On fracture toughness of orthotropic metallic materials under cyclic loading

Abstract

A VT-6 titanium alloy rolled sheet, which is initially isotropic and subject to kinematic hardening, is used as an example to analyze the effect of kinematic hardening on crack growth resistance under uniaxial cyclic loading. Crack growth resistance is characterized by the number of cycles to failure, critical crack length, and critical stress intensity factor. The subject of study is plane specimens with an edge notch. It is shown that prestrain changes the anisotropy of the specimens, which is determined as the ratio of the crack growth resistance in the rolling direction to that in the transverse direction. The crack path under a load applied at an angle to the axes of anisotropy is studied Keywords: orthotropic material, kinematic strain hardening, crack growth resistance, uniaxial cyclic loading Introduction. The crack growth resistance of materials under cyclic loading depends on many factors such as temperature, loading frequency, stress cycle, ambient medium, stress state mode [4,6]. The effect of plastic prestrain on the strength and life of materials under cyclic loading is studied in [7,12,13,15]. The influence of these factors on crack growth resistance was examined in [1,10,11,18,22]. The subject of the present study is initially isotropic materials. Some aspects of crack growth resistance of anisotropic materials were addressed in [17,[19][20][21][22][23]. The present paper examines the influence of plastic prestrain on the crack growth resistance and kinetics of orthotropic metallic materials subject to kinematic hardening under uniaxial cyclic tension (pulsating stress cycle).Experimental Technique. The subject of study is VT-6 titanium alloy, which is orthotropic when in as-received condition [9]. Specimens for tests were made from plates produced by rolling. The mechanical properties of the material (yield strength s Y , ultimate strength s u , uniform component of residual elongation e p , Young's modulus E, and Poisson's ratio m)