Peeling Mode Research Articles

Performance prediction applying different reduced turbulence models to the SMART tokamak

Abstract The SMall Aspect Ratio Tokamak (SMART) is currently being commissioned at the University of Seville and will be able to compare the performance of positive and negative triangularity plasmas at low aspect ratio. Predictive simulations have been performed for different machine scenarios and heating schemes using the TRANSP code. The objectives of these simulations are to predict the parameters expected in positive triangularity plasmas, to guide diagnostic development, and to validate transport models. Several reduced turbulence models have been used to predict electron and ion temperatures for the operational phase 2. All models provide similar results from approximately mid-radius to the separatrix but important discrepancies are found in the core region. These positive triangularity results are compared with experiments from a similar size machine like GLOBUS-M2. The multi-mode model (MMM) shows the best agreement. Simulations with different boundary conditions have been performed and no strong differences have been observed between them. The impact of neutral beam injection (NBI) on the predicted profiles has also been addressed. Rotation reduces turbulence levels so higher temperatures are achieved when included in the simulations. Studying the different contributions to the thermal diffusivities, it is observed that electron temperature gradient (ETG) turbulence dominates at the plasma core while micro-tearing modes (MTM) dominate at the edge in the electron channel. In the ion channel, the neoclassical contribution is dominant at the core and at the very edge while the Weiland component, which includes ion temperature gradient mode (ITG), trapped electron mode (TEM), kinetic ballooning mode (KBM), peeling mode (PM) and collisionless and collision dominated magnetohydrodynamic (MHD) modes governs the mid-radius region. For phase 3, two plasmas with different electron densities have been studied. The case with lower density matches well a specific discharge of GLOBUS-M2. The higher density plasma shows high performance with β N ≈ 3.8 .

Nonlinear simulations of the peeling-ballooning instability of super H-modes in the HL-3 tokamak

As the newly built tokamak in China, HL-3 will explore high-performance operation scenarios, such as super H-mode. The energy confinement and core parameters in the super H-mode can be much larger than that in the normal H-mode. Based on the pedestal simulation code EPED, the operation space of the super H-mode is obtained in HL-3. Magnetic shear decreases with increasing triangularity; consequently, a super H-mode can be achieved. The threshold of triangularity for accessing a super H-mode in HL-3 is around 0.4. By using BOUT++, a nonlinear simulation study of the pedestal instabilities in the super H-mode equilibrium is executed for the first time. As expected, the low n peeling mode, which can cause much of the energy loss (17%) from the pedestal region, is dominant in the super H-mode. Such a large collapse in the pedestal region would lead to a transition from super H-mode to H-mode. It is crucial to expand the parameter space of the super H-mode or mitigate the edge-localized mode (ELM) size for sustaining the super H-mode operations. The E × B velocity shear is found to play an important role in controlling the ELMs in HL-3. The small E × B velocity shear leads to a large growth rate but results in a small ELM size around the peeling boundary. The ELM size is closely related to both the growth rate of peeling-ballooning mode and the duration time of the linear phase. In contrast, a large E × B velocity shear can stabilize the instabilities near the ballooning boundary. Next, the parameter space of the super H-mode can be enlarged.

Cohesive failure analysis of carbon-fiber composite patch repair in perforated steel tubular elements

The use of composite materials to repair corroded steel structural components has expanded in the offshore oil and gas sector. The effective use of composites requires a meticulous process for choosing appropriate constituent elements. In this regard, numerical modeling is an efficient tool to better understand the impact of associated variables and enables the identification of failure causes and simulation of failure propagation. This study aims to assess the mechanical behavior of the adhesive layer at the steel - composite material interface in the repair of perforated tubular structures under bending, compression, and bending-compression. A numerical model is developed simplifying the examination and characterization of the cohesive failure mechanisms and modes occurring between the laminate patch repair and the perforated steel tubular element. The stress distribution and cohesive failure at the interface are then thoroughly investigated. The impacts of the inclusion of fillets at the patch repair ends to smoothen the transition between the composite material and the tube and the repair length are also evaluated. A Python subroutine is developed to identify the failure mode mechanisms to characterize the adhesive areas subjected to peel, shear, or mixed modes. Results suggest that pure shear mode is predominant in most of the repair locations across the three types of loading. For bending loads, the cohesive failure close to the cutout shows prominent shear mode. In the other loading conditions, the adhesive nearly fails in the vicinity of the cutouts (i.e., damage values are close to 1) in a predominant near pure shear failure mechanism. The use of fillets displaces the failure location for bending load, hence increasing the failure load level. Repairs were more extensive under Bending Moment load conditions compared to other load types. The mode ratio analysis and methodology presented in this work offer valuable tools for understanding the causes of failure modes.

