Gregg M Janowski | University of Alabama at Birmingham (original) (raw)

Papers by Gregg M Janowski

The journal of prosthetic dentistry/The Journal of prosthetic dentistry, Jul 1, 2024

Proceedings, annual meeting, Electron Microscopy Society of America, 1992

The II-VI semiconducting alloys, such as mercury zinc telluride (MZT), have become the materials ... more The II-VI semiconducting alloys, such as mercury zinc telluride (MZT), have become the materials of choice for numerous infrared detection applications. However, compositional inhomogeneities and crystallographic imperfections adversly affect the performance of MZT infrared detectors. One source of imperfections in MZT is gravity-induced convection during directional solidification. Crystal growth experiments conducted in space should minimize gravity-induced convection and thereby the density of related crystallographic defects. The limited amount of time available during Space Shuttle experiments and the need for a sample of uniform composition requires the elimination of the initial composition transient which occurs in directionally solidified alloys. One method of eluding this initial transient involves directionally solidifying a portion of the sample and then quenching the remainder prior to the space experiment. During the space experiment, the MZT sample is back-melted to e...

Noise Control and Acoustics, Nov 14, 1999

Low velocity impact response (LVIR) of glass reinforced polymer composites (GRPCs), which have th... more Low velocity impact response (LVIR) of glass reinforced polymer composites (GRPCs), which have the potential to self repair both micro- and macro-damage, has been investigated. This class of materials falls under the category of passive smart polymer composites. The self-repairing mechanism is achieved through the incorporation of hollow fibers in addition to the normal solid reinforcing fibers. The hollow fibers store the damage-repairing solution or chemicals that are released into the matrix or damaged zone upon fiber failure. Plain-weave S-2 glass fabric reinforcement, DERAKANE vinyl ester 411-C50 and EPON-862 epoxy resin systems were considered for this study. Different tubing materials were investigated for potential use for storing the repairing chemicals instead of the actual hollow repair-fibers and included borosilicate glass micro-capillary pipets, flint glass Pasteur pipets, copper tubing and aluminum tubing. Composite panels were fabricated by using vacuum assisted resin transfer molding (VARTM) process. The present investigation addressed fabrication of self-repairing composite panels, the processing quality, selection of storage material for the repairing solution and, release and transportation of repairing solution.

The influence of test conditions on the low velocity impact (LVI) response and damage evolution i... more The influence of test conditions on the low velocity impact (LVI) response and damage evolution in neat resin plaques was investigated and documented. Specifically, the effect of impactor mass, velocity, and corresponding impact energy on the LVI response and damage evolution in unreinforced DERAKANE vinyl ester 411-350-resin system was studied. An instrumented drop weigh test machine was used to conduct the low velocity impact tests. The room temperature response of the material to impact loading and damage evolution was investigated using the impact load histories, impact plots and fractography analysis. This study is built upon previous work by the authors on LVI of neat resin systems, particularly those that have emerged as a new class of resins in liquid molding process. The study was motivated by the need for data and understanding of the failure characteristics of the individual constituents of a composite material such as in modeling of damage propagation and failure criteria analysis. For constant impact velocity, the time-to-maximum load (tm), total impact duration (tt), and the energy-to-maximum load to total energy absorbed (Em/Et) ratio increased, and energy absorbed after peak load (Ep) decreased with the mass of the impactor. For constant impactor mass, the time-to-maximum load and total impact duration decreased, the Em/Et ratio remained fairly the same, and energy absorbed after peak load increased with velocity; i.e., the impact velocity and mass had opposing effects on the time-to-maximum load, the total impact duration, Em/Et and energy absorbed after peak load. A single layer of plain-weave S2-glass fabric was incorporated in some of the unreinforced plaques in order to analyze the influence of reinforcement on the impact response and damage evolution. Insertion of a fabric layer aided in containment of the damage within the bounds of the specimen and to isolate the failure characteristics, which enabled further analysis of the impact response and damage evolution.

