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Paul Allison

Associate Professor

The P.G. Allison Research Group conducts research characterizing the structure-property-processing relations of a variety of material systems to support basic and applied research projects. The research examines many different material systems, including ferrous and non-ferrous alloys, ceramics,...
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experience

Assistant Professor  
The University of Alabama, August 2014 to Present, Tuscaloosa, Alabama United States



Research Mechanical Engineer  
US Army Corps of Engineers, August 2009 to August 2014

Research Mechanical Engineer in the Concrete and Materials Branch of the Geotechnical and Structures Laboratory located at the US Army Engineer Research and Development Center. The group conducts research and provides engineering support relating to construction materials (concrete and steel), advanced cement-based materials, advanced metallic and ceramic materials, bio- and bio-inspired materials, alternative cementitious binders, and geologic materials in support of US Army and US Army Corps of Engineers civil works and military engineering missions. My research focused primarily on the structure-property relations of materials for civil and military infrastructure systems with a focus on force protection and infrastructure durability. Specialties: Mechanical property testing, microstructure characterization, and finite element analysis.

Graduate Research Assistant  
Mississippi State University, August 2005 to July 2009

• Experimental quantification of structure-property relations of a powder metallurgy steel for model correlation and validation of an internal state variable plasticity-damage model and multistage fatigue model. • Performed tension, compression, and torsion tests at ambient and high temperatures and at low and high strain rates. • Performed low-cycle fatigue tests at zero and non-zero mean stresses. • Characterized microstructure of specimens using scanning electron microscopy and optical microscopy.

education

Mississippi State University  
PhD, Mechanical Engineering, Jan, 2005 to Jan, 2009


publications

In-situ nanomechanical studies of deformation and damage mechanisms in nanocomposites monitored usin     
Published by (Materials Letters)
Authors: Paul Allison, Robert Moser, Brian Jordon, Jeffrey Schirer, Richard Martens, Mei Chandler.  Published June 11, 2014

Mechanical properties and structure of the biological multilayered material system, Atractosteus spa     
Published by (Acta Biomaterialia)
Authors: Paul Allison, Robert Moser, Charles Weiss, Brandon Lafferty.  Published November 10, 2012

During the last few decades, research on biological systems such as abalone shell and fish armor revealed that these biological systems employed carefully- arranged hierarchical multilayered structures to achieve properties of high strength, high ductility, and light weight. Knowledge of such structures may enable pathways to design bio-inspired materials for various applications. This study was conducted to investigate the spatial distribution of structure, chemical composition, and mechanical properties in mineralized fish scales of the species, Atractosteus spatula. Microindentation tests were conducted and cracking patterns and damage sites in the scales were examined to investigate the underlying protective mechanisms of fish scales under impact and penetration loads. A difference in nanomechanical properties was observed, with a thinner, stiffer and harder outer layer (indentation modulus ≈69 GPa and hardness ≈3.3 GPa) on a more compliant and thicker inner layer (indentation modulus ≈14.3 GPa and hardness≈0.5 GPa). High resolution SEM imaging of a fracture surface revealed that the outer layer contained oriented nanorods embedded in a matrix, and that the nanostructure of the inner layer contained fiber-like structures organized in a complex layered pattern. Damage patterns formed during microindentation show complex deformation mechanisms. Images of cracks identify growth through the outer layer, then deflection along the interface before growing and arresting in the inner layer. High magnification images of the crack tip in the inner layer show void-linking and fiber-bridging exhibiting inelastic behavior. The observed difference in mechanical properties and unique nanostructures at different layers may have contributed to the resistance of fish scales to failure by impact and penetration loading.

