Stress Distributions in Rotating Disks Subjected to Creep at Elevated Temperature

1957 ◽  
Vol 24 (2) ◽  
pp. 299-305
Author(s):  
A. M. Wahl
Keyword(s):  
Elevated Temperature ◽  
Creep Rate ◽  
Stress Distribution ◽  
Power Function ◽  
Constant Temperature ◽  
Creep Rupture ◽  
Flow Rule ◽  
Rotating Disks ◽  
Inside Diameter ◽  
Long Time

Abstract Assuming a creep rate proportional to a power function of the stress, curves of stress distribution as a function of the radius have been calculated for several cases of rotating disks subject to steady-state creep at elevated temperature. The disks are assumed to have central holes and to be uniformly loaded at the periphery (to simulate blade loading in turbine disks). It is also postulated that the Tresca (maximum-shear) criterion and the associated flow rule govern. The following cases are treated: (1) Disk of constant temperature and thickness with various ratios of outside to inside diameter and with various values of the exponent n in the assumed power function stress-creep rate relation. (2) Disk of constant temperature and variable thickness, the thickness at the periphery being equal to half that at the hub, for various n-values. (3) Disk with variable temperature such that the creep rate at the outside diameter is ten times that at the inside diameter for the same stress, various n-values being assumed. Limits of radial peripheral loading beyond which the derived stress-distribution curves are not valid are also determined. The results indicate that a considerable nonuniformity in stress distribution under creep conditions may exist, particularly for the lower n-values; thus creep-rupture strengths of such disks for long-time loading conditions may be lower than would be expected if based on average stress values, particularly for materials having limited ductility in long-time creep-rupture tests.

Analysis of Creep in Rotating Disks Based on the Tresca Criterion and Associated Flow Rule

1956 ◽  
Vol 23 (2) ◽  
pp. 231-238
Author(s):  
A. M. Wahl
Keyword(s):  
Steady State ◽  
Creep Rate ◽  
Constant Temperature ◽  
Variable Thickness ◽  
Constant Thickness ◽  
Flow Rule ◽  
Test Results ◽  
Rotating Disks ◽  
Tresca Criterion ◽  
Associated Flow Rule

Abstract An analysis of creep deformations in rotating disks based on the Tresca criterion and the associated flow rule is presented. Assuming steady-state creep conditions and a creep rate equal to a function of stress times a function of time, the method is applied to the following cases: (a) Disk with constant thickness and constant temperature, (b) disk with variable thickness and constant temperature, and (c) disk with variable thickness and variable temperature. In many cases, the equations can be expressed in closed form. Comparison is made with test results on rotating disks at elevated temperature as reported in a previous paper. Based on certain stress-creep-rate relations, the method is also applied to the problem of calculating the transient change in stress when the stress distribution changes from an initial to a steady-state condition during the starting period. It is suggested that the simplification effected by the use of these methods may be of value for design purposes pending the development of more accurate methods based on test results.

Creep Deformation Behavior and Microstructural Degradation During Creep of Pre-Strained 25Cr-20Ni-Nb-N Steel

2007 ◽  
Author(s):  
Nobuhiko Saito ◽  
Nobuyoshi Komai
Keyword(s):  
Creep Rate ◽  
Creep Deformation ◽  
Deformation Behavior ◽  
Minimum Creep Rate ◽  
Strengthening Mechanism ◽  
Creep Rupture ◽  
Microstructural Degradation ◽  
Solution Treated ◽  
Long Time ◽  
Strained Materials

The purpose of this study is to clarify the creep deformation behavior and microstructural degradation during creep of pre-strained 25Cr-20Ni-Nb-N steel (TP310HCbN), which has the highest creep strength among austenite stainless steels used for boiler tubes. The creep rupture strengths of the 20% pre-strained materials tested at 650°C under 210 MPa and 180 MPa were higher than those of solution-treated materials. However, the long time creep rupture strengths of the 20% pre-strained materials tested at 700°C and 750°C were lower than those of solution-treated materials. Thus, the creep strengths of the prestrained materials depend on test temperature and stress. Furthermore, the minimum creep rate of the 20% pre-strained materials and re-solution-treated materials tested at 650°C under 300MPa were 1.2 × 10−9 and 1.6 × 10−8 s−1, respectively. Thus, the minimum creep rate of the 20% pre-strained materials was lower than for re-solution-treated materials. The creep strengthening mechanism of the pre-strained materials at 650°C was considered to be that high-density dislocations were maintained until the late stage of creep. On the other hand, the creep rupture strengths of the 20% pre-strained materials were lower than those of solution-treated materials tested at over 700°C because of agglomeration and coarsening of precipitates and the recovery of dislocations.