Journal of Prosthetic Dentistry, Aug 1, 2022

Noise Control and Acoustics, Nov 15, 1998

The room temperature impact response of DERAKANE 411-350 vinyl ester neat resin system (unreinfor... more The room temperature impact response of DERAKANE 411-350 vinyl ester neat resin system (unreinforced matrix) has been investigated as a function of sample thickness and impact energy level. Vinyl ester resins are of interest in ballistic applications such as in armored vehicles. The response of neat resin to impact loading was investigated using the impact load histories (load-time and load-deflection traces), impact plots and fractography analysis. The maximum load or peak contact force, energy to maximum load, total energy and deflection at maximum load were found to increase in a nearly parabolic manner with increase in impact energy level, whereas time-to-maximum load or impact duration at the peak load decreased linearly. Total energy-to-impact energy ratio changed in a step-wise manner with impact energy. The slope of the load-deflection (load-time) traces, which is related to the impact modulus or relative stiffness of the material, increased with impact energy level and sample thickness. The change of slope with impact energy level and sample thickness indicated the dependence of impact modulus on the impact energy level and target geometry. The threshold impact energy levels, which were associated with the onset of catastrophic matrix failure and extensive tensile strength losses, were identified from the impact plots. Multiple radial cracking, perforations in the form of a truncated cone at the point of impact and support induced damage were identified as the dominant failure characteristics.

Proceedings ... annual meeting, Electron Microscopy Society of America, Aug 1, 1993

Bulk growth of II-VI semiconductors such as HgZnTe (MZT) is difficult because of the gravity-indu... more Bulk growth of II-VI semiconductors such as HgZnTe (MZT) is difficult because of the gravity-induced convection that occurs during solidification. This convection can lead to crystal defects (primarily dislocations and subgrain boundaries) and composition inhomogeneities which may limit device performance. Crystals grown in the low-gravity environment of space should have fewer of these defects. However, the limited duration of space shuttle experiments and the need for uniform composition make it imperative that the initial composition transient that occurs in directionally solidified alloys be eliminated. One proposed solution to this problem is back-melting. In the first stage of this process, a section of the specimen is directionally solidified and the remainder is quenched. The quenched portion is then remelted and directionally solidified. In the flight experiment, the remelting and second directional solidification step will be carried out in space.

Proceedings ... annual meeting, Electron Microscopy Society of America, Aug 1, 1991

The II-VI semiconducting compounds are of particular interest due to the ability to compositional... more The II-VI semiconducting compounds are of particular interest due to the ability to compositionally tune them to detect infrared radiation in the 0.5 to 30 μm range. With the demand for advanced imaging systems, there is an immediate need for bulk II-VI materials with improved compositional homogeneity and structural perfection. The performance of optical semiconductors is very sensitive to the presence of defects such as dislocations, precipitates, and boundaries.

Journal of the American Dental Association, Dec 1, 2015

The purpose of this study was to determine the presence of a correlation between flexural strengt... more The purpose of this study was to determine the presence of a correlation between flexural strength and simulated crown strength; a correlation between crown strength and mode of fracture; an effect of aging on the flexural strength; and an effect of aging on the crown strength. Two hundred forty zirconia specimens were fabricated with 2 different designs, fully contoured crown shape specimens (n = 120) and rectangular coupons (n = 120), to provide 10 specimens each of 6 brands of zirconia (Lava Plus High Translucency [3M ESPE], Argen HT [Argen Corp], Zirlux [Ardent], BruxZir [Glidewell Laboratories], ZenoStar [Wieland Dental], and DDBioZX(2) [Dental Direkt]). One-half of each sample type was given a severe, simulated low-temperature aging treatment. The coupons were tested by 3-point flexural strength, and crowns were tested after luting to metallic abutments using resin cement. Statistical significance was evaluated by 2-factor analysis of variance (P = .05). Aging increased the mean (standard deviation [SD]) flexural strength for the following groups: Argen HT (995 [140] megapascals versus 677 [121] MPa before aging), Zirlux (939 [101] MPa versus 826 [169] MPa before aging), and ZenoStar (954 [81] MPa versus 764 [77] MPa before aging). There were statistical differences for the mean (SD) crown strengths for the following aged crowns: DDBioZX(2) had higher magnitudes (9,755 [1,095] MPa) than ZenoStar (8,864 [976] MPa), whereas Lava Plus High Translucency crowns had higher magnitudes (9,871 [942] MPa) than ZenoStar (8,864 [976] MPa). There was no effect of aging on the crown strength. There were statistical differences in the mode of fracture for the zirconia crowns between the following groups: nonaged and aged BruxZir (P = .014), nonaged and aged ZenoStar (P = .0226), and nonaged and aged Lava Plus High Translucency (P &amp;amp;amp;amp;amp;amp;amp;lt; .0001). There was no correlation between flexural strength and crown strength. There was no direct correlation between ranking of flexural strength and crown strength in the range of properties exhibited by these dental zirconias. Flexural strength does not predict simulated clinical strengths for crowns.