Analytical solution for the interfacial stress and energy release rate at failure initiation of the three-point bending test (ISO 14679:1997)

Determining adhesive failure in adhesively bonded joints is still challenging in the field. While the three-point bending test (3PBT) (ISO 14679:1997) has been helpful in identifying critical forces and displacements related to bond strength, it only allows for a qualitative assessment of the bond line. Recently, a new quantitative methodology has been developed to determine critical stress and fracture toughness using the coupled stress–energy criterion and the 3PBT. However, these assessments require a significant effort using semi-analytical or finite element (FE) analysis. Therefore, the present study proposes a reliable set of analytical equations to determine peel and shear stress distributions using a weak interface formulation and 1D Euler–Bernoulli approach. More precisely, a particular numerical method computes the integration constants from these equations. A new method has been proposed for calculating the interfacial stiffness in peel and shear mode, based on the material and geometrical parameters of the geometry. This method differs from the previous approach, where the interfacial stiffness was calibrated from the experimental behavior of the test. The whole approach has been validated through experimental and numerical analysis, including the costly 3D FE analysis. An analytical expression for interfacial energy release is suggested, developed following the works of Fraisse and Schmit on J-integral assessment of sandwich-type overlaps and depending on the applied force and a rotation, which could be experimentally measured. Therefore, this work is significant progress in determining bond strength using a simple mechanical test and equations applicable to various industries.

Predictive modeling of NSTX discharges with the updated multi-mode anomalous transport module

The objective of this study is twofold: firstly, to demonstrate the consistency between the anomalous transport results produced by updated Multi-Mode Model (MMM) version 9.0.4 and those obtained through gyrokinetic simulations; and secondly, to showcase MMM’s ability to predict electron and ion temperature profiles in low aspect ratio, high beta NSTX discharges. MMM encompasses a range of transport mechanisms driven by electron and ion temperature gradients, trapped electrons, kinetic ballooning, peeling, microtearing, and drift resistive inertial ballooning modes. These modes within MMM are being verified through corresponding gyrokinetic results. The modes that potentially contribute to ion thermal transport are stable in MMM, aligning with both experimental data and findings from linear CGYRO simulations. The isotope effects on these modes are also studied and higher mass is found to be stabilizing, consistent with the experimental trend. The electron thermal power across the flux surface is computed within MMM and compared to experimental measurements and nonlinear CGYRO simulation results. Specifically, the electron temperature gradient modes (ETGM) within MMM account for 2.0 MW of thermal power, consistent with experimental findings. It is noteworthy that the ETGM model requires approximately 5.0 ms of computation time on a standard desktop, while nonlinear CGYRO simulations necessitate 8.0 h on 8 K cores. MMM proves to be highly computationally efficient, a crucial attribute for various applications, including real-time control, tokamak scenario optimization, and uncertainty quantification of experimental data.

