Stress of composites

Figure 18. Thermal cycling and irradiation effects on the failure stress of composite materials. (Reproduced from reference 9.)...

Carbon fiber in polycarbonate composites absorbs water.Figure 11.15 shows compressive yield stress of composite vs. aging time in boiling water. Compressive yield stress increases with fiber addition as well as with the aging time. Aging in boiling water also enhances Young modulus of the composite. 

Because the deformation of embankment fill changed the distribution of stress of composite foundation, it was pay more attention to select reasonable discount coefficient of piles and effective coefficient of soil. 

Fig. 7. Variation of longitudinal stress of composite leaf spring.

Figure 4.13 Distribution curves of the axial stress of composite materials under different interface elastic moduli (fj).

In the stress analysis of composite materials, the parameters are as follows. The elastic modulus of resin matrix = 1.67 GPa, Poisson s ratio = 0.2, yield strength = 3.5 MPa the elastic modulus of the SiC whisker Ef = 410 GPa, Poisson s ratio Vf = 0.17 the exterior stress o is set to 0.8 Mpa and the volume fraction of the whisker in the composite material is 12.5%. The distribution curve of the axial stress of composite material reinforced with whiskers with different L/D ratios is shown in Figure 4.15. In the figure, Zj(//) stands for the axial... 

Figure 4.15 Distribution curve of axial stress of composite material reinforced by whiskers with different L/D ratios.

As shown in Figure 4.15, with an increase of the L/D ratio of whiskers, the distribution curve of the axial stress of composite material moves upward, and the stress borne by whiskers and resins increases. At the same time, the stress borne by the resin matrix changes only slightly. The L/D ratio of the whisker has a significantly greater impact on the whisker stress than on the resin matrix. 

From Table 6.10 we can see that the bending stress of composite materials increases when filled with 5%-20% calcium carbonate whiskers the bending stress of the composite material filled with 5% whiskers increases 23.4% over that of pure PP the fracture bending strain of the composite materials filled with 20%-30% whiskers increases significantly. 

The electrode pattern or configuration was found to have an impact on the ER effect, depending on what type of ER fluids sandwiched in between [139-143J. Instead of smooth surface electrodes, various patterned electrodes of a honeycomb-shaped metallic mesh structure, a concentric circle configuration, and a radial shape usually can increase the ER effect up to 2.3 times. Figure 67 shows several electrode surface patterns. Figure 68 shows the yield stress of composite particle with 1,3-butylene glycol... 

Figure 68 Yield stress of composite particle with 1,3-butylene glycol dimethacrylate/butyl acrylate copolymer core and titanium hydroxide and phthalocyanine blue pigment shell dispersed in silicone oil (15 voI%) vs. the...

Propellants cast into rockets are commonly case-bonded to the motors to achieve maximum volumetric loading density. The interior of the motor is thoroughly cleaned, coated using an insulating material, and then lined with a composition to which the propellant binder adheres under the environmental stresses of the system. The insulation material is generally a mbber-type composition, filled with siUca, titanium dioxide, or potassium titanate. SiUca-filled nitrate mbber and vulcanizable ethylene—propylene mbber have been used. The liner generally consists of the same base polymer as is used in the propellant. It is usually appHed in a thin layer, and may be partially or fully cured before the propellant is poured into the rocket. 

Polyesters are known to be produced by many bacteria as intracellular reserve materials for use as a food source during periods of environmental stress. They have received a great deal of attention since the 1970s because they are biodegradable, can be processed as plastic materials, are produced from renewable resources, and can be produced by many bacteria in a range of compositions. The thermoplastic polymers have properties that vary from soft elastomers to rigid brittie plastics in accordance with the stmcture of the pendent side-chain of the polyester. The general stmcture of this class of compounds is shown by (3), where R = CH3, n = >100, and m = 0-8. 

