Shear behaviour of structural silicone adhesively bonded steel-glass orthogonal lap joints

This paper outlines an experimental study on the shear behaviour of structural silicone adhesively bonded steel-glass orthogonal lap joints. In the combination of steel plate and glass panel to form a hybrid structural glazing system, bonded joints with structural silicones can provide certain flexibility which relieves stress peaks at critical points of glass panel. The cohesive failure and its related fracture pattern of test joints with varied geometries of adhesives are examined experimentally. It is shown that the presence of two failure modes as discrete voids and macro cracks is closely related to the adhesive thickness. The effects of geometric parameters of adhesives on the joint shear strength are examined. It is demonstrated that the joint shear strengths are increased with increased individual overlap length, reduced adhesive thickness or increased adhesive width while the shear deformation corresponding to maximum shear force is mostly influenced by adhesive thickness. Mechanical contributions for those effects are analyzed accordingly. Finally, an analytical formula allowing for the equilibrium of strain and force on the adhesive and adherend is proposed for the analysis of shear strength. It is demonstrated that calculated normalized shear force ratios predicted by proposed formula agree well with those from experimental results.     

Shear creep behaviour of elastomeric adhesives

The shear creep behaviour of elastomeric adhesives has been investigated at various temperatures, loading stresses and adhesive thicknesses. Three adhesive types were included in the study: two polysulphides, one silicone and one polyurethane elastomer. The creep compliance of the two polysulphide adhesives could be described by an Arrhenius-type relationship incorporating time, temperature and stress. The silicone and polyurethane adhesives, on the other hand, showed an initial creep response followed by a long period of zero creep over the ranges of temperature and load studied.     

钢轨接头用结构胶粘剂的研制与应用

介绍了一种钢轨接头胶接用的结构胶粘剂的制备、性能以及应用情况。该胶可在温（１２０℃）,０．５h固化,具有优良的剪切强度和韧性以及良好的耐湿性、耐介质性能。该胶粘剂室温贮存期可达２a,适合铁路部门批量生产钢轨绝缘胶接接头。     

Mechanical analysis of structural adhesive for marine joints

A structural adhesive from I.C.R., X07 Extreme®, was fully characterised through tensile test, static and dynamic lap-shear strength test, cleavage peel test and DSC. Lap-shear tests were performed by using either aluminium, stainless steel and glass fibre reinforced polymer as substrate and after aging the specimen under extreme environmental conditions. The performance of this novel adhesive was compared to that of a structural adhesive of a competitor. The work summarises the typical procedures intended for the qualification of a structural adhesive for marine joints.     

An innovative approach to fatigue disbond propagation in adhesive joints

An innovative approach to characterize the resistance of adhesively bonded joints to fatigue disbond propagation (FDP) is presented. A constitutive equation, known as the modified crack layer (MCL) model, is employed to extract parameters characteristic of the adhesive joint's resistance to FDP. These parameters are γ', the specific energy of damage, which reflects the fatigue disbond resistance of the adhesive joint and the dissipative characteristic of the joints, β'. Stress-controlled tension-tension fatigue experiments were conducted on lap joints fabricated from aircraft grade aluminum 2024-T3 and 3M structural adhesive. The disbond length was measured periodically along the edges of the bonded area at the four corners and the corresponding number of cycles was recorded. This is in order to calculate the disbond growth rate. The hysteresis loop was also recorded for each measurement from which both the energy release rate, J*, and the change in work, W_i, were determined. It was found that the proposed model describes the behavior of the adhesively bonded joints over the entire range of the energy release rate. Thus, the proposed model can provide a basis upon which the relationships between the microstructure and/or the processing conditions and the resistance of adhesively bonded joints to FDP can be constructed. Such relationships can guide the development of adhesively bonded joints with superior resistance to debonding and should aid in their lifetime assessment.     

Physical behaviour of oil shale at various temperatures and compressive loads: 2. Thermal expansion under various loads

The thermal expansion of oil shale for various applied compressive loads, grades and orientations of the bedding plane to the applied load have been measured. It was determined that increasing the compressive load decreases the maximum expansion. Under loads <4.827 MPa the expansions of oil shale specimens with perpendicular and parallel orientations increased with grade. Under loads of 0.345–4.827 MPa increasing the grade decreased the expansion of 45 ° orientated specimens.     

