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Publications

Search Publications by Akobuije Chijioke

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Displaying 1 - 14 of 14

CHARACTERIZATION OF LASER DOPPLER VIBROMETERS USING ACOUSTO-OPTIC MODULATORS

December 31, 2020
Author(s)
Michael Gaitan, Jon C. Geist, Benjamin J. Reschovsky, Akobuije Chijioke
We report on a new approach to characterize the performance of a laser Doppler vibrometer (LDV). The method uses two acousto-optic modulators (AOMs) to frequency shift the light from an LDV by a known quantity to create a synthetic velocity shift that is

Error Quantification in Dynamic Applications of Weakly Nonlinear Transducers

November 3, 2020
Author(s)
Lautaro D. Cilenti, Akobuije Chijioke, Balakumar Balachandran
Characterization and quantification of dynamic measurements is an ongoing area of research in the metrological community as new calibration methods are being developed to address dynamic measurement applications. The development undertaken to date largely

Design Considerations to Improve Charpy Instrumented Strikers

March 16, 2020
Author(s)
Nicholas Vlajic, Akobuije Chijioke, Enrico Lucon
Instrumented impact testing allows the applicability of conventional Charpy tests to be extended toward assessing mechanical properties such as dynamic fracture toughness and dynamic tensile properties. In this work, we present design considerations for

Generalized source-conditions and uncertainty bounds for deconvolution problems

October 1, 2018
Author(s)
Jake D. Rezac, Andrew M. Dienstfrey, Nicholas A. Vlajic, Akobuije D. Chijioke, Paul D. Hale
Many problems in time-dependent metrology can be phrased mathematically as deconvolution problems. In such cases, measured data is modeled as the convolution of a known system response function with an unknown input signal, and the goal is to estimate the

Investigations on SI-Traceable Dynamic Calibration of Instrumented Charpy Strikers

May 14, 2018
Author(s)
Akobuije D. Chijioke, Nicholas A. Vlajic, Enrico Lucon, Edward C. Mulhern
In this Technical Note, we report on investigations toward an SI-traceable dynamic calibration of instrumented Charpy strikers, performed at NIST from January to December 2017. Although Charpy tests are few-millisecond-duration events in which dynamic

Traceable Dynamic Calibration of Force Transducers by Primary Means

July 8, 2016
Author(s)
Nicholas Vlajic, Akobuije Chijioke
We describe an apparatus for traceable, dynamic calibration of force transducers using harmonic excitation, and report calibration measurements of force transducers using this apparatus. In the apparatus, the force applied to the transducer is produced by

Stress Analysis of Conical Contact Joints in the NIST 4.45 MN Deadweight Machine

May 10, 2016
Author(s)
Nicholas A. Vlajic, Akobuije D. Chijioke, Ricky L. Seifarth
Structural analysis of conical contact joints in the NIST 4.45 MN Dead Weight Machine using finite element analysis is presented in this paper. This analysis was undertaken due to the observation of surface damage in these joints. Parametric studies are

Elasticity of Mass Artifacts in Sinusoidal Force Calibration

September 4, 2015
Author(s)
Akobuije D. Chijioke, John C. Bankert
Dynamic calibration of force transducers using sinusoidal acceleration of load mass objects requires the accurate determination of the displacement field in such masses, in order to relate accelerations measured at one or a few locations on the load mass

Primary Sinusoidal Calibration of Force Transducers up to 2 Kilohertz

September 4, 2015
Author(s)
Akobuije D. Chijioke, Nicholas A. Vlajic
We report the implementation of a swept-sine dynamic force calibration system at NIST. This system is designed to perform primary calibration of force transducers at frequencies up to 2 kHz and forces up to 2 kN. We show an example calibration of a strain

Dynamic Force Calibration

October 1, 2014
Author(s)
Akobuije D. Chijioke, Nicholas A. Vlajic
The consequences of not knowing the value of measured forces in terms of meaningful units are significant. In the first place it becomes impossible to standardize an operation based on the measured force value so that it is independent of the particular

NIST 1-kilonewton sine force calibration system

January 22, 2014
Author(s)
Akobuije D. Chijioke, Ricky L. Seifarth, Zeina J. Kubarych
Many force-measurement applications are of a dynamic nature, and in recent decades there has been much progress in demonstrating and developing dynamic calibration systems for force transducers. The National Institute of Standards and Technology (NIST), U