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.

Load History Effects on Crack Driving Force for Cracks in Residual Stress Fields

2008 ◽  
Author(s):  
Richard Charles ◽  
David W. Beardsmore ◽  
Huaguo Teng ◽  
Chris T. Watson
Keyword(s):  
Fracture Toughness ◽  
Residual Stress ◽  
Driving Force ◽  
Thermal Loading ◽  
Stress Fields ◽  
Residual Stress Field ◽  
Element Analysis ◽  
Crack Driving Force ◽  
History Effects ◽  
Material Fracture

Fracture mechanics assessments of engineering components and structures containing defects are made by comparing an estimate of the crack driving force KJ with an effective fracture toughness KJc. The assessments must account for the combined effect of primary loads, such as internal pressure in pressurised components, and secondary stresses arising from welding and/or thermal loading. Elastic-plastic finite element analysis, or simplified methods set out in standard assessment procedures, can be used to estimate the crack driving force KJ as a function of the applied primary load on the component. The effective fracture toughness KJc should take account of the material fracture toughness and the crack tip constraint. For the assessment of defects in weld residual stress fields, it is usually assumed that the defect is inserted into the as-welded stress distribution in such a way that traction free crack surfaces are created simultaneously at all positions on the crack faces. However, it may be beneficial to take account of any relaxation in the residual stress field that might arise during proof-testing or in-service cyclic loading, and to consider a more gradual, progressive introduction of the defects. These benefits could, in principle, result in a reduction in the crack driving force. This paper describes work that has been undertaken to provide estimates of the crack driving force KJ for a fully-circumferential defect in a circumferential repair weld in a cylindrical pipe. Calculations have been carried out to establish KJ for a number of cases where different pressure overloads are applied to the uncracked pipe and different methods of crack insertion are applied. Estimates of the margin of safety on fracture toughness and pressure loading were calculated. At the outset, it was assumed that the fracture toughness of relevance for the defects is the material fracture toughness KJc* derived from strain free, high constraint fracture toughness specimens. No allowance was made for constraint effects associated with the finite geometry or initial strains in the pipe. The values of KJ were derived from values of J calculated using the JEDI post-processing code; this allows for initial inelastic strains present in the model prior to the start of the crack insertion process.

Measurement and Modelling of Residual Stresses in Fracture Toughness Specimens Extracted From Large Components

2008 ◽  
Author(s):  
S. J. Lewis ◽  
S. Hossain ◽  
C. E. Truman ◽  
D. J. Smith ◽  
M. Hofmann
Keyword(s):  
Fracture Toughness ◽  
Residual Stress ◽  
Residual Stresses ◽  
Driving Force ◽  
Large Scale ◽  
Structural Integrity ◽  
Mechanical Load ◽  
Crack Driving Force ◽  
Neutron Diffraction Technique ◽  
Fracture Specimens

A number of previously published works have shown that the presence of residual stresses can significantly affect measurements of fracture toughness, unless they are properly accounted for when calculating parameters such as the crack driving force. This in turn requires accurate, quantitative residual stress data for the fracture specimens prior to loading to failure. It is known that material mechanical properties may change while components are in service, for example due to thermo-mechanical load cycles or neutron embrittlement. Fracture specimens are often extracted from large scale components in order to more accurately determine the current fracture resistance of components. In testing these fracture specimens it is generally assumed that any residual stresses present are reduced to a negligible level by the creation of free surfaces during extraction. If this is not the case, the value of toughness obtained from testing the extracted specimen is likely to be affected by the residual stress present and will not represent the true material property. In terms of structural integrity assessments, this can lead to ‘double accounting’ — including the residual stresses in both the material toughness and the crack driving force, which in turn can lead to unnecessary conservatism. This work describes the numerical modelling and measurement of stresses in fracture specimens extracted from two different welded parent components: one component considerably larger than the extracted specimens, where considerable relaxation would be expected as well as a smaller component where appreciable stresses were expected to remain. The results of finite element modelling, along with residual stress measurements obtained using the neutron diffraction technique, are presented and the likely implications of the results in terms of measured fracture toughness are examined.

