Conductive rubbers made by adding conductive carbon black to EVA,EPDM, and EVA–EPDM blends

Abstract

Electrically conductive rubbers have been prepared by the incorporation of conductive carbon black into ethylene/vinyl acetate (EVA) copolymers, ethylene/propylene/diene monomer (EPDM) terpolymers, and a 50 : 50 EVA–EPDM blend. The electrical and mechanical properties of these composites have been studied. The percolation limit for high conductivity in the filled rubbers depends on their compatibility as well as the viscosity and polarity of the rubbers. The electrical resistivity decreases with increasing temperature and the activation energy for conduction decreases with increasing filler loading. The temperature dependence of resistivity can be correlated with data from DSC, XRD, and DMTA measurements. Electrical set and electrical hysteresis have been observed during heating–cooling cycles. The change in resistivity with applied pressure is also reported.     

Artificial neural networks – an aid to welding induced ship plate distortion?

Abstract

A preliminary study on the potential application of artificial neural networks in welded structures was expanded to metal inert gas welding of steel plates of grades D and DH 36. The main controllable variables were plate thickness, steel grade, plate cutting process, and heat input. A series of welded plates of each grade was manufactured, covering plate thicknesses of 6 and 8 mm. The topography of each welded plate was evaluated after tacking the plates together and after welding, allowing the actual distortion to be calculated. It was established that a multilayer perceptron network architecture configuration accurately represented the distortion for the 6 mm thickness plate, and for the 8 mm thickness plate after treatment of the data. The data generated were used to develop the PREDICTOR software package, which allows a distortion prediction to be produced, and to carry out a sensitivity analysis. Heat input was found to be the most sensitive factor related to distortion, with carbon content of the plates, yield/tensile strength ratio, carbon equivalent, and steel grade also having significant effects. Some test plates were modelled using finite element method software packages: the initially poor agreement was improved via the addition of significant detail, but the finite element model by its nature will normally predict symmetrical distortion from a symmetric weld, whereas the artificial neural network model developed was capable of predicting the asymmetric distortion observed in reality.     

Effects of latent heat of fusion on thermal processes in laser welding of aluminium alloys

Abstract

Based on the Green's function method, a mathematical model allowing for the latent heat of fusion and solidification is developed to describe the steady state, two-dimensional heat flow during welding of thin plates. It is demonstrated that the latent heat has a pronounced effect on shape and size of the weld pool and mushy zone. The thermal efficiency of base metal fusion by a line heat source η _t can exceed 0·4839 considerably if the latent heat is taken into account. It is shown that the known simplified approaches for considering the latent heat can introduce large errors into the estimation of η _t. The calculated and experimental weld pool shapes are compared.     

Deformation of bowed silicon chips due to adhesion and applied pressure

One potential method to accomplish high-rate nanomanufacturing is to develop processes which allow for rapid transfer of nano-scaled devices from a template to a device wafer. In order to accomplish this transfer, the device wafer must make intimate contact with the template. A similar situation exists in wafer bonding, except that in that case the two wafers remain in bonded contact due to the work of adhesion even after the applied pressure is removed. In high-rate nanomanufacturing intimate contact must be maintained during transfer, while allowing for easy separation afterwards. Wafers typically have waviness and bow which cause a deviation of many micrometers from flatness over the 15-mm length scale of a typical chip. This non-flatness can be a serious problem in the transfer of nanometer-scale elements. In this investigation, a model is developed to examine the effects of applied pressure, bow radius and the work of adhesion on the flattening of a spherically/cylindrically bowed chip. This model uses elastic plate theory and the work of adhesion. An operating window is found which provides intimate contact while allowing for separation once the pressure is removed. It is also shown that the effect of adhesion is to produce a discontinuity in the internal bending moment, at the separation boundary, which is proportional to the square-root of the product of the work of adhesion and the flexural rigidity. This "moment-discontinuity" method can be applied to other problems involving adhesion of elastic plates.     

Peel testing of adhesively bonded thin metallic plates with control of substrate plastic straining and of debonding mode mixity

A new peel test method has been developed for allowing debonding of adhesively bonded, thin metallic substrates. The rolling of the substrates on rollers allows control of the plastic dissipation during substrate bending and prevents dissipation associated with substrate unbending. The measured debonding toughness is shown to be independent of substrate thickness when proper account is taken of the work required for straining the adhesive layer. Mechanical analysis shows that control of plastic dissipation in substrates remains effective, as long as the ratio of the plate thickness to the roller radius is large enough to prevent wound-up. Mode mixity during debonding can be conveniently modified by changing the radii of the rollers. This possibility of altering mode mixity allows a better control of the occurrence of the cohesive, or near-interfacial debonding mechanisms. Evidence is given for the fact that the debonding mechanism is not governed by the minimum in the debonding toughness. A significant increase of debonding toughness with increasing mode mixity is observed only when the substrate roughness is high.     

Determination of elastic constants from measured natural frequencies of specially orthotropic cantilever plates

Abstract

The present paper examines the possibility of evaluating the elastic constants of specially orthotropic rectangular thin plates from the measured natural frequencies of cantilever plates. An expression is developed for orthotropic rectangular thin cantilever plates to determine natural frequencies, and its validity is demonstrated through finite element analysis as well as using published test results.     

SOLUTION OF DIFFERENT HOLES SHAPE BORDERS OF FIBRE REINFORCED COMPOSITE PLATES BY INTEGRAL EQUATIONS

Accurate boundary conditions of composite material plates with different holes are founded to settle boundary condition problems of complex holes by conformal mapping method upon the nonhomogeneous anisotropic elastic and complex function theory. And then the two stress functions required were founded on Cauchy integral by boundary conditions. The final stress distributions of opening structure and the analytical solution on composite material plate with rectangle hole and wing manholes were achieved. The influences on hole-edge stress concentration factors are discussed under different loads and fiber direction cases, and then contrast calculates are carried through FEM.     

A Theoretical Improved Adhesively Bonded Bi-material Beam Model for FRP–RC Hybrid Beams

In this paper we present an improved bi-material beam theory with adhesive interface, which has been applied to the study of the interfacial behavior in a concrete beam reinforced by an externally bonded fibre reinforced polymer (FRP) plate. The work explicitly considers the interfacial slip effect on the structural performance by including the effect of adherend shear deformations. This new method needs only one differential equation to determine both shear and normal interfacial stress whereas the others solutions in the literature need two differential equations. Compared with previously published analytical results, this one improves the accuracy of predicting the interfacial stresses and the solution is in a closed form. This research is helpful in the understanding of the mechanical behavior of the interface and design of FRP–reinforced concrete (RC) hybrid beams.