The Notched Strength and Fracture Criterion in Plain Woven Glass/Epoxy Composites With a Crack

J. Ocean Eng. Technol. 1993;7(2):57-67.

노치부를 가진 Glass/Epoxy 복합재료의 노치강도 평가와 불안정 파괴조건

김정규,김도식

한양대학교 기계설계학과,한양대학교 기계설계학과

Keywords: Notched Strength Evaluation, Characteristic Length, Point Stress Criterion, Energy Release Rate, Stree Intensity Factor, Shape Correction Factor

핵심용어: 노치강도평가, 특성길이, 점응력조건, 에너지해방율, 응력확대계수, 형상보정계수

Abstract

The fracture behavior of plain woven glass/epoxy composite plates with a crack is investigated under static tensile loading. It is shown in this paper that the characteristic length associated with the point stress criterion depends on the crack length. To predict the not ched tensile strength, the point stress criterion proposed by Whitney and Nuismer are modified. An excellent agreement is found between the experimental results and the analytical prediction of the modified point stress criterion. The condition of unstable crack growth in the presence of a per-existing flaw(machined notch) is examined by means of the maximum stress intensity factor $K_max$ using maximumload P$_max$. The values of $K_max$ evaluated from energy release rate G$_max$(the compliance me thod) indicate a wide difference. Therefore in regard to anisotropy and heterogeneity of the composite materials studied, the modified shape correction factor f(a/W) is obtained. $K_max$evaluated by the compliance method a little or insignificantly depends on the initial crack length a, the specimen thickness B, the crack angle .theta. and the specimen geometry.