Loading...

Investigation of the Recovery Time and Hyper-Viscoelastic Properties of the Brain Tissue

Mohajery, Mohammad | 2018

961 Viewed
  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 51192 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Ahmadian, Mohammad Taghi
  7. Abstract:
  8. FE simulations have been widely used to investigate the response of the brain tissue in various circumstances. The accuracy of the material models critically affects the results of the numerical simulation. However, despite the numerous studies aiming for the material modeling of the brain, there is still divergence between the results reported in the literature. A part of this discrepancy is due to the inherent difference between samples. Nonetheless, another part of it is resulted from the differences between testing protocols used by researchers. In some protocols multiple mechanical tests are performed on each sample. Enough recovery time should be considered between consecutive test cycles otherwise, the tissue won’t return to its reference state due to the viscoelastic behaviour of the brain tissue. Hence, the results won’t represent the original behaviour of the brain tissue. To investigate the optimum recovery time, unconfined compression tests up to 33 and 17 percent strain were performed on cylindrical brain samples with the mean diameter and height of 18.0 and 15.0 mm respectively. Each sample was subjected to two consecutive load-unload cycles separated by a specific recovery time (10, 60, 120, 180, 240, and 300s). Loading speeds in the protocol 1 (33% strain) were 5, 25, and 125 mm/min and for the protocol 2 (17% strain) were 25 and 125 mm/min. To estimate the differences between two cycles, three criteria namely effective height ratio (EHR), normalized root-mean-square error (NRMSE), and coefficient of variation (R2) were employed. Eventually, three constitutive models titled Exp-Ln, Ogden, and Yeoh were used to model hyperelastice behaviour of the brain tissue. Moreover, Prony series were used to model viscoelastic behaviour. Analysis showed that 180 s and 120 s are enough for recovery of the brain tissue in the protocol 1 and 2 respectively. Moreover, there is an inverse relationship between the recovery time and the loading speed. After the calibration of the hyper-viscoelastic models using compression and relaxation test data, two term Ogden and two term Prony series identified as the most suitable models
  9. Keywords:
  10. Mechanical Properties ; Hyperviscoelastic Materials ; Hyperelastic Materials ; Viscoelastic Properties ; Recovery Period ; Brain Tissue ; Residual Strain ; Hyper-Viscoelastic Properties

 Digital Object List

 Bookmark

No TOC