Bondline Strength Research Articles

Stabilization of Fish Protein-Based Adhesive by Reduction of Its Hygroscopicity.

Protein-based fish adhesives have historically been used in various bonding applications; however, due to the protein's high affinity for water absorption, these adhesives become destabilized in high-moisture environments, resulting in reduced bondline strength and early failure. This limitation makes them unsuitable for industrial applications with higher demands. To address this issue, water-insoluble raw powder materials such as iron, copper, or zeolite were incorporated into natural fish adhesives. In this study, the hygroscopicity, dry matter content, thermal analysis (TGA/DSC), FT-IR spectroscopy, surface tension measurements, vapour permeability, and scanning electron microscope (SEM) of the modified adhesives were determined. In addition, the bonding properties of the modified adhesives were evaluated by the tensile shear strength of the lap joints, and mould growth was visually inspected. The resulting modified protein-based adhesives demonstrated improved stability in high humidity environments. Enhancing the hygroscopic properties of protein-based fish adhesives has the potential to unlock new opportunities and applications, providing a healthier and more environmentally sustainable alternative to petroleum-based adhesives.

Effect of wood moisture content and adhesive open time on the adhesion strength of wet bonded Pinus radiata wood

AbstractGluing wood in the wet state can reduce warping, splitting, and increase processing volume recovery. Adhesive open time and moisture content may play an important role in bond line strength, but there are no specifications for wet wood bonding. Wood specimens at two different moisture contents were glued with three polyurethane adhesives and tested in shear on the bond line. Open time of 15 min was superior to 4 and 40 min. All adhesives performed better when wood was glued at 30% moisture content than at 101%, but only the 15- and 40-min open time met the minimum shear requirement.

Structural evaluation of RC overhang cantilever slab strengthened with FRP near‐surface mounted (NSM) composites for bridge applications

AbstractThis paper presents the findings of a large‐scale experimental study that focus on assessing structural behavior of reinforced concrete (RC) cantilever slabs with carbon/epoxy fiber‐reinforced polymer (CFRP) composite strips using a near‐surface‐mounted (NSM) approach. The NSM/CFRP system evaluated in this study was implemented in strengthening the shoulders of the Slide Canyon Bridge in California, USA. The experimental phase is divided into two main parts: (i) determining the design parameters for NSM, including the bondline strength through pull‐out tests, and (ii) conducting a practical evaluation of the bending behavior of original and retrofitted RC cantilever slabs, each with varying NSM reinforcement and three different development lengths. Results of this study indicated that the use of NSM‐CFRP has a considerable benefit in that it significantly improves ductility and changes the failure mode of the unstrengthened RC slab from the typical brittle shear‐based failure mode to a more ductile flexural‐based failure mode. The large‐scale slab specimens' performances, which had different development lengths, showed little variance, except for the slab specimen with a development length of 457.0 mm that exhibited an appreciable flexural stiffness as compared to other specimens evaluated in this study. In order to simulate the serviceability and ultimate behavior of the RC slab specimens, linear and nonlinear finite element analyses were performed. A satisfactory agreement between numerical and experimental results was achieved especially at load level prior the initiation of large‐size cracks.

Bond-line strength, chemical properties and cellulose crystallinity of welded pine and itauba wood

ABSTRACT The aim of this research was to evaluate the bond-line strength and chemical changes of pine (Pinus taeda) and itauba (Mezilaurus itauba) joints welded by rotary friction and the use of the internal standard method with Rietveld refinement for the determination of the absolute cellulose crystallinity of wood samples. The specimens were composed of itauba dowels welded in substrates made of pine and itauba wood. The shear engaged by tensile pullout of the dowels was determined by mechanical tensile tests. Furthermore, macrostructural evaluation of the specimens and attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) and X-ray diffraction (XRD) tests were performed. The cellulose crystallinity was determined quantitatively by the internal standard method with Rietveld refinement and compared with the Segal and the deconvolution qualitative methods. The results reveal that itauba dowels welded in itauba substrates produce stronger joints (0.81 MPa) and slighter chemical changes than in pine substrates (0.62 MPa). The welded bond-line of itauba dowel and pine substrate has greater cellulose crystallinity than that of itauba dowel and substrate. The cellulose crystallinity is qualitatively consistent for the three applied methods, however, quantitatively, there are divergences between them.

