We studied consecutive impact loading on woven high-modulus polyethylene rope, which is used in robotics fields. An impact tester was developed to conduct the experiments. Five consecutive impact loads (five drops) were applied to the rope and the stiffness of the loading part that corresponds to each drop was evaluated. The stiffness of the woven ropes was affected strongly by consecutive impact loading. The change in stiffness is undesirable in some applications such as in robotic fields. Therefore, we have proposed a method that can optimize changes in stiffness by applying a preload before impact testing (preload treatment). The experimental results show that preload is an efficient way to reduce changing rope stiffness. We have also proposed an empirical equation that can estimate the rope stiffness after arbitrary preload treatment, and this equation is a function of the number of drops and the static preload level. The equation can be used to determine the preload treatment conditions to stabilize the stiffness of the woven ropes before they are used in engineering fields.
This paper uses classical laminate theory (CLT) and experimental methods to predict the longitudinal specific modulus of braided high modulus polyethylene (HMPE) rope without a matrix. When applying conventional CLT, the modulus, braided angle of strand, and packing factor (PF), i.e., the cross-sectional area ratio of the strand to the rope, are required. Because the void (space between strands) and PF of braided rope without a matrix readily change during the application of load, and given the difficulty measuring PF experimentally, it is difficult to predict the modulus by conventional CLT. This paper proposes the use of the unit of N/tex in place of conventional MPa for CLT. This study demonstrates that changes in PF due to void changes can be neglected when using the N/tex unit. The predicted longitudinal specific modulus of the rope using N/tex unit was found to be in qualitatively agreement with the longitudinal modulus measured experimentally.
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