Response of Composite Laminates to Contact Loads and Relationship to Low-Velocity Impact

Experimental results are presented for contact and low-velocity-impact re sponses of composite laminates by rigid spheres. The contact phenomenon is different in small and large indentation stages, which is due to occurrence of laminate damage. The contact force corresponding to the onset of laminate damage is found to be independent of the indentor size. In the small indentation stage where the plate is intact, the change of laminate stacking sequence has an insignificant effect on the force-indentation relation ship. However, the force-indentor size relationship does not follow the modified contact law for thin laminates indented by large indentors. Beyond the small indentation stage, damage occurs. The size of the delamination area is proportional to the applied loads and the number of repeated loading cycles. The passage of the delamination crack front can be detected using strain gauges. Also, the indentation spring becomes stiffer under repeated loading. Finally, the delamination damage and the strain history in a laminate at low- velocity impact are found to be very similar to those in the contact test except that vibra tion was observed in the impact test.