Development of High-Speed Tensile Test System for Ligaments and Skeletal Muscles

Abstract

Although the effects of strain rate on the mechanical properties of ligaments and tendons has been one of the most popular subjects of investigation, many issues remain to be clarified. Moreover the strain rate conditions in most studies were not fast enough for the examination of injury prevention in traffic accidents. As for skeletal muscle, only a few dynamic tensile tests have been done, but the mechanical properties of activated skeletal muscle have not been studied. With this as a background, the purpose of the current study is to develop a new tensile test system to evaluate the mechanical properties of ligaments and skeletal muscles at various strain rates and to perform preliminary tests to evaluate the effects of strain rate. We designed a new hybrid type tensile tester which has an AC servomotor for quasi-static tests and a N2 gas actuator for high-speed tests. The results of preliminary experiments with MCL showed the stress-strain curves to be almost linear for tensile velocities between 0.01 and 10 mm/sec. However, the stress-strain curves changed drastically into a convex shape under high-speed condition. As for the tibialis anterior muscle, the failure sites were mainly the muscle-tendon junction (MTJ) in an active state, in contrast to the muscle belly in a passive state. At 200 mm/sec tensile velocity, failure stress in the active state was greater than that in the passive state.