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RESEARCH PAPERS: New Investigations Relating to Stress Concentrations Under Creep Conditions

J. Basic Eng. 1962;84(2):207-213. doi:10.1115/1.3657279.

Extended research on creep rupture of notched specimens, conducted at the University of Michigan under Air Force sponsorship, is analyzed along with recent publications of others. The combined results suggest that notch strengthening is general for all alloys studied under some test conditions and is not specific to individual materials or to a given ductility level. Quantitative explanation of notch rupture behavior in terms of unnotched-specimen properties is handicapped by present uncertainties in the basic factors controlling creep-rupture life under variable multiaxial stress.

Commentary by Dr. Valentin Fuster
J. Basic Eng. 1962;84(2):214-218. doi:10.1115/1.3657280.

The effect of a “V” notch on the tensile creep behavior of Cr-Mo steel at elevated temperature was studied to elucidate the reasons for notch strengthening or notch weakening. Special attention was paid to changes in notch profile and dimensions, as well as to structural changes of the notched portion of the specimens with the lapse of time up to rupture. Some interesting results were obtained which are different from those of an ordinary tensile test or a creep test on smooth bars, and which are useful to the complete analysis of the stress distribution at the notch-root section of the notched specimens at any time after loading and, in turn, to clarify reasons for notch strengthening.

Commentary by Dr. Valentin Fuster
J. Basic Eng. 1962;84(2):220-221. doi:10.1115/1.3657284.
Abstract
Topics: Rupture , Size effect
Commentary by Dr. Valentin Fuster
J. Basic Eng. 1962;84(2):222-225. doi:10.1115/1.3657286.

A notch-sensitive forging was tested at 1300 F to measure the effect of machining practice and of limited variations in Kt and specimen size upon notch rupture life. Within the limits studied, specimen size appeared predominant. A discontinuity was observed in the dependence of notch life upon stress.

Commentary by Dr. Valentin Fuster
J. Basic Eng. 1962;84(2):228-232. doi:10.1115/1.3657289.

Creep-rupture times at 1200 and 1400 deg F were compared for notched versus unnotched bars and for thin-walled tubes in uniaxial tension versus combined tension and internal pressure to give a 1:1 ratio of longitudinal and transverse principal stresses. Relative response to multiaxial stresses of cast DCM alloy with low ductility was not essentially different from that of René 41 alloy with higher ductility. Creep rupture times of the tubular specimens under combined stresses correlated better in terms of the shear stress invariant than of maximum principal stress.

Commentary by Dr. Valentin Fuster
J. Basic Eng. 1962;84(2):233-235. doi:10.1115/1.3657291.

Rupture life of a cast nickel-base alloy was increased by the presence of a mild notch even for test temperatures and nominal stresses at which unnotched specimens had fracture elongations of only about 0.5 per cent.

Commentary by Dr. Valentin Fuster
J. Basic Eng. 1962;84(2):236-238. doi:10.1115/1.3657292.

A method is described by which an empirical creep law, relating stress, strain, and strain rate, may be obtained from a single constant-load creep test. An example to illustrate the method is given, and the empirical creep law is compared with the results of several constant stress creep tests.

Topics: Creep , Stress
Commentary by Dr. Valentin Fuster
J. Basic Eng. 1962;84(2):239-242. doi:10.1115/1.3657295.

A life-fraction rule is often used to predict the rupture life of a piece of elevated-temperature equipment exposed to several temperature and stress conditions. It is based on the assumption that the fraction of rupture life used up in a specific time at one stress and temperature is independent of previous conditions and therefore can be estimated from tests in which exposure conditions were held constant. Test data are needed to substantiate the validity of this rule. The results of 23 constant-stress creep-rupture tests on an ASTM A201A carbon steel have shown this rule to be valid when all of the test conditions caused appreciable creep strain. Even so, it may not be valid for prolonged service above 1100 F followed by service at lower temperatures. Creep rates are reasonably predictable for constant-stress conditions when only temperature is changed. The transient creep rate accompanying a change in stress continues long enough to make creep-rate predictions unreliable. Periodic shutdowns during tests at constant stress and constant temperature have little effect on either rupture life or creep rate.

Commentary by Dr. Valentin Fuster
J. Basic Eng. 1962;84(2):243-246. doi:10.1115/1.3657296.
Abstract
Commentary by Dr. Valentin Fuster

RESEARCH PAPERS: Additional Research Papers

J. Basic Eng. 1962;84(2):247-256. doi:10.1115/1.3657297.
Abstract
Topics: Nuclear fuels
Commentary by Dr. Valentin Fuster
J. Basic Eng. 1962;84(2):257-264. doi:10.1115/1.3657298.

Crack propagation in 4 × 10-in. laminated specimens of 1100 H-19 aluminum foil under uniaxial tensile loads perpendicular to the crack direction has been investigated. While the crack behavior is similar to that found in monolithic sheets the laminates exhibit a brief arresting of crack growth before onset of sudden fracture. It was further established that the Griffith-Irwin energy-dissipation rate is a constant for any particular laminate configuration.

Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
J. Basic Eng. 1962;84(2):278-286. doi:10.1115/1.3657302.

Future advances in rocket engine-case design are aimed at exploiting the capabilities of new high-strength steels. One mode of failure of such pressure vessels occurs due to plastic instability. This paper presents the results of analyses of the plastic instability behavior of pressure vessels made of Ladish D6A C steel using three methods of analysis of varying degrees of refinement. The Mises flow rule and associated flow equations are used to analyze the instability conditions for three ratios of the axial to the circumferential stress: 1/2 , 1, 2. The results of the analysis are compared with experimental data. The most precise method of analysis which includes the elastic strain gives instability pressures which agree with experiments with errors of less than 3 1/2 per cent.

Commentary by Dr. Valentin Fuster
J. Basic Eng. 1962;84(2):287-293. doi:10.1115/1.3657303.

Apparatus has been designed and built for conducting creep tests under constant-stress or constant-load conditions. An exact mathematical solution describing the shape of the cam lever for constant stress is given. This solution applies for the large strains usually found for ductile metals and alloys, as long as the strain is uniform. The initial specimen length employed in a constant-stress creep test ordinarily is fixed by the dimensions of the cam system used. It is shown by the present analysis that the initial specimen length may be changed if an approximate adjustment is made in the initial setting of a properly designed cam lever. The direction of the load axis remains fixed and therefore the apparatus has the advantage of a more complex level-beam machine. The results of a number of creep tests under constant-stress conditions are reported.

Commentary by Dr. Valentin Fuster
J. Basic Eng. 1962;84(2):294-296. doi:10.1115/1.3657304.

Tests were conducted on uranium under constant load and cyclic temperature. The work reported was different from earlier tests in that longer periods were used for the temperature cycle.

Commentary by Dr. Valentin Fuster
J. Basic Eng. 1962;84(2):297-301. doi:10.1115/1.3657305.

Much has been learned in the past ten years about the dynamic performance of the human operator in control tasks primarily involving visual stimuli. In many human activities, however, sight is complemented or superseded by other senses. One important sense modality whose dynamic use is as yet poorly understood is touch. This paper describes an experimental technique for investigating human operator dynamics in tasks where tactile stimulus information is of primary importance; some exemplary results are presented.

Commentary by Dr. Valentin Fuster

DISCUSSIONS

Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster

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