汽车用半结构胶的研制

介绍采用聚氨酯改性环氧树脂制备半结构胶的方法,性能及应用情况。重点讨论聚氨酯改性环氧树脂的合成及半结构胶各组份对性能的影响,ＣＡ—３、ＣＡ—４两种型号的半结构胶已在“依维柯”等车型上应用。     

Behavioural analysis of adhesive-bonded structural joints in space vehicles

In space structures, the design of adhesive-bonded joints generally involves a very low safety ratio as opposed to a high one, indicating reliability. This requires careful choice of the criteria applied to account for external factors (mechanical, static and dynamic, and thermal effects). The situation is complicated by the behaviour of the materials involved, particularly composites, which undergo large distortions and whose fracture criteria depend on load cycles. In addition, polymerization effects in joints between different material,, such as metals and composites, must also be taken into account. In this paper a calculation tool is presented for bonded structures, and procedures for the accurate determination of the mechanical properties of adhesive materials are given.     

有机硅压敏胶的合成与性能

以硅橡胶和MQ硅树脂为原料,通过羟基缩合反应制备了有机硅压敏胶。用FT—IR和GPC表征了其结构。讨论了硅橡胶和MO硅树脂的原料配比、硅橡胶的黏度、MQ硅树脂的分子质量等因素对压敏胶力学性能的影响：测定了压敏胶的初粘性、1800剥离强度和持粘性等性能。结果表明,用MQ硅树脂与运动黏度为100×10^-4m^2／s的硅橡胶在质量比为2：3时,可得到具有良好粘接性能的有机硅压敏胶。     

Dynamic compressive behavior of basalt fiber reinforced concrete after exposure to elevated temperatures

This paper investigated the dynamic behavior of basalt fiber reinforced concrete (BFRC) after elevated temperatures by using a 100‐mm‐diameter split Hopkinson pressure bar apparatus. Changes in weight and ultrasonic pulse velocity (UPV) were also studied. The results indicate that the weight losses of BFRC before cooling increase with temperature, while a reduction in weight loss value is observed after water cooling. The UPV values of BFRC decrease constantly as temperature increases, and the measured velocities under the same temperature increase with fiber content as temperature exceeds 200 °C. For a given temperature, the strain rate, dynamic strength, critical strain, and impact toughness of BFRC increase with impact velocity. For a given impact velocity, the increasing temperature generally leads to an increase in strain rate and critical strain and results in a decrease in dynamic strength and impact toughness except in the case of 200 °C. At 200 °C, however, a marginal reduction, even an improvement in dynamic strength is observed, and the impact toughness initially decreases, then increases with loading rate when compared with that at room temperature. Basalt fiber is effective in improving the strength performance, deformation capacity, and energy absorption property of concrete after high temperature. Copyright © 2015 John Wiley & Sons, Ltd.     

Failure behavior of adhesively bonded joints with a rubber modified epoxy adhesive under tensile-shear combined cyclic loading

Rubber-modified epoxy adhesives are used widely as structural adhesive owing to their properties of high fracture toughness. In many cases, these adhesively bonded joints are exposed to cyclic loading. Generally, the rubber modification decreases the static and fatigue strength of bulk adhesive without flaw. Hence, it is necessary to investigate the effect of rubber-modification on the fatigue strength of adhesively bonded joints, where industrial adhesively bonded joints usually have combined stress condition of normal and shear stresses in the adhesive layer. Therefore, it is necessary to investigate the effect of rubber-modification on the fatigue strength under combined cyclic stress conditions. Adhesively bonded butt and scarf joints provide considerably uniform normal and shear stresses in the adhesive layer except in the vicinity of the free end, where normal to shear stress ratio of these joints can cover the stress combination ratio in the adhesive layers of most adhesively bonded joints in industrial applications.

In this study, to investigate the effect of rubber modification on fatigue strength with various combined stress conditions in the adhesive layers, fatigue tests were conducted for adhesively bonded butt and scarf joints bonded with rubber modified and unmodified epoxy adhesives, wherein damage evolution in the adhesive layer was evaluated by monitoring strain the adhesive layer and the stress triaxiality parameter was used for evaluating combined stress conditions in the adhesive layer. The main experimental results are as follows: S–N characteristics of these joints showed that the maximum principal stress at the endurance limit indicated nearly constant values independent of combined stress conditions, furthermore the maximum principal stress at the endurance limit for the unmodified adhesive were nearly equal to that for the rubber modified adhesive. From the damage evolution behavior, it was observed that the initiation of the damage evolution shifted to early stage of the fatigue life with decreasing stress triaxiality in the adhesive layer, and the rubber modification accelerated the damage evolution under low stress triaxiality conditions in the adhesive layer.     

