Effect of autoclave cure time and bonded surface roughness on the static and fatigue performance of polyurethane film Adhesive Single lap joints

This study investigates the effect of autoclave cure time and bonded surface roughness on the static and fatigue performance of film-adhesive single lap joints. Joint static performance is assessed in terms of its load transfer capacity in a quasi-static tensile-shear test to failure. Effect on fatigue life under a mean and cyclic tensile-shear amplitude is also investigated. Two levels autoclave cure (soak) time and two levels of bond surface roughness are investigated. All other autoclaving process variables are kept constant; namely, the ramp rate of temperature rise/cooling, pressurization/depressurization, as well as the cure temperature and cure pressure levels. Test joints are made of aluminium-aluminium or aluminium-magnesium adherends, joined with a polyurethane film adhesive. The results suggest that: an increase of the surface roughness is beneficial to static strength and detrimental to fatigue strength; an increase of the autoclave soak (cure) time is beneficial both to static and fatigue strength. Test data, failure mode analysis, discussion, observations and conclusions are provided.     

Effect of temperature on the joint strength of a silyl-modified polymer-based adhesive

Temperature is a very important factor that must be fully considered in the study on the adhesive joint strength. In this paper, a silyl-modified polymer-based adhesive ISR 70-08 which is widely used in engineering was studied. Dog-bone specimens were fabricated and tested at ?40°C, room temperature (RT), and 90°C. Results show a decrease in the main mechanical properties with increasing temperature. Butt joints (BJs), single-lap joints (SLJs), and Scarf joints (SJs) were fabricated and tested at different temperatures. A quadratic polynomial expression was an ideal choice to express the joint strength as a function of temperature which was obtained using the least-squares method. Temperature combinations of ?40°C, 0°C, and 90°C were obtained to study the effect of temperature on the joint strength more easily for this adhesive. A three-dimensional surface, consisting of temperature, adhesive angle, and joint strength was presented to facilitate the application of bonding structures in engineering     

书籍装订用单组分聚氨酯热熔胶的研究

介绍了一种制备书籍装订用聚氨酯热熔胶粘剂的方法。考察了合成聚氨酯预聚物的最佳工艺条件及原料配比;然后进行配方复配。结果表明:最佳配方所得产品性能完全达到国家对书本装订高速胶的要求,并显示出优良的弹性和韧性。该产品生产工艺简单,成本低廉,可操作性强。用于书籍装订生产既可弥补EVA型胶的缺陷又不会提高生产成本,可为生产和使用厂家带来可观的经济效益。     

聚氨酯衬层表面特性的研究方法探讨

综述了接触角法(CA)、衰减全反射/傅里叶变换红外光谱法(ATR/FT-IR)、X射线光电子能谱法(XPS)等几种表面分析技术的特点和应用领域,结合聚氨酯(PU)衬层的特点,提出了适用于表征PU衬层表面特性的一些方法。     

Effect of hole drilling at the overlap on the strength of single-lap joints

Bonded unions are gaining importance in many fields of manufacturing owing to a significant number of advantages to the traditional fastening, riveting, bolting and welding techniques. Between the available bonding configurations, the single-lap joint is the most commonly used and studied by the scientific community due to its simplicity, although it endures significant bending due to the non-collinear load path, which negatively affects its load bearing capabilities. The use of material or geometric changes in single-lap joints is widely documented in the literature to reduce this handicap, acting by reduction of peel and shear peak stresses at the damage initiation sites in structures or alterations of the failure mechanism emerging from local modifications. In this work, the effect of hole drilling at the overlap on the strength of single-lap joints was analyzed experimentally with two main purposes: (1) to check whether or not the anchorage effect of the adhesive within the holes is more preponderant than the stress concentrations near the holes, arising from the sharp edges, and modification of the joints straining behaviour (strength improvement or reduction, respectively) and (2) picturing a real scenario on which the components to be bonded are modified by some external factor (e.g. retrofitting of decaying/old-fashioned fastened unions). Tests were made with two adhesives (a brittle and a ductile one) varying the adherend thickness and the number, layout and diameter of the holes. Experimental testing showed that the joints strength never increases from the un-modified condition, showing a varying degree of weakening, depending on the selected adhesive and hole drilling configuration.     

