Applied Mechanics and Materials Vols. 217-219

Abstract: The geometrical model for serrated chip was set up by studying the characteristic of typical chip during high speed machining. According to the adiabatic shear theory under the condition of high speed machining, friction force and flow velocity on back surface of chip as well as shear force and shear velocity on sliding plane were obtained by establishing mechanics and kinetic models via analyzing equilibrium forces exerted on the saw-tooth chip at the moment when the catastrophic thermoplastic instability occurred on slippage plane, then energy equation for cutting was offered. With strain, strain ratio, cutting temperature and deformation hardening considered, deformation equation was found using the principle of minimum energy. Finally, deformation equation and factors that affect deformation during high speed cutting were ascertained by combining analysis of deformation curve with cutting theory.

Abstract: Fatigue fracture is the main failure form of welded structures. Fatigue strength of welded joints is far below that of base metal under the combined effect of stress concentration, molten slag defects in weld toe and residual tensile stress. Fatigue damage mechanism and main factors that affect fatigue strength of welded structures are analysis and summarized respectively. This paper emphasizes on introducing the research progress of various measures to improve the fatigue properties, including weld toe grinding, TIG dressing, local-heating and local extrusion method, hammering and shot blasting and ultrasonic peening treatment.

Abstract: High quality mesh model is the premise and key condition to get accuracy numerical simulation results in casting process. However, it is usually difficult to build effective mesh model by professional casting simulation software ProCAST if solid model is too complex. Finite element mesh model transferring method has been introduced in this paper to transfer high quality mesh model into ProCAST by element imaging algorithm. With the help of the powerful meshing function of Pro/E, UG and ANSYS, the nodes and elements information has been picked up and image to new mesh model which is compatible with ProCAST. By this way, high quality mesh model can be introduced into casting process numerical calculation easily. It provides an effective and efficient way for the complex casting finite element mesh model.

Abstract: The environment and load condition of tubing is severe in high pressure wells. The sealability and joint strength of tubing string plays an important role in production operation. In this study, the makeup, sealability and joint strength was analyzed from conditions of make-up loading, tension loading, compression loading and internal pressure loading by finite element method. The makeup torque, the contact pressure distributions of metal seal along the axis and the stress distributions of threaded connection are given. The results show that under tension loading, compression loading and internal pressure, the overall stress level of threaded connection is lower than of pipe. The anti-compression performance and joint strength of threaded connection is greater than of pipe. The contact pressures of metal seal maintain relatively high level of contact pressures under tension loading, compression loading and internal pressure. Tension loading and compression loading reduces the sealing performance and the internal pressure increases the sealing performance from the integral of the contact pressure.

Abstract: The present work shows an experimental study for a first approach of a surface roughness predictive model of UNS A97075 aluminum pieces obtained by dry turning tests based on the cutting forces. In a first step, a design of experiments (DOE) 25 was employed to analyse the influence of the cutting parameters and type of tool on the surface roughness with the objective to find out a combination of cutting conditions that allow obtaining a range of values of surfaces roughness according to the aeronautical specifications requierements. The factors considered for this design were the feed rate, spindle speed, depth of cut, type of tool (nose radious) and machined length (zone of the workpiece where the surface roughness measurements are taken). The obtained data was analysed by means of the analysis of variance (ANOVA) method. And secondly, with the previous selected conditions selected it was developed by multiple regression a model to predict the surface roughness by measuring the cutting forces generated during the dry turning tests of aluminum alloy UNS A97075 pieces. The predictive model of surface roughness obtained includes statistical values calculated from the forces sygnal in time and frequency domains.

Abstract: This paper summarizes components and phases involved in the cupola melting process, then brings out a composition forecasting model based on the minimum Gibbs energy principle and the equilibria calculation algorithms of multiphase and multicomponent. Besides, the relationship between the melting parameters and the composition of molten iron is set up by using BP neural network based on the idea of indirect constraints. Finally, the paper probes the feasibility of the composition forecasting model with two examples. The application result shows that the prediction with this method can achieve strong practicability and popularization value.

Abstract: The hardness of SiC single crystal is very closer to that of diamond, which makes it greatly difficult to process SiC single crystal. It is usually machined by lapping, but this technique requires a long machining time, resulting in low productivity, So we examine the possibility of ELID grinding in SiC single crystal. Results show that with the use of ELID, mirror surfaces can be achieved with high efficiency.

Abstract: Driven by the huge market demand, the glass lenses made of various optical glasses are required to be more diversified in sizes/shapes, to have better form accuracy/ surface roughness, to be more environmental durable, and to be more competitive in price. In comparison to conventional refractive lens, diffractive lens (diffractive optical element, DOE) has the advantages of being thinner and lighter, and is widely used in optical systems such as lighting and photovoltaic systems. Glass moulding process(GMP) is regarded as a very promising technique for mass producing high precision optical components such as spherical/ aspheric glass lenses and free-form optics. However, only a handful of materials can sustain the chemical reaction, mechanical stress and temperature involved in the glass moulding process. Besides, almost all of these mould materials are classified as hard-to-machine materials. This makes the machining of these materials to sub-micrometer form accuracy and nanometer surface finish a rather tough and expensive task. As a result, making service life of mould longer has played a critical part in the GMP industry. The excessive stress and/or temperature involved in the moulding process are amongst the main reasons for pre-matured mould failure. This research aimed to analyze the stress/strain conditions and the obtained dimensional accuracy under various molding parameters by simulations. Molding experiments were subsequently carried out to verify the simulated results. A glass DOE of 14.8 mm in diameter and 3.36 mm in thickness are successfully produced in this research and the difference between the simulated and the molded DOE is around 15μm.

Abstract: Aiming at the disadvantages of intermittent indexing in the existing straight bevel gear machining methods, a continuous indexing machining method is proposed based on the principle of cycloid rotational indexing. The principle of rotational indexing machining of straight bevel gear is explained by the mathematical method of the space curve approximating straight line. On this basis, the mathematical models of forming motions are established. The relations of useful parameters are built with these models, and then the cutting point trajectory is obtained. The parameters are adjusted according to the approximation straightness of curve segment to generatrix on tooth surface. By means of calculation and numerical simulation of an example, the feasibility of the rotational indexing machining method for straight bevel gear is proved.

Abstract: Deformation mechanism of low-rigidity thin part caused by clamping force is studied in this paper. A coupled thermo-mechanical simulation process of aluminum alloy 6061 is developed using the finite element method with Abaqus. The results of simulation are verified by experimental measurements of cutting force and surface residual stress. Then using the model investigates the effect on residual stresses along the thickness of aluminum alloy 6061 load and unloadthe clamping forces. The deformation condition is also studied after removing fixing.