An Analysis of a Crack in Weld by Using Near-Field as Well as Far-Field Crack Parameters

1990 ◽  
Vol 112 (4) ◽  
pp. 304-312 ◽  
Author(s):  
M. Nakagaki ◽  
C. W. Marschall ◽  
F. W. Brust
Keyword(s):  
Stainless Steel ◽  
Crack Growth ◽  
Near Field ◽  
Base Material ◽  
Crack Tip ◽  
Ductile Material ◽  
Stress Strain ◽  
Material Interface ◽  
Steel Welds ◽  
Strain Interaction

A study of ductile crack growth characteristics in stainless steel welds is reported in this paper. A hybrid-type analysis of combined experimental, analytical, and predictive procedures on the subject is addressed. The study focuses on the effects of a stress/strain interaction phenomenon occurring between the crack tip and the weld-base material interface. Clear dependence of the crack initiation fracture characteristics on the weld size relative to the specimen size was found. Also, fracture toughness of a tungsten inert gas weld is shown to be comparable to that for the base stainless steel metal, whereas that of a submerged arc weld is shown to be significantly lower than the base metal. Because of the stress/strain nonproportionality associated with a local unloading due to crack growth in a ductile material, the use of a crack-tip parameter such as ΔTP* or Jˆ-integral was emphasized. On the other hand, prediction of a crack instability was attempted using a less rigorous J-estimation scheme procedure.

Simulating Residual Stresses Using a Modified Wedge-Loaded Compact Tension Specimen

2013 ◽  
Author(s):  
P. Kapadia ◽  
H. Zhou ◽  
C. M. Davies ◽  
R. C. Wimpory ◽  
K. M. Nikbin
Keyword(s):  
Stainless Steel ◽  
Residual Stresses ◽  
Crack Growth ◽  
Crack Tip ◽  
Compact Tension ◽  
Image Correlation ◽  
Internal Stresses ◽  
Fe Model ◽  
Creep Ductility ◽  
Crack Tip Plasticity

Residual stresses are induced in components when fabrication processes produce internal stresses or local deformation and cause accelerated creep damage and cracking during service at elevated temperatures. A method of inducing residual stresses in laboratory fracture specimens is proposed where an oversized wedge is inserted into the crack mouth of a compact tension, C(T), type specimen. In this way the extent of internal stresses can be controlled in order to minimise the level of crack tip plasticity which inherently reduces the remaining strain to failure. Numerical simulations of wedge insertion into specimens made of 316H austenitic stainless steel have been developed to calibrate the wedge insertion process. These models have been experimentally validated using surface strains measured during the wedge insertion, using Digital Image Correlation (DIC), and Neutron Diffraction (ND) measurements. The validated Finite Element (FE) model is used to determine the wedge insertion depth required to maximise the residual stresses without causing significant crack tip plasticity. The validated numerical simulation is used to determine the wedge insertion depths of further wedge-loaded C(T) specimens made from uniformly pre-compressed 316H stainless steel. The reduced creep ductility of this material increases the rate of crack growth under creep conditions. This method of inducing residual stresses with limited crack tip plasticity allows creep crack growth under simulated secondary loading conditions to be investigated without the influence of non-uniform creep ductility caused by work hardening.

Specimens for Simultaneous Mode II, III and II+III Fatigue Crack Propagation: Elasto-Plastic Solution of Crack Tip Stress-Strain Field

2014 ◽  
Vol 891-892 ◽  
pp. 1585-1590 ◽  
Author(s):  
Jana Horníková ◽  
Pavel Šandera ◽  
Stanislav Žák ◽  
Jaroslav Pokluda
Keyword(s):  
Fatigue Crack ◽  
Crack Growth ◽  
Strain Field ◽  
Simple Procedure ◽  
Crack Tip ◽  
Small Scale ◽  
Shear Mode ◽  
Mode Ii ◽  
Threshold Region ◽  
Stress Strain

Determination of fatigue crack growth characteristics under shear-mode loading is a rather complicated problem. To increase an efficiency and precision of such testing, special specimens enabling simultaneous propagation of shear cracks under II, III and II+III loading modes started to be used rather recently. K-calibration of these specimens was performed and, after unique pre-crack and heat-treatment procedures, effective thresholds in several metallic materials could be measured. However, a description of crack growth rate in terms of appropriate fracture mechanics quantities demands a precise assessment of plastic zone size under various shear-mode loading levels. This contribution is focused on the numerical elasto-plastic analysis of stress-strain field at the crack tip in specimens made of a pure polycrystalline (ARMCO) iron. The results reveal that the small scale yielding conditions are fulfilled in the near-threshold region. Starting from ΔK values approximately two times higher than the threshold, however, the ΔKJ or ΔJ approach should already be utilized. Probably the most interesting result of the analysis lies in a simple procedure that enables us to separate individual loading components ΔKJ,II and ΔKJ,III, applied in the mixed-mode II+III part of the specimen, by comparing elasto-plastic and elastic solutions.

Cyclic Crack Growth Rate of Irradiated Austenitic Stainless Steel Welds in Simulated BWR Environment

2011 ◽  
Author(s):  
Y. Chen ◽  
B. Alexandreanu ◽  
W. J. Shack ◽  
K. Natesan ◽  
A. S. Rao
Keyword(s):  
Stainless Steel ◽  
Austenitic Stainless Steel ◽  
Crack Growth ◽  
Neutron Irradiation ◽  
Growth Rates ◽  
Reactor Core ◽  
Cracking Behavior ◽  
Steel Welds ◽  
The Impact ◽  
Crack Growth Rates

Reactor core internal components in light water reactors are subjected to neutron irradiation. It has been shown that the austenitic stainless steels used in reactor core internals are susceptible to stress corrosion cracking after extended neutron exposure. This form of material degradation is a complex phenomenon that involves concomitant conditions of irradiation, stress, and corrosion. Interacting with fatigue damage, irradiation-enhanced environmental effects could also contribute to cyclic crack growth. In this paper, the effects of neutron irradiation on cyclic cracking behavior were investigated for austenitic stainless steel welds. Post-irradiation cracking growth tests were performed on weld heat-affected zone specimens in a simulated boiling water reactor environment, and cyclic crack growth rates were obtained at two doses. Environmentally enhanced cracking was readily established in irradiated specimens. Crack growth rates of irradiated specimens were significantly higher than those of nonirradiated specimens. The impact of neutron irradiation on environmentally enhanced cyclic cracking behavior is discussed for different load ratios.

scholarly journals Role of Predeformation in the Modification of Crack Tip Oxidation Resistance

1993 ◽  
Author(s):  
D. Zheng ◽  
A. H. Rosenberger ◽  
H. Ghonem
Keyword(s):  
Crack Growth ◽  
Near Field ◽  
Low Frequency ◽  
Crack Tip ◽  
Auger Spectroscopy ◽  
Tip Resistance ◽  
Different Levels ◽  
Growth Experiments ◽  
Qualitative Estimation

The effects of predeformation on the high temperature, low frequency crack growth rate of wrought Alloy 718 is investigated. A series of crack growth experiments were carried out on specimens with different levels of deformation, in addition to specimens in the as received conditions. The experiments included continuous measurements of the crack length and its near field crack tip displacements, fractographic analysis of fracture surface facets and qualitative estimation of the slip density in the crack tip region. Furthermore the thickness of surface oxide layers formed during the fracture process was determined using Auger Spectroscopy. Results of this study show that predeformation enhances the crack tip resistance to environmental effects. This result has been analyzed on the basis of the concept that the deformation-associated slip line density controls the chromium oxide build up taking place along the effected grain boundaries in the crack tip region.

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