Unresolved Issues With Regard to Creep and Creep Fatigue Life Prediction

2002 ◽  
Author(s):  
J. Oh ◽  
N. Katsube ◽  
F. W. Brust
Keyword(s):  
Cyclic Loading ◽  
Damage Evolution ◽  
Life Prediction ◽  
Loading Condition ◽  
Cyclic Strain ◽  
Rupture Process ◽  
Steady State Creep ◽  
Creep Failure ◽  
Cyclic Loading Condition ◽  
Creep Fatigue

This paper studies intergranular creep failure of high temperature service material under a stress-controlled unbalanced cyclic loading condition. The grain boundary rupture process was numerically analyzed using Tvergaard’s axisymetric model. The present numerical model incorporated the experimentally verified Murakami-Ohno cyclic strain hardening creep law and Norton’s creep law. The numerical results show that void growth accelerates under cyclic loading condition. Also, analysis shows that a steady state creep law is not sufficient to analyze damage evolution under cyclic loading conditions.

Studies on the Effect of Cyclic Loading on Grain Boundary Rupture Time

2005 ◽  
Vol 129 (1) ◽  
pp. 1-10
Author(s):  
J. Oh ◽  
F. W. Brust ◽  
N. Katsube
Keyword(s):  
High Temperature ◽  
Cyclic Loading ◽  
Grain Boundary ◽  
Loading Condition ◽  
Cavity Growth ◽  
Symmetric Model ◽  
Creep Failure ◽  
Cyclic Loading Condition ◽  
Constant Loading ◽  
Material Life

This paper studies intergranular creep failure of high-temperature service material under a stress-controlled unbalanced cyclic loading condition. The experimentally verified Murakami–Ohno strain-hardening creep law and Norton’s creep law are incorporated into the Tvegaard’s axis-symmetric model for the constrained grain boundary rupture analysis. Based on the physically realistic Murakami–Ohno creep law, it is shown that the cavity growth becomes unconstrained upon the stress reversal from compression to tension. This leads to the prediction that the material life under a cyclic loading condition is shorter than that under a constant loading. Based on the classical Norton’s law, the predicted material life under a cyclic loading condition remains the same as that under a constant loading. The obtained numerical results qualitatively match recent experimental results by Arai, where the life under a cyclic loading can be much shorter than that under a constant loading. There are many cases where engineers use a simple Norton’s creep law because of its simplicity. The present work suggests that more physically realistic creep laws should be used when cyclic loading must be considered.

On the Development of Physically Based Life Prediction Models in the Thermo Mechanical Fatigue of Ni-Base Superalloys

2011 ◽  
Vol 465 ◽  
pp. 47-54 ◽  
Author(s):  
Stephen D. Antolovich ◽  
Robert L. Amaro ◽  
Richard W. Neu ◽  
A Staroselsky
Keyword(s):  
High Temperature ◽  
Damage Evolution ◽  
Life Prediction ◽  
Prediction Models ◽  
High Temperature Fatigue ◽  
Mechanical Fatigue ◽  
Use Of Resources ◽  
Physically Based ◽  
Creep Fatigue ◽  
Materials Used

In a world increasingly concerned with environmental factors and efficient use of resources, increasing operating temperatures of high temperature machinery can play an important role in meeting these goals. In addition, the cost of failure of such devices is rapidly becoming prohibitive. For example, in an airline crash airframe and engine manufacturers are, on average, held liable for 1,000,000 euros per fatality excluding the loss of property. Thus there is considerable pressure to make machinery that can operate much more safely at high temperatures. This means that the old ways of guarding against high temperature fatigue failure (e.g. factor of safety, S/N curves, creep life) are no longer acceptable; more reliable, accurate, and efficient means are needed to manage life, durability and risk. In this paper, high temperature fatigue is considered in terms of past successes and current challenges. Particular emphasis is placed on understanding damage mechanisms and their interactions both in terms of scientific interest and technological importance. Materials used in nuclear reactors (e.g. selected steels and solid solution Ni-base alloys) and in hot sections of jet engines (e.g. superalloys) are used as vehicles to illustrate damage evolution and interaction. Phenomenological life prediction models are presented and compared with physics-based damage evolution/interaction models which are based on observed physical processes such as creep/fatigue/environment interactions. It is shown that in many cases, in spite of the emphasis on creep-fatigue interactions, the most damaging forms of damage that occur under thermo-mechanical fatigue (TMF) loading result from the interaction of slip bands with oxidized boundaries.

scholarly journals The influence of stress level on the ratcheting magnitude and progress rate in steel alloys under uniaxial loading conditions

2021 ◽  
Author(s):  
Prasanth Chandrasekar
Keyword(s):  
Cyclic Loading ◽  
Plastic Strain ◽  
Strain Rate ◽  
Loading Condition ◽  
Stress Amplitude ◽  
Fatigue Loading ◽  
Mean Stress ◽  
Cyclic Loading Condition ◽  
Ratcheting Strain ◽  
Cyclic Damage

Engineering materials in their service life undergo symmetric or asymmetric fatigue loading, which leads to fatigue damage in the material. Ratcheting damage is due to the application of mean stress under cyclic loading condition. From deformation behavior perspective, application of mean stress under stress-controlled fatigue loading gives rise to accumulation of plastic strain in the material. Ratcheting strain increases with an increase in applied mean stress and stress amplitude. In addition, ratcheting behavior will increase in cyclic damage with the rise in strain accumulation and it can be illustrated by a shift in the hysteresis loop towards large plastic strain amplitudes. This study focuses on the ratcheting behavior of different steel materials under uniaxial cyclic loading condition and suggests a suitable method to arrest ratcheting by loading the materials at zero ratcheting strain rate condition with specified mean stress and stress amplitudes. The three dimensional surface is created with stress amplitude, mean stress and ratcheting strain rate for different steel materials. This represents a graphical surface zone to study the ratcheting strain rates for various mean stress and stress amplitude combinations.

Shear Performance of Rock Joint Reinforced by Fully Encapsulated Rock Bolt Under Cyclic Loading Condition

2019 ◽  
Vol 52 (8) ◽  
pp. 2681-2690 ◽  
Author(s):  
Xuezhen Wu ◽  
Yujing Jiang ◽  
Bin Gong ◽  
Zhenchang Guan ◽  
Tao Deng
Keyword(s):  
Cyclic Loading ◽  
Loading Condition ◽  
Rock Joint ◽  
Rock Bolt ◽  
Cyclic Loading Condition ◽  
Shear Performance
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