Evaluation of the Curing of the Primer on Shear Bond Strength of Orthodontic Brackets: An Original Research

ABSTRACT Background: The aim of this study was to evaluate the effect of separately curing the unfilled resin for increased bond strength of the orthodontic brackets as the literature shows both studies that support and contradict this aspect. Methodology: The sample consisted of 120 specimens randomly grouped into four of 30. The tooth was cleaned of tissue and debris and stored in a distilled water solution until the procedures of bonding. The surface of the enamel was conditioned with pumice, and acrylic blocks were designed for the tooth to be mounted onto them. The buccal surfaces of all the teeth were prepared by etching the enamel with 37% phosphoric acid for a time period of 30 seconds and washed for 20 seconds under running water. Stainless steel brackets (Victory Series™ MBT, 0.022 Slot) were used for all the samples in the study, and the bonding procedure was conducted on the same day for all the groups. The artificial saliva was used for the storage of samples for 24 h after bonding, and shear bond strength testing was conducted using an Instron machine in shear or peel mode at a crosshead speed. Results: The highest mean bond strength calculated was for the conventional technique (17.45 mpa), while it was the lowest for no primer adhesive (11.21 mpa). Group IV had a greater distribution of ARI scores than groups I, II, and III. Conclusion: Group IV achieved the highest bond strength when compared to other groups, with an ARI score of 3. Group III had less bond strength, likely due to incomplete curing of the primer due to insufficient exposure to light. Transbond XT can be used without primer, making bonding, debonding, and cleaning procedures easy and less time-consuming.

How fluctuation intensity flux drives SOL expansion

Predictions of heat load widths λq based on particle orbits alone are very pessimistic. This paper shows that pedestal peeling-ballooning (P-B) magnetohydrodynamic (MHD) turbulence broadens the stable scrape-off layer (SOL) by the transport, or spreading, of fluctuation energy from the pedestal. λq is seen to increase with Γε , the fluctuation energy density flux. We elucidate the fundamental physics of the spreading process. Γε increases with pressure fluctuation correlation length. P-B turbulence is seen to be especially effective at spreading, on account of its large effective mixing length. Spreading is shown to be a multiscale process, which is enhanced by the synergy of large and small-scale modes. Pressure fluctuation skewness correlates well with the spreading flux–with the zero crossing of skewness and Γε spatially coincident–suggesting the role of coherent fluctuation structures and the presence of intermittency in λq broadening. λq∼Bp−1 scaling persists for the broadened SOL. We show that the spreading flux increases for increasing pedestal pressure gradient ∇P0 and for decreasing pedestal collisionality υped∗ . This trend is due to the dominance of peeling modes for large ∇P0 and low υped∗ . Ultimately, we see that a state of weak MHD turbulence, as for small ELMs, is very attractive for heat load management. Our findings have transformative implications for future fusion reactor designs and call for experimental investigations to validate the observed trends.

MHD simulations of formation, sustainment and loss of quiescent H-mode in the all-tungsten ASDEX Upgrade

Periodic edge localized modes (ELMs) are the non-linear consequences of pressure-gradient-driven ballooning modes and current-driven peeling modes becoming unstable in the pedestal region of high confinement fusion plasmas. In future tokamaks like ITER, large ELMs are foreseen to severely affect the lifetime of wall components as they transiently deposit large amounts of heat onto a narrow region at the divertor targets. Several strategies exist for avoidance, suppression, or mitigation of these instabilities, such as the naturally ELM-free quiescent H-mode (QH-mode). In the present article, an ASDEX Upgrade (AUG) equilibrium that features a QH-mode is investigated through non-linear extended magneto-hydrodynamic simulations covering the dynamics over tens of milliseconds. The equilibrium is close to the ideal peeling limit and non-linearly develops saturated modes at the edge of the plasma. A dominant toroidal mode number of n = 1 is found, for which the characteristic features of the edge harmonic oscillation are recovered. The saturated modes contribute to heat and particle transport preventing pedestal build-up to the ELM triggering threshold. The non-linear dynamics of the mode, in particular its interaction with the evolution of the edge safety factor, are studied, and suggest a possible new saturation mechanism for the QH-mode. The simulations show good qualitative and quantitative agreement with experiments in AUG. In particular, the processes leading to the termination of QH-mode above a density threshold are studied, which results in the transition into an ELM regime. In the vicinity of this threshold, limit cycle oscillations are observed.

