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Automobile components are usually subjected to complex varying loads. Thus, fatigue failure is a common mode of failure in automobile components. Accurately predicting the fatigue life is the key point for light weight and also reliability design of automobile components. Various life prediction theories are being used in the automotive industry for damage analysis using material S-N curves. However, due to variability in manufacturing, material spec etc. it is difficult to predict the experimental lives using conventional theories. Probability based statistical modeling is prevalent in the industry for life prediction. Probabilistic plots of cycles to failure to constant amplitude loads are plotted and used for prediction purpose. As the component is subjected to varying loads in real world, defining a single parameter i.e. damage would be more relevant compared to loads.

BIW (Body-in White) is a type of vehicle structure formed by spot welding of different sheet metal components. The BIW structure should be designed to support the maximum load potential under various performance conditions. Thus the structure should have good strength as well as stiffness. Torsion Stiffness of BIW is the amount of torque required to cause a unit degree of twist. It is often considered as a benchmark of its structural competence due to its effect on various parameters like ride, handling, lateral load distribution and NVH performance of vehicle. The paper aims to design and develop a test methodology and test fixtures for measuring the BIW torsion stiffness with repeatability of test results and also have an (R2>0.99) for the measured values in the test.