Effect of tow-drop gaps on the damage resistance and tolerance of Variable-Stiffness Panels

Abstract

This paper presents an experimental study of the effects of tow-drop gaps in Variable Stiffness Panels under drop-weight impact events. Two different configurations, with and without ply-staggering, have been manufactured by Automated Fiber Placement and compared with their baseline counterpart without defects. For the study of damage resistance, three levels of low velocity impact energy are generated with a drop-weight tower. The damage area is analyzed by means of ultrasonic inspection. Results indicate that the influence of gap defects is only relevant under small impact energy values. However, in the case of damage tolerance, the residual compressive strength after impact does not present significant differences to that of conventional straight fiber laminates. This indicates that the strength reduction is driven mainly by the damage caused by the impact event rather than by the influence of manufacturing-induced defects.

Microstructure and tensile properties of carbon–epoxy laminates produced by automated fibre placement: Influence of a caul plate on the effects of gap and overlap embedded defects

“…However, the test results showed that an open hole has a stronger negative influence than that of a gap singularity. The effects of impact and compression after impact were also studied, experimentally and numerically [20,21].…”

Manufacturing-Induced Imperfections in Composite Parts Manufactured via Automated Fiber Placement

“…The angle between adjacent courses determines the shape and size of the resulting gaps and overlaps [22]. Within the transitions zones of gaps and overlaps (transition from pristine to defective laminate) fiber angle deviations and fiber waviness may occur [48,51,69,[71][72][73][74][75][76]. The imperfection size is the determining factor for the formation of fiber waviness [48,56,57,71,77].…”

“…Some research groups [56,57,72,78,79] quantify the effects of gaps and overlaps on material and laminate level. Faló et al [73,74] experimentally investigate the damage tolerance of unconventional laminates. They find no statistically significant influence of gaps and overlaps on the strength of laminates with impact damage under compression.…”

Structural composites for multifunctional applications: Current challenges and future trends

“…Moreover, the staggering of plies can largely reduce the effect of defects in un-notched VSP composites [27]. The influence of defects on the impact damage tolerance of steered laminates was found to be relevant only for very low impact energies [28].…”