Research is underway to establish an increased level of confidence
in existing numerical techniques for predicting transient behavior
when the fan of a jet engine is released and impacts the fan containment
system. To evaluate the predictive accuracy that can currently
be obtained, researchers at the NASA Lewis Research Center used
the DYNA 3D computer code to simulate large-scale subcomponent
impact tests that were conducted at the University of Dayton Research
Institute (UDRI) Impact Physics Lab.
In these tests, 20- by 40-in. flat metal panels, contoured to
the shape of a typical fan case, were impacted by the root section
of a fan blade. The panels were oriented at an angle to the path
of the projectile that would simulate the conditions in an actual
blade-out event. The metal panels were modeled in DYNA 3D using
a kinematic hardening model with the strain rate dependence of
the yield stress governed by the Cowper-Simons rule. Failure was
governed by the effective plastic strain criterion.
The figure shows the model of the fan blade and case just after
impact. By varying the maximum effective plastic strain, we obtained
good qualitative agreement between the model and the experiments.
Both the velocity required to penetrate the case and the deflection
during impact compared well. This indicates that the failure criterion
and constitutive model may be appropriate, but for DYNA 3D to
be useful as a predictive tool, methods to determine accurate
model parameters must be established.
Simple methods for measuring model parameters are currently being developed. In addition, alternative constitutive models and failure criteria are being investigated.
Previous articleLast updated April 30, 1997
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