Optimal vibration attenuation of an adhesively-bonded cantilevered single-lap joint

In this study the three-dimensional transient vibration attenuation of an adhesively-bonded cantilevered single-lap joint was controlled using actuators. First, the vibration attenuation of the adhesive joint, which was disturbed by applying a concentrated load to the free edge of the lower adherend, was determined without a control force. In order to reduce displacement level and vibration attenuation time, a variable transverse control force was applied to a point on the lower adherend surface using an actuator. The transient variation of the control force was expressed by a periodic function so that the damped vibration of the adhesive joint was decreased. The optimal transient variation of the control force applied by the actuator is an optimization problem requiring the minimization of the objective function including the total elastic strain and kinetic energies, and the actuator work. In addition, the optimum placement of the actuator on the surface of the lower adherend is the second optimization problem. Optimal transient control force history and optimal actuator position were determined using the Open Loop Control Approach and Genetic Algorithm. The peak displacement reduced by 69.6% and the attenuation time decreased by 33%. In addition, the control performance of two actuators was investigated. Thus, the first actuator was located at the optimal position of a single actuator case, and then the optimal transient variations of the control forces applied by both actuators and the optimal position of the second actuator were determined. An additional decrease of 30% in the total energy of the adhesive joint and in the total work of both actuators in comparison to the single actuator case was found, whereas the difference in the vibration attenuation time of the adhesive joint was minor.     

Effect of Adhesive Thickness on Transverse Low-Speed Impact Behavior of Adhesively Bonded Similar and Dissimilar Clamped Plates

This study investigates the effect of adhesive thickness on the transverse low-speed impact behavior of adhesively bonded similar (Al–Al, St–St) and dissimilar (Al–St, St–Al) clamped plates using the three-dimensional explicit finite element method. The contact force and plastic dissipation histories are studied for various impact energies and adhesive thicknesses. The residual plastic strains in both adhesive layer and the two plates increase with increasing impact energy. The central transverse deflections become maximal in Al–Al, moderate in Al–St, St–Al and minimal in St–St bonded plates. The back plates of all configurations deform noticeably. The stiff steel plate results in a shorter contact time, a higher contact force, a lower plastic dissipation energy and the impact energy is absorbed by the adhesive layer rather than by the front and back plates, whereas Al–Al plates dissipate it as much as the adhesive layer. The total contact time gets longer with increasing impact energy. St–St bonded plates experience larger damaged regions in both plates and adhesive layer than those in Al–Al bonded plates. The adhesive thickness has only a minor effect on the magnitude of the contact force and contact time, whereas a stiffer (St) front or back plate affects considerably the contact force and total contact time. Increasing the adhesive thickness decreases apparently residual plastic strains in plates and the adhesive layer, the central transverse deflection. A thick adhesive layer results in a minor increase in the kinetic energy of impactor, a shorter total contact time, a lower plastic dissipation energy and smaller damaged areas on the back faces of the lower plate, along the adhesive–plate interfaces.     

Free Vibration Analysis and Design of an Adhesively Bonded Corner Joint with Double Support

This study carries out the three dimensional free vibration analysis of an adhesively bonded corner joint and investigates the effect of an additional horizontal support to the adhesive corner joint with single support on the first ten natural frequencies and mode shapes. In the presence of a horizontal support the effects of the vertical support length, the adhesive thickness, the plate thickness, and the joint length on the natural frequencies and modal strain energies of the adhesive joint were also investigated using the back-propagation Artificial Neural Network (ANN) method and the finite element method. The natural frequencies and modal strain energies increased with increasing plate thickness, whereas an adverse effect was observed for increasing joint length. Both horizontal and vertical support lengths exhibited similar effects but the adhesive thickness had a negligible effect. The plate thickness and the joint length are dominant geometrical parameters in comparison with both horizontal and vertical support lengths. The proposed ANN models were combined with the Genetic Algorithm in order to determine the optimal corner joint in which the maximum natural frequency and minimum elastic modal strain energy are achieved for each natural frequency and mode shape of the adhesive corner joint and the optimal dimensions were given versus one geometrical parameter.     

