Determination of Product Fragility
The first step towards determination of the amount of cushioning a product requires is to establish the amount of
mechanical shock the product can survive on its own.
The "fragility" of the article is conventionally expressed in terms of a "G" value. That is, "fragility" refers to the maximum shock that an article can withstand without suffering damage. G is the gravitational constant and the cushioning G-value indicates the deceleration or negative acceleration
(in this case the braking, down to a speed of zero, of a dropped product hitting the ground) that an item can withstand without being damaged. The more fragile a product is, the less G-sit can withstand. The function of cushioning is to extend the time for the speed reduction and thereby reduce the deceleration.
[
G is a unit for acceleration, equal to the acceleration of gravity: 1g ≈ 9,81 m/s2.
Deceleration is “negative acceleration”, in this case the braking, down to a speed of zero, of
a dropped product hitting the ground.
The function of cushioning is to, through its compression, extend the time t(s) for this speed reduction v(m/s), thereby reducing the deceleration a(m/s2): A = v / t
The lower deceleration a(m/s2) a product of given mass m(kg) is exposed to, the lower is the force impact F(N) on the product: F = m * a ]
Knowledge of the product to be packaged is critical. Field experience may indicate the types of damage previously experienced. Engineering judgment can also be an excellent starting point. Sometimes a product can be made more rugged or can be supported to make it less sensitive to damage.
Ideally, the fragility of a product is determined in a laboratory by subjecting it to a series of gradually more severe shocks (decelerations) in order to find the lowest severity impact that will damage the product. The highest deceleration, which did not cause damage, is then known to be the product’s G-factor. In that case it is important to be aware of the cost for a destroyed product.
Approximate Fragility of typical Packaged Articles.
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Extremely Fragile
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Aircraft altimeters, gyroscopes, items with delicate mechanical alignments
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15-25 g's
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Very Delicate
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Medical diagnostics apparatus, X-ray equipment
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25-40 g's
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Delicate
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Display terminals, printers, test instruments, hard disk drives
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40-60 g's
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Moderately Delicate
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Stereo and television receivers, floppy disk drives
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60-85 g's
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Moderately Rugged
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Household appliances, furniture
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85-115 g's
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Rugged
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Table saws, sewing machines, machine tools
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115 g's +
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It may be necessary to determine fragility levels for a product in various orientations, as it is not uncommon for a product to exhibit greater strength in one direction than another. The fragility levels should possibly not be estimated, but defined through test data.
If the
G-factor is estimated too high
, and the product is unable to survive as much shock as anticipated, the packaging will be under-designed and significant shipping damage is likely to occur. On the other hand, if the G-factor is estimated too low, and the product can actually withstand more shock than anticipated, the packaging will be over-designed and unnecessarily large and/or expensive. In other words, it’s very important to determine the
G-factor.