A new configuration for testing thin layers of solder is introduced and employed to study the eff... more A new configuration for testing thin layers of solder is introduced and employed to study the effects of strain rate and thickness on the mechanical response of eutectic Sn-Pb solder. The solder in the test is loaded under a well defined state of pure shear stress. The stress and deformation in the solder are measured very accurately to produce a reliable stress-strain curve. The results show that both the stress needed for plastic deformation and ductility increase with increasing strain rate.
Journal of The Mechanics and Physics of Solids, 1985
Abstract T he pressure-shear plate impact technique is used to study material behavior at high ra... more Abstract T he pressure-shear plate impact technique is used to study material behavior at high rates of deformation. In this technique, plastic waves of combined pressure and shear stresses are produced by impact of parallel plates skewed relative to their direction of approach. Commercially pure alpha-titanium and 6061-T6 aluminum are tested under a variety of pressure and shear tractions by using different combinations of impact velocities and angles of inclination. A laser interferometer system is used to monitor simultaneously the normal and transverse components of motion of a point at the rear surface of the target plate. The experimental results are compared with numerical solutions based on an elastic/viscoplastic model of the material. Both isotropic and kinematic strain hardening models are used in the computations. The results indicate that unlike the normal velocity profiles, the transverse velocity profiles are sensitive to the dynamic plastic response and, thus, can be used to study material behavior at high strain rates. For the materials tested the results suggest that the flow stress required for plastic straining increases markedly with increasing strain rate at strain rates above 10 4 s −1 . Hydrostatic pressure of the order that exists in the tests (up to 2 GPa) does not affect the plastic flow in 6061-T6 aluminum and appears to have at most a minor effect on the deformation of the titanium.
MATLAB: An Introduction with Applications 4th Edition walks readers through the ins and outs of t... more MATLAB: An Introduction with Applications 4th Edition walks readers through the ins and outs of this powerful software for technical computing. The first chapter describes basic features of the program and shows how to use it in simple arithmetic operations with scalars. The next two chapters focus on the topic of arrays (the basis of MATLAB), while the remaining text covers a wide range of other applications. MATLAB: An Introduction with Applications 4th Edition is presented gradually and in great detail, generously illustrated through computer screen shots and step-by-step tutorials, and applied in problems in mathematics, science, and engineering.
An elastic/viscoplastic theory that includes anisotropic strain hardening is presented. The theor... more An elastic/viscoplastic theory that includes anisotropic strain hardening is presented. The theory is a combination of the elastic/viscoplastic formulation of Perzyna [4] and the anisotropic hardening model for time-independent plasticity of Mroz [6]. The theory is used in the analysis of pressure-shear plate impact experiments on commercially pure alpha titanium. Good agreement between theory and experiment is observed.
In this work, we have proposed a sensor for strain measurement in high-temperature environments u... more In this work, we have proposed a sensor for strain measurement in high-temperature environments up to 800°C by employing two regenerated fiber Bragg gratings. Two seed gratings (SGs) are inscribed in high Ge-doped and B/Ge-codoped fibers, respectively, which possess different temperature sensitivities. To achieve two gratings with different strain sensitivities, one of the gratings is chemically etched to reduce the fiber diameter for strain sensitivity enhancement. A thermal annealing process is carried out to activate the grating regeneration in the SGs. The temperature and strain calibration experiments indicate that the proposed structure has uncertainty values of 23.42 με and 5.83°C over the ranges of 0-1000 με and 20°C-800°C, respectively.
Almtract-The response of hot-roll~l 1020 steel over a wide range of temperatures and strain rates... more Almtract-The response of hot-roll~l 1020 steel over a wide range of temperatures and strain rates is investigated. Pure shear tests have been conducted at strain rates of 5 x 10-4, 2 and 1000 s-1, and temperatures of 25, 200, 400, and 600°C. Results show that temperature and strain rate greatly affect material response. In general, the stress decreases with increasing temperature and docreasing strain rate. At temperatures of 200-400°C, however, effects of dynamic strain aging are very significant. At this temperature range, negative strain rate sensitivity is observed as well as a region of increasing stress with increasing temperature. Constitutive equations are developed for modeling the material response. The relations are based on a model of thermally activated motion of dislocations that include the effect of dynamic strain aging. The parameters in the constitutive relations are dete:rmined, and there is good agreement between the model and the tests.
