Effect of Rotational Stiffness Evolution at Crack Part on Critical Crack Size in SFR

2012 ◽  
Author(s):  
Takashi Wakai ◽  
Hideo Machida ◽  
Shinji Yoshida
Keyword(s):  
Evaluation Method ◽  
Large Diameter ◽  
Crack Size ◽  
Evolution Model ◽  
Piping System ◽  
Rotational Stiffness ◽  
Critical Crack ◽  
Rotational Spring Model ◽  
Size Evaluation ◽  
Critical Crack Size

This paper describes the efficiency of the deployment of rotational stiffness evolution model in the critical crack size evaluation for Leak Before Break (LBB) assessment of Sodium cooled Fast Reactor (SFR) pipes. The authors have developed a critical crack size evaluation method for the thin-walled large diameter pipe made of modified 9Cr-1Mo steel. In this method, since the SFR pipe is mainly subjected to displacement controlled load caused by thermal expansion, the stress at the crack part is estimated taking stiffness evolution due to crack into account. The stiffness evolution is evaluated by using the rotational spring model. In this study, critical crack sizes for several pipes having some elbows were evaluated and discuss about the effect of the deployment of the stiffness evolution model at the crack part on critical crack size. If there were few elbows in pipe, thermal stress at the crack part was remarkably reduced by considering the stiffness evolution. In contrast, in the case where the compliance of the piping system was small, the critical crack size could be estimated under displacement controlled condition. As a result, the critical crack size increases by employing the model and LBB range may be expected to be enlarged.

Determination of Critical Crack Size Utilizing a Fracture Mechanics Test in Equipment Under Fatigue

2009 ◽  
Author(s):  
Irene Garcia Garcia ◽  
Radoslav Stefanovic
Keyword(s):  
Heat Treatment ◽  
Fracture Mechanics ◽  
Crack Size ◽  
Operational Experience ◽  
Element Analysis ◽  
Critical Crack ◽  
Circumferential Welds ◽  
Fea Model ◽  
Critical Crack Size

Equipment that is exposed to severe operational pressure and thermal cycling, like coke drums, usually suffer fatigue. As a result, equipment of this sort develop defects such as cracking in the circumferential welds. Operating companies are faced with the challenges of deciding what is the best way to prevent these defects, as well as determining how long they could operate if a defect is discovered. This paper discusses a methodology for fracture mechanics testing of coke drum welds, and calculations of the critical crack size. Representative samples are taken from production materials, and are welded employing production welding procedures. The material of construction is 1.25Cr-0.5Mo low alloy steel conforming to ASME SA-387 Gr 11 Class 2 in the normalized and tempered condition (N&T). Samples from three welding procedures (WPS) are tested: one for production, one for a repair with heat treatment, and one for repair without heat treatment. The position and orientation of test specimen are chosen based on previous surveys and operational experience on similar vessels that exhibited cracks during service. Fracture mechanics toughness testing is performed. Crack finite element analysis (FEA) model is used to determine the path-independed JI-integral driving force. Methodology for the determination of critical crack size is developed.

Critical crack size in the fracture of metals

2007 ◽  
Vol 52 (7) ◽  
pp. 937-939
Author(s):  
V. A. Ivanskoĭ
Keyword(s):  
Crack Size ◽  
Critical Crack ◽  
Critical Crack Size

scholarly journals On the fracture toughness of snow

2004 ◽  
Vol 38 ◽  
pp. 1-8 ◽  
Author(s):  
Jürg Schweizer ◽  
Gerard Michot ◽  
Helmut O.K. Kirchner
Keyword(s):  
Fracture Toughness ◽  
Crack Size ◽  
Laboratory Measurements ◽  
Critical Crack ◽  
Arrhenius Relation ◽  
Linear Fracture ◽  
Different Temperatures ◽  
Increasing Temperature ◽  
Critical Crack Size ◽  
Key Parameter