Free Vibration Analysis and Design of an Adhesively Bonded Corner Joint with Double Support

This study carries out the three dimensional free vibration analysis of an adhesively bonded corner joint and investigates the effect of an additional horizontal support to the adhesive corner joint with single support on the first ten natural frequencies and mode shapes. In the presence of a horizontal support the effects of the vertical support length, the adhesive thickness, the plate thickness, and the joint length on the natural frequencies and modal strain energies of the adhesive joint were also investigated using the back-propagation Artificial Neural Network (ANN) method and the finite element method. The natural frequencies and modal strain energies increased with increasing plate thickness, whereas an adverse effect was observed for increasing joint length. Both horizontal and vertical support lengths exhibited similar effects but the adhesive thickness had a negligible effect. The plate thickness and the joint length are dominant geometrical parameters in comparison with both horizontal and vertical support lengths. The proposed ANN models were combined with the Genetic Algorithm in order to determine the optimal corner joint in which the maximum natural frequency and minimum elastic modal strain energy are achieved for each natural frequency and mode shape of the adhesive corner joint and the optimal dimensions were given versus one geometrical parameter.     

Transverse Low-Speed Impact Behavior of Adhesively Bonded Similar and Dissimilar Clamped Plates

This study concentrates on the transverse low-speed impact behavior of adhesively bonded similar and dissimilar clamped plates using the three-dimensional explicit finite element method. The contact force and plastic dissipation histories of the adhesively bonded dissimilar plates, such as aluminum–aluminum (Al–Al), aluminum–steel (Al–St), steel–aluminum (St–Al) and steel–steel (St–St) layered structures, were studied for different values of the impactor mass, radius and velocity (impact energies). The residual plastic strains in both adhesive layer and plates increased with increasing impact energies. The impactor radius had only a minor effect on the contact force histories for all configurations. The peak transverse deflection in the impact region was maximal in Al–Al, decreased in Al–St, St–Al plates and became minimal in St–St bonded plates. Impact effect was evident in the back plates of all four configurations. Al–Al plates dissipated impact energy as much as the adhesive layer, whereas the adhesive layer rather than plates absorbed the impact energy in Al–St, St–Al and St–St bonded plates and this state became evident in the St–St bonded plates. The number and locations of the steel plates considerably affected impact force history, impact time as well as the plastic dissipation level; thus, the contact force increased, the contact time shortened and the dissipated energy decreased. As the impact energy was increased the impact period got longer. Damage areas in the adhesive layer were minimal in Al–Al bonded plates but maximal in St–St bonded plates.     

Free vibration analysis of an adhesively bonded functionally graded double containment cantilever joint

In this study, Genetic Algorithms (GAs) combined with the proposed neural networks were implemented to the free vibration analysis of an adhesively bonded double containment cantilever joint with a functionally graded plate. The proposed neural networks were trained and tested based on a limited number of data including the natural frequencies and modal strain energies calculated using the finite element method. GA evaluates a value generated iteratively by an objective function and this value is calculated by the finite element method. The iteration process restricts us apparently to use directly the finite element method in our multi-objective optimisation problem in which the natural frequency is maximised and the corresponding modal strain energy is minimised. The proposed neural networks were used accurately to predict the natural frequencies and modal strain energies instead of calculating directly them by using the finite element method. Consequently, the computation time and efforts were reduced considerably. The adhesive joint was observed to tend vertical bending modes and torsional modes. Therefore, the multi-objective optimisation problem was limited to only the first mode which appeared as a bending mode. The effects of the geometrical dimensions and the material composition variation through the plate thickness were investigated. As the material composition of the horizontal plate becomes ceramic rich, both natural frequency and modal strain energy of the adhesive joint increased regularly. The plate length and plate thickness were more effective geometrical design parameters whereas the support length and thickness were less effective. However, the adhesive thickness had a small effect on the optimal design of the adhesive joint as far as the natural frequencies and modal strain energies are concerned. The distributions of optimal solutions were also presented for the adhesive joints with fundamental joint lengths and material compositions in reference to their natural frequencies and corresponding modal strain energies.     

