45 degrees to the loading direction because of the dendritic structure.

A Simple Inelastic Constitutive Model for Evaluation of Stable Cyclic Stress Response Under Nonproportional Straining

This paper proposes a simple two-surface model for cyclic incremental plasticity based on combined Mroz and Ziegler kinematic hardening rules under nonproportional loading. The model has only seven material constants and a nonproportional factor which describes the degree of additional hardening. Cyclic loading experiments with fourteen strain paths were conducted using Type 304 stainless steel. The simulation has shown that the model was precise enough to calculate the stable cyclic stress-strain relationship under nonproportional loadings.