Dynamic models for power transmission monitoring in non-stationary conditions based on IAS signals

•Semi-analytical dynamic model of transmission including gears, shafts, bearings.•Gear-bearing interactions through shaft speed generate modulations in IAS signal.•Bearing spall and gear spall and crack are investigated in non-stationary conditions.•Richness of IAS signals is directly related to cyclic excitations and modal behavior.•Impacts of damages suggest new analyses and indicators for transmission monitoring. This paper describes a dynamic model of two stage gear power transmission including shafts, ball and roller bearings as well as spur and helical gears. The fundamental objective of this model is to introduce a simulator of realistic signals for monitoring the dynamic behavior of such transmissions in non-stationary operating conditions. Special attention is paid to the couplings between mechanical components through the shaft rotation. The analyses carried out are mainly based on the Instantaneous Angular Speed (IAS) as an alternative signal to classical vibrations. Simulations have demonstrated the relevance of IAS as a tool for health monitoring of common gear or bearing faults in non-stationary operating conditions. Suggested angular approaches offer the ability to separate excitations from the transfer function of the system. The interactions between bearings and gears appear as modulation sidebands and suggest a new way to use demodulation methods. Finally, the influence and the detectability of damages on both mechanical components (spall on bearings, spall and crack on gears) using the mentioned techniques are discussed, offering new incomes for signal processing tools in gear transmission monitoring.