Optimal design of an adhesively-bonded corner joint with single support based on the free vibration analysis

This study investigates the three-dimensional free vibration behaviour of an adhesively-bonded corner joint with single support. The modulus of elasticity, Poisson's ratio and density of adhesive were found to have negligible effects on the first 10 natural frequencies and mode shapes of the corner joint. The effects of the geometrical parameters, such as support length, plate thickness, adhesive thickness and joint length, on the natural frequencies, mode shapes and modal strain energies of the adhesive joint were also investigated using both the finite element method and the back-propagation artificial neural network (ANN) method. The free vibration and stress analyses were carried out for the corner joints with various random geometrical parameters so that a suitable ANN model could be trained successfully. The support length, plate thickness and joint length all played important roles in the natural frequencies, mode shapes and modal strain energies of the corner joint, whereas the adhesive thickness for the range of adhesive thickness studied had only a minor effect. The Genetic Algorithm was also combined with the present ANN models in order to determine the optimum geometrical dimensions which satisfied the maximum natural frequency and minimum modal strain energy conditions for each natural frequency and mode shape of the adhesively-bonded corner joint.     

Geometrically non-linear analysis of an adhesively bonded modified double containment corner joint — I

In this study, the geometrically non-linear analysis of an adhesively modified double containment corner joint was carried out using the incremental finite element method based on the small strain-large displacement (SSLD) theory. The plates, support, and adhesive layers were assumed to have linear elastic properties. The joint was analysed for two different loading conditions: one normal loading to the horizontal plate plane P _y and one horizontal loading at the horizontal plate free edge P _x . In addition, the small strain-small displacement (SSSD) analysis of this adhesive joint was also carried out in order to compare the capability of the two theories in predicting the effect of large displacements on the stress and deformation states of the joint members. Both analyses showed that stress and strain concentrations occurred around the adhesive free ends, corresponding to the vertical and horizontal slot free ends, and along the outer fibres of the horizontal and vertical plates. The peak stresses appeared at the slot corners inside the adhesive fillets and at the horizontal and vertical plate outer fibres corresponding to the two slot free ends. The variations of the Von Mises stresses at these critical adhesive and plate locations were evaluated versus increasing loads. The SSLD theory predicted an evident non-linear effect, as a result of the large displacements, on the stress variations for the loading P _x , whereas this non-linear effect disappeared on the stresses for the loading P _y ; thus, the stresses presented very close variations to those obtained by the SSSD theory. However, the SSSD theory predicted a lower stress variation proportional to the increasing load for both loading conditions. In the case of the loading P _y , the right vertical adhesive fillet and both plates appeared as the most critical joint regions, whereas the lower horizontal fillet and both plates were determined as the most critical regions for the loading P _x . The behaviour of all joint members towards the applied load is strictly dependent on the boundary and loading conditions. Finally, the SSSD theory may be misleading in the prediction of the stress and deformations, but the SSLD theory includes the non-linear effect of the large displacements and rotations and gives more realistic results, although it requires more computational effort. In addition, it was observed that the geometrical parameters, such as the support length, vertical support length, and vertical slot depth, had a considerable effect on the peak adhesive and plate stresses, depending on the loading condition.     

Glass/epoxy composites and aluminium alloy joint using Kevlar® intermediate layer and nanoclay-reinforced epoxy adhesive

Adhesive lap joint between glass fibre/epoxy composites and aluminium alloy (2014 T4) was prepared by an in situ moulding process using a matched die mould. The surface of aluminium alloy was treated with chromic acid before adhesive bonding. Lap shear strength and fatigue life were evaluated in tensile mode and tension–compression mode (at 40% of lap shear load of adhesive joint), respectively. Knurling on the surface of aluminium alloy improved the lap shear strength of the adhesive joint but did not influence the fatigue life of the same. Lap shear strength and fatigue life of adhesive joint made with neat epoxy adhesive and reinforcement of an intermediate layer of Kevlar^® between glass/epoxy composite and aluminium alloy were observed to be 0.44?kg/mm² and 3.6?×?10⁵ cycles, respectively. In another case, lap shear strength and fatigue life of similar type of adhesive joint made from nanoclay (Cloisite 30B)-reinforced epoxy adhesive and without reinforcement of an intermediate layer of Kevlar^® were observed to be 0.38?kg/mm² and 2.3?×?10⁵ cycles, respectively. Whereas, lap shear strength and fatigue life of adhesive joint made from nanoclay-reinforced epoxy adhesive along with the reinforcement of an intermediate layer of Kevlar^® were 0.48?kg/mm² and 3.9?×?10⁵ cycles, respectively. Therefore, adhesive joint made from nanoclay-reinforced epoxy adhesive along with the reinforcement of an intermediate layer of Kevlar^® was the best.     