The effect of cataphoretic and powder coatings on the strength and failure modes of EN AW-5754 aluminium alloy adhesive joints

The aim of this study is to determine the effect of cataphoretic and powder coatings and also the method of application the primer on the adherends surface on the strength and failure modes of EN AW-5754 aluminium alloy adhesive joints. The study is performed on lap joints made of EN AW-5754 aluminium alloy, subjected to three different types of surface treatment; namely a) polyurethane cataphoretic coating, b) powder coating based on black mat RAL 9005 UL polyester resin and c) no coating. The tested adhesive joints were made using a one-component polyurethane adhesive Terostat 8596, which was dedicated for automotive and cured under a constant load of 0.018 MPa at 20 ± 2 °C. In addition, this study investigates the effect of the application of Terostat 8519P adhesion promoter which is a liquid polyurethane-based primer containing solvents and which is corresponding to Terostat 8596 polyurethane adhesive. Terostat 8519P adhesion promoter was applied in two different ways: a) to one substrate and b) to both substrates. The produced adhesive joints were subjected to strength tests using the Zwick/Roell Z150 testing machine. The examination of fracture in the tested adhesive joints was performed in accordance with the EN ISO 10365 standard. The shear strength results have demonstrated that both the method of application of the adhesion promoter (Terostat 8519 P) and the presence of cataphoretic coating had an influence on adhesive joints strength. The use of the adhesion promoter significantly affects the strength of both uncoated EN AW-5754 aluminium alloy adhesive joints and the adhesive joints subjected to powder coating. The use of the adhesion promoter has a less significant effect on the cataphoretic-coated samples.     

Effects of applied pressure and temperature during curing operation on the strength of tubular single-lap adhesive joints

Adhesive joints have been widely used for fastening thin adherends because they can distribute the load over a larger area than the mechanical joint, require no holes, add very little weight to the structure and have superior fatigue resistance. However, the load capabilities of adhesive joints are affected by both applied pressure and temperature during cure, as well as by service environments because the adhesion characteristics of adhesives are very sensitive to manufacturing and environmental conditions. In this study, the tensile load capabilities of tubular single-lap adhesive joints with an epoxy adhesive were experimentally investigated with respect to service temperature and the applied pressure and temperature during curing operation. The effects of the applied pressure on the tensile load capabilities of tubular single-lap adhesive joints were studied by measuring the actual cure finish temperature using thermocouples and dielectrometry. From the experiments, it was found that the actual cure finish temperature of tubular single-lap adhesive joints increased as applied pressure increased, which increased residual thermal stress in the adhesive layer to decrease the load capabilities of adhesive joints. From finite element analysis and experimental results of tubular singlelap adhesive joints, the optimal geometry condition for adhesive joints was also investigated.     

Effect of heat treatment temperature and surface roughness to the PDMS-FR4 adhesive bonding

The current work investigates the use of liquid polydimethylsiloxane (PDMS), with a 10:1 ratio of prepolymer:curing agent?=?10:1 as the intermediate layer for adhesive bonding with Flame Retardant 4 (FR4). The spin coating of liquid PDMS on FR4 allows irreversible adhesive bonding with the solid PDMS. The strength of the proposed adhesive bonding technique has been investigated under different treatment temperatures: oven-heated at 60?°C, 70?°C, and 80?°C, cooled down in the room temperature of 25?°C, and exposed to direct sunlight at 35?°C. All the samples were left for 6?h. Investigations were conducted to analyze the effect of FR4 surface roughness on the strength and quality of the adhesive bonding. The standard procedure of American Standard Test Measurement (ASTM) D1002 was followed to verify the strength of PDMS-FR4 adhesive bonding. Strongest adhesive bonding, free from air bubbles, was obtained from a sample with smooth surface of FR4 that has undergone a cooling down treatment in the room temperature of 25?°C. FR4 was coated by solder mask to obtain smooth surface. The techniques reported in this paper are simple, straightforward, and effective to be implemented with FR4 as a base material for adhesive bonding with PDMS, thus eliminating expensive and complicated operating equipment as widely used in the oxygen plasma-assisted bonding treatment. Another benefit from this adhesive bonding technique is the fact that it avoids the use of expensive oven or hot plate.     

