John Usher


John S. Usher, Ph.D., P.E. is a Professor of Industrial Engineering. He served as Acting Dean of Engineering from July 2015 through June 2017, as the Associate Dean for Administration, Planning and Faculty Affairs, August 2012 through June 2015, and as Chair of the Department of Industrial Engineering from July 2005 through August 2012.


  • Ph.D. in Industrial Engineering, North Carolina State, 1987
  • M.Eng. in Industrial Engineering, University of Louisville, 1981
  • B.S. in Industrial Engineering, University of Louisville, 1980


Weibull growth modeling of laser-sintered nylon 12- 2013

Purpose - This paper seeks to present the results of an experiment to investigate the effect of six part orientation (XY, XZ, YX, YZ, ZY, ZX) and a wide range of energy densities on ultimate tensile strength (UTS) and elongation of laser-sintered nylon 12 (PA-12) test specimens. Design/methodology/approach - ASTM Type 1 specimens were built on a DIM Sinterstation 2500 + and tensile tested on an lnstron 5569 A. The resulting data were fit to non-linear regression models based on the well-known Weibull growth model to predict each response based on the total energy density used in each trial. Findings - The resulting regression models provide excellent fits with low sum of squared errors and normally distributed residuals. The resulting material properties are highly affected by the energy density and the build orientation. However, once sufficient energy density is applied, properties tend to converge to consistent values. To achieve maximum UTS of approximately 52 MPa, it is recommended that values of energy density above 0.25 W-s per mm(3) be used. To achieve maximum elongation of approximately 15-16 percent, it is recommended that values of energy density above 0.40 W-s per mrn(3) be used when building parts in the XY, XZ, YX, YZ orientations. Parts built in the ZX orientation exhibit lower elongation values at or below 12 percent for even high values of energy density. Originality/value - This paper extends previous work of Starr, Gornet and Usher on the relationship between material properties, part orientation and energy density by proposing the use of the Weibull growth model. Recommendations are provided to assist users in the selection of correct energy density to achieve desirable mechanical properties in each specified orientation.

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