Influence of adhesive layer properties on laser-generated ultrasonic waves in thin bonded plates

This paper studies quantitatively the generation of Lamb waves in thin bonded plates subjected to laser illumination, after considering the viscoelasticity of the adhesive layer. The displacements of such plates have been calculated in the frequency domain by using the finite element method, and the time domain response has been reconstructed by applying an inverse fast Fourier transform. Numerical results are presented showing the normal surface displacement for several configurations： a single aluminum plate, a three-layer bonded plate, and a two-layer plate. The characteristics of the laser-generated Lamb waves for each particular case have been investigated. In addition, the sensitivity of the transient responses to variations of material properties （elastic modulus, viscoelastic modulus, and thickness） of the adhesive layer has been studied in detail.

Improvement of Bonding Strength of AZ31B Magnesium Alloy by Anodizing and Chromium-free Conversion Treatments

The influences of chromium-free chemical conversion treatment and anodizing treatment on bonding strength of AZ31 magnesium alloy were studied by lap-shear test, SEM and electrochemical methods. Both chemical conversion treatment and anodizing can increase the bonding strength. The anodizing treatment gives higher bonding strength and better corrosion resistance than chemical conversion treatment. The increase of bonding strength by the treatmetlts may be attributed to the uneven surface structures with micro-pores, resulting in increased bonding areas and the embedding effect.

Adhesive Bonding and Self-Curing Characteristics of α-Starch Based Composite Binder for Green Sand Mould/Core

Interactions between different components in α-starch based composite binder for green sand mould/core were investigated by using XRD, IR spectra, 1H NMR spectra and SEM. Several adhesive hardening structures and theories of the binder at room temperature were proposed according to the interactions between various compositions. Thus, the reasons for the binder to have excellent combination properties and unique adhesive bonding and self-curing characteristics were explained by these theories successfully. And the theories are of great directive importance to design and development of composite binder for green sand mould/core.

The dynamic stress intensity factor analysis of adhesively bonded material interface crack with damage under shear loading

This paper studies the dynamic stress intensity factor （DSIF） at the interface in an adhesive joint under shear loading. Material damage is considered. By introducing the dislocation density function and using the integral transform, the problem is reduced to algebraic equations and can be solved with the collocation dots method in the Laplace domain. Time response of DSIF is calculated with the inverse Laplace integral transform. The results show that the mode Ⅱ DSIF increases with the shear relaxation parameter, shear module and Poisson ratio, while decreases with the swell relaxation parameter. Damage shielding only occurs at the initial stage of crack propagation. The singular index of crack tip is -0.5 and independent on the material parameters, damage conditions of materials, and time. The oscillatory index is controlled by viscoelastic material parameters.

Propagation of Iamb waves in adhesively bonded multilayered media

The effect of introducing attenuation on Lamb wave dispersion curves is studied in this paper. Attenuation is introduced to a three-layered composite plate by an adhesive bond layer with viscous behavior. No changes are required to the transfer matrix formulation for the propagation of elastic waves. By introduction of a complex wavenumber, the model can be used to the propagation of attenuative Lamb waves. Numerical examples for a three-layered aluminium-epoxy-aluminium plate show that attenuation values of each mode in plates are related not only to attenuation, but also to the thickness of the bonded layer, which is in agreement with practical situations.

Modeling and Simulation of a Bonding Process for Space Solar Cells

A bonding process for space solar cells implemented by an automated coating and bonding system was theoretically investigated for future parametric studies to achieve better bonding quality. First, the mechanical properties of silicone adhesive and the vacuum suction cup were experimentally analyzed. Based on the constitutive relationship of four parts in the bonding process, the dynamic bonding process was modeled systematically, and numerically simulated by a commercial finite element analysis code, Adina. The final bonding edge-alignment error and the thickness and uniformity of the adhesive layer were obtained from simulation and validated by experiments. A simulation platform was created for predicting the final bonding quality via adjusting bonding parameters when dimensions of the solar cells and adhesive were changed.