The strength of laminates is usually predicted from a combination of laminated plate theory and a failure criterion for the individual larnina. A general treatment of composite failure criteria is beyond the scope of the present discussion. Broadly, however, composite failure criteria are of two types noninteractive, such as maximum stress or maximum strain, in which the lamina is taken to fail when a critical value of stress or strain is reached parallel or transverse to the fibers in tension, compression, or shear or interactive, such as the Tsai-Hill or Tsai-Wu (1,7) type, in which failure is taken to be when some combination of stresses occurs. Generally, the ply materials do not have the same strengths in tension and compression, so that five-ply strengths must be deterrnined ... 

Resins are also used for permanent tooth-colored veneers on fixed prostheses, ie, crown and bridges. Compositions for this application include acryflcs, vinyl—acryflcs, and dimethacrylates, as well as silica- or quartz-microfilled composites. The resins are placed on the metallic substrates of the prostheses and cured by heat or light. These resins are inexpensive, easy to fabricate, and can be matched to the color of tooth stmcture. Acrylic facings do not chemically adhere to the metals and are retained only by curing the resin into mechanical undercuts designed into the metal substrate. They have relatively low mechanical strength and color stability, and poor abrasion and strain resistance they also deform more under the stress of mastication than porcelain veneers or facings. 

There is a simple way to estimate the modulus of a fibre-reinforced composite. Suppose we stress a composite, containing a volume fraction Vfo( fibres, parallel to the fibres (see Fig. 6.3(a)). Loaded in this direction, the strain, e , in the fibres and the matrix is the same. The stress carried by the composite is... 

A composite material used for rock-drilling bits consists of an assemblage of tungsten carbide cubes (each 2 fcm in size) stuck together with a thin layer of cobalt. The material is required to withstand compressive stresses of 4000 MNm in service. Use the above equation to estimate an upper limit for the thickness of the cobalt layer. You may assume that the compressive yield stress of tungsten carbide is well above 4000 MN m , and that the cobalt yields in shear at k = 175 MN m . What assumptions made in the analysis are likely to make your estimate inaccurate ... 

The modulus of the polymer is an average of the stiffnesses of its bonds. But it obviously is not an arithmetic mean even if the stiff bonds were completely rigid, the polymer would deform because the weak bonds would stretch. Instead, we calculate the modulus by summing the deformation in each type of bond using the methods of composite theory (Chapter 25). A stress d produces a strain which is the weighted sum of the strains in each sort of bond... 

Fig. 25.1. (a) When loaded along the fibre direction the fibres and matrix of a continuous-fibre composite suffer equal strains, (b) When loaded across the fibre direction, the fibres and matrix see roughly equal stress particulate composites ore the some. ( ) A 0-90° laminate has high and low modulus directions a 0-45-90-135° laminate is nearly isotropic. 

A unidirectional fibre composite consists of 60% by volume of continuous type-1 carbon fibres in a matrix of epoxy. Find the maximum tensile strength of the composite. You may assume that the matrix yields in tension at a stress of 40 MPa. 

Example 3.9 For the 2 mm thick unidirectional carbon fibre/PEEK composite described in Example 3.6, calculate the values of the moduli, Poisson s Ratio and strains in the global direction when a stress of = 50 MN/m is applied. You should use... 

In a unidirectional Kevlar/epoxy composite the modular ratio is 20 and the epoxy occupies 60% of the volume. Calculate the modulus of the composite and the stresses in the fibres and the matrix when a stress of 50 MN/m is applied to the composite. The modulus of the epoxy is 6 GN(m. ... 

A single ply of carbon/epoxy composite has the properties listed below and the fibres are aligned at 25° to the x-direction. If stresses of... 

The inherent anisotropy (most often only orthotropy) of composite materials leads to mechanical behavior characteristics that are quite different from those of conventional isotropic materials. The behavior of isotropic, orthotropic, and anisotropic materials under loadings of normal stress and shear stress is shown in Figure 1-4 and discussed in the following paragraphs. 

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