Effect of Material Hardness on Water Lubrication Performance of Thermoplastic Polyurethane under Sediment Environment

Water-lubricated stern tube bearings are widely used in marine shaft systems, where their lubrication performance determines the efficiency and navigation safety of ships. The hardness of materials is an important factor affecting the tribological performance of water-lubricated bearings under sediment conditions. This study investigated the wear behavior of thermoplastic polyurethane (TPU) materials with different shore hardnesses under sediment conditions. Four kinds of TPU with different shore hardness were selected. The test results showed that the shore hardness of TPU depended on the content of the TPU hard segment. With increasing hardness, the absorption peak strength of the functional groups increased, and the increase in hardness could enhance the tensile strength of the TPU materials. In all test groups, the friction coefficient of TPU with 60 and 70 A hardness was relatively stable. The total wear volume of TPU with 70 A hardness was 45.9% lower than that of TPU with 60 A hardness. TPU with 70 A hardness had better ductility and embedded possession. The wear modes of TPU with 70 A hardness were crimping and micro-plowing. Only mild wear occurred on the wear surface of TPU with 70 A hardness. The main wear mechanisms of the TPU with 70 A hardness were abrasive wear and fatigue wear under sediment conditions. In summary, TPU with 70 A hardness was the most suitable for water-lubricated stern bearings under sediment conditions. The data from this study provide deep insight into the wear process of TPU materials with different hardness under sediment conditions and may be useful for selecting the proper TPU material hardness for water-lubricated stern bearings.