NDT-based Performance Prediction for Wrinkled Composites under Compressive Load

  • Ningbo Xie

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)


The work in this thesis aimed to develop a method to transfer the three-dimensional (3D) non-destructive characterised data into finite-element models containing as-manufactured structural details. Two types of fibre-misalignment defects: out-of-plane wrinkles and in-plane waviness, were investigated and a quasi-isotropic layup [45o/90 o /-45 o /0 o]ns was chosen as the representative industrial layup sequence for validation purposes. A pivotal part of the work was the development of the transfer process to automatically and faithfully convert the output of non-destructive characterisation inversion methods into finite-element models containing these two types of defect.

For out-of-plane wrinkles, using this transfer method and previously validated modelling techniques, a series of models were exercised under compressive load to identify the hierarchy and interdependences of wrinkle parameters, covering the wrinkle severity, shape and extent. The outcome indicated that the maximum out-of-plane wrinkle angle from the load direction was the governing factor to influence the compressive strength and this should be the key parameter to be measured non-destructively when wrinkles are detected in the components.

For in-plane waviness, it was studied both experimentally and numerically. First, the in-plane waviness was introduced into 0 plies by a specially designed rig and four waviness-severity coupons were manufactured to investigate the compressive damage process influenced by this in-plane waviness. Two High-speed cameras were used, focusing on the edge and the front face of the coupon waviness region to capture the failure modes and their sequences. X-ray CT techniques were also applied to identify the internal failure activities when the loading process was interrupted for some samples, before the ultimate damage was reached. Numerical models were then created in Abaqus/Explicit following a similar method to the out-of-plane case but requiring significant further development in order to faithfully model samples that could also be created experimentally. These were validated against the experimental recordings. Both experimental and numerical studies showed the dominant failure modes were delamination and splitting due to in-plane waviness incorporated in the samples.
Date of Award25 Sept 2018
Original languageEnglish
Awarding Institution
  • The University of Bristol
SupervisorRobert A Smith (Supervisor) & Stephen R Hallett (Supervisor)

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