Prediction of Creep Crack Initiation Under Transient Stress Conditions

2006 ◽  
Author(s):  
Catrin M. Davies ◽  
Noel P. O’Dowd ◽  
Kamran M. Nikbin ◽  
George A. Webster
Keyword(s):  
Steady State ◽  
Stress Distribution ◽  
Crack Initiation ◽  
Creep Strain ◽  
Crack Tip ◽  
Steady State Creep ◽  
Creep Model ◽  
Small Scale ◽  
Creep Crack ◽  
Initial Loading

A method to predict the time for creep crack initiation (CCI) from a stationary crack tip is presented. The method is relevant to situations where small scale yield or widespread plasticity conditions prevail on initial loading. Initiation is considered to occur at the attainment of a critical creep strain at a small distance from the crack tip. The model proposed here considers the integrated effects of creep strain accumulation as the stress distribution changes from that on initial loading (controlled by J) to the steady state creep stress distribution (controlled by C*). Material properties are chosen to represent Type 316H stainless steel at 550°C and plane strain conditions are considered. For the conditions examined, the CCI times predicted are significantly shorter times than those predicted using a steady state creep model.

Steady State Crack Growth in Shape Memory Alloys

2013 ◽  
Author(s):  
Selcuk Hazar ◽  
Wael Zaki ◽  
Ziad Moumni ◽  
Gunay Anlas
Keyword(s):  
Steady State ◽  
Stress Distribution ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Crack Growth ◽  
Crack Tip ◽  
Reverse Transformation ◽  
Small Scale ◽  
Local Algorithms ◽  
Non Local

Shape memory alloys experience phase transformation from austenite to martensite around crack tip. When the crack advances, martensitic transformation occurs at the tip and the energy that goes into transformation results in stable crack growth like in the case of plastic deformation. In literature, there are studies on steady-state crack growth in elasto-plastic materials with small scale yielding around crack tip that use stationary movement methods similar to non-local algorithms. In this work, Mode I steady-state crack growth in an edge cracked Nitinol plate is modeled using a non-local stationary movement method. The Zaki-Moumni (ZM) constitutive model is utilized for this purpose. The model is implemented in ABAQUS by means of a user-defined material subroutine (UMAT) to determine transformation zones around the crack tip. Steady-state crack growth is first simulated without considering reverse transformation to calculate the effect of transformation on stress distribution in the wake region, then reverse transformation is taken into account. Stress distribution and transformation regions calculated for both cases are compared to results obtained for the case of a static crack.

Analysis of 316H Creep Crack Initiation Data at 550℃ using A Crack Tip Constraint Parameter

2021 ◽  
pp. 107746
Author(s):  
Seung-Ho Lee ◽  
Hyun-Woo Jung ◽  
Yun-Jae Kim ◽  
Kamran Nikbin ◽  
Robert A. Ainsworth
Keyword(s):  
Crack Initiation ◽  
Crack Tip ◽  
Creep Crack ◽  
Crack Tip Constraint

High Temperature Rotors: Failure Mechanisms and Remnant Life Assessment

2006 ◽  
Author(s):  
Xiaoling Zhang
Keyword(s):  
High Temperature ◽  
Cyclic Loading ◽  
Crack Initiation ◽  
Crack Growth ◽  
Creep Strain ◽  
Operating Temperature ◽  
Failure Mechanisms ◽  
Creep Rupture ◽  
High Operating Temperature ◽  
Creep Crack

This paper presents the common failure mechanisms of high temperature rotors and the engineering approaches to their remnant life prediction. • Rotor bore fatigue crack growth — cracks from original forging defects or induced during long service life may grow under cyclic loading into its critical size causing fast fracture. • Shaft surface fatigue-creep interaction — high tensile residual stress relaxation under high operating temperature causes creep crack initiation. The cracks would then grow under the combination of cyclic loading and high operating temperature. • Remanent creep life at the centre of the rotor is based on the time while accumulated creep strain reaches its threshold level. • Creep rupture could occur at other locations such as the outside surface of the shaft at discs/shaft radii or blade fixings. Finite element method is a powerful tool to analyse stresses, temperature transients, creep strain and reference stress for creep rupture. Fracture mechanics analyses with R5 & R6 approaches were used to estimate the crack initiation and growth rates, the critical crack sizes and the type of the failure. Appropriate Paris law and Norton creep laws were used for fatigue and creep crack growth. Depending on the failure mechanism, a rotor’s remnant life is defined in terms of allowable starts and operating hours.

