2. Increases resistance to corrosion 3. Improves machinability in free-cutting steels Silicon (Si) 2%  (9% with 18.5% (not much changed by carbon) Hardens with loss in plasticity (Mn  Si  P) Increases hardenability moderately Negative (graphitizes) Sustains hardness by solid solution 1. Used as generalpurpose deoxidizer 2. Alloying element for electrical and magnetic sheet 3. Improves oxidation resistance 4. Increases hardenability of steel carrying nongraphitizing elements 5. Strengthens lowalloy steels Titanium (Ti) 0.75% (1%  with 6%  (less with lowered temp) Provides agehardening system in high Ti-Fe alloys Probably increases hardenability very strongly as dissolved. The carbide effects reduce hardenability Greatest known (2% Ti renders 0.50% carbon steel unhardenable) Persistent carbides probably unaffected. Some secondary hardening 1. Fixes carbon in inert particles a. Reduces martensitic hardness and hardenability in

TABLE 5.2 Minimum Design Live Loads (Continued) c. Minimum design loads for materials Material Load, lb/ft3 Material Load, lb/ft3 Aluminum, cast Bituminous products: Asphalt Petroleum, gasoline Pitch Tar Brass, cast Bronze, 8 to 14% tin Cement, portland, loose Cement, portland, set Cinders, dry, in bulk Coal, anthracite, piled Coal, bituminous or lignite, piled Coal, peat, dry, piled Charcoal Copper Earth (not submerged): Clay, dry Clay, damp Clay and gravel, dry Silt, moist, loose Silt, moist, packed Sand and gravel, dry, loose Sand and gravel, dry, packed Sand and gravel, wet Gold, solid Gravel, dry Gypspum, loose Ice Iron, cast Lead Lime, hydrated, loose Lime, hydrated, compacted Magnesium alloys Mortar, hardened; Cement Lime Riprap (not submerged): Limestone Sandstone Sand, clean and dry Sand, river, dry Silver Steel Stone, ashlar: Basalt, granite, gneiss Limestone, marble, quartz Sandstone Shale, slate Tin, cast Water, fresh

c  68.1  (5.263) where E  modulus of elasticity, psi p  density of the struck body, lb/ ft3 If an impact imparts a velocity v, ft / s, to the particles at one end of a prismatic bar, the stress, psi, at that end is v  E  0.0147v Ep  0.000216pcv (5.264) c if is in the elastic range. In a compression wave, the velocity of the particles is in the direction of the wave. In a tension wave, the velocity of the particles is in the direction opposite the wave. In the plastic range, Eqs. (6.263) and (5.264) hold, but with E as the tangent modulus of elasticity. Hence, c is not a constant and the shape of the stress wave changes as it moves. The elastic portion of the stress wave moves faster than the wave in the plastic range. Where they overlap, the stress and irrecoverable strain are constant. (The impact theory is based on an assumption difficult to realize in practice that contact takes place simultaneously over the entire end of the bar.) At the free end of a bar, a compressive stress wave is reflected as an equal tension wave, and a tension wave as an equal compression wave. The velocity of the particles there equals 2v. At a fixed end of a bar, a stress wave is reflected unchanged. The velocity of the particles there is zero, but the stress is doubled, because of the superposition of the two equal stresses on reflection. For a bar with a fixed end struck at the other end by a moving mass weighing Wm lb, the initial compressive stress, psi, is  0.0147v Ep (5.265) o o where vo is the initial velocity of the particles, ft / s, at the impacted end of the bar and E and p, the modulus of elasticity, psi, and density, lb/ ft3, of the bar. As the velocity of Wm decreases, so does the pressure on the bar. Hence, decreasing compressive stresses follow the wave front. At any time t  2L/c, where L is the length of the bar, in, the stress at the struck end is  e2t /  (5.266) o where e  2.71828,  is the ratio of Wb, the weight of the bar, to Wm, and