Evaluation of high-performance pressure-sensitive adhesives and VHB™ acrylic foam tapes bonded aluminum joints subjected to environmental aging

A range of 3M^? high performance pressure-sensitive adhesives (PSAs) and 3M^? VHBTM^? acrylic foam tapes were used to bond 25.4 mm × 3.175 mm aluminum 2024 T-4 adherends in both single-lap joint (SLJ) and three-point end-notch flexure (ENF) configurations. The samples were subjected to two types of aggressive environments to simulate extreme service conditions: freeze–thaw and heat–cool cycling, both for 21 days. Impulse-frequency response vibration and electrochemical impedance spectroscopy (EIS) were used for monitoring bond quality non-destructively. Data were first obtained on a set of specimens at room conditions (i.e., before being subjected to freeze–thaw, or heat–cool cycling), referred to as "baseline" in this paper. After obtaining baseline data, several batch sets were subjected to quasi-static lap-shear and dynamic impact loadings to compare the mechanical and electrochemical properties before and after environmental cycling. EIS results show that moisture absorption caused a reduction in low-frequency impedance, whereas decrease in adhesive thickness caused a reduction of impedance over the entire frequency range. The impulse-frequency response vibration NDE technique was able to detect the changes in loss factor (damping) of adhesive joints after environmental aging. Quasi-static lap-shear loading of SLJs showed that acrylic foams took less failure load compared to PSA tapes, and SLJs subjected to dynamic impact showed all PSAs and acrylic foams taking about the same impact load to failure, except the softer acrylic foam.     

Free Vibration Analysis of an Adhesively Bonded Functionally Graded Tubular Single Lap Joint

In this study, the three-dimensional free vibration analysis of an adhesively bonded functionally graded tubular single lap joint was carried out using the finite element method. The functionally graded tubes of the adhesive joint are composed of ceramic (Al₂O₃) and metal (Ni) phases varying through the tube thickness. The adhesive material properties, such as modulus of elasticity, Poisson's ratio, and density were found to have negligible effect on the first ten natural frequencies and mode shapes of the adhesive joint. The optimal design parameters of the adhesive joint, such as overlap length, inner radius of the inner tube, outer and inner tube thicknesses, and the through-the-thickness material composition variation were searched using both the artificial neural networks (ANNs) and the genetic algorithms (GAs). For this purpose, the natural frequencies and modal strain energy values were calculated for an adhesive joint with random geometrical properties and material compositions through the tube thicknesses, and were used for training the proposed artificial neural network models. The outer tube thickness, the inner tube-inner radius, and the compositional gradient exponent had considerable effect on the natural frequencies, mode shapes, and modal strain energies of the functionally graded tubular single lap joint, whereas the overlap length and the inner tube thickness had a minor effect. The GAs integrated with ANNs was employed to determine optimal design parameters satisfying both maximum natural frequency and minimum modal strain energy conditions for each natural mode of the tubular adhesive joint.     

多向受力状态下复合材料预紧力齿连接接头应力分析

为了探究复合材料空间桁架桥中关键节点预紧力齿连接接头在多向受力状态下的应力分布,对复合材料空间桁架桥建立多尺度有限元模型。该多尺度模型不仅可以同时获得桁架桥整体结构性能与局部接头应力状态,还可以有效反映两者的相互作用关系。通过该模型,对接头在多向受力状态下的应力分布展开研究,研究表明:预紧力齿接头受力之后,齿面正应力较过盈装配完成时有5 MPa以内的衰减;且多向受力接头较单向受力接头衰减缓和,衰减后多向受力接头齿面正应力略高于单向受力接头齿面正应力;多向受力接头各齿荷载分配比例与单向受力基本一致,均为两侧高中间低;多向受力接头复合材料管横向剪切应力较单向受力接头有一定增大,但最不利荷载工况下的横向剪切应力为15.7 MPa,远小于材料横向剪切强度,接头处于安全状态。所得结果可为复合材料预紧力齿接头设计提供参考依据。     