AbstractThe release of a dry-snow slab avalanche involves brittle fracture. It is therefore essentially a non-linear fracture mechanics problem. Traditional snow-stability evaluation has mainly focused on snow strength measurements. Fracture toughness describes how well a material can withstand failure. The fracture toughness of snow is therefore a key parameter to assess fracture propagation propensity, and hence snows lope stability. Fracture toughness in tension KIc and shear KIIc was determined with notched cantilever-beam experiments in a cold laboratory. Measurements were performed at different temperatures and with different snow types of density ρ = 100–300 kgm–3, corresponding to typical dry-snow slab properties. The fracture toughness in tension KIc was found to be larger (by about a factor of 1.4) than in shear KIIc. Typical values of the fracture toughness were 500–1000 Pam1/2 for the snow types tested. This suggests that snow is one of the most brittle materials known to man. A power-law relation of toughness KIc on relative density was found with an exponent of about 2. The fracture toughness in tension KIc decreased with increasing temperature following an Arrhenius relation below about –8°C with an apparent activation energy of about 0.16 eV. Above –6°C the fracture toughness increased with increasing temperature towards the melting point, i.e. the Arrhenius relation broke down. The key property in dry-snow slab avalanche release, the critical crack size under shear at failure, was estimated to be about 1 m.

Fracture Resistance in GFRP-BMC Composites Induced by Sub-Millimeter Length Fiber Dispersion

2012 ◽  
Vol 706-709 ◽  
pp. 907-913
Author(s):  
Michael C. Faudree ◽  
Yoshitake Nishi
Keyword(s):  
Fracture Resistance ◽  
Unsaturated Polyester ◽  
Glass Fibers ◽  
Acoustic Emissions ◽  
Crack Size ◽  
Critical Crack ◽  
Fiber Dispersion ◽  
Static Tensile ◽  
Styrene Butadiene ◽  
Critical Crack Size

Based on previous results of both an increase of nearly 40% in static tensile strain by shortening fiber length from commercial 6.4 mm to 0.44 mm in an unsaturated polyester/styrene-butadiene GFRP-BMC composite containing 20 mass% short E-glass fibers and their acoustic emissions (AE), the fracture resistance mechanics of sub-mm length fiber dispersion reinforcement is proposed. Since the 40% strain increase acts to improve strength and toughness, the mechanics is useful. This paper aims to present the mechanism of strain-driven improvement where microcracks are prevented from propagating beyond the critical crack size (2ac) for thermoset polymers, resulting in an increased and more dispersed total microcrack surface area as recorded by AE raising fracture strain.

NUMERICAL METHODS RESEARCH AND FRACTURE FAILURE ANALYSIS FOR CRITICAL CRACK SIZE

2019 ◽  
Vol 2019.27 (0) ◽  
pp. 1542
Author(s):  
Kaikai SHI ◽  
Xiaoming BAI ◽  
Yanli YUAN ◽  
Liangang ZHENG ◽  
Jianguo CHEN ◽  
...  
Keyword(s):  
Numerical Methods ◽  
Failure Analysis ◽  
Crack Size ◽  
Critical Crack ◽  
Fracture Failure ◽  
Critical Crack Size

Influence of Predetermined Surface Defect to the Bendability of Ultra-High-Strength Steel

2012 ◽  
Vol 504-506 ◽  
pp. 901-906 ◽  
Author(s):  
Antti Määttä ◽  
Antti Järvenpää ◽  
Matias Jaskari ◽  
Kari Mäntyjärvi ◽  
Jussi A. Karjalainen
Keyword(s):  
Surface Defects ◽  
High Strength Steels ◽  
Steel Structures ◽  
High Strength ◽  
Crack Size ◽  
Critical Crack ◽  
Bending Radius ◽  
Ultra High Strength Steels ◽  
Materials Used ◽  
Critical Crack Size

The use of ultra-high-strength steels (UHS) has become more and more popular within last decade. Higher strength levels provide lighter and more robust steel structures, but UHS-steels are also more sensitive to surface defects (e.g. scratches). Practically this means that the critical crack size decreases when the strength increases. The aim of the study was to study if the formula of critical crack size is valid on forming processes of UHS-steels. Surface cracks with different depths were created by scratching the surface of the sheet by machining center. Effect of the scratch depth was determined by bending the specimens to 90 degrees. Bents were then visually compared and classified by the minimum achieved bending radius. Test materials used were direct quenched (DQ) bainitic-martensitic UHS steels (YS/TS 960/1000 and 1100/1250). Results from the bending tests were compared to the calculated values given by the formula of critical crack size.

