Fracture Initiation in Low Strength Steel Pressure Vessels

1970 ◽  
Vol 92 (1) ◽  
pp. 79-85 ◽  
Author(s):  
A. Cowan ◽  
N. Kirby
Keyword(s):  
Yield Strength ◽  
Crack Opening ◽  
Fracture Initiation ◽  
Pressure Vessels ◽  
Plastic Collapse ◽  
Low Alloy Steel ◽  
Opening Displacement ◽  
Bend Testing ◽  
Failure Conditions ◽  
Energy Failure

Tests to failure have been made on 5 ft dia × 1 in. thickness steel pressure vessels containing longitudinal slits through wall thickness representing natural defects. Steels of from 33,000 to 70,000 psi yield strength have been tested over a range of temperatures with defects of 6, 12 and 24 in. length. When the toughness exceeds 20/30 ft lb Charpy V-notch energy, failure occurs by plastic collapse, and failure conditions can be predicted from the tensile properties of the steel. At lower levels of toughness the concept of a constant crack opening displacement (COD) at fracture initiation of defects in pressure vessels and in notched bend specimens can be used to predict vessel failure conditions. Recognition must be made of the variables found in COD notched bend testing, and tests are necessary to determine the most embrittled area of a pressure vessel. Examples are given of the method of application of COD and the degree of embrittlement possible in a low alloy steel.

Fracture Resistance of Wire-Wrapped Cylinders

1973 ◽  
Vol 95 (1) ◽  
pp. 219-226 ◽  
Author(s):  
A. K. Shoemaker ◽  
T. Melville ◽  
J. E. Steiner
Keyword(s):  
Yield Strength ◽  
Fracture Resistance ◽  
Crack Extension ◽  
Shear Fracture ◽  
Steel Wire ◽  
Crack Opening ◽  
High Strength ◽  
Opening Displacement ◽  
Propagating Crack ◽  
The Wire

Steel cylinders wrapped with steel wire have the capability of offering not only an economical high-strength structure, but also a structure with improved fracture resistance compared with that of an unwrapped cylinder of equivalent strength. Accordingly, 2000-psi-pressure hydraulic burst tests were therefore conducted to determine the fracture resistance of 36-in-dia, 60-ksi yield-strength, 1000-psi-pressure wire-wrapped cylinders at different levels of shell notch ductility, which was varied by testing at different temperatures. The cylinders were prestressed with 1/4-in-dia cold-drawn wire, and the shells contained part-through-wall flaws. A similarly flawed unwrapped cylinder was tested for comparison. The working-stress level was 72 percent of the specified minimum yield strength in the shell and 60 percent of the minimum tensile strength in the wire. The results showed that at a pressure double that of the unwrapped shell, no crack extension occurred at a temperature at which the steel exhibited fully ductile shell behavior (+110 deg F). A 2-ft crack extension occurred at a temperature (+10 deg F) at which the steel was still in the transition temperature range from ductile-to-brittle behavior (about 20 percent shear fracture), but a brittle crack (−70 deg F) propagated to the end of the wire-wrapped shell. Except for the brittle propagating crack, wire wrapping appears to provide sufficient constraint of a shell defect or propagating crack to limit bulging and crack-opening displacement. A model based on the compatibility in displacements between the crack opening and the local wire strain is presented for calculating the arrest conditions of the propagating crack in the test at 10 deg F. The same flaw size was critical at the constant failure pressure for all test temperatures, and showed that, as predicted, ductile initiation occurs even at the −70 deg F temperature in both the wrapped and unwrapped-cylinder tests. A circumferential flaw was shown to be less critical than a longitudinal flaw of the same size.

Predicting the Fracture Initiation Transition Temperature in High Toughness, Low Transition Temperature Line Pipe With the COD Test

1974 ◽  
Vol 96 (4) ◽  
pp. 330-334 ◽  
Author(s):  
R. J. Podlasek ◽  
R. J. Eiber
Keyword(s):  
Transition Temperature ◽  
Static Loading ◽  
Crack Opening ◽  
Fracture Initiation ◽  
Full Scale ◽  
Pipe Material ◽  
Opening Displacement ◽  
Line Pipe ◽  
High Toughness ◽  
Critical Flaw

This paper describes the use of the crack opening displacement (COD) test to predict the fracture initiation transition temperature of high toughness, low-transition temperature in line pipe. A series of COD tests using t × t and t × 2t specimens made from this line pipe material. The COD test was conducted over a range of temperatures and the point where the upper shelf COD values began to decrease with decreasing temperature was defined. To verify the full-scale significance of this temperature, a series of three experiments was conducted on 48-in. (1.22m) dia line pipe to bracket the transition temperature defined in the COD Test. The results suggest that the COD transition temperature can ve used to define the fracture initiation temperature for static loading in pipe. In addition, in the transition temperature region, the full-scale results, while limited in number, suggest that the COD values could possibly be used to predict the critical flaw sizes in the pipe material.

