Problem Of Debonding Research Articles

Experimental and numerical estimation of complex stress intensity factor for the completely debonded anti-crack embedded into a weak matrix using domain integral method

The problem of interface debonding is of fundamental importance in understanding the stress transfer mechanism and behavior of weak interfaces present due to rigid stiffeners. A domain integral method based on Betti’s reciprocal theorem was adopted to compute the complex stress intensity factor (SIF) for the completely debonded anti-crack (discontinuity) with mixed boundary conditions. The domain integral approach is based on two admissible mechanical states, which comprise of actual and auxiliary elastic fields. The singular auxiliary fields in terms of angular variations for the completely debonded anticrack were obtained using the full-field solution. The obtained angular variations were compared with the Williams eigenvalue problem for completeness. The displacement and strains were obtained using digital image correlation (DIC) experiments and numerical simulation for parallel and perpendicular orientations of the discontinuity. The obtained DIC strain contours revealed the presence of anti-symmetric and symmetric variation on the bonded side of the anti-crack. The complex SIF is estimated experimentally and numerically based on the domain integral method to seek a better comparison with the analytical estimate. The SIF estimated for the perpendicular orientation is higher than the parallel orientation.

Evaluation Of Silano Adhesive Efficiency in Improvement of Shear Binding Strength of Synthetic Teeth to Thermo-Plastic Denture Material

Background: One of the most serious problems concerning denture performance is the possibility of prosthetic tooth displacement due to increased chewing efficiency. The nature of the mechanical bonding between thermoplastic denture base materials and acrylic teeth has aggravated the problem of tooth debonding. The study aiming to examine the strength of shear bond between prosthetic teeth and thermoplastic base material utilizing silano (silane coupling agent) and mechanical surface modifications (Alumin-ablasting, T. Shape hole) of tooth ridge lap pre and post (100 hrs.) of accelerated ageing conditions. Materials and method: The surface treatments of (120) maxillary central incisors were chosen and grouped into 6 groups of 20 samples each. Each group split into before and after (100hrs.) according to ageing (n=10). Measurement of shear bonding strength applied by a universal testing equipment with 0.5mm/min crosshead speed. Statistical analyses were done using one-way ANOVA test and Tukey’s (HSD) test. Results: Statistics showed high significant variation in average binding force after several surface manipulations in contrast to the control group at (P < 0.000). Regarding surface manipulations, dual treatment of “Alumina-blasting + silano “revealed significant elevation of binding strength in compare to “alumina-blasting” alone (P < 0.001). Similarly, with “T. hole + silano” yielded in greatly increased bonding strength compared to using “T. hole” alone (P < 0.001). a great reduction in bonding strength value was indicated along all treated groups after ageing process (P < 0.000) except the group treated with “T. Hole + silano” show non-significant variations at (p = 0.112). Conclusion: combination treatment (chemo-mechanically) with “T. Hole + silano” improve shear binding strength and not effected with ageing process.

Evaluation Of Fusion Liquid Efficiency In Improvement Of Shear Binding Strength Of Synthetic Teeth To Thermo-Plastic Denture Material

Background: Due to increased chewing capability, one of the most common problems with dentures is that prosthetic teeth can come loose from the denture. The mechanical design of the connection between thermoplastic base materials and acrylic teeth has increased the problem of tooth debonding.
 Objective: The current study was conducted to assess the shear bind strength of artificial teeth to thermoplastic resin utilizing fusing liquid and mechanical modifications (Alumin-ablasting, T. hole) of tooth ridge lap before and after 100 hours of accelerated ageing.
 Materials and method: A total 120 maxillary central incisors have been chosen and grouped into 6 groups of 20 samples each, according to surface treatments. each group subdivided into before and after 100hrs according to artificial ageing (n=10). Shear bond strength test conducted by a universal measurement apparatus with crosshead speed 0.5mm / min. Data were statistically analyzed by one-way ANOVA and Tukey’s (HSD).
 
 Results: Various surface treatments techniques significantly affected the shear bond strength with statistical high difference in mean bond strength after various surface treatments compared to the control group at (p < 0.001). Regarding surface treatment, Dual treatment of “alumina-blasting + fusion liquid” showed considerably elevated strength compared to alumina-blasting alone at (p < 0.001). also “T. hole +fusion liquid” treatment yielded a significant elevation in strength reading compared to T. hole alone at (p < 0.001). Great significant full in strength value was noted in all groups post 100hrs of artificial ageing process at (p < 0.001). The combined surface treatment revealed the lowest percentage reduction in SBS yielded in (T. Hole + fusion), (Alumina-blasting + fusion) than T. hole alone and alumina-blasting alone after 100hrs of artificial ageing process.
 Conclusion: Surface treatment with T. hole + fusion liquid or alumina-blasting + fusion liquid enhanced SBS.

