Classification of Core Materials Used for Structural Sandwich Marine Transomes

摘要

Possibly the most structurally demanding region of a marine vessel, the transom must endure repeated dynamic assaults while providing for the secure mounting of the drive system. In order to asses the suitability of core materials used in this application, a battery of dynamic and static tests was proposed. To assess the core's fatigue endurance, fully reversing (R=-1) three-point flexural fatigue was performed on structural sandwich laminates, employing thick fiberglass facings to ensure that failures occurred exclusively within each of the cores. Capability to maintain secure mounting of the drive was evaluated by both static ASTM C 365 "Flatwise Compression" testing as well as measuring fastener torque vs. fastener compression for specimens equipped with standard 1/2-inch hardware. After torque-compression testing, replicate specimens with the same pre-torque were subjected to both ambient room conditions as well as an aggressive vacuum/pressure cycling while immersed in water, then evaluated for core compression "creep" by assessing the additional fastener tightening to recover the initial pre-torque. Core variants for this study included "BC" plywood, two glass-reinforced and one unreinforced plyurethane cores and a novel thermoplastic polyester foam core, all with desntiies in the range of 20 to 30 lb/ft~3 (320 to 480 kg/m~3). An optimal core material choice for structural sandwich transoms was demonstrated as a result of this study.