scholarly journals PREVENTION OF CRACK FORMATION IN DETAILS IN PROVISION OF RELIABLE COMPOUNDS WITH A TENSION

2018 ◽  
Vol 12 (3) ◽  
pp. 76-81
Author(s):  
Сергей Попов ◽  
Sergey Popov ◽  
Анатолий Русанов ◽  
Anatoliy Rusanov
Keyword(s):  
Fracture Toughness ◽  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Crack Resistance ◽  
Structural Defects ◽  
Outer Diameter ◽  
The Press ◽  
External Part ◽  
The Impact

When repairing agricultural machinery, the pressing of repair bushings for the restoration of worn parts is widely used. In the process of assembling a joint in the external part, cracks are often formed, which can be caused either by defects in its surface or by structural defects. Therefore, increasing the crack growth resistance of the press connection during assembly is an urgent task. The work analyzes the impact of the geometry of the external part on the resistance to fracture. Since it is possible to obtain complete information on defects by nondestructive testing methods only in individual cases, a technique for modeling the defects of the surface crack of a semielliptical shape was used. To evaluate the crack resistance, the force criterion of fracture mechanics is used - the stress intensity factor. As a result, it was found that the relationship between the thickness of the wall of the external part and its outer diameter makes a significant impact on the fracture toughness of the compression joint, which makes it possible to reduce the probability of nucleation and development of cracks by changing these parameters. Such a technique can be used in cases where the mechanical assembly is used for assembling the connection - by means of a press and a thermal one - with heating of the external part, methods of assembly. The greatest strength of the connection is achieved by cooling the internal part during assembly, but in this case the probability of formation and growth of cracks increases. This is due to a decrease in the critical stress intensity factor (fracture toughness), which is a mechanical characteristic of crack resistance when the temperature of the external part is lowered. The effect of this factor can be reduced by using a combined method of assembling the joint by cooling the internal and heating the external part. To evaluate the fracture resistance at low temperatures, it is optimal to carry out full-scale tests, where the cooling and heating temperatures of the press connection parts act as experimental factors.

Method for the Determination of Hard Alloys’ Maximum Performance Temperature in the Context of the Metal-Cutting Tools’ Usage Quality Estimation Technique

2017 ◽  
Vol 737 ◽  
pp. 59-63 ◽  
Author(s):  
D.S. Vasilega ◽  
A.S. Shtin
Keyword(s):  
Fracture Toughness ◽  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Crack Resistance ◽  
Hard Alloy ◽  
Metal Cutting ◽  
Impact Resistance ◽  
Hard Alloys ◽  
Maximum Performance

The article seals with the study of hard alloy (WC-Co) crack resistance (fracture toughness), depending on the temperature. Three representatives of one-carbide hard alloys (WC 94% Co 6% (fine grain); WC 92%, Co 8%; and WC 85%, Co 15% alloys) were chosen to determine the temperature influence on the stress intensity factor. During the obtained dependences’ analysis, we revealed that the hard alloy maximum performance temperature could be determined by the maximum value of stress intensity factor KIC. The relation between the temperature of hard alloy (WC-Co) maximum crack resistance (fracture toughness) and the temperature of these materials’ maximum performance, is shown here as a result of experimental study of the dependence of impact resistance from temperature. In addition, the hard alloys’ maximum performance temperature determination technique is developed.

On notch fracture mechanics

2021 ◽  
Vol 87 (2) ◽  
pp. 56-64
Author(s):  
G. Pluvinage
Keyword(s):  
Fracture Toughness ◽  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Plastic Zone ◽  
Fracture Resistance ◽  
Notch Radius ◽  
Notch Stress Intensity Factor ◽  
Blunt Notch ◽  
Notch Stress

