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Although investigations have shown that the theory of limit design applies to beams and some frames made of mild steel, it is not certain whether it applies in the same way to the light alloys. Steel frames satisfy the limit design prediction of a failure mechanism not only because steel is very ductile but also because steel exhibits strain hardening. Light alloys such as high-strength aluminum alloy exhibit very little strain hardening. Two load tests were carried out on redundant beams made of the aluminum alloy to see if the mechanism condition of limit design was reached before failure took place in the beam. Measurements of beam deflections and moments are compared to the deflections and moments predicted by the theory of inelastic bending. The theory of inelastic bending is based on the stress-strain diagram and takes account of strain hardening and a failure strain. Tables of unit functions derived from the stress-strain diagram of the aluminum alloy are presented for use with the inelastic bending theory. In both tests, the mechanism condition of limit design was reached before failure took place. Shortly after the mechanism condition was reached, a fracture occurred in the flange on the tension side of the beam. Thus the type of failure indicates that not all structural configurations will achieve the mechanism condition. Beyond the limit of elastic deformation (17 kips load) and up to a load of about 27 kips, the beam moments were similar to those predicted by the inelastic bending theory. From 27 kips load to failure at 32 kips, the moments were distributed in the beam differently than the predicted moments due to the presence of high shear force. The load-deflection curves are the same as the curves from the theory, although measured deflections were always greater. The ultimate curvature at the section of failure was greater than predicted from the theory. There were some shortcomings of the tests. The tests were originally set up to be unfavourable towards the limit design theory. However, stiffeners were added at the plastic hinge locations to prevent web failure, and the presence of the stiffeners was helpful in allowing redistribution of moments to take place in much the same way as strain hardening does in steel beams. Also the presence of the stiffeners and stiffener holes made interpretation with the inelastic bending theory uncertain. Finally there were some errors in measuring the moments by means of strain gauges. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

The theory of limit design originally was developed for structural steel construction. Tests carried out on mild steel beams and frames are in agreement with the theory. Unfortunately a limited number of tests have been carried out on other ductile materials such as light alloys. Therefore more tests are required in order to investigate whether the theory of limit design is also applicable, with or without modification to aluminum alloys. The failure mechanism predicted in limit design materializes in steel frames not only because steel is very ductile but also because steel has strain hardening. Aluminum alloys exhibit very little strain hardening. In the research described here there were two objects. The first object was to investigate the applicability of limit design to aluminum alloys. The second object was to check experimentally the theory of inelastic bending. Three load tests were carried on continuous beams made of aluminum alloy to see if the mechanism condition was attained before failure of the beam. Moments and deflections predicted by the theory of inelastic bending were compared against measurement of beam moments and deflections. The theory of inelastic bending considers the effect of strain hardening. Tables of unit function derived from the stress-strain diagram of aluminum alloy (65S-T6) are presented so that they may he used when the theory of inelastic bending is applied. The first test failed prematurely due to crippling of the compression flanges. In the second and the third test the mechanism condition of limit design was reached shortly before failure of the tension side of the beam under the load point by fracture. Thus the type of failure indicates that not all structures will achieve the mechanism condition. The failure load and the ratio of moments at failure, as predicted by the theory of inelastic bending was equal to 15.53 Kips and 1.13 respectively. Test results indicated a failure load of 16 Kips and a ratio of moments at failure equal to 1.1. The load-deflection curves were the same as the curves from the theory. At failure the deflection under the load was 5.57 inches compared to computed theoretical deflection of 5.46 inches. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

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The effect on microstructure and strength properties of hypereutectic aluminum - 20% silicon alloys of various refining additions has been studied by means of metallographic observations, hardness tests and a quantitative determination of the interparticle spacing for the primary silicon. A mechanism has been proposed to explain the observed coarsening of the eutectic which accompanies primary silicon refinement, and the combined effect of the improvement of primary dispersion and increased eutectic coarseness on strength properties has been discussed. Refining mechanisms for the refining additions used have been suggested and the reasons for the observed effect of the various refining additions on the shape of primary silicon have been presented. An explanation is offered for the increase in primary refinement which results from an increase in the time the alloy is held molten after fluxing with phosphorus penta-chloride. The apparently anomalous behavior of phosphorus-copper refined alloys has been explained on the basis of the degree of dissemination of the phosphorus in the molten alloy. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

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