Free Edge Strain Concentrations in Real Composite Laminates: Experimental-Theoretical Correlation

Abstract

The magnitude of tile maximum shear strain at the free edge of axially loaded [e2/-e2]s and [(±e)2]s composite laminates was investigated experimentally and numerically to ascertain the actual value of _ strain concentration in resin matrix laminates and to determine the ; accuracy of finite element results. Experimental results using moire : interferometry show large, but finite, shear strain concentrations at the free edge of graphite-epoxy and graphite-polyimide laminates.Comparison of the experimental results with those obtained using several different finite element representations showed that a four node isopari ametric finite element provided the best and most trouble free numerical J results. The results indicate that the ratio of maximum shear strain at the free edge to applied axial strain varies witn fiber orientation and 1 does not exceed nine for the most critical angle which is 15°.

An Experimental and Numerical Investigation of the Free Edge Problem in Composite Laminates

“…In an experimental study involving moiré interferometry, Czarnek et al [35] verified the existence of edge effects and steep displacement gradients for angle-ply laminates loaded uniformly in extension. The existence of high interlaminar shear strain concentrations at the free edge of angle-ply laminates was also experimentally verified by Herakovich et al [38] and Boeman [45] using high sensitivity moiré interferometry.…”

Efficient computation of order and mode of three-dimensional stress singularities in linear elasticity by the boundary finite element method

“…Experimental evidence for the existence of severe free-edge stress fields and the possible hazard of interlaminar failure modes as a result of interlaminar stress concentrations has been given by e.g. Pipes and Daniel (1971), Whitney and Browning (1972), Herakovich et al (1985), Herakovich (1989a,b), Kim (1989) and Whitney (1989). Since the stress field in the vicinity of edge interfaces between dissimilar laminate layers is dominated by a mathematical singularity, there is also a multitude of investigations available in which the asymptotical behaviour of the state variables near free interface edges is considered.…”

Micro-Deformations in C3000/PMR15 Woven Composite

“…In the past decade, Post and co-workers [10][11][12][13][14][15][16][17][18][19] have investigated many types of composite laminates using Moire methods. However, to our knowledge, this sophisticated technique has never been used to study the mechanical behavior of bundles in woven composites.…”