Ashley Spear

• Ph.D. Civil Engineering
• Professor (Associate) at University of Utah

The surface topography of 3D printed parts differs from that of wrought or machined parts of the same material. This work specifically focuses on Inconel 718 specimens manufactured with laser powder bed fusion (L-PBF). Predicting the surface topography of the as-built surfaces based on the L-PBF process parameters is important to manufacture parts...

Subtle differences among additive manufacturing (AM) processing parameters lead to variations in pore networks and complicate the prediction of void-sensitive mechanical behaviors, including location of fracture. The current work expands upon a recently developed pore metric, the void descriptor function (VDF), by accounting for interactions among...

Customized additively manufactured (laser powder bed fused (L-PBF)) stents could improve the treatment of complex lesions by enhancing stent-artery conformity. However, geometric irregularities inherent for L-PBF stents are expected to influence not only their mechanical behavior but also their interaction with the artery. In this study, the influe...

A framework for generating tetrahedral meshes of polycrystalline microstructures with optimal element-size distribution, as determined by the underlying defects (e.g., cracks and voids), is proposed. The framework utilizes a conformal surface mesh of each grain boundary and a point-cloud file to describe, respectively, the polycrystal and its under...

The efficacy of an elasto-viscoplastic fast Fourier transform (EVPFFT) code was assessed based on blind predictions of micromechanical fields in a sample of Inconel 625 produced with additive manufacturing (AM) and experimentally characterized with high-energy X-ray diffraction microscopy during an in situ tensile test. The blind predictions were m...

Metal additive manufacturing (AM) presents advantages such as increased complexity for a lower part cost and part consolidation compared to traditional manufacturing. The multiscale, multiphase AM processes have been shown to produce parts with non-homogeneous microstructures, leading to variability in the mechanical properties based on complex pro...

Skull fracture is a common finding for both accidental and abusive head trauma in infants and young children, and may provide important clues as to the energy and directionality of the event leading to the skull fracture. However, little is understood regarding the mechanics of skull fracture in pediatric skull, and how accidental fall parameters c...

The mechanical response of open-cell metallic foams depends strongly on their hierarchical structure, which ranges from the grain scale, to the scale of individual struts, to the scale of the bulk foam. The objective of this study is to investigate the effect of grain structure on the compressive mechanical response of open-cell metallic foam using...

Advances in additive manufacturing enable the production of tailored lattice structures and thus, in principle, coronary stents. This study investigates the effects of process-related irregularities, heat and surface treatment on the morphology, mechanical response, and expansion behavior of 316L stainless steel stents produced by laser powder bed...

Carbon fiber reinforced composites are finding increased usage in a wide variety of applications, ranging from aerospace to energy harvesting to sporting goods and more. Carbon fiber manufacturing is an extremely time- and cost-intensive process with more than 70 processing variables. To better understand the processing-structure-property relations...

Modern aerospace applications require lightweight materials with exceptionally high strength and sti_ness. Carbon nanotube (CNT)-reinforced composites have great potential in addressing these requirements. However, one critical factor limiting the potential of CNT-reinforced composites is the limited load transfer capability between CNTs through a...

The aim of the current study is to investigate the suitability of a solutionizing recrystallization (RC) heat-treatment to improve the yield strength of laser powder-bed fusion (L-PBF) Inconel 718 (IN718), while decreasing deformation anisotropy under uniaxial compression. Scanning electron microscopy measurements show an increase in grain size, de...

Infant skull fractures are common in both accidental and abusive head trauma, but identifying the cause of injury may be challenging without adequate evidence. To better understand the mechanics of infant skull fracture and identify environmental variables that lead to certain skull fracture patterns, we developed an innovative computational framew...

Porosity, a commonly occurring void defect in casting and additive manufacturing, is known to affect the mechanical response of metals, making it difficult or impossible to predict response variability. We introduce a new method of uniquely characterizing pore networks using a void descriptor function (VDF), which can be used to predict ductile-met...

This study investigates the effects of build orientation and laser-energy density on the pore structure, microstructure, and tensile properties of Inconel 718 manufactured by laser powder bed fusion. Three different build conditions were selected for comparison based on previous research (namely, the conditions that resulted in the worst and best f...

In this work, we investigate the performance of data-driven modeling for mechanical property prediction of a simulated microstructural dataset. The dataset comprises realistic microstructural subvolumes of metal additive-manufactured stainless steel 316L and corresponding effective mechanical properties that were generated with a physics-driven mod...

The microstructures of additively manufactured (AM) metal components have been shown to be heterogeneous and spatially variable when compared to conventionally manufactured counterparts. Consequently, the mechanical properties of AM-metal parts are expected to vary locally within their volume. For AM structural components intended to operate in ext...

Convected particle domain interpolation, which is known to boost the accuracy of the material-point method, is applied in a form called convected-particle tetrahedron interpolation (CPTI). CPTI exploits the efficiency of tetrahedral tessellations to represent complex structural geometries, while still solving field equations on a rectilinear backgr...

A method is introduced for determining the size of a representative volume element for microstructurally small cracks (RVEMSC) in heterogeneous, linear-elastic domains. RVEMSC is defined as the minimum volume required around a crack front such that crack-front parameters are converged with respect to volume size. This method uses finite element mod...

Metallic open-cell foams are promising structural materials with applications in multifunctional systems such as biomedical implants, energy absorbers in impact, noise mitigation, and batteries. There is a high demand for means to understand and correlate the design space of material performance metrics to the material structure in terms of attribu...

Readers should note that this article was originally published without the electronic supplementary material with which it is now published.

