A “Toolbox” for Forensic Engineers

168 Forensic Materials Engineering: Case Studies
Figure 5.28 X-radiograph of chair arm showing serious internal defects caused
by poor shape of gas pocket.
between a hollow interior and the solid skin. Under the watchful eyes of both
experts, the samples were duly taken to a local hospital and exposed to the
x-ray beam, one of the arms being shown in Figure 5.27 together with its
corresponding x-ray negative (Figure 5.28). The x-ray image showed big
differences in wall thickness, the inside walls tending to be much thinner
than the outside (probably due to tool temperature variation). The gas pocket
had penetrated the attachment zone at the bottom of the arm, while another
side was solid and had not been affected at all. Thus the problems of the
technique had been present from the start, which would have been apparent
had someone bothered to investigate the trial moldings produced not by the
client, but by the defendant machine makers. The additional problems with
the lever on the machine seemed indicative of the lack of adequate backup,
but did not appear directly connected with the product problems. Another
chair arm showed the same kind of problem (Figure 5.29), and the x-radiograph
was checked by sectioning the arm after the action had been settled
(Figure 5.30). The case for the plaintiff was now very strong, but would it
proceed to a long and expensive court trial?
Just before trial was due to start, lawyers for the two sides met and
hammered out a surprising deal. The machine maker was suffering from a
downturn in business and was storing a large number of new machines in
warehouses. The plaintiff needed to reequip its factory and replace aging
molding machines. So the defendants agreed to sell several new machines at
a discount equivalent to the damages claimed by the factory for the failure