Polymer, Feb 1, 2007

Phase morphology and mechanical properties of the blends of Nylon 6 with scrap poly(vinyl butyral... more Phase morphology and mechanical properties of the blends of Nylon 6 with scrap poly(vinyl butyral) (PVB) film and poly[styrene-block-(ethylene-co-butene)block-styrene] (SEBS) have been investigated. Scanning electron microscopic photographs revealed that the spherical PVB particles are finely and uniformly dispersed in the Nylon 6 matrix without changing the shape of the particles. The average particle sizes in all over the blend compositions for Nylon 6/PVB were slightly increased with PVB content, but the dispersed phase is tightly adhered to the matrix phase, with PVB content in the range of 20-35 wt % PVB. Elongation at break and notched Izod impact strength of all the blends were enhanced, which implies good interfacial adhesion. The rubberlike PVB film adhering to the Nylon 6 phase is suggested to give an improved impact strength and toughness. In particular, the optimum PVB content for the best impact strength is found to be in the vicinity of 20-35 wt %, and this composition exhibits better moisture resistance than the other blend compositions. All of the blends up to 35 wt % PVB show higher mechanical properties than those of Nylon 6 blended with conventional impact modifier SEBS. Thus, plasticized PVB film, which is recycled from the process of automobile safety glasses, is applicable as an impact modifier or a toughening agent of Nylon 6.

Al/Al{sub 3}Ti composite materials possess a combination of high modulus, moderate strength, and ... more Al/Al{sub 3}Ti composite materials possess a combination of high modulus, moderate strength, and improved wear resistance and, therefore, hold promise for medium temperature applications. Previous work suggested that the Al{sub 3}Ti reinforcement could be formed in-situ while consolidating the Al matrix during reactive liquid phase sintering of elemental powders. In the present study, the microstructure evolution as a function of sintering time and temperature was characterized for Al-Cu/Al{sub 3}Ti composite materials with between 0 and 50 vol.% Al{sub 3}Ti, and preliminary mechanical property determinations were made. Both partially and fully-reacted microstructures were observed the partially-reacted structure consisted of Ti particles surrounded by Al{sub 3}Ti in an Al/Cu matrix. Intermediate Al-Ti phases, such as Ti{sub 3}Al and TiAl, were not resolvable. The Al{sub 3}Ti particles were found to have the D0{sub 22} crystal structure despite the presence of Cu in the compacts. The tensile and compressive yield strengths were influenced by the degree of completion of the Ti reaction as well as the target volume fraction of Al{sub 3}Ti. Strengths were observed to decrease relative to the unreinforced matrix for the 10 and 20 vol.% Al{sub 3}Ti materials and to be greater than the matrix for the higher volume fractions. Itmore » was also found that the strength of the composite materials was significantly increased by heat treatment.« less

Materials Science and Technology, 2001

... Young's modulus s0 Ramberg Osgood reference stress n Ramberg Osgood work hardening e... more ... Young's modulus s0 Ramberg Osgood reference stress n Ramberg Osgood work hardening exponent c Ramberg Osgood proportionality constant ... particles.22 Simulations using FEA have been used to show that particles containing centrally located penny shaped cracks ...

