Fatigue and impact load: Experimental investigation on mechanical behavior of high modulus polyethylene yarns

Synthetic ropes have been used as alternatives for wire ropes owing to their low specific weight and excellent mechanical characteristics. They are essential for offshore mooring in deep water because, at these depths, the weight of steel cables and chains would exceed the forces supported by the platform structure. In addition, they are used in several applications, such as robotics, mountain climbing, fire rescue and lifting loads, sternum closure after medical surgery. They are even used as artificial muscles and active endoscopes because of their high flexibility. These applications are typically characterized by the presence of dynamic loads. Thus, this study aims to experimentally investigate the mechanical behavior of high-modulus polyethylene yarns, supplied by three different manufacturers. The yarns were analyzed after being subjected to impact load and after experiencing fatigue. The interaction between impact load and fatigue was also studied. First, the force, strain, and energy absorbed after the impact load were verified. Subsequently, the influence of the impact load on the fatigue life of the materials was analyzed. Finally, thermal analysis (DSC and TGA) and chemical analysis (FTIR, DRX, and EDS) were performed to compare the materials. It was observed that the mechanical and thermal behaviors of the three materials differed, and there was a reduction in fatigue life, which depended on the impact load due to yarn degradation. Finally, it is concluded that properties such as tensile strength should not be used as the sole parameter for dimensioning polymeric materials, because they exhibit different material properties in several tests despite possessing similar tensile strength.