Reference volume consideration in limit load determination

Gudimetla, Phani Suresh Reddy (2010) Reference volume consideration in limit load determination. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Reference volume plays an important role in finding out the limit loads of mechanical components and structures. In the current research work, new and simplified methods are proposed in order to determine the reference volume (i.e., elastic and plastic reference volumes) for any given general mechanical component or structure. -- Many methods have been developed for estimating limit loads in general components and structures; these methods depend on an upper bound multiplier which takes the total volume into consideration. Considering total volume results in overestimating the upper bound multiplier. To overcome this deficiency, two methods are proposed in this research to find reliable estimate of limit load using the reference volume. -- The Elastic Reference Volume Method is developed by extending the well established pressure bulb concepts in soil mechanics to general mechanical components. This method is basically for second category components, like components with notches or cracks. The results obtained are within the range of 2 to 5 percent lower bounded to non-linear results. On the other hand, for the first category components which are well designed, the Plastic Reference Volume Method is developed. The results obtained are with in the range of 2 to 7 percent lower bounded to non-linear results. -- To obtain a reliable lower bounded limit loads, other than the dead volume effect peak stress effect is also need to be corrected. A new method which can correct both the reference volume effect and the peak stress effect is developed. This method given a lower bounded mα tangent multiplier for all the examples. The results are compared with the non-linear analysis results and results are found to be very close estimates (< 2 percent) to the non-linear results. -- Taking the practical material usage in industry into consideration, a new method is developed for finding out limit loads of components or structures made of anisotropic materials by incorporating the reference volume correction. The usage of anisotropic materials in industries is increasing day by day, and so is the need for finding out accurate limit loads for components considering such material properties. The results are found to be in good agreement with the non-linear results. -- Whenever a component or a structure is subjected to continuous loading and the stress exceeds the yield limit, the component undergoes strain hardening. It is very important to consider this strain hardening effect while obtaining the limit loads for optimal utilization of material. A new method developed in this research will take the strain hardening effect upto a 5% strain limit into consideration, while calculating the limit loads. Multipliers obtained using this approach are found higher then the ones obtained by regular limit analysis, suggesting the usage of reserved strength.

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