Determining Bond Strength Research Articles

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.

IGMPlot: A program to identify, characterize, and quantify molecular interactions.

We describe the development and features of a program called IGMPlot, which is based on the independent gradient model (IGM) and its local descriptor . The IGM approach analyzes the gradient of the electron density (ED) in a molecular system to identify regions of space where chemical interactions take place. IGMPlot is intended for use by both experimental scientists and theoretical chemists. It is standalone software written in C++, with versions available for multiple platforms. Some key features are: probing and quantifying interactions between two given molecular fragments, determining bond strength (IBSI), estimating the atomic contributions to an intermolecular interaction and preparing data to build 2D and 3D representations of interaction regions. The software has been updated to include new features: critical point analysis of the ED, assessing ED asymmetry of a given bond (PDA) and a new descriptor called designed to enhance the IGM- analysis. The program can be found at: http://igmplot.univ-reims.fr.

Experimental and theoretical study on bond behavior of helically wound FRP bars with different rib geometry embedded in ultra-high-performance concrete

Fiber reinforced polymer (FRP) bar reinforced ultra-high-performance concrete (UHPC) members have attracted wide interest due to their excellent durability and mechanical properties. Determining bond strength is of great importance to the design of FRP bar reinforced UHPC members. This study investigates the effects of bar type, concrete type and rib geometry on the bond behavior of helically wound FRP bars embedded within UHPC. Pull-out tests on a total of 48 specimens with three types of concrete (0%, 1% and 2% steel fiber content), three types of bar (steel, basalt FRP and glass FRP) and three types of surface condition (smooth, shallow ribbed and deep ribbed) have been conducted. The results show that the bond strength of FRP bars embedded within UHPC is greatly affected by rib height. Indeed, FRP bars with deep ribs can reach a bond strength comparable to that of ribbed steel bars. A novel bond strength model for FRP bars embedded within UHPC, considering the effect of rib geometry, has been proposed and validated by the experimental results and existing data in the literature.

Improving bond strength of recycled coarse aggregate concrete using chopped basalt fibers

This paper investigates theoretically and experimentally the influence of using basalt fiber (BF) on bond strength of recycled coarse aggregate (RCA) concrete. The natural aggregate (NA) was replaced by RCA with 20 %, 40 %, 60 %, 80 %, and 100 %. BF was added with three different percentages. Ninety concrete cubes were tested under pull-out loading to failure using steel bar diameters 12, 14, and 18 mm. The behavior of specimens was analyzed by recording ultimate tensile loads and crack patterns. The experimental bond strengths were correlated with the theoretical strengths calculated using equations of different international codes in addition to existing models by previous researchers. The experimental results revealed that the bond strength improved when the RCA levels and BF contents increased. The 80 % RCA and 1.5 % BF showed the highest increase. Also the bond strength decreased as the bar diameter increased. The mode of failure for all specimens in this study was splitting failure and BF caused ductile failure. The experimental bond strengths were higher than the calculated theoretical strengths. Thus, theoretical equations can be used for determining bond strength of RCA.

Thin flexible lab-on-a-film for impedimetric sensing in biomedical applications

Microfluidic cytometers based on coulter principle have recently shown a great potential for point of care biosensors for medical diagnostics. Here, we explore the design of an impedimetric microfluidic cytometer on flexible substrate. Two coplanar microfluidic geometries are compared to highlight the sensitivity of the device to the microelectrode positions relative to the detection volume. We show that the microelectrodes surface area and the geometry of the sensing volume for the cells strongly influence the output response of the sensor. Reducing the sensing volume decreases the pulse width but increases the overall pulse amplitude with an enhanced signal-to-noise ratio (~ max. SNR = 38.78 dB). For the proposed design, the SNR was adequate to enable good detection and differentiation of 10 µm diameter polystyrene beads and leukemia cells (~ 6–21 µm). Also, a systematic approach for irreversible & strong bond strength between the thin flexible surfaces that make up the biochip is explored in this work. We observed the changes in surface wettability due to various methods of surface treatment can be a valuable metric for determining bond strength. We observed permanent bonding between microelectrode defined polypropylene surface and microchannel carved PDMS due to polar/silanol groups formed by plasma treatment and consequent covalent crosslinking by amine groups. These experimental insights provide valuable design guidelines for enhancing the sensitivity of coulter based flexible lab-on-a-chip devices which have a wide range of applications in point of care diagnostics.

