Abstract
Titanium-alloy weldments have been extensively used in engineering structures, and accurate estimation of the fatigue life is beneficial for avoiding catastrophic failures in titanium-alloy structures. The weld pore is a common defect in these weldments that significantly influences the fatigue process. In this study, the weld-pore size and depth and its effect on the fatigue life of Ti-6Al-2Zr-1Mo-1V (TA15) alloy weldments are investigated by adopting fatigue tests and fracture observations. The results show that fatigue crack initiations occurred at the weld pores for all specimens. The diameter and depth of all weld pores on fracture surfaces were then measured, and an indicator, P, was proposed, defined as a combination of pore diameter and depth. It was found that all the fatigue cracks initiated from the pore have the smallest P indicator, which suggests that P can be used to judge the location of crack initiation in an individual sample. Moreover, a model was developed based on P to estimate the fatigue life of weldments, considering the effects of weld-pore size and depth. Finally, analogous fatigue tests were carried out for model verification, and results show that the proposed model has a higher accuracy compared with several typical models. The findings of this study can be helpful in estimating the fatigue life and fatigue design of titanium-alloy weldments.
Highlights
Titanium alloy is widely used in engineering structures because of its properties [1].Ti-6Al-2Zr-1Mo-1V (TA15) alloy, a kind of α + β titanium alloy, has moderate room temperature strength, good thermal stability and excellent weldability, and increasingly extensive applications in the aerospace industry, mainly for primary large-scale supporting components [2]
This study investigates, through quantitative of weld-pore size and depth, the welding method before fatigue design.aFor this paper, analysis fatigue tests and scanning electron microscope crack-initiation location and the effect of weld pores on the fatigue life of
Relationships between the stress amplitude and the fatigue life of all the specimens are shown in model proposed by Weibull: Np = S0f (Sa − Sac )b where Sac is the fatigue limit, and S0f and b are constants related to the materials
Summary
Titanium alloy is widely used in engineering structures because of its properties [1].Ti-6Al-2Zr-1Mo-1V (TA15) alloy, a kind of α + β titanium alloy, has moderate room temperature strength, good thermal stability and excellent weldability, and increasingly extensive applications in the aerospace industry, mainly for primary large-scale supporting components [2]. Titanium alloy is widely used in engineering structures because of its properties [1]. Welding is a common joining method used in these components that has the advantage of being lightweight, while weldments are always fatigue-prone in structures [3,4]. The fatigue performance of titanium-alloy weldments significantly affects the structure’s durability and reliability [5], and has become a research focus in recent years. The crack nucleation mechanism is related to different mechanical properties between the α phase and β phase. The α phase is harder than the β phase; elastoplastic behavior incompatibilities at the α/β interface results in crack nucleation [6]. Titanium alloy with a fine microstructure, such as an equiaxed structure, exhibits better crack-initiation resistance than a coarse microstructure, such as a lamella structure [7].
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