Ultrasonic analysis of nonlinear response and strength of adhesive bonds

A theoretical investigation has been carried out to obtain information on the adhesive bond strength from ultrasonic test results. It is postulated that failure of an adhesive bond is preceded by nonlinear behavior in thin boundary layers at the interfaces of the adhesive and the adherends. The nonlinear adhesive bond behavior is represented by a relation between tractions and gross displacement increments across the adhesive layer. Intertia of the adhesive layer is taken into account, and the effect of a nonlinear adhesive response on the reflection and transmission of longitudinal waves is investigated for the case of normal incidence. A procedure is presented to obtain the nonlinear relation from reflected wave results. As an alternative to a completely nonlinear analysis, the case of prestressing the adhesive layer in the nonlinear range and superimposing a small ultrasonic disturbance has been considered, but the inertia of the adhesive is neglected for this case. For this case, the propagation of interface waves and horizontally polarized plate waves is discussed. Finally, for the nonlinear case the generation of higher harmonics has been investigated, and it has been shown that certain nonlinear parameters can be obtained from the spectrum of higher harmonics.     

Effect of CNT dispersion methods on the strength and fracture mechanism of interface in epoxy adhesive/Al joints

The tensile and shear strengths of adhesively bonded aluminum (Al) joints were inspected in the presence of amino functionalized multi-wall carbon nanotubes (MWCNTs). Tensile and shear tests were carried out using butt and lap-shear joints. The main goal was to compare the effects of dispersion methods of functionalized-CNT into epoxy on the mechanical performances and failure mechanisms of Al joints. Two different types of dispersion procedures, distributing CNT in the hardener (HH method) and distributing CNT in the resin (RR method), were applied. To identify the failure mechanisms, the morphology of fracture surfaces were analyzed using scanning electron microscopy (SEM). Comparing two dispersion methods against one another ascertained that following the RR method for dispersing CNTs in the adhesive displayed larger shear strength, while applying HH method offered fairly greater tensile strength. Moreover, dispersing CNTs in the resin induced more uniform dispersion of CNTs as compared to distributing nanofillers in the hardener. Following RR method, CNTs good dispersion as well as the presence of effective crack growth dissipating mechanisms, increased the shear strength of CNT reinforced adhesive joint. Incorporating CNTs using HH approach encouraged the plastic void formation of epoxy around the agglomerated CNTs, and as a consequence, promoted the plastic deformation under tension.     

Bond strength and adhesive interface analysis using EDTA as a dentin conditioner

This study evaluated dentin bond strength and dentin-resin interfacial morphology using phosphoric acid-etching and EDTA-conditioning. The occlusal enamel of twenty-four human third molars was removed to expose the dentin surfaces, which were polished with a SiC paper (600 grit). Teeth were randomly divided into three groups (n = 8): etching with 37% phosphoric acid (15 s), conditioning with 0.1 M EDTA (60 s) and 0.5 M EDTA (120 s). Adhesive (XP Bond, Dentsply) was applied and three layers (2 mm each) of composite (EsthetX, Dentsply) were placed and light-activated separately (20 s). Teeth were sectioned to obtain specimens for the microtensile bond strength test (1 mm² at cross section). Half of the specimens was tested in a universal testing machine (EZ Test, Shimadzu) after 24 h and the other half after storage for 10 months. Failure mode and adhesive interface were analyzed using scanning electron microscopy. Data were analyzed by mixed models for repeated measures (PROC MIXED) and Tukey-Kramer test, considering a significance level of 5%. Mean bond strength values (SD) after 24 h and 10 months were, respectively (in MPa): phosphoric acid: 37.3 (7.7) / 33.9 (6.7); 0.1 M EDTA: 14.7 (7.3) / 15.1 (10.1); 0.5 M EDTA: 25.1 (7.7) / 21.1 (14.1). Dentin treatment with EDTA and phosphoric acid resulted in hybrid layer and resin tags formation. Mixed failures were prevalent for all groups tested after 24 h. Storage for 10 months changed the failure mode for the 0.5 M EDTA group to adhesive failure (between dentin and bonding agent). EDTA applied for 60 s yielded lower bond strength results compared to phosphoric acid and EDTA (120 s), but there was no significant reduction after 10 months of storage for any of the tested groups.     