The effect of triangularity on predicted pedestals for the CFETR

In this work, the dominant unstable magnetohydrodynamic mode and its stable region in the pedestal of the China Fusion Engineering Test Reactor are studied by numerical modeling with the peeling-ballooning theory over a wide range of triangularities (δ) and collisionalities (υ*). A new accessible stable region is found at δ<−0.1 for large βN,ped and υ*. This new stable region expands toward lower βN,ped and υ* with decreasing δ and is totally covered by the peeling unstable region with δ=−0.5 because of the increasing trapped particle fraction (ft,eff). The sensitivity of this new stable region to the kinetic ballooning mode constraint and elongation is studied. For negative and low δ<0.1, the boundary of the first stable region is determined from the ballooning mode. For δ>0.1, the peeling mode becomes dominant as the boundary approaches low s with low υ*, while the ballooning mode is still dominant at the boundary with high υ*. When δ increases beyond 0.46, the first stable region is expanded, and access to the second stable region of the ballooning mode opens up. The entire newly connected region of the first and second stable regions keeps expanding with further increases in δ until δ=0.6. Beyond this value, the ballooning mode becomes more unstable with increasing δ, while the peeling mode is approximately unchanged with increasing δ in this range. The change in the dominant mode and the stable region with increasing δ can be explained by the trade-off between the stabilization effect from the deeper poloidal magnetic well and destabilization due to the enlarged drive term.

Classification of Edge Instabilities at Globus-M2 Tokamak

Among the peripheral instabilities observed at the Globus-M2 tokamak, two types of edge localized modes (ELMs) are brought into focus: ELMs synchronized and desynchronized with the sawtooth oscillations. The desynchronized ELMs appear in regimes that are characterized by high values of pressure in the pedestal, pped ≥ 3 kPa, and they are observed in discharges with the toroidal magnetic field BT > 0.6 T and plasma current IP > 0.3 MA. The desynchronized ELMs belong to the type-III/V with the dominating effect of the peeling mode. The synchronized ELMs were observed in a wider range of discharge parameters, including at BT < 0.6 T and IP < 0.3 MA. Calculations of the stability of the peeling-ballooning (PB) mode showed that at pedestal width ψnorm = 0.09 and pped > 3.5 kPa, destabilization of PB modes is possible without additional influence. Experimental data shows that the microtearing mode plays a dominant role in the pedestal. The microtearing mode does not allow the pedestal at Globus-M2 tokamak to reach the state of the unstable kinetic ballooning mode (KBM), which explains the low predictive power of the EPED model at this tokamak.

Effect of Varying Stiffness and Functionalization on the Interfacial Failure Behavior of Isotactic Polypropylene on Hydroxylated γ-Al2O3 by MD Simulation.

This study focuses on polymer-metal joints consisting of isotactic polypropylene (iPP) or iPP grafted with maleic anhydride (iPP-g-MA) and hydroxylated γ-Al2O3, which is a model for an oxidized aluminum surface, and investigates the contributions of the Young's moduli of iPP and iPP-g-MA and chemical functionality (MA groups) in iPP-g-MA to the interfacial failure behaviors using the molecular dynamics (MD) simulation method. First, our calculations demonstrated that the tensile strength observed in interfacial failures of the joints increases as Young's modulus of the polymer in the joints increases. This is because a higher stiffness makes it harder for a void to form within the polymer matrix under the applied tensile strain and to reach the interface. Second, in iPP-g-MA-γ-Al2O3 joints, MA groups work more effectively to improve the interfacial strength as the Young's modulus of the polymer in the joints increases. For iPP-g-MA with a lower Young's modulus, the polymer molecules are pulled off the surface in a peel mode with increasing normal strain due to their greater flexibility. This results in a gradual removal of the MA groups and thus reduces their contribution. Meanwhile, for a higher Young's modulus, iPP-g-MA molecules at the interface are removed in a tensile mode because of their increased stiffness. This leads to more MA groups required to be detached from the surface at the same time to cause interfacial failure, thus increasing the contributions of the MA groups.