Damage Failure Analysis of Z-Pins Reinforced Composite Adhesively Bonded Single-Lap Joint

In order to study themechanical properties of Z-pins reinforced laminated composite single-lap adhesively bonded joint under un-directional static tensile load,damage failure analysis of the joint was carried out bymeans of test and numerical simulation.The failure mode and mechanism of the joint were analyzed by tensile failure experiments.According to the experimental results,the joint exhibits mixed failure,and the ultimate failure is Z-pins pulling out of the adherend.In order to study the failure mechanism of the joint,the finite element method is used to predict the failure strength.The numerical results are in good agreement with the experimental results,and the error is 6.0%,which proves the validity of the numerical model.Through progressive damage failure analysis,it is found that matrix tensile failure of laminate at the edge of Z-pins occurs first,then adhesive layer failure-proceeds at the edge of Z-pins,and finally matrix-fiber shear failure of the laminate takes place.With the increase of load,the matrix-fiber shear failure expands gradually in the X direction,and at the same time,the matrix tensile failure at the hole edge gradually extends in different directions,which is consistent with the experimental results.

Dynamic fracture analysis of adhesive bonded material under normal loading

Dynamic fracture behavior of a Griffith crack along the interface of an adhesive bonded material under normal loading is studied. The singular integral equations are obtained by employing integral transformation and introducing dislocation density functions. By adopting Gauss-Jacobi integration formula, the problem is reduced to the solution of algebraic equations, and by collocation dots method. their solutions can be obtained Based on the parametric discussions presented in the paper, the following conclusions can be drawn： （1） Mode I dynamic stress intensity factor （DSIF） increases with increasing initial crack length and decreasing visco-elastic layer thickness, revealing distinct size effect; （2） The influence of the visco-elastic adhesive relaxation time on the DSIF should not be ignored.

BONDING OF MINIATURE PARTS WITH ADHESIVES AND VISION BASED PROCEDURE INSPECTION

Bonding with adhesives is an important technique for building up hybridmicrosystems. Some adhesives are tested with capillary dispensing system for microassembly, andvolume of droplets less than 10 nl with good repeatability can be acquired. 1-part UV curingadhesive hardens rapidly and is suitable for bonding of transparent microparts. Light-activatedadhesive starts the curing process in an adjustable short period of time after the radiation ofvisible light, and thus suits bonding of non-transparent microparts. A method is proposed forbonding the guides of a miniature linear motor being developed by collaborate research center 516(SFB516) in Germany. With the method high assembly accuracy in the vertical direction can beguaranteed. By making small grooves on the stator for containing adhesive, the deterioration of theaccuracy due to the thickness of adhesive layer can be avoided. The criteria on deciding the size ofthe groove are given and analyzed. Vision based inspection method is introduced for automaticassembly of the guides. The dispensing volume and position of dispensed adhesive droplets can bedetected for ensuring the bonding quality.

Stability of focal adhesion enhanced by its inner force fluctuation

Cells actively sense and respond to mechanical signals from the extracellular matrix through focal adhesions. By representing a single focal adhesion as a cluster of slip bonds, it has been demonstrated that the cluster often became unstable under fluctuated forces. However, an unusual case was also reported, where the stability of the cluster might be substantially enhanced by a fluctuated force with a relatively low fluctuation frequency and high fluctuation amplitude.Such an observation cannot be explained by the conventional fracture theory of fatigue. Here, we intensively investigate this intriguing observation by carrying out systematic parametric studies. Our intensive simulation results indicate that stability enhancement of this kind is in fact quite robust, which can be affected by the stochastic features of a single bond and the profile of the fluctuated forces such as the average value of bond force. We then suggest that the fluctuation of traction force within a focal adhesion might enhance its stability in a certain way.

Comparing Properties of Adhesive Bonding,Resistance Spot Welding,and Adhesive Weld Bonding of Coated and Uncoated DP 600 Steel

Zinc coated dual phase 600 steel （DP 600 grade） was investigated, utilisation of which has gradually increased with each passing day in the automotive industry. The adhesive bonding （AB）, resistance spot welding （RSW）, and adhesive weld bonding （AWB） ioints of the zinc coated DP 600 steel were investigated. Additionally, the zinc coating was removed using HCL acid in order to investigate the effect of the coating. The microstructure, tensile shear strengths, and fracture properties of adhesive bonding （AB）, resistance spot welding （RSW）, and adhesive weld bonding （AWB） joints of the coated and uncoated DP 600 steel were compared. In addition, a mechani cal-electrical-thermal coupled model in a finite element analysis environment was utilised. The thermal profile phe nomenon was calculated by simulating this process. The results of the tensile shear test indicated that the tensile load bearing capacity （TLBC） values of the coated specimens among the three welding methods were higher than those of the uncoated specimens. Additionally, the tensile strength of the AWB joints of the coated and uncoated specimens was higher than that of the AB and RSW joints. It was determined that the fracture behaviours and the deformation caused were different for the three welding methods.

