Flexural modulus and yield strength

For those copolymers where other physical property data was available, an attempt was made to correlate the run number with the flexural modulus and the tensile strength at yield. Results are given in Figures 9 and 10 for a limited number of points. This data should be obtained from carefully annealed samples or ones with similar thermal histories however, a clear trend is seen in both figures. The run number does relate to crystallinity and to attendant physical properties such as flexural modulus and tensile strength. 

For any given application, certain mechanical properties will be of more importance than others. It is therefore, essential to identify and rank the most relevant properties and formulate or purchase the least expensive composite material that satisfies the requirements. The key mechanical properties for most applications are modulus (tensile or flexural), yield strength, impact strength and possibly HDT. A distinction is often made between reinforcing and nonreinforcing fillers, but unfortunately, the term reinforcement is rarely defined explicitly. Fibres are usually considered to reinforce and isotropic fillers are not, with platy fillers somewhere in between. As shown later, it is not appropriate to define reinforcement in terms of particle shape, because that definition breaks down with variations in anisotropy and particle size. In agreement with Ram [59], the definition of reinforcement as the simultaneous improvement of both modulus and yield strength will be used in this chapter... 

The incorporation of 10-30% of glass fibre into the formulation of either non-fire retardant or fire retardant grades produces improvement in tensile strength, flexural modulus and percentage elongation at break and, in the case of the fire retardant grade in the percentage strain at yield. 

Figure 2.7 (a) Compressive modulus, (b) compressive yield strength, (c) flexural modulus, and (d) flexural yield strength of SWCNT-,... 

In the flexural mode, the yield strength of melt eompoimded increased slowly up to 10% wt. filler and quiekly dropped off to roughly half of the original value when 20% wt. fly ash was present. (Figure 4) However, inconsistent was observed in dry-blended samples. In terms of modulus, the melt-eompounded specimens show a linear increase in values in proportion to the % wt. filler. (Figure 5) An improvement of almost 20% in stiflhess was observed when 20% wt. fly ash was melt-eompounded in PE. Unfortunately, similar trend eould not be drawn on the dry-blended due to inconsistency. 

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