Proceedings, annual meeting, Electron Microscopy Society of America, 1993

Recent improvements in biomaterials have led to the development of coatings such as hydroxyapatit... more Recent improvements in biomaterials have led to the development of coatings such as hydroxyapatite (HA), a calcium phosphate phase. One of the main reasons for the interest in HA as a coating material for titanium bone implants is that it is component of bone and teeth and would be expected to be biocompatible.HA can be deposited by ion beam sputtering, which produces a thin, adherent coating which is initially amorphous. Studies of HA sputter deposited onto titanium have shown that the bond strength increases if the samples are heated-treated under vacuum and decreases if heat-treated in air (Figure 1). The present study will characterize the microstructural evolution of HA which was deposited on a model substrate, Si, after heat treatment.Coatings of HA were ion beam sputter deposited onto single crystal [001] silicon wafers. The HA-coated silicon wafers were heat treated in air or vacuum at either 500 or 600°C for one hour.

Transactions of the North American Manufacturing Research Institute of SME

ABSTRACT

2009 Annual Conference & Exposition Proceedings

During the fall of 2008 at the University of Alabama at Birmingham, a new course (EGR/MA 265-Math... more During the fall of 2008 at the University of Alabama at Birmingham, a new course (EGR/MA 265-Mathematical Tools for Engineering Problem Solving) was offered in a joint effort by the School of Engineering and the Department of Mathematics combining differential equations and calculus III into a four-hour semester-long course to aid in the transition of students from pure mathematics into engineering. This course was offered as an alternate track to the traditional calculus III and differential equations courses. Due to the time constraints within any one semester, a careful review of topics was made after interviewing every professor within the five departments of the School of Engineering who taught courses requiring calculus III or differential equations as a pre-or co-requisite. Initially, major areas to emerge were first-order linear ordinary differential equations; second-order linear ordinary differential equations with constant coefficients; multivariable functions, partial differentiation, and multiple integrals. The professors of the new course decided that they may be able to include integral theorems and an introduction to partial differential equations. In addition to the traditional material that these courses would typically provide, many application-based homework assignments and projects were given to provide engineering context. Each project assignment was given the same weight as a test but the projects were far more exploratory. Students were provided static notes in PDF format as well as dynamic notes in notebook player file format provided via the use of Mathematica Player by Wolfram to illustrate visually many of the concepts taught. Anonymous student comments via Individual Development and Educational Assessment (IDEA) surveys-an internal course evaluation tool-indicated that student perception of the course was generally positive.

.................................................................................................... more ...................................................................................................................... iii DEDICATION .................................................................................................................... v ACKNOWLEDGMENTS ................................................................................................. vi TABLE OF CONTENTS .................................................................................................. vii LIST OF TABLES ............................................................................................................. ix LIST OF FIGURES ............................................................................................................ x LIST OF ABBREVIATIONS .......................................................................................... xiii

$Research paper thumbnail of Stability of point defects in SrTiO$_{3}$ substrates during thin film deposition$

at Birmingham-During deposition of multiferroic films on SrTiO 3 , the substrate is subjected to ... more at Birmingham-During deposition of multiferroic films on SrTiO 3 , the substrate is subjected to ambients similar to those known to alter the oxygen vacancy concentration and conductivity. We have performed electron paramagnetic resonance (EPR) measurements on SrTiO 3 substrates at selected stages during film deposition as well as during controlled heat treatments. Fe 3+ , Cr 3+ and an Fe-oxygen vacancy complex, Fe 3+ V o , were monitored during isochronal and isothermal vacuum (10 −6 Torr) and 1 atm O 2 heat treatments between 200 and 800 • C. As expected, processing steps involving O 2 at 950 • C reduces the concentration of Fe 3+ V o , consistent with the O 2 annealing study. Film deposition at 650 • C, 5x10 −7 Torr with 10% ozone returns the Fe 3+ V o signal to the original intensity, consistent with vacuum treatments which follow 1 atm O 2 annealing. Surprisingly, isochronal and time-dependent vacuum and O 2 annealing produce the same trend for the Fe 3+ V o signal for T > 500 • C. The results of all the studies suggest that electrostatic changes, as evidenced by variations in the intensity of Fe 3+ and Cr 3+ , as well as oxygen vacancy migration can alter substrate characteristics during film growth.