Journal of Composite Materials

The cavitation damage resistance of several fiber reinforced polymeric composite systems was evaluated before and after seawater immersion via a modified ASTM G-32 method utilizing a stationary specimen. For both dry and saturated condi tions, a carbon fiber/thermoplastic toughened epoxy matrix composite (IM7/977-2T) was found to perform the best under cavitation attack, while carbon fiber/thermoplastic matrix (AS4/PEEK) was found to be the least resistant. Glass/epoxy composites (E-Glass/5920, Scotch Ply 1002) were intermediate in erosion resistance. Moisture absorption was seen to decrease the erosion resistance of both E-Glass/5920 and AS4/APC-2 materials, while increasing the resistance of SP 1002; IM7/977-2T was not affected by immersion. All mate rials show decreasing erosion rates due to material recession from the cavitation cloud and increasing collapse-shielding with exposure time. A reduction in water hammer pressure was estimated by incorporating finite material impedance into the water hammer equation. Using simplifying assumptions, a 15 percent reduction in water hammer pressure is calculated.

An analytical solution is obtained for the elastic response of a three coax ial cylinder model of a composite to thermal and mechanical loading. Calculations of the thermal stresses for various fiber coatings reveal certain relationships between the coating stresses that make it possible to solve for the plastic flow of the coating. In the case of a high expansivity coating, the elastic solution indicates that the radial and hoop stresses are the extreme stresses which satisfy the conditions for Tresca flow in the r-θ plane. However, as the temperature changes, plastic flow is shown to relax the hoop stress to the extent that it becomes less than the axial stress which violates the condition for Tresca flow. In order to obtain solutions for plastic flow in the coating it is then necessary to consider plastic flow in more than a single plane. The Prandtl-Reuss flow rule can be used to solve for flow in three planes but because of the mathematical complexity it is necessary to use numeri cal techniques for the calculations. As an alternative, analytical solutions are developed for flow in two planes using an approximation for the Prandtl-Reuss flow. Three different solutions are obtained to include flow in the r-θ r-z, z-r z-θ, and θ-r θ-z planes. Each of these is applied for a different expansivity value of the fiber coating with various linear work hardening coefficients of the coating.

Inheriting previous studies on the optimal cool-down path of the compos ite laminate, this article incorporates the consideration of a new element-humidity-to analyze the residual stresses which develop in a composite material laminate after termi nation of cool down due to further exposure to humid environment.

In recent years, there has been a widespread assumption that composite materials and structures offer enhanced vibration and acoustic properties. This assumption has to be evaluated or validated. The objective of this article is to address the subject of vibration characteristics and the related force transmissibility properties of composite structures. For a given composite beam made of Hercules AS4/3501-6 graphite/epoxy with a layered structure sequence of (0,0,30, - 30)_{6 S} , resonance frequencies, structural damping, responses, impedances, and force transmissibility properties are determined, discussed, and compared with those of a steel beam. This article proposes a procedure to evaluate the vibration properties of individual composites. The cnterion defined for performance com parison between composite materials and conventional materials is also discussed.

Straight-sided double cantilever beam (DCB) fracture specimens have been used previously for long-duration environmentally assisted crack growth (EACG) testing. However, the applied strain-energy release rate G decreases with crack extension. In this study the width taper required to achieve constant-G during crack growth in a dou ble cantilever beam (DCB) fracture specimen is determined for the case of general load ing. The width taper b(a) is a function of the initial specimen compliance, C _o, the crack length, a, and the stiffness of the loading frame, κ. The compliance of DCB specimens tapered for testing under three loading conditions were verified experimentally. These were constant-load (κ → 0), constant-strain (k → ∞), and critical spring loading (κC _o → 0.5). Specimens designed for critical spring loading are suggested for use in long-term (EACG) experiment,, Limitations on the proposed test method related to nonlinear material behavior (e.g., crack bridging) are discussed.