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 chuckhole 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
ACCELERATION ACCELERATION gs time(milliseconds) time(mIlliseconds) a Figure 13.1 Representation of mechanicalshock
Figure 13.1 Representation of mechanical shock
边sh a package shock may typically be 20 milliseconds(. 020 seconds)long and have a magnitude or height"of 150 gs. 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 ugh 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
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
V=0 V=V V=VI IMPACT REBOUND Total velocity change =I VII+I VR Figure 13.2 A falling package
Figure 13.2 A falling package