Effect of preload treatment on elastic modulus of braided synthetic fiber rope for static loading

This paper studies the effect of preload treatment on the elastic modulus of braided high modulus polyethylene (HMPE) rope for static loading in tendon-driven robot. Two different methods of preload treatment were applied on HMPPE rope namely preload in tensile and cyclic loadings. A suitable load level of preload treatment was also investigated in order to apply in the real application. Furthermore, the cause of the lowest elastic modulus of the stabilized rope was identified by performing preload treatment on the strand constituting the rope. After completing preload treatment, the preloaded rope and strand were tested in five cyclic loadings further in order to examine the stability of rope modulus. To detect the change in construction geometry of the rope during preload treatment and cyclic loading of preloaded rope in term of rope diameter and strand angle, acoustic emission (AE) testing and a high speed camera were used. Results show that preload treatment in tensile loading could be conducted as an alternative method to replace the preload treatment in cyclic loading which is commonly used. It is also found that elastic modulus of the preloaded rope and strand at the first cycle have smallest value compared to the other cycles (cycles 2–5). This phenomenon is caused by elastic recovery of the material itself which could occur after preload treatment.