Effect of adhesive air-drying time on bond strength to dentin: A systematic review and meta-analysis

ObjectiveThe objective of this review was to evaluate the effect of air-drying time on the adhesion (bond) strength of adhesives to dentin in previously published studies and to conduct a meta-analysis to quantify the differences in the bond strength obtained after the different air-drying times.MethodsAn electronic search was performed using the Medline, Cochrane library, and Scopus databases. The included studies were laboratory studies that investigated the effect of adhesive air-drying time on adhesion (bond) strength of resin-based adhesives to coronal dentin. Studies which evaluated the effect of adhesives air-drying time on physical and mechanical properties of adhesives, interfacial properties, bond strength to root dentin, enamel, or bond strength of indirect composite restoration or orthodontic bracket, were excluded. The methodological quality of included studies was assessed. Meta-analysis was performed using Comprehensive Meta-Analysis software, version 2.0 (Biostat, Englewood, NJ, USA). The results of the meta-analysis were subjected to a further one-way analysis of variance, followed by the Tukey post hoc multiple comparison using R-software, version 3.4.3 (R Foundation for Statistical Computing, Vienna, Austria).ResultsThirteen studies fulfilled the inclusion criteria of this review, while only five studies were included in meta-analysis. The effect of adhesive air-drying time on the bond strength was significant in eight studies (61.5%), material-dependent in four studies (30.8%), and not significant in one study (7.7%). Eight studies (61.54%) presented a medium-risk of bias, three studies (23.08%) presented a low-risk of bias, and two studies (15.38%) presented a high-risk of bias. The analysis of micro-tensile bond strength (μTBS) of adhesives showed statistically significant difference between different air-drying times (p<0.05). The highest mean μTBS values were: 52.9 ± 11.38 MPa (obtained after air-drying of adhesives for 30 s), followed by 48.26 ± 9.77 MPa (15 s), and 37.76 ± 1.45 (25 s), while the lowest mean μTBS was 33.98 ± 2.30 MPa and 35.79 ± 6.63 MPa (5 s) obtained after 10 s and 5 s respectively.ConclusionThe air-drying time of adhesives is crucial to the adhesion strength to coronal dentin. Adhesive air-drying for shorter durations (5–10 s) may be insufficient to obtain adequately durable bonding to dentin, instead, Air-drying should be performed for longer durations (15–30 s), considering the pressure and distance of air-drying source.     

螺杆钻具定子注胶工艺对橡胶与金属粘合强度的影响

从定子管材的表面处理、粘结剂涂刷方式、注胶方式和硫化工艺等方面阐述影响橡胶与定子粘合强度的因素。金属的表面处理应根据定子热处理和机加工过程中存在的油污的类别选择合适的处理方式及清洗剂;粘合工艺的重点是根据配方选择合适的粘结剂、涂刷方式、涂刷厚度和隔绝空气污染;注胶方面应考虑注胶压力、速度、温度及方式,减少胶料对粘结剂的冲刷;硫化工艺方面,控制好硫化罐内温度、压力的均匀性等。     

The effects of Al surface treatment,adhesive thickness and microcapsule inclusion on the shear strength of bonded joints

The influences of various Al surface treatments, adhesive thicknesses as well as the incorporation of synthesized microcapsules into epoxy adhesive on the shear strength of adhesive/ Al joints have been investigated using lap-shear tensile tests. First, the influence of adhesive thickness on the shear strength of joints has been presented. Then, the effects of various Al surface treatments on the surface roughness of Al and shear strength of joint have been researched. Atomic force microscopy was used to study the Al surface morphologies and textures. Finally the few micron-sized polymeric microcapsules were synthesized and the shear performances of microcapsule filled epoxy adhesives were inspected. It was observed that the HCl acid based etching increased both micro-roughness and nano-texture of the Al surface and led to the peak shear strength. Moreover, HCl-nitric acid treatment offered the maximum value for the cohesive failure. Capsule inclusions into the adhesive displayed different influences on the joint shear performances depending on the capsule morphology and the surface treatment of Al.     

