Computation of fracture mechanics parameters for structures with residual stresses

2007 ◽  
Vol 31 (4) ◽  
pp. 318-325 ◽  
Author(s):  
Zohra Gaiech ◽  
Hocine Kebir ◽  
Laurent Chambon ◽  
Jean Marc Roelandt
Keyword(s):  
Fracture Mechanics ◽  
Residual Stresses

Design of Oil Injection Quills for Hypercompressors Cylinders

2011 ◽  
Author(s):  
Guido Volterrani ◽  
Carmelo Maggi ◽  
Marco Manetti
Keyword(s):  
Finite Element Analysis ◽  
Fracture Mechanics ◽  
Residual Stresses ◽  
High Stress ◽  
Element Analysis ◽  
Threaded Connection ◽  
Advanced Technologies ◽  
Inner Diameter ◽  
Oil Injection ◽  
Autofrettage Pressure

Fatigue impacts the life of all components subject to alternating loads, including lube oil injection quills. These occurrences are more frequent if a defect (initial flaw) nucleates in the component due to corrosion, high stress, machining imperfections, etc. The design of components undergoing high fluctuating pressures needs advanced technologies, like autofrettage, and design methods, like FEM or fracture mechanics. This component can be identified as a cylinder with different outside diameters and notches deriving from the geometry variation and threaded connection. The inner diameter is the most stressed area and will require an adequate stress analysis. A sensitivity analysis of the autofrettage pressure can be performed to identify the most appropriate residual stresses on the inner diameter and to obtain a threshold defect larger than the minimum detectable. Fracture mechanics allows the analysis the propagation of an initial defect with materials having different properties and considering different autofrettage pressures. Finite Element Analysis is used to validate the residual stresses predicted by calculation for each autofrettage pressure. An optimized solution of the hypercompressor injection quill can be designed.

Strategies for Treating Weld Residual Stresses in Probabilistic Fracture Mechanics Codes

2011 ◽  
Author(s):  
Frederick W. Brust ◽  
R. E. Kurth ◽  
D. J. Shim ◽  
David Rudland
Keyword(s):  
Fracture Mechanics ◽  
Residual Stresses ◽  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
Nuclear Power ◽  
Power Plants ◽  
Degradation Mechanism ◽  
Welding Process ◽  
Corrosion Cracking ◽  
Uncertainty Sources

Risk based treatment of degradation and fracture in nuclear power plants has emerged as an important topic in recent years. One degradation mechanism of concern is stress corrosion cracking. Stress corrosion cracking is strongly driven by the weld residual stresses (WRS) which develop in nozzles and piping from the welding process. The weld residual stresses can have a large uncertainty associated with them. This uncertainty is caused by many sources including material property variations of base and welds metal, weld sequencing, weld repairs, weld process method, and heat inputs. Moreover, often mitigation procedures are used to correct a problem in an existing plant, which also leads to uncertainty in the WRS fields. The WRS fields are often input to probabilistic codes from weld modeling analyses. Thus another source of uncertainty is represented by the accuracy of the predictions compared with a limited set of measurements. Within the framework of a probabilistic degradation and fracture mechanics code these uncertainties must all be accounted for properly. Here we summarize several possibilities for properly accounting for the uncertainty inherent in the WRS fields. Several examples are shown which illustrate ranges where these treatments work well and ranges where improvement is needed. In addition, we propose a new method for consideration. This method consists of including the uncertainty sources within the WRS fields and tabulating them within tables which are then sampled during the probabilistic realization. Several variations of this process are also discussed. Several examples illustrating the procedures are presented.

Fatigue Crack Growth in Notched Parts With Compressive Mean Load

1972 ◽  
Vol 94 (1) ◽  
pp. 243-247 ◽  
Author(s):  
H. Saal
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Fracture Mechanics ◽  
Residual Stresses ◽  
Mild Steel ◽  
Crack Growth ◽  
Notch Root ◽  
Compressive Load ◽  
Notched Specimens ◽  
Mechanics Model

A fracture mechanics model is proposed to describe fatigue crack propagation in notched specimens. This model accounts for residual stresses which are present at the notch root after unloading from maximum compressive load. This is of particular interest for specimens subjected to compressive mean load. According to the model, cracks will stop growing at the boundary of the plastically deformed zone if the specimen is subjected to compressive load only. Validity of the model was verified with notched specimens of mild steel.

