Sandwich panels are composites which consist of two thin laminate outer skins and lightweight (e.g., honeycomb) thick core structure. Owing to the core structure, such composites are distinguished by stiffness. Despite the thickness of the core, sandwich composites are light and have a relatively high flexural strength. These composites have a spatial structure, which affects good thermal insulator properties. Sandwich panels are used in aeronautics, road vehicles, ships, and civil engineering. The mechanical properties of these composites are directly dependent on the properties of sandwich components and method of manufacturing. The paper presents some aspects of technology and its influence on mechanical properties of sandwich structure polymer composites. The sandwiches described in the paper were made by three different methods: hand lay-up, press method, and autoclave use. The samples of sandwiches were tested for failure caused by impact load. Sandwiches prepared in the same way were used for structural analysis of adhesive layer between panels and core. The results of research showed that the method of manufacturing, more precisely the pressure while forming sandwich panels, influences some mechanical properties of sandwich structured polymer composites such as flexural strength, impact strength, and compressive strength.
This paper reports the results of the effect of sea water, natural ageing, and cross-impact loading on flexural strength and residual flexural strength of epoxy laminates with glass woven fabrics and hybrid reinforcement with glass and carbon woven fabrics. The tests were conducted on samples with different fibre reinforcement both before and after low energy cross-impact loading. Carbon fabrics decreased residual strength of the composites.
Due to small repeatability of results of impact strength of adhesive joints, particularly those performed on di erent test machines, the authors were inspired to conduct experimental and numerical research in this eld. e investigation used the Block Shear Test.e authors compared impact strength of samples which were loaded in a normative and nonnormative manner and also the dependence in impact strength with regard to the distance between the impactor's edge and the surface of the bonded joint. e numerical calculations were carried out in the program Ansys, using the Explicit Dynamics module. e authors proposed a way of modelling the impactor of the pendulum hammer. It was found that a change in the direction of applying the load to the sample and rotating the loaded sample piece in relation to the edge of the impactor results in a signi cant change in the Max Principal Stresses. Numerical investigations show that lower values of Max Principal Stresses occur in joints which are characterized by larger impact strength, determined experimentally. It was also noted that moving away the edge of the impactor from the surface of the adhesive joint increases normal stresses perpendicular to the surface of the joint.
Elements of aircraft that are in direct interaction with the environment are exposed to the destructive effects of weather phenomena and the factors influencing them, as well as local environmental phenomena. One such factor is ultraviolet radiation emitted by the sun. This article presents the results of the influence of solar radiation (UV) on the strength properties of laminates with different types of reinforcement. The composites are susceptible to impact damage; therefore, to investigate the effect of UV radiation on such damaged composite, part of the samples were subjected to impact loads. The composites were made of the epoxy resin Epidian 52 with hardener Z1, and reinforced with glass fabric and carbon fabric. In order to carry out the research, we designed two devices – one for the production of low-energy impact and a second device to expose composite on UV radiation. As a result of studies, it was found that the UV radiation has a negative impact on the aesthetic qualities of the composite as well as the flexural strength of the materials. The decrease in strength of the samples subjected to shock loads and the influence of UV radiation is at a level slightly above 50%.
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