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RESEARCH PAPERS

J. Eng. Mater. Technol. 1975;97(1):1-9. doi:10.1115/1.3443254.

The mechanical behavior of semi-continuously cast Al-Al2 Cu and Al-Al3 Ni eutectics has been studied in tension at temperatures between 350–500 deg C (Al-Al2 Cu) and 500–625 deg C (Al-Al3 Ni). The microstructures of both eutectics were found to be relatively unstable at elevated temperatures, even in the absence of deformation, as a result of their fine, imperfect microstructures in the as-cast condition. During deformation spheroidization occurred rapidly, so that the fibrous/lamellar reinforcement was largely eliminated. During hot deformation of the Al-Al2 Cu eutectic, the “degenerate” lamellar structure was gradually replaced by an equiaxed microduplex structure via polygonization of both phases. This structure subsequently demonstrated superplastic flow, with an increase in the strain-rate sensitivity index from about 0.3 to about 0.5. Final failure resulted from nucleation of cavities at Al2 Cu - Al2 Cu - Al triple junctions with cavity growth along Al2 Cu-Al2 Cu grain boundaries. The Al-Al3 Ni eutectic did not exhibit superplastic flow probably due to the lower volume fraction of the Al3 Ni phase, which “spheroidized” during deformation. A process for fabricating wire by a continuous process from the melt is outlined.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1975;97(1):10-13. doi:10.1115/1.3443252.

Sheet metal laminates are becoming more widely used because of advantageous combinations of the properties of their component parts. Theoretical equations have been developed to predict the tensile properties of laminates to aid selection from the list of many possible combinations of different materials. The equations have been used to predict the values of the tensile properties of copper/steel and aluminum/steel composites; these predictions have been checked against measured values. An empirical rule of mixtures is often used to predict the properties of laminates; the theoretical analysis has been used to justify, or otherwise, the use of this simple linear realtionship.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1975;97(1):14-20. doi:10.1115/1.3443253.

Experiments were conducted to determine the effect of interface friction and specimen geometry on the useful ductile flow limit of 1100 aluminum and 1095 steel at room temperature. The tests consisted of measuring the equatorial strains during simple upsetting of circular cylinders. From the measured strains the surface stress components were calculated. All occurrences of fracture were observed to be the normal type. In some cases no surface cracks were observed and a possible explanation is given in the paper.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1975;97(1):21-24. doi:10.1115/1.3443255.

The surface finishes produced by taper reaming of holes in a composite structure of aluminum alloy and ultra-high strength steel are examined for both dry and lubricated cutting conditions. In dry reaming cutting occurred under built-up-edge (BUE) conditions whereas when a mineral cutting oil was used no significant BUE was formed. Reaming under the latter conditions resulted in a more undulating steel surface finish but a much smoother surface finish for the aluminum alloy.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1975;97(1):25-32. doi:10.1115/1.3443256.

Initial-yield results on SAE 1017 steel are presented for: four different specimens under combined axial load and twisting moment for servo controlled loading; and six different specimens under various combinations of servo controlled axial strain and shear strain. Subsequent yield curves determined by small strain offset multiple probes on a given specimen are presented covering all four quadrants of axial stress-shear stress space. The resulting families of subsequent yield curves allows conclusions to be drawn concerning the effects of plastic strain and strain aging. All curves were found to be convex and normality of the plastic strain increment vector was obeyed. The response to plastic straining allowed discussion of corner formation, translation, rotation, Bauschinger and cross effects of subsequent yield curves and formation of a limit curve. A comparison is made between the experiments and the Prager kinematic hardening model and the Ziegler modification.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1975;97(1):33-38. doi:10.1115/1.3443257.

Analysis of transient and steady state stress-strain hysteresis behavior of several structural metals reveals a new parameter, defined as the “Yield Range Increment”, which uniquely denotes the various transient phenomena including cyclic hardening, softening, relaxation, and creep and the steady state cyclic stress-strain behavior. All transient and steady state hysteresis branches of a given material appear to be identical in shape, after their Yield Range Increments, which are suitable portions of the initial “elastic” parts, are deleted. A mathematical model incorporating the Yield Range Increment is proposed. With the determination of the functional relationship between the newly proposed parameter and the several input variables of cyclic loading, this approach should lead to a unified approach for describing the cyclic stress-strain response of materials.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1975;97(1):39-44. doi:10.1115/1.3443258.

This paper presents a numerical method for the solution of problems of moving heat sources with change of phase and with any boundary condition. Calculated results of two specific cases are shown: one for a plane moving source in a rod and the other for a line source in a plate. It is found that for low heat input and/or low initial temperature, the change of phase does not affect significantly the temperature distribution in the medium, were it of solid only. However, the higher the heat input and/or the initial temperature, the larger is the effect of phase-change to the temperature field.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1975;97(1):45-51. doi:10.1115/1.3443259.

