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Some Problems on the Theory of Creep

Description: "The term creep of metals is applied to the phenomenon in which, at temperatures beyond a certain limit, the metal subjected to a load slowly undergoes deformation with time. Very slow deformations for a prolonged period are cumulative and lead either to inadmissible changes in the dimensions of a structural part or to its failure. The theory of creep constitutes part of the mechanics of dense media and the mechanical formulation of the problem may be given as the following: a body is subjected to the action of a given system of forces, or initial displacements are prescribed on its surface" (p. 1).
Date: April 1953
Creator: Rabotnov, Y. N.
Partner: UNT Libraries Government Documents Department

Theory of Dynamic Creep

Description: An analysis is given of the causes of the increase in the creep of a material under dynamic loads. A theory of dynamic creep is proposed based on the after-effect theory of Becker. Three circumstances that must be taken into account when theoretically treating dynamic creep are provided.
Date: September 1955
Creator: Predvoditelev, A. A. & Smirnov, B. A.
Partner: UNT Libraries Government Documents Department

Creep and Relaxation in Metals and Ceramics : A Bibliography, 1950-March 1959

Description: "This is a selected bibliography of books, journal articles and reports published on creep and relaxation in metals and ceramics from 1950 to March 1959. Particular attention has been paid to studies on or applicable to the consideration of creep and relaxation in beryllium oxide. Emphasis has alro been placed on studies of phenomenological materials behavior and high temperature studies."
Date: April 15, 1959
Creator: Maynard, Glenn R. & Lane, Zanier D.
Partner: UNT Libraries Government Documents Department

Mechanism of beneficial effects of boron and zirconium on creep-rupture properties of a complex heat-resistant alloy

Description: Report presenting an investigation of the mechanism by which the addition of boron and zirconium improves the creep-rupture properties of an alloy of 55 percent nickel, 20 percent chromium, 15 percent cobalt, 4 percent molybdenum, 3 percent titanium, and 3 percent aluminum at 1600 degrees Fahrenheit. The creep-rupture properties were improved because the boron and zirconium have a pronounced stabilizing effect on the grain boundaries of the alloy. Results regarding the microstructures in initial condition, changes in microstructure during exposure at 1600 degrees Fahrenheit, interpretation of other microstructural changes, relation of mechanism to published information, causes of effect of boron and zirconium on grain-boundary stability, role of carbon, and generality of results are provided.
Date: August 1958
Creator: Decker, R. F. & Freeman, J. W.
Partner: UNT Libraries Government Documents Department

Creep-Rupture Tests of Beryllium

Description: "A program of creep-rupture tests of several bars of Beryllium has been completed. The tests were made at 1200, 1400, 1550, and 1700 F. in protective atmospheres of tank helium or hydrogen. The results are given in a summary table and by creep and design curves. A description of the test set-up is included."
Date: January 9, 1951
Creator: Manjoine, M. J.
Partner: UNT Libraries Government Documents Department

The Creep of Zirconium in Water

Description: Introduction:"Very little is known about the mechanical properties of zirconium and, in view of this the Atomic Energy Commission requested Sylvania to evaluate the creep characteristics of this metal at various temperatures. Tests at room temperature (25 C) and at 200 C have been completed, the tests having been conducted in air. The data obtained from these tests form the basis of this report. Future tests will be conducted in an atmosphere of water at the desired testing temperature."
Date: 1950
Creator: Brunstetter, D. R. & Alexander, B. H.
Partner: UNT Libraries Government Documents Department

Creep Behavior of Structural Joints of Aircraft Materials Under Constant Loads and Temperatures

Description: "The results of 55 creep and creep-rupture tests on structural joints are presented. Methods are described by which the time to rupture, the mode of rupture, and the deformation of joints in creep may be predicted. These methods utilize creep data on the materials of the joint in tension, bearing, and shear" (p. 1).
Date: January 1957
Creator: Mordfin, Leonard & Legate, Alvin C.
Partner: UNT Libraries Government Documents Department

A variational theorem for creep with applications to plates and columns

Description: A variational theorem is presented for a body undergoing creep. Solutions to problems of the creep behavior of plates, columns, beams, and shells can be obtained by means of the direct methods of the calculus of variations in conjunction with the stated theorem. The application of the theorem is illustrated for plates and columns by the solution of two sample problems.
Date: March 5, 1957
Creator: Sanders, J. Lyell, Jr.; McComb, Harvey G., Jr. & Schlechte, Floyd R.
Partner: UNT Libraries Government Documents Department

A variational theorem for creep with applications to plates and columns

Description: From Summary: "A variational theorem is presented for a body undergoing creep. Solutions to problems of creep bending and creep collapse of plates, columns, beams, and shells can be obtained by means of the direct methods of the calculus of variations in conjunction with the stated theorem. The application of the theorem is illustrated for plates and columns by the solution of two sample problems."
Date: May 1957
Creator: Sanders, J. Lyell, Jr.; McComb, Harvey G., Jr. & Schlechte, Floyd R.
Partner: UNT Libraries Government Documents Department

