Simplified method for predicting ultimate failure of one-sided composite patched aluminum center crack tension specimens

Abstract

Two material configurations, applications methods, and geometric scales of specimen were used to study the effect that one-sided low modulus composite patch repairs have on crack tip plastic strain to develop a simplified ultimate failure pre- diction method. Digital image correlation and three-dimensional finite element analysis with first order elements were used to understand unpatched and patched center crack tension specimen failure behavior of small scale specimens. The change in crack tip plastic strain behavior due to application of the one-sided composite patch, both measured and predicted, was the foundation for a simplified ultimate failure prediction method. Numerically predicted change in free surface plastic strain area due to the patch as a function of crack opening displacement was found to identify a crack opening displacement prior to the transition of crack tip behavior from small scale to large scale yielding and failure for small scale specimens. The method was validated with small scale specimen full field test data and observed large scale specimen test response. When the composite patch remained perfectly bonded to the aluminum, numerical predictions correlated well with measured response. Proposed method predicted failure loads increased more than 90% over linear elastic fracture mechanics based predictions and were lower than measured ultimate failure.