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Design of a lightweight trailer load pushed completely against one side of a trailer. The scenario load on the floor and pressure on the side panels led to 60 mm displacement of the side panels in the aluminium trailer. This displacement would probably be visible when a trailer was being loaded. A trailer might look unstable when being loaded and turning corners because of the visible displacement of the side panels. Looking at the results Liz and Hans concluded that the stresses in the side panels were low enough so there was no strength problem only a stiffness problem. To check whether the load scenarios were realistic Liz asked the customer whether he had ever seen any displacement in the side panels of an aluminium trailer when the trailer was fully loaded. The customer said that he saw no displacement in the side panels of the aluminium trailer. Liz thought that this might be due to the fact that there was no hydrostatic pressure from the sand on the side panels. The internal friction of the sand might prevent the pile of sand from completely sliding to the side panel. Because both Liz and Hans had no experience with calculations concerning internal friction in a pile of sand, and the time they had for this preliminary design was limited, the decision was made that the side panels should have the same stiffness as the side panels of the existing aluminium trailer. So they decided to skip the load on the floor and pressure on the side panels scenario completely. Instead of this they calculated the stiffness of the side panels of the existing aluminium trailer and designed the composite trailer side panels to have similar stiffness. The customer indicated that he had seen no displacement of the side panels in an aluminium trailer as it turned corners. The calculation using the load scenario given above led to 290 mm displacement in the side panels in an aluminium trailer. If this really happened then it would be visible. Liz and Hans decided that a load scenario where the complete load of sand pushed against the side panel in a corner was too severe. They decided to use a load scenario used in a previous project for turning a corner. This load scenario was used for hand calculations. Only two loading scenarios remained for the finite element modelling calculations: Load on the floor: 32 tonne, dynamic factor 2 makes 32 tonne x 2g Torsion: a torsion moment of 1 Nmm will be used Turning a corner: this will not be calculated using FEM but “by hand” Braking: this will not be calculated using FEM but “by hand” As described above the other scenarios were not realistic according to the engineers. One of the scenarios was discarded as irrelevant, i.e. load on the floor and pressure on the side panels. One of the scenarios was calculated differently, 139
Ethical issues in engineering design i.e. turning a corner. One scenario had been changed, i.e. load on the floor. One scenario, torsion, was not changed, but this is not really a load scenario. A load scenario is meant to be used to describe what loads can be expected. To determine torsional stiffness one unit torsion is placed on a model. When the two scenarios, mentioned before, were introduced in the finite element model, the maximum displacement of the floor was 33 mm. 7 Liz and Hans reasoned that this displacement was calculated using 2g so the displacement would only be 16,5 mm if the trailer is at rest. This was actually within the requirement of maximum 20 mm but Liz preferred a larger margin. 140 Hans: ‘In fact, let’s look at the relative displacements. Because I think that that is what is important, and it is probably a lot less. This is really the bending of the floor. You see the yellow part is not 0.’ Liz: ‘Yellow is 6.’ Hans: ‘It is 7, the displacement ranges from 7 to 33 mm so the bending 33-7=26 divided by 2. The bending is 13 mm by 1g.’ From this quote it can be seen that Liz and Hans decided the bending over the largest span should be less than 20 mm not the total overall displacement. The bending over the largest span was 13 mm. The bending was therefore well within the requirement. The stresses and strains within the materials were lower than the allowable stresses and strains and therefore the concept composite trailer was stiff and strong enough. Liz and Hans had also calculated very quickly whether a heavy driver walking through the trailer would cause the trailer to bend too much. To calculate this they considered a mass of 200 kg on a surface of 20 cm 2 , this should simulate a heavy weight driver standing on one foot. The strains in the floor were found to be below allowable strains and the driver would not have the feeling that the floor was saggy. The load scenarios turning a corner and braking were calculated by hand, not using finite element modelling. 8 Load scenarios were still needed to make the braking and turning corners calculations. Estimations of the mass and acceleration during braking and turning a corner were necessary. The engineers —————————————————————————————————— 7 Notice that this is different from the 23 mm that the engineers attained before but the material thicknesses had also changed. As I indicated before, material thicknesses and properties were changed simultaneously with the load scenarios. 8 These calculations are called “hand calculations” but for most calculations a computer program (Mathlab) is used to solve the equations. This computer program is widely used throughout the engineering world for analytical and numerical calculations. The difference with the finite element program is that finite element calculations are always numerical solutions, and that, to perform such calculations a model of the product or part needs to be made. It is not necessary to make a model when using Mathlab.
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Ethical issues in engineering desig
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Dit proefschrift is goedgekeurd doo
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Contents 1 Introduction 9 1.1 Resea
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Contents 7.3 Safe in what sense? 13
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2 Engineering ethics and design pro
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Engineering ethics and design proce
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2.2.2 Design problems Engineering e
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3 Introduction to the case-studies
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Introduction to the case-studies Em
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Towards warranted trust in engineer
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Samenvatting Ethische aspecten in o
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Samenvatting 1a. De soort ethische
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Samenvatting Sommige details worden
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Samenvatting buiten beschouwing gel
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Samenvatting zijn. Als alleen de no
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Samenvatting zelf waardevol vinden
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Appendix 2 Members of the DutchEVO
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Appendix 2 Ryan: Industrial designe
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Curriculum Vitae Anke van Gorp was
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Simon Stevin Series in the Philosop
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