Stress Ratio and Notch Effects on the Very High Cycle Fatigue Properties of a Near-Alpha Titanium Alloy

Abstract

Ultrasonic fatigue tests up to 1010 cycles were performed on a turbine engine titanium alloy (Ti-8Al-1Mo-1V) at the stress ratio (R) of −1 with smooth specimens and at R = −1, 0.1 and 0.5 with notched specimens. As a result, with increase of fatigue life, the source of reduced fatigue life caused by multi-point surface crack initiation changes from crack propagation stage to crack initiation stage in the high cycle fatigue regime. Notch effect further promotes the degeneration of high cycle and very high cycle fatigue strength at R > −1. The bilinear model, extended from the Goodman method, can better estimate the mean stress sensitivity of this titanium alloy. The fatigue mean stress sensitivity and fatigue-creep mean stress sensitivity of this material increased with the increase of fatigue life. The new model, based on the Murakami model, can provide more appropriate predictions for notch fatigue strength.

Influence of the volume content of α + β colonies on the very high cycle fatigue behavior of a titanium alloy

“…Figure 6A shows the fatigue life data and S – N curves of the titanium alloy in the two heat treatment states 8,23 . The solid mark indicates that the fatigue crack initiates from the surface, and the semisolid mark represents that the fatigue crack originates from the interior.…”

“…As a result, the hardness of the HR and DA materials is 322 and 305 HV1, respectively. The detailed information about the chemical compositions and mechanical properties can also be found in our previous studies 5,8,11,23 …”

“…In recent years, the high reliability and ultra‐long service life have become the development objective and urgent requirement of key equipment, such as aeroengines and gas turbines. Hence, the VHCF behavior of advanced structural materials has gained more and more interests from researchers in the field of fatigue researches 3–10 …”

The Effect of Stress Ratios on the Very High Cycle Fatigue Behavior of 9%Cr Turbine Steel at 630 °C

“…In this study, the geometric parameter of the region (A) was used to calculate the ΔK of the crack tip. Equation (2) of Δ K A [ 31 , 32 ] is shown as follows, where n is a constant related to the location of crack initiation, and n is 0.65 for surface-induced and 0.5 for interior-induced crack, respectively. is the applied cyclic stress range, it can be obtained from the S–N curves.…”

“…In this study, the geometric parameter √ area of the region (A) was used to calculate the ∆K of the crack tip. Equation (2) of ∆K A [31,32] is shown as follows,…”