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

2006 ◽  
Vol 21 (2) ◽  
pp. 512-521 ◽  
Author(s):  
Ilja Hermann ◽  
Sanjit Bhowmick ◽  
Yu Zhang ◽  
Brian R. Lawn
Keyword(s):  
Plate Thickness ◽  
Steep Descent ◽  
Glass Layer ◽  
Fracture Modes ◽  
Fracture Evolution ◽  
Dental Crowns ◽  
Brittle Layer ◽  
Cyclic Indentation ◽  
Sphere Radius ◽  
Radial Cracks

A study is made of top-surface cracks induced in brittle trilayers by cyclic indentation with a hard sphere in water. The trilayers consist of an external brittle layer (veneer) fused to an inner stiff and hard ceramic support layer (core), in turn adhesively bonded to a thick compliant base (substrate). These structures are meant to simulate essential aspects of dental crowns, but their applicability extends to a range of engineering coating systems. The study follows on from like studies of brittle monoliths and brittle-plate/soft-substrate bilayers. Competing fracture modes in the outer brittle layer remain the same as before: outer and inner cone cracks and radial cracks, all of which form in the near-contact zone and propagate downward toward the veneer/core interface. Inner cone cracks and radial cracks are especially dangerous because of their relatively steep descent through the outer layer as well as enhanced susceptibility to mechanical fatigue. Experiments are conducted on model glass/alumina/polycarbonate systems, using video cameras to record the fracture evolution in the transparent glass layer in situ during testing. Each fracture mode can lead to failure, depending on the maximum contact load and other variables (plate thickness, sphere radius). The potentially beneficial role of a stiff intervening core is discussed, along with potentially deleterious side effects of residual thermal-expansion-mismatch stresses.

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.

Coating/Substrate Modulus Mismatches and Margin Geometry Effects on Contact Damage in Curved Brittle Coating Systems

2008 ◽  
Vol 41-42 ◽  
pp. 49-55
Author(s):  
Tarek Qasim
Keyword(s):  
Dental Composite ◽  
Contact Damage ◽  
Principal Stresses ◽  
Composite Support ◽  
Dental Crowns ◽  
Low Elastic Modulus ◽  
Brittle Layer ◽  
All Ceramic ◽  
Side Walls ◽  
Radial Cracks

The effects of coating/substrate modulus mismatch and margin geometry on contact damage in bi-layer systems were investigated. Following an earlier study, convex specimens having curvature of 12 mm inner coating diameter and 1mm thick brittle layer on a polymeric and dental composite support bases were produced. Sample coating geometry at the margins was varied by grinding the edge of the glass shells in various shapes. The specimens were tested by applying single cycle load at the specimen’s axis of symmetry using flat indenter of low elastic modulus. The effects of margin geometry and support layer modulus on radial crack initiation and damage evolution was examined, with particular attention paid to the relevance of such damage to lifetimelimiting failures of all- ceramic dental crowns. Finite element modeling was used to evaluate stress distribution in the glass coating. Experimental trends interrupted with peak maximum principal stresses at the margins. The results of this study illustrate that the fracture behaviour of brittle layered structures is not dominated by certain variables. It is demonstrated that critical loads for initiation of radial cracks are sensitive to support layer modulus as well as margin geometry. Support layer modulus plays an important role in crack propagation and subsequent damage patterns, especially at specimen side walls.

Cracking in Ceramic/metal/polymer Trilayer Systems

2002 ◽  
Vol 17 (5) ◽  
pp. 1102-1111 ◽  
Author(s):  
Hong Zhao ◽  
Pedro Miranda ◽  
Brian R. Lawn ◽  
Xiaozhi Hu
Keyword(s):  
Epoxy Adhesive ◽  
Model Systems ◽  
Fracture Modes ◽  
Aluminum Sheets ◽  
Dental Crowns ◽  
Layer Structures ◽  
Metal Thickness ◽  
Brittle Layer ◽  
Side Walls ◽  
Metal Properties

