Risk Of Debonding Research Articles

Modified PEEK Resin Bonded Fixed Dental Prosthesis for a Young Cleft Lip and Palate Patient

This clinical report presents the use of a modified poly ether-ether ketone material as an alternative material for the fabrication of resin-bonded fixed dental prosthesis (RBFDP) framework. This new material can be used for patients allergic to metals, maintaining the same high esthetic demand of ceramics, presenting light weightness and a flexibility similar to bone as a distinct advantage over ceramic materials. The use of a BioHPP RBFDP framework could be considered as an alternative restoration for the replacement of missing lateral incisors in young patients with cleft palate defects. This modified PEEK material known as BioHPP, is a biocompatible, non allergic, rigid material with good mechanical properties, wear resistance, chemical stability, high polishing and low absorption properties. BioHPP frameworks can be manufactured either via CAD/CAM or via the conventional lost wax technique. The low modulus of elasticity, combined with the use of indirect composite resin as a veneering material, provide a distinct advantage over ceramics or metal ceramics on dampening the occlusal forces, reducing the risk of debonding. (J Esthet Restor Dent 28:201-207, 2016).

Flexural performance of RC beams strengthened with near surface mounted CFRP strips

The near surface mounted (NSM) fiber reinforced polymer (FRP) reinforcement is emerging as a promising alternative strengthening technique to externally bonded reinforcement (EBR) for increasing the load carrying capacity of reinforced concrete (RC) members. NSM FRP technique has several advantages, in comparison with the EBR method, such as reducing the risk of debonding, and a better protection from the external sources of damage. In this research, the performance and effectiveness of the NSM and EBR techniques for the flexural strengthening of RC beams are compared. In order to achieve this objective, six full-scale, RC beams were strengthened with different carbon FRP (CFRP) schemes and tested. Such beams were designed to fail in a flexural mode. Test results indicated that if the same amount of CFRP is used, beams strengthened with NSM strips achieved higher ultimate load than those strengthened with EBR. Such increase in the ultimate load ratio ranged between 12% and 18%. Furthermore, a design approach for computing the moment capacity of RC flexural members strengthened with NSM CFRP strips is developed and presented in this paper.

Effect of Dynamic Loading on Wellbore Leakage for the Wabamun Area CO2-Sequestration Project

Summary The most viable options for permanent removal of carbon dioxide (CO2) from the atmosphere include large-scale injection of CO2 from stationary sources, such as coal-fired power plants and heavy-oil production, into brine-filled formations. One of the main risks identified with storing CO2 in the subsurface is the potential for leakage through existing wells penetrating the caprock. The wellbore system has several components that can fail and create leakage pathways, including type and placement of wellbore casing and cements, completion method, abandonment, and wellbore expansion or contraction by changes in temperature and pressure. Of the 1,000 wells in the study area near Wabamun Lake, Alberta, 95 wells penetrated the immediate caprock above the proposed Nisku injection formation and were identified as potential leakage pathways. The leakage risk of these wells was evaluated on the basis of knowledge of the well design, current well status, and historical regulations in the area. Only four wells, for the subset of 27 wells studied, were identified as requiring workover, which was less of a problem than anticipated. To evaluate the risk of creating leakage pathways by thermal and pressure changes caused by CO2 injection, a 3D finite-element model was built by use of poroelastoplastic material models for cement and formation. Multistage simulations for casing/cement and cement/ formation interactions with temperature-enabled elements were conducted. A parametric study of cement properties was conducted to investigate cement design and its mechanical properties for injection wells. The simulation results indicated that thermal cooling might reduce near-wellbore stresses, which would increase the risk of integrity loss in casing/cement and cement/formation. The parametric study revealed that the risk of debonding and tensile failure would increase with increasing Young’s modulus and Poisson’s ratio of the cement under dynamic-loading conditions. In addition, low mechanical cement strength would increase the risk of shear failure in the cement.

Field Monitoring of Rebar Debonding in Concrete Bridge Decks under Traffic-Induced Vibrations

Concrete deck resurfacing is conducted through staged construction under active traffic conditions in lanes adjacent to the newly poured concrete. Many engineers are concerned about the potential of cracking and rebar debonding and other factors, such as shrinkage, thermal expansion and contraction, and live loads. There is a need to evaluate these detrimental effects with techniques that are reliable under field conditions. In this paper, results are presented from a field study that measured peak rebar velocities during concrete pours. The peak velocities were then compared with experimentally established limits for the cracking potential of the concrete surrounding the rebar. However, it is often more feasible to process accelerometer measurements to obtain velocity indirectly from common processing techniques, such as direct integration. A numerical approach was developed to mitigate the various sources of error in the integration and produce accurate estimates of velocities and displacements from raw accelerometer data. The comprehensive field testing of a rehabilitated bridge span was conducted to capture the dynamic response of the bridge girders, stringers, and deck reinforcement. The bridge was monitored during the pour of a simple span and for several hours after the initial concrete placement. The response predicted by the numerical analysis compared well with the field results: the time histories of velocity and displacement were accurately reconstructed. A comparison with the established limits of peak particle velocity suggested that vibrations induced by typical truck traffic during the initial concrete setting period should not pose any significant risk of debonding.

