Modeling and Testing of Impact Damage in Composite Pressure Vessels

Abstract

Composite pressure vessels are becoming widely used for transporting gas, lately also hydrogen. In order to enable extensive use of the pressure vessels, it is critical to ensure their societal acceptance, and thus safety under transportation. Being able to judge the damage of an impacted pressure vessels is one important aspect from a safety and economical point of view. The lack of knowledge about the behaviour of damaged pressure vessels results in needlessly discarding damaged vessels with acceptable levels of damage. This thesis considers impact damage on glass fibre reinforced polymer pipes, produced by filament winding. Pipe specimens were subjected to well-defined impacts for two energy levels and the damage was reproduced numerically. Interlaminar damage was modelled by cohesive elements between composite layers. Intralaminar damage was modelled by the Hashin failure criterion on continuum shell elements. Experimental impacts produced unexpected highly asymmetrical delaminations. These delaminations were reproducible in shape and size for all specimens. The numerical model predicted the asymmetrical delaminations within the scatter of the experimental results for both energy levels tested. By studying the interlaminar behaviour of the delamination in the model, the buckling mode of the pipe was found to determine the direction of delamination. The intralaminar damage (fibre failure and matrix cracking) was inconsistent for the experimental impacts. Results ranged from no fibre damage, to large cracks with total fibre failure. Both the location and extent of fibre damage for the heavily damaged specimen could be reproduced numerically. Material properties that are critical for the modelling were identified.