This report details continuing work examining the fatigue life durability of a US Army Trailer. This report describes, through example, a process to evaluate and reduce the experimental data needed for a Mechanical Systems Physics-of- Failure analysis. In addition the report describes the process used to validate the computer simulation models.

Purpose

Evaluate and reduce the experimental data obtained during testing of an instrumented trailer.

Project Results

The results of the project can be split into three areas; experimental data evaluation, dynamic model comparison, and fatigue life validation.

In the experimental data evaluation, it was hypothesized that the hydraulic surge brakes contributed to the fatigue-related failures of the trailer drawbar. Using principal component statistical analysis, it is shown that the surge brakes have little effect on the fatigue damage. Additionally, the principal component analysis reveals that the vertical accelerations and the yaw rate of the trailer were the primary contributors to the strain, which was measured close to the point of failure.

The multi-body dynamic simulation model was compared to measured accelerations and angular rates. The longitudinal and vertical accelerations were the best matches, using both Power Spectral Density (PSD) and statistical distribution comparisons. The worst comparison data was the transverse acceleration and yaw rate. Reasons for the poor matches for these signal components are both the tire model, which does not generate lateral forces based on terrain geometry, and the profilometry data used in the simulations, since it represents only the terrain elevation along the longitudinal path of the vehicle and not the spatial geometry of the terrain under the tire contact patch.

Finally, the fatigue life predictions were calculated using both rigid- and flexible-body simulations and experimental results. The fatigue life predictions show that using a CAE procedure for durability analysis is feasible provided that care is taken in the development of the CAD and dynamics models. The flexible body is necessary for obtaining accurate life predictions, however, using the flexible body simulation requires careful selection of the static correction mode shapes. High frequency modes should not be included since the trailer frame is a low frequency structure.