Leakages Through Radial Cracks in Cement Sheaths: Effect of Geometry, Viscosity and Aperture

2021 ◽  
Author(s):  
Ragnhild Skorpa ◽  
Torbjorn Vralstad
Keyword(s):  
Radial Cracks

scholarly journals Microstructure and Fracture Toughness of Fe–Nb Dissimilar Welded Joints

Metals ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 86
Author(s):  
Qiaoling Chu ◽  
Lin Zhang ◽  
Tuo Xia ◽  
Peng Cheng ◽  
Jianming Zheng ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Fracture Toughness ◽  
Weld Metal ◽  
Thermal Cycle ◽  
Peak Load ◽  
Local Phase ◽  
Weld Formation ◽  
Lamellar Structures ◽  
Average Hardness ◽  
Radial Cracks

The relation between the microstructure and mechanical properties of the Fe–Nb dissimilar joint were investigated using nanoindentation. The weld metal consists mainly of Fe2Nb, α-Fe + Fe2Nb, Nb (s,s) and Fe7Nb6 phases. Radial cracks initiate from the corners of the impressions on the Fe2Nb phase (~20.5 GPa) when subjected to a peak load of 300 mN, whereas the fine lamellar structures (α-Fe + Fe2Nb) with an average hardness of 6.5 GPa are free from cracks. The calculated fracture toughness of the Fe2Nb intermetallics is 1.41 ± 0.53 MPam1/2. A simplified scenario of weld formation together with the thermal cycle is proposed to elaborate the way local phase determined the mechanical properties.

Competing fracture modes in brittle materials subject to concentrated cyclic loading in liquid environments: Bilayer structures

2005 ◽  
Vol 20 (10) ◽  
pp. 2792-2800 ◽  
Author(s):  
Sanjit Bhowmick ◽  
Yu Zhang ◽  
Brian R. Lawn
Keyword(s):  
Cyclic Loading ◽  
Driving Forces ◽  
Plate Thickness ◽  
Brittle Materials ◽  
Illustrative Case ◽  
Initial Growth ◽  
Tensile Stresses ◽  
Fracture Modes ◽  
Plate Flexure ◽  
Radial Cracks

A preceding study of the competition between fracture modes in monolithic brittle materials in cyclic loading with curved indenters in liquid environments is here extended to brittle layers on compliant substrates. The fracture modes include outer and inner cone cracks and radial cracks that initiate from the near-contact zone and penetrate downward. Outer cone cracks are driven by stresses from superposed Hertzian and plate flexure fields; inner cone cracks also grow within these fields but are augmented by mechanical driving forces from hydraulic pumping into the crack fissures. Radial cracks are augmented by mechanical driving forces from developing quasiplasticity zones beneath the indenter. Basically, the crack-growth rates are governed by a crack velocity relation. However, the hydraulic and quasiplastic mechanical forces can cumulate in intensity with each cycle, strongly enhancing fatigue. Plate flexure generates compressive stresses at the top surface of the brittle layer, somewhat inhibiting the initiation, and tensile stresses at the lower surface, strongly enhancing the far-field propagation. The tensile stresses promote instability in the crack propagation, resulting in through-thickness penetration (failure). Experiments on a model bilayer system consisting of glass plates bonded to thick polycarbonate bases are presented as an illustrative case study. In situ observations of the crack evolution from initial growth to failure reveal that each fracture mode can dominate under certain test conditions, depending on plate thickness, maximum load, and sphere radius. Implications concerning the failure of practical layer systems, notably dental crowns, are discussed.

Vibrations of circular plates with clamped v-notches or rigidly constrained radial cracks

1995 ◽  
Vol 181 (2) ◽  
pp. 185-201 ◽  
Author(s):  
O.G. Mcgee ◽  
A.W. Leissa ◽  
C.S. Huang ◽  
J.W. Kim
Keyword(s):  
Circular Plates ◽  
Radial Cracks

Stress Intensity Factors for Radial Cracks in a Pre-Stressed, Thick-Walled Cylinder of Strain-Hardening Materials

1983 ◽  
Vol 105 (2) ◽  
pp. 117-123 ◽  
Author(s):  
S. L. Pu ◽  
P. C. T. Chen
Keyword(s):  
Stress Intensity ◽  
Strain Hardening ◽  
Yield Condition ◽  
Function Technique ◽  
Maximum Pressure ◽  
Simple Method ◽  
Fatigue And Fracture ◽  
Useful Life ◽  
Radial Cracks ◽  
High Internal Pressure

A simple method which combines the weight function technique and finite element results is used to obtain mode I stress intensity factor solutions for radially cracked cylinders subjected to a high internal pressure. The method is especially effective for cylinders having residual stresses due to a manufacturing pre-stress process to increase the maximum pressure the cylinder can contain and to improve the cylinder’s useful life against fatigue and fracture. The method is quite general for various assumptions involving the plastic stress-strain relations, the yield condition, the strain-hardening, and the compressibility of the cylinder material.

