Adherend Specimens Research Articles

Adhesive bonding of noble metals with a thiohydantoin primer

ObjectiveThe purpose of this study was to assess the effects of an experimental primer containing acetone solution and a sulfur-containing functional monomer, 10-methacryloyloxydecyl-(2-thiohydantoin-4-yl)propionate (MDTHP), on the bonds between noble metals and acrylic resin. MethodsThe experimental primer used as the control for comparison consisted of 6-(4-vinylbenzyl-n-propyl)amino-1,3,5-triazine-2,4-dithione (VBATDT) in acetone. These primers were prepared as equimolar functional monomers (0.1 mol%). A self-polymerizing acrylic resin initiated with tri-n-butylborane (TBB) was used as the luting agent. Four elemental metal disks (silver, copper, palladium, and gold) were used as adherend specimens. All the disks were wet-ground with silicon carbide paper (#1500). Bonding reactions were performed on 12 combinations of the four metals, and the disks were either primed with MDTHP or VBATDT or were unprimed (control). Shear bond strengths were determined pre- and post-thermocycling (5–55 °C, dwell time 60 s, 20,000 cycles). The results were statistically analyzed via a non-parametric test (α = 0.05). ResultsThe post-thermocycling shear bond strengths of the MDTHP primer were as follows (median, n = 11): 13.2 MPa on silver, 25.9 MPa on copper, 4.1 MPa on palladium, and 11.3 MPa on gold. The MDTHP primer showed higher post-thermocycling shear bond strength on all the four metals. Additionally, on silver and copper, the MDTHP bond strengths were higher than on the other metals. SignificanceWithin the limitation of current of experimental setting, the MDTHP compound may be applicable as a functional monomer for bonding noble metal alloys.

Joining Behavior of Jute/Sisal Fibers Based Epoxy Laminates Using Different Joint Configurations

ABSTRACT The natural fiber-based polymeric composites are being used extensively in various engineering applications, especially in the non-structural parts and components. Although, a large number of primary processing techniques, such as hand-layup and compression molding are available for fabrication of parts, still the secondary processing in terms of joining and machining is inevitable. The joining of composite parts becomes necessary in case of complicated and intricate product designs. Adhesive joining is one of the most commonly used processes for polymer-based composite materials. It is a cheap, easy, and smooth bonding process and does not necessitate the drilling of holes for the purpose of mechanical fastening. In the present experimental investigation, the joint strength of woven fiber mat (sisal, jute, and hybrid) reinforced epoxy composites has been investigated using different joint configurations, namely, single lap, double-strap butt, and scarf joint. The effect of adhesives has also been explored by joining composites with two types of epoxy resins and corresponding hardener. It was observed that the hybrid composites recorded better joining performance for both types of adhesives. Moreover, the Field Emission Scanning Electron Microscopy (FE-SEM) has been used to understand the failure mechanisms during tensile testing of adhesively bonded natural fiber-reinforced composite laminates. The three-dimensional assembly models of adherend specimens were created using the SOLIDWORK V.16 modeling software. ANSYS-V.18.2 WORKBENCH was employed for the analysis of the joint performance. The maximum shear stress and the total deformation results were determined. The finite element analysis (FEA) results were compared with experimental findings and were found to be in good agreement.

Influence of Roughness on the Mechanical Adhesion of Single Lap Joints

The single lap joints analysis has been developed from different perspectives, including overlap length, adhesive thickness, spew fillet formation, stress distribution, and manufacturing parameters. This paper describes recent results in the study of the roughness influence on the mechanical adhesion of single lap joints in composite test specimens made of glass fiber with a polymeric matrix. Analysis techniques were based on both finite element and experimental approaches. For the above-explained purpose, two cases were simulated: one with a surface roughness of the adherend in the joint overlap, and another one with a minimal roughness surface in the overlap zone. It was considered that the adhesive behaves like an isotropic material. As for the specimens used in the experimental tests, the surface roughness of the adherends was controlled by using an anti-adhering fabric, and the adherend specimen's surface without roughness was controlled using glass as a mould. The numerical results were validated experimentally by means of tensile tests. In the simulation where substrates with surface roughness were used, it was observed that the maximum shear stress at the joint ends decreases by 21% when compared with the model developed with adherends without roughness. Nevertheless, in the test specimen with roughness, a redistribution of the stresses exists that move from the adhesive to the substrates, which causes an increase of the single lap joint resistance. The same was observed in the experimental tests where an increase of four times in the load supported by the joint was obtained.