Direct bulk-fill resin composite restorations: Characterization of pulpal floor gaps in deep occlusal cavities and current restorative minimization strategies — An overview

Introduction: When a single mass of bulk-fill resin composite is inserted in a deep occlusal cavity and light cured, it undergoes restrained shrinkage due to bonding to surrounding cavity walls. This shrinkage generates stresses within the mass which are not uniformly distributed due to variations in adhesive bonding to enamel and dentin of surrounding cavity walls. This behavior creates a problem of internal debonding and gap formation at the pulpal floor that results in postoperative sensitivity and persistent tooth pain, as well as failure of the restoration, over the time, due to biodegradation of resin-dentin bond. Aims: This paper provides a thorough overview on the debonding problem and gap formation at pulpal floors in deep occlusal cavities restored directly with bulk-fill resin composites. It also reviews the techniques currently available in the literature for reducing this problem. Materials and Methods: The data was searched and collected from 2021-2022. A total of 51 articles were included in this review. Results and Discussion: Three restorative techniques were recently reported as possible solutions for this problem, all aiming at relieving the developed shrinkage stresses and reducing the pulpal floor gap formation. In the first technique, an intermediate layer of bulk-fill resin composite was placed on the pulpal floor and cured. While in the second technique, a fiber-reinforced layer of bulk-fill resin composite was placed on the pulpal floor and cured. In these two techniques, the restoration was completed by filling the cavity with a mass of bulk-fill resin composite and curing it. As for the third technique “the semi-split bulk-filling technique”, a diagonal gap was cut in the uncured mass of bulk-fill resin composite, extending halfway in pulpal direction through the composite bulk, followed by curing. Then, the created gap was filled with the same bulk-fill resin composite to complete the restoration and followed by curing. Conclusion: The three restorative techniques reported in this paper are possible solutions to the problem of debonding and gap formation at pulpal floors in deep occlusal cavities restored directly using bulk-fill resin composites. They all relieve the developed shrinkage stresses and reduce the pulpal floor gap formation.

Evaluation Of Fusion Liquid Efficiency In Improvement Of Shear Binding Strength Of Synthetic Teeth To Thermo-Plastic Denture Material

Background: Due to increased chewing capability, one of the most common problems with dentures is that prosthetic teeth can come loose from the denture. The mechanical design of the connection between thermoplastic base materials and acrylic teeth has increased the problem of tooth debonding.
 Objective: The current study was conducted to assess the shear bind strength of artificial teeth to thermoplastic resin utilizing fusing liquid and mechanical modifications (Alumin-ablasting, T. hole) of tooth ridge lap before and after 100 hours of accelerated ageing.
 Materials and method: A total 120 maxillary central incisors have been chosen and grouped into 6 groups of 20 samples each, according to surface treatments. each group subdivided into before and after 100hrs according to artificial ageing (n=10). Shear bond strength test conducted by a universal measurement apparatus with crosshead speed 0.5mm / min. Data were statistically analyzed by one-way ANOVA and Tukey’s (HSD).
 
 Results: Various surface treatments techniques significantly affected the shear bond strength with statistical high difference in mean bond strength after various surface treatments compared to the control group at (p < 0.001). Regarding surface treatment, Dual treatment of “alumina-blasting + fusion liquid” showed considerably elevated strength compared to alumina-blasting alone at (p < 0.001). also “T. hole +fusion liquid” treatment yielded a significant elevation in strength reading compared to T. hole alone at (p < 0.001). Great significant full in strength value was noted in all groups post 100hrs of artificial ageing process at (p < 0.001). The combined surface treatment revealed the lowest percentage reduction in SBS yielded in (T. Hole + fusion), (Alumina-blasting + fusion) than T. hole alone and alumina-blasting alone after 100hrs of artificial ageing process.
 Conclusion: Surface treatment with T. hole + fusion liquid or alumina-blasting + fusion liquid enhanced SBS.

Mechanical Connectors to Enhance the Interfacial Debonding of Concrete Overlays

Concrete bonded whitetoppings and overlays usually fail due to a loss of bond between the layers as a consequence of direct actions (traffic loads) or indirect actions (temperature differences or shrinkage in the layers). These actions generate stresses in the interface that may exceed the strength capacity of the union between layers. This paper proposed an innovative solution for this problem that consisted of placing mechanical connectors in the overlay interfaces to provide them with post-cracking strength and maintaining the monolithic response of the pavement. Three experimental programs on real-scale pavements with two types of mechanical connectors were studied under heavy traffic in terms of structural performance. Findings reveal that this technique might be an excellent solution to the problem of interfacial debonding.