Fracture and deformation in model brittle-outerlayer/metal-core/polymer-substrate trilayer systems in concentrated loading are studied. Model systems for experimental study are fabricated from glass microscope slides glued with epoxy adhesive onto steel and aluminum sheets, and the resulting laminates glued onto polycarbonate substrate bases. Critical loads to initiate two basic fracture modes in the glass layers—cone cracks at the top surfaces and radial cracks at the undersurfaces—are measured as a function of metal thickness byin situobservation through the glass side walls. Finite element modeling (FEM) is used to quantify these competing fracture modes. The more damaging radial fracture mode is attributed to flexure of the glass layers on soft underlayers. Although much of this flexure can be eliminated by removing the soft adhesive interlayer between glass and metal, yield in the metal limits the potential increases in critical load for radial cracking. Trilayer systems consisting of porcelain fused to Co-, Pd- and Au-alloy core support layers relevant to dental crowns are then analyzed by FEM. The hardness (especially) and elastic modulus of the metal are identified as the primary controlling material parameters, with modulus and strength of the brittle layer as supplemental parameters. Guidelines for improving metal-based crownlike layer structures are thereby developed via optimization of metal properties and relative layer thicknesses.

The Effects of Cyclic Loading on Fracture Modes in Brittle Layer Structures: Relevance to Failure of Dental Crowns

2008 ◽  
Vol 41-42 ◽  
pp. 21-26 ◽  
Author(s):  
Sarah Lam ◽  
Kimble Halliday ◽  
Tarek Qasim
Keyword(s):  
Cyclic Loading ◽  
Hard Spheres ◽  
Vertical Component ◽  
Dental Crowns ◽  
Layer Structures ◽  
Brittle Layer ◽  
Moist Environment ◽  
Loading Tests ◽  
Cyclic Loading Tests ◽  
Radial Cracks

The effects of cyclic loading on contact damage in curved bi-layer systems are investigated. Dome structures consisting of glass shells, filled with epoxy resin, simulate the essential structure of monolithic all-ceramic dental crowns on natural tooth dentine. Cyclic loading, with only a vertical component, was carried out with the Multi-Functional Chewing Simulator (Willytec. Munich, Germany). The specimens were tested by indentation with hard spheres of tungsten carbide, with the load applied axially at the apex of the dome. This project reports some new results on the effect of cyclic loading on curved bi-layer systems. In addition, the effect of aqueous environments is addressed. In both air and water tests, observations taken throughout the cyclic loading course indicated that the outer cone cracks inhibited the propagation of radial cracks. Results confirm that crack initiation occurred more rapidly in wet conditions of testing, emphasizing the influences of the moist environment of the oral cavity. Furthermore, the experiments took into account the evolution of inner cone cracks observed in wet cyclic loading tests. The new results are important since nearly all-dental crowns exhibit some curvature. The implications of the results on the failure of dental crowns are discussed.

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.

In-Vitro Hertzian Fatigue Properties of Glass Infiltrated Ceramic Composites for Dental Crowns

2005 ◽  
Vol 486-487 ◽  
pp. 225-228 ◽  
Author(s):  
Yo Seung Song ◽  
Il Seok Park ◽  
Ju-Woong Jang ◽  
Deuk Yong Lee ◽  
Se Jong Lee
Keyword(s):  
Artificial Saliva ◽  
Cyclic Fatigue ◽  
Ceramic Composites ◽  
Strength Degradation ◽  
Fatigue Properties ◽  
Dental Crowns ◽  
Contact Loads ◽  
Large Numbers ◽  
Radial Cracks

Hertzian cyclic fatigue properties of the glass-infiltrated alumina and spinel were evaluated using a WC sphere of radius of 3.18 mm in exact in vitro environment (artificial saliva) at contact loads from 200 N to 1000 N to investigate indentation damage and strength degradation. At 200 N, no strength degradation was observed up to 106 contact cycles. As the load increased from 200 N to 1000 N, the reduction in strength was found when the transition from ring to radial cracking occurred. The degree of strength degradation after critical cycling was more pronounced probably owing to the chemical reaction of the artificial saliva with the glass phase along the radial cracks introduced during the large numbers of contact cycles.

