Interlaminar Properties and Failure Strength of Thick-Section, Vacuum-Assisted Resin-Infusion Molded (VARIM) Composites

In this paper a combined experimental and analytical study is presented on determination of interlaminar properties and strength of thick vacuum-assisted resin-infusion molded (VARIM) composite. In the experimental program, glass fabric/vinyl ester composites of different thicknesses up to 120 plies (5.6 inches) were fabricated for microstructural evaluation, thermal analyses and mechanical tests. DSC and MDSC analyses were used to evaluate through-thickness distributions of curing degree and glass transition in the thick composite. Interlaminar tensile and shear tests were conducted on specially designed specimens in a servo-hydraulic test system. Optical and electron microscopy was performed to determine composite interlaminar microstructure, defects, damage and failure modes associated with different loading modes. Features of interlaminar defects and their sizes and locations in the thick VARIM composite laminates were obtained; their influences on interlaminar mechanical properties and failure modes were studied. Effects of composite microstructure and defects were determined on interlaminar deformation, strength and failure modes. The study is of fundamental importance in understanding of thick-section, VARIM composite interlaminar deformation and failure. The results provide critical information of through-thickness interlaminar mechanical properties and strength for subsequent material development, manufacturing, design and integrity assessment of large, thick-section glass/vinyl ester composite wind turbine blades and offshore structures.