The crushing response of braided and CSM glass reinforced composite tubes

Results from an experimental and analytical study on the behavior of braided and continuous strand mat (CSM) glass fiber composite tubes under quasi-static crush open end (chamfered) while the other end is clamped. This procedure causes the tube to `flareʹ outwards into fronds and results in the progressive failure of the tube in the axial and hoop directions without global tube buckling. Axial force and axial displacements are measured during these tests in order to assess energy absorption. In addition, readings from strain gages that are placed at critical locations on the tube walls are used to understand the state of strain and stress on the tube walls away from the crush end. During a crush test, the axial load ascended to a maximum value and subsequently settled to a plateau value about which the load oscillated during the progressive crushing of the tube. Oscillations remained small for CSM tubes while the braided ones had larger and more distinct periodicity. Results from an analytical model that best simulates the failure of these tubes are presented. The model is based on an axisymmetric formulation of the cylindrical shell equations in conjunction with ideas from classical fracture mechanics and continuum damage mechanics.