Experimental damage tolerance evaluation of thick fabric carbon/epoxy laminates under low-velocity and high-velocity impact and compression-after-impact
Experimental damage tolerance evaluation of thick fabric carbon/epoxy laminates under low-velocity and high-velocity impact and compression-after-impact
Date
2022
Authors
Hoorn, N. van
Kassapoglou, C.
Turteltaub, S.R.
Brink, W.M. van den
Journal Title
Journal ISSN
Volume Title
Publisher
Netherlands Aerospace Centre NLR
Abstract
Impact experiments of thick fabric carbon/epoxy laminate specimens, with small thickness ratio, are
conducted at distinct energy levels and thicknesses to characterize the damage process. These
specimens and loading conditions are representative of a new generation of critical structural
components in aviation, such as wing spars, landing gear beams and fittings, that are increasingly
being made entirely from composites. The tests address the need to better understand the damage
process for specimens with a small thickness ratio since existing experimental impact data for large
thickness ratio (thin laminates) may not be directly applicable. Two energy levels, two different fabric
layups, and two impact methods (drop-weight and gas-cannon) were used. Data from high-speed
cameras were processed in a novel way, providing the force during impact. C-scans and micrographs
were used to characterise damage. The results show that specimens with a thickness ratio of 5 (20 mm
thick) experience more bending compared to specimens with a ratio 2.5 (40 mm thick). For gas-cannon
impacts, this results in a higher delaminated area. The drop-weight impacts show almost no differences
in damage size for the thickness range analysed. The influence of layup on the global impact response
is negligible, but locally it can result in significant variations in dent depth. The dent depth scales linearly
with the impact energy and the delaminated area linearly with the impact velocity. There is no clear
correlation between the compression-after-impact failure mechanisms and the residual strength. Impact
damage, at the current energy levels, showed a minimal reduction of residual strength.
Description
This report is based on an article published in the Journal of Composite
Materials, 3 January 2022, by SAGE Journals.