Implementation of a probabilistic machine learning strategy for failure predictions of adhesively bonded joints using cohesive zone modeling

Adhesive bonding as an assembly procedure in aviation products is very efficient from both weight and recurring cost points of view. However, even with strict inspections, process control, and quality assurance protocols, it is difficult to evaluate and predict joint strength and performance. To manage this risk, regulators require determination of the maximum allowed disbond size as part of bonded joint design. This study proposes a methodology for determination of the bond-line strength characteristics based on a comprehensive test data from 88 Mixed Mode Bending (MMB) specimens. The Cohesive Zone Model (CZM) was employed to simulate disbond propagation, and nearly 2000 finite element simulations were conducted with a wide range of failure parameters. Combined experimental and numerical data was analyzed using the Gaussian Process Regression (GPR) machine learning algorithm to obtain the optimized CZM failure parameters. Statistical analysis was conducted to determine safety factors and B-Basis cohesive zone failure parameters, ensuring sufficient reliability of the failure predictions. The proposed failure parameters were validated by means of several benchmark problems, including single bonded lap joints and a bonded scarf joint, showing very good agreement with the test data.

Nonlinear numerical simulation and experimental verification of bondline strength of CFRP strips embedded in concrete for NSM strengthening applications

AbstractThis article presents results of an investigation that focuses on assessing bondline strength of carbon/epoxy fiber reinforced polymeric (CFRP) precured strips embedded in concrete for near‐surface‐mounting (NSM) strengthening applications. In this study, experimental evaluation and nonlinear numerical analysis of CFRP/concrete interfacial bond behavior are investigated. In this study, 15 pull‐out tests were performed on different reinforced concrete (RC) U‐shaped column specimens with different NSM groove configurations to evaluate the effect of groove size, groove depth, and adhesive bondline thickness on overall performance of the CFRP‐NSM system and to identify the optimum groove dimensions. Experimental results indicated that changing groove geometries of the NSM‐FRP reinforcements significantly affect bondline strength and associated mode of failures of NSM‐CFRP system. It was also shown that increasing bondline length lead to an increase in ultimate failure load and CFRP rupture strain. Based on results of this study, NSM materials with lower longitudinal moduli and higher rupture strains (e.g., E‐glass/epoxy or basalt/epoxy), may increase toughness and enhance performance of the NSM strengthening system.

Influence of pressure on bond-line shear strength in laminated veneer products

ABSTRACT In this study, the bond-line strength of different bonding pressure of veneers in dry (9% moisture content) and wet (immersed in water) conditions was investigated. The results show that peeled European beech veneers need approximately 0.5– 1.2 MPa pressure to achieve a proper bond-line when a urea-formaldehyde adhesive was used. The pressure variation within this range did not significantly affect the strength of the dry veneer, but the strength of the wet veneers decreased as the bonding pressure increased. The type of failure varied, especially for the wet veneers. At high pressure, the wood were stronger than the cohesive strength of the adhesive and the strength of the adhesion between the adhesive and the wood. High pressure, however, caused a compression of the bond-line and resulted in a lack of adhesion.

