Effects of Autoclaving on the Ballistic Performance of Ultra High Molecular Weight Polyethylene Composites

Roth, Melissa J.

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Effects of Autoclaving on the Ballistic Performance of Ultra High Molecular Weight Polyethylene Composites

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Ultra high molecular weight polyethylene (UHMWPE) composites are becoming increasingly used in lightweight armor due to their low weight, high specific energy absorption, and high elastic wave velocity. These properties are due to the high crystallinity of the polymer chains, which are sensitive to processing conditions. To achieve good consolidation and matrix flow, the composites are initially pressed at pressures upwards of 24 MPa at a temperature just below the melting point of UHMWPE. Some tensile strength of the fibers is lost during this process. If the composite is to be combined with another armor component such as a ceramic, it then goes through a second heat treatment in an autoclave so that it can be softened enough in order to shape it to the ceramic to obtain a good bond between the materials. Due to the proprietary nature of the UHMWPE composite processing methods and resin content, little work has been done to quantify if and how the autoclaving process affects ballistic performance of composite armor systems. This study compared the mechanical properties of DSM Dyneema® HB210 (polyurethane matrix) and HB212 (rubber matrix) composites before and after autoclaving by measuring composite density, shear strength, tensile strength, flexural strength, and crystallinity. Ballistic performance of the composites was tested in a standalone configuration against 17 gr fragment simulating projectiles (FSPs) and in conjunction with a ceramic against a standard rifle threat. It was shown that autoclaving did affect the mechanical properties and fragment protection of the composites. Of note was an improvement in the resistance to fragment penetration for the HB212 following the autoclave procedure. When tested in conjunction with a ceramic, no change in performance was seen between the pre- and post- autoclaved samples.

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