Effect of moisture on pure mode I and II fracture behaviour of composite bonded joints

The effect of moisture on the fracture properties of composite bonded joints under pure mode I and pure mode II was analysed in this work. The double cantilever beam and end notched flexure tests were used for mode I and mode II fracture characterisation, respectively. Three different moisture conditions (55% and 75% of relative humidity (RH) and immersion in distilled water (IW)) were tested to assess its influence on the fracture behaviour under both pure loading modes. It was verified that fracture energy is drastically affected for the immersion in water in both loading modes. A cohesive zone model was also used to estimate the influence of RH on the cohesive parameters defining the law that mimics accurately the fracture process for each case. It was concluded that alterations on the cohesive laws reflect an increase of material brittle behaviour with the increase of the moisture uptake.     

Modelling damage and creep crack growth in structural ceramics at ultra-high temperatures

A continuum damage model based on multiaxial ductility exhaustion of accumulated creep strains is proposed to predict creep crack growth (CCG) in structural ceramics at ultra-high temperatures where it is known that power law creep operates. The paper focuses on monolithic ZrB₂ ultra-high temperature ceramic (UHTC), for which a reasonable set of material creep data is available. The predominant deformation mechanism shown by ZrB₂ at temperatures greater than 1800 K and at stresses above 200 MPa is power law creep. Using the creep constitutive properties that have been found for this material, the proposed methodology is applied to a representative three-point bend geometry, which is planned to be tested. Relevant Fracture Mechanics parameters such as stress intensity factor, K, and steady state creep parameter, C^*, are evaluated and compared with available models. In this way the essential properties required to develop predictive damage simulations are investigated, underlining the importance of having accurate material test data.     

Numerical study of the local behaviour of adhesive bonds under dynamic loading

Nowadays, adhesively bonded structures are widely used in the transport sector for the development of lightweight vehicles. In order to guarantee passenger safety, it is thus necessary to understand the behaviour of such assemblies under dynamic and combined loadings. This paper presents a numerical study of the local behaviour of adhesively bonded assemblies under dynamic loading. In the first part, the ASTM D950-03 block impact test is studied. This device does not enable a homogeneous loading of the adhesive and causes stress concentrations. On the basis of existing quasi-static works, strategies are then implemented at a local scale. By combining a specific substrate geometry and by limiting the stiffness gradient between the substrates and the adhesive, results show that it is possible to obtain a qualitatively acceptable stress fields in the adhesive for mechanical characterization under dynamic loadings. The Arcan TCS device mentioned below uses such solutions to characterize the mechanical behaviour of bonded joints subjected to combined quasi-static loadings. In this study, the question of its extensibility to dynamic loadings by the use of an impactor guided into a drop tower is investigated. A dedicated finite element model is built under the plane stress assumption. The stress distributions in the adhesive are analysed through time and space for several loading conditions. The stress versus time signals are then compared with the results coming from modal analysis in order to highlight the vibration behaviour of the device, directly linked to the configuration.     

胶粘剂特性和厚度对劈裂载荷作用下胶接接头应力分布的影响

运用三维弹塑性有限元法对劈裂栽荷作用下的胶接接头(即劈裂接头)承载后的应力分布特征进行了分析，重点研究了胶粘剂层厚度对劈裂接头应力分布的影响。结果表明，胶粘剂的性能对应力分布有较大影响，提高胶粘剂强度和减小胶层厚度，均导致胶层应力集中加剧，各向正应力峰值呈上升趋势，各向剪切应力则正好相反；并且劈裂接头中应力分布以三向主应力为主，剪切应力的存在亦不可忽略。故在不引起过大应力集中和较大胶层缺陷条件下采用高强度的胶粘荆和较厚胶层对提高劈裂接头强度有利，实验结果与有限元分析相吻合。     

Effect of heat-treatment on compressive response of 3D printed continuous carbon fiber reinforced composites under different loading directions

