In furniture, strength of wood plays a critical role in various ways. Bending strength may determine the integrity of legs and stretchers in chairs and tables, the rails or posts of beds, or the planks of benches and leaves of tables. Hardness usually predicts how well surfaces resist indentation under practical use or abuse.
The strength of wood in compression perpendicular to the grain - in particular, the elastic strain limit - is important to the performance of joints such as mortise and tenon and dowel joints. Racking loads may concentrate excessive compression loads on mating parts of joints, but in addition, self-induced compression set resulting from restrained swelling under variable moisture conditions is a major cause of joint failure. In evaluating the failure of furniture, it is rare that components break in two; it is more common that objects seem to simply fall apart, indicating that the limiting strength was related to joints. In turn, the root of the failure might well be attributed to the manner in which the object or its joints were designed or fabricated, rather than to the strength properties of the wood per se. The nature and properties of various forms of furniture construction are discussed below and their deterioration and failure are discussed in Chapter 7.
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