Nanomechanical and chemical characterization of the interface between concrete, glass–ceramic bondin     
Published by (Contruction and Building Materials)
Authors: Paul Allison, Robert Moser, Charles Weiss, Sean Morefield.  Published November 01, 2012

A glass–ceramic coating made by fusing dicalcium silicate and tricalcium silicate to the surface of glass-enameled steel has been successfully used to increase the bond between reinforcing steel and concrete and provide corrosion protection for the steel. A very strong interface that consists of hydrated cement and enameled glass over the top of a second strong interface between the enameled glass and the surface of the steel results from the outer layer of water-reactive silicates hydrating on contact with fresh concrete. Currently the mechanical characteristics (hardness, elastic modulus and strain-rate sensitivity), micromorphology, and the variation in interface chemical composition are being examined. Preliminary results indicate that the more gradual transition between the mechanical properties of the steel and the paste combined with improved integration between the coating and cement hydration products in the paste results in the increased bond strength observed in macroscale tests. Results from this study to characterize the developed coating are being used to engineer new optimized enamels for this unique application.

Strain-controlled low-cycle fatigue properties of extruded 6061-T6 aluminum alloy     
Published by (Journal of Materials Engineering and Performance)
Authors: Paul Allison, Brian Jordon.  Published September 06, 2012

Tungsten toxicity, bioaccumulation, and compartmentalization into organisms representing two trophic     
Published by (Environmental Science & Technology)
Authors: Paul Allison.  Published August 08, 2012

Infilling of porous materials with various polymorphs of calcium carbonate by an electromigration te     
Published by (Journal of Applied Electrochemistry)
Authors: Paul Allison, Robert Moser, Ruth Hidalgo-Hernandez, Charles Weiss.  Published October 29, 2012

Production of mixed carbonate phases using ammonium carbonate-metal acetate reactions     
Published by (Bioinspired, Biomimetic and Nanobiomaterials)
Authors: Paul Allison, Charles Weiss, Robert Moser, Ruth Hidalgo-Hernandez, Sean Morefield.  Published July 23, 2012

Materials such as bone, nacre and fish scales have unique structures that give the material strength as well as ductility. The ultimate goal of our research is to develop new composite materials that have improved strength and ductility compared to conventional materials. The US Army Engineer Research and Development Center is incorporating these design principles to develop hierarchical materials for structural applications. In the present study, the mineralogy and morphology of calcium-containing carbonates precipitated by reacting (NH4)2CO3 with mixed Ca, Sr, Mg, and Mn-acetates was investigated. As the proportion of the non-Ca component increased, the products shifted toward double carbonates and mixtures of double carbonates with single carbonates. Characterization by scanning electron microscopy and X-ray diffraction to determine crystal sizes, morphology, and structure of precipitated phases indicated a potential for re-crystallizing the products to form new composite materials. Ongoing research efforts are focused on using information obtained in the present study to develop composites by hydrothermal recrystallization of metastable phases.

Sensitivity and uncertainty analysis of microstructure–property relationships for compacted powder m     
Published by (Powder Metallurgy)
Authors: Paul Allison.  Published June 01, 2010

In an earlier study, the authors presented a characterisation of the FC-0205 Ancorsteel powders containing 0·6 and 1·0% Acrawax to define the evolution of the failure line and cap surface of the modified Drucker/Prager cap model during compaction. Using the results of that study (i.e. FC-0205 material parameters), this paper presents sensitivity and uncertainty analysis of the microstructure–property relationships for powder metallurgy compaction. It is found for all of the responses of interest (the compressibility curve, the interparticle friction, the material cohesion, the cap eccentricity and the elastic modulus) that the most dominant parameter is the initial (or tap) density. It is also observed that the uncertainty in output parameters for the case of 1% wax is much larger than those for the case of 0·6% wax, due to the large uncertainty in the failure stress (in particular, the compressive failure stress).

Modulus dependence on large scale porosity of powder metallurgy steel     
Published by (Journal of Materials Engineering and Performance)
Authors: Paul Allison.  Published July 05, 2011

Microstructure–property relations of a steel powder metal under varying temperatures, strain rates,     
Published by (Materials Science and Engineering: A)
Authors: Paul Allison, Mark Horstemeyer, Youssef Hammi, Matthew Tucker.  Published November 25, 2011

Improvement in the geopolymer-to-steel bond using a reactive vitreous enamel coating     
Published by (Construction and Building Materials)
Authors: Paul Allison, Robert Moser, weiss, Brett Williams.  Published September 01, 2013