A comprehensive fatigue life predictive model for electronically conductive adhesive joints under constant-cycle loading

This paper describes a novel fatigue life prediction methodology aimed at providing the design engineer an easy fatigue life predictive tool using experimental data for thermo-mechanical load cyclic fatigue under constant maximum load (P max) and load ratio (R = P min/P max = σmin/σmax). This encompasses an integrated approach to joint testing, analysis and modeling. Utilizing the proposed methodologies, we aim to predict the changes in fatigue life of the adhesive, based on the whole spectrum of test variables including temperature, humidity and load ratio. For this purpose, joints were prepared using stainless steel adherend specimens and a commercial silver-filled electronically conductive adhesive, and tested under monotonic and cyclic fatigue conditions, at 28°C, 20% relative humidity, 50°C, 90°C and elevated humidity levels. Load–number of cycles (P–N) curves were generated using two specimen geometries at two different load ratios (R), at a cyclic frequency of 150 Hz. Using the experimental data, a life predictive methodology was developed and validated. Furthermore, the usefulness of the above-mentioned fatigue life predictive capability was extended to varying stress states.

A novel cumulative fatigue damage model for electronically-conductive adhesive joints under variable loading

This paper describes a novel cumulative fatigue damage life predictive model aimed at providing the design engineer an easy fatigue life predictive tool using experimental data. This encompasses an integrated approach of joint testing, analysis, and modeling. For this purpose, joints were prepared using stainless steel adherend specimens and a commercial silver-filled electronically conductive adhesive, and tested under monotonic and cyclic fatigue conditions, at 28°C, 20% relative humidity. Load–number of cycles (P–N) curves were generated for these specimens using load ratio R = 0.1 and R = 0.5 (R = P min/P max = σmin/σmax) at a cyclic frequency of 150 Hz. Fatigue life and failure behaviors due to cumulative fatigue damage were assessed using a novel experimental program. Experimental results revealed that most of the fatigue damage occurs during the latter part of the fatigue process and the combination of lower load ratio and higher maximum applied load has the most detrimental effect on the failure of the joint. Finally, a novel analytical model for fatigue life prediction under variable cyclic conditions was proposed using experimental data and a detailed stress analysis.

Fatigue and failure behaviors of silver-filled electronically-conductive adhesive joints subjected to elevated humidity

Conductive adhesives are used in electronics packaging applications for hybrid, die-attach and display assemblies. There are a number of issues of concern in the design of joints bonded using electronically-conductive adhesives (ECAs). An important issue is the cyclic fatigue behavior of conductive adhesive joints under elevated humidity environments, in which failures may occur due to cyclic mechanical and/or thermal stresses. This paper addresses the effect of elevated humidity levels on the fatigue and failure behaviors of ECAs. For this purpose, joints were prepared using stainless-steel adherend specimens and a commercial ECA, and tested under monotonic and cyclic fatigue conditions, at two humidity levels, namely 20% and 90% relative humidity at 28°C. Furthermore, joint failure mechanisms were analyzed using optical techniques, and joint conductivity measurements. Load versus number of cycles (P–N) curves were generated using these specimens at three different load ratios (R), namely 0.1, 0.5 and 0.9, at a cyclic frequency of 150 Hz. The P–N curves were parallel and the failure modes were found to be predominantly interfacial, accompanied by a significant decrease in joint conductivity.

