Impact on natural fibre-reinforced polypropylene composites: Failure modes

Natural cellulosic fibres are becoming increasingly popular in the field of composites due totheir abundance, low cost, biodegradability and recyclable nature. Composites with high specific properties can be produced, since natural fibres have lower density compared to, for example, glass. The corresponding weight and cost saving in addition to the fibres I sound proofing and heat insulation capabilities has contributed to the use of these materials in the automotive industry (interior car trims, headliners, dashboards, package trays, etc). Irrespective of the application for natural fibre composites, these materials face varying forms of impact damage. Natural fibre composites exhibit varying failure modes depending on the nature of impact on the material. In this work, the impact failure of natural fibre composites under low and ballistic velocities is investigated. The low velocity impact involved Charpy impact and drop weight impact techniques. For the ballistic impact tests, a 1.1 g, 5.56 mm diameter Fragment Simulating Projectile (FSP) was used as per Nato Stanag 2920 ballistic standard. The ballistic shots were fired normal to the target with a Block Manometric Cannon Interchange (BMCI) gun. It was found that the failure at low velocity impact was dominated by fibre fracture, fibre pull out, matrix cracking and delamination. At ballistic velocities, failure modes included transverse shear cut-out, fibre failure, delamination and spalling.