The effect of damage on the energy absorption potential of composite structures
This thesis describes work undertaken to investigate the effects of damage on the energy absorption potential of composite tubes. Tubes of various geometries and manufactured from either continuous filament random mat (CoFRM) or glass braid and polyester resin were subjected to various types of damage before testing. Damage types consisted of drilled holes, to simulate the use of drilling components for the need of assembly, impacts, to simulate damage that may occur through tool drops or items being kicked up during use and PET inserts to simulate delamination. Large glass CoFRM/polyester tubes with an outer diameter of 89.1mm and varying wall thicknesses were crushed quasi-statically at a speed of 5mmlmin. Small CoFRM and braided glass/polyester tubes with an outer diameter of 38.1mm and a 2mm wall thickness were tested quasi statically and dynamically at a speed of 5m1s. Tubes were tested undamaged and containing various sizes of holes, simulated delamination and impacts. Specific energy absorptions (SEA) and failure modes were compared. Threshold values of damage size have been found for each tube and test type, above which unstable failures and subsequent unpredictable reductions in energy absorptions occur. The small CoFRM tubes showed a decrease in SEA as the test rate increased and this was attributed to the rate dependency of the resin, causing greater fragmentation allowing fibres to bend more easily and without fracturing. The braided small tubes showed an increase in SEA as the test rate increased due to a change in the mode of failure attributed to a higher compressive strength at the increased rate. Relatively small hole sizes and impacts, of 5mm and 1.5J-3J, were seen to reduce the energy absorption of the materials tested at quasi-static test speeds. However, an increase in damage tolerance was identified as test rate increased and this was attributed to an increase in compressive strength and fracture toughness, and reduction in crush load, as the speed of test increased.