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Fatigue design has to account for the scatter of component geometry, material behavior and loading. Scatter of the first two variables is mainly due to manufacturing and material sourcing. Loading on the other hand depends decisively on operating conditions and customer usage. Loading is certainly most difficult to determine. Tests on proving ground or even long-term real time measurements are used to obtain actual load time histories. Because of the costs of measurements and safety measure, real-time measurements are used exceptionally to gain changes in the usage profile. In this paper, an attempt has been made to find the difference in the extrapolated data to the actual data. A comparison has been made between the actual road distance of 2000 km to the extrapolated data of 100 km, 500 km and 1000 km to 2000 km. The front Axle channel is taken for the study.

For high degree of engine performance, it is imperative that all critical parts are designed and optimised through durability assessment. The conventional engine development programme based on actual engine test on test bed is time consuming and expensive, and is being replaced by use of simulation tools and accelerated component testing. The present work is a systematic fatigue strength evaluation programme for connecting rod of an up-rated Naturally Aspirated, Direct Injection, Inline Diesel Engine The established staircase method of fatigue test is slightly modified to minimise the effect of scatter in the results and to arrive at a consistent and dependable factor of safety. Also analytical tools like Finite Element Analysis (FEA) and Statistical Techniques were used; which helped to keep design and tooling iterations to a minimum and facilitated connecting rod development in the given time frame.

One of the primary concern during assessment of structural integrity of vehicle bodies is the quality of joints used therein. The increased trend in vehicle weight reduction (through use of thin sheet panels) calls for more critical evaluation of the quality of such joints. The electric Resistance Spot Welding (RSW) is one of the largely used joining process for vehicle body structure. Besides the quality of sheet metal, the quality of RSW joints is largely governed by the process parameters e.g. weld current, hold time, squeeze time etc. The quality of RSW joints for durability can be assessed by mechanical strength and fatigue life. The paper presents a methodology for durability assessment of such joints using laboratory specimens and arriving at optimum values of process parameters to maximise the fatigue life. The methodology presented makes extensive use of Design of Experiment (DOE) techniques for better reliability of the results.

Strain controlled tests were performed on 35 C8 steel specimens (IS 3930-1979) to determine cyclic stress-strain curve (CSSC) by Companion Specimens Test (CST), Multiple Step Test (MST) and Incremental Step Test (IST) procedures. A good agreement was found between the CSSCs obtained by CST and MST procedures. The CSSCs obtained by IST procedure using Incremental Step Loading Blocks (ISLB) of different maximum strain amplitude indicate that the parameters of CSSC depend on the maximum strain amplitude in the ISLB and resulted in a family of CSSCs. The dependence of CSSC parameters on the maximum strain amplitude in the ISLB are approximated by polynomials. Fatigue lives estimated based on IST results for irregular strain-time histories were found to be comparable with the experimentally evaluated fatigue lives.