Theoretical study of effect of hyper-resistivity on linear stability of ballooning mode

The coupling of ballooning mode and peeling mode forms the so-called peeling-ballooning mode, which is widely used in the physical explanation of the edge localized mode (ELM). The nonlinear platform simulation based on the non-ideal peeling-ballooning mode model successfully explained the ELM experimental results. Therefore, exploring the influences of various non-ideal effects on the ballooning mode in the edge transport barrier is very important in controlling the ELM in the future fusion reactors. Among the reports on non-ideal effects, there are few reports involving the effect of hyper-resistivity caused by anomalous electron viscosity on ballooning mode. It has been found that the hyper-resistivity has a destabilizing effect on the ballooning mode, but the associated physical mechanism is still unclear. Therefore, it is necessary to systematically explore the influence of hyper-resistivity on the ballooning mode theoretically by introducing hyper-resistivity into the ballooning mode model. The linear growth rate of ideal and non-ideal ballooning mode are solved by the shooting method for the derived eigenvalue equation of non-ideal ballooning mode containing hyper-resistivity, finite resistivity and diamagnetic drift effects, and the dependence of ballooning mode on hyper-resistivity is also explored under different conditions. The results show that the hyper-resistivity may destabilize the ballooning mode, and the physical mechanism is that the current diffusion effect caused by the hyper-resistivity weakens the stabilizing effect of the magnetic field line bending on the ballooning mode. When both the resistivity and hyper-resistivity are considered, they are in a competitive relationship. When the ratio of hyper-resistivity to resistivity is relatively high, hyper-resistivity plays a dominant role, and the destabilizing effect of resistivity will be shielded by hyper-resistivity, and vice versa. The destabilization effect of hyper-resistivity on ballooning modes is enhanced with the increase of the toroidal mode number. The hyper-resistivity will destabilize the original stable modes once the toroidal mode number exceeds a certain threshold. Further studies show that the threshold is inversely proportional to the ratio of hyper-resistivity to resistivity. The research results have important reference value for the control of edge localized modes in low-collisionality edge plasma in future fusion reactors.

Impact of pedestal density gradient and collisionality on ELM dynamics

BOUT++ turbulence simulations are conducted to capture the underlying physics of small ELM characteristics achieved by increasing separatrix density via controlling strike points from vertical to horizontal divertor plates for three EAST discharges. BOUT++ linear simulations show that the most unstable modes change from high-n ideal ballooning modes to intermediate-n peeling–ballooning modes and eventually to peeling–ballooning stable plasmas in the pedestal. Nonlinear simulations show that the fluctuation is saturated at a high level for the lowest separatrix density. The ELM size decreases with increasing separatrix density, until the fraction of this energy lost during the ELM crash becomes less than 1% of the pedestal stored energy, leading to small ELMs. Simulations indicate that small ELMs can be triggered either by the marginally peeling–ballooning instability near the peak pressure gradient position inside the pedestal or by a local instability in the pedestal foot with a larger separatrix density gradient. The pedestal collisionality scan for type-I ELMs with steep pedestal density gradient shows that both linear growth rate and ELM size decrease with increasing collisionality. On the contrary, the pedestal collisionality and pedestal density width scan with a weak pedestal density gradient indicate small ELMs can either be triggered by a high-n ballooning mode or by a low-n peeling mode in a low collisionality region 0.04–0.1. The simulations indicate the weaker the linear unstable modes near marginal stability with small linear growth rate, the lower nonlinearly saturated fluctuation intensity and the smaller turbulence spreading from the linear unstable zone to stable zone in the nonlinear saturation phase, leading to small ELMs.

