Impact Load Factors - Rice University（影响负荷的因素莱斯大学）.pdf

Prof. J.E. Akin, Rice University Impact Load Factors for Static Analysis Often a designer has a mass, with a known velocity, hitting an object and thereby causing a suddenly applied impact load. Rather than conduct a dynamic analysis an amplified static analysis is used, at least for the preliminary design. In a static stress analysis the static force (or weight of the mass) must be increased by an 鈥淚mpact Factor鈥 so as to obtain a good approximation of the maximum dynamic deflection and stress. For hard elastic bodies the Impact Factor, for vertical impacts, is always greater than or equal to two. It is not unusual for the vertical Impact Factor to be more than 10, 100, or more than 1,000. The following figure shows an amplified static load, P, used to estimate the maximum deflection and stress in a beam due to the dynamic response of a cantilever beam having a weight, W, dropped vertically onto it. A static force P approximates the dynamic effects of a falling weight W In the study of the mechanics of solids, an energy balance approximation is used to estimate the required static load. That approximation assumes that all of the kinetic energy of the moving mass is converted, with an efficiency of 饊寕, to strain energy in the body. If you assume that no noise, or heat, or inelastic response, and neglect the mass of the struck member then 饊寕 = 1 and the collision is 100% efficient. There are several handbook equations that provide corrections to the elementary theory based on the ratio of the striking mass to the member mass. Those corrections seldom give an efficiency of less than 饊寕 = 0.95. In the case of a weight dropped vertically from a height, h, the vertical Impact Factor is 肀 = 1 + 鈭? + 砘?鈩庰€寕