Effect of ACQ treatment on surface quality and bonding performance of four Malaysian hardwoods and cross laminated timber (CLT)

The objective of this study is to determine the effects of alkaline copper quaternary (ACQ) treatment on the surface quality and bonding performance of four Malaysian hardwood species, namely batai, sesenduk, rubberwood and kedondong. The samples were impregnated with 2% ACQ preservatives and bonded with phenol-resorcinol–formaldehyde resin for cross laminated timber (CLT) fabrication. The changes in density and the retention of both ACQ and copper after the treatment were recorded. Surface roughness and wettability of both treated and untreated samples were measured. Block shear and delamination tests were performed to evaluate the bond-line strength of CLT. The study revealed that the average surface roughness (Ra) of each species increased significantly. Wettability of batai, sesenduk, rubberwood and kedondong was significantly higher than that of the untreated samples suggesting an improvement in surface wettability. For single-species CLT, treated rubberwood has the highest shear strength followed by kedondong, sesenduk and batai with values of 9.53 N/mm2, 6.00 N/mm2, 5.68 N/mm2 and 4.19 N/mm2, respectively. While for mixed-species CLT, the combination of ACQ-treated rubberwood-sesenduk-rubberwood has the highest block shear strength with a value of 8.05 N/mm2. No delamination was observed from all samples. ACQ treatment was found to not affect the block shear strength significantly. Therefore, ACQ preservatives can be used to produce CLT with good bonding performance.

Bondline strength of glued-in threaded rods in new and ancient chestnut (Castanea sativa Mill.) wood

Glued-in rods (GIR) are being increasingly used in connections of new timber structures, complying with design rules mostly based on tests with new softwood specimens. However, the system also shows great potential for use in strengthening and rehabilitation of ancient timber structures, in which hardwoods were often used, namely in the Central and Southern European countries. Aiming at contributing to the scarce information available for these particular applications, an experimental program is carried out, consisting of the production and testing of both new and ancient chestnut timber specimens, the latter cut out from beams of demolished buildings. Given the limited number of specimens available, the bonding length was selected as the only variable parameter, although the hole diameter, the bond line thickness and others also play a relevant role on the behaviour of these connections. The relevant dimensions were set in order to preclude the steel yielding failure mode, desirable in actual applications, to favour the cohesive or adhesive failure modes at the wood-adhesive interface and the timber splitting failure mode, where most of the unanswered issues stand. All specimens were first tested with a pull-pull setup, and the unfailed sides were later tested in pull-push mode. The results were compared to the estimates provided by some of the existing design methods proposed in the literature.

Bonding Wood Veneer with Biobased Poly(Lactic Acid) Thermoplastic Polyesters: Potential Applications for Consolidated Wood Veneer and Overlay Products

This study reports on the use of poly(lactic acid) (PLA) as a renewable thermoplastic adhesive for laminated panels using birch, spruce, and pine veneers. Consolidated panels were prepared from veneer and PLA foils by hot-pressing from 140 to 180 °C to achieve minimum bondline temperatures. Evaluation of panel properties revealed that the PLA-bonded panels met minimum tensile strength and internal bond strength performance criteria. However, the adhesion interface which developed within individual bondlines varied with distinctions between hardwood and softwood species and PLA grades. Birch samples developed greater bondline strength with a higher pressing temperature using semi-crystalline PLA, whereas higher temperatures produced a poorer performance with the use of amorphous PLA. Panels formed with spruce or pine veneers had lower bondline performance and were also similarly distinguished by their pressing temperature and PLA grade. Furthermore, the potential for PLA-bonded laminated panels was demonstrated by cold water soak testing. Samples exhibiting relatively greater bondline adhesion had wet tensile strength values comparable to those tested in dry state. Our study outcomes suggest the potential for PLA bonding of veneers and panel overlays with the added benefits of being renewable and a no added formaldehyde system.

