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This paper describes the procedure of root cause analysis and evaluation of the life of a component that is prone to fatigue failures. The durability testing of components subjected to continuous vibrations in their operating conditions tend to fail after long period of exposure. This makes it difficult and time consuming to test and analyse them in the actual operating conditions. This paper establishes a method of accelerated durability testing for failure modes and life cycle based on the results of Frequency Response Function and modal analysis. This helped in reducing the product development / improvement time.

The duration for the development of a new vehicle model is continuously decreasing. This does not permit adequate time for proving component assemblies and vehicles to be evaluated for durability by conventional measures. However, increasing competition and quality consciousness calls for an assured life with a high degree of confidence. This has forced the test engineers to look for techniques for accelerating the durability evaluation. The technique calls for concepts for compressing the evaluation time. This can be achieved by compression in both time as well as frequency domain. Further, it also calls for correct techniques for the mixing of roads, extrapolation of data acquired over a small distance to the vehicle life, evaluation and elimination of non or less damaging inputs, etc. This paper reviews some of the existing techniques and describes case studies of how accelerated testing can be applied in vehicle development.

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.

The braking systems for vehicles are undergoing a continuous development and improvement. The recent trend in motorcycle industry is to go for front disc brake system to have the advantage of less stopping distance and efficient braking over conventional drum brakes. In India the present practice of replacing the drum brake assembly with disc brake assembly, without redesigning of complete assembly of shock absorber may adversely affect its durability. This paper presents a detailed study made through service load data acquisition and analysis on the strength of front shock absorber tube. It was observed that with disc brake there is considerable increase in bending stress on the inner steel tube of shock absorber during braking. This paper highlights the comparison of strain distribution of the shock absorber tubes in disc brake and drum brake and concludes with a need for better design/material for shock absorber tube.

Road surface, payload and speed of the vehicle are important parameters, which affect the life of a vehicle. This paper discusses the relationship between road/load/speed and damage to the vehicle as a whole and automotive structure in particular. This will help the designer to understand non-linear relationship between different service conditions and damage and to arrive at realistic input spindle loads for design considerations. This will also help the evaluation engineer in the development of durability cycle by correlating different environmental conditions with actual service conditions.

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.