Correlation Analysis Between Time-Dependent Creep Crack-Tip Stress and Constraint Effect on Creep Crack Initiation Time

2020 ◽  
Author(s):  
Seung-Ho Lee ◽  
Hyun-Woo Jung ◽  
Yun-Jae Kim ◽  
Kamran Nikbin ◽  
Robert A. Ainsworth
Keyword(s):  
Crack Initiation ◽  
Correlation Analysis ◽  
Creep Crack Growth ◽  
Crack Tip ◽  
Compact Tension ◽  
Time Dependent ◽  
Initiation Time ◽  
Constraint Effect ◽  
Creep Crack ◽  
Crack Tip Stress

Abstract In this study, to qualify the constraint effect on creep crack initiation, the correlation analysis between proposed constraint parameter Q’ using time-dependent creep crack-tip stress and creep crack initiation time variable Ai was performed. Ai implies the influence of constraint effect on creep crack initiation. The procedure to calculate the Ai and the Q’-parameter was presented. To evaluate various status of constraint effect, creep crack growth tests for twenty-one compact tension specimens of Type 316H stainless steel at 550°C were investigated. The results of correlation analysis explain the reason for the different initiation time at the same C* level in respect of constraint effect.

scholarly journals Characterization and Modeling of Room-Temperature Compressive Creep Behavior of a Near α TA31 Titanium Alloy

Metals ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 1190
Author(s):  
Weixin Yu ◽  
Shusen Hou ◽  
Zhijun Yang ◽  
Jinyong Zhang ◽  
Shaoting Lang
Keyword(s):  
Titanium Alloy ◽  
Steady State ◽  
Strain Rate ◽  
Compressive Stress ◽  
Creep Behavior ◽  
Room Temperature ◽  
Steady State Creep ◽  
Creep Model ◽  
Compression Tests ◽  
Creep Stage

The creep behavior of a near α TA31 titanium alloy under different compressive pressures has been studied by long-time (up to 500 h) compression tests at room temperature. The experimental results show that several thresholds of the compressive pressure were found to exist in the compression process of the TA31 alloy. When the compressive stress is lower than 0.80Rp0.2, there is no creep. There is a steady-state creep stage at the compressive stresses between 0.85Rp0.2 and 0.93Rp0.2, in which the strain rate is approximately a constant value. When the compressive stress reaches a threshold stress between 0.93Rp0.2 and 0.95Rp0.2, the sample enters the accelerating creep stage directly. The creep model of TA31 alloy has been built by using the regression method, from which the creep strain rate of TA31 titanium alloy in the steady-state creep stage under different compressive stress levels can be calculated. The mean difference between the calculated and the experimental value is 2.54%, indicating the creep model can efficiently predict the creep behavior of TA31 alloy.

Relationship between the steady-state creep strain rate and time to fracture of pearlitic and austenitic steels

1985 ◽  
Vol 17 (6) ◽  
pp. 744-749 ◽  
Author(s):  
F. F. Giginyak ◽  
T. N. Mozharovskaya ◽  
B. T. Timofeev ◽  
V. P. Ulin
Keyword(s):  
Steady State ◽  
Strain Rate ◽  
Creep Strain ◽  
Steady State Creep ◽  
Creep Strain Rate ◽  
Austenitic Steels ◽  
Time To Fracture
Sign in / Sign up

Export Citation Format

Share Document