Fault Tree Analysis on Debonding Risk of Trench Anchor

Fault Tree Analysis on Debonding Risk of Trench Anchor

The influence of elastic modulus mismatch between tooth and post and core restorations on root fracture

To investigate the influence of elastic modulus mismatch between tooth and post and core restorations on mechanisms of root fracture. Three-dimensional mathematical models of a root filled maxillary premolar tooth with supporting periodontium were constructed. The tooth was restored with a cast Ni-Cr alloy or fibre-reinforced composite post and core that was bonded or nonbonded to dentine. In the nonbonded simulation, a nonlinear contact analysis was executed to simulate a friction and a potential sliding phenomenon in the interface between tooth and post and core. Risks of root fracture and debonding at the bonded interface were estimated based on the principal stress of the root and the shear stress on the interface, respectively. The fracture risk of the bonded cast post and core was lower than that of the composite post and core, although the cast restoration exhibited eight times greater stress than the composite. The risk of root fracture based on the tensile stress of the tooth structures was higher with the bonded composite post and core than that with the cast post and core. These stresses doubled when the restorations were not bonded to the tooth structures. The risk of debonding of the cast post and core based on the shear stress was approximately twice that of the composite post and core. The elastic modulus mismatch appears to be a factor responsible for the debonding of post and cores from root canals, with the potential to increase the risk of root fracture indirectly.

Effect of residual stresses on the propagation of interface cracks between dissimilar brittle materials: Contribution of two and three-dimensional analyses

Abstract A methodology is proposed to assess the contribution of residual stresses to the debonding risk in multilayers used as cells for energy conversion at elevated temperature. The conditions of an interface crack extension, given by the Energy Release Rate (ERR) and mode-mixity, are fully investigated for thermal and mechanical loadings. Mode-mixity is calculated from Finite Element Modeling (FEM) thanks to an extension of Matos’ approach to 3D crack geometries. The methodology is applied on the configuration of straight crack propagating all along the width of a bimaterial interface. It is shown that values of ERR given by 2D plane models can be used as bounds of three-dimensional numerical results far from free surfaces. For thermal loading, anti-plane mode and ERR are found to rise near the edge with a magnitude that can not be predicted by 2D analysis. Furthermore, it has been found that thermal stresses tend to shift both the ERR and phase angle values induced by mechanical loading. More particularly, thermal stresses can be detrimental in some configurations since the combination with a mechanical loading strongly increases the crack opening mode.

Finite element prediction of interfacial stresses in structural members bonded with a thin plate

The strength or stiffness of a reinforced concrete (RC), metallic or timber member can be increased by bonding a thin FRP or steel plate to its external surface. In such plated members, debonding of the thin plate from the original member is often the controlling failure mode, and such debonding depends strongly on the interfacial stresses in the adhesive layer between the member and the plate. This paper is concerned with the prediction of these interfacial stresses using the finite element method. The paper is primarily focused on simply-supported straight plated beams subjected to a uniformly-distributed load as a widely studied benchmark case. Five different finite element modeling approaches based on different assumptions for the deformations of the three components of such a plated beam (beam, adhesive layer and plate) are described. The predictions of the five models are then compared with each other and with analytical solutions of different levels of sophistication. These comparisons illustrate clearly how each assumption affects the predicted interfacial stresses and identify the beam–spring–beam (B–S–B) model as a relatively simple yet sufficiently accurate model for practical use in predicting interfacial stresses and debonding failure in more complex structural members bonded with a thin plate. To illustrate the versatility and power of the B–S–B type model, interfacial stresses in two more complicated structures (a plated flat panel and a plated curved panel) obtained from the same type of model are presented and discussed. These results provide useful insight into the risk of debonding in such plated panels.

Parameters affecting the debonding risk of bonded overlays used on reinforced concrete slab subjected to flexural loading

This research aims at better understanding the mechanisms involved in the cracking behaviour of bonded overlays used on reinforced concrete beams and slabs. The project involves the testing of reinforced concrete beams (1.8 m × 0.2 m × 0.2 m) repaired with concrete overlays using four different types of surface preparation and subjected to cyclic flexural loading. The concrete beam specimens were simply supported with a point load at midspan. Structural capacity (evolution of the apparent rigidity, maximum deflection, failure mode) and cracking behaviour (flexural cracking and interface debonding) were monitored. Technical data indicate that good adhesion alone is insufficient to guarantee bond durability. A total of 20 beam interfaces were prepared by scarification, sandblasting, chipping with a light jackhammer, and water jetting. A number of cores were tested to evaluate interface strength by direct shear and direct tension. Roughness was characterized quantitatively using a newly developed optometric method. The results indicate that cracking behaviour depends on the bond strength and on the surface roughness produced by a specific surface treatment. The relationships between adhesion, structural behaviour, and roughness were evaluated, and an updated debonding mechanism is proposed to take into account the influence of roughness. To achieve a monolithic behaviour, the surface treatment must generate critical adhesion and roughness levels. In addition to this roughness, the debonding risk decreases rapidly and monolithic behaviour is reached.

