PSD Profiles for Dynamic and Durability Tests of Military Off-Road Vehicle Racks

In a military off-road vehicle, generally designed to operate in an aggressive operating environment, the typical comfort requirements for trucks and passenger cars are revised for robustness, safety and security. An example is the cabin space optimisation to provide easy access to many types of equipment required on-board. In this field, racks hung to the cabin chassis are generally used to support several electronic systems, like radios. The dynamic loads on a rack can reach high values in the operative conditions of a military vehicle. Rack failures should be prevented for the safety of driver, crew and load and the successful execution of a mission. Therefore, dynamic and durability tests of these components, including the fixtures to the vehicle, are required. The capability to apply in a laboratory a dynamic load equivalent to the one experienced in a real mission opens the possibility to make durability tests in a controlled environment, to repeat them according to a defined methodology, potentially to accelerate the tests themselves, with clear benefits if the same validation should be done, otherwise, just on a proving ground. The definition of the excitation profiles for accelerated tests is not an easy task for the considered vehicle family. This paper proposes some guidelines to define realistic Power Spectral Density (PSD) profiles for dynamic and accelerated durability tests, based on the on-board actual vibrations measured levels. The PSD profiles are a combination of the vibration acquired on-board on several different stationary paths, synthesised on the vehicle life cycle environmental profile. The proposed approach aims at limiting expensive on-road tests for the dynamic and durability assessments of military vehicle equipment's.