Abstract
This thesis presents the results of a comparative study on the thermal deformation of a bimetallic diesel engine piston using finite elements and holographic interferometry. As a result of the complexity of the piston design and the unknown in-built stresses certain assumptions were necessary in the generation of the finite elements model. By using the holographic technique for direct measurement of the deformation for a 45° sector of the piston surface it was possible to check the effects of these assumptions and to improve the accuracy of the model.The comparison was carried out for two temperature ranges: 50°C to 60°C and 130°C to 140°C. At the lower temperature range the predicted profile was found to have a greater inward curvature at about mid-skirt height when compared to the measured profile. This was attributed to the assumptions made in the model with regard to the method of attachment of the steel sleeve insert to the piston skirt. At the higher temperature range, the original model was found to be incapable of predicting the true deformation profile. This is due to a separation that occurs between the insert and the skirt at a temperature above 130°C. Attempts made to match the predicted and measured profiles by releasing the insert from the skirt in the finite element analysis were only partly successful, suggesting that the true separation process is complex and may not be easily modelled. The holographic measurement, however, provided the true deformation profile of the piston at the two temperature ranges.
A comparative study on the use of the holographic method and ESPI (electronic speckle pattern interferometry) for the measurement of piston deformation has also been carried out. In this part of the study, a simplified ESPI method was used for measuring two displacement components simultaneously using an out-of-plane sensitive interferometer. A critical comparison of the two techniques as applied to the measurement of a thermally deforming piston has also been made.
| Date of Award | 1991 |
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| Original language | English |
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