A summary of NACA research on the strength and creep of aircraft structures at elevated temperatures

Description: Report summarizing research on the strength and creep of aircraft structural elements and components at elevated temperatures. Experimental data for aluminum alloy columns, plates, stiffened panels, and multiweb box beams are presented for temperatures up to 600 degrees Fahrenheit and compared with results predicted from materials data.
Date: May 31, 1956
Creator: Heldenfels, Richard R. & Mathauser, Eldon E.
Partner: UNT Libraries Government Documents Department

Recent research on the creep of airframe components

Description: Report presenting the results of research on the creep of airframe components at elevated temperatures. Experimental lifetime data from creep tests of stainless-steel plates and aluminum-alloy unstiffened circular cylinders are presented and compared with results predicted from isochronous stress-strain curves.
Date: July 1957
Creator: Mathauser, Eldon E.; Berkovits, Avraham & Stein, Bland A.
Partner: UNT Libraries Government Documents Department

Creep buckling of columns

Description: Report presenting formulas for the determination of the creep deflection-time characteristics of an initially curved idealized H-section column. The results were obtained from closed-form solutions of the differential equation of bending of a beam column with creep properties of a nonlinearly viscoelastic nature. Critical time is tabulated and plotted for a wide range of parameters involved.
Date: January 1954
Creator: Kempner, Joseph & Patel, Sharad A.
Partner: UNT Libraries Government Documents Department

Analysis of the Creep Behavior of a Square Plate Loaded in Edge Compression

Description: From Introduction: "In reference 1 results of creep tests and empirical method for predicting collapse times are presented for plates loaded in compression on two opposite edges and with the remaining edges unloaded and supported in V-groove fixtures. Other approximate methods for handling plates having types of edge support are suggested in reference 2; however, experimental verification for these methods is quite limited. In reference 3 an analysis based on small-deflection theory is made of the creep deflection of a simply supported plate composed of a linear viscoelastic material - that is, a material in which the stress and strain and their appropriate time derivatives are related in a linear fashion."
Date: September 1958
Creator: McComb, Harvey G., Jr.
Partner: UNT Libraries Government Documents Department

Interaction of Bearing and Tensile Loads on Creep Properties of Joints

Description: The interaction of bearing and tensile loads on the creep behavior of joints was studied. A specimen was designed for this study which possessed some of the general features of pin and rivet joint connections and an apparatus was constructed to apply both bearing and tensile loads to the joint model. Deformation measurements were made by use of a photogrid printed on the joint model.
Date: October 1956
Creator: Bodine, E. G.; Carlson, R. L. & Manning, G. K.
Partner: UNT Libraries Government Documents Department

A Survey of Creep in Metals

Description: "This report summarizes numerous theories relating to creep phenomena and the extent of current knowledge on the subject. Various possible mechanisms by which creep occurs both in single crystals and in polycrystals are described. An extensive bibliography of published works in this field is also included" (p. 1).
Date: November 1951
Creator: Schwope, A. D. & Jackson, L. R.
Partner: UNT Libraries Government Documents Department

Creep Bending and Buckling of Linearly Viscoelastic Columns

Description: Note presenting the general dynamic equation of creep bending of a beam loaded laterally and axially as derived for a linearly viscoelastic material whose mechanical properties can be characterized by four parameters. The equation derived was used to obtain the creep bending deflection of a beam in pure bending and of a column with initial sinusoidal deviation from straightness.
Date: January 1954
Creator: Kempner, Joseph
Partner: UNT Libraries Government Documents Department

Quantitative Treatment of the Creep of Metals by Dislocation and Rate-Process Theories

Description: Note presenting an equation for the steady-state rate of creep, which has been derived by applying the theory of dislocations to the creep of pure metals. The form of this equation is in good agreement with empirical equations describing creep rates. A discussion of the way the theory can be applied to alloys, in particular heat-resisting alloys, is also provided.
Date: April 1946
Creator: Nowick, A. S. & Machlin, E. S.
Partner: UNT Libraries Government Documents Department

Triangular and Intergranular Fracture of Ingot Iron During Creep

Description: Note presenting creep tests performed on coarse-grained ingot iron over a temperature range from 700 to 1350 degrees Fahrenheit to find whether the amount of grain-boundary sliding determined the fracture mode, either transgranular or intergranular. Transgranular fractures were obtained at temperatures below 800 degrees Fahrenheit and stresses above 20,000 psi. It is concluded that a vacancy-condensation mechanism is most probably responsible for high-temperature intergranular fracturing in ingot iron.
Date: August 1958
Creator: Shepard, L. A. & Giedt, W. H.
Partner: UNT Libraries Government Documents Department

