Experimental Investigation of In-Plane Constraint and Out-of-Plane Constraint Effects on Creep Crack Growth

2012 ◽  
Author(s):  
Jian-Ping Tan ◽  
Guo-Zhen Wang ◽  
Fu-Zhen Xuan ◽  
Shan-Tung Tu
Keyword(s):  
Experimental Investigation ◽  
High Temperature ◽  
Crack Growth ◽  
Creep Crack Growth ◽  
Specimen Thickness ◽  
Constraint Effect ◽  
Integrity Assessment ◽  
Creep Crack ◽  
Out Of Plane ◽  
Constraint Effects

In order to establish an accurate integrity assessment of structures containing defects at high temperature, it is necessary to clarify the constraint effect on creep crack growth (CCG) property. However, the experimental investigation of constraint effects on creep crack growth has been little studied. In this study, the effects of the out-of-plane constraint and the in-plane constraint were investigated and considered via data obtained from compact tension (CT) specimens with different thicknesses and single edge-notched tensile (SENT) specimen. The results show that the constraint effect induced by specimen thickness (out-of-plane) and specimen types (in-plane) on CCG rate is related to load level C*. In the lower C* region, there are obvious differences in the CCG rate for different specimens, while the CCG rates of the different specimens are within a scatter band in the higher C* region. Meanwhile, the CCG rate da/dt versus C* on log-log scale is composed of two straight lines with different slops instead of a single linear relation. Because the straight line slope in the lower C* region is smaller than that in the higher C* region, it would be non-conservative if the CCG rate in the lower C* was extrapolated from that in the higher C*. Therefore, in order to conduct integrity assessment and life prediction at high temperature accurately, it is necessary to obtain the actual CCG rate in the lower C* (long-term data), and the constraint effect induced by specimen thickness and loading modes should be considered.

Specimen Geometry Effects on Creep Crack Initiation and Growth in Parent Materials and Weldments

2011 ◽  
Author(s):  
Catrin M. Davies ◽  
Robert C. Wimpory ◽  
David W. Dean ◽  
Kamran M. Nikbin
Keyword(s):  
High Temperature ◽  
Crack Initiation ◽  
Crack Growth ◽  
Creep Crack Growth ◽  
Parent Material ◽  
Crack Growth Behaviour ◽  
Creep Crack ◽  
Significant Difference ◽  
Constraint Effects

High temperature crack growth in weldments is of great practical concern in high temperature plant components. Cracking typically occurs in the heat affected zone (HAZ) and often propagates into adjacent parent material (PM). Recently, the importance of constraint effects on creep crack growth behaviour has been recognised and creep crack growth testing on a range of specimen geometries has been performed. Experimental crack growth testing has been performed at 550 °C on a range of fracture specimens using sections taken from a non-stress-relieved 316 steel weldment. These specimens include the compact tension, C(T), middle tension, M(T) and circumferentially cracked bar, CCB, geometries. Results are presented from two long-term creep crack growth (CCG) tests performed on M(T) weldment specimens and these are compared with available data on C(T) and CCB weldment specimens together with both long and short term tests on parent material for a range of specimen geometries. The creep crack initiation (CCI) and growth (CCG) behaviour from these tests has been analysed in terms of the C* parameter. As high levels of residual stress exist in non-stress-relieved weldments, the residual stresses remaining in the weldment specimens have therefore been quantified using the neutron diffraction technique. Long-term (low-load) tests are required on PM specimen to observe specimen constraint effects in 316 steel at 550 °C. When interpreted in terms of the C* parameter the CCG behavior of PM and Weldment materials follow the same trendline on low constraint geometries. However, significant difference is observed in the CCG behavior of PM and weldments on the high constraint C(T) geometry. Long term tests on C(T) specimen weldments are required to confirm the results found.

Effect of the Out-of-Plane Constraint on Creep Crack Growth Property of Cr-Mo-V Type Steel

2011 ◽  
Author(s):  
Jian-Ping Tan ◽  
Guo-Zhen Wang ◽  
Fu-Zhen Xuan ◽  
Shan-Tung Tu ◽  
Zheng-Dong Wang
Keyword(s):  
Process Zone ◽  
Creep Crack Growth ◽  
Creep Damage ◽  
Load Level ◽  
Specimen Thickness ◽  
Constraint Effect ◽  
Creep Crack ◽  
Damage And Fracture ◽  
Out Of Plane ◽  
Crack Tips

