Effect of Stacking Sequence and Hygrothermal Aging on Fatigue Behavior of CFRP Laminates

Abstract

The application of carbon fiber reinforced polymer (CFRP) Multidirectional (MD) laminates in aircraft structures, marine industries, defence, sports, and wind power sectors has motivated the manufacturers to tailor-make the mechanical strength in desired directions. The complex stress field owing to multiple orientations with the loading direction increases the intricacy of failure analysis. Hence, the macroscopic and microscopic fracture behaviour of MD CFRP laminates with various stacking sequence under static and fatigue loading needs to be explored further. In this study, three different laminates were fabricated using IMA / M21 prepregs i.e. (+45, -45, +45, -45) 2S [MD45], (+45, -45, 0, 90) 2S [MDQI] and, (0, 90, 0, 90) 2S [MD90]. The effect of fiber orientation on ultimate tensile strength (UTS) and ultimate compressive strength (UCS) was studied along with probabilistic Weibull analysis of obtained results. The static strength decreased with the increase in orientation angle. Scanning electron micrographs revealed that irrespective of the lay-up sequence individual layers failed parallel to the fiber direction. Fiber breakage and delamination were the major failure modes in tensile samples while kinking, matrix failure, in-plane shear, stepped fracture, and fiber-matrix debonding were dominated in compression samples. newlineA concept of using constant amplitude fatigue data, experimental matrix crack density, and residual stiffness as a comparative life monitoring tool is presented. The fatigue data were generated for five stress ratios (R= and#963;min/and#963;max) i.e. R= 0.1 and 0.5 (Tension-Tension, T-T), -1, and critical stress ratio (Tension-Compression, T-C) and 5 (Compression- Compression, C-C) with a constant frequency of 2 Hz. The endurance limit of the S-N curve (maximum stress vs the number of cycles to failure) was in the range of 50-80 % of UTS, 30-60 % of UCS, and 30-70 % UCS in MD45, MDQI, and MD90 laminates respectively. The fatigue life cycle was correlated with matrix crack growth and stiffness degradation.