Different stress distributions for an elastic behavior are presented as analytical expressions for an ideal crack, a sharp notch and a blunt notch. The elastic plastic distribution at a blunt notch tip is analyzed. The concept of the notch stress intensity factor is deduced from the definition of the effective stress and the effective distance. The impacts of the notch radius and constraint on the critical notch stress intensity factor are presented. The paper ends with the presentation of the crack driving force Jρ for a notch in the elastic case and the impact of the notch radius on the notch fracture toughness Jρ,c. The notch fracture toughness Jρ,c is a measure of the fracture resistance which increases linearly with the notch radius due to the plastic work in the notch plastic zone. If this notch plastic zone does not invade totally the ligament, the notch fracture toughness Jρ,c is constant. This occurs when the notch radius is less than a critical one and there is no need to use the cracked specimen to measure a lower bound of the fracture resistance.

scholarly journals Fracture toughness as an alternative approach to quantify the ageing of insulation paper in oil

Cellulose ◽  
2021 ◽  
Author(s):  
C. Fernández-Diego ◽  
I. A. Carrascal ◽  
A. Ortiz ◽  
I. Fernández ◽  
D. Ferreño ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Dielectric Materials ◽  
Superior Performance ◽  
Mechanical Resistance ◽  
Insulation Material ◽  
Cellulose Materials ◽  
Over Time

AbstractOil-immersed transformers use paper and oil as insulation system which degrades slowly during the operation of these machines. Cellulose materials are used generally as insulation solid in power transformers. The degree of polymerization (DP), defined as number of repeating β-glucose residues in the cellulose molecule, is a critical property of cellulosic insulation material used in transformers, since it provides information about paper ageing and its mechanical strength. The fast-developing electric power industry demanding superior performance of electrical insulation materials has led to the development of new materials, as well as different drying techniques performed during transformer manufacturing and service when required. Both developments have caused some practical difficulties in the DP measurement. Moreover, the increasing interest in synthetic dielectric materials replacing cellulose materials requires measuring alternative properties to the DP to quantify the degradation of insulation solids over time. In this sense, this paper proposes the possibility of analyzing paper degradation through fracture toughness. This approach is different from the study of mechanical properties such as tensile strength or strain because it provides a tool for solving most practical problems in engineering mechanics, such as safety and life expectancy estimation of cracked structures and components which cannot to be considered through the traditional assessment of the mechanical resistance of the material. An accelerated thermal ageing of Kraft paper in mineral oil was carried out at 130 °C during different periods of time, to obtain information on the kinetics of the ageing degradation of the paper. Double-edged notched specimens were tested in tension to study their fracture toughness. The evolution of the load–displacement curves obtained for different ageing times at the ageing temperature of 130 °C was utilized to the determination of the stress intensity factor. Furthermore, different kinetic models based on this stress intensity factor were applied to relate its evolution over time as a function of the temperature. Finally, the correlation between the DP and stress intensity factor, which depends on the fiber angle, was also defined. Graphic abstract

Finite Element Fracture Mechanics Study of Web Connections with Tapered Beam Flange Plates

2010 ◽  
Vol 452-453 ◽  
pp. 473-476 ◽  
Author(s):  
Hong Bo Liu ◽  
Long Jun Xu ◽  
Shuang Li ◽  
Yong Song Shao
Keyword(s):  
Fracture Toughness ◽  
Stress Intensity Factor ◽  
Finite Element ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Bottom Surface ◽  
Seismic Load ◽  
Bottom Flange ◽  
Moment Frames ◽  
Tapered Beam

Brittle fracture was identified in many of prequalified weld joints in steel moment frames in the 1994 Nothridge earthquake. Then analyses of response and damage mechanism of beam-to-column connections under seismic load were widely studied in the world, but few people conduct the research on seismic-resistant behavior of beam-to-column web connections. To quantify the variation of stress intensity factor to weld root flaw sizes beam-to-column web connections with tapered beam flange plates, detailed 3D finite element analyses is used to study fracture toughness requirements in beam-to-column web connections, considering the large deformation, large strain, bolts pretension, bolt contact-slide, as well as material harden and soften. Fracture toughness demands are evaluated in terms of the mode I stress intensity factor. The stress intensity factor is calculated through a J-integral approach. The fracture toughness demands are studied for the flaw on the top of the beam flange and the bottom surface, respectively. Results indicate that the likelihood of top flange fractures is smaller than that of bottom flange fracture. Stress intensity factor is not uniform and is largest in the edge of beam flange. The fracture toughness in the edge of beam flange for web connections with step beam flange plates is 15% less than that for tapered beam flange plates.

