scholarly journals The effects of long-range residual stress, elastic follow-up and applied load on creep crack incubation and material toughness

2015 ◽  
Vol 50 (7) ◽  
pp. 455-469 ◽  
Author(s):  
David J Smith ◽  
Anilkumar M Shirahatti
Keyword(s):  
Residual Stress ◽  
Long Range ◽  
Applied Load ◽  
Creep Crack

Experiments to Determine the Influence of Residual Stress and Elastic Follow-Up on Creep Crack Initiation

2013 ◽  
Author(s):  
A. M. Shirahatti ◽  
C. E. Truman ◽  
D. J. Smith
Keyword(s):  
Residual Stress ◽  
High Temperature ◽  
Crack Initiation ◽  
Residual Stresses ◽  
Crack Growth ◽  
Applied Load ◽  
Measurement Techniques ◽  
Test Rig ◽  
Creep Crack

Components used in the power generation sector are often continuously exposed to high temperatures and corrosive environments. Failure processes, such as net section rupture, creep crack growth or fatigue crack growth therefore occur within the high temperature regime. The presence of residual stresses plays an important role in the subsequent failure of engineering components and structures. Residual stresses can arise from almost all manufacturing and fabrication processes and can also arise during service. Tensile residual stresses may combine with in-service loads to promote failure at a load the designer would view as safe. A quantitative understanding of how residual stresses interact with applied service loads is thus required for accurate safety assessments. In this paper a test rig based on a three bar structural model is used to introduce long range residual stresses in a 316H steel C(T) specimen at high temperature. The residual stresses induced are characterized easily without use of time consuming residual stress measurement techniques. The complete test rig is then subjected to an applied load. The magnitude of the residual and applied stress in the 316H C(T) specimen is a function of the initial misfit displacement, applied load and relative stiffness of the components of the test rig. The experimental results show that a test rig with a higher elastic follow-up value will have more crack growth compared to a rig with a lower elastic follow-up. Also, both tests demonstrate that as the crack grows, relaxation of residual stress in the C(T) specimen occurs, and it is compensated by a change in residual stress distribution in other parts of the rig. Furthermore, creep crack initiation data is compared with load controlled tests conducted. It is found that the time for the crack to initiate is increased in the case of mixed boundary conditions compared to load controlled conditions.

scholarly journals Use of Elastic Follow-Up to Study the Effect of Displacement Controlled Loading on Plastic Collapse Pressures for Circumferentially Cracked Pipes

2015 ◽  
Author(s):  
Guiyi Wu ◽  
David J. Smith ◽  
Martyn J. Pavier
Keyword(s):  
Residual Stress ◽  
Long Range ◽  
Structural Integrity ◽  
Axial Displacement ◽  
Plastic Collapse ◽  
Integrity Assessment ◽  
Circumferential Crack ◽  
Displacement Condition ◽  
Global Collapse

Structural integrity assessments of pressurised pipes consider plastic collapse as a potential failure mode. This paper uses finite element analysis to explore the effect of the pipe end boundary conditions on the collapse pressure. Two end conditions are considered: a fixed axial load and a fixed axial displacement. The fixed axial displacement condition represents a long-range axial residual stress. In the R6 structural integrity assessment procedure long-range residual stress is associated with elastic follow-up. However, no guidance is given on whether the level of elastic follow-up is sufficient to justify treating long-range residual stress as a primary stress. In this paper, a method is proposed to estimate elastic follow-up of an internally pressurised pipe containing a fully circumferential crack. It is found that the elastic follow-up is related to the length of the pipe. A short pipe that contains a fully circumferential crack, subjected to a displacement induced axial stress, has a global collapse that is not modified by the fixed displacement condition. The short pipe corresponds to a small elastic follow-up factor, Z. However, as the elastic follow-up factor increases, the presence of long-range residual stress starts to make a contribution to global collapse. When elastic follow-up is significant, a long-range residual stress has the same effect on global collapse as does a mechanical stress.

scholarly journals Prediction of Residual Stress Relaxation of Shot Peened 2024-T351 Aluminum Alloy: Part 1

2011 ◽  
Vol 462-463 ◽  
pp. 1355-1360
Author(s):  
Omar Suliman Zaroog ◽  
Aidy Ali ◽  
Sahari B. Barkawi
Keyword(s):  
Residual Stress ◽  
Stress Relaxation ◽  
Shot Peening ◽  
Applied Load ◽  
Cold Work ◽  
Cyclic Tests ◽  
Initial State ◽  
Loading Cycle ◽  
Residual Stress Relaxation ◽  
Alloy Part