The effect of primers on adhesive properties and strength of adhesive joints made with polyurethane adhesives

The paper presents selected aspects of the effect of primers on adhesive properties and strength of aluminium sheet adhesive joints, made using polyurethane adhesives. The strength of adhesive joints was determined based on two cure time variants: 15 and 64 h. It was found that the longer cure time at a humidity of 33% is more desired, as it leads to a substantial increase in strength of the tested adhesive joints. In addition, two variants of surface preparation were applied: degreasing and degreasing followed by the application of a primer (a pro-adhesive agent). It was observed that the primer application prior to the application of an adhesive leads to a significant increase in strength compared to the variant where the adhesive application is preceded only by degreasing. Moreover, the aluminium sheet surface that was subjected to cataphoretic painting and priming exhibits better adhesive properties. It has a higher value of both surface free energy and its dispersion and polar components compared to the surface that was only subjected to degreasing.     

Surface roughness effects on the stress analysis of adhesive joints

A finite element program was used to perform a parametric analysis of stresses generated by adherend surface roughness in lap and butt joints. Roughness asperities were idealized as having tip radius of curvature R1, height H1, and slopes A1. Failure criteria (maximum stress, yield, and fracture) were related to the geometric parameters by functions of the form: $\text{σ = σ}{}_{\mathrm{o}}\text{+ cR}{}^{\mathrm{r}}\text{H}{}^{\mathrm{h}}\text{A}{}^{\mathrm{a}}$The specific material properties used for the analysis were those of tooth enamel and an orthodontic cement. Qualitatively however, these results are applicable to all structural adhesives.     

Evaluation of mechanical and laser surface pre-treatments on the strength of adhesive bonded steel joints for the automotive industry

Recent research efforts in the automotive industry have been focused on the integration of high-strength steels within lightweight vehicles by using improved joining techniques. The present work falls in this subject area and is focused on the analysis of adhesive bonded dual-phase steel/epoxy joints for the automotive industry. Two quasi-static loadcases were considered, i.e. single-lap and T-peel tests, and various surface preparation strategies were evaluated. In particular, the mating surfaces were pre-treated by using pulsed laser irradiation with a fiber laser (1064 nm) and comparisons were made with degreasing and sand blasting. Moreover, the effects of bondline thickness and adhesive type were also assessed. To this aim, two epoxy adhesives with fairly different mechanical behavior (i.e. strain hardening versus elasto-plastic) were deployed for joints fabrication. Finally, T-peel tests were also carried out after sample cycling under controlled high humidity and temperature (i.e. accelerated aging). The obtained results highlighted the beneficial effect of laser irradiation on the joints’ mechanical behavior under both static and hydrothermal loadings.     

Effect of surface pre-treatment on surface characteristics and adhesive bond strength of aluminium alloy

In this work aluminium alloy surfaces have been subjected to three different methods of surface pre-treatments such as solvent degreasing, FPL (Forest Products Laboratory) etching and priming using an epoxy based primer. The treated surfaces were evaluated for surface energy, contact angle, surface topography, surface roughness and adhesive strength characteristics. The influence of surface pre-treatments on the variation of polar, dispersive and total surface energy of the surfaces is addressed. A wettability test was performed on the surfaces using an epoxy adhesive in order to assess the influence of the pre-treatment techniques on substrate/adhesive interaction. Theoretical work of adhesion values for the various pre-treated surfaces were calculated using the contact angle data and further tested experimentally by adhesive bond strength evaluation by tensile testing of a single lap aluminium-epoxy-aluminium assembly. The method of surface pre-treatment showed a profound effect on the surface topography and roughness by AFM. This study reveals that a combination of high surface energy and high surface roughness of the substrate along with good wettability of the adhesive contributed to the highest joint strength for the aluminium alloy through the FPL etching pre-treatment.     

