Investigation of permanent indentation due to low velocity impact on glass fibre reinforced plastics

Abstract

Structural applications of advanced lightweight composites may be exposed to low energy impacts such as ‘tool drops’ during the service of an aircraft. This type of impact will often create barely visible impact damage (BVID) on the surface with extensive internal ‘hidden’ damage. To investigate the occurring damage mechanisms in glass fibre reinforced composite materials, low velocity impact tests as well as quasi-static (QS) indentation tests were conducted. Three energy levels (25 J, 50 J and 75 J) were chosen for the impact tests and the maximum indentor displacement of these tests was taken as termination criterion for the QS indentation tests. The load-displacements curves of both testing configurations showed strong deviations as the QS indentations tests formed a plateau at significantly lower loads, where the reaction force of impact tests further increased. Microsections of the specimen revealed excessive fibre breakages in the indentation tests as the main reason. This failure further led to higher indentation depth values compared to the impacted specimen. As reason for the differences the strain-rate dependency of glass fibres is assumed.