Distribution Of Bond Strengths Research Articles

Study of interfacial stress distribution of SiC fibre reinforced titanium matrix composites under transverse tensile loading

A combination of the transverse tensile test and the unilaterally coupled finite element method was used to evaluate the interfacial normal bond strength and stress distribution of titanium matrix composites (TMCs). In addition, in order to identify the interface shear failure mode of TMCs under transverse loading, both the push out test and the finite element method have been used to characterise the interfacial shear strength of TMCs, which is one of the interfacial failure criterions. The results showed that the interfacial normal bond and shear strengths of SiCf/Ti–6Al–4V were 300 and 350 MPa respectively, and the interface failure mode of TMCs under the transverse tensile test was radial failure rather than shear failure. Moreover, the effect of residual stress on radial stress was also discussed in detail in this paper.

Effect of specimen gripping device, geometry and fixation method on microtensile bond strength, failure mode and stress distribution: Laboratory and finite element analyses

ObjectivesInnumerous modifications have been proposed for the microtensile test since its introduction; however, testing parameters are not often well described and wide variations in bond strength are commonly reported. The aim of this study was to evaluate the effect of the test specimen's gripping device, specimen geometry and fixation method on microtensile bond strength, failure mode, and stress distribution when using an etch-and-rinse 2-step adhesive system bonded to human dentin. MethodsResin-based composite bonded to occlusal dentin from 21 human molars was used to fabricate dumbbell- and stick-shaped test specimens which were divided into three groups: Di – dumbbell-specimens placed in a Dircks device; GeS – stick-specimens gripped in a Geraldeli's device with Superglue; GeZ – stick-specimens gripped in a Geraldeli's device with Zapit. Specimens were tested to failure in tensile mode and the failure mode was examined under stereomicroscopy and fracture initiation sites were verified by scanning electron microscopy and energy dispersive X-ray spectroscopy. Three-dimensional models of each device/specimen were created and finite element calculations were performed. ResultsThe effect of the gripping devices on the bond strength was not significant, unless the bond test areas were normalized. The failure mode was influenced by the type of device. Dircks device was less sensitive to human error than Geraldeli's, and produced a more uniform stress distribution at the dumbbell specimen adhesive layer than did the Geraldeli's device at the stick layer. SignificanceMicrotensile testing parameters can directly influence the results and consequently inter-study comparisons.

Study of Interfacial Stress Distribution in SiC Fiber Reinforced Titanium Matrix Composites on Transverse Tensile Tests

A combination of the transverse tensile test and the unilaterally coupled finite element method was used to evaluate the interfacial normal bond strength and stress distribution of titanium matrix composites (TMCs). In addition, in order to identify the interface shear failure mode of TMCs under transverse loading, both the push-out test and the finite element method have been developed to characterize the interfacial shear strength of TMCs, which is the interfacial shear failure criterion. This article studies the results of the experiments, which suggested that the interfacial normal bond and shear strength of SiCf/Ti-6Al-4V were 300 and 350 MPa, respectively, and the interface failure mode of TMCs under the transverse tensile test was radial failure rather than shear failure. Moreover, the effect of residual stress on the radial stress is also discussed in detail in this article.

3D Simulation of Internal Tablet Strength During Tableting

This study presents a new approach to model powder compression during tableting. The purpose of this study is to introduce a new discrete element simulation model for particle-particle bond formation during tablet compression. This model served as the basis for calculating tablet strength distribution during a compression cycle. Simulated results were compared with real tablets compressed from microcrystalline cellulose/theophylline pellets with various compression forces. Simulated and experimental compression forces increased similarly. Tablet-breaking forces increased with the calculated strengths obtained from the simulations. The calculated bond strength distribution inside the tablets showed features similar to those of the density and pressure distributions in the literature. However, the bond strength distributions at the center of the tablets varied considerably between individual tablets.

Numerical simulation of the liquid-induced erosion in a weakly bonded sand assembly

The paper presents a numerical study on the erosion of sand particles where hydrodynamic forces induced by liquid flow are considered to be dominant in a weakly bonded sand assembly under conditions relevant to sand production. The numerical approach employed is the coupled discrete element method (DEM) and computational fluid dynamics (CFD). The sand assembly modelled is composed of sand particles which are weakly bonded. Bond breakage occurs when the resolved normal and shear stresses in the bond exceed the bond strength. The disaggregated sand particles are then transported by liquid and considered as produced sand. The simulated results show that the main features of sand erosion can be captured by the CFD-DEM approach. It is also shown that the increase of axial compaction enhances sand erosion, and the increase in radial confining pressure can cause continuous sanding. The effects of different variables on erosion rate are examined, showing that particle–fluid interaction force is indeed the main driving force for sand erosion. Cavity formation is also examined by simply assigning a non-uniform bond strength distribution to the sand assembly. Cavities tend to form and grow within weaker regions. The results show that the proposed model offers a promising method, which should be further developed, to elucidate mechanisms governing the erosion of sand particles at a particle scale.

