文档介绍：Lesson 14
Test Method for Product Fragility
第14课产品脆值试验方法
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 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 ∆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 : Typical damage boundary curve
Shock: Damage Boundary
Implications of :
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 le