Testing methods for shear strength of bond line between concrete and different types of engineered wood

This paper identified a reliable testing method for determining the shear strength of bond lines between concrete and engineered wood. The identification was carried out based on analytical derivations and experimental tests on concrete (compressive strength of 24.8 MPa) and engineered wood composite connections glued by two types of epoxy. Forty specimens were tested under two commonly used test setups, i.e. 20 double-shear tests on timber-concrete composite specimens with a bond length of 50 mm and another 20 compression-shear tests on specimens with a bond length of 300 mm. The result analysis showed that there was no significant statistical difference between the shear strength of the bond lines (around 2.3 MPa) as well as between the failure modes obtained (dominated by concrete failure), regardless of the considered bond lengths and adhesive types investigated. The analysis used a quasi-non-linear fracture mechanics model, considering the boundary conditions of the tests. The analytical model revealed that the ultimate shear stress is approximately uniformly distributed both in the double-shear and in the compression-shear tests, so the spatially averaged shear stress value can approximate the critical shear stress of the bond line with sufficient accuracy. However, if the failure occurred in the wood or the strength of the concrete was higher, the shear stress distribution at ultimate load in the compression-shear tests with a bond length of 300 mm would not be uniform. The maximum shear stress value, which is significantly larger than the average one, occurred at the fixed (or supporting) end of the bond line. Even so, in the shear tests with a bond length of 50 mm, the average ultimate shear stress value was still close to the shear strength with a difference smaller than 5%. Hence, a bond length of 50 mm is recommended for determining the shear strength of a bond line between normal strength concrete and engineered wood when using a push-out shear test setup.

Mode-I fracture toughness and surface morphology evolution for contaminated adhesively bonded composite structures

This study explores the effect of environmental contamination level on mode-I failure and fracture surface evolution of adhesively bonded composite joints. We examined a common adhesive/adherend material system (Hysol EA9394/Hexcel IM7-G/8552) exposed to a typical aviation hydraulic fluid (MIL-PRF-87257) at varying contaminant concentrations. The macroscopic bond line fracture toughness measurement by double cantilever beam test exhibited a progressive deterioration with increasing contaminant concentration. Even a trace level (3 µg/cm2) resulted in a 15% reduction of average bond line strength and 30% drop in bond line toughness. An Arrhenius-type correlation between interface toughness and contaminant concentration was observed, with potential to predict the bond line toughness deterioration level. Increasing the contaminant concentration changed the fracture surface morphology from ductile-to-brittle failure mode, driven by diminished plasticity within the adhesive layer. Finite element method employing cohesive surfaces was also utilized to rationalize the experimentally observed trends. The combined experimental and numerical results suggest that the bond line contamination deteriorates the interfacial toughness through two mechanisms: (i) weakening the interfacial bonding strength, and thereby reducing the intrinsic interfacial toughness, and (ii) shielding the plastic energy dissipation within the adhesive layer, and leading to a reduction in the overall effective bond line toughness.

A new concept of wood bonding design for strength enhanced southern yellow pine wood products

Bonding strength in the structure of engineered wood products and composites is one of the vital properties for their application. Up to now, numerous research efforts have been made on improving durability, wettability, and strength of resins or adhesives. However, there are only a few reports on how to improve bond line strength according to wood feature itself. In this study, a new conceptual bonding design based on wood radial section feature was reported. In this design, finger-joint like bonding interfaces were generated by hot pressing two resin coated wood radial sections together at optimized pressure of 300lb per square inch (psi). By this design, the wet bonding strength of the bond line has potential to be higher than dry bonding strength. Meanwhile, with a compression ratio of 7.3% of wood strips, the obtained dry bonding or shear strength has been significantly increased up to 33.9%, as compared to end matched tangential controls. Wood specific gravity played an important role in this design. A proper compression ratio explored here in the radial section was about 17%. This work has provided a new route to improve wood bonding strength in an environmentally friendly way. Its impact on bending strength and dimensional stability of bonded wood structures needs to be further investigated.