In vitro orthodontic bracket bonding to porcelain

This in vitro study investigated the influence of using different combinations of bracket, adhesive, and light-curing source on the tensile bond strength to porcelain and on failure patterns at debonding. Tensile tests were performed using: one ceramic bracket versus one metal bracket, two orthodontic composites; type bisphenol A-glycidyldimethacrylate and urethane dimethacrylate (UDMA), and four light-curing units with the same range of emission spectrum but various light intensities: three light-emitting diode (LED) units and one halogen-based unit. One hundred and sixty porcelain samples were randomly divided into 16 equal groups. The porcelain surface was conditioned with 9 per cent hydrofluoric acid before silane application. The composite was photo-polymerized for 40 seconds. After storage in water at 37°C for 24 hours, the samples were subjected to tensile force until bond failure. Bond strength and bond failure mode were recorded; results were analysed (α = 0.05) using R language; linear model with constant variance for the bond strength and multinomial distribution for the failure mode. The bond strength in all groups was sufficient to withstand orthodontic treatment (>6 MPa). There was no statistical difference between the adhesives, but comparing bracket × light interaction, it was significantly higher with the ceramic bracket. No significant differences were seen between the metal bracket groups, but for the ceramic bracket, the results were significantly higher with the LED light. No fracture was observed in porcelain with the metal bracket but it occurred in 35 per cent of the ceramic bracket samples and the risk was higher when using UDMA composite and lower with LED high intensity light.

Glassy Nature of Water in an Ultraconfining Disordered Material: The Case of Calcium−Silicate−Hydrate

We present the structural and dynamic nature of water ultraconfined in the quasi-two-dimensional nanopores of the highly disordered calcium-silicate-hydrate (C-S-H), the major binding phase in cement. Our approach is based on classical molecular simulations. We demonstrate that the C-S-H nanopore space is hydrophilic, particularly because of the nonbridging oxygen atoms on the disordered silicate chains which serve as hydrogen-bond acceptor sites, directionally orienting the hydrogen atoms of the interfacial water molecules toward the calcium-silicate layers. The water in this interlayer space adopts a unique multirange structure: a distorted tetrahedral coordination at short range up to 2.7 Å, a disordered structure similar to that of dense fluids and supercooled phases at intermediate range up to 4.2 Å, and persisting spatial correlations through dipole-dipole interactions up to 10 Å. A three-stage dynamics governs the mean square displacement (MSD) of water molecules, with a clear cage stage characteristic of the dynamics in supercooled liquids and glasses, consistent with its intermediate-range structure identified here. At the intermediate time scales corresponding to the β-relaxation of glassy materials, coincident with the cage stage in MSD, the non-Gaussian parameter indicates a significant heterogeneity in the translational dynamics. This dynamic heterogeneity is induced primarily because of the heterogeneity in the distribution of hydrogen bond strengths. The strongly attractive interactions of water molecules with the calcium silicate walls serve to constrain their motion. Our findings have important implications on describing the cohesion and mechanical behavior of cement from its setting to its aging.

Microtensile bond strength distributions of three composite materials with different polymerization shrinkages bonded to dentin.

To assess the detrimental effects that polymerization contraction causes on the interfacial microtensile bond strength (μTBS) to dentin of three light-curing resin composites: two conventional bis-GMA-based composite resins (Filtek Z250, TPH Spectrum) and a low shrinkage material (Filtek Silorane [SIL]). Flat surfaces of labial dentin were made in 46 bovine teeth and restored in single (group A) or in three separate (group B) one-increment visible-light cured resin composite blocks, with similar locations among teeth. After 24 h, restored teeth were sectioned perpendicular to interfaces, producing rectangular compound specimens (385 specimens were produced in group A, and 132 in group B), and submitted to tension (crosshead speed 1mm/min) until failure. μTBS results were adjusted to bonded area and transformed to percentages of maximum values within each tooth (PTens). In A groups, distances of specimens to the gingival ends of each restoration were transformed to PDistances: the percentage of that distance within its specimen. Spearman's nonparametric correlation test showed that for Z250, TPH and SIL, in A groups, a material's correlation coefficient was positive for the first half of restorations (0% to 50% PDistances) and negative for the second (50% to 100%). For all materials, PTens values in extremes of restorations (pooled 0 and 100% PDistances) in A groups were smaller than corresponding values in B groups. These differences were statistically significantly (Student's t-test) only for Z250 and TPH. Even in cases of favorable configuration factor, polymerization shrinkage in large restorations can reduce interface mechanical characteristics. The relevance of this decrease has still to be established.

