Lesson 13 Mechanical Shock Theory 第13课 机械冲击理论
Lesson 13 Mechanical Shock Theory 第13课 机械冲击理论
Introduction ◼ Throughout the distribution system, packages are manhandled and mishandled in various ways: dropped, thrown, kicked and otherwise roughly abused; fall from conveyors or forklifts and crash to the floor; subjected to a variety of vehicle impacts; trucks starting, stopping, hitting chuckholes and railroad crossings, railcar humping, jolting and other moderately violent actions; suffers an impact with another object：floor, truck bed, pallet, bulkhead or another package. ◼ A mechanical shock occurs when an object's position, velocity or acceleration suddenly changes. Such a shock may be characterized by a rapid increase in acceleration followed by a rapid decrease over a very short period of time. ◼ Figure 13.1: the acceleration versus time plot for most shocks
Introduction ◼ Throughout the distribution system, packages are manhandled and mishandled in various ways: dropped, thrown, kicked and otherwise roughly abused; fall from conveyors or forklifts and crash to the floor; subjected to a variety of vehicle impacts; trucks starting, stopping, hitting chuckholes and railroad crossings, railcar humping, jolting and other moderately violent actions; suffers an impact with another object：floor, truck bed, pallet, bulkhead or another package. ◼ A mechanical shock occurs when an object's position, velocity or acceleration suddenly changes. Such a shock may be characterized by a rapid increase in acceleration followed by a rapid decrease over a very short period of time. ◼ Figure 13.1: the acceleration versus time plot for most shocks
Figure 13.1 Representation of mechanical shock
Figure 13.1 Representation of mechanical shock
A package shock may typically be 20 milliseconds (0.020 seconds) long and have a magnitude or "height" of 150 g's. need to know both the magnitude of the acceleration and the duration of the shock. The Free Falling Package ◼ the length of time it takes a package to fall from a drop height, h ◼ the downward velocity at which it will be traveling a moment before impact; , the impact velocity: ◼ As is shown in Figure 13.2. A package will rebound a little or a lot depending on the nature of the package and the surface it hits. g h t 2 = g h t 2 = g h t 2 = g h t 2 = v gh I = 2 vI = 2gh
A package shock may typically be 20 milliseconds (0.020 seconds) long and have a magnitude or "height" of 150 g's. need to know both the magnitude of the acceleration and the duration of the shock. The Free Falling Package ◼ the length of time it takes a package to fall from a drop height, h ◼ the downward velocity at which it will be traveling a moment before impact; , the impact velocity: ◼ As is shown in Figure 13.2. A package will rebound a little or a lot depending on the nature of the package and the surface it hits. g h t 2 = g h t 2 = g h t 2 = g h t 2 = v gh I = 2 vI = 2gh
Figure 13.2 A falling package
Figure 13.2 A falling package