RPV Structure Integrity Assessment With Surface Cracks Under PTS

2017 ◽  
Author(s):  
Wei Lu ◽  
Zheng He
Keyword(s):  
Fracture Toughness ◽  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Stress Distribution ◽  
Intensity Factor ◽  
Thermal Shock ◽  
Surface Crack ◽  
Parameter Analysis ◽  
Integrity Assessment ◽  
Pressurized Thermal Shock

As one of the most critical barrier of pressurized-water reactor, Reactor Pressurized Vessel (RPV) is exposed to high temperature, high pressure and irradiation. During the lifetime of RPV, the core belt material will become brittle under the influence of neutron irradiation. The ductile-brittle transition temperature will increase and upper shelf energy will decrease. Thus the structure integrity evaluation of RPV concerning brittle fracture is one of the most important tasks of RPV lifetime management. The non-LOCA accident of Rancho Seco nuclear power plant in 1978 indicates that the emergent cooling transients the sudden cooling down may accompany with the re-pressurize of main loop. The combination of pressure loads and thermal loads may induce a large tensile stress in RPV internal surface, which is the so called pressurized thermal shock (PTS). Due to the existence of welding cladding on the inner surface of RPV, the discontinuity of stress distribution on the cladding-base interface of RPV wall will make calculation of stress-intensity-factor (SIF) difficult. In present research, a two dimensional axial-symmetrical model is built and Finite Element Method (FEM) is adopted to calculate the transient thermal distribution and stress distribution. The influence function method is adopted to calculate crack SIF. Stress distributions in the base and cladding are decomposed respectively and SIFs are calculated respectively to obtain the crack SIF. ASME method is used to calculate the fracture toughness. Present PTS program is validated by the comparative benchmark calculation (the International Comparative Assessment Study of Pressurized Thermal-Shock in Reactor Pressure Vessels). The calculated SIF from present program lies in the reasonable region of the comparing group results. A LOCA transient is investigated with a semi-elliptical surface crack on the RPV beltline region. The temperature and stress distribution along the vessel wall during the transient are given. The stress intensity factors at the deepest and interface point are given respectively. The integrity of RPV under PTS transient is evaluated by comparing stress intensity factor with fracture toughness. Results indicate that the stress intensity factor will not exceed the fracture toughness of the RPV material. The difference between the stress intensity factor and fracture toughness reach a minimum value at the crack tip temperature 20°C. Present research gives a reliable and efficient program to perform RPV structure integrity assessment with surface crack under PTS, which is suitable for further parameter analysis and probabilistic analysis.

Consideration of Reduction in Stiffness due to Cracking and the Impact on Standard Stress Intensity Factor Solutions

2017 ◽  
Author(s):  
Daniel M. Blanks
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Stress Intensity Factors ◽  
Nozzle Geometry ◽  
Intensity Factors ◽  
Factor Solution ◽  
Small Component ◽  
Embedded Crack ◽  
The Impact

