Materials Science Forum Vols. 575-578

Abstract: By the approaches of the theory of complex functions, dynamic propagation problems on the surfaces of mode I crack subjected to unit-step loads and instantaneous impulse loads located at the origin of the coordinates were studied for Aluminum alloys, respectively. Analytical solutions to stresses, displacements, dynamic stress intensity factors and dislocation distribution functions are gained by the methods of self-similar functions. The problems considered can be very facilely transformed into Riemann-Hilbert problem and their closed solutions are obtained rather straightforward by Muskhelishvili’s measure.

Abstract: the inverse analysis to material parameters is often translated into an optimization for an objective function, based on the correlation between the material parameters and the foregone information. But mostly because of the non-linear correlation, a good optimization algorithm with the capabilities to avoid being trapped by local optima is required during the process of optimization. So the present paper proposes a new global optimization algorithm, which couples the dynamic canonical descent algorithm and the improved Powell’s algorithm. The high efficiency of the new algorithm is shown on four known problems classically for testing optimization algorithms and finally, in the non-linear inverse analysis, the new algorithm is used for optimizing an objective function to get material parameters rightly.

Abstract: Axisymmetric nonlinear bending of the functionally graded circular plates is investigated in the present work. The material properties of plates are assumed to be graded in the thickness direction according to a simple power law distribution in terms of the volume fractions of the constituents, and to be temperature-dependent. Based on the classical nonlinear plate theory, the governing equations for the problem are derived, and then a shooting method is employed to numerically solve the equations. Effects of material constant, temperature- dependent properties and boundary conditions on the nonlinear bending behavior of the FGM plate are discussed in details.

Abstract: In this paper, by some technological process, the reusable filtration materials has been made by using the main waste residue of ceramic industry—waste ceramics as the aggregate and mixing with proper binder and pore-forming agent. The production process of filtration materials and the character of light CaCO3 as pore-forming agent were described; For the selected raw materials, changed the ratio and aggregate granularity, the influence of ceramic aggregate content on the aperture, aperture distribution, porosity and bending strength of filtration materials and the influence of aperture distribution of aggregate on sample’s capability have been revealed based on the XRD analysis, SEM observation and bending strength measurement of filtration materials; at the same time, the influence of sintering temperature on the porosity and bending strength of filtration materials was also studied. The results show that the better filtration effect and better chemical durability, the higher bending strength (15MPa) of the synthetical filtration materials can be obtained when the content of aggregate, the particle size and the sintering temperature are respectively 50~55wt%, 150~1804m and 1205°C.

Abstract: Mechanical behaviour at creep and superplasticity of coarse grain and monocrystalline aluminum under torsion, of coarse grain molybdenum, of fine grain zinc alloy and amorphous cobalt alloy under tension are discussed from unified positions. It is shown that realization of their superplasticity requires fulfillment of structure-kinetic principle.

Abstract: Different cooling parameters, including the initial cooling temperature, finishing cooling temperature and cooling rate, have a significant effect on the final microstructures and properties for pipeline steels. In present work, Gleeble-1500 thermal-mechanical simulator was used to investigate the microstructural evolution of X70 pipeline steels under different cooling conditions, and the microstructures obtained were analyzed using optical microscope and transmission electron microscope. The experimental results showed that when the initial and finishing cooling temperatures are controlled in the range of 740~760°C and 500~520°C respectively, the microstructure of X70 pipeline steels reveals a proper content (about 12%) of pre-eutectoid ferrite besides acicular ferrite and M/A (Martensite/Austenite) island, which can guarantee an optimum combination of strength and ductility. In contrast to the conventional way using CCT curve, this methodology shows a higher accuracy and operability, and used in industrial production to achieve good effect.

Abstract: The residual stresses induced in fiber-reinforced functionally graded composites cooling down from the processing temperature are determined with concentric cylinder model and analytical solutions of inhomogeneous governing equations for displacement components, which include particular solution and general solution of the corresponding homogeneous equations. The analytical solutions presented here are general for power-law variations of the elastic moduli of the functionally graded matrix. With a power exponent, analytical expressions for the residual stresses of fiber-reinforced functionally graded composites can be obtained. By changing the power exponent and the coefficient of the power terms, the solutions obtained here could be applied to fiber-reinforced functionally graded composites with different properties. The results show that the large difference exists between functionally graded composites and common-used composites consisting of two phases of homogenous materials. The variation of matrix modulus and fiber percentage have a great deal of effects on the residual stresses in functionally graded composites.

Abstract: The paper is aimed to exploit a creep constitutive mode of TC11 titanium alloy based on RBF neural network. Creep testing data of TC11 titanium alloy obtained under the same temperature and different stress are considered as knowledge base and the characteristics of rheological forming of materials and radial basis function neural network (RBFNN) are also combined when exploiting the model. A part of data extracted from knowledge base is divided into two groups: one is learning sample and the other testing sample, which are being performed training, learning and simulating. Then predicting value is compared with the creep testing value and the theoretical value deduced by primary model, which validates that the RBFNN model has higher precision and generalizing ability.

Abstract: The hot ductility of Fe-18Cr-12Mn-0.55N high nitrogen austenitic stainless steel was investigated in Gleeble-2000 thermomechanical simulator. The experimental results show that the hot ductility curve of test steel is comprised of high-temperature brittlement region at the test temperatures higher than 1150°C, high-temperature ductility region at the test temperatures from 850°C to 1150°C and middle-temperature half brittlement region at the test temperatures lower than 850°C. High-temperature brittlement and middle-temperature half brittlement are caused by the appearances of δ ferrite and the precipitation of Cr2N phase at austenitic grain boundaries, respectively, and the excellent hot ductility at test temperatures between the two brittlement temperature regions results from the stable single phase austenitic microstructure.

Abstract: Formation of austenite strongly influences the microstructures and mechanical properties of dual phase steels. In present work, austenization process during intercritical annealing was studied in a Fe-C-Mn steel using Gleeble-1500 thermal simulator and quantitative microscopy. The experimental results show that austenite formation is separated into three different stages: (i) growth of high carbon austenite into pearlite rapidly until pearlite dissolution is completed; (ii) slower growth of austenite into ferrite; (iii) very slow equilibration between ferrite and austenite. The thermodynamic and kinetic analyses show that growth of austenite into ferrite is controlled by carbon diffusion in austenite in the primary stage and manganese diffusion in ferrite in the subsequent stage because diffusion coefficient of Mn in ferrite is several orders of magnitude smaller than that of C in austenite. The slow final equilibration between ferrite and austenite is obtained by manganese diffusion through the austenite. Based on the analysis, one dimensional diffusion model of intercritical austenization was developed and solved using finite volume method on the assumption that solute flux was local balance at interface, and the kinetics calculated was compared with experimental results. Simulated results indicate that growth of austenite reaches paraequilibrium in about one second, but remains thousands of seconds to reach final equilibrium. Simulated concentration profiles show that manganese atoms transferred from ferrite congregate in austenite near phase interface, which is consistent with the experimental phenomenon.