Continuous fibre composites

Galculate the upper and lower values for the modulus of the composite material, and plot them, together with the data, as a function of Vf. Which set of values most nearly describes the results Why How does the modulus of a random chopped-fibre composite differ from those of an aligned continuous-fibre composite ... 

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. 

Fig. 25.2. The stress-strain curve of o continuous fibre composite (heavy line), showing how it relates to those of the fibres and the matrix (thin lines). At the peak the fibres are on the point of failing.

Multl-directlonal continuous fibre composite (Quasl-lsotroplc)... 

R. L. Hewitt and M. C. de Malherbe, An Approximation for the Longitudinal Shear Modulus of Continuous Fibre Composites, Journal of Composite Materials, April 1970, pp. 280-282. 

Large aspect ratio Because the reinforcements are nanosized, the large aspect ratio (length/diameter) could make the composite behave like a continuous fibre composite. This scenario is unlikely as the aspect ratios of the NWs used are "- 100-200, which are lower than the value of "-T000 or so for a transition between short-fibre reinforced composite behaviour and the long-fibre reinforced one [18]. The specimen dimensions are also much larger than the NW dimensions. The anomalous increase from the relatively smaller sized specimens is ruled out. 

A solid structural substance produced by a combination of two or more materials that retain their identities. Typically, one of the materials combined is the strengthening agent, the other being the matrix (a thermoset or a thermoplastic resin). The word composite is also used for systems that are reinforced (reinforced where cumulative properties are superior to the individual components) by addition of certain solid particles (i.e., short fibre composites - long fibre composites - continuous fibre composites). 

Blackman BRK, Bruimer AJ, Davies P. Delamination fracmre of continuous fibre composites mixed-mode fracture [Chapter 4.3]. In Moore DR, Pavan A, Williams JG, editors. Fracture mechanics test methods for polymers, adhesives and composites. Elsevier 2001. pp. 335-59. http //dx.doi.org/10.1016/S1566-1369(01)80040-6. 

The best initial mechanical properties are achieved with continuous fibre composites. Table 2.3 gives some representative values. The numbers refer to the properties of the materials in their original (as-manufactured) condition. After several years in service, the properties will not be the same, even in the absence of obvious mechanical damage. It is customary to cite the change in properties with time as a measure of the extent of deterioration, and % retention has become by implication a measure of durability. Not all properties change equally rapidly and the selection of significant properties requires careful consideration. 

Table 2.3 Representative properties of unidirectional, continuous-fibre composites (stress parallel to fibre direction) at room temperature... 

The solid line in Figure 8 is a least squares fit of the data. It has a slope of 0.92 and an intercept of 0.28 o strain. This line reflects the average behaviour of the fibres during deformation. The dashed line in Figure 8 has a slope of unity and corresponds to e = e which would be the behaviour expected from the Cox model (r8) r an ideal uniaxially-aligned continuous fibre composite with no complication due to thermal stresses. The experimental line confirms that the surface fibres are on average subjected to a thermal compressive strain of 0.287. if it is assumed that the linear dependence of peak position upon e shown in... 

Short fibre composites (a) tend to have low fibre concentration sheet forming is suited to continuous fibre composites or (b) long discontinuous fibre composites. 

Sheet forming in polymer matrix composites 129 Continuous fibre composites... 

As noted earlier in this handbook, continuous fibre composites with fibres accounting for 50% or more of the material volume present the highest properties possible. Unfortunately, continuous fibres make forming - and sheet forming in particular - difficult to control. Before specifying continuous fibre components made by sheet forming, a designer should determine whether a discontinuous fibre product could meet the need. 

Figure 2.5 Debonding, fibre fracture, and fibre pull-out in a unidirectional continuous fibre composite, after Mallick (1997).

Long-fibre composites are mainly used with hand lay-up systems using polyester or epoxides as the matrix in which glass fibres are suspended. It is possible in long-fibre composites to calculate the strength and stiffness more accurately using conventional composite theory. For example, in a unidirectional continuous fibre composite, the equation for the total stress, in the composite can be shown to be ... 

Table 4.2 Theoretical energy absorbed by aligned continuous fibre composites, as calculated by Eqs 4.89 to 4.91 (after Hibbert and Hannant [74]) ...

R.L. Hewitt, M. de Malherbe. An aj>proximation for the longitudinal shear modulus of continuous fibre composites.. Compos. Mater., 4,280-282,1970. 

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