Kink band evolution in polymer matrix composites under bending: A digital image correlation study

Polymer matrix composites are attractive structural materials in automotive, defense, and aerospace industries due to their high strength to low weight ratios. However, due to their low shear strength, compression dominated failure mechanisms such as plastic microbuckling lead to the development of kink bands, which are a key strength-limiting factor in modern polymer matrix composites. This phenomenon has been studied extensively, particularly for uniaxial compression; however, experimental measurements of the strain fields leading to and developing inside these bands under bending are not well explored. In this study, digital image correlation is used to measure strains inside kink bands developing during three-point bending of cross-plied [0/90] laminated composite Dyneema™ HB80. Measurements indicated large normal and shear strains developed inside the band in a way that suggested systematic increases in ply rotation angle as the band evolved with increased bending deflection. Results also suggested intermittent buckling events involving fiber bundles that correlate with oscillations observed in the load–displacement curve. Optical microscopy of failed samples showed failure resulted from a combination of plastic microbuckling and axial splitting.