A Statistical Approach for Optimizing the Fracture Toughness of a Composite Laminate

Abstract

Delamination is one of the most critical failure modes in laminated composite structures due to its abrupt and damaging character. In the present investigation a methodology is developed using Designed Experiments and Taguchi concepts to analyze the contribution and significance of several factors to the mode I delamination fracture toughness of a composite structure. The factors tested were selected based on their degree of influence on the fracture toughness and their tailoring adjustability. Considering these two criteria, the most important factors in optimizing a laminate's strength include crack (delamination) length, stacking sequence, width, thickness, and length of the structure. Most importantly, the effect of their first order interactions, i.e., concurrent effect, on a damaged laminate is investigated. All the factors are regarded at two levels and a Fractional Factorial experiment is conducted. Taguchi arrays are used to select the combination of factors that will maximize the amount of information from the minimum number of experiments. The idea of significant factors and their interactions is then used to obtain a response surface equation. Estimation of the structure's interlaminar fracture toughness follows once the response surface equation is identified. The developed methodology significantly reduces the required number of experiments and qualitatively describes the effect of various factors, and their interactions, on the fracture toughness. Experimental and analytical results, employing the optimal combination of factors as determined by the presented method, are in good agreement.