Comparative Study of the Results of Various Experimental Tests Used for the Analysis of the Mechanical Behaviour of an Adhesive in a Bonded Joint

The use of adhesively bonded joints is often limited by a lack of reliable models able to accurately predict their behaviour in industrial applications, in which the stress distribution is often complex. The mechanical behaviour of an adhesive in a bonded joint is often heavily dependent on its stress state (i.e., the tensile–shear combinations). Thus, a large experimental database is required to accurately represent the complex behaviour of an adhesive in a bonded joint. On the one hand, the initial yield surface (initial elastic limit) often has to be described taking into account the two stress invariants, hydrostatic stress and von Mises equivalent stress, and on the other hand the non-linear behaviour of the adhesive is also quite complex to model. However, the mechanical response of adhesively bonded joints often presents quite large stress concentrations; thus, the analysis of experimental tests is made particularly difficult. Obtaining reliable experimental results makes it possible to contribute to optimization of an adhesive in a bonded joint. This paper presents comparisons between results of different experimental tests (with bulk and bonded joints), some of them are designed to greatly limit the edge effects. Results are presented for two adhesives under proportional monotonic loadings. The two adhesives have very different behaviours (a ductile adhesive and a brittle adhesive) and two different surface preparations of aluminium substrates (a mechanical preparation and a chemical preparation recommended by the adhesive manufacturer) were studied.     

Shear and peel stress analysis of an adhesively bonded scarf joint

The shear and peel stress distributions in a scarf joint made of two isotropic adherends with blunt adherend tips are analysed using a linear elastic analysis. The limits of the analysis with respect to adherend tip thickness have been investigated. A finite difference method is used to solve the differential equations for the shear and peel stress distributions over the joint. The boundary conditions used limit the analysis to the two adherends having the same thicknesses, lengths, and material properties. The adherends are modelled as plates with extensional and bending stiffnesses bonded together with an elastic interlayer. The stresses across the adhesive layer are assumed to be constant. The current analysis applied to cases known from the literature shows good agreement with the shear stresses but the peel stresses are overestimated.     

2—THE SYSTEMATIC OPTIMIZATION OF THE AQUEOUS COMPRESSION-JET WOOL SCOUR. PART II: SCOURING TRIAL FOR OPTIMUM PRODUCTION CAPACITY

A factorial experiment performed on the aqueous compression-jet scour with three independent variables is reported. These variables were the feed-rate of greasy wool, the speed of the layer of wool, and the jetting pressures. The wools were processed to gilled slivers, on which mean-fibre-length determinations were made. The effects of the independent variables on the dependent variables of residual grease and dirt and mean fibre length (the last-named being a measure of the degree of entanglement of the scoured wool) were evaluated. The results obtained indicated the operating conditions to be used to achieve the optimum production capacity.     

Studies on polycrystalline layered ceramic oxide: LiFeVO4

Abstract

A new polycrystalline layered ceramic oxide, LiFeVO₄, has been prepared by a standard solid state reaction technique. The preparation conditions were optimised using thermogravimmetric analysis (TGA) technique. Material formation under the reported conditions was confirmed by X-ray diffraction studies. A preliminary structural analysis indicated that the crystal structure was orthorhombic with lattice parameters: a=4·3368 Å, b=13·1119 Å and c=16·3426 Å. The phase morphology and surface property were studied by scanning electron microscopy. Complex impedance analysis of the sample indicated bulk contribution to electrical properties at T≤125°C, grain boundary effects at the temperatures ≥125°C, negative temperature coefficient of resistance (NTCR) effect and evidence of temperature dependent electrical relaxation phenomena in the sample. The dc conductivity σ_dc shows typical Arrhenius behaviour when observed as a function of temperature. The activation energy value was estimated to be 0·24 eV. The value of σ_dc, evaluated from complex impedance spectrum, shows a jump of nearly two orders of magnitude at higher temperature (～1·24 × 10^?5 S cm^?1 at 350°C) when compared with that of σ_dc (1·14 × 10^?6 S cm^?1 at 50°C). Alternating current conductivity spectrum obeys Jonscher's universal power law. The results of σ_ac v. temperature are also discussed.     

Characterization of adhesive ageing using mechanical and electrochemical inspection

Two methacrylate adhesives, commonly used in railway applications, were tested before, during and after accelerated humid ageing. First, bulk tensile samples were fabricated in order to perform mechanical characterization before ageing. Then, the samples were placed in a humid environment and the influence of water on the Young's modulus and the tensile strength was determined. In parallel, Electrochemical Impedance Spectroscopy (EIS) measurements were carried out with methacrylate-adhesive-coated aluminum panels in order to extract parameters related to the porosity and adhesion of adhesives which are both dependent on water penetration. Finally, the mechanical characterization of adhesively-bonded lap joints with aluminum substrates was performed before and after accelerated humid ageing. All these experiments allowed to distinguish the two adhesives tested. It was found that the bulk adhesive samples which presented the best mechanical properties before ageing did not guarantee a good bonded-joint behavior after ageing. More importantly, the combination of EIS with mechanical tests allows to significantly reduce very much the number of experiments and, thus, the cost of industrial validation tests.     

