Fixture Stiffness Impact on Spindle Coupled Multi-Axial Input Durability Test for Front or Rear Axle with Non-isolated Subframes

The half vehicle spindle-coupled multi-axial input durability test has been broadly used in the laboratory to evaluate the fatigue performance of the vehicle chassis systems by automotive suppliers and OEMs. In the lab, the front or rear axle assembly is usually held by fixtures at the interfaces where it originally connects to the vehicle body. The fixture stiffness is vital for the laboratory test to best replicate the durability test in the field at a full vehicle level especially when the subframe of the front or rear axle is hard mounted to the vehicle body. In this work, a multi-flexible body dynamics (MFBD) model in Adams/Car was utilized to simulate a full vehicle field test over various road events (rough road, braking, steering). The wheel center loads were then used as inputs for the spindle coupled simulations of the front axle with a non-isolated subframe. Three types of fixtures including trimmed vehicle body, a rigid fixture with softer connections and a rigid fixture with stiffer connections are considered in the front axle simulations. The strain response on the chassis structural components is compared from the full vehicle on-field simulation to the half vehicle on-rig simulations. Results indicate that the trimmed vehicle body test is similar to the full vehicle test in strain response only for some components and events. The impact of the boundary difference (inertia-reacted in full vehicle test verses fixed-reacted half vehicle test) is substantial. It was also found that there were minor differences in strain response among the two types of rigid fixtures for most of the cases. It's concluded that the fixture stiffness impact is relatively minor if they are not able to exactly match the vehicle body stiffness. The study provides valuable insights for engineers to select the appropriate fixtures for the half vehicle spindle coupled multi-axial durability test.