A Novel Fracture Mechanics Specimen to Investigate the Effect of Residual Stress and Crack-Tip Constraint on Fracture

2011 ◽  
Author(s):  
Simon Kamel ◽  
Tiyaporn Vanagosoom ◽  
Prakash Shanthenu ◽  
Catrin M. Davies ◽  
Kamran M. Nikbin
Keyword(s):  
Fracture Toughness ◽  
Residual Stress ◽  
Finite Element Analysis ◽  
Crack Tip ◽  
Residual Stress Field ◽  
Element Analysis ◽  
Load Line ◽  
Low Constraint ◽  
Crack Tip Constraint ◽  
Fracture Toughness Specimen

A novel fracture toughness specimen design is presented for investigating the effects of residual stress and crack tip constraint on fracture. The specimen design, denoted here as an SC(T) specimen, is a hybrid of a blunt-notched C(T) specimen and an SEN(T) specimen. The SC(T) specimen is mechanically pre-compressed on the C(T) load line to introduce a residual stress in the ligament ahead of a blunt notch. Following pre-compression, a crack is introduced into the tensile residual stress field. The SC(T) specimen can then be loaded either on the C(T) or SEN(T) load line to examine the effects of residual stress under high constraint or low constraint conditions respectively. Finite element analysis is performed to examine the sensitivity of the specimen dimensions on crack tip constraint and to demonstrate the introduction of residual stress into the specimen.

Residual Stress and Constraint Effects on Fracture in the Transition Temperature Regime

2008 ◽  
Author(s):  
K. S. Lee ◽  
A. H. Sherry ◽  
M. R. Goldthorpe
Keyword(s):  
Fracture Toughness ◽  
Residual Stress ◽  
Residual Stresses ◽  
Numerical Study ◽  
Notch Root ◽  
Crack Tip ◽  
Pressure Vessel Steel ◽  
Vessel Steel ◽  
Low Constraint ◽  
Crack Tip Constraint

This paper presents the results of a combined experimental and numerical study aimed at quantifying the influence of self-balancing residual stresses on the fracture toughness constraint benefit of a ferritic pressure vessel steel tested in the cleavage fracture regime. Tests were performed on standard and pre-compressed, high constraint, compact-tension (CT) and low constraint, single-edge-notched tension (SENT) specimens at a temperature close to the Master Curve reference temperature T0. Pre-compression is undertaken prior to pre-cracking to establish a residual stress across the uncracked ligament, which is highly tensile at the pre-crack notch root and balanced by compressive stresses further ahead of the notch. The pre-crack is subsequently introduced into material ahead of the notch, within the tensile residual stress region, specimen by electro-discharge machining and fatigue. The tests demonstrate an influence of tensile residual stresses on the apparent fracture toughness properties for both CT and SENT specimens. The tests on low constraint specimens illustrate the constraint benefit on cleavage toughness for this material, and the influence of residual stresses in reducing this benefit. The paper shows how the observed behaviour can be quantified through using two parameter fracture mechanics. Here, the J-integral is determined by taking full account of the influence of preloading on the crack driving force. Both the elastic-T-stress and the elastic-plastic Q-stress are calculated and demonstrated as constraint indexing parameters. The results demonstrate a reduction in constraint benefit for cracks located within highly bending residual stress fields. Thus, when exploring any possible benefit in fracture toughness due to crack tip constraint, it is critical that the combined influence of the primary and secondary stresses on crack tip constraint be taken fully into account.

Numerical and experimental investigations of effects of residual stresses on crack behavior in Aluminum 6082-T6

2012 ◽  
Vol 226 (9) ◽  
pp. 2178-2191 ◽  
Author(s):  
Mohammadreza Farahani ◽  
Iradj Sattari-Far ◽  
Davood Akbari ◽  
Rene Alderliesten
Keyword(s):  
Fracture Toughness ◽  
Residual Stress ◽  
Finite Element ◽  
Stress Field ◽  
Residual Stresses ◽  
Crack Growth ◽  
Crack Tip ◽  
Residual Stress Field ◽  
Integrity Assessment ◽  
Crack Tip Constraint