A technique consisting of stress-freezing photoelasticity coupled with a Taylor Series Expansion of the maximum local in-plane shearing stress known as the Taylor Series Correction Method (TSCM) is applied to the determination of stress intensity factors (SIF’s) in flat bottomed surface flaws of flaw depth/length ratios of approximately 0.033. Flaw depth/thickness ratios of approximately 0.20 and 0.40 were studied as were plate width/crack length ratios of approximately 2.33 and 1.25, the former of which corresponded to a nearly infinite width. Agreement to well within 10 percent was found with the Rice-Levy and Newman theories using a depth-modified secant correction and equivalent flaw depth/length ratios. The Shah-Kobayashi Theory, when compared on the same basis, was lower than the experimental results. Using a modified net section stress correction suggested by Shah, agreement with the Shah-Kobayashi Theory was greatly improved but agreement with the other theories was poorer. On the basis of the experiments alone, it was found that the SIF was intensified by about 10 percent by decreasing the plate width/crack length from 2.33 to 1.25.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1975;97(1):52-56. doi:10.1115/1.3443261.

It is known that some composite materials or high-polymers behave differently in simple tension and compression. The present paper is concerned with a bending analysis of a different modulus elastic plate subjected to a uniform lateral load. Employing the istoropic different modulus material model developed by Ambartsumyan and Khachatryan, the basic governing equations of an axisymmetric large deflection of a thin circular plate are derived under the usual assumption of Kirchhoff-Love. The differential equations are written approximately in finite-difference forms and solved numerically by an iteration method. Discussion and comparison of results are made with respect to different values of the ratio of tensile to compressive elastic moduli, Et /Ec .

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1975;97(1):57-65. doi:10.1115/1.3443262.

The relationship between the geometry and the membrane stresses of a thin shell under internal or external pressure is analyzed through the concept of prolateness. Prolateness is a quantitative measure of the local deviation from the spherical surface and it varies in a complex manner throughout a thin shell formed by hydraulic pressure. It is found that for the metals tested the surface is locally a sphere only at the pole and at an annular ring; elsewhere, it is oblate or prolate. The stress distributions in the shell being formed are also determined. Their variation as the forming progresses reveals that the material deforms quite differently at the beginning and at the end of the process.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1975;97(1):66-73. doi:10.1115/1.3443263.

High strength-to-weight ratio materials are becoming of increasing importance in the automotive industry. Some aluminum alloy sheets offer strength equivalent to low-carbon sheet steel at one third of the weight. However, for these alloys no production stamping experience exists and little meaningful laboratory data have been accumulated. This study was conducted to provide such laboratory information. Complete tensile properties and forming limit curves (FLC), as measured by a laboratory technique developed by the author, were determined for the aluminum alloys with a wide range of properties and were compared to the properties of low-carbon steel. All the aluminum alloys were found to have lower FLC’s, lower r values and equal or lower strain hardening capacities than sheet steel. Therefore their formabilities will be less than those of steel for all modes of sheet forming. This predicted press performance was verified for some of these alloys in limited press trials on a deck lid (inner panel) stamping.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1975;97(1):74-80. doi:10.1115/1.3443264.

A number of cases of brittle fracture in welded structures can be explained by an accelerated aging resulting from the use of welding thermal cycles on strain-hardened steels. This paper presents new experimental results of an investigation of this phenomenon as well as a rationale for it. Results on rimmed steels indicate that there is a critical temperature, below the A1 transformation point, which results in the maximum loss of notch toughness. The magnitude of the embrittlement suggests that the standard test recommended for strain aging susceptibility of these steels should be modified to provide better measure of the effect. Some further practical recommendations are made about these steels.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1975;97(1):81-84. doi:10.1115/1.3443265.

This is the first part of a study of thermal stresses and metal movement during welding. This part discusses analysis of two-dimensional thermal stresses and metal movement during bead-on-plate and butt welding. A finite-element formulation has been derived, based on the variational principle. The formulation includes temperature dependence of material properties as well as the yield criterion.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1975;97(1):85-91. doi:10.1115/1.3443266.

This is the second part of a study of thermal stresses and metal movement during welding. Part I described the finite-element analysis of two-dimensional thermal stresses and metal movement during bead-on-plate and butt welding. Part II presents results of experiments on bead-on-plate and butt welds in 6061-T6 aluminum alloy. Measurements were made of changes of temperature, thermal strains, and metal movement during welding. The paper then compares experimental data with analytical results. Good agreements were obtained between experimental and analytical results.

Commentary by Dr. Valentin Fuster

TECHNICAL BRIEFS

J. Eng. Mater. Technol. 1975;97(1):92-93. doi:10.1115/1.3443267.
Abstract
Topics: Wire , Torsion
Commentary by Dr. Valentin Fuster

BOOK REVIEWS

J. Eng. Mater. Technol. 1975;97(1):94. doi:10.1115/1.3443268.
FREE TO VIEW
Abstract
Commentary by Dr. Valentin Fuster

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