Effects of varying material properties on the load deformation characteristics of heel cushions

Sun, Pi-Chang; Wei, Hung-Wen; Chen, Chien-Hua; Wu, Chun-Hao; Kao, Hung-Chan; Cheng, Cheng-Kung

doi:10.1016/j.medengphy.2007.07.010

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Volume 30, Issue 6 , Pages 687-692, July 2008

Effects of varying material properties on the load deformation characteristics of heel cushions

Pi-Chang Sun
- Orthopedic Biomechanics Laboratory, Institute of Rehabilitation Science and Technology, National Yang Ming University, No. 155, Sec. 2, Li-Nung St, Taipei 11221, Taiwan
- Division of Physical Medicine and Rehabilitation, Taoyuan Veteran Hospital, Taoyuan, Taiwan
Hung-Wen Wei
- Orthopedic Biomechanics Laboratory, Institute of Rehabilitation Science and Technology, National Yang Ming University, No. 155, Sec. 2, Li-Nung St, Taipei 11221, Taiwan
Chien-Hua Chen
- Orthopedic Biomechanics Laboratory, Institute of Rehabilitation Science and Technology, National Yang Ming University, No. 155, Sec. 2, Li-Nung St, Taipei 11221, Taiwan
Chun-Hao Wu
- Orthopedic Biomechanics Laboratory, Institute of Rehabilitation Science and Technology, National Yang Ming University, No. 155, Sec. 2, Li-Nung St, Taipei 11221, Taiwan
Hung-Chan Kao
- Orthopedic Biomechanics Laboratory, Institute of Rehabilitation Science and Technology, National Yang Ming University, No. 155, Sec. 2, Li-Nung St, Taipei 11221, Taiwan
Cheng-Kung Cheng
- Orthopedic Biomechanics Laboratory, Institute of Rehabilitation Science and Technology, National Yang Ming University, No. 155, Sec. 2, Li-Nung St, Taipei 11221, Taiwan
- Corresponding author. Tel.: +886 2 28267020; fax: +886 2 28202519.

Received 13 April 2007; received in revised form 11 July 2007; accepted 15 July 2007. published online 21 September 2007.

Abstract

Various insole materials were used in attenuation of heel-strike impact. This study presented a compression test to investigate the deformation characteristics of common heel cushions. There were two materials (thermoplastic elastomer “TPE” and silicone) with three hardness and six thickness being analyzed. They underwent consecutive loading–unloading cycles with a load control mode. The displacement of material thickness was recorded during cyclic compression being applied and released from 0 to 1050N. The energy input, return and dissipation were evaluated based on the load deformation curves when new and after repeated compression. The TPE recovered more deformed energy and thickness than the silicone after the first loading cycle. The silicone would preserve more strain energy with increasing its hardness for the elastic recovery in the unloading process. The deformed energy was decreased as the original thickness did not completely recover under cyclic tests. The reduction in hysteresis area was gradually converged within 20 cycles. The silicone attenuated more impact energy in the initial cycles, but its energy dissipation was reduced after repeated loading. To increase hardness or thickness should be considered to improve resilience or accommodate persistent compression without flattening. The careful selection of cushion materials is imperative to meet individual functional demands.