The results presented here are part of an ongoing research program, to develop strain rate depend... more The results presented here are part of an ongoing research program, to develop strain rate dependent deformation and failure models for the analysis of polymer matrix composites subject to high strain rate impact loads. A micromechanics approach is employed in this work, in which state variable constitutive equations originally developed for metals have been modified to model the deformation of the polymer matrix, and a strength of materials based micromechanics method is used to predict the effective response of the composite. In the analysis of the inelastic deformation of the polymer matrix, the definitions of the effective stress and effective inelastic strain have been modified in order to account for the effect of hydrostatic stresses, which are significant in polymers. Two representative polymers, a toughened epoxy and a brittle epoxy, are characterized through the use of data from tensile and shear tests across a variety of strain rates. Results computed by using the developed constitutive equations correlate well with data generated via experiments. The procedure used to incorporate the constitutive equations within a micromechanics method is presented, and sample calculations of the deformation response of a composite for various fiber orientations and strain rates are discussed.
The torsional split-Hopkinson-bar technique is modified for high-strain-rate testing at elevated ... more The torsional split-Hopkinson-bar technique is modified for high-strain-rate testing at elevated temperatures by heating the specimen rapidly and keeping the rest of the apparatus at room temperature. Tests have been conducted with specimens made of several materials (Haynes-188, 1020 steel, and 1151 steel) at temperatures ranging from 650°C to 1060°C and strain rates on the order of 1000 s–1.
This investigation compared the stress production characteristics of five abutment angulations fo... more This investigation compared the stress production characteristics of five abutment angulations for a specific implant system. Materials and Methods: Photoelastic resin was cast directly to a 3.75 x 10-mm Branemark fixture (Nobelpharma USA, Inc, Chicago, IL) in a 50 x 70 x 13-mm mold. A strain gauge rosette was also incorporated in the resin t o allow precise determination of normal stresses at a specific point. Each 4-mm abutment (15", 25", and 35"from Implant Innovations (West Palm Beach, FL) and 0" and 30" from Nobelpharma) was assembled on the fixture, subjected t o 178N load, and viewed with a circular polariscope. Observed fringes were photographed and strain indicator readings were recorded. Results: Mean observed fringe order and mean principal stress and strain at the location of the rosette were determined. Conclusion: At the location of the rosette, all five of the abutments produced principal strains (compressive and tensile) within the physiological zone for bone. The rosette was located approximately 4 mm away from the fixture. Higher stresses and strains can be expected in regions closer to the implant.
A new configuration for testing thin layers of solder is introduced and employed to study the eff... more A new configuration for testing thin layers of solder is introduced and employed to study the effects of strain rate and thickness on the mechanical response of eutectic Sn-Pb solder. The solder in the test is loaded under a well defined state of pure shear stress. The stress and deformation in the solder are measured very accurately to produce a reliable stress-strain curve. The results show that both the stress needed for plastic deformation and ductility increase with increasing strain rate.
Journal of The Mechanics and Physics of Solids, 1985
Abstract T he pressure-shear plate impact technique is used to study material behavior at high ra... more Abstract T he pressure-shear plate impact technique is used to study material behavior at high rates of deformation. In this technique, plastic waves of combined pressure and shear stresses are produced by impact of parallel plates skewed relative to their direction of approach. Commercially pure alpha-titanium and 6061-T6 aluminum are tested under a variety of pressure and shear tractions by using different combinations of impact velocities and angles of inclination. A laser interferometer system is used to monitor simultaneously the normal and transverse components of motion of a point at the rear surface of the target plate. The experimental results are compared with numerical solutions based on an elastic/viscoplastic model of the material. Both isotropic and kinematic strain hardening models are used in the computations. The results indicate that unlike the normal velocity profiles, the transverse velocity profiles are sensitive to the dynamic plastic response and, thus, can be used to study material behavior at high strain rates. For the materials tested the results suggest that the flow stress required for plastic straining increases markedly with increasing strain rate at strain rates above 10 4 s −1 . Hydrostatic pressure of the order that exists in the tests (up to 2 GPa) does not affect the plastic flow in 6061-T6 aluminum and appears to have at most a minor effect on the deformation of the titanium.
MATLAB: An Introduction with Applications 4th Edition walks readers through the ins and outs of t... more MATLAB: An Introduction with Applications 4th Edition walks readers through the ins and outs of this powerful software for technical computing. The first chapter describes basic features of the program and shows how to use it in simple arithmetic operations with scalars. The next two chapters focus on the topic of arrays (the basis of MATLAB), while the remaining text covers a wide range of other applications. MATLAB: An Introduction with Applications 4th Edition is presented gradually and in great detail, generously illustrated through computer screen shots and step-by-step tutorials, and applied in problems in mathematics, science, and engineering.
