![]() The modified board had 11% lower mass (calculated). Indeed, flex modulus for this particular Trex product, calculated from the above experiment, was 221,000 psi, not 175,000 psi. This can be explained by an inaccurate value of the flexural modulus reported by the manufacturer. In reality, the immediate deflection was of 0.095 in., that is, 26% lower than predicted, not higher. If the load is outside of this relationship (higher), a deflection wonld be higher than calculated using formulas. ĭeflection of the loaded board can be predicted provided that the load and its location on the board is known, as well as the span, the moment of inertia, and the flexural modulus of the board, and assnming that the load and the deflection are within the linear relationship between each other. ), flexural modulus applicable for stair tread with 24" span should be at least 2,054,000 psi, which is much higher than that for typical wood (Table 7.34). ), flexural modulus should be at least 776,416 psi, and composite deck boards of such stiffness are not available as yet on the current market (see Table 7.34), except those made of wood. For a solid board of a standard dimension (5.5" X 1.25", I = 0.895 in. This would be applicable to a hollow GeoDeck Heavy Duty composite deck board (8.1" X 1.55,1 = 1.858 in., E = 374,000 psi, and EX I = 694,892 lb X in. span (allowed deflection 0.133"), a composite board should have aEX I value of 548,016 lb X in. Ĭalculations show that for a stair tread with a 24-in. Trex deck board, for example, has flexural modulus equal to 175,000 psi (hsted on Trex technical data sheet). However, not aU composite deck boards would satisfy even this low support span requirement. Average properties of all composites are shown in Table 6. Flexural modulus of elasticity was calculated from the load-deflection relation between 0 and the maximum load. (Note that the known value of the flexural modulus, E, of the substrate was 126GPa).Ībsorbed energy was calculated from the area under the load-deflection curves. Values of back-calculated modulus for the joints as a function of measured crack length. These values are considered to be adequate for the comparison of the local stress of the molding compound (Table I). The average TEC and average Flexural Modulus were calculated using Equation (2). The temperature dependence of the material properties of the molding compound should be considered to calculate the stress accurately. These characteristics are tensile strength, tensile and flexural modulus, impact strength, HDT A and B. įigure 6.8 plots the reinforcement ratios for short glass fibre reinforced polyamide (PA-GF) versus neat polyamide for six important characteristics calculated versus density and material cost. It is calculated by drawing a tangent to the steepest initial straight-line portion of the load-deflection curve and using an appropriate formula. The flexural modulus is the ratio, within the elastic limit, of stress to corresponding strain. A newer version of this instmment, the TA Instmments 983 DMA, can also make measurements at fixed frequencies as weU as creep and stress-relaxation measurements. The flexural modulus, E is calculated from the resonant frequency, and the makeup energy represents a damping function, which can be related to the loss modulus, E". An amount of energy equal to that dissipated by the specimen is added on each cycle to maintain a constant ampHtude. A bar-like specimen is clamped between two pivoted arms and sinusoidally oscillated at its resonant frequency with an ampHtude selected by the operator. Another resonant frequency instmment is the TA Instmments dynamic mechanical analy2er (DMA). ![]()
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