Specific modulus materials

Fiber-reinforced plastics have been widely accepted as materials for structural and nonstructural applications in recent years. The main reasons for interest in FRPs for structural applications are their high specific modulus and strength of the reinforcing fibers. Glass, carbon, Kevlar, and boron fibers are commonly used for reinforcement. However, these are very expensive and, therefore, their use is limited to aerospace applications. 

Figure 5.57 Design chart of specific modulus versus specific strength (see inset for type of strength determination). Reprinted, hy permission, from M. F. Ashhy, Materials Selection in Mechanical Design, 2nd ed., p. 44. Copyright 1999 hy Michael F. Ashhy.

Given the modulus and strength values that have been predicted and measured for CNTs, they are potentially an ideal reinforced material for high performance polymer composites with outstanding specific modulus and specific strength with only low concentrations of CNTs (11,39-42). However, one issue of practical importance for nanocomposite is the separation and dispersion of the CNTs within the matrix,... 

The constant of proportionality, E, is Young s modulus (Figure 10.6). As weight is an important consideration in many applications, the specific modulus is often quoted as a material parameter ... 

Using the statistical software package SPSS, it was possible to establish a relationship between the tensile and elastic properties of the materials studied in this work. This has been carried out for the cross-direction of the material only as this is considered to be the relevant direction for compression in a knee brace. It was established that there is a good correlation between the tension ratio (tr), working extension (we) and differential extension factor (def) with both specific modulus (m) and breaking extension (be). A multi-linear regression equation for the dependent variables tr, we and def with the independent variables be and m was established for each material and the equations are shown in Table 3. 

Material Material Modulus /[GPfl] Density /[gcm ] Specific modulus /[GPag cm ]... 

Specific modulus Modulus divided by material density. 

Inspection of the data in Table 6.7 reveals that in absolute terms the flexural moduli of the common structural metals aluminium and steel are respectively 7 and 20 times greater than their present glass-reinforced polymer competitors. When a comparison is made of the specific flexural modulus property, then the difference between the metals and structural plastic reduces to about 3 5 times. For example, steel is about three times stifler than polycarbonate. Exceptionally, however, glass-filled EPDM and RIM urethane still have specific modulus properties of approximately 20-65 times less than the reinforced hard plastic resins and metals. Therefore, as a simple material replacement comparison, for a RRIM urethane or glass-filled EPDM, to replace a metal component and maintain the same stiffness inevitably means using a much greater volume of polymer... 

The properties of Dyneema fibers in comparison to other high performance fibers have given rise to a real new class of materials. The first diagram gives a plot of specific strength vs specific modulus. Especially in specific strength Dyneema has unique properties and it is clear that there still remain possibilities for further improvement. In specific modulus Dyneema has higher values than aramids and almost equals certain types of carbon fiber. 

Table 1. Specific Modulus, Strength, and CTE of Typical Fibers and Bulk Materials. 

The lightest structural component for a specified deformation, i.e. strain or deflection, under a specified load is the one with the highest specific modulus. This is calculated as the ratio of the Young s modulus to the density of the material. For comparison purposes in Fig. 11.2 is plotted the specific modulus for several materials, including typical reinforcing fibres. Carbon-reinforced composites possess higher specific modulus when compared against aluminium and steel [1]. 

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