Continuing prior work, which established a simulation workflow for fatigue
performance of elastomeric suspension bushings operating under a schedule of
6-channel (3 forces + 3 moments) road load histories, the present work validates
Endurica-predicted fatigue performance against test bench results for a set of
multi-channel, time-domain loading histories. The experimental fatigue testing
program was conducted on a servo-hydraulic 3 axis test rig. The rig provided
radial (cross-car), axial (for-aft), and torsional load inputs controlled via
remote parameter control (rpc) playback of road load data acquisition signals
from 11 different test track events. Bushings were tested and removed for
inspection at intervals ranging from 1x to 5x of the test-equivalent vehicle
life. Parts were sectioned and checked for cracks, for point of initiation and
for crack length. No failure was observed for bushings operated to 1 nominal
bushing lifetime. After 3 nominal bushing lifetimes, cracks were noted in
several locations. Corresponding fatigue simulations considered rubber’s
hyperelastic and fracture mechanical behavior (including strain crystallization
effects), the nonlinear mapping from loads to strains, interpolation of the
multichannel loading history to produce strain history using the Endurica EIE
solver, and the computation of fatigue life using the Endurica DT incremental
fatigue solver. The simulation indicated crack development at 2.0 nominal lives
for cracks on the outside diameter of the flange end, 2.6 lives for cracks on
the inside diameter of the flange end, and 4.8 lives for cracks in the center of
the inner metal. Predicted crack development was in general agreement with
observed crack development in terms of both location and duration, with some
indication that crack precursors on the rubber-metal interface may be slightly
larger than assumed based on characterization of the bulk rubber itself.