Core deformation and failure are therefore decisive factors for the energy absorption capability and impact behavior of sandwich panels. At higher impact velocities a critical condition is reached when local contact stress exceeds local strength, leading to laminate bending failure, core/skin interface delamination and core compression failure. If impact speed is low, sandwich panels may respond by bending and little damage occurs if the kinetic energy of the impacting object is absorbed elastically by the panel. After the fracture of the skin, the impacting object may damage and penetrate into the core. matrix cracking, debonding, fiber failure) may appear individually or interact, resulting in complex skin failure modes under impact. The common damage mechanisms in sandwich composites (e.g. Generally, structural sandwich components have low resistance to out-of-plane impact due to the thin outer composite skins and the highly deformable cores. impact and penetration damage) has become important in the transportation industry. In addition to the aforementioned issues, in order to reliably predict the structural safety of composite sandwich structures, understanding the adverse effect of in-service impact events (e.g. Since the degradation process of a composite sandwich structures depends on the environmental conditions, type of skins and core material, and production process, it is therefore necessary to evaluate the mechanical properties through accelerated aging tests in order to predict long-term performances of sandwich composites. As result, environmental effects must be considered during the design process. Moreover, attention should be focused on environmental degradation of the interface between core and facesheets. The environmental effects are, in general, peculiar to the polymeric matrix, , as well as the fiber–matrix interaction and are linked to a wide variety of phenomena that can ultimately lead to swelling or even to the dissolution of the polymeric matrix of the composites. Since the mechanical properties of composite structures exposed to environmental influences such as humid air, temperature and ultraviolet radiation may be degraded with time, a decrease in performance over time can be expected. In particular, impact and environmental durability data for sandwich panels involving glass/phenolic skins and Nomex honeycomb core have not been reported before, to the authors’ best knowledge. Despite the great interest on composite structures, only few publications contain information about mechanics and material characteristics of phenolic impregnated sandwich structures. Phenolic resin is mainly considered for its inherently fire-retardant properties that evolve low levels of smoke and combustion products during a fire, compared to other types of resins-i.e., epoxy, polyester and vinylester-that burn and release large amounts of heat, smoke and toxic fumes that pose a risk to people, especially in the confined space of vehicles, and make it difficult for fire fighters to extinguish the fire. Īmong the currently available sandwich composite materials, phenolic resin-impregnated glass fiber reinforced plastics and aramid paper honeycomb (Nomex) are considered for the structural design of load carrying components of civil transportation vehicles in the present work. However, problems with the fire resistance of organic matrix composites are seen by many as the most significant factor hindering their rapid expansion into a wide range of engineering applications in transport and infrastructure. Examples of sandwich composites employed in transportation vehicles can be found in, as structural floor and roof panels, in as front structure, in, as body panels, and in as nonstructural interior panels. Therefore, using composite sandwich structures not only reduces weight, thereby improving fuel economy and increasing payload capacity, but also enables the design of aerodynamic, stable vehicles with a low center of gravity. For example, a reduction of the mass of a railway car body could lead to weight savings in the traction system, suspension, brakes and other subsystems. A reduction in structural weight of one large component usually triggers positive synergistic effects for other parts of the vehicle. As designers in the transportation industry strive to reduce fuel consumption and improve safety, composite sandwich structures that provide improved stiffness-to-weight ratio, are becoming an attractive alternative to metals for mass transport applications.
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