Structural Qualification of Composite Propeller Blades Fabricated by the Resin Transfer Molding Process

摘要

The unique challenges for developing design allowables for a resin transfer molded propeller blade are discussed. Preliminary allowables were determined based on coupon tests for the initial blade design. Nonstandard specimen geometries were investigated in order to provide valid failure modes and associated strength values for the spar, shell and adhesive bond joint in terms of static and fatigue strengths out to 10~8 cycles. Full-size blade component tests were performed to verify or substantiate the preliminary allowables. Analyses of failure modes on the full-size specimens directed the structural qualification process. This included follow-up coupon fatigue tests and expansion of the full-size test matrix. The general conclusions are that coupon tests are necessary for determining elastic constants and for effects of batch variation, environment, and for shape of fatigue curves, but generally do not provide enough guidance to design a resin transfer molded (RTM) structure without some full-size test experience. This is due to the absence of edge, surface and width effects found in coupons and the inclusion of thermal, manufacturing and geometry effects found in the full-size specimens. These and other scale effect issues therefore dictate the need to test full-size specimens early on in the normal building block approach. The number of full-size tests is generally higher for an RTM blade or structure than for a metal blade or for a standard prepreg, thin composite structure, since statistical treatment of the full-size fatigue data is necessary for establishing final design allowables. This top-of-the-pyra-mid approach to structural qualification can make RTM unique from prepreg or metal structures.