A discrete element model to describe failure of strong rock in uniaxial compression

A bonded particle model is investigated by means of an extended Discrete Element Method with respect to failure of strong rock in uniaxial compression. A coordination number based inflation scheme is presented, which generates isotropic sphere packings that are featuring a higher average coordination number than conventional procedures. A progressive failure model is proposed, which promotes crack propagation and localization and allows adjusting brittleness of fracture. Failure of the granular solid is discussed in detail. The fracture process is studied in dependence of the introduced failure models. The influence of particle size and bond strength distributions, particle numbers, particle layering in finite sphere packings and end constraints is addressed. Comparison to published experimental results reveals that many of the observed features of rock failure are reproduced.

A Probabilistic Model for Predicting the Resistance of Aggregates in Asphalt Mixes to Fracture

ABSTRACT Increased loads on asphalt pavements have lead to the development of asphalt mixes that rely on stone-on-stone contacts in resisting applied loads. These mixtures tend to experience high forces at the contact points that could cause aggregate fracture and make the asphalt pavements more prone to distresses such as cracking and permanent deformation. This paper introduces an approach to express the probability of aggregate fracture in asphalt mixes as a function of the contact bond strength and internal force distribution at the contact points. The internal force distribution was obtained using a discrete element model of the internal structure of asphalt mixtures subjected to loading. The contact bond strength was determined using statistical analysis of the results of a single aggregate crushing test. The developed approach can be used to determine the asphalt mixture design and aggregate properties that minimize fracture and achieve desirable mixture performance.

Discrete Element Modeling of Constant Strain Rate Compression Tests on Idealized Asphalt Mixture

Discrete element modeling has been used to simulate constant strain rate compressive tests for an idealized asphalt mixture comprising approximately single-sized sand particles. A range of constant strain-rate compressive tests to failure have been undertaken in the laboratory and the axial stress-strain response has been carefully measured. The peak stress (compressive strength) of the material was found to be as a power-law function of the equivalent (temperature compensated) strain rate in the viscoelastic region of behavior. The internal geometry of the idealized asphalt mixture has been reproduced in PFC-3D and internal damage (cracking) in the material was modeled by allowing bond breakage between adjacent particles. Elastic contact properties have been used to investigate the effect of random variations in internal sample geometry, the distribution of bond strengths between adjacent particles and the coefficient of friction between particles where the bond has broken. A simple viscoelastic Burger's model was used to introduce time dependent shear and normal (tensile) contact stiffnesses and an elastic contact has been assumed for the compressive normal contact stiffness. To reduce the computation time, both viscosities in the Burger's model were scaled which has been shown to have the same effect as scaling the loading velocity (strain rate) by the same factor. A strain rate dependent bond breakage criterion has been developed and model results were found to compare well with the experimental data.

A Probabilistic Model for Predicting the Resistance of Aggregates in Asphalt Mixes to Fracture

ABSTRACT Increased loads on asphalt pavements have lead to the development of asphalt mixes that rely on stone-on-stone contacts in resisting applied loads. These mixtures tend to experience high forces at the contact points that could cause aggregate fracture and make the asphalt pavements more prone to distresses such as cracking and permanent deformation. This paper introduces an approach to express the probability of aggregate fracture in asphalt mixes as a function of the contact bond strength and internal force distribution at the contact points. The internal force distribution was obtained using a discrete element model of the internal structure of asphalt mixtures subjected to loading. The contact bond strength was determined using statistical analysis of the results of a single aggregate crushing test. The developed approach can be used to determine the asphalt mixture design and aggregate properties that minimize fracture and achieve desirable mixture performance.