一种中温固化高强度环氧胶粘剂的研制

以E-51、E-44为主体树脂,加入奇士增韧剂研制出一种中温固化高强度环氧胶粘剂.该胶粘剂在加入占粘料质量分数30%左右的增韧剂后,选用自制固化剂SL-1,在50 ℃×1 h+80 ℃×1 h条件下固化,其拉伸剪切强度可达42.1 MPa.     

Improving electrical and mechanical properties of a conductive nano adhesive

In this experimental study, lap shear strength and electrical conductivity of nanohybrid adhesives containing multi-walled carbon nanotubes (MWCNT) and silver (Ag) nanoparticles were investigated. Ag nanoparticles were produced via arc-discharge method in liquid nitrogen. For characterizing the Ag nanoparticles, X-ray diffraction analysis, transmission electron microscopy, and scanning electron microscopy (SEM) were performed. Tensile lap shear properties were determined in accordance with ASTM D 1002-10 standard. Mechanical and the electrical properties of nanohybrid adhesives were compared with neat epoxy adhesive. The best electrical conductivity of nanohybrid adhesive was obtained for the 1% wt MWCNT-2% wt Ag-contained sample. However, the samples which contain 0.5% wt. MWCNT–0.5% wt. Ag nanoparticles reached the highest lap shear strength. The results showed that Ag nanoparticles enhance the conductivity in the presence of MWCNT. It is concluded that the MWCNT act as conductivity bridges among epoxy adhesive and facilitate the electron transfer. As seen in the tensile test results, the ductility of the adhesive was improved by adding the nanoparticles in to the epoxy resin.     

Past experiences in the development of tests for adhesive bond strength

In the mid-1970s an extended research program was conducted with the goal of developing nondestructive evaluation techniques for the measurement of adhesive bond strength. Since the details of much of that work are published in documents that are not readily available, a review of that work is presented. Included will be the philosophy of the research plan, specific technical results achieved, and conclusions.     

鞋用水性PU胶的制备、检测及使用

系统地介绍了鞋用水性聚氨酯(PU)胶的制备和检测方法，针对使用中的常见问题制定了对策，并分析了PU胶的质量、技术上的不足和这方面的研究进展。     

Recent developments in the laser spallation technique to measure the interface strength and its relationship to interface toughness with applications to metal/ceramic,ceramic/ceramic and ceramic/polymer interfaces

This paper summarizes recent developments in the laser spallation technique for measuring the tensile strength of planar thin film interfaces. In this technique, a laser-produced compressive stress pulse in the substrate, reflecting from the coating's free surface, pulls the interface in tension and leads to its failure if the tensile amplitude is high enough. Earlier, the critical stress amplitude that accomplishes the removal of the coating was determined through a computer simulation of the process. Recently, the technique was modified so that the interface stress can be determined directly by recording the coating or substrate free-surface velocities using a Doppler interferometer. The recorded surface velocity is related to the interface stress via an elastic wave mechanics simulation. Interface strengths of several metal/ceramic, ceramic/ceramic and ceramic/polymer systems are summarized from our recent efforts. In addition, two developments, the first a novel interferometer to record velocities from rough surfaces, and the second a technique to produce subnanosecond rise-time stress pulses with no asymptotic post-peak decay, are discussed which further allows the technique to be applied to rough thermal spray coatings and also to films as thin as 0.1 μm. Finally, it is shown how the tensile strengths obtained from the laser spallation experiment can be related to the interface fracture energies through a Griffith-type relationship, which, in turn, is derived by using the concepts of universal bonding correlations. It is shown that the estimated values obtained through this relationship are in good agreement with experimentally obtained values if the interfaces are free of defects, suggesting that the laser spallation experiment measures a fundamental strength value that is intrinsic to the material system and makes the measured value a suitable parameter for characterizing the interface.     