Gel Debonding from a Rigid Substrate

We consider the problem of debonding of a thin gel domain from a rigid substrate. Starting with a variational approach involving the total energy of a gel, we formulate the boundary value problem of the governing equations in two-space dimensions. We consider the case that the aspect ratio, $\eta $ , the quotient of the thickness of the film with respect to its length, is very small. We assume that the gel is partially debonded at the dimensionless horizontal location denoted by $0<\delta <1$ . The appropriate limiting problem with respect to $\eta $ , with fixed $\delta $ , yields an approximate solution corresponding to a deformation that is homogeneous both on the bonded part and on the debonded part of the gel, but whose gradient and vertical component are discontinuous across the interface $x=\delta $ . This approximate solution determines, up to first order, the energy release rate on $\delta $ , giving the critical value for the gel thickness at which it becomes unstable against debonding.

Adhesion and debonding in a model of elastic string

We study the problem of adhesion and debonding of an elastic body interacting with a rigid substrate through a layer made of soft breakable adhesive material. The general problem is formulated in the multidimensional vectorial case, while a detailed analysis is carried for the one dimensional case leading to the study of a 1D semilinear wave equation. The initial boundary value problem is affected by the presence of a source term characterizing the interaction of the string withe the adhesive layer. This discontinuous force jumps to zero when a critical value of the displacement is reached. We obtain conditions for the initial boundary value problem ensuring the regularity of the solutions and the attachment–detachment conditions. Finally, we focus on a numerical investigation of the problem by considering regularizations of the source term and different initial conditions.

To Compare and Evaluate the Bond Strength of Acrylic Denture Teeth with Heat Cure Acrylic Resin and Thermoplastic Denture Base Material after Different Surface Treatments of Acrylic Teeth - An In Vitro Study

Background: Denture teeth made of acrylic resin are preferred because they chemically bond to denture base material but the problem of debonding is also common with the use of acrylic teeth. Many attempts have been done to improve bond strength of acrylic teeth which involves mechanical and chemical means. With the use of recently introduced thermoplastic denture base materials, the problem of tooth debonding has been increased due to the mechanical nature of the bond between these materials and the acrylic teeth. There is limited literature on bond strength of acrylic teeth and flexible denture materials and the methods to enhance it. The present study evaluates and compares the bond strength between acrylic teeth and heat cure resins and thermoplastic resins after different known denture tooth surface treatment methods, including use of methyl methacrylate; sandblasting and prefabricated vertical groove. Method: A total of 180 maxillary right central incisors were selected and divided into six groups of 30 samples each, according to the surface treatments and denture base material (heat cure or thermoplastic resins) used for processing. The bond strength of all specimens were tested in Universal Testing Machine. The obtained data were subjected to statistical analysis. Result: Results showed that there was statistical significant difference in mean bond strength after various surface treatments and processing of acrylic teeth with either heat cure or flexible denture material. Interpretation &amp; Conclusion: The present findings suggest that vertical groove in the ridge lap area has highest bond strength amongst the groups processed with flexible denture material, and treatment of specimens with methyl methacrylate monomer for 5 sec has highest bond strength amongst all groups.

Effect of Trichloromethane on the Bond Strengths between Acrylic Teeth and Different Heat-cured Denture Bases: A Comparative Study

This study is to evaluate the role of 1:1 v/v 30% trichloromethane and monomer solvent in enhancing the durability of bonding between cross-linked acrylic teeth and different heatcured denture bases with or without mechanical preparations made on ridge lap portion of the artificial teeth. Two high impact denture base resin materials (Trevalon HI, DeTrey, UK, and DPI Tuff, Mumbai) and one nonhigh impact denture base resin material (DPI Quick Set, Mumbai) were selected to form three groups. Each group contains 30 specimens prepared by five different methods. A mixture of 30% trichloromethane and monomer, mixed in the ratio of 1:1 and applied for 1 minute on the ridge lap area of experimental specimens of methods--B, C, D and E (Specimens of method--A being control group, where no alterations were made at the ridge lap portion of acrylic teeth) before curing. Hounsfield universal testing machine is employed to evaluate the comparative bond strengths. No significant difference was seen in bond strengths between specimens of experimental methods in all groups. When each group was assessed separately method B specimens in group 1 (739.2 N), group 2 (758 N) and method D specimens in group 3 (729 N) showed highest mean bond strengths. Control group specimens showed the least bond strength (400-460 N) in all groups with more adhesive failures. Ridge lap portion of the specimens treated with chemical solvent as in method B showed increased bond strength in groups 1 and 2. Hence, this is a preferred method. Evaluation of effect of different chemical and mechanical preparations at the ridge lap areas of acrylic teeth before acrylization helps the clinician and technician to overcome the problem of debonding of teeth from denture bases and in turn provides better quality prosthesis to the patient.