Strength of cylindrical butt joints bonded with epoxy adhesives under combined static or high-rate loading

The influence of loading rates and the combined stress states of tension and shearing on the strength, strain, and absorbed energy of an adhesively bonded joint was experimentally investigated. Cylindrical butt joint specimens were prepared and strength tests were performed on the specimens with a servo-controlled hydraulic testing machine that combined tension and torsion loading. Two types of epoxy adhesives, ductile and brittle, were applied to the specimens. The tests were performed under a quasi-static condition of 6.67×10⁻² MPa/s and a high-rate loading condition of 1.00×10³ MPa/s. The results of the combined loading tests showed that the states of the fractured surfaces were not affected by the loading rates. As for the ratio of tensile and shear loading, adhesive failure tended to partially occur when the ratio of shear loading was very high. The strength points for the specimens bonded with each adhesive were distributed in a stress plane of tension and shearing and could be fitted with a curve that was described by an equation with exponential parameters that were not influenced by the strain rate; however, other parameters that described the intercepts were influenced. The failure strains and absorbed energies for the brittle adhesive were slightly dependent on the strain rate, but this dependency was unclear for the ductile adhesive.     

Nonlinear dynamics of curved IPMC actuators undergoing electrically driven large deformations

The nonlinear dynamics of curved ionic polymer–metal composite (IPMC) actuators having large tip displacement and periodical jumping locomotion was investigated experimentally. Through snap-through phenomena, the actuator generates much larger tip displacement and shows abrupt jumps in the transitions of upswings and downswings with low input energy. Two curved IPMC cantilever actuators having two different constant curvatures of 0.01 mm^?1 and 0.02 mm^?1 were fabricated through thermal treatment from flat IPMCs, simultaneously with no residual stress. As-fabricated IPMC actuators were tested to evaluate the effect of initial curvature under static and dynamic electrical excitations. Unlike the case of the flat IPMC actuator, asymmetric characteristics in step and harmonic responses were investigated in the curved IPMC actuators. Also, at relatively higher input voltage, snap-through phenomena were observed with much larger transverse displacements and periodical abrupt jumps of the instant speed. This revealed jumping movements between the multiple equilibrium points. The results show that optimum curvatures for better bending performance of curved cantilever IPMCs exist and that this snap-through mechanism could be applied to IPMC actuators by considering their soft and flexible properties and the geometric structures.     

环氧树脂胶黏剂在石墨粘接接头的热分解动力学

引言 与传统的铆接、螺栓连接工艺相比,粘接技术因具有操作灵活、简便、生产效率高、生产成本低等优点,而广泛用于化工、汽车、航空、航天等现代结构工程,在工程设计和制造领域的应用持续增长[1-3].     

Debond and failure characteristics of a double-lap adhesively bonded joint

A novel double-lap joint design was used to bond steel adherends using a structural epoxy adhesive. Different levels of debond were built into the joint using a mold release agent during fabrication. The damping capacity measurements of the debonded specimens were obtained using a FFTbased impulse-frequency response vibration technique. The joint strengths were obtained by loading the specimens to failure in a servo-hydraulic MTS 850 test system. It was observed that the failure strength of the joint correlated well with the loss factor (a measure of damping). Empirical equations for predicting the strength of the joint in terms of the loss factor or resonant frequency are presented. A torsional vibration test rig was also used to evaluate the damping properties and to predict the mechanical properties of the bulk adhesive used in the fabrication of the adhesive joint. SEM fractographs of both the bulk adhesive specimen and the debonded joints are examined and the modes of failure presented.     