Dynamic fatigue and failure behavior of silver-filled electronically conductive adhesive joints at ambient environmental conditions

Electronically-conductive adhesives (ECAs) have been used for electronics packaging applications. Today this technology is used in electronics for laptop computers, camcorders, watch electronics, hard-drive suspensions and in various other electronic equipments. Even though ECAs have excellent potential for being efficient and less costly alternative to lead-solder interconnects, they still possess a number of problems with respect to durability and design to meet specific needs. One of the issues that requires understanding is the fatigue behavior due either to mechanical or thermal stresses varying in a cyclic manner. This study intends to address the fatigue and failure behavior of ECAs under ambient operating conditions. For this purpose, joints were prepared using stainless steel adherend specimens bonded with a commercial ECA, and tested using monotonic and cyclic loadings at ambient environmental conditions (28°C and 20% relative humidity). S–N curves were generated using these specimens at four different load-ratios (R), namely 0.1, 0.3, 0.5, 0.7 and 150 Hz cyclic frequency. The S–N curves were not parallel, exhibited non-linear behavior with diminishing slope at higher R values.

Fatigue and failure behavior of silver-filled electronically-conductive adhesive joints subjected to elevated temperatures

The use of adhesives to replace mechanical connectors and other joining methods has enjoyed rapid growth in recent years. There are a number of issues of concern in the design of joints bonded using electronically-conductive adhesives (ECAs). One of these is the cyclic fatigue behavior of conductive adhesive interconnects under different environmental conditions, in which fatigue failure might occur due either to mechanical or thermal stresses varying in a cyclic manner. This paper addresses the effect of elevated temperatures on the fatigue and failure behavior of ECAs. For this purpose, joints were prepared using stainless steel adherend specimens bonded with a commercial ECA, and tested using monotonic and cyclic loadings, at two elevated temperatures, namely 50°C and 90°C. When the temperature was increased to 90°C, close to the glass transition temperature of the adhesive, we observed consistently parallel fatigue curves at different load ratios (R = P min /P max) for joints, as in the case of 50°C test condition, along with significant reduction in fatigue lives. Joint failure mechanisms were also analyzed using optical techniques, and joint conductivity measurements.

The formulation of powder coatings using solid state shear extrusion

AbstractThe feasibility of producing homogeneous powder coating formulations without melting is investigated using Solid State Shear Extrusion (SSSE). A detailed comparison between conventional melt extrusion and SSSE processing conditions of identical formulations is accomplished by following the behavior and degree of polymerization during curing. Commercially available polyester and epoxide powder coating premix formulations were processed by SSSE using a Brabender® laboratory‐scale twin‐screw extruder and further pulverized in a ball mill. Calculations based on particle size before and after comminution in single batch ball mill studies indicate a reduction in energy requirements for SSSE during pulverization. Metal coupons were coated with dry pulverized formulations using an electrostatic fluidized bed coating system. The dynamics of curing were followed for a series of bake time exposures. The sol was separated from the gel using Soxhlet methods and characterized by gel permeation chromatography (GPC). A comparison of experimentally determined gel points and gelation dynamics showed general agreement between both processing methods. The critical yield stress, determined from preliminary mechanical testing of modified thick adherend specimens crack‐line‐loaded in compression, was also determined. Results showed the SSSE process to be equivalent to melt extrusion.

Mixed-mode fracture characterization of adhesive joints

A novel load jig is presented which allows mixed-mode fracture testing of adhesive joints and composite laminates over the entire range from mode I to mode II, by using a single equal adherend double-cantilever-beam specimen. Experiments performed with the load jig showed that G IIC was approximately three times higher than G IC for the tested adhesive system consisting of FPL-etched 7075-T6 aluminium adherends bonded with Cybond 4523GB (American Cyanamid) epoxy adhesive. Experimental data showed that G C was independent of crack length and that there was no dependence of G IC on adherend thickness. Comparison of G IIC values obtained by using the load jig to test conventional end notch flexure (ENF) specimens indicated that there are relatively small friction effects between crack faces in mode II testing of ENF specimens. The experimental data were also used to evaluate three different analytical techniques for the mode partitioning of unequal adherend specimens.

