Blast performance of composite sandwich structures with hybrid laminate skins

Abstract

This research project has investigated the performance of composite sandwich panels with hybrid skins against air and underwater blast loading. The loads are equivalent to those that could arise from sea mine detonation. Composite sandwich materials offer many benefits over conventional ship building materials. However, due to their variability and subsequent unpredictability, widespread use of composite sandwich panels in structural applications across the naval industry has been slow. The panel variability and interactions between the various constituent materials can, however, be utilised. Hybrid composite skins aimed to increase the blast resilience of composite sandwich panels by promoting energy absorbing damage mechanisms caused by the differing skin materials. Preliminary calculations and impact loading revealed the differences in panel performance that can be achieved by varying the hybrid skin layups. Placing glass-fibre as the outermost layer receiving the impact was shown to be beneficial. Additionally, it was advantageous to place carbon-fibre as the rearmost layer due to its high tensile strength and stiffness. These preliminary results were used to inform panel selection for full-scale blast testing. A number of full-scale air blast experiments were performed. Six types of composite sandwich panel were subjected to varying blast loads, benchmark conventional sandwich panels were tested where possible. The blast loads included large charges at large stand-off distances, small near-field charges as well as repeat blast loading. The experimental results revealed that hybrid composite panels with 50% glass-fibre and 50% carbon-fibre by volume achieve high blast resilience under the blast conditions tested. These 50:50 hybrids have the necessary strength and stiffness to prevent excessive skin or core damage whilst allowing an acceptable level of deflection. Under blast conditions, the presence of the two materials in the hybrid skin is the dominating factor. The layup of the hybrid skins has a minimal effect on overall performance. Instrumentation methods were extended compared to previous blast experiments. Spatial correlation between strain gauges mounted on the front skin and rear skin digital image correlation strain was achieved and polyvinylidene fluoride gauges were used in a large scale blast environment. The repeatability of the experimental setup and method was demonstrated. Lastly, one large scale underwater blast experiment was performed. Full-field panel response was recorded using digital image correlation. The results revealed the significant influence of water depth along with the severe deflection and damage sustained by the panel. Digital image correlation captured the underwater deflection profile of the panel from its initial position to the typically observed 'bath tub' shape for the first time. All experiments have demonstrated the significant blast resilience possessed by composite sandwich panels.