This paper investigated the effects of heat-treatment and loading directions on compressive properties of 3D printed continuous carbon fiber reinforced composites (CCFRC). After heat-treatment at different conditions, specimens with different stacking sequences were compressed under different loading directions. The effect of heat-treatment on the porosity and crystallinity of composites was investigated. The porosity of short carbon fiber reinforced composites decreased but that of CCFRC increased after heat-treatment at 200°C. The compressive properties of specimens were investigated in combination with changes in porosity and crystallinity. It was found that the compressive properties of composites usually increased with decreasing porosity induced by heat-treatment. While the fiber direction was parallel to the applied loading direction, the yield strength of C-CCFRC and S-CCFRC increased from 208.1 to 281.6 MPa and from 218.5 to 264.4 MPa, respectively, though the porosity increased. After heat-treatment at 100°C for 4 h, the crack initiation of CCFRCs was delayed during compressive tests. Besides, heat-treatment could change failure modes of CCFRC after heat-treatment at 200°C for 4 h. More specifically, heat-treatment at 200°C for 4 h could result in delamination and a decrease in energy absorption of C-CCFRC (from 7.23 to 4.05 J).     

Dynamic compressive response of zirconium diboride-silicon carbide composites at high-strain rates

The quasi-static, dynamic compression experiments and micromechanical model were employed to declare the dynamic compressive response of ZrB₂–20%SiC composite at high-strain rates. The quasi-static compressive strengths were measured to determine the range of initial microcrack length in ZrB₂–20%SiC composite. The effects of the strain rate on dynamic compressive strength, critical stain, as well as fracture mechanisms were discussed based on experimental results. Dynamic mechanical properties of ZrB₂-based composites display obvious strain rate dependence. The dynamic increase factor in the compressive strength shows a rapid increase above a transition strain rate of 1228 s⁻¹. Moreover, a micromechanical model considering initial microcrack lengths is used to predict dynamic compressive strengths, which agree with the experimental results. Additionally, the critical strain has a linear increase tendency with the increase of strain rate. The dynamic compressive fracture mechanism of ZrB₂–20%SiC composite is relative to the combination effect between strain rate and microstructure. The size of flaw distribution is critical below the transition strain rate resulting in bigger fragments, whereas the flaw density is primary with more and smaller fragments above the transition strain rate.     

Application of a new constant G load-jig to creep crack growth in adhesive joints

A novel constant energy release rate load-jig, capable of applying loads in the full range of mode mixes from pure mode I to pure mode II, was developed for studying creep crack growth in structural adhesive joints. Since the load-jig applies only pure bending moments to uniform double cantilever beam (DCB) specimens, the expressions for the energy release rate and mode ratio are both simple and accurate. The new load-jig was used to study mixed-mode creep crack growth in DCB specimens which had either an intact fillet or a steady-state failure zone. Both a rubber-toughened and a mineral-filled epoxy adhesive were tested at room temperature, which is far below the glass transition temperature for either structural adhesive. In all cases, crack speeds were observed to decelerate, indicating that the adhesive were self-toughening over time. In addition, crack growth was observed to propagate by the initiation and coalescence of microcracks, rather than by the continuous advancement of a crack tip.     

Dynamic mechanical behaviour of polyamide 11/Barium titanate ferroelectric composites

Dynamic mechanical analysis and tensile test have been used to characterize the mechanical behaviour of hybrid composites. Barium titanate (BaTiO₃) is the submicron filler and polyamide 11 (PA 11) the matrix. The influence of volume fraction and particles size (ranging from 100 nm to 700 nm) of the inorganic phase on the composites mechanical properties have been checked. BaTiO₃ dispersion in the matrix increases the tensile modulus of the composites and an evolution from ductile to fragile is observed for volume fractions above 12 vol%. The volume fraction dependence of the glassy shear modulus is well described by the Hashin and Shtrikman model indicative of an interaction lack between the organic and inorganic phases. The decrease of the glassy shear modulus with the filler size has been associated with the existence of softer organic/inorganic interfaces, in agreement with the previous hypothesis. The non linear variation of the rubbery modulus versus particles content is well described by the rubber elasticity model applied to a hydrogen bond network.     

Endurance of gel‐filled silicone breast implants as a function of maximum load in cyclic compression tests

The mechanical behaviour of gel‐filled silicone breast implants is examined under compressive load. First the implants are tested by applying various loads in a repetitive fashion until shell rupture occurs. Subsequently the results are presented allowing an assessment of the correlation between the number of loading cycles and the maximum compressive load. Finally it is possible to estimate the endurance of the silicone breast implants. Using a power law, a correlation between endurance and maximum load is revealed. © 2018 Society of Chemical Industry