Spray Deposition Methods for Improving Interfacial Strength of Copper–Epoxy Systems

A simple spray method using a plain orifice atomizer has been developed for depositing γ-aminopropyltriethoxysilane (APS) from solutions in water and in methanol onto copper surfaces. The evaporative patterns of the sprayed droplets were studied to determine the distribution of deposited APS and the percent coverage of the surface. The peel strengths between copper foil and epoxy resin were measured with and without APS deposition. It was shown that the application of APS resulted in a considerable increase in interfacial adhesion. APS applied from a 1 wt% solution in methanol resulted in a higher peel strength than when applied from a 1 wt% aqueous solution; the opposite was true with 0.2 wt% APS solutions, indicating a trade-off between deposited APS film thickness and surface coverage. In all cases, a higher concentration of APS gives a higher peel strength. APS was very effective when chemisorption occurred at the surface but much less effective when only physisorption took place. A study of the fracture surfaces showed cohesive failure inside the epoxy layer, and that the deposited APS on the copper surfaces had a long-range effect which was seen deep into the epoxy layer, well away from the copper surface.     

The Coupled FEM Analysis of the Transient Temperature Field During Inertia Friction Welding of GH4169 Alloy

The inertia friction welding process is a non-linear process because of the interaction between the temperature field and the material properties as well as the friction force. A thermo-mechanical coupled finite element model is established to simulate the temperature field of this process. The transient temperature distribution during the inertia friction welding process of two similar workpieces of GH4169 alloy is calculated. The region of the circular cross-section of the workpiece is divided into a number of four-nodded isoparametric elements. In this model, the temperature dependent thermal properties, time dependent heat inputs, contact condition of welding interface, and deformation of the flash were considered. At the same time, the convection and radiation heat losses at the surface of the workpieces were also considered. A temperature data acquisition system was developed. The temperature at some position near the welding interface was measured using this system. The calculated temperature agrees well with the experimental data. The deformation of the flash and the factor affecting the temperature distribution at the welding interface are also discussed.     

Constitutive Relationship of IN718 Alloy for Thermoviscoplastic and Microstructure Evolution Coupled Analysis

The interaction between thermomechanical parameters and microstructure evolution is so intense that it must be considered during the finite element method (FEM) simulation of the hot plastic working process, for materials that are difficult to deform. Taking the microstructure evolution into account, a novel type of constitutive relationship has been put forward for the IN718 alloy. The microstructure evolution model was first established for the dominant microstructure evolution processes. Then the microstructure evolution models and the method to determine the local flow stress of the corresponding microstructure for current thermomechanical parameters and deformation history were presented. Once the local flow stresses of different structures and their volume contributions were defined, the apparent flow stress of the material could be determined as the weighted sum of the local flow stresses and volume contributions. To validate the proposed method, a thermoviscoplastics and microstructure evolution coupled analysis for a forging process of a critical IN718 disk forging was performed. The predicting results were in close agreement with the experimental data.     

A Technique to Eliminate Redundant Inter-Processor Communication on Parallelizing Compiler TINPAR

Optimizing inter-processor (PE) communication is crucial for parallelizing compilers for message-passing parallel machines to achieve high performance. In this paper, we propose a technique to eliminate redundant inter-PE messages. This technique utilizes data-flow analysis to find a definition point that corresponds to a use point where the definition and the use occur in different PEs. If several read accesses occurred in the same PE use the data defined at the same definition point in another PE, redundant inter-PE messages are eliminated as follows: only one inter-PE communication is performed for the earliest read access and the previously received data are used for the following read. In order to guarantee the consistency of the data, a valid flag and a sent flag are provided for each chunk of received data. The control of these flags is equivalent to the coherence control by the self invalidation on a compiler aided cache coherence scheme.     

A New Digital Sense Multiple Access (DSMA) Protocol for High-Speed Wireless Networks

In this paper, we propose a new digital sensemultiple access with delayed transmission (DSMA/DT)protocol for reverse channel in high-speed wirelessnetworks. The new protocol is motivated by theobservation that the existing DSMA protocol does not yieldsatisfactory throughput for long round-trip propagationand processing delay, which occurs in outdoor high-speedenvironments or when the receiver hardware requires long signal processing time. The newDSMA/DT protocol is intended to reduce the performanceimpacts of the round-trip delay. Look-ahead busy/idleflag, seizure queueing, and reserved time slots are also devised for the new protocol. Whilerequiring at most two additional status bits on theforward channel and no additional hardware capability,these features further enhance the protocol performance and enable constant-bit-rate service withlittle added complexity in control. The channelthroughput of the DSMA/DT protocol and the optionalfeatures are analyzed. Closed-form expressions for thethroughput are obtained. For non-negligible round-tripdelay relative to packet transmission time, ournumerical results show that the new protocol improvesthe throughput by as much as 60% when compared to theexisting DSMA protocol. For superior performance andsimplicity, the DSMA/DT protocol will be appropriate foruse in high-speed wireless networks.