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Acoustic characteristics of hydraulic dampers used in passenger cars are investigated. Experimentation work is carried out with servo hydraulic machine. Semi-anechoic chamber is used to isolate damper in order to study noise source in damper. Noise and vibration data analysis is performed with the help of OROS software. OROS provides noise and vibration testing solution. This is specifically used here for noise and vibration data acquisition and analysis for damper. Noise and vibration tests are performed by various frequencies and amplitude excitation inputs given to damper. As a part of low to mid frequency excitation, the amplitude of damper excitation is 20 mm in rebound and 10 mm in compression stroke of damper with data containing multiple input frequencies namely 0.5, 1, 1.5 and 2 Hz. This test condition ensured that the noise is perceived to car cabin by means of damper rather than filtration unit attached to damper.

Automotive shock absorber shims are subjected to deformation while generating the pressure differential across the rebound and compression chambers. Considering the contact, large deflection, and material this shim stack deformation will be nonlinear throughout the working velocity of shock absorbers. The deformation of shim stack mainly depends on number and geometry of deflection disk, number and geometry of ports, and clamping disk geometry on which shims are rested. During the rebound and compression stroke of the shock absorber, the oil flows through the piston and base valve ports. High pressure oil developed during mid and high velocity of shock absorber results in deflection of shim stack in piston and base valve assembly. This deflection leads to oil leakage through the shim stack which results in change in damping force by the shock absorber.

In an automotive twin tube shock absorber, thin structures used in piston and base valve sub-assembly are called shims. These shims are used in proper combination to achieve particular damping force characteristics and these shims will be operating continuously throughout the life of shock absorber. Any failure of shims during lab/ vehicle testing will increase the development time and cost considerably. Hence, predicting the operating life of shim assembly is very important during shock absorber development stage. In order to predict the life of the shim assembly, simulation techniques can be applied with fair degree of accuracy. Currently, during structural simulation of shim assembly, it is assumed that fluid pressure is acting uniformly over the entire shim to find stress intensity. This approximation is taken into account to predict the fatigue life of shim assembly. This paper proposes additional technique to carry out close to real life shim simulation.