Key Engineering Materials Vols. 324-325

Abstract: Recently, people devote to the development of Ni-free shape memory alloys in order to avoid the Ni-hypersensitivity and toxicity and pursue absolute safety. The shape memory effect and superelasticity have been reported in the biomedical Ti-Nb based alloys. The purpose of this paper is to report the phase constitution, tensile property, shape memory effect and corrosion resistance of the Ti-Nb alloys. The phase constitutions of the Ti-Nb alloys are investigated by means of X-ray diffraction (XRD). The results reveal that β+α′′ phases are presented in the Ti-35Nb alloy and only β phase in the Ti-52Nb alloy at room temperature. The tensile test and bending tests indicate that the Ti-35Nb alloy exhibits shape memory effect. The shape recovery ratio is near to 80% when the bending strain is 4.4% and decreases with the increase of the total bending strain. The corrosion resistance of the Ti-Nb alloys in the Hank's solution and artificial saliva (pH=7.4) at 37
are investigated by OCP, Tafel and anodic polarization methods. The results indicate that the Ti-35Nb alloy has a better corrosion resistance in the artificial saliva and can replace the Ti-Ni alloy in the dental application. In the non-oral condition, the Ti-52Nb alloy may be preferable.

Abstract: Magnetic nanoparticles have attracted intensive attention for their wide applications as biomaterials and magnetic storage materials. Polyurethane is one of the most biocompatible polymers and has been used widely in vivo. In this paper, the magnetite nanoparticles were synthesized by chemical precipitation under different conditions. The as-prepared samples were characterized by X-ray diffraction and transmission electron microscopy, and their magnetic properties were evaluated on a vibrating sample magnetometer. Then the magnetite nanoparticles with different amounts were doped into polyurethane directly and composite films were made. Reinforced by the inorganic particles, PU composite films were also characterized by Fourier transform infrared spectra and mechanical tests., and the surface morphology of the composite film was observed by Atomic Force Microscope The results showed the composite material was reinforced by magnetic nanoparticles and also showed magnetic behavior. This kind of composite materials have the potential to be used as hyperthermia treatment in biomedical field, like coatings on cardiovascular stents.

Abstract: In this work, potential problems with the application of polymer matrix composites (PMC) in extreme environments [1] is discussed. Then, two specific examples of the applications of PMCs in high voltage [2-7] and high temperature [8-15] situations are evaluated. The first example deals with damage evolution in high voltage composite insulators [2-7] with PMC rods subjected to a combined action of extreme mechanical, electrical and environmental stresses. These insulators are widely used in transmission line and substation applications around the world. Subsequently, advanced high temperature graphite/polyimide composites [8-15] are evaluated for aerospace applications. The composite investigated in this project were used to manufacture and successfully test a Rocket Based Combined Cycle (RBCC) third-generation, reusable liquid propellant rocket engine, which is one possible engine for a future single-stage-to-orbit vehicle [8].

Abstract: This paper quantifies the effects of geometry, the loading mode and the specimen size on fracture toughness of the API X65 steel, via plane strain finite element (FE) damage analyses using the GTN model. The validity of FE damage analyses is checked first by comparing with experimental test data for small-sized, cracked bar test. Then the analyses are extended to investigate the effects of the relative crack depth and the specimen size on fracture toughness. It is shown that fracture toughness of the API X65 steel increases with decreasing the relative crack depth and increasing the specimen size.

Abstract: TiCp/ZA-12 composites have been fabricated by XDTM method and stirring-casting techniques. The tests for mechanical properties reveal that the tensile strength and
 strength increase with increasing fraction of TiC particles. When the fraction of TiC particles increase up to 10%, the tensile strength and yield strength are 390MPa and 340MPa, respectively and they increase by 11% and 17% than that of matrix respectively. From the analysis of fractography we can see that mixed fracture of cleavage fracture and dimple fracture exists in the TiCp/ZA-12 composites, and fractured particles are not found. Finally the fracture model of composites has been established based on the experimental results.

Abstract: A new thermal spraying technique, electro-thermal explosion directional spraying (EEDS), was used to prepare NiAl intermetallic coatings. The microstructure, elements distribution and phase structures were determined by means of SEM, EDAX and X-Ray diffraction, respectively. Micro-mechanics properties were tested by using nano-indentation tester. The wear resistance of the coating was also investigated. Results showed that NiAl coating was characterized by compact construction. The main phase of the coating was Ni-Al and the content of oxide was little. The obvious elements diffusion showed that the bond between the coating and the substrate was metallurgical one. The nano-hardness and the modulus were 7.6 GPa and 218.8 GPa, respectively. The coatings processed good wear resistance and the main wear failure mechanism was the micro-plowing.

Abstract: Scattering of SH wave by a crack is studied in elastic half space with a removable rigid cylindrical inclusion by Green’s function, complex function and moving coordinate method. In half space, firstly the scattering wave function of removable rigid cylindrical inclusion is constructed; next a suitable Green’s function is solved for present problem, then using crack-division to make a crack. Thus the solution of problem can be obtained. Numerical examples are provided and discussed.

Abstract: The microscopic processes of internal force redistribution of structural system due to dead load failure or fatigue failure of structural element and failure mechanism of cumulative damage under outside loads is discussed in this paper. Considering the influence of cumulative damage to the residual strength and the reasonable time of dead load failure selected, the next step calculation of cumulative damage has a clear quantitative time. Reasonable expression is provided for the establishment of the equation of safety margin. By an example, the reliability index, which is gained by rough conservative considering the time of dead load failure selected, is compared with the reliability index, which is gained by using the method of this paper. The method of this paper coincides with the engineering fact by analysis. A reasonable method is provided for reliability analysis which structural system is considered dead load and fatigue failure at the same time.

Abstract: In the piezoelectric truss structure with many random parameters under incipient defect, taking into consideration the mechanical-electric coupling effect under electric load and mechanical load, the formula of safety margins of bar have been proposed by the fracture intensity, bar section area and loads as random variables. On the base of above research, stochastic finite element method is adopted to attempt to analyze reliability of the piezoelectric truss structure. In the end, the example is given to demonstrate the influence of voltage and of damage on reliability index of the piezoelectric truss system.

Abstract: In present paper, the mechanical properties and fracturegraphs of Mn-rich polycrystalline alloys are investigated by compression tests and scanning electron microscope (SEM) observations. It is shown that the fracture strength and the rupture strain decrease with the increase of Mn content. It is suggested that the substitution of Mn for Ga reduces the ductility of Ni-Mn-Ga alloys. SEM observations of fracture surface show us typical intergranular crack. There are many little holes and micro-cracks on the grain boundary, which weakens the bond strength of grain boundary causing the intercrystalline cracking.