In the structural integrity assessment, residual stresses play an important role. The residual stresses affect both the crack driving forces and the crack-tip constraint. To investigate the interaction of residual stresses with mechanical loading during the onset of crack growth in Aluminum 6082-T6, modified single edge-notched bending specimens were used. Aluminum 6082 has the highest strength of the 6000 series alloys with excellent corrosion resistance. A residual stress field was created in the specimens by pre-loading. To accurately quantify the residual stress field created during this test procedure, the strains were measured during loading and unloading and compared with finite element results. After the introduction of the residual stress field, the specimens were tested under three-point bending to determine the load versus displacement behavior and fracture toughness. Also, a post-processor for finite element calculation was developed to enable determination of the J-integral values for the specimens having residual stresses. The constraint parameters Q and R were calculated at the crack-tip to describe the stress field in this region. The parameter Q is used to characterize the loading and geometry constraint, and the parameter R is used for characterizing the crack-tip constraint due to residual stresses. It is observed that tensile residual stresses around the crack-tip increase the crack-tip constraint and decrease the fracture toughness of the bodies. By increasing the external load, the constraint parameter R goes toward zero and the effects of residual stresses on the crack growth resistance become negligible.

Quantification of Residual Stresses Induced by Prior Loading at High Temperatures

2011 ◽  
Author(s):  
Ali N. Mehmanparast ◽  
Catrin M. Davies ◽  
Robert C. Wimpory ◽  
Kamran M. Nikbin
Keyword(s):  
Fracture Toughness ◽  
Residual Stress ◽  
Residual Stresses ◽  
Crack Growth ◽  
Creep Crack Growth ◽  
Crack Tip ◽  
Crack Plane ◽  
Residual Stress Field ◽  
Compression Direction ◽  
Fracture Specimen

High temperature components generally undergo cyclic loading conditions. Prior tensile/compressive loading of a fracture specimen can induce compressive/tensile residual stress fields at the crack tip. These residual stresses will influence the subsequent fracture behaviour of the cracked body. This work forms part of a project to examine the influence of creep induced damage at a crack tip on subsequent fatigue crack growth and fracture toughness properties of austenitic type 316H stainless steel. Creep damage is introduced local to the crack tip of a fracture specimen by interrupting a creep crack growth test, performed at 550 °C. Prior to testing, the material was pre-compressed in order to strain harden the material. The compact tension, C(T), specimen geometry has been considered in this work. Since residual stresses are known to influence fatigue and fracture toughness properties of a cracked body, it is important that the residual stress levels at the crack tip are quantified. Neutron diffraction (ND) measurements have therefore been performed to quantify the extent of residual stress in these samples after initial loading, and compared to finite element model predictions. Two specimens have been considered with the crack plane orientated in parallel and perpendicular to the pre-compression direction. Compressive residual stresses of around 100 MPa have been measured directly ahead of the crack tip. Reasonable predictions of the principal residual stress distributions have been obtained by the simplified FE analysis. Though the tensile properties differ significantly in for specimens orientated parallel and perpendicular to the pre-compression direction, no significant differences in the residual stress field are predicted in the C(T) specimens orientated in both directions.

Effects of Temperature and Crack Tip Constraint on Cleavage Fracture Toughness in the Weld Thermal Simulated X80 Pipeline Steels

2011 ◽  
Vol 197-198 ◽  
pp. 1595-1598 ◽  
Author(s):  
Jie Xu ◽  
Yu Fan
Keyword(s):  
Fracture Toughness ◽  
Cleavage Fracture ◽  
Crack Tip ◽  
Coarse Grained ◽  
Material Microstructure ◽  
Element Analysis ◽  
Pipeline Steels ◽  
Different Temperatures ◽  
Effects Of Temperature ◽  
Crack Tip Constraint

This paper studies the effects of temperature and crack tip constraint on cleavage fracture toughness of the weld thermal simulated X80 pipeline steels. A large number of fracture toughness (as denoted by CTOD) tests together with 3D finite element analysis are performed using single edge notched bending (SENB) and tension (SENT) specimens at different temperatures. Coarse-grained heat-affected zone (CGHAZ) is considered as the material microstructure in preparation of the weld thermal simulated fracture mechanics specimens.

