Issue 29

S.K. Kudari et alii, Frattura ed Integrità Strutturale, 29 (2014) 419-425; DOI: 10.3221/IGF-ESIS.29.37 419 Technical note A new formulation for estimating maximum stress intensity factor at the mid plane of a SENB specimen: Study based on 3D FEA S. K. Kudari, K. G. Kodancha Research Centre, Department of Mechanical Engineering, B. V. B. College of Engineering and Technology, Hubli 580 031, Karnataka, India. s.kudari@rediffmail.com A BSTRACT . In this investigation, three-dimensional elastic finite element analyses have been conducted to compute the stress intensity factor ( K I ) in a SENB specimen with varied thickness ( B ) and crack-length to width ratio ( a/W ). The results indicate that the magnitude of K I depends on B , and significantly varies along the crack- front from surface to the center of the specimen. The maximum value of K I is found at mid plane of the specimen. Based on the present 3D finite element calculations an effort is made to propose the new analytical relationship between maximum K I and specimen a/W , which helps to estimate maximum K I by only knowing specimen geometry and applied load. K EYWORDS . SENB specimen; Finite element analysis; Maximum stress intensity factor. I NTRODUCTION n Fracture analysis, two-dimensional approach of LEFM is popular because of its simplicity in mathematical formulation and numerical analysis. In two-dimensional structural analyses, plane strain is governed by case where deformation is highly constrained for example plates with larger thickness, and plane stress is used for thin plates. Several methods have been developed in past, to compute the K I for engineering problems with complex geometry and loading [1]. Fett [2] has used boundary allocation method to compute K I solutions for components containing internal cracks. Chen and Lin [3] investigated the dependence of the K I from the imposed boundary conditions in a rectangular cracked plate. Based on the asymptotic solution of the singular stress field, and the common numerical solution (stresses or displacements) obtained by finite element method, a simple and effective numerical method is developed by Yihua Liu et al. [4] to calculate stress intensity factors. Due to complexity of the solution, the stress field around the crack-front in 3D continua is limited. Kwon and Sun [5] given the detailed literature review about the efforts in computating 3D stress intensity factor and presented 3D FE analyses to investigate the stress fields near the crack tip. The authors [5] suggested a simple technique to determine 3D K I at the mid plane of a specimen by knowing 2D K I and Poison’s ratio ( v ). Moreira et al. [6] studied the 3D effects in a central cracked plate by numerical determination of the stress field and K I variation through the thickness. As Single edge notch bend (SENB) specimen is more preferred for fracture tests hence, it is essential to have such study on this specimen. The aim of this investigation is to study the variation of K I along the crack-front considering a SENB specimen geometry having varied thickness ( B ) and crack length to width ratio ( a/W ). To calculate the maximum K I at mid plane of any fracture specimen, it is essential to conduct complex 3D FEA. Hence, it is always very difficult for a structural engineer to conduct 3D FEA for estimating K I at the mid plane of a specimen. Hence, based on the present 3D FE calculations, an attempt is made to propose a new analytical relationship between K I at the mid plane, a/W and applied I