Study of the interfacial adhesive strength of a heat-shrinkable multilayer film

A heat-shrinkable multilayer film is widely employed as labels of plastic bottles. A new heat-shrinkable multilayer film without an adhesive layer was designed in this study. The interfacial adhesive strength between the layers was controlled to avoid layer separation. We assumed a polyethylene terephthalate glycol-modified (PETG)/styrene-co-butadiene block copolymer/PETG shrinkable film substitute as the general poly(ethylene terephthalate) (PET)/polystyrene/PET shrinkable film. The interlayer adhesive strength between the layers was retained for industrial utilization even after drawing. Additional polybutadiene (PB) infiltrated the butadiene layer in the microphase-separated structure. Further addition of PB could not infiltrate the butadiene layer. The excessive PB contents coexisted with the interface between the layers, as observed by transmission electron microscopy (TEM). The segregated PB enhanced the interfacial adhesive strength. We concluded that the selective distribution of adhesive functional materials along the interface could appropriately retain its adhesive strength.     

Ultrasonic detection of kissing bonds at adhesive interfaces

Intimate mechanical contact between the adhesive and adherend counterparts can easily occur without an actual bond. Such apparently flawless, but severely defective 'kissing' bonds are especially dangerous because they often remain hidden from most types of conventional ultrasonic inspection. A special high-frequency, high-inspection angle ultrasonic technique is suggested to improve the detectability of such kissing bonds. It is shown to be essential to interrogate the adhesive-adherend interface from the adherend side without sending the ultrasound through the inherently inhomogeneous and highly attenuating adhesive layer.     

冷制高强快干淀粉胶粘剂

介绍了一种以淀粉为主要原料,在复合催化剂作用下,经双氧水室温氧化并添加高强快干添加剂和其他助剂,制备高强快干淀粉胶的方法,讨论了对淀粉胶性能的影响因素及其简要的作用机理,确定了能够满足最佳上机要求的配方。应用本方法制出的胶粘剂,通过中试制板,证明该胶具有干燥速度快、强度高等优点。     

Measurement of solder joint strength in freestanding chip-scale packages using a quantitative laser spallation technique

A previously developed laser spallation technique is adapted to measure in situ the tensile strengths of geometrically heterogeneous interfaces, in multilayer freestanding chip-scale packages that were baked for specific temperatures and times. The test procedure involved quantification of the stress waves inside the packages using interferometry, and subsequent stress field quantification, including that at the failed interface, using a wave mechanics simulation. The technique is generally applicable and can be used to test any type of freestanding package. In this work, it is demonstrated on freestanding 0.5?mm-pitch MicroStar BGA^TM packages. The ball grid array joint strengths for Pb-free solders on bare Cu pads were measured to be 942?±?91, 703?±?69, 666?±?70, 441?±?42, and 392?±?45?MPa for samples that were thermally aged for 3, 10, 20, 40, and 80?days, respectively. An important result of our study is that the critical laser energy for causing joint failure was found to be approximately proportional to the peak tensile stress at the joint. This validates the discussion earlier where no stress quantification was carried out, but the interfaces were characterized only in terms of the critical laser energies and the deteriorations in the material microstructure in the solder joint region caused by thermal aging were related to the reductions in the measured critical laser energies. This powerful result shows that in the future it may suffice to use the critical laser energy for material selection and quality control during manufacturing.     

Tensile and shear stresses induced in adhesive shear test specimens

The most widely used adhesive test specimen is the lap shear test. Variations of this test have been standardized by the American Society for Testing Materials (ASTM) and other societies or agencies. The results of these tests are generally given in terms of the failure load divided by the area of overlap, but a finite element analysis indicates that the maximum shear stress and the induced normal stress can be much larger than the average. An argument can be made that the induced secondary Mode I stresses, near the bond termini, are more closely related to failure than are the average shear stress or even the maximum shear stress. Experimental and finite element results are presented in this paper to show that this is indeed the case. In addition, ways to reduce these induced stresses in lap shear tests are discussed and evaluated.     