It is important to account for residual stress relaxation phenomenon in the design of the component. Specimens of 2024-T351 aluminium alloy were used in this study. The specimens were shot peened under three different shot peening intensities. Cyclic tests for two load magnitudes were performed for 1, 2, 10, 1000 and 10000 cycles. Residual stresses, microhardness and the cold work percentage were measured at initial state and after each loading cycle for the three shot peening intensities and for the two loads. The study revealed that most of the drop in the residual stress, microhardness and cold work happened in the first cycle are dependent on the applied load.

A Fundamental Study of the Interaction of Residual Stress and Applied Loading on Fracture

2010 ◽  
Author(s):  
C. J. Aird ◽  
M. J. Pavier ◽  
D. J. Smith
Keyword(s):  
Residual Stress ◽  
Finite Element ◽  
Stress Field ◽  
Crack Closure ◽  
Applied Load ◽  
Element Model ◽  
Residual Stress Field ◽  
Fundamental Study ◽  
Analytical Expression ◽  
Applied Loading

This paper presents the results of a fundamental finite-element based study of the crack-closure effects associated with combined residual and applied loading. First, an analytical expression for a representative two-dimensional residual stress field is derived. This residual stress field contains a central compressive region surrounded by an equilibrating tensile region. The analytical expression allows the size and shape of the field to be varied along with the magnitude of the residual stress. The residual stress field is then used as a prescribed initial stress field in a finite element model, in addition to a far field applied load. By introducing cracks of increasing length into these models, charts of stress-intensity-factor versus crack length are produced for different relative magnitudes of residual stress and applied load and for different sizes and shape of the residual stress field. These charts provide insight into the way in which crack-tip conditions evolve with crack growth under conditions of combined residual and applied loading and also enable conditions of crack closure and partial closure to be identified.

scholarly journals Effect of Elastic Follow-up on Creep Crack Incubation

2014 ◽  
Vol 3 ◽  
pp. 1485-1491 ◽  
Author(s):  
S. Khayatzadeh ◽  
D.W.J. Tanner ◽  
C.E. Truman ◽  
D.J. Smith
Keyword(s):  
Creep Crack

Elastic Follow-Up Factors to Estimate C(t) Under Secondary Loading

2012 ◽  
Author(s):  
Kuk-Hee Lee ◽  
Yun-Jae Kim ◽  
Robert A. Ainsworth ◽  
David Dean
Keyword(s):  
Crack Growth ◽  
Creep Crack Growth ◽  
Transient Creep ◽  
Independent Method ◽  
Finite Element Analyses ◽  
Creep Crack ◽  
Reference Stress ◽  
Growth Increase ◽  
Plastic Creep

This paper proposes a method to determine the elastic follow-up factors for C(t)-integral under secondary stress. The rate of creep crack growth for transient creep is correlated with C(t)-integral. The elastic follow-up behaviour, which occurs in structures under secondary loading, prevents a relaxation of stress during transient creep. Thus, both the value of C(t) and creep crack growth increase with an increasing elastic follow-up. An estimation solution for C(t) has been proposed by Ainsworth and Dean based on the reference stress method. In order to predict the value of C(t) using this solution, an independent method to determine the elastic follow-up factors for cracked bodies is required. This paper proposes that the elastic follow-up factors for C(t) can be determined by elastic-plastic analyses by using the plastic-creep analogy. Finite element analyses have been performed to verify this method.

Finite Element Study of Residual Stresses in a plate T-Joint Fatigue Specimen

1990 ◽  
Vol 204 (2) ◽  
pp. 127-134 ◽  
Author(s):  
D H B Mok ◽  
R J Pick
Keyword(s):  
Residual Stress ◽  
Finite Element ◽  
Residual Stresses ◽  
Applied Load ◽  
Small Region ◽  
Finite Element Code ◽  
Fatigue Specimen ◽  
Numerical Predictions ◽  
Weld Toe ◽  
Element Study

Using the finite element code ABAQUS to make numerical predictions, this paper studies the crack shape development and thickness effects on a series of welded plate T-joint fatigue specimens. It was found that redistribution of the residual stress only occurs in a small region near the weld toe, the extent depending greatly on the magnitude of the applied load.

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