Lesson 14 Test Method for Product Fragility 第14课产品脆值试验方法
Lesson 14 Test Method for Product Fragility 第14课 产品脆值试验方法
Test Method for Product Fragility o a shock machine is used to generate a damage boundary curve o a vibration system is used to map out the natural frequencies of a product
Test Method for Product Fragility ⚫ A shock machine is used to generate a damage boundary curve ⚫ A vibration system is used to map out the natural frequencies of a product
Shock: Damage Boundary Shock damage to products results from excessive internal stress induced by inertia forces Since F=ma shock fragility is characterized by the maximum tolerable acceleration level, i. e, how many gs the item can withstand Why damaged? How to reduce g's? The packaging material changes the shock pulse delivered to the product so that the maximum acceleration is greatly reduced(and the pulse duration is many times longer) The package designers goal To be sure that the g-level transmitted to the item by the cushion is less that the g-level which will cause the item to fail
Shock: Damage Boundary Shock damage to products results from excessive internal stress induced by inertia forces - Since F=ma, shock fragility is characterized by the maximum tolerable acceleration level, i. e, how many g’s the item can withstand. - Why damaged? - How to reduce g’s ? The packaging material changes the shock pulse delivered to the product so that the maximum acceleration is greatly reduced (and the pulse duration is many times longer). - The package designer’s goal: To be sure that the g-level transmitted to the item by the cushion is less that the g-level which will cause the item to fail
Shock: Damage Boundary The damage boundary theory is used to determine which shock inputs will cause damage to a product and which will not Two parts of a shock can cause damage 1. the acceleration level a 2. the velocity change Av(the area under the acceleration-time history of the shock, thought as the energy contained in a shock The critical velocity change(AVc): a minimum velocity change Which must be achieved before damage to the product can occur 1. Below AVc, no damage occurs regardless of the input a 2. EXceeding AVc, does not necessarily imply that damage results a If Av occurs in a manner which administers acceptable doses of acceleration to the product, the velocity change can be very large without causing damage b If Avc and Ac are both exceeded, damage occurs Figure 14.1: Typical damage boundary curve
Shock: Damage Boundary The damage boundary theory is used to determine which shock inputs will cause damage to a product and which will not. - Two parts of a shock can cause damage: 1. the acceleration level A 2. the velocity change ∆V (the area under the acceleration-time history of the shock, thought as the energy contained in a shock) - The critical velocity change(∆Vc): a minimum velocity change which must be achieved before damage to the product can occur. 1. Below ∆Vc, no damage occurs regardless of the input A 2. Exceeding ∆Vc, does not necessarily imply that damage results. a. If ∆V occurs in a manner which administers acceptable doses of acceleration to the product, the velocity change can be very large without causing damage. b. If ∆Vc and Ac are both exceeded, damage occurs. Figure 14.1: Typical damage boundary curve
Shock: Damage Boundary Implications of Fig. 14.1 a. if the input av<the products AVc, then the acceleration level of the input can be in the 100Gs 1000G's, 10,000G's, or even without causing damage. In fact the duration is so short that the product cannot respond the acceleration level of the event, only the energy input b if the input AV>the product's AVc, However, the only way to avoid damage is to limit the input a< the cushioned package performs: it translates the higa product's AC. This is usually one of the functions that acceleration events experienced on the outside of the container to lower acceleration events experienced inside at the unit
Shock: Damage Boundary Implications of Fig.14.1: a. if the input ∆V<the product’s ∆Vc, then the acceleration level of the input can be in the 100 G’s, 1000 G’s, 10,000 G’s, or even without causing damage. In fact, the duration is so short that the product cannot respond the acceleration level of the event, only the energy input. b. if the input ∆V>the product’s ∆Vc, However, the only way to avoid damage is to limit the input A < the product’s Ac. This is usually one of the functions that a cushioned package performs: it translates the high acceleration events experienced on the outside of the container to lower acceleration events experienced inside at the unit