| Effects of Aging and Plane Strain Constraint on the Ductility of an Aluminum Alloy |
MAR 82 |
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| Authors:
E. Ryan; S. Purushothaman; J. K. Tien
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 | The deformation and fracture behavior of 2024 plate in the underaged, peak-aged and overaged conditions were studied under uniaxial loading and under plane strain. The specimens were taken from a 0.83 cm thick plate in the T351 condition. After solution heat treating at 495 C for one hour and water quenching, the specimens were aged for 2, 12 or 36 hours. Overaging caused the maximum plane strain sensitivity. |
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| A Back-Stress-Based Rationale for Creep Behavior During Dynamic Aging |
AUG 80 |
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| Authors:
J. K. Tien; S. Purushothaman; M. W. Mahoney; N. E. Paton
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| Creep tests were conducted on Ti-5Al-5Zr-0.5Si at 811 K at strains from 10(super -8) to 10(super -7)/s. The back stress at low strain rates was found to be similar to the Orowan-Ashby stress required to bypass the silicide precipitates formed during creep on mobile dislocations. |
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| The Role of the Alloy Matrix in the Creep Behavior of Particle- Strengthened Alloys |
JUL 80 |
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| Authors:
O. Ajaja; T. E. Howson; S. Purushothaman; J. K. Tien
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| The role of the matrix strength in oxide-dispersion and gamma prime precipitate strengthened nickel alloys on creep rate was studied. A mathematical model is proposed. The apparent stress dependence on creep rate was determined as the major factor effecting alloy matrix creep behavior. |
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| Synchrotron Radiation Microradiography of Cracks in Aluminum Alloys |
APR 80 |
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| Authors:
S. Purushothaman; N. F. Panayotou; J. K. Tien
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| The feasibility was investigated of using the intense synchrotron X- radiation to microradiographically image both surface and internal cracks in reasonably thick (200 micrometers) specimens of aluminum base alloys. It is concluded that synchrotron microradiography can be successfully used to image such defects as fatigue microcracks, creep induced wedge cracks and notches with a reasonable contrast and within exposure times of about a minute or less. The resolution capability of ... |
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| On the Concept of Back Stress in Particle Strengthened Alloys |
80 |
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| Authors:
S. Purushothaman; O. Ajaja; J. K. Tien; HENRY KRUMB SCHOOL OF MINES NEW YORK
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| Creep back stress is discussed theoretically and the results of the analysis are compared to experimental values for particle strengthened nickel superalloys. The study concludes that back stress theory can identify creep strengthening contributions from second phase particles and matrix solid solution phase in these alloys. This theory is important in explaining the sharp applied stress and temperature dependencies on creep behavior for the alloys. |
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| GENERALIZED THEORY OF FATIGUE CRACK PROPAGATION--PART II: DERIVATION OF THRESHOLD AND PARIS REGIME CRACK GROWTH RATES |
AUG 78 |
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| Authors:
J. K. Tien; S. Purushothaman
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| This review gives examples of noncrystallographic fatigue crack propagation of the ductile and superimposed brittle types. Udimet 700 and Ti- 6Al-4V are used as examples of fatigue crack propagation which may be strongly constrained by crystallography. Mathematical models are given to describe the mechanisms for continuous ductile noncrystallographic crack growth, ledge controlled discontinuous advance of noncrystallographic crack fronts, and motion of crack fronts strongly constrained by crystallography. |
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| Kinetics of Environmental Fatigue Crack Growth in Nickel-Copper Alloy-- Part I: In Vacuum and Oxygen |
AUG 78 |
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| Authors:
S. Purushothaman; R. J. Richards; J. K. Tien; J. D. Frandsen
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| Fatigue crack growth rates have been determined in a nickel-copper alloy in the mild test environments of vacuum and oxygen. It is found that the fatigue crack growth mode in both vacuum and oxygen is ductile and the growth rate is sensibly independent of the maximum stress intensity levels and stress intensity ratio. The growth rate is found to be lower in vacuum than in oxygen, and the growth rate ... |
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| Kinetics of Environmental Fatigue Crack Growth in a Nickel-Copper Alloy- -Part II: In Hydrogen |
AUG 78 |
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| Authors:
R. J. Richards; S. Purushothaman; J. K. Tien; J. D. Frandsen; O. Buck
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| A systematic matrix of fatigue crack growth rate data in a hydrogen environment has been generated in a nickel-copper alloy and compared with the base line data in the milder oxygen and vacuum environments described in the preceding paper. It is found that crack growth in the hydrogen environment is characterized by high values of the Paris equation exponent and faster crack propagation rates as compared to those in the ... |
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| high-power, ultrasonic fatigue testing machine |
JUL 75 |
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| Authors:
J. K. Tien; S. Purushothaman; R. M. Arons; j. p. wallace
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| a machine capable of fatigue tesing high strength alloys at an ultrasonic frequency (20 khz), and a range of temperatures likely to be encountered by such materials in aerospace and power generation applications and in basic research, is described. the machine is assembled entirely from commercially available components used in ultrasonic joining processes. basically, it consists of a power supply module and heavy duty transducer capable of delivering up to ... |
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| high-power, ultrasonic fatigue testing machine |
JUL 75 |
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| Authors:
J. K. Tien; S. Purushothaman; R. M. Arons; j. p. wallace; O. Buck
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| a machine capable of fatigue testing high strength alloys at an ultrasonic frequency (20 khz), and a range of temperatures likely to be encountered by such materials in aerospace and power generation applications and in basic research, is described. the machine is assembled entirely from commercially available components used in ultrasonic joining processes. basically, it consists of a power supply module and heavy duty transducer capable of delivering up to ... |
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| SLOW CRYSTALLOGRAPHIC FATIGUE CRACK GROWTH IN A NICKEL-BASE ALLOY |
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| Authors:
S. Purushothaman; J. K. Tien
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| Fatigue crack propagation rates at very low cyclic stress intensity levels (1 to 3 MNm(Super -3/2) have been measured in cube-oriented, planar slip nickel-base superalloy monocrystals using a high frequency (20 kHz) resonant fatigue testing technique. It is found that crack propagation is entirely along the crystallographic slip planes and the crack growth rate does not drop off into a threshold behavior but follows a power law with a power ... |
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| ROLE OF BACK STRESS IN THE CREEP BEHAVIOR OF PARTICLE STRENGTHENED ALLOYS |
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| Authors:
S. Purushothaman; J. K. Tien
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| Based on the analysis of recent creep data on gamma prime strengthened wrought nickel-base superalloy, an oxide dispersion strengthened (ODS) nickel-base solid solution alloy, and an ODS nickel-base superalloy, it is concluded that creep in such particle strengthened systems can be mechanistically described through an effective stress dependence that includes a back stress consistent with the alloy microstructure. |
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