Investigation of optimal surface treatments for carbon/epoxy composite adhesive joints

Although an adhesive joint can distribute the load over a larger area than a mechanical joint, requires no holes, adds very little weight to the structure and has superior fatigue resistance, but it not only requires a careful surface preparation of the adherends but also is affected by service environments. In this paper, suitable conditions for surface treatments such as plasma surface treatment, mechanical abrasion, and sandblast treatment were investigated to enhance the mechanical load capabilities of carbon/epoxy composite adhesive joints. A capacitively coupled radiofrequency plasma system was used for the plasma surface treatment of carbon/epoxy composites and suitable surface treatment conditions were experimentally investigated with respect to gas flow rate, chamber pressure, power intensity, and surface treatment time by measuring the surface free energies of treated specimens. The optimal mechanical abrasion conditions with sandpapers were investigated with respect to the mesh number of sandpaper, and optimal sandblast conditions were investigated with respect to sandblast pressure and particle size by observing geometric shape changes of adherends during sandblast process. Also the failure modes of composite adhesive joints were investigated with respect to surface treatment. From the peel tests on plasma treated composite adhesive joints, it was found that all composite adhesive joints failed cohesively in the adhesive layer when the surface free energy was higher than about 40 mJ/m², because of high adhesion strength between the plasma treated surface and the adhesive. From the peel tests on mechanically abraded composite adhesive joints, it was also found that the optimal surface roughness and adhesive thickness increased as the failure load increased.     

Piezoelectric monitoring of the reliability of adhesive joints

Since the reliability of adhesively bonded joints for composite structures is dependent on many parameters such as the shape and dimensions of joints, type of applied load, and environment, so an accurate estimation of the fatigue life of adhesively bonded joints is seldom possible, which necessitates an in-situ reliability monitoring of the joints during the operation of structures. In this study, a self-sensor method for adhesively bonded joints was devised, in which the adhesive used works as a piezoelectric material to send changing signals depending on the integrity of the joint. In order to validate the method, the piezoelectric properties of the adhesive were measured during the fatigue test. Electrically conducting adherends were used as electrodes without embedded sensors, and the adhesively bonded joint was modeled as the equivalent parallel circuit composed of electric charge and capacitance. From the investigation, it was found that the electric charge increased gradually as cracks initiated and propagated in the adhesive layer, and had its maximum value when the adhesively bonded joint failed. So it is feasible to monitor the integrity of the joint during its lifetime. Finally, a relationship between the piezoelectric property of the adhesive and crack propagation was obtained from the experimental results.     

Transverse cracking of a simple lap joint under axial load

The failure mode of axially loaded simple, single lap joints formed between thin adherends which are flexible in bending is conventionally described as one of axial peeling. We have observed – using high-speed photography – that it is also possible for failure to be preceded by the separation front, or crack, moving in a transverse direction, i.e. perpendicular to the direction of the axial load. A simple energy balance analysis suggests that the critical load for transverse failure is the same as that for axial separation for both flexible lap joints, where the bulk of the stored elastic energy lies in the adhesive, and structural lap joints in which the energy stored in the adherends dominates. The initiation of the failure is dependent on a local increases in either stress or strain energy to some critical values. In the case of a flexible joint, this will occur within the adhesive layer and the critical site will be close to one of the corners of the joint overlap from which the separation front can proceed either axially or transversely. These conclusions are supported by a finite element analysis of a joint formed between adherends of finite width by a low modulus adhesive.     

Diagnosis criterion for damage monitoring of adhesive joints by a piezoelectric method

Adhesive joints have been widely used for fastening thin adherends because they can distribute the load over a larger area than mechanical joints, require no holes, add very little weight to the structure and have superior fatigue resistance. Since the reliability of an adhesive joint is dependent on many parameters, such as the shape of joint, type of applied load and environment, an accurate prediction of the fatigue life of adhesive joints is seldom possible, which necessitates an in situ damage monitoring of the joints during their operation. Recently, a piezoelectric method using the piezoelectric characteristics of epoxy adhesives has been successfully developed for adhesive joints because it can continuously monitor the damage of adhesively bonded structures without producing any defects induced by inserting a sensor. Therefore, in this study, the damage of adhesive joints was monitored by the piezoelectric method during torsional fatigue tests in order to develop the diagnosis criterion for damage monitoring of adhesive joints by the piezoelectric method. The diagnosis criterion was developed by analyzing damage monitoring signals under various test conditions and adopting normalized parameters.