A “Toolbox” for Forensic Engineers

420 Forensic Materials Engineering: Case Studies
also be totally reliable and robust, and thus constructed of wear and corrosion-resistant
materials. Two metal leaf springs and a metal coil spring are
the basis of the stored mechanical energy when primed, all working within
the elastic limit of the metal. In the Hookean region of behavior, applied
strain and the stress produced in the metal are completely reversible for
thousands of cycles, so the reliability of the device is assured.
13.4.5 The Protector
The device accused of infringing the Powerbreaker patent in the action
appeared, at first sight, to be very different from the Powerbreaker. It is known
as the Protector. A notional equilibrium diagram of the set-up of the primed
device is shown in Figure 13.23. The balance of forces in the primed state is
shown in Figure 13.24. The sequence of actions exhibited in Figure 13.25 show
how the Protector works. The Protector was developed by PDL, a plastics
molding company based in New Zealand, and was the subject of a European
Patent application (EPO PAT Appl. No. 526 071). The device consists of a set
of rigid levers and coil springs, which looks quite different as a reaction
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Figure 13.23 Sections of the Protector (from EP 526 071) showing various
working elements of the device.
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