Effect of Surface Roughness on the Shear and Tensile Strength of Hardwood Adhesive Joints: A Linear Elastic Model

This study analyzed the bond line strength of Eucalyptus sp. specimens submitted to shear and perpendicular to grain tensile forces, depending on the wood quality machined surface. The woods plans were glued with two different polyvinyl acetate adhesives. The bonding surfaces were milling with three different feed speeds; 6.0, 11.0 and 15.0 m/min, corresponding to the feed per tooth of the cutting tool; 0.86, 1.57 and 2.14 mm, respectively. The specimen types corresponded to the standards according to ABNT NBR 7190/1997. The cutting plane considered only the geometry of milling due to the bond line joint strength. To explain the experimental results, was proposed a linear elastic model to machined wood and bond line. For the two adhesives used, the experimental results suggest that the greatest perpendicular to grain tensile strength and shear strength were obtained to bond surface machined with the intermediate feed speed namely 11 m/min, for others two feed speeds and in the shear strength case, was not observed a distinction between them, in the perpendicular to grain tensile strength, the feed speed 6.0 m/min presented a higher strength than the machined surface with 15.0 m/min. The model reproduces the behavior of the experimentally results obtained for the two tests, and so it can be readily applied as a tool for evaluate the machining feed speed and the bond line joint strength.

Impact of cold temperatures on the shear strength of Norway spruce joints glued with different adhesives

As wood construction increasingly uses engineered wood products worldwide, concerns arise about the integrity of the wood and adhesives used. Bondline strength is a crucial issue for engineered wood applications, especially in cold climates. In this study, Norway spruce (Picea abies) joints (150 mm × 20 mm × 10 mm) were bonded with seven commercially available adhesives: polyurethane (PUR), polyvinyl acetate (PVAc), emulsion-polymer-isocyanate (EPI), melamine-formaldehyde (MF), phenol-resorcinol-formaldehyde (PRF), melamine-urea-formaldehyde1 (MUF1), and melamine-urea-formaldehyde2 (MUF2). Each adhesive was tested at six temperatures: 20, −20, −30, −40, −50 and −60 °C. Generally, within the temperature test range, temperature changes significantly affected the shear strength of solid wood and wood joints. As the temperature decreased, the shear strength decreased. PUR adhesive in most cases resulted in the strongest shear strength and MUF adhesive resulted in the weakest. MF and PRF adhesives responded to temperature changes in a similar manner to that of the PUR adhesive. The shear strengths of wood joints with PVAc and EPI adhesives were more sensitive to temperature change. At low temperatures, the variability of shear strengths increased with all adhesives. Percent wood failures of joints bonded with different adhesives in most cases were not sensitive to temperature changes.

Novel joints developed from partially un-moulded carbon-fibre-reinforced laminates

Two novel joints made from partially un-moulded carbon-fibre-reinforced plastic plates were designed to increase the strength of joints between carbon-fibre-reinforced plastic parts. In the partially un-moulded plate, a portion of the fabric stack was moulded with resin while the rest of the fabric stack remained dry. The plate was made using a manufacturing process developed from vacuum-assisted resin-transfer moulding. A new double-lap joint sandwiched a normal carbon-fibre-reinforced plastic plate between the dry fabric layers of a partially un-moulded plate. The other laminated joint overlapped the dry fabric layers of two partially un-moulded plates. Both joints were moulded by resin transfer. Tensile testing indicated that the two novel joints were more than twice as strong as a classical double-lap joint and half as strong as a normal, joint-free carbon-fibre-reinforced plastic plate. Additionally, the joints may potentially be made much stronger by modifying their shapes. In particular, the laminated joint may be made as strong as a normal carbon-fibre-reinforced plastic plate because its strength is determined by the fibre–matrix interface rather than the bondline strength, which is a key factor in determining the strength of a normal carbon-fibre-reinforced plastic plate.

