Tom ClaptonMechanical Engineering BEng
Comparison of Welded Joint Design for Construction and Mining Equipment
As buildings grow taller, aircraft grow bigger and we search for natural resources in some of the world's most inhospitable regions engineers are facing up to the structural challenges these projects present. Since the BOAC comet crash in 1950 oil companies, aerospace engineers and construction vehicle manufacturers have invested millions researching and improving the weakest parts of these large structures with a primary focus on welded joints. This investigation has its origins in the construction vehicle industry and a shift in manufacturing processes for a large structural component on a twenty tonne hydraulic excavator. The primary focus was to build upon previous research to formulate a comprehensive understanding of design suitability for a range of joint details with varying geometric parameters under fatigue loads. Quite simply fatigue in this investigation has the same effect as bending a paper clip backwards and forwards until it breaks - measuring the number of movements as the life cycles to failure. More specifically this study utilised ISO standard fatigue tests and current fracture modelling methods to accurately predict and measure fatigue life in a single sided load carrying fillet weld. The independent variable is the inclusion of a 45˚ or 55˚ plate preparation which presented characteristic defects that directly impacted on the fatigue life achieved across 3 stress ranges. In addition the study introduced innovative computer modelling techniques and physical testing methods such as Finite element analysis and scanning electron microscopy. Such methods provide a more accurate understanding of fatigue failure in the case of a simple welded joint, whilst reducing the time and expenditure needed to complete such a study. However, to ensure relevance within industry experimental data gathered was analysed using the process outline in BS7608/ TWI ‘Best Practice Guide on Statistical Analysis of Fatigue Data' and compared with the reference ‘mean' fatigue life curve to determine accuracy.