Matching Ability of Dental Shaded Zirconia Ceramics and Veneering Porcelain

2012 ◽  
Vol 512-515 ◽  
pp. 1751-1755
Author(s):  
Li Min Dong ◽  
Chen Wang ◽  
Ning Wen ◽  
Yuan Fu Yi ◽  
Qing Feng Zan ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Flexural Strength ◽  
Porcelain Body ◽  
Dental Restoration ◽  
Zirconia Ceramics ◽  
Posterior Teeth ◽  
Dental Crowns ◽  
Shock Resistance ◽  
Radial Cracks ◽  
Shade Guide

The matching properties of ceramics and veneering porcelain play an important role for the overall color and mechanical properties of dental crowns. The Vita VM9 veneering porcelain was coated on the surfaces of two zirconia, three-point flexural strength, heat shock resistance and the overall color after veneered with porcelain were tested. The results showed that the interlayer cracks, radial cracks or porcelain body cracks were not appeared in all samples during thermal shock experiments at 60~220°C. Their flexural strength was all above 700MPa and the overall color covered the common color of VITA-3D Master shade guide. There is good thermal compatibility between the two dental shaded zirconia ceramics and Vita VM9 veneering porcelain. The mechanical properties are suitable for clinical posterior teeth area restorative, and the overall color is also suitable for the requirements on the color and brightness of clinical dental restoration.

Impact Fracture Behavior in Alumina Ceramic Plates

2005 ◽  
Vol 297-300 ◽  
pp. 1327-1332
Author(s):  
Hyung Seop Shin ◽  
Sang Yeob Oh ◽  
Moon Saeng Kim ◽  
Masashi Daimaruya
Keyword(s):  
Fracture Behavior ◽  
Impact Force ◽  
Plate Thickness ◽  
Rear Surface ◽  
Impact Testing ◽  
Low Velocity ◽  
Damage Development ◽  
Apparent Stiffness ◽  
Radial Cracks ◽  
The Impact

In this study, a bar impact test of low velocity was carried out to gain an insight into the damage mechanism and sequence induced in alumina plates during quasi-static impact conditions. An experimental setup which could measure directly the impact force applied to the specimen and supply a compressive pre-stress to the specimen by utilizing an long bar impact was devised. During the bar impact testing, the influence of the pre-stress applied to the specimen along the impact direction on the fracture behavior was investigated. The measured impact force profiles explained well the damage behavior induced in alumina plates. The application of higher pre-stress to the specimen led to less damage due to the suppression of radial cracks which was caused by the increase in the apparent stiffness of the plate. The observed results showed the following sequence in damage development: The development of cone crack at the impact region, the formation of radial cracks from the rear surface of plate depending on the plate thickness, and the occurrence of crushing or fragmentation within the cone envelope.

Competing Damage Modes in All-Ceramic Crowns: Fatigue and Lifetime

2005 ◽  
Vol 284-286 ◽  
pp. 697-700 ◽  
Author(s):  
Yu Zhang ◽  
Brian R. Lawn
Keyword(s):  
Cyclic Loading ◽  
Cone Crack ◽  
Occlusal Contact ◽  
Compliant Substrates ◽  
Dental Crowns ◽  
All Ceramic ◽  
Ceramic Crowns ◽  
Radial Cracks ◽  
Brittle Layers ◽  
Dental Crown

A study is made of fracture from cyclic loading of WC spheres on the surfaces of brittle layers on compliant substrates, as representative of repetitive occlusal contact on dental crowns. Several damage modes—radial cracks at both top surface and cementation interface, and classical cone cracks as well as deep penetrating cone cracks from the top surface—have been identified and analyzed. The most dangerous fractures are radial cracks that initiate from either the top or bottom surfaces of the brittle layers and spread laterally to failure. In fatigue, these cracks are driven by chemical forces associated with the intrusion of water into the crack. Also dangerous are deep penetrating cone cracks which, unlike their classical cone crack counterparts, are mechanically driven by hydraulic pumping and can evolve rapidly with cyclic loading, threatening the lifetime of a dental crown veneer.

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