Compressive properties composites

Density and polymer composition have a large effect on compressive strength and modulus (Fig. 3). The dependence of compressive properties on cell size has been discussed (22). The cell shape or geometry has also been shown important in determining the compressive properties (22,59,60,153,154). In fact, the foam cell stmcture is controlled in some cases to optimize certain physical properties of rigid cellular polymers. 

Mechanical Properties. The performance of various polyester resin compositions can be distinguished by comparing the mechanical properties of thin castings (3 mm) of the neat resin defined in ASTM testing procedures (15). This technique is used widely to characterize subtle changes in flexural, tensile, and compressive properties that are generally overshadowed in highly filled or reinforced laminates. 

Generally, the sandwich composites combine light weight, good flexural stiffness and good stress distribution without weak points. Tensile and compression properties, particularly punching, can be weak. 

Lu, G.Y. and Mai, Y.W. (1994). A theoretical model for evaluation of interfacial properties of fiber reinforced ceramics with the slice compression test. Composites Sci. Technol. 51, 565-574. 

Suarez JC, Molleda F, Gu ernes A. Void content in carbon fiber/epoxy resin composites and its effects on compressive properties. In Miravete A, editor. Proceedings of ninth international conference on composite materials (vol VI Madrid). Spain, ICCM-9 Woodhead Publishing Limited, 1993. p. 589-96. 

Coprocessed tablet excipient composed of chitin and silicon dioxide [52] Chitin is a water-insoluble hydrophilic polymer that can absorb water and function as a disintegrant. Due to the unacceptable flow and compression properties of chitin, coprecipitation with silicon dioxide was used to provide a new excipient with excellent flow, compaction and disintegration properties when compared to the individual components or commercially available direct compression fillers and disintegrants. The optimal composition of the coprocessed excipient contains a silicon concentration of about 50% (w/w). 

This ASTM method is an adaptation of ASTM D 695 to as manufactured plastic/composite lumber and shapes (=whole profiles), unlike small cut specimen in ASTM D 695. In ASTM D 6108 the entire cross section (cut as specified) is loaded in compression. Hence, ASTM D 6108 describes test method for evaluating compressive properties of a product, whereas ASTM D 695 describes test method for evaluating compressive properties of a material. 

The compressive properties of a composite under aU loading conditions are strongly affected by moisture absorption because of the reduction in shear properties of the matrix polymer. The design of artefacts with polymer matrix composites needs to reflect the limitations of these materials in compression, especially in service where environmental conditioning is likely. 

This chapter reviews the state of knowledge regarding moisture absorption by aerospace composites in service. The discussion centres on the generic use of epoxy resins as matrices for polymer matrix composites. Some reference to other matrices is also made but we have limited this in order for the main principles to be understood. Moisture ingresses into these resins relatively slowly so that the effects on the mechanical properties are complex. The moisture mainly influences the thermo-mechanical properties of the matrix and so we concentrate on how thermal strains, tensile and compressive properties of the composites are affected. 

SMS Madhukar and L T Drzal, Effect of fiber-matrix adhesion on the longitudinal compressive properties of graphite/epoxy composites . Proceedings Fifth Technical Conference American Society for Composites, 1990, pp 849-858. 

Compression Properties - Table 4 lists the mean values for the ultimate compression strength for the 5X and 8X sets of SiOC-Nextel 312 composite test bars. The small increase in as-prepared compression strength for the 8X bars compared to the 5X test bars is less than expected. Given the higher density and lower porosity of the 8X bars, the compression strength would be expected to be significantly higher compared to the 5X bars. 

The tensile and compressive properties of knitted fabric composites are poor in comparison with the other types of fabric already discussed, but they are more likely to be chosen for their processability and energy-absorbing characteristics than their basic in-plane properties. 

Nguyen M, Leong KH, Herszberg I. The effects of deforming knitted glass preforms on the composite compression properties. In Proceedings 5th Japan SAMPE symposium, Tokyo, Japan 1997. 

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