Resume

• 40974

  Engineer in Training (EIT)

  Texas Board of Professional Engineers

  United States Air Force Master Instructor

  Unites States Air Force

• 2012

  Doctor of Philosophy (PhD)

  Mechanical Engineering

  The University of Texas at San Antonio

  (3.89 GPA)

• 2009

  Master of Science (MS)

  Masters Thesis: “A Complex Finite Element Method to Compute Accurate Weight Functions”

  Mechanical Engineering

  The University of Texas at San Antonio

  (3.21 GPA)

• 2003

  Bachelor’s Degree

  Civil Engineering

  Tau Beta Pi

  The University of Texas at San Antonio

  Magna Cum Laude (3.83 GPA)

• 1989

  Associate’s Degree

  Applied Science

  Bioenvironmental Engineering Technology

  Community College of the Air Force

• Matlab

  Finite Element Analysis

  Simulations

  Fortran

  LaTeX

  Data Analysis

  Algorithms

  Mathematical Modeling

  C

  Numerical Analysis

  2D weight function development using a complex Taylor series expansion method

  Harry Millwater

  Weight functions are a critical component of a damage tolerance fracture control planthat they allow the stress intensity factor to be computed quickly from the stress along the uncracked crack line. The traditional method to compute weight functions is to use several (2–4) reference stress solutions or auxiliary conditions to develop the coefficients inseries solution. While this method has been shown to provide good results in many scenarios

  the truncated series provides a source of error that is difficult to quantify and the method requires multiple high-quality reference solutions or other auxiliary information. In contrast

  the WCTSE method presented here

  provides a method to accurately and efficiently develop the weight function for an arbitrary geometry and loading scenario fromsingle complex variable finite element solution without other reference solutions or auxiliary information. The complex Taylor series expansion method is used within the finite element formulation to obtain the derivatives of the crack opening displacements with respect to crack length directly from the finite element analysis. These derivatives allow the direct evaluation of the weight function. The method requires a small perturbation of the crack length along the imaginary axis; the real coordinate mesh is unaltered. Since the real coordinate mesh is unaltered

  standard finite element meshes and meshing algorithms can be used. Given that the error in the weight function is controlled by the accuracy of the mesh

  typical convergence tests can be used to obtain high confidence in the weight functions. Several numerical examples are computed and compared to other well known published weight function solutions or finite element (J integral) or boundary element solutions.

  2D weight function development using a complex Taylor series expansion method

  Andrew Baines

  Harry Millwater

  Engineering Fracture Mechanics

  The WCTSE (Weight function Complex Taylor Series Expansion) method was recently proposed as a new method for generating 2D weight functions. WCTSE uses a complex variable finite element formulation (ZFEM) to directly compute the derivative of the crack opening displacement with respect to crack length needed for 2D weight functions. The original WCTSE method is further refined in this manuscript through two significant advancements: (1) the methodology has been implemented in the Abaqus commercial finite element program through the use of a user element

  and (2) the complex Taylor series expansion method is also used to compute the energy release rate directly from the complex variable finite element analysis; therefore

  an independent reference solution for the stress intensity factor is not required. The mode I weight function for a through crack approaching a hole is computed using Abaqus and verified against explicit J-integral results. The results are shown to be very accurate.

  Improved WCTSE method for the generation of 2D weight functions through implementation into a commercial finite element code

  Arturo Montoya

  Harry Millwater

  The complex-valued finite element method

  ZFEM

  is proposed as a new virtual crack extension method to compute the energy release rate. The energy release rate is computed as a numerical derivative of the strain energy with respect to a crack extension using the complex Taylor series expansion method (CTSE). This is accomplished using a finite element method with complex nodal coordinates and extending the crack by a very small quantity along the imaginary directions of the complex nodal coordinates. The resulting finite element formulation becomes complex valued with the imaginary component of the strain energy containing the energy release rate. This method retains the conceptual simplicity of numerical differentiation but eliminates numerical issues regarding perturbation of the crack size. Both two- and three-dimensional examples are provided. Numerical examples indicate that the energy release rate computed using ZFEM is of the same accuracy as the domain-based J integral formulation. The method is very general and can be applied to self-similar or non-self-similar crack extensions.

  A virtual crack extension method to compute energy release rates using a complex variable finite element method

  David

  Wagner

  United States Air Force

  The Kevric Company

  The University of Texas at San Antonio

  Finite Element Method (FEM) research

  developing and testing new algorithms

  programming in Fortran

  MatLab/Octave

  and Python

  custom Abaqus methods.

  The University of Texas at San Antonio

  Active Duty

  Bioenvironmental Engineering Technician: monitoring compliance with environmental protection

  industrial hygiene

  workplace safety; last four years as a teacher/trainer (Master Instructor).

  United States Air Force

  Internet Application Developer

  Developed internet

  database

  and office automation software for an engineering firm

  The Kevric Company