Provisional Results for an Experimental Investigation Into the Effect of Combined Primary and Secondary Stresses When Considering the Approaches of R6 and the Recently Developed g() Method

2011 ◽  
Author(s):  
Peter James ◽  
Paul Hutchinson ◽  
Colin Madew
Keyword(s):  
Fracture Toughness ◽  
Residual Stress ◽  
Experimental Investigation ◽  
Stress Field ◽  
Driving Force ◽  
Residual Stress Field ◽  
Crack Driving Force ◽  
Material Characterisation ◽  
Point Bend ◽  
Initial Results

Engineering components, particularly those containing weldments, may contain small crack-like defects that experience combinations of primary and secondary stresses during service. A new function, g(), has been introduced previously to quantify the influence of plasticity interaction under combined primary and secondary loading on a components crack driving force. This paper compares g() with experiments performed to consider g() over a range of plasticity values. This experimental programme was performed on scalloped notch three point bend specimens that had experienced a pre-compression to induce a residual stress field before being tested to failure over a range of temperatures (−150, −90 and −50 °C). Samples which did not undergo a pre-compression were also tested to provide an estimate of the materials fracture toughness at the temperature in question. Through analysing the experimental results it is clear that further material characterisation is required. This paper, therefore, only presents the initial results at this stage. However, as a pessimistic interpretation of the results has been made, and since both the existing R6 and the g() plasticity interaction parameters are acceptable, the experiments provide useful validation to both methods.

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 Effects on Cleavage Fracture

2007 ◽  
Author(s):  
A. H. Sherry ◽  
K. S. Lee ◽  
M. R. Goldthorpe ◽  
D. W. Beardsmore
Keyword(s):  
Fracture Toughness ◽  
Residual Stress ◽  
Residual Stresses ◽  
Cleavage Fracture ◽  
Driving Force ◽  
Compact Tension ◽  
Pressure Vessels ◽  
Crack Driving Force ◽  
Stress Effects ◽  
Definition Of

It is recognised that the driving force for the initiation and propagation of defects in materials may, under some circumstances, include contributions from both externally applied loads such as internal pressure in pressure vessels and piping and secondary stresses such as weld residual stresses. For non stress-relieved welds, residual stresses can provide a significant proportion of the crack driving force. This paper describes the results obtained from an experimental programme aimed at extending the understanding of residual stress effects on cleavage fracture. The paper describes the preparation and testing of standard and preloaded compact-tension specimens of an A533B pressure vessel steel at its Master Curve reference temperature. Standard tests on compact-tension specimens provide fracture toughness data which are broadly consistent with the conventional three-parameter Weibull model, with Kmin = 20 MPa√m and an exponent of about 4. The preloaded compact-tension specimens included a high level of tensile residual stress at the crack location. Fracture toughness data obtained using the test standards from these specimens fall significantly below the standard specimen data, since the contribution from residual stresses is ignored. However, when due account is taken of the residual stress on the crack driving force using a correct definition of the J-integral, the distributions of fracture toughness data from both specimen types are found to overlay each other. The definition of J used in this paper allows residual stress effects on fracture to be accounted for in a single fracture parameter.

Crack Tip Constraint Under Biaxial Loading in Elastic-Plastic Materials

2010 ◽  
Author(s):  
Z. X. Wang ◽  
Jian-ye Huang ◽  
Y. J. Chao ◽  
P. S. Lam
Keyword(s):  
Driving Force ◽  
Enhancement Factor ◽  
Structural Integrity ◽  
Biaxial Loading ◽  
Crack Tip ◽  
Element Analysis ◽  
Crack Driving Force ◽  
Integrity Assessment ◽  
Elastic Plastic ◽  
Crack Tip Constraint

Crack tip constraint is known to affect the fracture resistance of materials. The effect of biaxial loading on a center crack in an X100 steel plate has been investigated. The crack driving force and the constraint parameter are estimated based on the two-parameter J-A2 theory in elastic-plastic fracture mechanics with the aid of finite element analysis. The center-cracked plate is subject to various degrees of biaxiality (defined as the ratio of the transverse stress parallel to the crack and the opening stress normal to the crack). Using the constraint parameter (A2) in uniaxial loading condition as a reference value, a Constraint Enhancement Factor is introduced to facilitate the investigation of crack tip constraint under biaxial loading. The analysis carried out in this paper has established a relationship between the Constraint Enhancement Factor and the biaxiality. With the J-A2 fracture model, the critical applied load and the critical crack driving force can be expressed as functions of biaxial loading ratio. The methodology and analysis results can be used in structural integrity assessment of a pressure vessel or piping which contains a crack under biaxial loading.

