Materials Science Forum Vols. 575-578

Abstract: Strengthened coating on the surface of 35CrMo steel alloy was deposited by electrospark process using NiCr electrode. The bond strength and microhardness of the coating was checked and the microstructure of the strengthened coating was analyzed using the optical micro-scope, X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersion spectrum (EDS). The results show that the bond strength between the coating and the base metal is 495.1MPa, and the hardness of the coating surface is about 2 times than that of the base metal, and the property of the workpieces surface has become better. The coating is a metallurgical reacting bonding layer between the base metal and the NiCr electrode, and its main ingredients are FeNi and NiCrFe.

Abstract: In this particular work, the moving Gauss heat source model based on the gas tungsten arc welding and a new heat source model based on the laser-TIG hybrid welding were developed by the finite element analysis according to the physical characteristic of the TIG welding and the laser-TIG hybrid welding, Taking into account the advice of parameter modification, the modeling was respectively carried out by the single TIG and the laser-TIG hybrid welding for AZ31B magnesium alloy. The welding temperature field and the weld cross-section geometry were simulated separately with regard to dependence on the single TIG and the laser-TIG hybrid welding. Comparing the experimentally measured value with simulated value of the weld section geometry, the simulated and the experimentally determined weld section geometry by the single TIG welding and the hybrid welding showed a good agreement, at the same time, the microstructures of the joint were also discussed respectively.

Abstract: The surface material of Elastic-metal pads(EMP) is PTFE which has poor wearability . Ion implantation can improve the wearability of EMP surface .This paper investigated the wearability improvement of the EMP’s surface by Al2O3/PTFE film which generated by ion implantation. The accelerating voltage of the ion implantation apparatus is 40KV and the ion emitting energy of aluminum is 20KeV. The dosages of three kinds of Al3+ ion beams in the study are 1×1015 ions/cm2, 5×1015 ions/cm2 and 1×1016 ions/cm2 respectively. The aluminum ion’s density is 10uA/cm2. The vacuum pressure of the ion implantation is 3×10-3Pa. The experimental specimens modified by Al3+ ion implantation were tested by ESCA, XRD, AFM/FFM and nanometer probe , which got the chemical bond, phase structure and friction coefficient of the film. According to the experimental results, the mathematical model was built using the Fesow Geometric Model and the Halind Rang Theory. The computer simulation was made in which SRIM simulator program was employed. The ion implantation’s energy for the simulation is 20keV and the material density of PTFE is 2.56g/cm³. In addition, the dose is 5×1015 ions/cm², the time interval is 230 minutes and the velocity of Al3+ ion implantation is 2.15-2.20×1013 ions/minute. Finally the simulation curves of particle distribution, energy distribution and impairment etc. were plotted and discussed.

Abstract: A constitutive model for magnetic shape memory alloys is developed through a combined consideration of micromechanical and thermodynamic theories. Of special concern is the influence of different temperatures on field-induced reorientation strain for a NiMnGa single-crystal specimen. The theoretical results are found to be in general agreement with experimental data. It is shown that the method is accurate and simple.

Abstract: This paper starts with a discussion on the theory of finite deformation and various types strain energy functions of rubber like material, the material parameter of elastic law of Gao[3] is estimated by experiment and numerical simulation. Because there are various types of strain energy functions, a user subroutine is programmed to implement the strain energy function of Gao[3] into the program of MSC.Marc, which offers a convenient method to analyze the stress and strain of rubber-like material with the strain energy function that is needed. Two examples will be presented in this paper to demonstrate the use of the framework for rubber like materials. One is to simulate a foam tube in compression. The other one is to simulate a rectangle board with a circular hole. After numerical analysis, it is proved the numerical results based on Gao model are in perfect agreement with the results based on Mooney model and the estimated material parameters are valid.

Abstract: Short fiber reinforced Al-base composite can be manufactured various parts by plastic working. Elastic modulus has a large influence on the parts among the composite system. In the paper, model of finite-element analysis has been established. The influences of interface modulus on the law of stress-strain distribution, the strength and the modulus for the composite materials have been simulated by ANSYS in the condition of strong-bond, medium-bond and weak-bond interface. The results show that the stress-strain distribution is non-uniform, moreover the force on the fiber is greatly higher than that of the matrix within the composite materials; the strength of the composite materials is improved with the increasing of the interface modulus, but the increasing will be limited by the strength of fiber. Therefore the relation of ideal interface modulus with the fiber strength has been proposed. 70GPa of the interface modulus is thought to be better for M40 short fiber.

Abstract: In order to develop an environment-friendly method of forming a chemical conversion coating on 2024 aluminium alloy surface without the toxic hexavalent chromium compounds, in this paper a process with sodium molybdate and potassium permanganate as the main compositions of the treating bath has been investigated. Solution composition and process parameters have been optimized. The chemical conversion coating has good corrosion resistance, evaluated with dropping test. Micro-structure and components of the conversion coating have been studied by various micro-analysis methods, and the growth mechanism of the chemical conversion coating has also been investigated.

Abstract: Bonding degradation at interface is one of main damage forms of composites, especially under fatigue loading. Interfacial bonding degradation of FRC under two-stage tension loading is studied, which is base for variable-amplitude cyclic loading existing widely in actual engineering. Based on the shear-lag model and considered the asymmetry of interfacial damage, the mechanical governing equations of fiber and matrix are established and related solutions are obtained firstly. Two kinds of loading models are chosen, one is low-high alternate loading, and the other is low early and high late loading. By the aid of the Paris law and the energy release theory, a relationship between debond rate and cycle number is established. Then the interfacial debonding is simulated under the two-stage tension loading. The rules of the crack growth are analyzed for low-high two-stage loadings. It is found that stress amplitude has great influence on interfacial debonding under two-stage loading. Low stress amplitude in a certain range can postpone interfacial bonding degradation. And interfacial damage extent is greater than that under constant-amplitude fatigue loading. Present study is helpful for analyzing the fatigue damage of engineering materials and structures.

Abstract: The purposes of this study are to modify asphalt by retrieved waste-PE in packing (WPP) and to investigate the low temperature properties of the modified asphalt. The traditional testing methods such as low temperature ductility, low temperature penetration degree, penetration or Fraass breaking point think that PE can not improve the low temperature properties of asphalt effectively, while this study adopts a new method to test the low temperature properties of WPP modified asphalt through the freeze-to-crack test. The result indicated that, after the modification, the low temperature properties of asphalt are improved, which coincides with the fact. And the improvement of the low temperature properties can be explained by the function of Shear yield and crack pinning.