Three computational methods for modeling fracture are compared in the context of a class’ participation in the Third Sandia Fracture Challenge (SFC3). The SFC3 was issued to assess blind predictions of ductile fracture in a complex specimen geometry produced via additive manufacturing of stainless steel 316L powder. In this work, three finite-eleme...

The overarching aim of this paper is to explore the use of machine learning (ML) to predict the microstructure-sensitive evolution of a three-dimensional (3D) crack surface in a polycrystalline alloy. A convolutional neural network (CNN)-based methodology is developed to establish spatial relationships between micromechanical/microstructural featur...

The Sandia Fracture Challenges provide a forum for the mechanics community to assess its ability to predict ductile fracture through a blind, round-robin format where mechanicians are challenged to predict the deformation and failure of an arbitrary geometry given experimental calibration data. The Third Challenge (SFC3) required participants to pr...

Laser-induced keyholing occurs in additive manufacturing and welding processes, but the keyhole dynamics have not been well understood. A multiphase and multiphysics numerical model is used to predict the keyhole shapes recorded in the experimental observations and to predict transient and nonuni-form distributions of laser absorption, temperature,...

The development and use cases of an open-source filter for DREAM.3D that instantiates synthetic, grain-resolved, open-cell metal foam volumes are presented. The new capability allows for both synthetic-grain overlay of X-ray computed tomography data as well as fully synthetic foam geometry and grains. For the latter, a novel technique using Euclide...

This study investigates the relationships among the high-cycle fatigue life, surface roughness, and additive manufacturing processing parameters in laser powder bed fusion Inconel 718 in the as-built condition. Standardized fatigue specimens were manufactured using 25 different sets of processing parameters by varying laser power, scan speed, layer...

A framework for the simulation of fully arbitrary three-dimensional crack growth in heterogeneous materials is proposed. The framework relies on iteratively updating a voxel-based representation of a heterogeneous material and crack surface. The voxel-based framework operates by generating a conformal surface mesh from the voxel-based representatio...

The microstructure of additively manufactured (AM) metals has been shown to be heterogeneous and spatially non-uniform when compared to conventionally manufactured metals. Consequently, the effective mechanical properties of AM-metal parts are expected to vary both within and among builds. Here, we present a framework for simulating process–(micro)...

The complex mechanical response of open-cell foams depends strongly on the hierarchy of length scales inherent in them, from engineering-part scale to the ligament scale through the grain scale down to the crystal-lattice scale. A first step toward understanding and predicting the coordinated mechanical response across length scales requires charac...

Systematic correlation analysis was performed between simulated micromechanical fields in an uncracked polycrystal and the known path of an eventual fatigue-crack surface based on experimental observation. Concurrent multiscale finite-element simulation of cyclic loading was performed using a high-fidelity representation of grain structure obtained...

The goal of this work is twofold: 1) to determine the angular deflection and displacement of the NREL 5 MW reference wind turbine tower under different atmospheric thermal stratifications, and under overlapping wind turbine wake effects using a comprehensive numerical analysis; 2) to develop and verify a generalized analytical model allowing to eff...

Three stochastic open-cell aluminum foam samples were incrementally compressed and imaged using X-ray Computed Tomography (CT). One of the samples was created using conventional investment casting methods and the other two were replicas of the same foam that were made using laser powder bed fusion. The reconstructed CT data were then examined in Pa...

With the exciting potential of additive manufacturing of metals to produce geometrically complex structures come many unknowns and uncertainties regarding the process-microstructure-property relationships of the additively manufactured (AM) parts, especially in comparison to their conventionally manufactured counterparts. This work attempts to eluc...

In an effort to reproduce computationally the observed evolution of microstructurally small fatigue cracks (MSFCs), a method is presented for generating conformal, finite-element (FE), volume meshes from 3D measurements of MSFC propagation. The resulting volume meshes contain traction-free surfaces that conform to incrementally measured 3D crack sh...

An experimental methodology based on post-mortem measurements is proposed to quantify rates of propagation and crack-surface crystallography of a 3-D, naturally nucleated, microstructurally small fatigue crack (MSFC) in a polycrystalline aluminum alloy (Al–Mg–Si). The post-mortem characterization involves: scanning electron microscopy-based fractog...

Nickel-based superalloys are used widely in gas turbine engines for their excellent tensile strength and creep resistance at high temperatures. To improve damage assessment measures and aid in the design of next generation materials, there is a necessity to understand the fatigue cracking processes down to the microstructural scale. Microcrack nucl...

Critical steps toward designing and developing modern materials include observing, simulating, and predicting 3D deformation and cracking mechanisms at various length scales. In this work, advanced characterization and simulation techniques are employed to study the micromechanisms involved in nucleation and propagation of fatigue cracks in an alum...

This study examines the expected cost of repairing earthquake damage in a set of 30 archetype reinforced concrete moment frame buildings. Varying in height from 1 to 20 stories, these archetype buildings are representative of office buildings with special RC moment frames, designed according to modern seismic codes. Economic losses associated with...

Motivation to decrease weight and cost of composite-overwrapped pressure vessels used in space exploration leads to designs that challenge the current qualification standards and methods for predicting fatigue life of the structures. Namely, as thickness of the metallic, overwrapped liners is reduced (potentially to tens of grains through-thickness...

A surrogate-model methodology is described for real-time prediction of the residual strength of flight structures with discrete-source damage. Starting with design of experiment, an artificial neural network is developed that takes discrete-source damage parameters as input and then outputs a prediction of the structural residual strength. Target r...

In order to help building stakeholders make more informed seismic design decisions, PEER's performance-based earthquake engineering (PBEE) framework quantifies structural performance in terms of dollars, deaths, and downtime. Specifically, this research project focuses on the dollars aspect of building performance, or in other words, the repair cos...