Shock √2gh=443m/sec 1.if v,=0 after t=0.002s(hitting onto floor), then a= 2200 m/sec2, G=224 At the moment of impact, the cup would, in effect, weigh 224 times normal(44.8 kilograms) Unless it was a very unusual cup, breakage could be guaranteed 2. if v,=0 after [=0.008s( rubber pad), then a= 554 m/sec2 G=56
Shock 1. if (hitting onto floor), then a= 2200 m/sec2 , G=224 At the moment of impact, the cup would, in effect, weigh 224 times normal (44.8 kilograms). Unless it was a very unusual cup, breakage could be guaranteed. 2. if ( rubber pad), then a= 554 m/sec2 , G=56 v 2gh 4.43m/sec i = = v after s t = 0 = 0.002 v after s t = 0 = 0.008
Shock 3. if v, =0 after t=0.01s(sponge layer), then a=443 m/sec2 G=44 Adding still more layers would eventually reduce the g level to the point where the cup would not break This would be one way of determining what cushioning protection the cup needed to protect it from a 1 m drop It can be seen from the cup example that time is needed over which to dissipate the impact velocity and that this time is gained by the deflection of a resilient cushioning material. This is the basic principle of cushioning against shock
Shock 3. if (sponge layer), then a= 443 m/sec2 , G=44 Adding still more layers would eventually reduce the G level to the point where the cup would not break. This would be one way of determining what cushioning protection the cup needed to protect it from a 1 m drop. It can be seen from the cup example that time is needed over which to dissipate the impact velocity and that this time is gained by the deflection of a resilient cushioning material. This is the basic principle of cushioning against shock. v after s t = 0 = 0.01
Shock o a quick estimate of cushion material thickness can be made if the cushion material is treated as a linear undampened spring. The deflection necessary to maintain a desired acceleration is calculated as follows 2h where D required deflection, h= anticipated drop height, G= fragility level (critical acceleration) This formula provides the minimum distance over which the deceleration must take place in order not to exceed the critical acceleration
Shock ⚫ A quick estimate of cushion material thickness can be made if the cushion material is treated as a linear, undampened spring. The deflection necessary to maintain a desired acceleration is calculated as follows: where D = required deflection, h = anticipated drop height, G = fragility level (critical acceleration) This formula provides the minimum distance over which the deceleration must take place in order not to exceed the critical acceleration. ( 2) 2 − = G h D
Shock Example] for a product with a fragility factor of 40 G and an anticipated 1 m drop 2×1m D 0.053m(53mm) 40-2 The 53 mm deflection distance is the minimum stopping distance consistent with maintaining 40G or less. Stopping in any lesser distance would raise acceleration to over 40G and cause damage the 53 mm deflection is the theoretical deflection distance not the cushion thickness to determine actual cushion thickness, it is necessary to know how far the
Shock [Example] for a product with a fragility factor of 40 G and an anticipated 1 m drop, The 53 mm deflection distance is the minimum stopping distance consistent with maintaining 40 G or less. Stopping in any lesser distance would raise acceleration to over 40 G and cause damage. The 53 mm deflection is the theoretical deflection distance, not the cushion thickness. To determine actual cushion thickness, it is necessary to know how far the 0.053 m(53 mm) 40 - 2 2 1 = = m D
Shock proposed material will compress before reaching maximum strain, or " bottoming out Static stress working range refers to the load per unit area that will cause a resilient material to deflect but not to flatten out completely typical optimum strains for three commonly used cushion materials are on the order of the following Expanded polystyrene(EPS) 40% Polyethylene foam(or EPE 50% Polyurethane (PUR) 70%
Shock proposed material will compress before reaching maximum strain, or “bottoming out”. ⚫ “Static stress working range” refers to the load per unit area that will cause a resilient material to deflect, but not to flatten out completely. typical optimum strains for three commonly used cushion materials are on the order of the following: Expanded polystyrene (EPS) 40% Polyethylene foam (or EPE) 50% Polyurethane(PUR) 70%