Reinforcement structure, mechanical flexural strength

It has been known for some time that considerable improvement of the mechanical properties of alumina in terms of flexural strength, fracture toughness, yield strength and elastic modulus can be achieved by adding particles of stabilised zir-conia as a structural reinforcement (see Chapter 4.1.2). Such ceramics are known as ZTA (zirconia-toughened alumina), duplex ceramics or dispersion ceramics. 

With respect to the laminates as a structural material, regardless of the type of reinforcement, there are known some behaviour characteristics during the mechanical loading of laminates. Composites with woven reinforcement demonstrate (Dauda et al. 2009) a linear relationship between stress and deformation. Whereas the reinforcement of laminates in the form braided reinforcement show a non-linear dependence is determined by an angle of orientation of the fibre bundles with respect to the axis of symmetry. The increase in flexural strength and modulus values affects the volume fraction of fibres in the composite volume, and the surface density of the strengthening. 

The characteristic MFC structure in the PET/PP blends could be created after compression molding as well as after injection molding at temperatures below of PET, although in the case of IM, the distribution of the PET fibrils in the PP matrix is almost random. The flexural strength and modulus of the IM blends with MFC structure are superior by60-70% to those of the neat PP and blends without an MFC structure this fact demonstrates the reinforcing effect of the PET fibrils. The compression molded PET/PP and LCP/PPE samples with an MFC structure possess much better mechanical properties in the draw direction than those of the IM specimens, because of the uniaxial orientation of the PET and LCP fibrils. 

Techniques for production of 3-D structures of high tenacity aramid fiber have also been developed, offering excellent fatigue resistance to abrasion, flexure, and stretching. One such system is on a wire frame basis, with mechanized frame building, and it is proposed as reinforcement for concrete pillars and other structures. As well as the strength of the fiber, this application exploits the high chemical resistance of aramid to acids, alkalis, and cement. 

The advantages of WPC include increased bending strength, stiffness (flexural and tensile modulus), reduced thermal expansion and cost. Mechanical properties such as creep resistance, modulus and strength are usually lower than those of solid wood. WPC are not being nsed in applications that require considerable structural performance [53], although in early 1984, cellulose flour was used to reinforce PA to give PA 12 [54]. 

Para-aramid fibres inherently have relatively poor surface adhesion properties unless pre-treated, but are available from the producers with enhanced adhesive properties. A particularly important feature of their mechanical behaviour is that beyond a certain flexural couple they undergo failure by fibrillation on the strained outer side and by a crushing mechanism, involving formation of kink bands in the structure, on the compressed inner side. This behaviour does not result in rupture, as observed with a brittle fibre, and therefore permits retention of some mechanical strength in the reinforcing material. 

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