Elastoplastic finite element stress analysis and strength evaluation of adhesive lap joints of hollow shafts subjected to tensile loads

The stress distributions in adhesive lap joints of dissimilar hollow shafts subjected to tensile loads have been analyzed by the elastoplastic finite element method, taking the nonlinear behaviors of the adhesive and the hollow shafts into consideration. A prediction method for the joint strength has been proposed based on the Mises equivalent stress distribution in the adhesive and the frictional resistance between the adhesive and the shaft after rupture of the adhesive. In the experiments, three different kinds of adhesive lap joints were made, i.e. the inner and outer hollow shafts were aluminum alloy/aluminum alloy, steel/steel, and steel/aluminum alloy combinations, and the tensile strength of each joint was measured. From the numerical calculations, in the case of the two hollow shafts made of the same material, the tensile strength increases with an increase of Young's modulus of the shaft and in the case of the two hollow shafts made of different materials, the tensile strength increases when the inner hollow shaft of larger Young's modulus is bonded to the outer one of smaller Young's modulus. Also, the effects of the overlap length and the inner diameter of the inner shaft on the tensile strength of the joint are discussed. By comparing the predicted values of the tensile strength with the experimental results, it was shown that the proposed prediction method could estimate the tensile strength of the adhesive lap joints of hollow shafts within an error of about 15%.     

Bonding adhesive strength for plasma spray with cathode spots of low-pressure arc after grit blasting and removal of oxide layer on metal surface

Cathode spots of a low-pressure arc can remove oxide layers and evaporate impurities on metal surfaces. Removal of the oxide layer using cathode spots is expected to solve recent obstacles due to chemical and mechanical cleaning methods. Various phenomena of cathode spots have been investigated for pre-treatment of atmospheric pressure plasma spray (APPS). This study treated the surface shapes of oxide and non-oxide samples using a composite pre-treating method: cathode spots after grit blasting. In addition, the samples are compared with conventionally treated cathode spots and mechanical blasted surfaces. Results show that roughness on the sample surfaces becomes higher in concomitance with the initial oxide layer thickness. This fact reveals the factors those dominant bonding strength on the pre-treated surface using cathode spots of a low-pressure arc. Bonding strength becomes higher in relation to the arithmetical mean height of the surface roughness caused by the initial oxide layer thickness. Bonding strength is higher when the mean spacing of profile irregularities is narrower. The bonding adhesive strength after treatment using cathode spots after grit blasting is greater than 90 MPa. However, cathode spot treatment must be limited not to destroy the projection formed by melting after grit blasting in an arc time up to 5 s. And basically the removal characteristics of oxide layer using the cathode spots were discussed on the trace, roughness, number of cathode spots in time and pressure, moving speed on the metal surface, etc.     

Evidence from infrared ellipsometry for covalent bonding at a polymer/polymer interface with relevance to "lock-up" in pressure-sensitive adhesive laminates

In a novel application, infrared spectroscopic ellipsometry is used to provide clear evidence for the formation of a covalent bond at a polymer/polymer interface. Specifically, there is evidence for the formation of a Si-O-C bond resulting from a reaction between the silyl (SiH) group of a poly(hydrogen methyl siloxane) crosslinker used in poly(dimethyl siloxane) and the carboxylic acid group of poly(acrylic acid). This covalent bond formation could explain the source of the "lock-up" that is sometimes found between acrylic pressure-sensitive adhesives and a silicone-coated release liner.     

Improving the water resistance and adhesion strength of a mixed alkali silicate adhesive by optimizing the molar ratio and curing conditions

Abstract

It is important to eliminate the use of organic adhesives that are harmful to humans and cause environmental pollution. Environmentally friendly, harmless inorganic adhesives are being actively studied. Here, we found that optimized curing was possible when the curing time was controlled via temperature adjustment. We first prepared basic alkali silicate solutions, containing sodium, potassium, and lithium silicate, and compromised them in terms of water resistance. Adhesive strength was measured according to ASTM D3165 using a universal testing machine. The target material, a stainless steel (SUS) specimen, was prepared as described by ASTM D3165. Moreover, to develop fast thermal curing, the effects of two parameters were investigated: curing time and temperature. The temperature range tested was 80–140?°C for 2–36?h; we assessed adhesive strength. The maximum shear strength was obtained after thermal curing at 80?°C for 36?h, 120?°C for 12?h, and 140?°C for 2?h. However, when thermal curing proceeded past the maximum shear strength, the shear strength decreased, attributable to a reduction in the adherent area.