Ethical issues in engineering design - 3TU.Centre for Ethics and ...

Ethical issues in engineering design
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Hans: ‘Then you should do both calculations. Make the calculations
for their aluminium trailer and for our concept and compare them.’
The displacement of the floor was 34,5 mm, which was too much according to
the engineers’ self imposed requirement for a maximum of 20 mm. A discussion
was started as to whether this should be local bending of the floor or the total
displacement of the floor with regard to the initial unloaded situation. At the end
of this discussion it was decided that the safety factor of 1,5 should not be
included. The safety factor was used to get from limit to ultimate load and the
engineers seemed to change their minds about what load to use in the load
scenarios. At first the engineers calculated the displacement of the floor using
ultimate load and then they decided to use limit load. They argued that the
displacement is one of the stiffness requirements and these should always be
calculated using limit load. According to Liz and Hans a structure is allowed to
fail to a certain extent at ultimate load, so ultimate load is way too severe for a
stiffness requirement. The use of limit instead of ultimate load reduced the
displacement of the floor to 34,5 : 1,5= 23 mm (calculations were linear elastic),
which was much closer to the required maximum of 20 mm.
The safety factor, 1,5, was also removed from the load scenario for turning a
corner, but the displacement of the side panels remained more than 1 m.
Subsequently, the dynamic factor (2) was also removed from the scenario but the
displacement remained at about a meter. Liz and Hans started to doubt whether
it was realistic to assume that the complete load of sand will push against the side
panel. After the discussions the load scenarios were changed to the following.
Load on the floor: 32 tonnes, dynamic factor 2 makes 32 tonnes x 2g
Load on the floor and pressure on the side panels: floor 32 tonnes x 2g and
hydrostatic pressure on the side panels “density of the sand” x “the height” x
g
Turning a corner: during turning a corner the pile of sand is within a gravitational
field, 32 tonnes x 1g on the floor and on the side panel
Torsion: a torsion moment of 1 Nmm will be used
As can be seen in the previous quote Liz and Hans also decided to make a finite
element model of the existing aluminium trailer for comparison. These above
load scenarios were used to calculate the displacements in the finite element
models of the existing aluminium trailer and for the concept composite trailer.
The load scenario turning a corner still led to extreme displacements of the side
panels, 290 mm in the aluminium trailer and 770 mm in the concept trailer. The
engineers started thinking about whether the trailer would roll over when the