Composite Materials Case Studies

For the solid board (see above) at a span of 16 in., the allowed deflection is 167180 = 0.089 . In this particnlar case of the solid board, the deflection would be equal to 0.148 . Too much. The span would not pass. 

Even for a span of 12 in., with the allowed deflection of 12 /180 = 0.067 , the deflection for this solid board under concentrated load of 300 lbs would be 0.063 , that is, only slightly less than the allowed one. 

That is why Trex recommends its composite boards only for a 12-in. span, and only for thick 2X6- and 2 X 8-in. boards, when used as a stair tread. For a standard 5/4 X 6-in. board, Trex recommends only a maximum center-to-center spacing of 

For the hollow GeoDeck board (see above) at a span of 16 in. with the allowed deflection of 0.089 , the calculated deflection would be equal to 0.093 . Close, but not enough. To pass with these numbers for flex modulus (374,000 psi) and moment of inertia (0.733 in. ), a span should be of 15-3/4 . In reality, the hollow GeoDeck Traditional board passed the requirement for 16-in. span for stair tread (L/180) at 301 lb concentrated load (average of 15 tests), a pound above the required 300 lb. 

Calculations show that for a stair tread with a 24-in. span (allowed deflection 0.133 ), a composite board should have aEX I value of 548,016 lb X 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. ). For a solid board of a standard dimension (5.5 X 1.25 , I = 0.895 in. ), 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 thin solid board, such as 5.5 X 15/16 (/ = 0.378 in. ), 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). 

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As for enviromnental resistance, there exists a design chart that is somewhat useful for this case study, but, more importantly, may be of use in other designs. The compatibility of various materials in six common environments is shown in Figure 8.16. The suitability of a material for each of the six environments improves as you move from the center of the chart outward. In this case, resistance to organic solvents is of primary importance. We see that all ceramics and glasses, all alloys, and some polymers such as poly(tetrafluoroethylene), PTFE, will provide excellent resistance. Composites will provide good resistance, which may be satisfactory for our application. 

For the present case study (Strategy WGS 1), seven generations of 72 catalytic materials each have been prepared and tested. CO conversion at standard conditions for the ten best compositions of each generation is shown in Fig. 10.7. 

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