Determining bond strength of seven-wire strands in prestressed concrete

The three mechanisms governing the strand-concrete (S-C) bond in pretensioned concrete (PTC) systems are: (i) adhesion, (ii) mechanical interlock, and (iii) friction. These mechanisms can be influenced by various parameters like the compressive strength of concrete (fc), applied prestress (fps), and embedment length of the strand (le). The existing test methods for S-C systems use unstressed strands and defines bond strength (τb), as the stress corresponding to a slip of 2.5 mm at free end (say, τ2.5). The unstressed strands and τ2.5 approach may lead to unconservative results and significant scatter. This paper presents the experimental program on the effects of fc (43 and 62 MPa), fps (0.1 fpu and 0.7 fpu), and le (500 and 1000 mm) on the bond stress-slip (τ-s) behaviour in PTC systems. Analysis of the results of tests on 24 specimens indicated that (i) defining the τb as τ2.5 at the free end is not suitable for PTC specimens and (ii) the τ2.5 at live end exhibits significant scatter and is dependent on the embedment length, le. Consequently, the paper proposes a conceptual model on strand-concrete bond behavior and a rational method to determine τb as the stress corresponding to the yield bond stress (τyield). The determined τyield is independent of fps and le and exhibits less scatter than τ2.5. Finally, the use of taut strand specimens is recommended as they are easier to prepare than stressed strand specimens, to determine τyield.

Using Electron Density to Predict Synthon Formation in a 4-Hydroxybenzoic Acid: 4,4′-Bipyridine Cocrystal

Experimental charge density distribution studies complemented by quantum mechanical theoretical calculations of 4-hydroxybenzoic acid (4HBA) (1), 4,4′-bipyridine (44BP) (2), and one polymorphic form of the cocrystal containing 4HBA and 44BP molecules in a 2:1 ratio (3), have been carried out via high resolution single-crystal X-ray diffraction. Synthon formation was found to be the main driving force for crystallization in both (1) and (3) with a carboxylic acid homosynthon present in (1) and a heterosynthon in (3) comprised of a carboxylic acid from 4HBA and a pyridine nitrogen and aromatic hydrogen from 44BP. Topological analysis revealed the bonding in the homosynthon to be stronger than the heterosynthon (305.88 versus. 193.95 kJ mol–1) with a greater number of weak interactions in (3) helping to stabilize the structure. The distance from the hydrogen and hydrogen bond acceptor to the bond critical point (bcp) was also found to be a significant factor in determining bond strength, potentially having a...

Bond strength and development length of glass fiber-reinforced polymer bar in unconfined self-consolidating concrete

Although there are different models for determining bond strength and development length of glass fiber-reinforced polymer bar in normal concrete, they cannot evaluate the interfacial behavior of glass fiber-reinforced polymer bar in self-consolidating concrete accurately. This study presents more precise and efficient models for bond strength and development length of glass fiber-reinforced polymer bar in self-consolidating concrete than existing equations. The performance of a model depends very much on test data. Previous researches do not have enough data of bond strength and development length of glass fiber-reinforced polymer bar in self-consolidating concrete. So, more extensive data are needed to investigate the efficiency and accuracy of a model. To solve this problem, direct pull-out tests are performed in this study. Unlike existing models for bond strength and development length, proposed models perform very well for predicting bond strength and development length of glass fiber-reinforced polymer bar in self-consolidating concrete. The new models considerably decrease the deviation of existing models.