Stress Intensity of Debonding for A Rigid Inclusion Near An Angle Dislocation

The study of debonding is of importance in providing a good understanding of the bonded interfaces of dissimilar materials. The problem of debonding of an arbitrarily shaped rigid inclusion in an infinite plate with a point dislocation of thin plate bending is investigated in this paper. Herein, the point dislocation is defined with respect to the difference of the plate deflection angle. An analytical solution is obtained by using the complex stress function approach and the rational mapping function technique. In the derivation, the fundamental solutions of the stress boundary value problem are taken as the principal parts of the corresponding stress functions, and through analytical continuation, the problem of obtaining the complementary stress function is reduced to a Riemann-Hilbert problem. Without loss of generality, numerical results are calculated for a square rigid inclusion with a debonding. It is noted that the stress components are singular at the dislocation point, and a stress concentration can be found in the vicinity of the inclusion corner. We also obtain the stress intensity of a debonding in terms of the stress functions. It can be found that when a debonding starts from a corner of the inclusion and extends to another corner progressively, the stress intensity of the debonding increases monotonously; once the debonding extends over the corner points, the value of the stress intensity of the debonding gradually decreases. The relationships between the stress intensity of the debonding and the direction and position of the dislocation are also presented in this paper.

Hollow Threaded Rebar for Cross Hole Sonic Logging Access Tubes Combined with Longitudinal Concrete Reinforcing in Drilled Shafts

AbstractCrosshole Sonic Logging (CSL) of drilled shafts requires 1.5-in (38-mm) or 2-in (51-mm) I.D. sonic access tubes to be installed inside the steel reinforcement cage. The sonic access tubes do not contribute to the structural capacity of the drilled shaft. The proposed use of Ischebeck TITAN T73/56 CSL/Hollow Threaded Rebar for Cross Hole Sonic Logging Access Tubes Combined with Longitudinal Concrete Reinforcing in Drilled Shafts (patent pending) is discussed as an alternative method of construction and CSL probe access. The T73/56 hollow threaded rebar/sonic access tube performs as a high strength rebar while at the same time creating a 2.2-in (56-mm) I.D. sonic access tube. The deformed high strength hollow bar provides better adhesion to concrete thus reducing the problem of debonding associated with smooth PVC and steel pipe. A cost comparison using conventional rebar with added sonic access tubes is discussed. The use of T73/56 CSL/Hollow Threaded Rebar as a value engineering alternative can re...

Shear tests of carbon fiber plates bonded to concrete with control of snap-back

In the present paper the problem of brittle debonding between carbon-fiber plates (FRP) and concrete was studied by means of single lap shear tests. Driving the test by controlling the displacement of the free edge of the plate made it possible to describe the pull-out curve up to complete debonding, including the snap-back branch. This permitted to observe that, in the present tests, failure mode and brittleness strongly depend upon the bond length. In particular, specimens with long bond length display a snap-back in the pull-out curve, whereas specimens with short bond length display a softening. Besides, debonding occurs with a transition from mode II to a mixed mode fracture as the bond length decreases, showing different failure mechanisms and a remarkable reduction of the dissipated fracture energy. Moreover, the measured bond-slip relationships show a reduction of the bond strength close to the free edge of the plate that is caused by peeling stresses. Finally, results of the experimental tests are compared with finite element simulations with standard bond-slip laws.

Green Function of a Point Dislocation in Thin Plate with a Partially Debonded Inclusion

The study of debonding is of importance in providing a good understanding of the bonded interfaces of dissimilar materials. The problem of debonding of an arbitrarily shaped rigid inclusion in an infinite plate with a point dislocation of thin plate bending is investigated in this paper. Herein, the point dislocation is defined with respect to the difference of the plate deflection angle. An analytical solution is obtained by using the complex stress function approach and the rational mapping function technique. In the derivation, the fundamental solutions of the stress boundary value problem are taken as the principal parts of the corresponding stress functions, and through analytical continuation, the problem of obtaining the complementary stress function is reduced to a Riemann-Hilbert problem. Without loss of generality, numerical results are calculated for a square rigid inclusion with a debonding. It is noted that the stress components are singular at the dislocation point, and a stress concentration can be found in the vicinity of the inclusion corner.