Compressive Strength and Creep of 17-7 PH Stainless-Steel Plates at Elevated Temperatures

Description: Note presenting compressive strength test results from room temperature to 1000 degrees Fahrneheit and compressive creep test results from 700 to 1000 degrees Fahrenheit for plates of 17-7 PH stainless steel, Condition TH 1050, which were edge-supported in V-groove fixtures. The combinations of average stress, temperature, and time that produce given amounts of creep strain or failure are shown on master curves which facilitate interpolation of the test results.
Date: July 1958
Creator: Stein, Bland A.
Partner: UNT Libraries Government Documents Department

Effects of Environment on the Low-Cycle Fatigue Behavior of Type 304 Stainless Steel

Description: The low-cycle fatigue behavior of Type 304 stainless steel has been investigated at 593 degrees C in a dynamic vacuum of better than 1.3 x 10⁻⁶ Pa (10⁻⁸ torr). The results concerning the effects of strain range, strain rate and tensile hold time on fatigue life are presented and compared with results of similar tests performed in air and sodium environments. Under continuous symmetrical cycling, fatigue life is significantly longer in vacuum than in air; in the low strain range regime, the effect of sodium on fatigue life appears to be similar to that of vacuum. Strain rate (or frequency) strongly influences fatigue life in both air and vacuum. In compressive hold-time tests, the effect of environment on life is similar to that in a continuous-cycling test. However, tensile hold times are nearly as damaging in vacuum as in air. Thus, at least for austenitic stainless steels, the influence of the environment of fatigue life appears to depend on the loading waveshape.
Date: December 1979
Creator: Argonne National Laboratory. Materials Science Division.
Partner: UNT Libraries Government Documents Department

Mechanics and Mechanisms of Creep and Ductile Fracture

Description: The main aim of this dissertation is to relate measurable and hopefully controllable features of a material's microstructure to its observed failure modes to provide a basis for designing better materials. The understanding of creep in materials used at high temperatures is of prime engineering importance. Single crystal Ni-based superalloys used in turbine aerofoils of jet engines are exposed to long dwell times at very high temperatures. In contrast to current theories, creep tests on Ni-based superalloy specimens have shown size dependent creep response termed as the thickness debit effect. To investigate the mechanism of the thickness debit effect, isothermal creep tests were performed on uncoated Ni-based single crystal superalloy sheet specimens with two thicknesses and under two test conditions: a low temperature high stress condition and a high temperature low stress condition. At the high temperature, surface oxidation induced microstructural changes near the free surface forming a layered microstructure. Finite element calculations showed that this layered microstructure gave rise to local changes in the stress state. The specimens also contained nonuniform distribution of initial voids formed during the solidification and homogenization processes. The experiments showed that porosity evolution could play a significant role in the thickness debit effect. This motivated a basic mechanics study of porosity evolution in single crystals subjected to creep for a range of stress states. The study was performed using three-dimensional finite deformation finite element analysis of unit cells containing a single initially spherical void in a single crystal matrix. The materials are characterized by a rate-dependent crystal plasticity constitutive relation accounting for both primary and secondary creep. The effect of initial void spacing and creep exponent was also explored. Based on the experimental observations and results of finite element calculations a quantitative mechanistic model is proposed that can account for both bulk and surface ...
Date: August 2013
Creator: Srivastava, Ankit
Partner: UNT Libraries

Effect of overheating on creep-rupture properties of M-252 alloy

Description: Report presenting a study on the influence of periodic overheats of 2-minutes duration to four different temperatures on the creep-rupture properties of M-252 alloy at 1500 degrees Fahrenheit. The purpose of the study was to provide information regarding the estimation of the effects of overheating on creep-rupture performance of gas-turbine parts. Results regarding normal rupture properties of experimental materials, overheats on heat HT-28, overheats on heats 837 and 43642, comparative effects of overheating on S-816, HS-31, and M-252 alloys, mechanism of damage from overheating, interpretation of results in terms of overheating in a turbine, and some limitations of results are provided.
Date: March 1958
Creator: Rowe, John P. & Freeman, J. W.
Partner: UNT Libraries Government Documents Department

Effect of overheating on creep-rupture properties of S-816 alloy at 1,500 degrees F

Description: The effects of overheats to temperatures of 1650, 1800, 1900, and 2000 F were evaluated in terms of the changes in creep-rupture characteristics at 1500 F of S-816 alloy under stresses within the range of rupture strengths of the alloy for 100 to 1000 hours. Overheat periods were predominantly of 2-minute duration and were applied cyclically at approximately 5- or 12-hour intervals. The possible damage from overheating was believed to include internal metal structure changes induced by exposure to the higher temperatures and loss of life by creep if stress was present during the overheats.
Date: December 1957
Creator: Rowe, John P. & Freeman, J. W.
Partner: UNT Libraries Government Documents Department