Formulation of Cross-Hardening in Creep and its Effect on the Creep Damage Process of Copper

1986 ◽  
Vol 108 (2) ◽  
pp. 167-173 ◽  
Author(s):  
S. Murakami ◽  
Y. Sanomura ◽  
K. Saitoh
Keyword(s):  
Creep Damage ◽  
Principal Stress Rotation ◽  
Stress Rotation ◽  
Polycrystalline Metals ◽  
Proposed Model ◽  
Slip Planes ◽  
Damage Process ◽  
Cross Hardening ◽  
Active Slip ◽  
Anisotropic Creep

The present paper is concerned with the modelling of creep and creep damage in polycrystalline metals and the experimental evaluation of the proposed model. By ascribing the reduction of creep rates caused by the principal stress rotation (i.e., cross-hardening) to the intersection mechanism of dislocations on active slip planes in crystal grains, a constitutive equation of creep describing the cross-hardening is first formulated. Then, in view of the metallurgical observations on the nucleation and the growth of grain boundary cavities in the creep damage process, an evolution equation of anisotropic creep damage is expressed as a function of the stress, a second rank damage tensor and the creep rate of the material. Finally, the validity of the proposed theory is discussed by performing systematic creep damage tests of thin-walled copper tubes under nonsteady multiaxial states of stress at 250°C.

scholarly journals A state-dependent soil model and its application to principal stress rotation simulations

2018 ◽  
Vol 14 (11) ◽  
pp. 155014771880875
Author(s):  
Zhongtao Wang ◽  
Peng Liu ◽  
Andrew Hin Cheong Chan
Keyword(s):  
Cyclic Loading ◽  
Principal Stress ◽  
Static Condition ◽  
Calibration Method ◽  
Model Parameters ◽  
Principal Stress Rotation ◽  
Stress Rotation ◽  
Stress Orientation ◽  
State Dependent ◽  
Proposed Model

The plastic strain caused by principal stress rotation is one of the most important factors contributing to substantial deformation under earthquake, wave or traffic loading. The original Pastor–Zienkiewicz Mark III model, a well-known model for the analysis of the dynamic response under cyclic loading, is unable to consider the effects of principal stress orientation as well as state-dependent dilatancy. In this article, a new constitutive model for sand is developed to consider both aforementioned effects based on the original Pastor–Zienkiewicz Mark III model. There are 14 model parameters in total for the static condition and three extra parameters for cyclic loading, and a corresponding calibration method of model parameters is proposed. The predictive capability of the proposed model is verified with the results of a series of experiments on sand, including undrained monotonic tests in different fixed principal stress orientations and undrained cyclic rotational shear tests. The comparisons indicate that the proposed model can effectively incorporate the effects of principal stress orientation and state-dependent dilatancy.

Atomic Diffusion Induced Damage of Ni-Base Super Alloy at Elevated Temperature

2016 ◽  
Author(s):  
Motoki Takahashi ◽  
Ken Suzuki ◽  
Hideo Miura
Keyword(s):  
Power Plants ◽  
Creep Damage ◽  
Rotor Blades ◽  
Atomic Scale ◽  
Atomic Diffusion ◽  
Kernel Average Misorientation ◽  
Damage Process ◽  
Creep Loading ◽  
Ebsd Method ◽  
Base Superalloy

Ni-base superalloys consisting of binary phases such as cuboidal γ’ (Ni3Al) precipitates orderly dispersed in the γ matrix (Ni-rich matrix) have been generally used for rotor blades in energy power plants. However, fine dispersed γ’ precipitates are coarsened perpendicularly to the applied load direction during high temperature creep loading. As this phenomenon called “Rafting” proceeds, the strengthened micro texture disappears and then, cracks starts to grow rapidly along the boundaries of the layered texture. Thus, it is very important to evaluate the change of the crystallinity of the alloy in detail for explicating the atomic scale damage process. In this study, the change of the micro-texture of the Ni-base superalloy (CM247LC) was observed by using EBSD method. The change in the crystallinity was evaluated using both Kernel Average Misorientation (KAM) and image quality (IQ) values. The KAM value indicates the dislocation density and the IQ value shows the order of atom arrangement in the observed area. As a result, KAM value showed no significant change with increasing the creep damage. On the other hand, the IQ value monotonically shifted to lower values and the average IQ value gradually decreased as the creep loading time increased. Decreasing IQ value without change in KAM value implies that the density of point defects such as vacancies mainly increased under creep loading and ordered Ll2 structure became disordered. Therefore, the creep damage of this alloy is mainly dominated by not the accumulation of dislocations, but the increase in the disorder of atom arrangement in the micro texture caused by the diffusion of component elements.

scholarly journals Volume Texture of a Deformed Quartzite Observed With U-Stage Microscopy and Neutron Diffractometry

1999 ◽  
Vol 31 (4) ◽  
pp. 239-248 ◽  
Author(s):  
H. Ghildiyal ◽  
E. Jansen ◽  
A. Kirfel
Keyword(s):  
Neutron Diffraction ◽  
Pole Figure ◽  
North West ◽  
Pole Figures ◽  
Slip Planes ◽  
Subsequent Calculation ◽  
Kaoko Belt ◽  
Universal Stage ◽  
Active Slip

The volume texture of a naturally deformed quartzite from the Kaoko belt, North-West Namibia, has been analysed by both universal stage microscopy and neutron diffraction. Universal stage microscopy is restricted to the determination of the base pinacoid preferred orientation in quartzite. For a more complete description of the texture, the orientations of additional crystal planes, such as first and second order prisms as well as positive and negative rhombs, must be known. Neutron methods allow the evaluation of pole figures of all Bragg reflecting planes, of which those of the first order prisms being considered to be the most active slip planes, are of particular interest. Drawbacks of neutron diffraction, i.e. the faking of an eventually absent inversion centre and lack of resolution, can be overcome by pole figure inversion and subsequent calculation of desired pole figures. Both, universal stage microscopy and neutron diffraction yield well comparable results, of course only with respect to the pole figure of the c-axis.

LOAD SEQUENCE ANALYSIS IN FATIGUE LIFE PREDICTION

2015 ◽  
Vol 39 (4) ◽  
pp. 819-828 ◽  
Author(s):  
Moises Jimenez ◽  
Jose Martinez ◽  
Ulises Figueroa
Keyword(s):  
Life Prediction ◽  
Rear Axle ◽  
Element Analysis ◽  
Proposed Model ◽  
Damage Process ◽  
Load Sequence ◽  
Number Of Cycles ◽  
Total Damage ◽  
Damage Rule

In this work, the load sequence effect is analyzed in fatigue test. One of the assumptions of the Miner’s rule is that the total damage is equal to the sum of the damages absorbed; however, different models have been proposed to take the effect of the load sequences under two load levels into account. To analyze this effect, a case study of a rear axle mounting bracket has been performed, analyzing six different sequences of three load levels, defined as Low, Medium and High. A Finite Element Analysis was also performed using MSC Tools. With these results and a series of test at constant amplitude, the component S-N curve was made. 24 tests at room temperature were performed in order to evaluate the damage process. It was found that, under a block of three load levels, the sequence of each block has an effect in the total amount of damage under the same number of cycles. With this information it is possible to improve the life prediction through the modification of the damage rule. The proposed model uses a factor which depends on the ultimate strength and yield point. This is an advantage over other approaches, as the other models need additional dynamic tests to obtain coefficients to perform the life prediction.

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