Towards Cr（VI）-free anodization of aluminum alloys for aerospace adhesive bonding applications： A review

For more than six decades, chromic acid anodizing （CAA） has been the central process in the surface pre-treatment of aluminum for adhesively bonded aircraft structures. Unfortunately, this electrolyte contains hexavalent chromium （Cr（VI））, a compound known for its toxicity and carcinogenic properties. To comply with the new strict international regulations, the Cr（VI）-era will soon have to come to an end. Anodizing aluminum in acid electrolytes produces a self-ordered porous oxide layer. Although different acids can be used to create this type of structure, the excellent adhesion and corrosion resistance that is currently achieved by the complete Cr（VI）-based process is not easily matched. This paper provides a critical overview and appraisal of proposed alternatives to CAA, including combinations of multiple anodizing steps, pre- and post anodizing treatments. The work is presented in terms of the modifications to the oxide properties, such as morphological features （e.g., pore size, barrier layer thickness） and surface chemistry, in order to evaluate the link between fundamental principles of adhesion and bond performance.

Investigation of hybrid microring lasers adhesively bonded on silicon wafer

Thermal characteristics are numerically investigated for the hybrid AlGaInAs/InP on silicon microring lasers with different ring radii and widths. Low threshold current and low active region temperature rise are expected for a microring laser with a narrow ring width. Based on the thermal analysis and the 3D simulation for mode characteristics, a hybrid AlGaInAs/InP on silicon microring lasers with an inner n-electrode laterally confined by the p-electrode metallic layer is fabricated using an adhesive bonding technique. A threshold current of 4 mA is achieved for a hybrid microring laser with a radius of 20 μm and a ring width of 3.5 μm at 12°C, and the corresponding threshold current density is as low as 1 kA∕cm^2. The influence of the location of silicon waveguide on output performance is studied experimentally for improving the output coupling efficiency. Furthermore,continuous-wave electrically injected lasing up to 55°C is realized for a hybrid microring laser with a radiusof 30 μm and a ring width of 3 μm.

Realization of an Automated Microassembly Task Involving Micro Adhesive Bonding

An automated approach is proposed for a microassembly task, which is to insert a 10 μm diameter glass tube into a 12 μm diameter hole in a silicon substrate, and bond them together with ultraviolet （UV） curable adhesive. Two three-degree-of-freedom micromanipulators axe used to move the glass tube and the dispensing needle, respectively. Visual feedback is provided by an optical microscope. The angle of the microscope axis is precisely calibrated using an autofocus strategy. Robust image segmentation method and feature extraction algorithm are developed to obtain the features of the hole, the glass tube and the dispensing needle. Visual servo control is employed to achieve accurate aligning for the tube and the hole. Automated adhesive dispensing is used to bond the glass tube and the silicon substrate together after the insertion. On-line monitoring ensures that the diameter of the adhesive spot is within a desired range. Experimental results demonstrate the effectiveness of the proposed strategy.

Mechanical Performance Evaluation of Multi‑Point Clinch–Adhesive Joints of Aluminum Alloy A5052‑H34 and High‑Strength Steel JSC780

The clinch–adhesive process,which combines mechanical clinching and adhesive bonding,is one of the most applied pro-cesses for joining aluminum alloy and steel in the manufacturing of vehicle bodies.In this hybrid process,the clinching joints and adhesive bonds are coupled and influenced by each other,posing challenges to the process design and joining strength evaluation.To understand the influence of the clinching process on the performance of the adhesive layer,this study analyzes the mechanical behavior of clinch–adhesive joints between high-strength steel JSC780 and aluminum alloy A5052-H34 with different stack-up orientations and varying numbers of clinching points.The results reveal that,under the steel-on-top condition,the clinching process causes a discontinuous distribution of the adhesive layer,which significantly decreased the bonding strength.In contrast,under the aluminum-on-top condition,the clinching process has a lesser impact on the distribution of the adhesive layer,resulting in much higher strength than the steel-on-top condition.Simulation mod-els are constructed to quantify the effect of clinching points on the performance of the adhesive layer.The results highlight the need to consider diverse cohesive zone model parameters for the different stack orientations and clinching points in the design of clinch–adhesive aluminum alloy/steel structures.