Al-Si 도금된 보론강 레이저 소스에 따른 레이저 용접부의 미세조직과 기계적 성질에 미치는 핫스탬핑 처리의 영향

In this study, the effect of laser source(CO2 and Nd:YAG) on the microstructure and tensile properties of laser welded Al-Si coated boron steel(1.2mmt) was investigated with before and after hot-stamping. In case of as welds condition, fracture occurred in base metal unrelated to the laser source. It could be explained that tensile strength of fusion zone composed of martensite and bainite is higher than that of base metal that contains a lot of ferrite despite dilution of Al and Si from coating layer to fusion zone. In case of hot-stamping condition, the fracture occurred in fusion zone irrelevant to laser source and the tensile strength was lower than hot stamped base metal. In the CO2 laser welds, Fe3(Al,Si) formed near the bond line was transformed into ferrite during hot-stamping. Therefore tensile strength of bond line is lower than that of base metal and center of fusion zone and the fracture occurred in the bond line. On the other hand, in the Nd:YAG laser welds, the higher concentration of Al formed the ferrite in the fusion zone during hot-stamping treatment. Also, the thickness of centerline was thinner than that of base metal. Therefore, it is considered that fracture occurred in centerline of fusion zone due to effect of concentration stress, and it leaded to a lower tensile strength and elongation.

Bondline strength evaluation of cocure/precured honeycomb sandwich structures under aircraft hygro and repair environments

Effects of moisture accumulated into the adhesively bonded composite structures on their bondline mechanical strengths are investigated through a series of comparative experiments. Those composite structures include a honeycomb sandwich structures fabricated by the cocure and the precure processes. Mass of moisture accumulated into the closed cells of the honeycomb sandwich panel specimens has been calculated. A pressure due to the vapor expansion in each cell of the sandwich panel has also been obtained for the minimum repair pressure to be applied to the laminate patched area by vapor pressure–temperature relations from the thermodynamic steam table, the ideal gas state equation and two vapor pressure equations. The bondline strengths of the laminated skins on the flat surface of honeycomb have been compared by the flatwise tension test and climbing drum peel test for dry, wet and repair-after-wet specimens, respectively.

Debonding Failure of Sandwich-Composite Cryogenic Fuel Tank with Internal Core Pressure

A summary of the failure analyses and testing that were conducted to determine the cause of the X-33 liquidhydrogen tank failure is presented. Ply-level stress analyses were conducted to explain the formation of microcracks in the plies of the inner and outer facesheet laminates of the honeycomb sandwich walls of the tank under known thermal and mechanical loads. The microcracks allowed the ingression of liquid- and gaseous-hydrogen and gaseous-nitrogen purge gas that produced higher than expected sandwich core pressures in the tank. Single cantilever beam tests were used to determine the toughness of the interface between the facesheets and honeycomb core. Fracture mechanics analyses were developed to determine strain-energy release rates for known foreign object debris shapes and sizes and known and statistically possible core internal pressures. The fracture mechanics analyses were validated by comparing with results of blowoff tests that were fabricated from undamaged tank sandwich material. Strain-energy release rates from the validated analyses were then compared with known and statistically possible values of toughness determined from the single cantilever beam tests. These analyses and tests were then used to substantiate a scenario for failure of the X-33 liquid-hydrogen tank that includes microcracking of the inner facesheets and ensuing ingression of hydrogen and nitrogen, a low bondline strength and toughness, and the presence of foreign object debris. Nomenclature ¯ A −1 jk =i nverse of the laminate stiffness matrix transformed to the local coordinates a, b = dimensions of debond Eii = elastic modulus in the ith principal material

A numerical study of the shear-strength-predicting capabilities of test specimens for wood–adhesive bonds

The sensitivity to geometrical imperfections of various test methods for wood–adhesive bonds was investigated using nonlinear finite element analysis. The adhesive layers in the specimens were modelled using a nonlinear softening, fracture mechanics model. The specimen types corresponded to the standards according to ASTM-D4680, ASTM-D905, EN-302-1 and a modified version of the ASTM-D3535 specimen. The results show that the prediction of bond line strength is highly dependent on both the specimen type used and adhesive properties such as strength, fracture energy and the shape of the stress-slip behaviour of the adhesive layer. For example, it was shown that the ASTM-D905 specimen was not able to rank the adhesives in terms of local bond line strength in the correct order. Another finding is that the sensitivity to geometrical imperfections and erroneous load application in the test methods is also highly dependent on specimen and adhesive type.