Fatigue life and residual strength of a short- natural-fiber-reinforced plastic vs Nylon

A new natural fiber composite made of high density polyethylene (HDPE) and short birch fibers (SBF) was developed to replace high-performance thermoplastics (Polyamide) commonly used in gears manufacturing. 3-point flexural quasi-static tests were achieved on bending specimens to assess mechanical properties. Comparison between these results and those of polyamide (PA) and neat polyethylene has showed that the polyethylene reinforced with 40%wt of SBF presents tensile and flexural mechanical properties that are higher than those of the PA11 or the neat polyethylene. After static characterisation, fatigue tests were performed to determine ε-N curves and the evolution of residual strength. Then, the fatigue behavior of the studied composite has been compared with that of PA66 and of ultra-high molecular weight polyethylene (UHMWPE). It has been noticed that polyethylene reinforced with 40%wt of SBF presents a high cycle fatigue strength (HCFS) that is more important than that of PA66 and UHMWPE. Consequently, the studied composite represents a good alternative to replace Nylon in spur gears manufacturing.