scholarly journals Numerical Study of Fracture Characteristics of Deep Granite Induced by Blast Stress Wave

2021 ◽  
Vol 2021 ◽  
pp. 1-22
Author(s):  
Zheming Zhu ◽  
Weiting Gao ◽  
Duanying Wan ◽  
Meng Wang ◽  
Yun Shu
Keyword(s):  
Shear Failure ◽  
Numerical Study ◽  
Numerical Models ◽  
Rock Fracture ◽  
Initial Pressure ◽  
3D Models ◽  
In Situ Stress ◽  
Vertical Pressure ◽  
The Difference ◽  
Radial Cracks

To study the characteristics of rock fracture in deep underground under blast loads, some numerical models were established in AUTODYN code. Weibull distribution was used to characterize the inhomogeneity of rock, and a linear equation of state was applied to describe the relation of pressure and volume of granite elements. A new stress initialization method based on explicit dynamic calculation was developed to get an accurate stress distribution near the borehole. Two types of in situ stress conditions were considered. The effect of heterogeneous characteristics of material on blast-induced granite fracture was investigated. The difference between 2D models and 3D models was discussed. Based on the numerical results, it can be concluded that the increase of the magnitude of initial pressure can change the mechanism of shear failure near the borehole and suppress radial cracks propagation. When initial lateral pressure is invariable, with initial vertical pressure rising, radial cracks along the acting direction of vertical pressure will be promoted, and radial cracks in other directions will be prevented. Heterogeneous characteristics of material have an obvious influence on the shear failure zones around the borehole.

Contact Damage of Dental Multilayers: Viscous Deformation and Fatigue Mechanisms

2005 ◽  
Vol 127 (1) ◽  
pp. 33-39 ◽  
Author(s):  
M. Huang ◽  
X. Niu ◽  
P. Shrotriya ◽  
V. Thompson ◽  
D. Rekow ◽  
...  
Keyword(s):  
Finite Element ◽  
Fatigue Loading ◽  
Analytical Models ◽  
Dental Ceramics ◽  
Contact Damage ◽  
Viscous Deformation ◽  
Dental Restorations ◽  
Multilayered Systems ◽  
Elastic Layers ◽  
Radial Cracks

This paper presents the results of recent experimental and finite element studies of contact damage in model dental multilayered systems with equivalent elastic properties to those of crown/join/dentin layers that are found in dental restorations. Subsurface radial cracks are observed to form after Hertzian indentation fatigue loading. In order to explain the possible failure mechanisms, the viscous deformation of the foundation (dentinlike ceramic filled polymer) and epoxy join layers are measured. Finite element and analytical models are then developed in an effort to explain the observed contact-induced deformation of the composite multilayered system. Our results suggest that: viscous deformation of the join and foundation layers can give rise to increased tensile stresses in the top elastic layers (glass or zirconia); defects at the bottom of the top layers (induced by grinding steps before crown attachment) are also shown to promote ratcheting phenomena that can lead to stress build-up in the top layers; and viscous flow of the cement can cause the subcritical crack growth in the dental ceramics.

Modeling of contact-induced radial cracking in ceramic bilayer coatings on compliant substrates

2003 ◽  
Vol 18 (5) ◽  
pp. 1275-1283 ◽  
Author(s):  
Chun-Hway Hsueh ◽  
Pedro Miranda
Keyword(s):  
Flexural Rigidity ◽  
Ceramic Coatings ◽  
Analytical Expression ◽  
Bilayer Coating ◽  
Compliant Substrates ◽  
Dental Crowns ◽  
Plates On Elastic Foundation ◽  
Radial Cracks ◽  
Good Agreement ◽  
Bilayer Coatings

Contact-induced radial cracking in ceramic coatings on compliant substrates was analyzed recently. Radial cracks initiate at the coating/substrate interface beneath the contact where maximum flexural tension occurs, and an analytical expression for the onset of radial cracking in monolayer coatings was formulated on the basis of the classical solution for flexing plates on elastic foundation. In the present study, the analytical expression was derived for the case of ceramic bilayer coatings on compliant substrates, which have significant applications in the structure of dental crowns. It was found that the analytical solution for bilayer-coating/substrate systems can be obtained from that of monolayer-coating/substrate systems by replacing the neutral surface position and the flexural rigidity of monolayer coating with those of bilayer coating. The predicted critical loads for initiating radial cracking were found to be in good agreement with existing measurements and finite element results for glass/alumina, glass/glass-ceramic, and glass/Y2O3-stabilized ZrO2polycrystal bilayers on polycarbonate substrates. Limitations of the present analysis are discussed.

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