A Non-Linear Finite Element Approach Applied to Diesel Piston Combustion Bowl Rim Strength Assessment

摘要

The single piece aluminium alloy piston remains the dominant and preferred design offering for highly loaded diesel engines. Piston manufacturers have progressively developed aluminium alloys, machining capability, and design geometries to cope with increasing thermal and mechanical loading. In conjunction with these developments, the methodology used to analyse the pistons has also improved as software and digital computers have advanced. This advancement has permitted larger more detailed models and more sophisticated simulation of the material behaviour, in response to the loading and contact conditions applied to pistons. Transient finite element analysis was first applied to diesel pistons in the late 1970's using a linear elastic approach, coupled with a life assessment based on limited low cycle fatigue data. This methodology gave valuable insights into the mechanism of piston failures, particularly at the combustion bowl rim of diesel pistons. The life assessments derived from this approach, however, tended to be approximate and could only be used as a comparative tool to assess alternative designs and materials. This limitation arose from the linear elastic stress approach, which ignored the important effects of non-linear strain behaviour, especially under the elasto-plastic conditions that exist around the combustion bowl rim. In combination with the improvements in analysis techniques, developments in strain based material property measurement gave further insights into the non-linear behaviour of the piston alloy and provided important data for modelling. These developments have been incorporated into a new methodology for analysing the stress and strain response at the bowl edge, which allows a more accurate approach to life assessment and opportunities to enhance the piston design still further.