Few comprehensive studies on the effects of stacking sequence and rein forcement form (unidirectional versus woven) have been published to date and much of the available data is contradictory. In the present study, instrumented impact tests were used to characterize such effects for carbon fiber reinforced thermoplastic toughened epoxy laminates. Impact resistance was characterized in terms of load and energy parameters measured during penetration tests. These parameters were related to damage in the lami nates by conducting rebound tests followed by ultrasonic imaging and microscopy. The results clearly demonstrated a relationship between the onset of damage and the first peak in the load versus deflection plots obtained in the penetration tests. No major effects of stacking sequence or reinforcement form were apparent in terms of the energy required for the onset of damage in the laminates. Energy to maximum load was found to be highly de pendent on stacking sequence. Substitution of woven reinforcement for unidirectional tape in a quasi-isotropic layup resulted in a substantial decrease in the energy to maximum load. The results in terms of peak load showed similar trends. No effects of stacking se quence or reinforcement form were observed in terms of energy after peak load. It is ap parent from this work that stacking sequence and reinforcement form can have significant effects on impact resistance particularly at higher impact energies.

Fiber and void volume fractions of polymeric composite materials are often measured as indicators of part quality. However, accurate fiber and void volume fraction measurements require that the fiber density be known to a high degree of accuracy. Helium pycnometry offers the potential for accurate fiber density measurements. In this study, helium pycnometry was used to measure the density of E-glass, S2-glass, and carbon fibers. Results were compared with those of other fiber density measurement techniques. The density of E-glass was determined to be 2.6173 g/cc. S2-glass was found to have a density of 2.4858 g/cc. Measured carbon fiber densities were 1.7635 g/cc for Toray T300, and 1.7758 g/cc for Hercules IM7.

This paper describes a method for predicting key structural properties of carbon fiber reinforced composite materials containing ply waviness several times the nominal ply thickness. These socalled marcelled regions have been observed in a number of highly loaded thick structural components. The origins of these defects are not fully understood, although several contributing factors have been identified. The goal of this work is to develop an analysis based disposition criterion for components where fabrication process changes cannot be readily implemented to eliminate marcel defects. Work to date has focused on developing a micro-mechanics-based procedure for modeling the strength and stiffness properties of a marcelled region given basic properties of the material and simple geometric parameters of the marcel that can be measured nondestructively. The result is a general constitutive model that can be used in global structural analysis packages to assess the effects marcel defects have on component performance. Analyses of test coupons containing marcelled regions have been carried out to illustrate the method and establish the validity of the modeling approach. Results indicate that the degree to which marcel defects affect structural properties depends not only on the maximum fiber misalignment angle, but also on the location and size of the marcelled region and nominal applied strain field.

Little, if any, information regarding the effects of seawater immersion on the impact resistance of composite materials has been published to date. In the present study, instrumented impact tests were used to characterize such effects for two glass fiber reinforced epoxy composites. One material consisted of continuous nonwoven E-glass fibers in a conventional epoxy resin and the other consisted of woven E-glass fibers in a rubber toughened epoxy resin formulated specifically for marine applications. In the conventional epoxy system, the energy for incipient damage increased significantly following seawater immersion due to plasticization of the matrix by the absorbed moisture. Both glass/epoxy systems experienced substantial reductions in peak load and energy absorbed at peak load as a result of moisture-induced degradation of the fibers and fiber/matrix interface. Energy after peak load decreased in the conventional epoxy system following immersion. Total energy absorbed was reduced significantly for both glass/epoxy systems following seawater immersion. These results indicate that moisture-induced degradation can significantly reduce the impact resistance of glass fiber reinforced epoxy composites.

This article describes the development of a method for applying PEEK coatings to C/PEEK substrates by plasma spraying. Uniform, well-bonded PEEK coatings have been achieved using this technology. The process temperature is a critical parameter. "Hotter" coatings exhibit less porosity and better adhesion than "colder" coatings. No significant degradation of the PEEK has been observed as a result of the plasma-spray process as verified by DSC and TGA. Use of a plasma postheat cycle improves the uniformity and surface finish of the coating by reducing the number of unmelted PEEK particles on the surface of the coating. Use of a plasma preheat cycle provides a 52% increase in tensile bond strength of the coating. Plasma and reactive gas surface treatments do not appear to have any significant effect on bond strength when used in conjunction with a plasma preheat cycle. The optimized plasma-spray parameters developed in this study produce PEEK coatings 0.254 to 0.381 mm thick which are black in color and exhibit a moderate degree of porosity which is evenly distributed. Individual pores are isolated rather than interconnected and do not vary in size or distribution with substrate thickness, postheating, or annealing. No interface is visible between the PEEK coating and the C/PEEK substrate at magnifications up to 500 x. Tensile bond strengths of 13.37 ± 0.83 MPa have been measured on 3.175 mm thick C/PEEK substrates and similar tests on 12.7 mm thick C/PEEK substrates have yielded values of 24.28 + 0.65 MPa. The as-sprayed PEEK coatings are essentially amorphous and require an annealing treatment in order to ensure a reasonable degree of crystallinity. This treatment does not affect the bond strength of the coating.

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