Plasticity and Fracture Modeling/Experimental Study of a Porous Metal under Various Strain Rates, Te     
Published by (Journal of Engineering Materials and Technology)
Authors: Paul Allison, Youssef Hammi, Mark Horstemeyer.  Published September 19, 2013

A microstructure-based internal state variable (ISV) plasticity-damage model was used to model the mechanical behavior of a porous FC-0205 steel alloy that was procured via a powder metal (PM) process. Because the porosity was very high and the nearest neighbor distance (NND) for the pores was close, a new pore coalescence ISV equation was introduced that allows for enhanced pore growth from the concentrated pores. This coalescence equation effectively includes the local stress interaction within the interpore ligament distance between pores and is physically motivated with these highly porous powder metals. Monotonic tension, compression, and torsion tests were performed at various porosity levels and temperatures to obtain the set of plasticity and damage constants required for model calibration. Once the model calibration was achieved, then tension tests on two different notch radii Bridgman specimens were undertaken to study the damage-triaxiality dependence for model validation. Fracture surface analysis was performed using scanning electron microscopy (SEM) to quantify the pore sizes of the different specimens. The validated model was then used to predict the component performance of an automotive PM bearing cap. Although the microstructure-sensitive ISV model has been employed for this particular FC-0205 steel, the model is general enough to be applied to other metal alloys as well.

A Fatigue Model for Discountinuous Particulate-Reinforced Aluminum Alloy Composite: Influence of Mic     
Published by (Journal of Materials Engineering and Performance)
Authors: Paul Allison, Robert "Bobby" McCullough, Brian Jordon, Andrew Brammer, K. Manigandan, T.S. Srivatsan.  Published October 01, 2013

ERDC/GSL TR-13-15 Electromigration and deposition of micro-scale calcium carbonate structures with c     
Published by (ERDC Technical Report)
Authors: Paul Allison, Robert Moser, Charles Weiss, Mei Chandler.  Published January 01, 2013

ERDC/GSL TR-13-16 Synthesis of carbonate-based micro/nanoscale particles with controlled morphology     
Published by (ERDC Technical Report)
Authors: Paul Allison, Robert Moser, Charles Weiss, Mei Chandler.  Published January 01, 2013

ERDC/GSL TR-13-17 Spatially-resolved characterization techniques to investigate impact damage in ult     
Published by (ERDC Technical Report)
Authors: Paul Allison, Robert Moser, Mei Chandler.  Published January 01, 2013

Characterization Of Multi-layered Fish Scales (Atractosteus spatula) Using Nanoindentation, X-ray CT     
Published by (Journal of Visualized Experiments)
Authors: Paul Allison, Brandon Lafferty, Robert Moser, Rogie Rodriguez, Brett Williams, Aimee Poda, Alan Kenn.  Published July 01, 2014

Microstructure, Texture, and Mechanical Properties of Friction Stir Spot Welded Rare-Earth Containin     
Published by (Materials Science and Engineering: A)
Authors: Paul Allison, Harish Rao, Rogie Rodriguez, Brian Jordon.  Published 

Abstract The effect of friction stir spot welding process parameters on the microstructure, texture, and mechanical properties of ZEK100 (Mg-1.0 wt%Zn-0.5 wt%RE-0.5 wt% Zr) Mg alloy was investigated. Lap-shear joints were prepared using two different tool rotational speeds (1500 and 2250 rpm) and three different shoulder plunge depths (0.0, 0.2, 0.6 mm). Microstructure analysis revealed significant grain refinement in the stir zone, when compared to the base material. Electron backscatter diffraction analysis revealed a strong texture development in the keyhole periphery and adjacent regions despite the presence of RE-elements, however, no significant texture variation was observed within the process parameters. These results suggest that the ultimate failure of the weld is more attributed to macroscopic features such as the bond width and upper sheet thickness rather than texture development. Keywords Friction stir spot welding; Magnesium alloys; Rare-earth element; Electron backscattering diffraction (EBSD); Texture development

Finite Element Modeling of Multilayered Structures of Fish Scales     
Published by (Journal of Mechanical Behavior of Biomedical Materials)
Authors: Paul Allison, Robert Moser, Rogie Rodriguez, Alan Kennedy.  Published January 01, 2014