Characterization of deformation localization mechanisms in polymer matrix composites: A digital image correlation study

Polymer matrix composites (PMCs) are attractive structural materials due to their high strength to low weight ratios. However, due to their low shear strength, failure can occur due to kink bands that develop on compression via plastic microbuckling. This phenomenon has been modeled extensively; however, experimental measurements of the strain fields leading to and developing inside these bands are scarce, as the sample preparation for digital image correlation (DIC) requires a microscale speckle pattern, which is hard to obtain using inks as PMCs they absorb them. In this study, two dimensional DIC is used to measure strains inside kink bands during 3-point bending of Dyneema HB80 samples. A novel micro-scale speckle pattern along with precision optics have been used to measure strains within the kink band, which had a width of approximately 600 micrometers. The speckle pattern was created by dropping copper particles through fine mesh sifters on a thin adhesive film that was applied and cured on the side surface of beam samples. This led to speckle dots that have a minimum of 15–20, μm mean diameter along with an inter-spacing ≤10, μm through the kinkband width. Images were captured during sample loading and processedusing ARAMIS^™ software. Measurements indicate a mixture of large shear and normal strains (∼30%) in Dyneema HB80 inside the kink band.