Analysis and design data for adhesively bonded joints

Abstract Software based on published analytical methods and implemented on an IBM PC microcomputer enables the engineer to determine the stress distribution and to design adhesively bonded joints of simple configurations. For complex configurations the finite element software CA.ST.OR 2D can be used. In this paper, methods and specimens enabling the determination of the mechanical characteristics of interest to the designer are reviewed and described. These mechanical properties can be obtained on the bulk adhesive (in tension and compression) or on adhesively bonded joints in shear (thick adherend specimens). Results obtained on five epoxy-based structural adhesives are presented. The validity of both the design software and the mechanical test methods is proven experimentally using adhesively bonded single lap joints.

Bonding of a light-curing glass-ionomer cement to dental amalgam

In the clinical situation, the need may arise for placement of a glass-ionomer cement over an existing amalgam restoration. This study assessed the tensile bond strength of a recently developed light-curing glass ionomer (Vitrabond) to dental amalgam (Dispersalloy), with and without the use of Scotchbond dual cure as an intermediary. Amalgam adherend specimens were prepared, then aged in water at 37°C for seven days. Immediately before being bonded, the amalgam surfaces were finished flat on 600-grit paper. Forty specimens were used for bonding in this condition, and another 40 were covered with a thin layer of Scotchbond, which was light-cured for 10 s. The glass-ionomer was applied to the adherend surface in two increments, each ligh-cured for 30 s. After being bonded, half the specimens were stored in water at 37°C, while half were stored in an environment of 95 ± 5% RH at 37°C. The 24-hour tensile bond strengths, in MPa, were: for specimens stored in water, without Scotchbond 8.4 ± 1.2, with Scotchbond 4.7 ± 1.3; and for specimens stored in 95 ± 5% RH, without Scotchbond 9.2 ± 2.1 with Scotchbond 4.6 ± 1.5. The data were further analyzed by the Weibull distribution function. It was concluded that a strong reliable bond can be achieved between Vitrabond and set Dispersalloy, and that the use of Scotchbond as an intermediary is contra-indicated.

Torsional Shear Strength of Adhesive-Bonded Butt Joint Specimens

Recently, considerable attention has been paid to the strength problem of the adhesive-bonded joint because of its wide usage to many mechanical structures, e. g., automobile, airplane and so on. But there exists some uneasiness for use of this type of joint, for no reasonable design standard has been established yet.So, the authors planned and conducted a series of the experiments to research the effect of surface roughness of the adherend specimen on the adhesive strength under the torsional shear loading condition by using a thin wall cylindrical butt joint specimen, where an epoxy resin (Epikote 828) mixed with a hardner (TEPA) was used as an adhesive, structural steel (JIS. S45C) as an adherend and furthermore polysulfide (Thicol, LP-3) as a plasticizer.The rigidity of the adhesive and the absorbed energy of the adhesive-bonded specimen in impact tests were varied to some extent by controlling the post curing temperature or by adding the plasticizer, and thus obtained three sorts of the adhesive-bonded specimens having different mechanical properties were used in this experiment.From the results, it was observed that the surface roughness of the adherend specimen gave the influence on the shear strength in somewhat different manner depending on the mechanical properties of the adhesive used. To explain the strength behavior obtained in this study, discussions were tried based on fracture modes considered in connection with the adhesive/adherend interfacial feature of each adhesive-bonded butt joint specimen.

Comparison of Lap Shear Test Specimens

Abstract The single lap shear test specimen, a method for measuring the shear strengths of structural adhesives, was evaluated in a combined experimental and analytical study. The shear strengths of two structural adhesives were measured with the conventional thin adherend lap shear specimen and with several thick adherend configurations. Shear strengths obtained from thin specimens were too low: failure was controlled by the tensile (peel) strength of the adhesive/adherend interface rather than by the adhesive shear strength. Equally significant was the finding that the relative shear strengths of the two adhesives measured with the thin specimen configuration were opposite the results from the thick adherend specimens. The apparent shear strengths from thick adherend test specimens increased with increasing adherend thickness, an expected result; however, they decreased with increasing adhesive thickness, a trend which did not agree with published analyses. This anomaly is explained by finite element analyses of the shear and normal stress gradients in the adhesive layer.