An Interpretation of the Mechanics of Crack Growth by Fatigue

1965 ◽  
Vol 87 (1) ◽  
pp. 230-236 ◽  
Author(s):  
B. Cotterell
Keyword(s):  
Brittle Fracture ◽  
Crack Propagation ◽  
Crack Length ◽  
Crack Growth ◽  
Driving Force ◽  
Maximum Stress ◽  
High Strength ◽  
Crack Driving Force

A theory for the growth of cracks by fatigue is developed that is analogous to the brittle fracture of high strength materials. It is argued that it is possible to describe crack growth with a curve of resistance which is dependent on the alternating stress at low rates of crack propagation. At higher rates there is much less dependency on the alternating stress. Once such curves have been prepared the rate of crack growth can be found from the value of the crack driving force. This force is dependent mainly on the maximum stress and crack length.

Numerical Simulation of Residual Stresses due to Multipass Welding in High Strength Steel Plates and Validation against Experimental Measurements

2018 ◽  
Vol 941 ◽  
pp. 269-273
Author(s):  
Constant Ramard ◽  
Denis Carron ◽  
Philippe Pilvin ◽  
Florent Bridier
Keyword(s):  
Residual Stress ◽  
Residual Stresses ◽  
High Strength Steel ◽  
High Strength ◽  
Steel Plates ◽  
Contour Method ◽  
Hole Drilling ◽  
Experimental Measurements ◽  
Element Analysis ◽  
Multipass Welding

Multipass arc welding is commonly used for thick plates assemblies in shipbuilding. Sever thermal cycles induced by the process generate inhomogeneous plastic deformation and residual stresses. Metallurgical transformations contribute at each pass to the residual stress evolution. Since residual stresses can be detrimental to the performance of the welded product, their estimation is essential and numerical modelling is useful to predict them. Finite element analysis of multipass welding of a high strength steel is achieved with a special emphasis on mechanical and metallurgical effects on residual stress. A welding mock-up was specially designed for experimental measurements of in-depth residual stresses using contour method and deep hole drilling and to provide a simplified case for simulation. The computed results are discussed through a comparison with experimental measurements.

A Fatigue Crack Driving Force Parameter

2008 ◽  
Author(s):  
Ying Xiong ◽  
Zengliang Gao ◽  
Junichi Katsuta ◽  
Takeshi Sakiyama
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Driving Force ◽  
Crack Tip ◽  
Force Model ◽  
Crack Driving Force ◽  
R Ratio ◽  
Two Parameter ◽  
Better Than

Most of the previous parameters that utilized as a crack driving force were established in modifying the parameter Kop in Elber’s effective SIF range (ΔKeff = Kmax–Kop). This paper focuses on the physical meaning of compliance changes caused by plastic deformation at the crack tip, the test was carried out for structural steel under constant amplitude loading, and differences of several parameter ΔKeff in literature are analyzed quantificationally. The effect of actual stress amplitude at the crack tip on fatigue crack growth is investigated, and improved two-parameter driving force model ΔKdrive(=Kmax)n(ΔK^)1−n) has been proposed. Experimental data for several different types of materials taken from literature were used in the analyses. Presented results indicate that the parameter ΔKdrive is equally effective or better than ΔK(=Kmax-Kmin), ΔKeff(=Kmax-Kop) and ΔK*(=(Kmax)α(ΔK+)1−α) in correlating and predicting the R-ratio effects on fatigue crack growth rate.

X-Ray Residual Stress Measurement on Stress Corrosion Fracture Surfaces

1992 ◽  
Vol 36 ◽  
pp. 543-549
Author(s):  
Masaaki Tsuda ◽  
Yukio Hirose ◽  
Zenjiro Yajima ◽  
Keisuke Tanaka
Keyword(s):  
Fracture Toughness ◽  
Residual Stress ◽  
Fracture Surface ◽  
Stress Corrosion ◽  
Stress Measurement ◽  
High Strength Steels ◽  
High Strength ◽  
X Ray Diffraction ◽  
X Ray ◽  
Fracture Surfaces

X-ray fractography is a new method utilizing the X-ray diffraction technique to observe the fracture surface for the analysis of the micromechanisms and mechanics of fracture. X-ray residual stress has been confirmed to be a particularly useful parameter when studying the fracture surfaces of high strength steels. The method has been applied to the fracture surface of fracture toughness and fatigue specimens.

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