Analysis of Snap-Back Instability due to End-Plate Debonding in Strengthened Beams

The problem of end-plate debonding of the external reinforcement in strengthened concrete beams is analyzed in this paper. As experimentally observed, this mode of failure is highly brittle and poses severe limitations to the efficacy of the strengthening technique. A numerical analysis of the full-range behavior of strengthened beams in bending is herein proposed to study the stages of nucleation and propagation of interfacial cracks between the external reinforcement and the concrete substrate. This is achieved by modeling the nonlinear interface behavior according to a cohesive law accounting for Mode Mixity. The numerically obtained load versus midspan deflection curves for three- or four-point bending beams show that the process of end-plate debonding is the result of a snap-back instability, which is fully interpreted in the framework of the Catastrophe Theory. To capture the softening branch with positive slope, the interface crack-length control scheme is proposed in the numerical simulations. The results of a wide parametric study exploring the effect of the relative reinforcement length, the mechanical percentage of fiber-reinforced polymer sheets, the beam slenderness, and the ratio between Mode II and Mode I fracture energies are collected in useful diagrams. Finally, an experimental assessment of the proposed model completes the paper.

Numerical Analyses of Hybrid‐Bonded FRP Strengthened Concrete Beams

Abstract: To overcome the problem of debonding, a new hybrid‐bonded fiber‐reinforced polymers (HB‐FRP) strengthening system has recently been developed. This HB‐FRP technique can increase the interfacial bond strength several folds. In this work, a finite element (FE) model for HB‐FRP strengthened beams is developed to simulate the responses of the new structural system. The interfacial behaviors between the FRP and the concrete are simulated with a shear friction model. Comparisons between the predictions from this model and the test results demonstrate the accuracy of the FE model. The mechanism of the HB‐FRP system and failure modes are then studied using the proposed model.

Effects of geometric nonlinearities on damage propagation in patched beam-plates subjected to pressure loading

The problem of edge debonding of patched beam-plates subjected to transverse pressure is examined using two related mathematical models; one which incorporates geometric nonlinearities and the other which neglects them. The models, developed in a prior study, present the energy release rates in self-consistent functional form and yield closed form analytical solutions for the specific problem of interest. Results of numerical simulations based on each model are presented in the form of debond growth paths and compared. The growth paths are subsequently presented with corresponding pre-growth load-deflection paths to further examine the differences resulting from each model. It is seen that significant discrepancies occur between the behaviors predicted by the two models, both with regard to the onset of damage propagation and with regard to the stability of the process, as well as with regard to the pre-growth behavior, demonstrating the critical influence of geometric nonlinearities on the phenomena of interest.

Dynamic fracture: an example of convergence towards a discontinuous quasistatic solution

Considering a one-dimensional problem of debonding of a thin film in the context of Griffith’s theory, we show that the dynamical solution converges, when the speed of loading goes down to 0, to a quasistatic solution including an unstable phase of propagation. In particular, the jump of the debonding induced by this instability is governed by a principle of conservation of the total quasistatic energy, the kinetic energy being negligible.

Rupture dynamique et fissuration quasi-statique instable

Considering a one-dimensional problem of debonding in the context of Griffith theory, we show that the dynamical solution converges, when the speed of loading goes to 0, to a quasi-static solution including an unstable phase of propagation. In particular, the jump of the debonding induced by this instability is governed by a principle of balance of the total quasi-static energy, the kinetic energy being negligible. To cite this article: P.-E. Dumouchel et al., C. R. Mecanique 335 (2007).

Analysis of FRP–concrete debonding via boundary integral equations

The problem of debonding of FRP plates glued over a concrete element is studied making use of boundary integral equations. Mode II cohesive crack model is adopted for the interface, whereas linear elasticity is used for the two materials outside the process zone. Symmetric Galerkin boundary element method is used, adopting the arc-length technique to follow the equilibrium path beyond its critical point. It is shown that, due to the presence of a softening branch in shear stress-slip law, the behavior of a specimen undergoing debonding may be strongly non-linear, and is associated with a very brittle failure mechanism. For bond lengths longer than minimum anchorage length, a snap-back branch typically occurs after the attainment of the maximum force. Two different test setups have been numerically simulated and results in good agreement with experimental tests are found.