Validation of pure tensile and shear cohesive laws obtained by the direct method with single-lap joints

Joining with structural adhesives in the aeronautical industry dates back to some decades, although only more recently this technique has been implemented to load bearing parts in other industries. This technique enables joining steel with aluminium or fibre-reinforced composites, with a major weight advantage. Cohesive Zone Models (CZM) are an accurate design method for bonded structures but, depending on the adhesive type and specimen's geometry, the accuracy of the strength predictions may be highly compromised by the choice of the cohesive laws. This work presents a validation of tensile and shear CZM laws of three adhesives obtained by the direct method applied to Double-Cantilever Beam (DCB) and End-Notched Flexure (ENF) tests, respectively. The validation is carried out by considering a mixed-mode bonded geometry (the single-lap joint) with different overlap lengths (L_O) and adhesives of distinct ductility. Initially, the precise shape of the cohesive law in tension and shear of the adhesives is estimated, followed by their simplification to parameterized triangular, trapezoidal and linear-exponential CZM laws. Validation of the CZM laws was accomplished by direct comparison of the load-displacement (P-δ) curves and maximum load (P_m) of the single-lap joints as a function of the tested L_O values. The strength predictions were accurate for a CZM law shape consistent with the adhesive type, although the differences between CZM shapes were not too significant.     

Evaluation of different modelling conditions in the cohesive zone analysis of single-lap bonded joints

Cohesive Zone Models (CZM) are widely used for the strength prediction of adhesive joints. Different simulation conditions, such as damage initiation and growth criteria, are available for use in CZM analyses to provide the mixed-mode behaviour. Thus, it is highly relevant to understand in detail their influence on the simulations’ outcome. This work studies the influence of different conditions used in CZM simulations to model a thin adhesive layer in single-lap joints (SLJ) under a tensile loading, for an estimation of their influence on the strength prediction under diverse geometrical and material conditions. Validation with experimental data is considered. Adhesives ranging from brittle to highly ductile and overlap lengths (L_O) between 12.5 and 50 mm were considered. Different studies were considered: Variation of the elastic stiffness of the cohesive laws, different mesh refinements, study of the element type, and evaluation of several damage initiation and growth criteria. The analysis carried out in this work confirmed the known suitability of CZM for static strength prediction of bonded joints and pointed out the best set of numerical conditions for this purpose. Inaccurate results can be obtained if the choice of the modelling conditions is not the most suitable for the problem.     

固化工艺对HT1012铜粉导电胶剪切强度的影响

研究了固化工艺参数对由HT1012型铜粉导电胶制备的单搭接接头剪切强度的影响。结果表明，在所采取的研究条件下，随着晾置时间的推移，导电胶剪切强度起初增加但随后减小；当固化温度为60℃、晾置时间取定为10min时，固化时间为3h所对应的剪切强度较高；当变动固化温度时，固化温度提高会引起剪切强度下降。     

Effect of surface roughness on methane hydrate formation and its implications in nucleation design

As a new form of energy with substantial potential, natural gas hydrate will play a crucial strategic role in the future due to its vast reserves and broad industrial application prospects. To better comprehend the nucleation and growth mechanism of clathrate hydrate, an enhanced thermodynamic model was proposed based on the wall roughness model and nucleation theory. In general, we discovered that the nucleation of hydrate on a smooth wall surface conforms to the conclusion of classical nucleation theory. However, curvature and surface roughness are frequently characterized by hydrophilicity's inhibition of hydrate and hydrophobicity's enhancement. The specific situation is more complex and requires specific analysis and discussion. Nonetheless, this also explains the uneven distribution of hydrate nucleation induction time. Our research reveals a fundamental method for designing or manipulating the heterogeneous nucleation of hydrates. We foresee promising applications in hydrate-related technologies based on the fractal structure of the substrate's surface.     