In order to establish an accurate integrity assessment of structures containing defects at high temperature, it is necessary to clarify the constraint effect on creep crack growth (CCG) property. However, the effect of the out-of-plane creep constraint induced by the specimen thicknesses has been little studied. In this study, the CCG properties and fracture mechanism of Cr-Mo-V type steel at 566°C were investigated by using the compact tension specimens with different thicknesses. The results show that the data of the CCG rate da/dt versus C* lie within a relatively tight scatter band on log-log scale for the specimens with different thicknesses at higher values of C*. In addition, the differences of CCG rate becomes large with C* decreasing. It means that the effect of out-of-plane constraint on CCG rate is dependent on the load level (C*). The reason for the similar CCG rate is that the creep damage and fracture mechanism of void growth at grain boundary ahead of crack tips in the specimens with different thicknesses does not essentially change. The size rc of the creep damage and fracture process zone in front of crack tips is related to the specimen thickness, and the damage rate fields over the process zone are similar for the specimens with different thicknesses. The deformation near the crack tip obscures the constraint effect. Based on a reference stress field under plane strain state and the creep process zone rc, in-plane and out-of-plane constraint parameter Rd and Td were defined and the creep crack-tip constraint effect induced by specimen thickness were quantitatively examined. The factors of creep time and load level (C*) influencing the constraint effect were analyzed.

Assessment of Power Plant Components With Flaws and Defects Operating in the Long-Term Creep Range

2019 ◽  
Author(s):  
Magdalena Speicher ◽  
Thorben Bender ◽  
Andreas Klenk ◽  
Falk Mueller ◽  
Christian Kontermann ◽  
...  
Keyword(s):  
High Temperature ◽  
Fracture Mechanics ◽  
Crack Initiation ◽  
Crack Growth ◽  
Creep Crack Growth ◽  
Material Behavior ◽  
Critical Crack Length ◽  
Creep Crack ◽  
Combining Data ◽  
Crack Problems

Abstract Originating from defects and flaws in high temperature components crack initiation and crack propagation under service conditions can occur. Fracture mechanics data and procedures are needed to study crack problems and to support an advanced remnant life evaluation. During subsequent research in the past 35 years, data were determined for different high temperature materials. Methodologies and concepts taking into account the specific material behavior were developed in order to be able to describe crack initiation and crack growth and have appropriate assessment methods available. For creep crack initiation two criteria principles were used and for creep crack growth assessment based on the integral C* parameter were applied. Furthermore, a method for determination of critical crack length was developed allowing decisions whether modified stress analysis methods are sufficient or more complicated fracture mechanics methods are needed. To provide data and methodologies in a user-friendly way, a program system combining data and methods was implemented. The paper describes developed features and shows comparisons to other methods. The methods can be applied for design purposes as well as remnant life assessments.

Mismatch Constraint Effect for Bimaterial Interfacial Creep Crack

2016 ◽  
Vol 853 ◽  
pp. 286-290
Author(s):  
Yan Wei Dai ◽  
Ying Hua Liu ◽  
Hao Feng Chen
Keyword(s):  
High Temperature ◽  
Elevated Temperature ◽  
Stress Field ◽  
Structural Integrity ◽  
Creep Crack Growth ◽  
Constraint Effect ◽  
Creep Crack ◽  
Engineering Practices ◽  
Material Mismatch ◽  
Mismatch Effect

Mismatch effect of weldments is important for the assessment of structural integrity at elevated temperature. The interfacial creep crack is a common model which can be found in lots of engineering practices. Recently, the constraint effect is also considered to be significant for the evaluation of creep crack growth under high temperature. In this paper, a model for bimaterial interfacial creep crack is introduced to study the mismatch constraint effect. The stress field for bimaterial interfacial creep crack is investigated. An M*-parameter is proposed to characterize the constraint effect caused by material mismatch for bimaterial creep crack. A comparison is made between the geometry constraint caused by specimen loading and mismatch constraint caused by inhomogeneous material.

The Influence of Creep-Fatigue Interaction on High Temperature Crack Growth in 316 Steel Weldments

2009 ◽  
Author(s):  
C. M. Davies ◽  
David W. Dean ◽  
A. N. Mehmanparast ◽  
K. M. Nikbin
Keyword(s):  
High Temperature ◽  
Crack Growth ◽  
Static Load ◽  
Growth Models ◽  
Creep Crack Growth ◽  
Crack Tip ◽  
Parent Material ◽  
Creep Crack ◽  
Static Creep ◽  
Temperature Crack

High temperature crack growth in weldments is of great concern and generally occurs along the boundary between the heat affected zone (HAZ) and parent material (PM) of welded components in high temperature plants. Static creep and low frequency cyclic crack growth tests have been performed on compact tension, C(T), specimens manufactured from sections taken from a 316 steel weldment at 550 °C, where the crack tip was located along the fusion line within the HAZ. The data has been analyzed in terms of both the creep-brittle and creep-ductile crack tip parameters, K and C*, respectively. The cyclic test results have been compared to static creep crack growth tests on 316 steel weldments and homogeneous parent material specimens, and to crack growth models. The cracking rates of the cyclic crack growth tests are found to be higher than that of the of the static load creep crack growth tests on weldments. The data may be bounded by the high frequency fatigue and the static load creep crack growth predictions. However, further work is required to establish the fatigue and subsequently the creep component of the cyclic load crack growth tests on weldments.

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