Effects of Wood Density And Interlocked Grain on the Shear Strength of Three Amazonian Tropical Hardwoods
Keywords:
Interlocked grain, shear strength, tropical woods, Amburana cearensis, Aspidosperma macrocarpon, Clarisia racemosaAbstract
Three tropical hardwoods, ishpingo (Amburana cearensis A.C. Smith), pumaquiro (Aspidosperma macrocarpon Mart.), and tulpay (Clarisia racemosa Ruiz and Pav.), were studied to determine the effects of wood density and interlocked grain on the shear strength parallel to grain. The maximum angular deviation (MAD) and the interlocked grain index (IG) were used to evaluate interlocked grain. The parameters were determined for interlocked grain samples and for ASTM D 143 shear blocks. There was a strong relationship between the interlocked grain parameters for the three species. MAD was simpler to evaluate compared to IG. The interlocked grain was highly variable within wood species. Failure of sheared blocks was irregular and in general followed the interlocked grain pattern. Hence, apparent shear strength was calculated using either a measured shear area (actual shear strength) or a fixed shear area of 2500 mm2 (nominal shear strength). Wood density positively affected the apparent shear strength of the wood. The relationships were stronger for actual shear strength compared to nominal shear strength. For all species studied, the interlocked grain negatively affected actual shear strength. The relationships between nominal shear strength and interlocked grain parameters were positive for ishpingo and tulpay, but negative for pumaquiro. Finally, we concluded that the ASTM D 143 block shear test method should be adapted for woods with heavily interlocked grain.References
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