Metal Foams: A Design Guide

Energy management: packaging and blast protection 151
Table 11.1 Limiting g-factors, a*, for a number of objects
Object Limiting g-factor, a Ł
Human body, sustained acceleration 5–8
Delicate instruments; gyroscopes 15–25
Optical and X-ray equipment 25–40
Computer displays, printers, hard disk drives 40–60
Human head, 36 ms contact time 55–60
Stereos, TV receivers, floppy disk drives 60–85
Household appliances, furniture 85–115
Machine tools, engines, truck and car chassis 115–150
Table 11.2 Impact velocities for a range of conditions
Condition Velocity (m/s)
Freefall from forklift truck, drop height 0.3m 2.4
Freefall from light equipment handler, drop height 0.5m 3.2
Freefall of carried object or from table, drop height 1 m 4.5
Thrown package, freefall 5.5
Automobile, head impact, roll-over crash in car a 6.7
High drag parachute, landing velocity 7
Low drag parachute, landing velocity 13
Automobile, side impact, USA a 8.9
Europe a 13.8
Automobile, front impact, USA a 13.4
Europe a 15.6
a Current legislation.
Typical velocities for package design are listed in Table 11.2. They lie in the
range 2 to 13 m/s (4 to 28 mph). Package design seeks to bring the product,
travelling at this velocity, to rest without exceeding its limiting g-factor.
11.2 Selecting foams for packaging
Ideal energy absorbers have a long flat stress–strain (or load-deflection) curve
like those of Figures 11.1(a) and (b). The absorber collapses plastically at
a constant nominal stress, called the plateau stress, pl, up to a limiting