Abstract—This paper investigates the effect of activation time on the behavior of hybrid semi-active suspensions that incorporate Shape Memory Alloy (SMA) components with Magnetorheological (MR) damping or piezoelectric actuation. A two-degree-of-freedom quarter-car model is used to compare three configurations: passive + SMA, SMA + MR, and SMA + piezoelectric actuator when subjected to harmonic, stochastic, and bump-type road inputs. The model was implemented in Python and tested on the displacement of the sprung mass, acceleration of the sprung mass, Fast Fourier Transform (FFT) response, Root Mean Square (RMS) acceleration, deflection of the suspension, and tyreload variation. Two activation strategies are considered: fixed-time engagement and threshold-based logic, which is triggered by the vibration level. The results show that activation time is not an additional design consideration; delayed activation increases peak response and settling time, particularly under transient disturbances. Within the present simulation framework, the SMA + piezoelectric layout provides the largest numerical reduction in body motion and acceleration, whereas the SMA + MR layout offers a more conservative balance between performance and implementation complexity. Frequency-domain results indicate lower resonance amplitudes for the two hybrid layouts than for the passive benchmark. Because the analysis is simulation-driven, the results should be interpreted as comparative trends rather than experimentally validated performance limits. The study clarifies design balance in hybrid smart suspensions and provides a repeatable platform for future experimental and hardware-in-the-loop validation.

Keywords—hybrid semi-active suspension, shape memory alloy, magnetorheological damper, piezoelectric actuator, activation timing, vibration control

Cite: Ala'a Al-Falahat, "Dynamic Response and Activation-timing Effects in Hybrid Shape Memory Alloy Semi-active Vehicle Suspensions," International Journal of Mechanical Engineering and Robotics Research, Vol. 15, No. 4, pp. 423-432, 2026. doi: 10.18178/ijmerr.15.4.423-432

Copyright © 2026 by the authors. This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).