Key Engineering Materials Vols. 353-358

Abstract: Effect of the applying twin laser beam on the welding of AZ31 / A5052 dissimilar metals lap joint was studied. The direct welding and the welding with Al12Si filler wire were carried out. Flow behavior of the molten metal was analyzed by FEM simulation. For both welding methods, failure load of the joints increased by applying twin laser beam with reasonable beam distance. Twin laser beam technique could control temperature distribution and flow behavior of the molten metal.

Abstract: This research was concerned with study of failure strength of natural fiber reinforced composites. Tensile-shear tests were carried out with single-lap-adhesive-joined specimens consisting of polyester lap and composite lap. Composites were manufactured using the polyester as matrix and bamboo natural fiber layer as reinforcement. Two types of specimens with different reinforcement positions were tested to evaluate the failure strength of adhesive-single-lap-joined natural fiber reinforced composites. The test results were presented by tensile-shear strength graph comparing with finite element analysis. The failure mechanism was discussed in order to explain the lower tensile-shear strength of composite, and effect of position of bamboo natural fiber layer on the failure strength properties were explained.

Abstract: This research was concerned with study of fracture strength of adhesive-lap-joined composites. The tensile and peel tests were carried out with specimens manufactured hybrid stacked composites, because the orientation of fiber and the interfacial fracture between the matrix and the reinforcement had influence on failure strength of composites. Bamboo natural fiber layer was located between polyester layers. The objective of this study was to evaluate the effect of fiber orientation on failure strength properties of composites. The test results were presented by load-displacement graph and finite element analysis. As a result, the load-directional orientation and the thinner thickness of bamboo natural fiber layer have a good effect on peel and tensile-shear strength and failure shape of adhesive-joined hybrid stacked composite.

Abstract: The present study is a systematic investigation of the effects of microstructural changes, which have originated from the variations of filler metals and welding processes, on the J-R properties of simulated welds. Two AISI Type 347 weld metals, with different carbon contents, deposited by a GTAW process and two AISI Type 347 weld metals, with different carbon contents, deposited by a SMAW process were used in this study. The J-R tests were conducted at 316oC (600oF). The welds deposited by the GTAW process showed higher fracture resistances when compared to the welds deposited by the SMAW process. The J-R fracture resistance of the Type 347-GTAW processed weld with high carbon content was remarkably low when compared to the weld with low carbon. The J-R fracture resistances were decreased by coarse Nb(C, N) precipitates in the Type 347 weld deposited by the GTAW process. In the case of the SMAW welds, mainly coarse Ti-rich particles which had originated from the shielding of the welding rods deteriorated the fracture resistances.

Abstract: This research is concerned with a study of failure strength of natural fiber composite. Tensile-shear tests were carried out with the single-lap resistance welded joined specimens consisting of composite materials. Composite materials were manufactured using the polyester as a matrix and bamboo natural fiber layer as a reinforcement. Two types of specimen with different reinforcement positions were tested to evaluate the failure strength of natural fiber reinforced composite resistance welded joined specimens. The test results were presented by tensile-shear strength. The failure mechanism was discussed in order to explain the lower tensile-shear strength of composite and position of bamboo natural fiber layer on the failure strength properties were explained

Abstract: Structure adhesive bonding method is widely used in the industry because it is possible to joint complex shape and dissimilar materials. Especially in the car industry, requests of lightweight car have adhesive bonding method be applied in the many parts. Also it is possible for stress to distribute uniformly through the adhesive layer, and stress concentration is released. Since strength, stiffness durability is much better, this method is determined as the technique replaced weld defect. But, it has much shorter history then other joint method such as spot weld and mechanical joint method. Evaluation of strength and durability is not established. As the fundamental research of design of adhesive bonding joints, considers over-lap length, adhesive thickness, surface treatment and environment which affect strength and durability of single-lap joints. In this research, a real part of bus folding door was used and tested to compare durability of spot welding and adhesive bonding.

Abstract: The present paper describes the new methodology used for the development of the crackfree welding processes. The presented approach is based on the accurate experimental observations on binary Al-Si alloys, which clearly demonstrate that the crack initiation is a result of the accumulation of macroscopic tensile strain in a microscopic intergranular liquid film of segregates at the final stage of the weld metal solidification. The numerical model takes into account the effects of strain accumulation as well as the influence of thermo-dynamical and thermo-mechanical properties of the welded material. The new approach provides a clear phenomenological interrelation between the cracking susceptibility, parameters of the welding process and properties of the base and filler material. It is successfully applied for development of technological means for elimination of the solidification cracking during welding of aluminium alloys AA6056, such as a multi-beam welding.

Abstract: The purpose of this paper is to develop an estimation formula of stress concentration factors of butt-welded components under tensile loading. To investigate the influence of weld bead profiles on stress concentration factors of double V groove butt-welded joints, butt-welded specimens were made by CO2 gas metal arc welding. And the three main parameters, the toe radius, flank angle and bead height were measured by a profile measuring equipment. By using the measured data, the influence of three parameters on the stress concentration factors was investigated by a finite element analysis. It is shown that the three parameters have similar effects on the stress concentration factors. According to the simulation results, a formula to estimate the stress concentration factors of butt-weld welded structures was proposed and the estimated concentration factors from the formula were compared with the results obtained by the finite element analysis. The two results are in a good agreement.

Abstract: CVD diamond thick film was brazed to cemmented carbide using a Ag-Cu-Ti active filler metal. The brazing process was performed in a vacuum furnace under different processing condition. The interfacial microstructure and characterization between diamond and Ag-Cu-Ti filler metal were studied by SEM, EPMA and EDX. The morphology and distribution of new compound are shown for the first time (Figs). Results illustrate that a small amount of new compound TiC, TiCu compound exist in the interface. TiC layer exists in the interface and it's thickness is variational with the varying of processing condition such as peak heating temperature, keeping time and so on. New compound TiC accretes with the surface atoms of diamond in a special section, and particular orientation relationships are occasionally observed by examining the fracture section. TiCu layer near TiC exists in the interface. It is worth notice that too much TiC and TiCu in interface could weaken join strength because TiC and TiCu are brittle.

Abstract: Method of Lines (MOLs) is introduced to solve 2-Dimension steady temperature field of functionally graded materials (FGMs). The main idea of the method is to semi–discretized the governing equation of thermal transfer problem into a system of ordinary differential equations (ODEs) defined on discrete lines by means of the finite difference method. The temperature field of FGM can be obtained by solving the ODEs with functions of thermal properties. As numerical examples, six kinds of material thermal conductivity functions, i.e. three kinds of polynomial functions, an exponent function, a logarithmic function, and a sine function are selected to simulate spatial thermal conductivity profile in FGMs respectively. The steady-state temperature fields of 2-D thermal transfer problem are analyzed by the MOLs. Numerical results show that different material thermal conductivity function has obvious different effect on the temperature field.