Applied Composite Materials (v.13, #1)

Mechanical Properties of Composites Based on Low Styrene Emission Polyester Resins for Marine Applications by Christophe Baley; Y. Perrot; Peter Davies; A. Bourmaud; Yves Grohens (1-22).
Glass fibre reinforced polyester composites are used extensively for hulls and decks of pleasure boats. Boat-builders must optimise manufacturing technology, not only with respect to mechanical properties but also limiting volatile organic compounds (VOC) emissions. One way to achieve this is through modified polyester resin formulations such as low styrene content, low styrene emission or combinations of these. The resin matrix selection procedure is based on design specification (mechanical behaviour) but also manufacturing requirements and cost considerations. For this application post-cure is rarely used so it is important to optimise curing conditions. In this study the influence of the curing cycle on mechanical properties was examined first for two polyester resins. Then for one cycle (16 h at 40°C) the properties of eight resins have been determined. Significant differences in failure strain are observed, from 0.9% to 3.3%. The resins with improved VOC performance are the most brittle. The transverse tensile behaviour of these resins in composites with unidirectional glass fibre reinforcement and the limit of linearity for composites with glass mat both depend on these failure strains. These results are discussed in terms of admissible composite strains for boat design.
Keywords: composite materials; unsaturated polyester; transverse tensile; mechanical properties; styrene emission; glass fibres; unidirectional; mat

Ni and TiN coatings on alumina particles were achieved using a chemical vapor deposition (CVD) method. The coated alumina was then used as raw materials to prepare alumina/heat-resistant steel (HRS) composites. The effects of Ni/TiN coatings on the alumina/HRS interface strength and oxidation resistance at elevated temperature were investigated. It is found that the both coatings can improve the alumina/HRS interface bonding strength and Ni coating has a more significant effect. For the composite made from Ni-coated alumina and HRS, the interface exhibited a better oxidation resistance due to the dissolution of Ni coating into the HRS matrix. However, the composite of TiN-coated alumina/HRS has a poor oxidation resistance behavior because TiN still existed on the alumina/HRS interface.
Keywords: coatings; composites; interface properties

Local effects that occur in the vicinity of junctions between different cores in sandwich panels subjected to the in-plane axial force and bending moment are considered. These local effects manifest themselves in a rise of locally induced bending normal stresses in the sandwich faces and shear and normal stresses in the cores in the near vicinity of the core junctions. Intensity of the local effects is measured experimentally for a representative sandwich beam subjected to both types of loadings. The numerical simulations are performed using Finite Element Analysis, and they reveal significant rates of stress concentrations in the faces and cores adjacent to the core junctions. The intensity of the local effects is dependable on the geometry and elastic properties of the sandwich faces and a degree of dissimilarity of elastic properties of the adjoined cores.
Keywords: local effect; core junction; sandwich panel

A new design methodology is developed to mold the polymer spur gears with high strength fiber reinforcement only in the highly stressed region. High performance high cost short carbon fiber reinforced Nylon 66 is used in the highly stressed tooth region and low cost unreinforced Nylon 66 is used in the hub region. Two different geometries, circular and spline shaped hubs were used for developing the selective reinforced gears by multi-shot injection-molding process. Joint strength of the selectively reinforced gear was estimated using shear tests. Clear hub and tooth region separation without any distortion was observed in joint shear tests. A molten material due to fusion bonding was observed at the interfaces. The joint strength was also evaluated by conducting gear fatigue tests using a power absorption test rig at various torque levels and at a constant gear rotational speed. Monolithic reinforced gear and selective reinforced gears with spline hub exhibited similar fatigue behavior. The failure mode depends upon the test torque level. The selective reinforced gears with circular hub showed joint failures at high-test torque levels. Absence of mechanical interlocking feature in the circular hub geometry contributes to the joint failure. Thermal bond, part interference and mechanical interlocking feature provide sufficient joint strength to the selective reinforced gear with spline hub.
Keywords: gear; selective reinforcement; injection molding; joint strength; failure analysis