Effect of femtosecond laser beam angle and formed shape on surface roughness and shear bond strength between zirconia and resin cement

Achieving adhesion between resin cement and zirconia requires pretreatment of the surface. This in vitro study aimed to evaluate the effect of femtosecond laser beam angle and the shape of the formed surfaces, on the roughness and shear bond strength (SBS) of resin cement to zirconia ceramic. Seventy Y-TZP ceramic specimens were divided into seven groups (n = 10). A femtosecond laser irradiation was performed on the ceramic surface of three shapes (spiral (SP), square (SQ) and circular (CI) and at two angles (30 and 90°) to give SP-30, SQ-30 and CI-30 and SP-90, SQ-90 and CI-90, respectively. After treatment, the surface roughness of all specimens was evaluated using a profilometer. One specimen from each group was analysed using a scanning electron microscope. The bonded specimens were thermocycled 5000 times and then an SBS test was performed. Kruskal-Wallis and Mann-Whitney U tests were used to analyse surface roughness and SBS values. The control group had statistically lower surface roughness (R_a) values than the treated groups (p < 0.05). SP-30 and SQ-30 laser treated specimens showed higher R_a values than the other specimens. Statistically significant SBS values (p = 0.000) were observed between the groups. All laser treated samples showed greater SBS compared to the control group. SP-30, SQ-30 and SQ-90 groups showed the highest SBS values. Within the limitations of this experimental study, the highest mean values for R_a and SBS were achieved with SP and SQ surfaces using a 30° angle laser beam.     

表面粗糙度对镍镀层结合性能的影响

对玻璃基双层镍表面进行阳极活化以提高镍层之间的结合强度。阳极活化液组成和工艺条件为:NiCl2·6H2O 100 g/L,H3BO3 25 g/L,pH 4.0,温度45°C,阳极电流密度10~30 mA/cm2,时间5~15 min。研究了电流密度和处理时间对镍镀层表面形貌、孤岛结合力、表面粗糙度和界面结合强度的影响,探讨了双层镍表面粗糙度和界面结合强度的关系。结果表明,在30 mA/cm2下阳极活化10 min后,双层镍的界面结合强度为629.8 MPa,比盐酸活化试样高了近2倍。镍层表面粗糙度与界面结合强度之间有明显的对应关系,表面粗糙度越大,界面结合强度越高。采用阳极活化法可有效提高微机电系统微器件的可靠性。     

油墨行业用聚氨酯胶粘剂的研究

以聚酯二元醇和二苯甲烷二异氰酸酯 (MDI)为主要原料 ,制成了油墨用聚氨酯树脂 ,其外观为无色透明颗粒 ,软化点为 110～ 130℃ ,邵氏A硬度为 75～ 85 ,拉伸强度≥ 30MPa ,伸长率≥ 5 0 0 % ,用丁酮 (MEK)和环己酮为溶剂 ,配成固含量为 (15± 1) %的聚氨酯胶液 ,可满足油墨、复合膜等行业的需要 ,研究了多元醇分子质量、酸值 ,异氰酸酯指数及扩链剂用量等对PU胶性能的影响。     

Effect of alloy composition and surface pretreatment on the durability of adhesive-bonded aluminium alloy joints

Boeing wedge test data which indicate the influences of six surface pretreatments and four alloy compositions on the durability of adhesively bonded joints are reported. X-ray photoelectron spectroscopy data which indicate the effects of the same surface pretreatments and alloy compositions on the chemical compositions of the adherend surfaces are summarized. Possible correlations between the durability and X PS data are discussed. Three different methods of modifying the chromic acid anodize (Def 151) treatment of clad alloy adherends, in order to improve durability, are described and discussed.