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RESEARCH PAPERS

J. Eng. Mater. Technol. 1985;107(2):97-100. doi:10.1115/1.3225798.

A model for stress-strain behavior under hot working conditions has been proposed. Based on experimental data, equations for the dependence of flow stress on strain, strain rate, and temperature have been developed. Application to type 304 stainless steel and AISI 1055 steel has been demonstrated.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1985;107(2):101-109. doi:10.1115/1.3225781.

The stress-range and path-shape dependencies of multiaxial nonproportional cyclic hardening were studied for annealed type 316 stainless steel at 600°C by means of stress controlled tests. Cyclic experiments along circular stress paths with constant effective stresses in the axial-torsional stress plane were first performed. The significant cyclic hardening and its stress-range dependency observed for the circular stress cyclings were quantitatively shown in reference to the cyclic stress-strain curves resulted from uniaxial stress cyclings. Then, to discuss the effect of path-shape, the cyclic tests along square stress paths inscribed by the above circular paths, as well as the tests where uniaxial cyclings and torsional ones were alternated, were also carried out. As a result of these tests, the cyclic hardenings for square paths were found to be almost equivalent to those for their circumscribed circular paths. The other type of stress cyclings caused almost the same amount of cyclic hardenings as those for the circular cyclings of the identical stress-ranges.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1985;107(2):110-114. doi:10.1115/1.3225782.

Recent advances in computer based structural analysis have in turn led to increased demands for models that can accurately represent material stress-strain behavior. The constitutive representation of high elongation elastic (rubbery) material was thus reexamined. A new strain energy function is presented that appears to have advantages over previous formulations. Finite compressibility is included, and accuracy of material representation appears good over a wide range of conditions.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1985;107(2):115-118. doi:10.1115/1.3225785.

A criterion for optimal discretization of power stress-strain law curves is proposed. The criterion is based on the assumption that it is desirable to have the fewest possible line segments without exceeding some predetermined bound on the error. The formulation produces a system of simultaneous nonlinear equations which are solved using an iterative search technique. Solutions are presented in both graphical and tabular form for a wide range of strain hardening exponents and acceptable error bounds. It is shown that stress and energy density can be accurately and efficiently modeled using the optimal discretization.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1985;107(2):119-125. doi:10.1115/1.3225786.

Tests have been conducted to determine the effect of tensile-mean-strain on cyclic properties, low cycle fatigue, and total absorbed plastic strain energy to failure of ASTM A-516 Grade 70 carbon low alloy steel. Stable hysteresis loops at half-life are presented for different strain controlled tests. The cyclic properties were determined by a least squares fit technique. The results of tensile-mean-strain are compared with fully-reversed fatigue tests. The absorbed plastic strain energy per cycle was measured and compared with a proposed relationship for non-Masing material behavior. A relationship of the form Wf =KNf α is found to be a good representation of the data. It is observed that the material tends toward a steady-state condition independent of the level of the mean strain provided the fatigue life is greater than one thousand cycles.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1985;107(2):126-131. doi:10.1115/1.3225787.

Detailed knowledge of material properties is one of the most important aspects of predictive-adaptive computer models used to control hot strip mills. The paper critically reviews the techniques, in use today, that establish those properties and describes the development and the capabilities of an experimental facility designed to determine the material’s resistance to deformation. Preliminary results, obtained by constant strain rate compression testing as well as by simulation of the thermal-mechanical treatment strips receive in the finishing train, are presented.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1985;107(2):132-137. doi:10.1115/1.3225788.

The biaxial deformation behavior of HY 80 steel has been examined by testing thin wall tubes under combined axial tension and internal pressure. The effective stress-strain curves and the hardening response have been found to vary with the stress state. The plastic strain ratio at a given stress ratio deviates from the von Mises value except at the stress states near uniaxial tension, plane strain and equi-biaxial tension. Using Drucker theory, these deviations are eliminated and the resulting yield locus is in good agreement with both the Bishop-Hill theory and the experimental results. Influenced by the tube geometry, the instability strains at the onset of diffuse necking are decreased by an increase in hoop tension. The diffuse necking strains are reasonably predicted by the Swift and the Lankford-Saibel/Mellor criteria.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1985;107(2):138-144. doi:10.1115/1.3225789.

Axisymmetric compression tests of solid aluminum cylinders, over a wide range of “aspect ratios” (length/diameter) and both under dry as well as lubricated conditions, suggest that the resulting curvature of the “barrel” formed fits closely a circular arc and its radius follows a power law with the true axial compressive stress. The true compressive stress-strain curve, extrapolated from the experimental data in each test, shows that within the variety of lubricants used the Specific Forming Energy is minimum with teflon sheets as dry lubricant, and increases successively with silicon spray, motor oil, and dry friction.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1985;107(2):145-147. doi:10.1115/1.3225790.

