Fracture Resistance Biomechanisms of Walnut Shell with High-Strength and Toughening.

Walnut shell is lightweight material with high-strength and toughening characteristics, but it is different from other nut shells' microstructure with two or three short sclerotic cell layers and long bundle fibers. It is essential to explore the fracture resistance biomechanism of lightweight walnut shell and how to prevent damage of bionic structure. In this study, it is found that the asymmetric mass center and geometric center dissipated impact energy to the whole shell without loading concentration in the loading area. Diaphragma juglandis is a special structure improved walnut shell's toughening. The S-shape gradient porosity/elastic modulus distribution combined with pits on single auxetic sclerotic cells requires higher energy to crack expansion, then decreases its fracture behavior. These fantastic findings inspire to design fracture resistance devices including helmets, armor, automobile anti-collision beams, and re-entry capsule in spacecraft.

Difference analysis of phenomenological models with two variable forms for soft tissue quasi-static mechanical characterization.

It was important to understand the accurate mechanical properties of soft tissue for the evaluation of its injury, provide reliable protective ways or design effective human resist-injury devices. There was little study that clarified the difference between phenomenological models based on strain invariant and the principal stretches variables respectively although some quasi-static constitutive models of soft tissue were developed. In this study, we enumerate several typical hyperelastic models and derive the tensor equation of stress-strain based on continuum mechanics to fit the experimental data of human brain specimens under multiple loading modes in previous studies and give the coefficient of determination based on the least square fitting. It was suggested that two variable forms of phenomenological models with only the first strain invariant are consistent under uniaxial compression and tension, but the Cauchy stress tensor expressed by strain is completely different under simple shear loading. Also, the shear stress derived from the constitutive model based on strain invariants and principal stretchs has multiple relationships related to shear strain. The results in this study would be used to understand the more accurate mechanical characterization of soft tissue, which will allow us to evaluate the injury and develop much accurate injury criteria for soft tissue.

The effect of arch-support insole on knee kinematics and kinetics during a stop-jump maneuver.

BACKGROUND: Anterior cruciate ligament injuries commonly occur during sports that involve sudden stops or direction changes. Although athletes often use arch-support insoles in competition and training, little is known about the effect of foot insoles on knee biomechanics and jump take-off performances. OBJECTIVE: This study aimed to investigate the effects of arch-support insoles on knee kinematics and kinetics during the stop-braking phase and the subsequent jump take-off performances. STUDY DESIGN: That is a quasi-experimental study, repeated-measures design. METHODS: Twenty male healthy recreational university basketball athletes performed stop-jump with maximum effort in both arch-support and flat insole conditions. Paired t -tests were performed on knee kinetics and kinematics and jump performance variables to determine whether there were significant differences between insole conditions. RESULTS: Wearing arch-support insoles experienced larger ground reaction forces (GRFs), loading rates of peak vertical and posterior GRFs, peak knee adduction and rotation moments, and knee flexion angular velocity than the flat insoles ( P < 0.05). CONCLUSIONS: The increased GRFs and knee loading in arch-support insoles are indicative of a higher risk of anterior cruciate ligament injuries. The findings could be insightful to the knee mechanics that are related to performance and injury potential during stop-jump maneuvers.