Finite Element Analysis of the Effect of Mechanical Stress Improvement Process on Weld Residual Stress and Flaw Growth in a Thick-Walled Pressurizer Safety Nozzle

2017 ◽  
Author(s):  
Giovanni G. Facco ◽  
Patrick A. C. Raynaud ◽  
Michael L. Benson
Keyword(s):  
Residual Stress ◽  
Finite Element Analysis ◽  
Finite Element ◽  
Stress Field ◽  
Mechanical Stress ◽  
Residual Stress Field ◽  
Element Analysis ◽  
Wide Range ◽  
Improvement Process ◽  
Stress Prediction

The Mechanical Stress Improvement Process (MSIP) is generally accepted as an effective method to modify the residual stress field in a given component to mitigate subcritical crack growth in susceptible components [1] [2] [3]. In order to properly utilize MSIP, residual stress prediction is needed to determine the parameters of the MSIP application and the expected final residual stress field in the component afterwards. This paper presents the results of a 2D axisymmetric finite element study to predict weld residual stresses (WRS), and associated flaw growth scenarios, in a thick-walled pressurizer safety nozzle that underwent mitigation by application of MSIP. The authors have developed a finite-element analysis methodology to examine the effect of MSIP application on WRS and flaw growth for various hypothetical welding histories and boundary conditions in a thick-walled pressurizer safety nozzle. In doing so, a wide range of repair scenarios was considered, with the understanding that some bounding scenarios may be impractical for this geometry.

Finite Element Analysis of Temperature Filed and Stress Field of Reducer

2014 ◽  
Vol 881-883 ◽  
pp. 1447-1450
Author(s):  
Jing Zhang ◽  
Fei Wang
Keyword(s):  
Residual Stress ◽  
Finite Element Analysis ◽  
Finite Element ◽  
Temperature Field ◽  
Stress Field ◽  
Residual Stress Field ◽  
Element Analysis ◽  
Welding Temperature ◽  
Stress And Deformation ◽  
Residual Stress And Deformation

Abstract.The connection mode of reducer with straight tube on both sides are the welding connection. There are two weld at the both side of reducer and there has a great influence on residual stress and deformation in the process of welding . Based on the particularity of reducer welding, the paper is focus on the residual stress and deformation in the process of welding, using large-scale finite element analysis software ANSYS .The DN500X450 reducer model is established.The welding temperature field and residual stress field is analysis and calculation and analysis the influence on temperature and stress distribution of reducer. The results show that the maximum of the temperature and the residual stress is located in the big side and reduce the welding seam, and the obvious deformation also find in the big side and reduce joint . The reducing pipe’s distribution of temperature field and residual stress field are obtained,providing the basis to establish properly and optimize of welding process.

The Effects of Constraint and Compressive or Tensile Residual Stresses on Brittle Fracture

2009 ◽  
Author(s):  
Simon Kamel ◽  
Robert C. Wimpory ◽  
Michael Hofmann
Keyword(s):  
Fracture Toughness ◽  
Residual Stress ◽  
Brittle Fracture ◽  
Driving Force ◽  
High Strength ◽  
Element Analysis ◽  
Crack Driving Force ◽  
Temperature Fracture ◽  
Crack Tip Constraint ◽  
Two Parameter

Residual stress is a key feature in components containing defects which can affect the crack driving force and alter the crack tip constraint to give a modified fracture toughness. In this paper experimental and numerical investigations are performed on ‘C’ shape fracture mechanics specimens, extracted from a high strength low alloy tubing steel, to examine the effects of constraint and tensile or compressive residual stress on brittle fracture. The residual stress is introduced into the specimens by a tensile or compressive mechanical pre-load to produce, respectively, a compressive or tensile residual stress in the region where the crack is introduced. Neutron diffraction measurements are performed on the pre-loaded specimens prior to introduction of a crack, and compared with predictions of the residual stress from finite-element analysis, using tensile properties derived at room temperature. Fracture toughness tests are carried out on the as-received (non-preloaded) and pre-loaded specimens and the effect of residual stress on crack driving force and constraint is evaluated using the two-parameter J-Q approach.

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