Fatigue Damage of Glass/Vinyl Ester Thick Composites

Abstract

Abstract The focus of this study is to investigate the compression-compression fatigue damage of S2-glass/vinyl ester woven composites manufactured through Vacuum Assisted Resin Transfer Molding (VARTM). The compressive behavior and the relevant failure modes of composites are investigated prior to applying the cyclic load. The panels of thicknesses (0.15 in./3.81mm – 0.45 in./11.43 mm) are considered to quantify the process related defect such as void contents and fiber waviness in the thick composite laminates. Void content of each panel is determined through a bum-off test method using a Thermal Gravitational Analyzer (TGA). An optical microscope attached with a grid pattern transparent film is used to measure the waviness parameters of the laminate. The ultrasonic C-scan, A-scan and microscopic examinations are used to identify the manufacturing flaws related to VARTM. The effects of such defects on static compression and compression-compression cyclic behavior of thick composites are investigated. The failure strength, failure strain, modulus and number of cycles to failure at different stress levels for various laminate thicknesses are determined. Weibull plots are generated using both static compression strength and fatigue life cycles. Although the range of the thickness of the laminate was in the ratio of one to three, the variation in compressive strength data was rather nominal. The fatigue performance is observed to improve with the increase in thickness. In-situ monitoring of progressive damage under compressive and cyclic loading is conducted using acoustic emission (AE) method. AE parameters in the form of amplitude, energy and time plots are generated. The compressive and fatigue failure modes are identified by optical and scanning electron microscopic examinations. These failure modes are correlated with acoustic emission Non Destructive Evaluation (NDE) parameters.