Master of Science in Mechanical Engineering (MSME)
The purpose of this research is to try and understand hypercompressor packing ring failures better with a view of ultimately reducing or even eliminating their occurrences. In order to gain further understanding of packing ring failures, we seek to obtain an appreciation of the stresses they experience during operation. First we consider a conventional simulation of an axisymmetric packing ring and cup subjected to the typical pressure loading conditions experienced by these components when installed in a hypercompressor cylinder. The key locations of interest are along the bimaterial interface, and in particular at the ends of the interface. These ends effectively represent a butt joint in contact and a butt joint under pressure. To begin to gain an appreciation of the stresses at these locations, we undertake a finite element analysis (FEA) of the configuration with traditional interface and contact conditions. Unfortunately the traditional analysis does not produce stresses that appear to converge at either end as judged by simple convergence checks. As is indicated by previous research, a singularity is expected to occur at the butt joint under pressure, and thus diverging stresses. However, for the butt joint in contact the situation is less clear. Accordingly an asymptotic analysis of this configuration is undertaken. This shows that, in contrast to the butt joint under pressure, the butt joint in contact is singularity free. Thus ultimately a more refined FEA should converge. However, this would still result in diverging singular stresses for the other end of the interface, the butt joint under pressure. Thus a new approach is required for this butt joint. The adopted approach introduces frictionless adhesive conditions on all interfaces. This results in converging stresses at both interface ends on the same sequence of meshes as used in the initial FEA with traditional conditions. While more realistic stiffnesses need to be obtained and introduced into these adhesive laws for truly physically realistic stresses to result, the present proof-of-concept analysis does hold promise that ultimately such an analysis is possible.
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Lewis, Eric Richard, "On the stress analysis of bimetallic packing rings" (2007). LSU Master's Theses. 2686.