Back-face strain compliance calibration for the four-point bend specimen

Abstract

Back-face strain compliance (BFS compliance) for the four-point bend specimen has been calibrated for various crack length ratios. Finite element technique was employed to simulate four-point loading and calculate back-face strain of the bend specimen. The numerically determined strain variation along the back face indicates that the sensitivity to gage placement increases with crack length and back-face strain at the gage length less than 0.2W, where W is the width of the bend specimen, can be measured within 5% deviation of the maximum BFS. Non-dimensional back-face strain compliance, - E'BCW, was calibrated with FE analysis and experiment. The experimentally determined compliance indicates good agreement with the numerical compliance and can be expressed as a function of crack length ratio.