Analysis of Layer Waviness in Flat Compression-Loaded Thermoplastic Composite Laminates

A finite element analysis was used to investigate layer waviness effects in flat compression-loaded composite laminates. Stress distributions in the vicinity of the layer waves as well as the locations and modes of failure were investigated. Two layer wave geometries were considered, each modeled within an otherwise wave-free thermoplastic composite laminate. These two wave geometries, classified as moderate and severe, corresponded to layer waves fabricated in actual laminates and tested under uniaxial compression loading. Material nonlinearities obtained from intralaminar shear and 0 and 90 deg tension and compression testing were incorporated into the analysis. The nonlinearity observed in the intralaminar shear stress-strain behavior was assumed to be valid for interlaminar shear stress-strain behavior, and the nonlinearity observed in the 90 deg tension and compression stress-strain behavior was assumed to be valid for interlaminar normal stress-strain behavior. Failure was predicted using a maximum stress failure theory. An interlaminar tension failure was predicted for the severe layer wave geometry, producing a large compression strength reduction in comparison to the wave-free laminate. Fiber compression failure was predicted for the moderate layer wave, producing only a slight compression strength reduction. Although significant material nonlinearity was present in the interlaminar compression and shear response of the material, the inclusion of material nonlinearity produced only slight decreases in predicted compression strengths relative to predictions based on linear material behavior.