Mechanical Shock – Damage Boundary Curve Test
Consumer products usually encounter shocks in two conditions in the lifespan; one is Bumps and Bounces caused by vehicle on bumpy roads during the transportation, the other is drops caused by human negligence in handling the goods. Hand-held products such as cell phones and PDAs are more vulnerable to dropping impacts when no buffer protection is provided. Automotive electronics work in a much adverse environment than consumer products; especially when they are installed at tires, doors or trunks that sustain to more severe vibrations. Mechanical Shock Test, which offers prompt verification of structural strength in the product design stage for deciding whether proper buffering is required in the packing design, is one of crucial items for validating the design.
The following stresses are normally used for performing Damage Boundary Curve Tests:
The critical impact velocity (ΔVc)
Mainly used for simulating impact or drop of a product caused by improper handling of the end user, of which the impulse is short (as suggested by ASTM D3332, the impulse is normally less than 3ms). The lab generates a half-sine wave with low impact velocity by the mechanical impact machine, accompanied by a short impulse time (normally less than 3ms), upon the product. On completion of the first impact, a thorough inspection takes place on the appearance and functionality of the product. If no anomaly is found, a second impact is performed with the identical impulse time and a slightly increased impact velocity. The test goes on in this manner with gradually increased impact velocities until the product is damaged (which gives the critical design velocity ΔVc of the product). In the end, the sustainable impact velocity and the limit of drop height can be determined for the product in the unpacked condition.
The critical impact acceleration (ΔAc)
This is mainly used for simulation of strength capability of the product against a mechanical shock / free fall drop during the transportation; the simulation also helps identifying the packaging cost for an optimal buffering protection for the product. The lab generates a force of low acceleration by mechanical impact machine in a stepping wave upon the product, on completion of the first accelerating impact, a thorough inspection takes place on the appearance and functionality of the product. If no anomaly is found, a second impact is performed with a slightly increased acceleration from the impact machine. The test goes on in the same manner with gradually increased impact acceleration until the product is damaged (this is the critical design acceleration ΔAc of the product). This data is provided to the packing designer for an optimal packing design as well as the reference basis for carrying out drop test of the packing.
Refenced standards: ASTM D3332, DELL Packaging Test Plan- 45785 , HP 398129 X6
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