scholarly journals INDUCTION OF METASTASIS OF FROG CARCINOMA BY INCREASE OF ENVIRONMENTAL TEMPERATURE

1949 ◽  
Vol 89 (3) ◽  
pp. 269-278 ◽  
Author(s):  
Balduin Lucké ◽  
Hans Schlumberger
Keyword(s):  
Tissue Culture ◽  
Elevated Temperature ◽  
Constant Temperature ◽  
Rana Pipiens ◽  
Environmental Temperature ◽  
Kidney Tumors ◽  
Primary Tumors ◽  
Metastatic Dissemination ◽  
Leopard Frogs ◽  
Tumor Bearing

Metastasis of the kidney carcinoma of leopard frogs (Rana pipiens) has been induced by exposing tumor-bearing animals for approximately 50 days to a constant temperature of 28°C. Under these conditions 54 per cent of the frogs developed secondary growths, whereas in groups kept at 18° or at 7° metastatic dissemination was found in only 6 per cent. Moreover, at the elevated temperature the metastases were usually more numerous and more widely disseminated; they were also fairly uniform in size, suggesting that they had developed at nearly the same time. Dissemination of the kidney tumors was influenced by the nutritional state of the frogs, occurring more readily in well nourished than in poorly nourished animals. Periodic Roentgen ray examinations showed that the size of the primary tumors was not significantly or uniformly affected during the course of the experiments. No correlation was found between change in size of the kidney tumors and the incidence of their metastasis. Although the mechanism by which temperature induces metastasis of frog carcinoma cannot as yet be elucidated, previous experiments with this tumor indicate that certain factors at least may be involved: Elevation of temperature has been found to cause more ready detachment of cells of frog carcinoma in tissue culture; to bring about increased velocity of locomotion of the detached cells; to lead more promptly and efficiently to vascularization of transplants; and to effect their greater invasiveness.

Long Term Creep Properties of a Die-Cast Mg-Al-Ca Alloy

2007 ◽  
Vol 561-565 ◽  
pp. 163-166
Author(s):  
Yoshihiro Terada ◽  
Tatsuo Sato
Keyword(s):  
Creep Rate ◽  
Magnesium Alloys ◽  
Cast Alloy ◽  
Rupture Life ◽  
Testing Temperature ◽  
Creep Rupture ◽  
Die Cast ◽  
Cast Magnesium Alloys ◽  
Term Creep ◽  
Cast Magnesium

Creep rupture tests were performed for a die-cast Mg-Al-Ca alloy AX52 (X representing calcium) at 29 kinds of creep conditions in the temperature range between 423 and 498 K. The creep curve for the alloy is characterized by a minimum in the creep rate followed by an accelerating stage. The minimum creep rate (ε& m) and the creep rupture life (trup) follow the phenomenological Monkman-Grant relationship; trup = C0 /ε& m m. It is found for the AX52 die-cast alloy that the exponent m is unity and the constant C0 is 2.0 x 10-2, independent of creep testing temperature. The values of m and C0 are compared with those for another die-cast magnesium alloys. The value m=1 is generally detected for die-cast magnesium alloys. On the contrary, the value of C0 sensitively depends on alloy composition, which is reduced with increasing the concentration of alloying elements such as Al, Zn and Ca.