Elastic-Plastic Fracture Toughness: A Comparison of J-Integral and Crack Opening Displacement Characterizations

1975 ◽  
Vol 97 (4) ◽  
pp. 278-283 ◽  
Author(s):  
C. A. Griffis
Keyword(s):  
Crack Opening Displacement ◽  
Integral Formula ◽  
Crack Opening ◽  
Fracture Initiation ◽  
Maximum Load ◽  
Minimum Size ◽  
J Integral ◽  
Opening Displacement ◽  
Geometry Dependence ◽  
Crack Movement

The geometry dependence of the J-integral and crack opening displacement at fracture initiation, Ji and (COD)i, is examined for HY-80 steel using precracked bend specimens having thicknesses ranging from 1.6 to 53mm. The amount of crack growth at selected points on the load-deflection diagram was delineated using an unload-heat tint procedure. Resistance curves of J and COD versus crack extension were constructed to determine critical values of these parameters at incipient crack movement. Results are interpreted in terms of previously proposed minimum size requirements for valid Ji measurement. The adequacy of the Rice-Srawley J-integral formula for the bend specimen and the utility of J and COD values at maximum load are also considered.

Optimum Global Failure Prediction Model of Steam Generator Tube With Two Parallel Axial Through-Wall Cracks

2005 ◽  
Vol 127 (2) ◽  
pp. 123-128 ◽  
Author(s):  
Seong-In Moon ◽  
Young-Jin Kim ◽  
Jin-Ho Lee ◽  
Myung-Ho Song ◽  
Youn-Won Park
Keyword(s):  
Steam Generator ◽  
Crack Opening ◽  
Local Failure ◽  
Plastic Collapse ◽  
Opening Displacement ◽  
Steam Generator Tube ◽  
Collapse Model ◽  
Failure Models ◽  
Optimum Model

The 40% of wall criterion, which is generally used for the plugging of steam generator tubes, is applied only to a single crack. In the previous study (Moon et al. (2002)), a total number of 9 failure models were introduced to estimate the local failure of the ligament between cracks and the optimum coalescence model of multiple collinear cracks was determined among these models. It is, however, known that parallel axial cracks are more frequently detected during an in-service inspection than collinear axial cracks. The objective of this study is to determine the plastic collapse model which can be applied to the steam generator tube containing two parallel axial through-wall cracks. Three previously proposed local failure models were selected as the candidates. Subsequently interaction effects between two adjacent cracks were evaluated to screen them. Plastic collapse tests for the plate with two parallel through-wall cracks and finite element analyses were performed for the determination of the optimum plastic collapse model. By comparing the test results with the prediction results obtained from the candidate models, a crack opening displacement (COD) base model was selected as an optimum model.

The application of fracture mechanics to yielding materials

1965 ◽  
Vol 285 (1400) ◽  
pp. 34-45 ◽  
Keyword(s):  
Crack Opening Displacement ◽  
Notch Root ◽  
Crack Opening ◽  
Plate Thickness ◽  
Fracture Initiation ◽  
Steel Plates ◽  
Opening Displacement ◽  
Strain Criterion ◽  
Tension Tests ◽  
Fracture Size

The paper begins with a restatement of the ideas underlying the choice of a hypothesis of crack opening displacement for brittle fracture initiation, in situations in which sharply notched bodies of materials with well-defined yielding properties are subject to fracture either below or at general yield. It is maintained that a displacement is preferred to a strain criterion in order to encompass fracture size effects. Slow notched bend and tension tests conducted at various temperatures on 3 in. thick, mild steel plates are described, in association with autographic measurements of crack opening displacement at fracture. The latter criterion for fracture initiation is found to be largely vindicated. Minor departures from constancy of fracture displacement at given temperatures are examined in relation to variations of notch root triaxial stress intensification with the different specimen shapes and loading conditions. The effects are found to be consistent and especially traceable to the influence of plate thickness on the maintenance of plane strain conditions.

LESCALLOY 300M VAC ARC

Alloy Digest ◽  
1993 ◽  
Vol 42 (2) ◽  
Keyword(s):  
Fracture Toughness ◽  
Tensile Strength ◽  
High Strength ◽  
Melting Process ◽  
Heat Treating ◽  
Pressure Vessels ◽  
Low Alloy Steel ◽  
Steel Company ◽  
High Hardenability ◽  
Ingot Structure

Abstract LESCALLOY 300M VAC ARC is a low-alloy steel with an excellent combination of high hardenability and high strength coupled with good ductility and good toughness. Its tensile strength ranges from 280,000 to 300,000 psi. It is produced by the vacuum consumable electrode melting process to provide optimum cleanliness and preferred ingot structure. Its applications include aircraft components, pressure vessels and fasteners. This datasheet provides information on composition, physical properties, elasticity, and tensile properties as well as fracture toughness. It also includes information on forming, heat treating, machining, joining, and surface treatment. Filing Code: SA-321. Producer or source: Latrobe Steel Company. Originally published March 1976, revised February 1993.

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