Mechanical Response and Energy Stored During Deformation of Crystallizing TPU

  • Abdelmonem Lachhab
  • Eric Robin
  • Jean-Benoît Le CamEmail author
  • Frédéric Mortier
  • Yvon Tirel
  • Frédéric Canévet
Conference paper
Part of the Conference Proceedings of the Society for Experimental Mechanics Series book series (CPSEMS)


The present study investigates the thermomechanical behavior of closed-cell TPU foams. The effects of the density and the loading conditions on the softening, the residual strain and the hysteresis have first been characterized. The thermal responses exhibit numerous particularities. First, a threshold effect in terms of the density on the self-heating has been highlighted. Second, entropic effects are strongly weighted by energetic effects (internal energy variations) during the deformation. Typical changes in the thermal response highlight that SIC and crystallite melting occur during the deformation. The characteristic stretches of this phenomenon evolve with the maximum stretch applied. The lower the density, the lower the crystallinity. In the second part of this study, a complete energy balance is carried out during cyclic deformation of compact and foamed crystallizing TPUs. Results show that viscosity is not the only phenomenon involved in the hysteresis loop formation: a significant part of the mechanical energy brought is not dissipated into heat and is stored by the material when the material changes its microstructure, typically when it is crystallizing. Some of this energy is released during unloading, when melting occurs, but with a different rate, which contributes to the hysteresis loop. The part of the mechanical energy stored by the material has been quantified to investigate the effects of the loading rate and the void volume fraction on the energetic response of TPU. These effects cannot be predicted from the mechanical responses and the present study provides therefore information of importance to better understand and model the effects of the density and the loading conditions on the thermomechanical behavior of closed-cell TPU foams.


TPU foam Intrinsic dissipation Energy stored Strain-induced crystallization Infrared thermography 



The authors thank the Cooper Standard France company for supporting this work and for fruitful discussions. The authors thank also the National Center for Scientific Research (MRCT-CNRS and MI-CNRS) and Rennes Metropole for supporting this work financially.


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Copyright information

© The Society for Experimental Mechanics, Inc. 2019

Authors and Affiliations

  • Abdelmonem Lachhab
    • 1
    • 2
    • 3
  • Eric Robin
    • 1
    • 2
  • Jean-Benoît Le Cam
    • 1
    • 2
    Email author
  • Frédéric Mortier
    • 3
  • Yvon Tirel
    • 3
  • Frédéric Canévet
    • 3
  1. 1.Univ Rennes, CNRS, IPR (Institute de Physique de Rennes) – UMR 6251RennesFrance
  2. 2.LC-DRIME, Joint Research Laboratory, Cooper Standard – Institut de Physique UMR 6251Rennes CedexFrance
  3. 3.Cooper Standard FranceRennesFrance

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