An API 579-1/ASME FFS-1 Failure Assessment Diagram based Fitness-for-Service assessment was carried out on an embedded crack-like flaw found in a nozzle to shell weld in a pressure vessel. Stress intensity factors were initially calculated by utilizing stress results from a Finite Element Analysis (FEA) of an uncracked configuration, with the standard embedded crack stress intensity factor solution given in API 579-1/ASME FFS-1. Due to the complex nozzle geometry and flaw size, a second analysis was carried out, incorporating a crack into the FEA model, to calculate the stress intensity factors and evaluate if the standard solution could be applied to this geometry. A large difference in the resulting stress intensity factors was observed, with those calculated by the FEA with the crack incorporated into the model to be twice as high as those calculated by the standard solutions, indicating the standard embedded crack stress intensity factor solution may be non-conservative in this case. An investigation was carried out involving a number of studies to determine the cause of the difference. Beginning with an elliptical shaped embedded crack in a plate, the stress intensity factor calculated with an idealized 3D crack mesh agreed with the API 579-1/ASME FFS-1 solution. Examining other crack locations, and crack shapes, such as a constant depth embedded crack, revealed how the solution began to differ. The greatest difference was found when considering a crack mesh with a small component height (i.e. the distance measured perpendicular from the crack face to the top of the mesh). A close agreement was then found between the stress intensity factors calculated in the nozzle model and an idealized crack mesh with component heights representative of the true geometry. This revealed that reduced structural stiffness is a key factor in the calculation of the stress intensity factors for this geometry, due to the close proximity of the embedded crack to the inner surface of the nozzle. It was found that this reduction is potentially significant even with relatively small crack sizes. This paper details the investigation, and aims to provide the reader with an awareness of situations when the standard stress intensity factor solutions may no longer be valid, and offers general recommendations to consider when calculating stress intensity factors in these situations.

Effect of Heat Treatment on the Fracture Toughness of Glass Fibre Reinforced Polypropylene

2002 ◽  
Vol 10 (3) ◽  
pp. 211-218
Author(s):  
Jeng-Shyong Lin ◽  
Sheng-Kuen Wu
Keyword(s):  
Heat Treatment ◽  
Fracture Toughness ◽  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Glass Fibre ◽  
Initial Crack ◽  
Unstable Fracture ◽  
Heat Treated ◽  
Glass Fibre Reinforced

In this work, the effect of heat treatment on the fracture toughness of glass fibre reinforced polypropylene was studied. Polypropylene blended with short glass fibres was injection-moulded. The moulded parts were heat treated at 150°C for 30 min. The crack growth resistance curve (R-curve) was measured to evaluate the effect of heat treatment on the fracture toughness, and to determine the stress intensity factor at the point of instability, KR(ins). The fracture surface was examined using scanning electron microscope to analyze the fracture mechanism. The results show that the stress intensity factor at the unstable fracture point KR(ins) increases with the initial crack length.

Influences of Crack Face Bridging Stress and Microstructure on Fracture Toughness of Toughened Alumina Ceramics

2011 ◽  
Vol 462-463 ◽  
pp. 972-978
Author(s):  
Yoshihisa Sakaida ◽  
Hajime Yoshida ◽  
Shotaro Mori
Keyword(s):  
Fracture Toughness ◽  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Crack Opening ◽  
Stress Shielding ◽  
Crack Tip ◽  
Shielding Effect ◽  
Hot Press ◽  
Crack Face

Three types of polycrystalline alumina, one pressureless and two hot press sintered Al2O3, were used to examine the effects of the characteristics of microstructure and crack face bridging on fracture toughness. The crack opening displacements and microstructures along the pop-in crack of single edge precracked beam (SEPB) specimens were observed in situ at a constant applied stress intensity factor by scanning electron microscopy (SEM). The bridging stress distribution could be determined from the measured crack opening displacement by three-dimensional finite element analysis, and then the stress intensity factor and stress shielding effect at the crack tip could also be determined. Intergranular microcracks of toughened Al2O3 were deflected by a complicated microstructure, and crack closure due to bridging grains was observed near the crack tip. Bridging stress of Al2O3 was compressive perpendicular to the crack face and was distributed behind the crack tip. The maximum bridging stress of two hot press sintered Al2O3 was about twice as large as that of pressureless sintered Al2O3. The fracture toughness of hot press sintered Al2O3 was, therefore, higher than that of pressureless sintered Al2O3, because the total amount of bridging stress and stress shielding effect increased with increasing magnitude of microcrack deflection and the number of interlocking grains.

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