Resin-bonded fixed partial dentures: Ten-year follow-up

Purpose The aim of the study was to evaluate the survival rate of resin-bonded fixed partial dentures delivered between 1993 and 2003 in the Department of Prosthodontics of the University of Turin and in several private practices. Materials and Methods The analysis took into consideration the following variables: preparations, metallic alloys, metal preparation and conditioning of the inner surfaces, isolation during cementation, type of cement, kind of prostheses, number of abutments, and number of missing teeth included in the prostheses. Results The estimated survival probability for the first debonding or failure was 85% after 5 years and 71% after 10 years. Conclusions The use of dental dam during cementation reduced the risk of debonding. No differences in survival rate were found for the other parameters.— Reprinted with permission of Quintessence Publishing.

Effect of material properties on stresses at the restoration–dentin interface of composite restorations during polymerization

Background Numerous analyses for the shrinkage stress in the adhesive resin-based composite restorations mostly rely on numerical models. However, various finite element studies have inherent difficulties and inconsistencies associated with the use of different anatomy (tooth and restoration), boundary conditions (root and interfaces) and shrinkage models. As a consequence many numerical results remain inconclusive. Objective The objective of this paper is to develop a simplified analytical model of shrinkage stress and investigate effects of material properties of the restorative material, size of the restoration and volumetric shrinkage on the magnitude of the shrinkage stress in the vicinity of the dental-restoration interface. Methods The model is based on the following assumptions. The geometry is axisymmetric; all materials are linear-elastic; and the polymerization of the restoration material results in uniform volume shrinkage. An application of compatibility conditions leads to the system of five linear algebraic equations to five unknown variables, which can be easily resolved using standard techniques. Results An explicit equation for the tensile stress at the interface was obtained. It was shown that higher Young's modulus, Poisson's ratio and volume shrinkage of the restorative material normally lead to larger tensile stress at the interface, which increases the risk of debonding. The results obtained based in this work, in general, are in a good agreement with published results of finite element studies. Significance The model allows comparison of different adhesive restorative materials with respect to the fracture risk of the interface induced by the development of the shrinkage stress at the restoration–dentine interface during polymerization. The model can be used to validate more sophisticated computational models as well as to conduct various optimization studies and preliminary assessments of fracture risk.

Influence of stem geometry on mechanics of cemented femoral hip components with a proximal bond.

Nonlinear, three-dimensional, finite element models of cemented femoral hip components with a proximal stem-cement bond were developed with use of a Charnley stem geometry and a modified Charnley stem geometry that had a cylindrical cross section over the distal two-thirds of the stem (Distal-Round). Peak tensile stresses in the proximal cement mantle increased 63 and 74% for the Charnley and Distal-Round stems, respectively, when the proximal stem-cement interface was debonded. The shear stresses over the stem-cement interface with a proximal bond were 29% larger for the Distal-Round stem than for the Charnley stem. After the proximal stem-cement interface was debonded, the peak tensile stresses in the cement mantle were 15% larger for the Distal-Round stem than for the Charnley stem. The results illustrate that stresses within the proximal cement mantle could be substantially reduced for both Charnley and Distal-Round stems through use of a proximal stem-cement bond. However, the risk of debonding may be higher for the Distal-Round stem because of increased shear stresses, and once debonded the risk of further loosening due to failure of the cement mantle would also be higher for the Distal-Round stem.

Risk of debonding in three-unit resin-bonded fixed partial dentures

Resin-bonded fixed partial dentures are considered practical and conservative but have not always enjoyed longitudinal success. The long-term survival of 1637 three-unit resin-bonded fixed partial dentures was analyzed. A multistate analysis that included parameters such as debonding, rebonding, or renewal of the restoration was used. Five years after insertion 66.1% (±3.7%) of the originally inserted prostheses remained in place. If additional rebonding was computed, the probability of survival was 82.0% (±3.0%). Reconstruction of the metal frame after one or more dislodgements raised the success rate to 87.1% (±2.6%). Rebonded resin-bonded fixed partial dentures developed a greater risk of debonding. The risk of failure for refabricated fixed partial dentures was similar to that of the originally inserted resin-bonded fixed partial dentures. There were no signs of greater caries incidence after multiple recementation procedures.