BOND STRENGTH AND INTERFACIAL MORPHOLOGY OF A MULTIMODE ADHESIVE RESIN CEMENT TO ENAMEL AND DENTIN

Introduction: Resin cements are used for cementation of indirect restorations. A high-quality adhesion to tooth structure is primordial for the success of indirect cemented restorations. Objectives: Were to assess the shear bond strength of RelyX ultimate adhesive resin cement to both enamel and dentin when used in different application modes (self-etch and total-etch) and to study resin-tooth interfaces using SEM. Materials and methods: 40 enamel specimens and 40 dentin specimens were used in this study. Each substrate specimens were randomly divided into four groups of 10 specimens each according to resin cement applied: Enamel groups: Group A1: RelyX ultimate as total-etch; Group A2: RelyX ultimate as self-etch; Group A3: Variolink II; Group A4: Multilink automix. Dentin groups: Group B1: RelyX ultimate as total-etch; Group B2: RelyX ultimate as self-etch; Group B3: Variolink II; Group B4: Multilink automix. Resin cements were built over the surfaces following manufacturer's instructions in a plastic tube. All specimens were thermocycled (500 cycles, 5°/55°C, 15 sec dwell time) then shear bond strength was measured in MPa and data were analyzed using F-test (ANOVA) and Post Hoc test. Three specimens from each group were further sectioned, gold sputtered and evaluated under SEM. Results: All enamel groups showed a statistically significant difference for shear bond strength with P <0.001. Group A1 revealed the highest mean value of 35.60 MPa. While for dentin, there was no statistically significant differences among groups with P=0.053. Interfacial morphology of RelyX ultimate in total-etch mode showed better interface morphology and improved tag length compared to respective self-etch counterpart. Conclusions: An etching step prior to multi-mode adhesive resin cement increased its bond strength values and improved its penetration pattern to both enamel and dentin, also length of resin tags formed by total-etch adhesives seems not to play an important role in determining bond strength. Keywords: Resin cements, Adhesives, Multi-mode, dental substrates, bonding, interface.

Long-Term Soft Denture Lining Materials.

Long-term soft denture lining (LTSDL) materials are used to alleviate the trauma associated with wearing complete dentures. Despite their established clinical efficacy, the use of LTSDLs has been limited due to the unfavorable effects of the oral environment on some of their mechanical and performance characteristics. The unresolved issue of LTSDL colonization by Candida albicans is particularly problematic. Silicone-based LTSDL (SLTSDL) materials, which are characterized by more stable hardness, sorption and solubility than acrylic-based LTSDLs (ALTSDLs), are currently the most commonly used LTSDLs. However, SLTSDLs are more prone to debonding from the denture base. Moreover, due to their limitations, the available methods for determining bond strength do not fully reflect the actual stability of these materials under clinical conditions. SLTSDL materials exhibit favorable viscoelastic properties compared with ALTSDLs. Furthermore, all of the lining materials exhibit an aging solution-specific tendency toward discoloration, and the available cleansers are not fully effective and can alter the mechanical properties of LTSDLs. Future studies are needed to improve the microbiological resistance of LTSDLs, as well as some of their performance characteristics.

A simple method for measuring tensile and shear bond strength of ceramic-ceramic and metal-ceramic joining

A simple method for measuring the ceramic-ceramic and metal-ceramic bond strength was presented, by which uniaxial tensile stress normal to the interface or shear stress in the interface can be produced using uniaxial compression load on a cross-bonded sample. Both tensile and shear bond strength were obtained by this testing technique for Ti3SiC2-TiO2 and Ti3SiC2-Al2O3 composite as well as for glued steel samples, respectively. The novel method provided a solution for determining bond strength in solid (especially brittle) materials, and it is also demonstrated as a useful method for evaluating the tensile and shear strength of various glues.

A novel technique for determining bond strength development between cement paste and steel

A new technique for determining bond strength between cement paste and steel is described. Internal stess resulting from the hydration process is taken into account. Experimental results of bond strength development are presented. The role of the interface zone in determining bond strength is discussed with reference to information provided by SEM examination of debonded surfaces.

Determining bond strength in fibre-reinforced composites

Determining bond strength in fibre-reinforced composites

Determining bond strength in fibre reinforced composites

Determining bond strength in fibre reinforced composites

Determining bond strength in fibre-reinforced composites

Summary A pull-out technique suitable for determining the interfacial bond strength for various combinations of fibres and matrix is described. In this method, a thick fibre, 0·5 to 1·0 mm in diameter, is embedded perpendicularly through a matrix material contained in a special mould and is stressed on a tensile testing machine. The value of the maximum bond load corresponds to a sharp break in the load-extension curve. Results show that the bond strength between E-glass-fibre and cement is of the same order as that between steel and cement but higher than the values reported for asbestos and cement. The work has also shown that the strength of the bond between E-glass-fibre and gypsum plaster is of similar magnitude, but that it is affected significantly by variations in water/plaster ratio.

ADHESIVE BONDING OF VARIOUS MATERIALS TO HARD TOOTH TISSUES. I. METHOD OF DETERMINING BOND STRENGTH.

ADHESIVE BONDING OF VARIOUS MATERIALS TO HARD TOOTH TISSUES. I. METHOD OF DETERMINING BOND STRENGTH.