Thermo-viscoelastic Modelling of Rate Dependent Compaction Behaviour of Thermoset Prepreg and Reinforcements used in Manufacturing of Aerostructures

  • Siddhesh Sandeep Kulkarni

Student thesis: Master's Thesis


In processes such as Automated Fibre Placement (AFP) and Automated Tape Laying (ATL) in autoclave manufacturing, prepreg layers are compacted at temperatures higher than room temperature, for better flow of resin into the layers. The prepreg exhibits temperature dependent viscoelastic behaviour because of the reinforcement and semi-cured resin present in its structure. For process modelling of such manufacturing techniques, there is a need to develop a thermoviscoelastic model that can predict the time dependent compaction response of prepregs at different temperatures. For this study, experimental tests were considered to understand the relaxation response of a multi-layer laminate of 2/2 Twill weave glass prepreg (M26T) supplied by Hexcel® Industries, USA. Two types of tests were acquired; i.e. high pressure single step compaction tests in which prepreg was compacted to high volume fractions and thermo-mechanical rate dependent compaction-relaxation test with compaction performed until a targeted strain value at different isothermal temperature conditions. For reinforcements, we considered a dry fabric compaction test conducted under various loading histories ranging from single-step compaction, multistep compaction and cyclic loading to help understand the model parameters for isothermal conditions. A range of viscoelastic models from literature were explored and their capabilities were analysed. First, the quasilinear viscoelastic (QLV) model was considered and it was found that QLV model can capture rate dependent compaction for high pressure prepreg compaction data but not capable to incorporate different viscoelastic or compaction models as well as temperature effect into the model. The adaptive QLV captures the viscoelasticity that prepreg presented but unable to utilize the compaction stresses during ramp to calculate model constants. This model is also primitive as compared to the complexity that prepreg rate dependent compaction response presents. A thermo-visco-hyperelastic numerical model within thermodynamics framework was found to be the most flexible and adaptable to incorporate the traditional compaction model and temperature scaling function to capture rate dependent thermo-viscoelastic response during compaction and relaxation phenomena in uncured prepreg Following the finite strain viscoelastic theory, the rate dependent compaction behaviour was described using the strain energy function and can be represented by Maxwell Weichert Model. The non-linear compaction response was expressed by Gutowski model. The energy function of spring in each Maxwell element was chosen to follow Yeoh and/or Neo-Hookean model to capture relaxation response during compaction and relaxation. The model was first developed and tested for dry fabric experimental data to understand the capability of the model. Then the model was modified to incorporate thermal effect by using temperature scaling functions on each element of the Maxwell Weichert rheology that the model represents. The model was found to satisfactorily conform to thermoviscoelastic rate dependent compaction response of prepreg.
Date of AwardJul 2022
Original languageAmerican English


  • Prepreg
  • Dry Fabric
  • Thermoviscoelastic model
  • compaction
  • relaxation.

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