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TOOLS AND TECHNIQUES

Mixed-Mode Crack Propagation in Cruciform Joint using Franc2D A. M. Al-Mukhtar

Submitted: 20 February 2016 Ó ASM International 2016

Abstract The focus of this research was on determining the cracking behavior when parameter such as the biaxiality ratio was varied. The crack propagation under mixed-mode loading was simulated by means of finite element method. The stress intensity factors have been calculated by the linear elastic fracture mechanics approach using fracture analysis code-2D (Franc2D). The crack growth under opening modeI was considered because the crack growth occurs mainly along the direction where the mode-I stress component becomes the maximum. The numerical integration of Paris’ equation was carried out. The effect of normal and transverse applied load (rx, and ry, respectively) on crack propagation was presented. It was found that the fatigue crack growth was faster at a smaller biaxial stress ratio (k), i.e., higher ry on the horizontal crack plan. Moreover, fatigue strength values decrease as k decreases. The results confirm the use of fracture mechanics approach in biaxial fracture. Keywords Biaxial fatigue  Biaxial stress ratio  Cruciform joint  Franc2D  Mixed-mode fracture

Introduction The application of fracture mechanics approach to the biaxial fatigue crack growth has not been successfully developed A. M. Al-Mukhtar (&) Research Fellow, Technische Universita¨t Bergakademie Freiberg, Akademiestraße 6, 09599 Freiberg, Saxony, Germany e-mail: [email protected] A. M. Al-Mukhtar Automated Manufacturing Engineering Department, Al-Khwarizmi College of Engineering, University of Baghdad, Baghdad, Iraq

because of the difficulties of SIF solutions and the costs of the experimental procedures. Most fatigue experiments are performed under uniaxial constant amplitude loading. An accurate SIF solution using Franc2D for uniaxial tensile loads was obtained [1–12]. By changing the proportion of load or displacement of two axes, various stress distributions could be analyzed [13]. For the center crack cruciform specimen, the strain and yielding locus were determined. For the safety assessment of critical components, the crack growth behavior under mixed-mode loading should be evaluated [14]. However, considerable advances have been made in modeling of the cracked bodies [15], fatigue under biaxial loading conditions demands an appropriate testing technology and simulation [16]. Actually, the crack growth direction in cruciform specimen has to be determined under mixed-mode SIF (KI and KII), e.g., ErdoganSih criterion [17]. Then, the fatigue crack growth behavior under mixed-mode conditions is predicted well by the numerical simulation. Fracture analysis code (Franc2D) [18] has been used in SIF calculations for welded joint under uniaxial loading [1–7]. The numerical integration of Paris’ law and the backward calculation was used, see [2]. The objective of this study was to configure the fracture behavior of the cruciformtype sheet specimens that subject to a wide variety of bia