Fatigue behaviour of composite tubes under multiaxial loading

J Lambert, A R Chambers, etc. / Fatigue damage characterisation for wind turbine blade GFRPs using computed tomography
Fig. 1. µCT setup of a complete test specimen.
The XTek system uses two main scan types, “slow” and “fast”. During a slow scan, the specimen
stage stops rotating while each radiograph is taken, whereas with a fast scan the specimen is rotated
continuously. It was found that fast scans, taking 1910 different projection during the 360 o rotation,
offered the most efficient option. Scans took 1 hour and 7 minutes to perform. The reconstruction was
performed using the Metris CT Pro software, and the reconstructions were visualised using VGStudio
Max.
3 Results
3.1 Mechanical test results
The static test results yielded an average failure stress of 440 MPa with a standard deviation of 27
MPa. The fatigue tests that were conducted to failure gave the following results. All tests were
performed at 352 MPa alternating stress, corresponding to -/+ 40% UTS.
Fig. 2. Fatigue test results in the form of a single load level S-N plot, including the failure mode.
Two different failure mechanisms were observed as shown in Fig.3. The compressive failures, Fig
3.(a) were characterised by multiple large-scale delaminations along the whole gauge length between
many, if not all the plies (discussed further in section 3.3).
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