smart technologies for safety engineering

238 Smart Technologies for Safety Engineering
Figure 6.14 Original and optimized vertical displacements of impacted nodes (multiple-impact case):
(left) 30-element optimum structure; (right) 26-element near-optimum structure
characteristics are attributed to a limited number of chosen elements [34]. These elements are
called structural fuses, since they are meant to dissipate impact energy. In the considered optimized
truss beam structure (Figure 6.13) it is natural to consider the two elements located in
the upper layer of the two section pairs: 1, 2 and 10, 11 (see Figure 6.15). These two structural
fuses located in the elements, which accumulate the largest portion of the strain energy in the
elastic solution, are good candidates for location of the energy dissipation process. However,
in the previously considered case of the single asymmetric impact load, better locations for
structural fuses are sections 10, 11 (upper layer) and section 11 (lower layer).
The third step of the methodology considers optimum control strategies for the already
allocated structural fuses. Provided a real-time impact identification system is available [30],
an active control strategy can be pursued. The optimality is defined in terms of the energy
dissipated by the fuses in the process of plastic yielding:
U =
(33)
t≤T
σi(t)β 0 i (t)li Aiμi
which should be maximized for each of the considered impact scenarios. Equation (33) is
subject to the following constraints imposed on stresses and plastic distortions (maximum
strokes of structural fuses):
|σi(t)| < ˜σ (34a)
β 0 i (t) < ˜β (34b)
Figure 6.15 Location of structural fuses in the 26-element structure