Fatigue behaviour of composite tubes under multiaxial loading

16
Fifth International Conference on Fatigue of Composites
modulus shows a lesser decrease under pure tension/compression loads caused by the very low crack
density of the 0 o -layers and secondly, a rapid decrease in Young‟s modulus starting at 75 % of lifespan
caused by fibre breaking in the extensively delaminated 0 o -layers is observed. These delaminated layers
also lead to different final failure as mentioned below. The crack density of the 0 o -layers reaches lower
values under pure tension/compression loads than under pure shear loads, which results from the
different intralaminar stresses of these layers. External pure tension/compression loads lead to fibre
parallel stresses explaining the lower values of crack density. In contrast to this load case the 0 o -layers
obtain higher transverse tension stress leading to a higher crack density of the 0 o -layer under pure shear
loads.
Fig. 6. crack densities (left) and moduli + temperature development (right) under pure tension/compression loads.
Fig. 7. infrared image with local hot-spot shortly before final failure (left) and high speed image at failure initiation (right) under pure
tension/compression loads.
Looking at the temperature developments throughout tension/compression cyclic loading similar
decreases are measured within the first 10-15 %, whereas the maximum temperatures increase at an
earlier stage of fatigue life (at 50 % of lifespan). At this point of fatigue life delaminations initiate along