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Constitutive models for polymers and soft biological tissues


El Sayed, Tamer (2008) Constitutive models for polymers and soft biological tissues. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/KH16-4S81.


Soft materials such as polymers and biological tissues have several engineering and biomechanical applications. These materials exhibit complex mechanical behavior, characterized by large strains, hysteresis, rate sensitivity, stress softening (Mullins effect), and deviatoric and volumetric plasticity. The need to accurately predict the behavior of such materials has been a tremendous challenge for scientists and engineers.

This thesis presents a seamless, fully variational constitutive model capable of capturing all of the above complex characteristics. Also, this work describes a fitting procedure based on the use of Genetic Algorithms, which proves to be necessary for the multi-modal, non-convex optimization required to identify fitting material parameters.

The capabilities of the presented model are demonstrated via several fits of experimental tests on a wide range of materials. These tests involve monotonic and cyclic loading of polyurea, high-density polyethylene, and brain tissue, and also involve cyclic hysteresis, softening, rate effects, shear, and cavitation plasticity.

Application to ballistic impact on a polyurea retrofitted DH36 steel plate is simulated and validated, utilizing the soft material model presented in this thesis for the polymer and a porous plasticity model for the metal. Localization elements are also included in this application to capture adiabatic shear bands. Moreover, computational capability for assessing the blast performance of metal/elastomer composite shells utilizing the soft material model for the elastomer is also presented.

Another implemented application is in the area of traumatic brain injuries under impact/acceleration loading. Clinically observed brain damage is reproduced utilizing the model presented in this work and a predictive capability of the distribution, intensity, and reversibility/irreversibility of brain tissue damage is demonstrated.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:PVC foam H100 polyurea constitutive model damage
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Mechanical Engineering
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Ortiz, Michael
Thesis Committee:
  • Ortiz, Michael (chair)
  • Daraio, Chiara
  • Ravichandran, Guruswami
  • Bhattacharya, Kaushik
Defense Date:8 October 2007
Record Number:CaltechETD:etd-10242007-131150
Persistent URL:
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:4238
Deposited By: Imported from ETD-db
Deposited On:21 Nov 2007
Last Modified:17 Jan 2020 00:26

Thesis Files

PDF (Tamer_thesis.pdf) - Final Version
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