Effect of Cladding Residual Stress Modeling Technique on Shallow Flaw Stress Intensity Factor in a Reactor Pressure Vessel

2015 ◽  
Author(s):  
Joshua Kusnick ◽  
Mark Kirk ◽  
B. Richard Bass ◽  
Paul Williams ◽  
Terry Dickson
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Fracture Mechanics ◽  
Intensity Factor ◽  
Residual Stresses ◽  
Room Temperature ◽  
Pressure Vessels ◽  
Temperature Model ◽  
Probabilistic Fracture Mechanics ◽  
Reactor Pressure

Prior probabilistic fracture mechanics (PFM) analysis of reactor pressure vessels (RPVs) subjected to normal cool-down transients has shown that shallow, internal surface-breaking flaws dominate the RPV failure probability. This outcome is caused by the additional crack driving force generated near the clad interface due to the mismatch in coefficient of thermal expansion (CTE) between the cladding and base material, which elevates the thermally induced stresses. The CTE contribution decreases rapidly away from the cladding, making this effect negligible for deeper flaws. The probabilistic fracture mechanics code FAVOR (Fracture Analysis of Vessels, Oak Ridge) uses a stress-free temperature model to account for residual stresses in the RPV wall due to the cladding application process. This paper uses finite element analysis to compare the stresses and stress intensity factor during a cool-down transient for two cases: (1) the existing stress-free temperature model adopted for use in FAVOR, and (2) directly applied RPV residual stresses obtained from empirical measurements made at room temperature. It was found that for a linear elastic fracture mechanics analysis, the application of measured room temperature stresses resulted in a 10% decrease in the peak stress intensity factor during a cool-down transient as compared to the stress-free temperature model.

Two Means of Calculating Very Low Failure Probability

2011 ◽  
Author(s):  
Min Wang ◽  
David O. Harris ◽  
Dilip Dedhia ◽  
Xinjian Duan ◽  
Michael J. Kozluk
Keyword(s):  
Water Stress ◽  
Fracture Mechanics ◽  
Residual Stresses ◽  
Stress Corrosion ◽  
Failure Probability ◽  
Multiple Cracks ◽  
Convolution Integral ◽  
Subsequent Growth ◽  
Primary Water ◽  
Specific Degradation

Computation of large break probabilities in pipes when initiating cracks are the dominant degradation mode is difficult, because the problem is dominated by the probability of initiating multiple cracks around the pipe circumference and having them coalesce and grow to become long prior to penetrating the wall to become a leak. The purpose of this paper is to describe two techniques for evaluating very low large break probabilities in pipes with multiple initiating cracks: (i) combining initiation and growth probabilities by a convolution integral, and (ii) sorting through sets of sampled random variables and performing detailed (lifetime) calculations only for particularly “severe” sets. These techniques are demonstrated in an example problem involving primary water stress corrosion crack (PWSCC) initiation and subsequent growth in a piping weldment with high residual stresses by use of a probabilistic fracture mechanics code, PRAISE-CANDU, which is under development to address specific degradation issues in CANDU® reactors.

Residual Stresses and Fracture Mechanics

1995 ◽  
Vol 117 (4) ◽  
pp. 373-378 ◽  
Author(s):  
lain Finnie ◽  
Weili Cheng
Keyword(s):  
Fracture Mechanics ◽  
Residual Stresses ◽  
Surface Damage ◽  
The Other ◽  
Experimental Procedure ◽  
The Past ◽  
Compressive Stresses ◽  
Surface Flaws ◽  
Effect Of Surface

The first part of the paper discusses two problems in which the role of residual stresses may be treated using the procedures of fracture mechanics. One is the significant degradation of the tensile strength of glass due to the residual stresses produced by surface damage. The other is the effect of surface compressive stresses in inhibiting the detection of surface flaws. The second part of the paper discusses the inverse problem of using fracture mechanics solutions to measure residual stresses. This approach which has only been developed in the past decade leads to an experimental procedure which is easy to implement and is also more versatile than conventional methods.

Sign in / Sign up

Export Citation Format

Share Document