Tractors, agricultural machines comprising diverse interconnected assemblies, collaboratively perform specific functions to attain desired outputs. Among these assemblies, the footstep assembly—an affixed structure or platform facilitating convenient access for the operator to the tractor cabin or platform. The components of the footstep assembly are fabricated from sheet metal and are connected using various joining technologies, such as bolts, welds, and others. During field operations, several failures have been noted in the footstep component, specifically at the weld connections. This paper delineates a methodology for simulating and predicting the occurrences of weld joint failures in the sheet-metal components.
The inherent characteristics of the welding process lead to welded joints generally exhibiting a fatigue strength lower than that of the individual parts being joined. Additionally, welds are frequently applied at geometric features or points of section changes within a structure. As a result, even in a structurally sound design, it is often the welded joints that are more susceptible to fatigue failure. Hence, a comprehensive assessment of the durability of a welded structure requires placing considerable emphasis on a thorough fatigue evaluation of the welded joints.
Existing codes and guidelines employed for analyzing the fatigue of welded joints are primarily formulated for the civil and maritime industries, where the customary material thickness exceeds 5 mm. For sheet-metal components with material thickness typically ranging from 1-3mm, these codes are not applicable. This paper employs the "Volvo Method," a technique developed at Chalmers University in collaboration with Volvo Car Corporation. This method relies on Finite Element fatigue assessments of welded joints. In the Volvo Method, the structural stresses at the weld toe are computed based on the nodal forces and moments in the weld toe or weld root elements. The life of the weld joints is calculated using nCode-Designlife, the software that implements this method.
A correlation analysis was conducted between the Finite Element (FE) results acquired through Computer-Aided Engineering (CAE) and the results from Fatigue Testing of the footstep assembly obtained in the laboratory (FTL). The location of the failure in the CAE precisely corresponds to the location identified in the testing and in observed field failures. A good correlation is established between the fatigue life predicted in CAE and the results obtained from the lab test.
The methodology utilized in this paper is specifically designed for sheet-metal components, limiting its applicability to components with higher thickness.
The "Volvo Method" provides a strong correlation between Computer-Aided Engineering (CAE) and test results for simulating and predicting the fatigue failure of weld joints in sheet-metal components. Given that tractors comprise multiple assemblies such as Hood Assembly, Fender Assembly, Scuttle Assembly etc., manufactured from sheet-metal components, this methodology proves highly beneficial in simulating the performance and durability of these assemblies.
Keywords: Footstep Assembly, Sheet-Metal, Finite-Element Analysis (FEA), Weld Fatigue, nCode-Desiglife, Volvo Method, CAE (Computer-Aided Engineering), Correlation.