Discrete Element Modelling of Monotonic Compression Tests in an Idealised Asphalt Mixture

ABSTRACT Discrete Element Modelling (DEM) has been used to simulate constant strain rate tests on an idealised asphalt mixture containing approximately single-sized sand particles under monotonic compressive loading. Results have been compared to a range of constant strain-rate compressive tests to failure that have been undertaken in the laboratory. The internal geometry of the idealised asphalt mixture has been reproduced in PFC-3D and internal damage (cracking) in the material was modelled by allowing bond breakage between adjacent particles. Elastic contact properties have been used to investigate the effect of random variations in internal sample geometry, the distribution of bond strengths between adjacent particles and the coefficient of friction between particles where the bond has broken on the stress-strain behaviour. A simple viscoelastic Burger's model was introduced to give time dependent shear and normal (tensile) contact stiffnesses and an elastic contact has been assumed for the compressive normal contact stiffness. To reduce the computation time, the effect of scaling the viscosities in the Burger's model to simulate slower strain rates has been investigated. Results from the model compared well to the experimental data.

Bond strength test: role of operator skill

Test method, substrate material and operator variability are factors known to affect bond strength test outcomes. The aim of this study was to determine if, with increasing experience, individual operator skill in material handling influenced microshear bond strength outcomes. This retrospective study used data collected from six preliminary tests carried out successively on enamel microshear bond strength for two adhesives: Clearfil SE Bond (Kuraray) and Adper Single Bond 2 (3M ESPE) by one operator. Mean and median microshear bond strength values, standard deviations and coefficients of variation for each adhesive test group were calculated and assessed. A gradual increase in mean microshear bond strengths, a decrease in standard deviations and coefficients of variation over time for both adhesives and a progressively more uniform distribution of microshear bond strength results recorded in individual test sets was observed. The results suggest an improvement in bonding reliability as experience is gained. Operator skill in material handling appears to play a critical role in determining the outcome of bond strength testing. This same skill is probably relevant when using an adhesive for the first time clinically. It is important that clinicians become familiar with new adhesives in order to achieve optimal outcomes.

Molecular force spectroscopy of homophilic nectin-1 interactions

Nectins are Ca 2+ independent cell adhesion molecules localizing at the cadherin based adherens junctions. In this study, we have used atomic force microscopy to study interaction of a chimera of extra cellular fragment of nectin-1 and Fc of human IgG (nef-1) with wild type L-fibroblasts that express endogenous nectin-1 to elucidate the biophysical characteristics of homophilic nectin-1 trans-interactions at the level of single molecule. Bond strength distribution revealed three distinct bound states (or configurations) of trans-interactions between paired nectins, where each bound state has a unique unstressed off-rate and reactive compliance. Kinetic analysis of force-dependent off-rate of the bound state involving trans-interacting V–V domains between paired nectin-1 (unstressed off-rate ∼1.465 ± 0.779 s −1, reactive compliance ∼0.143 ± 0.072 nm) was found to be closest to E-cadherin, indicating that V–V domain trans-interactions are probably necessary to initiate and promote adhesions of E-cadherin at adherens junctions (AJs).

Effects of geometric and electronic structure on the finite temperature behavior ofNa58,Na57, andNa55cluster

An analysis of the evolutionary trends in the ground state geometries of Na$_{55}$ to Na$_{62}$ reveals Na$_{58}$, an electronic closed--shell system, shows namely an electronically driven spherical shape leading to a disordered but compact structure. This structural change induces a strong {\it connectivity} of short bonds among the surface atoms as well as between core and surface atoms with inhomogeneous strength in the ground state geometry, which affects its finite--temperature behavior. By employing {\it ab initio} density--functional molecular dynamics, we show that this leads to two distinct features in specific heat curve compared to that of Na$_{55}$: (1) The peak is shifted by about 100 K higher in temperature. (2) The transition region becomes much broader than Na$_{55}$. The inhomogeneous distribution of bond strengths results in a broad melting transition and the strongly connected network of short bonds leads to the highest melting temperature of 375 K reported among the sodium clusters. Na$_{57}$, which has one electron less than Na$_{58}$, also possesses stronger short--bond network compared with Na$_{55}$, resulting in higher melting temperature (350 K) than observed in Na$_{55}$. Thus, we conclude that when a cluster has nearly closed shell structure not only geometrically but also electronically, it show a high melting temperature. Our calculations clearly bring out the size--sensitive nature of the specific heat curve in sodium clusters.

