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Manufacturing defects introduced by selective laser melting of powder beds typically lead to lower fatigue strength and a larger scatter in fatigue life compared to conventional manufacturing methods. In this paper, the effect of build direction on the low cycle fatigue performance of laser powder bed fused Ti6Al4V alloy was studied. Tests under room temperature were conducted and fractographies were examined to identify the crack initiation source. Results show that fatigue cracks in all samples initiated from sub-surface pores. The roundness of pores was proved to have an influence on fatigue life. Therefore, pores were assumed as existing cracks and its roundness was used to modify a fracture mechanic-based life prediction model.

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In the present work, the performance of ultra-high molecular weight polyethylene (UHMWPE) barrier nets in marine environments is investigated by Fourier transform infrared spectroscopy, thermogravimetry, scanning electron microscopy, and tensile experiments. The chemical, morphological, thermal stability, and strength changes after aging in salt spray, hygrothermal, and ultraviolet (UV) environments are characterized. An environmental spectrum is designed to simulate a real service environment and predict the service life of UHMWPE. The results show that UV energy can activate UHMWPE molecules and lead to chain breaking, which lowers the breaking strength more efficiently than salt spray. In a hygrothermal environment, the UHMPE fibers bond into clumps, which causes a slight increase in breaking strength after the initial rapid decrease with aging time. The acceleration ratio of the environmental spectrum increases with increasing aging time, which may be caused by the cross-linking and degradation of macromolecular chains in the material. The environmental spectrum given by this work can be used to evaluate performance and predict the service life of UHMWPE barrier nets in marine environments.

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