Rate‐dependent compressive behavior of unidirectional carbon fiber composites

Abstract Unidirectional carbon fiber stitched composites were subjected to off‐axis compression under static and low‐velocity impact loading. Specimens were cut such that the fibers were at angles of 15°, 30°, 45° and 60° to the direction of loading. A modified compression fixture was used to carry out the tests. Static tests were carried out on a hydraulically activated MTS loading frame, where specimens were subjected to displacement controlled loading. Low‐velocity impact tests were conducted on a drop tower facility. A three‐strain‐gauge rosette was used to measure global strains. Load was measured using a load cell. Owing to the unique microstructure of the specimens, a modified three‐parameter characterization of the inelastic response was used, and the constants associated with this characterization were determined uniquely. Independently, Iosipescu shear tests were carried out to determine the shear response of the material under static and low‐velocity impact conditions. The shear response so determined was checked against the off‐axis test results. It is shown that rate‐dependent interfacial effects are predominant in these materials. Polym. Compos. 25:397–406, 2004. © 2004 Society of Plastics Engineers.