An elastic/viscoplastic theory that includes anisotropic strain hardening is presented. The theor... more An elastic/viscoplastic theory that includes anisotropic strain hardening is presented. The theory is a combination of the elastic/viscoplastic formulation of Perzyna [4] and the anisotropic hardening model for time-independent plasticity of Mroz [6]. The theory is used in the analysis of pressure-shear plate impact experiments on commercially pure alpha titanium. Good agreement between theory and experiment is observed.
In this work, we have proposed a sensor for strain measurement in high-temperature environments u... more In this work, we have proposed a sensor for strain measurement in high-temperature environments up to 800°C by employing two regenerated fiber Bragg gratings. Two seed gratings (SGs) are inscribed in high Ge-doped and B/Ge-codoped fibers, respectively, which possess different temperature sensitivities. To achieve two gratings with different strain sensitivities, one of the gratings is chemically etched to reduce the fiber diameter for strain sensitivity enhancement. A thermal annealing process is carried out to activate the grating regeneration in the SGs. The temperature and strain calibration experiments indicate that the proposed structure has uncertainty values of 23.42 με and 5.83°C over the ranges of 0-1000 με and 20°C-800°C, respectively.
Almtract-The response of hot-roll~l 1020 steel over a wide range of temperatures and strain rates... more Almtract-The response of hot-roll~l 1020 steel over a wide range of temperatures and strain rates is investigated. Pure shear tests have been conducted at strain rates of 5 x 10-4, 2 and 1000 s-1, and temperatures of 25, 200, 400, and 600°C. Results show that temperature and strain rate greatly affect material response. In general, the stress decreases with increasing temperature and docreasing strain rate. At temperatures of 200-400°C, however, effects of dynamic strain aging are very significant. At this temperature range, negative strain rate sensitivity is observed as well as a region of increasing stress with increasing temperature. Constitutive equations are developed for modeling the material response. The relations are based on a model of thermally activated motion of dislocations that include the effect of dynamic strain aging. The parameters in the constitutive relations are dete:rmined, and there is good agreement between the model and the tests.
The results presented here are part of an ongoing research program, to develop strain rate depend... more The results presented here are part of an ongoing research program, to develop strain rate dependent deformation and failure models for the analysis of polymer matrix composites subject to high strain rate impact loads. A micromechanics approach is employed in this work, in which state variable constitutive equations originally developed for metals have been modified to model the deformation of the polymer matrix, and a strength of materials based micromechanics method is used to predict the effective response of the composite. In the analysis of the inelastic deformation of the polymer matrix, the definitions of the effective stress and effective inelastic strain have been modified in order to account for the effect of hydrostatic stresses, which are significant in polymers. Two representative polymers, a toughened epoxy and a brittle epoxy, are characterized through the use of data from tensile and shear tests across a variety of strain rates. Results computed by using the developed constitutive equations correlate well with data generated via experiments. The procedure used to incorporate the constitutive equations within a micromechanics method is presented, and sample calculations of the deformation response of a composite for various fiber orientations and strain rates are discussed.
The torsional split-Hopkinson-bar technique is modified for high-strain-rate testing at elevated ... more The torsional split-Hopkinson-bar technique is modified for high-strain-rate testing at elevated temperatures by heating the specimen rapidly and keeping the rest of the apparatus at room temperature. Tests have been conducted with specimens made of several materials (Haynes-188, 1020 steel, and 1151 steel) at temperatures ranging from 650°C to 1060°C and strain rates on the order of 1000 s–1.
This investigation compared the stress production characteristics of five abutment angulations fo... more This investigation compared the stress production characteristics of five abutment angulations for a specific implant system. Materials and Methods: Photoelastic resin was cast directly to a 3.75 x 10-mm Branemark fixture (Nobelpharma USA, Inc, Chicago, IL) in a 50 x 70 x 13-mm mold. A strain gauge rosette was also incorporated in the resin t o allow precise determination of normal stresses at a specific point. Each 4-mm abutment (15", 25", and 35"from Implant Innovations (West Palm Beach, FL) and 0" and 30" from Nobelpharma) was assembled on the fixture, subjected t o 178N load, and viewed with a circular polariscope. Observed fringes were photographed and strain indicator readings were recorded. Results: Mean observed fringe order and mean principal stress and strain at the location of the rosette were determined. Conclusion: At the location of the rosette, all five of the abutments produced principal strains (compressive and tensile) within the physiological zone for bone. The rosette was located approximately 4 mm away from the fixture. Higher stresses and strains can be expected in regions closer to the implant.
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Papers by Amos Gilat