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A series of controlled impact experiments using a charpy pendulum were conducted to address the possibility of dynamic verification and calibration of instrumented tups. The methodology involved striking an instrumented pendulum tup against a rigidly fixtured transducer. The guiding principal is as follows: If a NIST traceable dynamic load cell is impacted by a service load cell, a comparison of the signals can be used to verify the performance of the service load cell. In this fashion, tups can be verified and calibrated electronically, without resorting to the use of standard test specimens. A relatively compliant Nylon bumper was placed between the pendulum tup and the fixed load cells to dampen the excitation of high frequencies during the impact event. During each impact, load-time signals measured by both the pendulum and fixtured tups were recorded, compared and Fourier analyzed. Results of the Fourier analysis justified a simple two-mass-two-spring model of the impact behavior. Results of the experiments are rationalized using the mass-spring model, and present guidelines for designing a verification system for both pendulum and drop-weight testing machines.
verifier tup, dynamic calibration, instrumented impact, Fourier analysis, viscous damping, stress waves, frequency spectrum, nylon alloy
Assistant Professor, The University of Illinois at Urbana-Champaign, Urbana, IL
GRC International Inc., Santa Barbara, CA