Creep Tests of Rotating Disks at Elevated Temperature and Comparison With Theory

1954 ◽  
Vol 21 (3) ◽  
pp. 225-235
Author(s):  
A. M. Wahl ◽  
G. O. Sankey ◽  
M. J. Manjoine ◽  
E. Shoemaker
Keyword(s):  
Elevated Temperatures ◽  
Experimental Program ◽  
Test Results ◽  
Rotating Disks ◽  
Creep Tests ◽  
Shear Theory ◽  
Heat Treated ◽  
Long Time ◽  
Average Tension ◽  
Creep Deformations

Abstract A theoretical and experimental program involving methods of calculating creep in rotating disks at elevated temperatures is described. This program consisted primarily of the following: (a) Obtaining forged disks from the same ingot of 12 per cent chrome steel, all disks being forged and heat-treated in the same manner; (b) making spin tests at 1000 F on three of these disks for periods up to about 1000 hr; ( ) making long-time tension-creep tests at 1000 F on many specimens cut out circumferentially from several of the other disks at stresses approximating those of the spin tests; (d) investigating theoretical methods of calculation of creep deformation in such disks; and (e) comparison of spin-test results with those calculated theoretically using average tension-creep data. It was found that available methods of calculating rotating disks based on the Mises criterion gave creep deformations too low compared to the test values, i.e., on the unsafe side for design. Considerably better agreement between test and theoretical results is obtained if the latter is based on the maximum-shear theory. Some discussion is given of the reasons for the better agreement obtained using the latter theory; these are believed to be related in part to the anisotropy of the forged material tested. Further tests on other materials are necessary before general conclusions can be drawn; however, in the absence of test data it is suggested that a conservative course in design for such disks is to apply the maximum-shear theory.

Structural Integrity Code and Regulatory Issues in the Design of High Temperature Reactors

2008 ◽  
Author(s):  
William J. O’Donnell ◽  
Amy B. Hull ◽  
Shah Malik
Keyword(s):  
High Temperature ◽  
Elevated Temperature ◽  
Structural Integrity ◽  
Cyclic Creep ◽  
Creep Rupture ◽  
Creep Fatigue ◽  
Asme Code ◽  
High Temperature Reactors ◽  
Gen Iv ◽  
Very High

Since the 1980s, the ASME Code has made numerous improvements in elevated-temperature structural integrity technology. These advances have been incorporated into Section II, Section VIII, Code Cases, and particularly Subsection NH of Section III of the Code, “Components in Elevated Temperature Service.” The current need for designs for very high temperature and for Gen IV systems requires the extension of operating temperatures from about 1400°F (760°C) to about 1742°F (950°C) where creep effects limit structural integrity, safe allowable operating conditions, and design life. Materials that are more creep and corrosive resistant are needed for these higher operating temperatures. Material models are required for cyclic design analyses. Allowable strains, creep fatigue and creep rupture interaction evaluation methods are needed to provide assurance of structural integrity for such very high temperature applications. Current ASME Section III design criteria for lower operating temperature reactors are intended to prevent through-wall cracking and leaking and corresponding criteria are needed for high temperature reactors. Subsection NH of Section III was originally developed to provide structural design criteria and limits for elevated-temperature design of Liquid-Metal Fast Breeder Reactor (LMFBR) systems and some gas-cooled systems. The U.S. Nuclear Regulatory Commission (NRC) and its Advisory Committee for Reactor Safeguards (ACRS) reviewed the design limits and procedures in the process of reviewing the Clinch River Breeder Reactor (CRBR) for a construction permit in the late 1970s and early 1980s, and identified issues that needed resolution. In the years since then, the NRC, DOE and various contractors have evaluated the applicability of the ASME Code and Code Cases to high-temperature reactor designs such as the VHTGRs, and identified issues that need to be resolved to provide a regulatory basis for licensing. The design lifetime of Gen IV Reactors is expected to be 60 years. Additional materials including Alloy 617 and Hastelloy X need to be fully characterized. Environmental degradation effects, especially impure helium and those noted herein, need to be adequately considered. Since cyclic finite element creep analyses will be used to quantify creep rupture, creep fatigue, creep ratcheting and strain accumulations, creep behavior models and constitutive relations are needed for cyclic creep loading. Such strain- and time-hardening models must account for the interaction between the time-independent and time-dependent material response. This paper describes the evolving structural integrity evaluation approach for high temperature reactors. Evaluation methods are discussed, including simplified analysis methods, detailed analyses of localized areas, and validation needs. Regulatory issues including weldment cracking, notch weakening, creep fatigue/creep rupture damage interactions, and materials property representations for cyclic creep behavior are also covered.

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