. The strength of materials; a text-book for engineers and architects. % Moisture. Along Grain. Across Grain. Pine .Oak .Deal .Teak . 9,20016,000 7,8009,800 470 890 440 1,000 4,9005,3002,7004,000 1,900 1,200 2,800 15-712-610-6100 The crippling stress is the stress at which the timberwas found to shear through about three-fourths of its area;considerable increase of load, however, was required beforecomplete shear occurred. Bending Strength.—Tests by bending form one of themost satisfactory methods of testing timber. If the sectionis rectangular, of breadth b and depth d and the span is I,then
. The strength of materials; a text-book for engineers and architects. % Moisture. Along Grain. Across Grain. Pine .Oak .Deal .Teak . 9,20016,000 7,8009,800 470 890 440 1,000 4,9005,3002,7004,000 1,900 1,200 2,800 15-712-610-6100 The crippling stress is the stress at which the timberwas found to shear through about three-fourths of its area;considerable increase of load, however, was required beforecomplete shear occurred. Bending Strength.—Tests by bending form one of themost satisfactory methods of testing timber. If the sectionis rectangular, of breadth b and depth d and the span is I,then we have for a breaking central load W as proved inChap. VII. Breakmg stress = -^ -^ -^ = ^-^^* Proc. I. M. E., 1906 (1). 68 THE STRENGTH OF MATERIALS As we indicated on p. 51 this breaking stress is some-times called the modulus of rupture. Youngs modulus may be calculated by finding the de-flection S for a given safe load W bv the formula 6 = - E = 4SEI W P. \\P 4:b(P .E 111 these bending tests it is a good plan to take a standard>ize of beam, l x V x Fig. 33.—Compression Faikire of Concrete Cube. STONE, CONCRETE, CEMENT AND LIKE BRITTLE MATERIALS Compressive Strength.—When stone, concrete, cementand like materials are tested in compression in the form ofcubes or short cylinders, fracture nearly always occurs bysplitting in diagonal planes in the manner indicated in Fig. is commonly referred to as a shear failure, the failurebeing attributed to the shear stresses on the diagonal planesat 45 to the axis. We have seen already (p. 10) that onsuch planes there is a shear stress of equal intensity to the BEHAVIOUR OF MATERIALS UNDER TEST 69 compressive stress. There are, however, strong reasons forsupposing that the fracture of brittle materials is due totension and the most careful experiments on cement andconcrete show that the shear strength is greater than thetensile strength (cf. p. 79). Tension Theory of Failure.—When a block of materialis compres
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