Experimental study on the panel size effects of the low velocity impact (LVI) and compression after impact (CAI) of laminated composites, part II: CAI

Abstract

This paper is part II of a study on the CAI responses of laminated composite panels. Panels with three in-plane sizes, two thicknesses, and two stacking sequences were studied using CAI fixtures based on and modified from the industrial standard. The three in-plane sizes are 152.4 mm × 101.6 mm, 177.8 mm × 177.8 mm, and 330.2 mm × 330.2 mm. The two thicknesses are 24-ply and 48-ply. The two stacking sequences are [45/-45/0/90/0/0]ns and [45/0/-45/90]ns. The material system is IM7/977-3. Load–displacement curves, 2D/3D DIC characterization, and ultrasound C-scans are presented. Two types of CAI deformation patterns have been observed. The first type of deformation is mostly in-plane with local buckling, and its corresponding CAI-induced failure concentrates around the impacted plate center. The second type of deformation is with global buckling, and the corresponding CAI-induced failure is unrelated to the LVI-induced damage footprints. Three driving forces for the CAI failure have been identified: LVI-induced damage, global buckling-induced excessive bending, and delamination of the lateral edges. The dominant driving force is dependent on the panel’s thickness-to-length/width ratio, which is found to be the most important geometric parameter affecting the CAI behavior. The experimental results imply that the standard coupon-size (152.4 mm × 101.6 mm) CAI test results do not accurately represent the compressive load-carrying capacity of a composite panel subjected to impact damage. The results reported in this paper call for a re-examination and revision of the existing industrial standard ASTM D7137 (2017) to assess CAI load-carrying capacity.