<![CDATA[The suspension system plays a critical role in maintaining vehicle ride comfort, stability, and safety by attenuating vibrations induced by road surface irregularities. Progressive degradation of shock absorbers reduces damping capability, leading to significant changes in vehicle dynamic behavior. This study investigates the effects of shock absorber degradation on vehicle dynamic responses using a four-degree-of-freedom (4-DOF) half-car model and proposes a Fault Severity Index (FSI) as a quantitative indicator of suspension fault severity. Numerical simulations were conducted in MATLAB considering damping coefficient degradation levels of 0%, 25%, 50%, 75%, and 90%. The results show that increasing degradation raised RMS displacement from 0.00133 m to 0.00430 m (223%), suspension travel from 0.00170 m to 0.00482 m (184%), and dynamic tire load from 229.8 N to 543.8 N. The proposed FSI increased progressively from 0 to 183.47, enabling quantitative discrimination of suspension fault severity. Curve-fitting analysis demonstrated that the relationship between degradation and RMS displacement was better represented by a quadratic model (R² = 0.9672) than by a linear model (R² = 0.8162). The findings indicate that RMS displacement, suspension travel, dynamic tire load, and the proposed FSI are the most sensitive indicators for detecting shock absorber degradation. The proposed FSI represents the main contribution of this study and shows strong potential for vibration-based condition monitoring and predictive maintenance of automotive suspension systems.]]>
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