Role of Multiple Bonds Between the Single Cell Adhesion Molecules, Nectin and Cadherin, Revealed by High Sensitive Force Measurements

Nectins and cadherins, members of cell adhesion molecules (CAMs), are the primary mediators for various types of cell–cell junctions. Here, intermolecular force microscopy (IFM) with force sensitivity at sub-picoNewtons is used to characterize the extracellular trans-interactions between paired nectins and paired cadherins at the single molecule level. Three and four different bound states between paired nectins and paired cadherins are, respectively, identified and characterized based on bond strength distributions where each bound state has a unique lifetime and bond length. The results indicate that multiple domains of nectins act uncooperatively, as a zipper-like multiply bonded system whereas those of cadherins act cooperatively, as a parallel-like multiply bonded system, consistent with a “fork initiation and zipper” hypothesis for the formation of cell–cell adhesion. The observed dynamic properties among multiple bonds are expected to be advantageous such that nectins search adaptively in the cell–cell exploratory recognition process while cadherins slowly stabilize in the cell–cell zippering process.

Turbulent hydrodynamic stress induced dispersion and fragmentation of nanoscale agglomerates

High pressure dispersion nozzles of 2.5–10 mm length and 125 μm diameter have been characterized in terms of fluid dynamics and dispersion experiments at 100–1400 bar. Elongational stresses at the nozzle entry ( 5 × 10 5 Pa ) and turbulent stresses up to 10 5 Pa at a Reynolds number of 25,000 in turbulent channel flow are identified crucial for desagglomeration and aggregate fragmentation. Maximum stresses are calculated on representative particle tracks and related to agglomerate breakage. Agglomerates in the experimental study are in the range of the Kolmogorov micro scale (100–400 nm) and therefore break due to turbulent energy dissipation in viscous flow. Bond strength distributions could be determined experimentally from particle size distributions and fluid dynamics simulations, with primary particle erosion determined as dispersion mechanism for diffusion flame silica particles. Nanoscale agglomerates show a power law scaling for breakage with scaling exponents diverging from theory of floc dispersion. This is attributed to their strong bonding by sinter necks.

A study on the effects of microparameters on macroproperties for specimens created by bonded particles

PurposeTo use distinct element simulation (PFC2D) to investigate the relationships between microparameters and macroproperties of the specimens that are modeled by bonded particles. To determine quantitative relationships between particle level parameters and mechanical properties of the specimens.Design/methodology/approachA combined theoretical and numerical approach is used to achieve the objectives. First, theoretical formulations are proposed for the relationships between microparameters and macroproperties. Then numerical simulations are conducted to quantify the relationships.FindingsThe Young's modulus is mainly determined by particle contact modulus and affected by particle stiffness ratio and slightly affected by particle size. The Poisson's ratio is mainly determined by particle stiffness ratio and slightly affected by particle size. The compressive strength can be scaled by either the bond shear strength or the bond normal strength depending on the ratio of the two quantities.Research limitations/implicationsThe quantitative relationships between microparameters and macroproperties for parallel‐bonded PFC2D specimens are empirical in nature. Some modifications may be needed to model a specific material. The effects of the particle distribution and bond strength distribution of a PFC2D specimen are very important aspects that deserve further investigation.Practical implicationsThe results will provide guidance for people who use distinct element method, especially the PFC2D, to model brittle materials such as rocks and ceramics.Originality/valueThis paper offers some new quantitative relationships between microparameters and macroproperties of a synthetic specimen created using bonded particle model.

Tensile, bending and shear strength distributions of adhesive-bonded butt joint specimens

Adhesive bonding is becoming one of the popular joining techniques in metal industries since it offers different options over other techniques such as welding and diffusion bonding. Any dissimilar metals are easily adhesive-bonded together. In this study, experiments were carried out in order to provide the statistical data with strength evaluation methods: tensile, shear and four-point bending tests for thermosetting epoxy resin based adhesive-bonded butt joints. The certification of the probability in the adhesive strength that shows the tendency of brittle fracture is studied. The effect of the adhesive sectional area on the adhesive strength is evaluated. For the tensile and shear tests, the strength distributions of 5 × 6 mm 2 sectional area specimens show higher probability than the 2 × 3, 3 × 4 and 4 × 5 mm 2 area specimens, and Weibull modulus of 5 × 6 mm 2, m = 4.049 and 4.412 for the tensile and shear tests respectively. For the four-point bending test, 3 × 4 mm 2 specimens have the highest probability value than others. And the shear test is less affected by sectional area comparing with other test methods. The adhesive bonding strength distribution between 304 stainless steels with thermosetting adhesives shows the highest probability in four-point bending test. The strength testing methods that have higher probability of strength are four-point bending, shear and tensile tests in order.