Stress and Fracture Analysis of Ceramic Lined, Composite or Steel Jacketed Pressure Vessels

2004 ◽  
Author(s):  
John H. Underwood ◽  
Anthony P. Parker
Keyword(s):  
Room Temperature ◽  
Fracture Analysis ◽  
Crack Size ◽  
Pressure Vessels ◽  
Interface Pressure ◽  
Temperature Stresses ◽  
Critical Crack ◽  
Steel Jacket ◽  
Differential Thermal Expansion ◽  
Critical Crack Size

Stress and fracture analysis of ceramic-lined cannon pressure vessels is described, for a Si3N4 or SiC liner and A723 steel or carbon-epoxy jacket and with an initial residual interface pressure between liner and jacket. Room temperature stresses for a steel jacket over ceramic are similar to those for a carbon-epoxy jacket, but both radial and hoop jacket stresses can exceed typical carbon-epoxy strength values. Elevated temperature liner stresses are reduced for a carbon-epoxy jacket, due to the effective increase in interface pressure caused by differential thermal expansion. Critical crack size for brittle fracture is larger for Si3N4 than SiC due to lower liner stresses and higher fracture toughness with a Si3N4 liner.

Case Studies of Aircraft Fuselage Cracking

2019 ◽  
Vol 33 ◽  
pp. 11-18 ◽  
Author(s):  
A.M. Al-Mukhtar
Keyword(s):  
Cyclic Loading ◽  
Corrosion Damage ◽  
Crack Size ◽  
Critical Crack ◽  
Aircraft Fuselage ◽  
Effective Role ◽  
Number Of Cycles ◽  
Fuselage Skin ◽  
Critical Crack Size ◽  
Cycles To Failure

Fatigue plays a significant role in the crack growth of the fuselage skin structures. In addition, the fuselage may suffer also from the corrosion damage, and the wear defects. The proper maintenance and scheduled test intervals can avoid the sudden skin failure. Therefore, the inspection interval has to be shortened. Nevertheless, the young machines may be also suffering from the unexpected skin rupture. The cracks are emanating from the rivets and the holes under cyclic loading. The stress concentration around the notch has an effective role under the effect of cyclic loading. The cracks propagate toward the high stressed area such as the notches or other crack locations. The propagation into a critical crack size is rather fast and causes a sudden aircraft fuselage cracking. Hence, the number of cycles to failure will be decreased dramatically. During the last decades, the fracture toughness, design, and the new alloying element have been enhanced. The previous fuselage failures show that the inspections against the cracking are recommended even after a few thousand of cycles. To prevent the crack extending, the crack arresting is recommended to use around the fuselage.

Properties of a Submicron-Honeycomb thin film

1990 ◽  
Vol 188 ◽  
Author(s):  
R. C. Furneaux ◽  
J. S. Crompton ◽  
D. J. Fitchett
Keyword(s):  
Cell Walls ◽  
Flexural Modulus ◽  
Crack Size ◽  
Geometrical Model ◽  
Bending Moments ◽  
Acid Anion ◽  
Critical Crack ◽  
Cell Dimensions ◽  
Critical Crack Size ◽  
Good Agreement

ABSTRACTA method has been developed of separating the porous film produced by anodizing aluminium from its substrate. Such films have a honeycomb morphology with pores that open at both surfaces. They are composed of essentially anhydrous alumina doped with acid anion from the anodizing electrolyte, and are electron diffraction insensitive. A geometrical model has been developed that describes how the pore morphology is determined by the anodizing voltage. Using this model, expressions are derived that relate cell dimensions to voltage-determined parameters and bulk properties such as porosity.The flexural modulus and tensile strength of honeycombs have been modelled by considering bending moments experienced by the cell walls. Thus, the properties were expressed in terms of cell dimensions. Here, the anodic film and honeycomb models are combined. These are used to analyze the mechanical properties of the films as determined by the anodizing parameters. A critical crack size is predicted and compared with the results of microstructural examinations. Good agreement is shown. Assumptions behind these findings and the implications arising are discussed.

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