Barrier and Seal Properties of Reactive Blending of Poly(butylene succinate) Based Blends

Poly Butylene Succinate (PBS) is one of the biodegradable polymers with good physical properties but its barrier properties such as the oxygen barrier are poor. The aim of this study was to investigate the barrier and seal properties of PBS by blending with biodegradable poly hydroxybutyrate-co-hydroxyvalerate (PHBV). PBS and PHBV (80/20 and 70/30 %w/w) with and without reactive agents were prepared using an internal mixer. Film specimens of 100 micrometers in thickness were prepared using compression molding. The morphology, barrier properties and peel-seal strength were investigated. Morphological observations using scanning electron microscope (SEM) showed an improved dispersion of PHBV in the blends after adding the reactive agents. The oxygen barrier and water vapor barrier were determined using ASTM D3985 and ASTM E96, respectively. The results showed that the addition of PHBV into the blend films led to lower OTR and WVTR when compared to the neat PBS. The addition of reactive agents can further improve the OTR and WVTR of PBS/PHBV blends due to the compact and dense structure of the films. Peel–seal behavior of the films was examined by the different sealing temperatures, which determined the failure mechanism after peeling. The blend films with reactive agents after sealing temperature between 105 and 115°C were peeled from the substrate with adhesive and cohesive failures showing the easy peel mode.

Characteristics of grassy ELMs and their impact on the divertor heat flux width

BOUT++ turbulence simulations are conducted for a 60 s steady-state long pulse high β p EAST grassy ELM discharge. BOUT++ linear simulations show that the unstable mode spectrum covers a range of toroidal mode numbers from low-n (n = 10–15) peeling–ballooning modes (P–B) to high-n (n = 40–80) drift-Alfvén instabilities. Nonlinear simulations show that the ELM crash is triggered by low-n peeling modes and fluctuation is generated at the peak pressure gradient position and radially spread outward into the scrape-off-layer, even though the drift-Alfvén instabilities dominate the linear growth phase. However, drift-Alfvén turbulence delays the onset of the grassy ELM and enhances the energy loss with the fluctuation extending to pedestal top region. Simulations further show that if the peeling drive is removed, the fluctuation amplitude drops by an order of magnitude and the ELM crashes disappear. The divertor heat flux width is ∼2 times larger than the estimates based on the HD model and the Eich’s ITPA multi-tokamak scaling (or empirical Eich scaling) due to the strong radial turbulence transport.

Critical role of current-driven instabilities for ELMs in NSTX

The impact of different extended-magnetohydrodynamic (MHD) contributions on the stability thresholds of peeling-ballooning modes in ELMing and ELM-free plasmas in the spherical tokamak NSTX is investigated with the initial value code M3D-C1. We show that ELMing discharges in NSTX are limited by resistive current-driven peeling modes, whereas non-ELMing wide-pedestal H-mode discharges are located near the ideal pressure-driven ballooning threshold. It is demonstrated that extended-MHD can lead to more reliable edge stability predictions than existing ideal-MHD models. Resistive peeling-ballooning modes are found to exist well before the ideal stability threshold is met, and kink-peeling modes exhibit considerable sensitivity to plasma resistivity. Other effects not considered in ideal-MHD models affect PB modes in NSTX in a weaker way. Gyroviscous stress appears stabilizing such that the stability boundary lies closer to the experimental point. Equilibrium rotation can suppress ideal core modes and thus isolate edge modes. These results are important for the development of a predictive pedestal model for low-aspect ratio tokamaks.

Biomimetic fracture model of lizard tail autotomy.

Lizard tail autotomy is an antipredator strategy consisting of sturdy attachment at regular times but quick detachment during need. We propose a biomimetic fracture model of lizard tail autotomy using multiscale hierarchical structures. The structures consist of uniformly distributed micropillars with nanoporous tops, which recapitulate the high-density mushroom-shaped microstructures found on the lizard tail's muscle fracture plane. The biomimetic experiments showed adhesion enhancement when combining nanoporous interfacial surfaces with flexible micropillars in tensile and peel modes. The fracture modeling identified micro- and nanostructure-based toughening mechanisms as the critical factor. Under wet conditions, capillarity-assisted energy dissipation pertaining to liquid-filled microgaps and nanopores further increased the adhesion performance. This research presents insights on lizard tail autotomy and provides new biomimetic ideas to solve adhesion problems.

