Effective reinforcing modulus

The use of theoretical models to predict the properties of CNT composites has been useful in dealing with certain aspects of these nanocomposites. In particular, Brinson et al. [41,106] addressed the issue of CNT waviness or curvature and its effects on composite properties. TEM observations of embedded CNTs have shown that they are not rectilinear but have some degree of waviness [99], which may be due to their crystalline defects and elastic flexibility. A reduction in the modulus of wavy CNTs can be expected due to CNT anisotropy. Finite element analysis was used to calculate what the effective reinforcing modulus would be... 

The effect of temperature on properties can be seen in Figure 2, which shows the effect on modulus of increasing temperature of unmodified and glass-reinforced nylon-6,6. Impact strength, however, shows a steady increase with temperature as it does with moisture. 

The mechanical properties of silicate- based glasses have been extensively studied due to their widespread use as containers, reinforcing fibers, and optical fibers. Consequently, there is a wealth of information on the influence of many variables on the mechanical properties of these glasses. We shall concentrate on (a) composition and temperature effects on modulus and strength and (b) an important method of strength enhancement in glass fibers. 

To illustrate the effect of modulus mismatch on structural performance consider the symmetrically repaired reinforced concrete prism shown in Fig. 6.4 and loaded axially in tension. The concrete has a modulus of elasticity in tension of 25 kN/mm. For material C ( t = 14 kN/mm ) the elastic stress induced in the concrete at mid-height of the prism will be 2.5 times that in the repair material at the same position. Conversely for material D ( , = 43 kN/mm ) the elastic stress carried by the repair material is now 1.5 times that... 

Non- or semi-reinforcing fillers These are usually added to reduce cost. In natural rubber or polychloroprene, they may be used alone, but with non-crystallizing polymers such as butadiene - acrylonitrile or styrene - butadiene copolymers, they can only be used in conjunction with a reinforcing filler. Their effect is to reduce tensile strength and elongation, tear resistance and resistance to set. The effect on modulus varies according to choice of filler, but it is always much weaker than that of a reinforcing filler. 

For the geotextile to provide an effective reinforcement function, it should have not only a high tensile strength, but also a high tensile modulus so that its resistance to tensile loads generated within the soil occurs at sufficiently small strains to prevent excessive movement of the reinforced soil structure. It is self-evident that decreases in these properties with time (i.e. creep behaviour) must be low, and that the polymers used should have resistance to degradation by the soil. An estimate of the anticipated reduction in strength can be determined from an analysis of creep strain versus time plots for various stress levels and a suitable reduction factor applied. 

Unlike in the case of spherical inclusions where the rigid inclusions cause stiffening of the composite by excluding volume of a deformable mattix, the presence of an interphase layer affects the tme reinforcing efficiency of the inclusions. Hence, the effective filler modulus of the inclusions have to be calculated as a function of interphase thickness and elastic modulus. This can be done effectively using simple rule of mixture ... 

Reinforcement compacted soils and aggregates have good compressive modulus but poor tensile modulus and consequently can be readily separated when subjected to sizeable tensile loads. Employing fibres of appropriate tensile moduli, geotextiles become effective reinforcing tension elements when embedded in compacted soils and aggregates. 

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