Work to maximum load

Higher temperatures result in permanent degradation. The amount of this irreversible loss in mechanical properties depends upon moisture content, heating medium, temperature, exposure period, and, to some extent, species. The effects of these factors on modulus of mpture, modulus of elasticity, and work to maximum load are illustrated in Figures 6—9 (6). The effects may be less severe for commercial lumber than for clear wood heated in air (Fig. 10). The permanent property losses shown are based on tests conducted after specimens were cooled to - 24° C and conditioned to a moisture content of... 

Fig. 7. Permanent effect of heating ia water on work-to-maximum-load and on modulus of mpture (MOR). Data based on tests of clear Douglas-fir and...

Gerhards (57) reviewed the results of 12 separate studies on strength properties of fire-retardant-treated wood conducted at the FPL and other laboratories. He concluded that modulus of rupture (MOR) is consistently lower and modulus of elasticity (MOE) and work to maximum load are generally lower for fire-retardant-treated wood than for untreated wood if fire-retardant treatment is followed by kiln drying. The effect may be less or negligible if the fire-retardant-treated wood is air dried instead of kiln dried. The most significant loss was in work to maximum load, a measure of shock resistance or brashness, which averaged 34 percent reduction. 

Fiber stress at proportional limit Modulus of rupture Modulus of elasticity Work to proportional limit Work to maximum load Impact bending... 

Work to Maximum Load. WML is the amount of work needed to actually fracture or fail a material, and it is the area under the stress-strain curve from zero to the ultimate strength of the material (Figure 6). Because WML is a measure of work both below and beyond the proportional limit it is derived by either graphical approximations or by means of calculus. 

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