Kink–ballooning mode in circular tokamak plasma

Peeling–ballooning modes, which are driven by gradients of parallel current and pressure in the pedestal, are widely accepted as the instability triggering large Edge Localized Modes (ELMs). However, the current-driven mode related to ELMs is not fully understood. This paper is about comparing the kink mode to the peeling mode, and the modified current profiles are specifically made to be simultaneously kink stable/peeling unstable or vice versa so that the two modes (or the modes coupled to peeling modes) can be compared. Caltrans-Corsica is used to generate a series of equilibria with modified edge current profiles. Based on these equilibria, the effects of edge current density on plasma instabilities are studied with the three-field BOUT++ elm-pb code. The results suggest that kink–ballooning modes can drive ELMs in some peeling-stable regions. Compared to the peeling–ballooning mode, kink–ballooning modes have comparatively lower poloidal resonant modes and growth rates at low toroidal mode numbers.

Bond Properties of Carbon Fiber Reinforced Polymer and Corrosion-Cracked Reinforced Concrete Interface: Experimental Test and Nonlinear Degenerate Interface Law.

Existing experimental research on bond properties of the interface between Carbon Fiber Reinforced Polymer (CFRP) and damaged concrete is limited, although CFRP strengthening technology has been widely used for corroded reinforced concrete structures. This work investigated the bond behavior of CFRP to the corrosion-cracked concrete interface, in which three factors were considered for experimentation, including corrosion degree, concrete strength and concrete cover thickness. The tests were conducted by developing a self-balancing double shear lap test device. In addition, a corrosion scene was provided simultaneously to simulate the external corrosion environment. The results showed that three peeling modes of CFRP sheets were observed with respect to corrosion degrees of the steel bars. The effects of the three factors on the stripping bearing capacity and effective bond length of CFRP sheets were discussed by systematic parametric analysis. Finally, a nonlinear degenerate law of CFRP-to-concrete interface considering the corrosion degree was improved and verified in this study.

Evaluation of Shear Peel Bond Strength of Different Adhesive Cements Used for Fixed Space Maintainer Cementation: An In Vitro Study.

Aim and objectiveThis study aims to compare the retentive strength of different adhesive cements used for band cementation of fixed space maintainer by comparing the shear peel bond strength and mode of failure for each adhesive material using three different adhesive cements.Materials and methodsEighty intact extracted teeth were used to assess the shear peel bond strength. Preformed bands were adapted to each tooth. Three cements compared in this in vitro study are glass ionomer cement [Ketac Cem radiopaque (3M ESPE)], resin-modified glass ionomer cement [RelyX luting 2(3M ESPE)], and self-adhesive resin cement [RelyX U200 (3M ESPE)]. The teeth were randomly divided to four groups of 20 samples each. All samples were stored at 37°C for 24 hours before testing. All specimens were tested in a tensile mode using a universal testing machine to determine shear peel bond. After debonding procedure, each specimen was visually assessed at the site of cement.ResultsThe results of our study showed that the greatest resistance to decementation was shown by self-adhesive resin cement (256.85 N) followed by resin-modified GIC (165.40 N) and GIC (127.40 N) (p < 0.001). Self-adhesive resin cement has the greatest shear peel bond strength (2.36 MPa) followed by resin-modified GIC (1.53 MPa), conventional GIC (1.22 MPa), and bands without cementation (0.29 MPa) (p < 0.001). In terms of adhesive remnant index (ARI) scores, it was seen that the decementation of bands of both conventional GIC and self-adhesive resin cements occurred at the band/enamel interface. However, resin-modified GIC showed varied results in the ARI scores.ConclusionThe findings of our study suggest that self-adhesive resin cements can be used for cementation of bands of fixed space maintainers. However, further research with short-term and long-term data is required to evaluate the ability of these cements for its application in vivo.How to cite this articleKaur J, Singh A, Sadana G, et al. Evaluation of Shear Peel Bond Strength of Different Adhesive Cements Used for Fixed Space Maintainer Cementation: An In Vitro Study. Int J Clin Pediatr Dent 2021;14(2):175–179.