Diameter ratio, height reduction ratio, and aspect ratio are very significant non-dimensional parameters that govern the geometry of barreling throughout the process of plastic deformation of cylinder under axial compression.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1985;107(2):148-153. doi:10.1115/1.3225791.

Recent approaches to controlling stress corrosion cracking in welded 304 stainless steel pipes have been based on various types of controlled heating procedures. When applied properly, the heating procedure introduces high compressive stresses in region of observed cracking. The compressive stresses are believed to be effective in deterring stress corrosion cracking. One procedure for applying controlled heating to the pipe employs induction heating and is called Induction Heating for Stress Improvement or IHSI. The effective utilization of induction heating requires an understanding of how the induction heating parameters are related to the resulting residual stresses. This paper describes the development of a computational model directed at evaluating the heat densities and temperature distributions for Induction Heating for Stress Improvement (IHSI). The basic mechanism of inducting differs from that of a welding arc in that induction heating produces a distribution of heat sources within the pipe wall while in weld arc heating, the heat source is confined to the surface. Thus the computational model requires two parts. The first part evaluates the induced electrical current and determines the density of heat sources in the pipe wall. The second part of the model uses these heating densities to evaluate the temperature distribution. Temperature dependent properties were found to be important in representing the induction heating phenomenon. However, including temperature dependent properties in the model leads to nonlinear equations which require iterative solution methods for each part of the model. The nonlinear characteristics of the equations also require iterations between the two parts of the model. The model includes the important parameters of the induction heating process and has shown good agreement with temperature data for two different pipe sizes. Because of the inherent nonlinearities in the model and the iterative methods required for general solutions, extensions of the model to improve the algorithimic efficiency are discussed.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1985;107(2):154-160. doi:10.1115/1.3225792.

The fracture of rotating disks that have cracks and/or notches is predicted employing the crack instability criterion based on the J-integral R-curve approach characterizing a material resistance to fracture. The J-integrals of cracked rotating disks are calculated by an elastic-plastic finite element method taking account of the thickness effects. Spin tests were carried out on disks having fatigue cracks and/or notches and the crack extensions as well as the bursting speeds of the disk specimens were measured. It is shown that the predicted values of bursting speed are in good agreement with those obtained by the experiment.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1985;107(2):161-165. doi:10.1115/1.3225793.

Constant-load-amplitude stage II fatigue crack growth rates at 4 K were measured for duplex stainless steel castings. The results show that at a ΔK of 60 MPa•m1/2 , da/dN = 7.6 × 10−4 mm/cycle for an alloy with 1 percent ferrite. For an alloy with 8 percent ferrite, da/dN is 35 percent, and for an alloy with 29 percent ferrite, da/dN is 260 percent greater than for the 1 percent ferrite alloy. However, the exponent in the Paris equation does not change appreciably (less than 18 percent) as the ferrite content changes from 1 to 29 percent.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1985;107(2):166-171. doi:10.1115/1.3225794.

Threshold and near threshold fatigue crack growth behavior was obtained for five carbon or low alloy cast steels at room temperature and −45°C (−50°F) with the load ratio R=0.05 and 0.5. Mean stress effects at both temperatures appear to be substantially dependent upon crack closure. ΔKth did not correlate well with other mechanical properties such as Su , Sy , Sy ′ or Sf . Threshold and near threshold fatigue crack growth resistance was generally improved at −45°C despite the fact that this temperature was below the NDT temperature for three of the five cast steels. SEM fractography also established that the NDT temperature is not associated with a possible ductile-brittle constant amplitude fatigue crack growth transition in cast steels. ΔKth values for these five cast steels appear to be quite favorable relative to values found in the literature for wrought steels.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1985;107(2):172-179. doi:10.1115/1.3225795.

Sustained-load crack-growth experiments were conducted under isothermal and nonisothermal conditions. Temperature cycling was conducted between 537° and 649°C. Hold times at minimum and/or maximum temperature were included in the temperature profiles. An analytical model was developed to predict crack-growth rates based solely on isothermal data. The linear cumulative damage model was able to predict crack-growth rates in Inconel 718 for all the temperature profiles investigated including a proof test.

Commentary by Dr. Valentin Fuster

DISCUSSIONS

Commentary by Dr. Valentin Fuster

BOOK REVIEWS

J. Eng. Mater. Technol. 1985;107(2):180. doi:10.1115/1.3225796.
FREE TO VIEW
Abstract
Topics: Porosity
Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 1985;107(2):180. doi:10.1115/1.3225797.
FREE TO VIEW
Abstract
Commentary by Dr. Valentin Fuster

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