Off-axis crushing of GFRP tubes

Four types of round composite tubes, [±75]3 glass/polyester, [0/±75]2 glass/epoxy, [±15]3 glass/polyester and [±15]3 glass/epoxy, were compressed under off-axis loadings to examine how the ply pattern and off-axis angle affect the energy absorption performances. The off-axis angle, i.e., the inclination angle of loading direction with respect to the tube axis, varied from 5 to 25° with an increment of every 5°. At a small off-axis angle, the specimen demonstrated similar crushing behavior to the axial crushing. At a moderate off-axis angle, three characteristic crushing stages were identified as triggering stage, sustained crushing stage and toppling stage. At a relative large off-axis angle, e.g. 20 and 25°, the toppling stage was soon arrived and the specimen absorbed little energy. Toppling character depends upon the composite ply pattern. [±75]3 glass/polyester specimen shows the strongest toppling tendency. For [0/±75]2 glass/epoxy specimen, 0 ply is beneficial in preventing toppling, but the crushing mode changes significantly while off-axis angle increases. Under off-axis loadings, [±15]3 specimens are likely to experience catastrophic failure. The transition characters of load-displacement history, tendency of toppling, fracture pattern and material utilization efficiency with respect to off-axis angle were discussed.