Advanced Materials Research Vols. 476-478

Abstract: In this paper, we investigated the structure of SmCo films with different thickness and the effects of Cr buffer layer on the structure and morphology of SmCo/Cu thin films. Our data revealed that the magnetic properties of the samples were enhanced by the crystallization of SmCo which was promoted by the optimized Cu underlayers. We also found that the surface roughness can be decreased by Cr layer and the texture can be improved by prolonging the annealing time for thick SmCo film. Thus, we concluded that the magnetic properties of SmCo/Cu films can be further optimized by varying the thickness of Cr buffer layers.

Abstract: Nanocrystalline diamond (NCD) films were prepared on polycrystalline aluminum oxide (Al2O3) substrates by microwave plasma chemical vapor deposition (MPCVD) technique using Ar/CH4/CO2 plasma. The main objective is to study the structure and mechanical properties of the NCD films. The NCD films micrograph were examined by scanning electron microscopy (SEM) and atom force microscopy (AFM). The structure and phase composition of the films were analyzed by X-ray diffraction (XRD) and visible Raman spectroscopy. Friction testing machine was used to test the friction coefficient of the films. It was found that the diamond films possess better structure and smooth surface. Compared to Al2O3 substrates, the friction coefficient of the NCD films was smaller and the wear resistance was improved significantly.

Abstract: An integrated evaluative function and prediction model and prewarning system for water bloom in lakes based on Elman neural network is proposed in this paper, in which main influence factor of outbreak of water bloom is analyzed by rough set theory. The study of the function involves some aspects: algal average activation energy of photosynthesis, integrated nutritional status index, and transparency, which are considered from the microcosmic level, the macroscopic level and the intuitionistic level respectively. The values of the function are classified properly. Combined with the basic features of outbreak of water-bloom, Elman network is studied from the angles of theory and experiment and a water-bloom prewarning system in short term based on Elman network is established. The results of simulation and application show that: Elman neural network improves the algorithm of BP neural network, it has long-term prediction period, strong generalization ability， high prediction accuracy; and needs a small amount of sample and this model provides an efficient new way for short-term water bloom prediction, And approaching ability of Elman network is more superficial than common static networks and its velocity of convergence is faster.

Abstract: Compact tension specimens cut from 2024-T351 aluminum-alloy plate were used for Vickers hardness tests under low-force scale and then for fatigue crack growth tests under sinusoidal loads, and the scattered data sets obtained including Vickers hardness, initiation cycle and specimen life, exponent m and intercept C of Paris-Erdogan law were collected as a factor set with five factor series for analysis of grey relational grade. Nominal value method was adopted for the preprocess referred to as grey relational generation to obtained new factor series, and then Hsia’s method was used to calculate the grey relational grades among new factor series. The analyzed result named global grey relational grade in matrix form with dimension of shows three main findings: (1) Vickers hardness has the largest influence on specimen life, and vice versa. (2) Vickers hardness, specimen life, and m have a large influence on each other. (3) C has the least influence on any other factors, and vice versa.

Abstract: Ti-15V-3Cr-3Al-3Sn, β-phase titanium alloy, is subjected to study the microstructure and mechanical behavior after thermohydrogen processing. It aims to study the relationship between microstructure modification and notched tensile test at room temperature. Meanwhile, the notched tensile test and fracture features of Ti-15-3 alloy without THP is also discussed. It follows that the hardness of Ti-15V-3Cr-3Al-3Sn would be clearly enhaced up to Hv 499 after thermohydrogen processing due to grain refinement. Besides, the notched tensile strength of the as-received specimen is about 904 MPa, and is increased to 959 MPa after THP, that is, Ti-15-3 alloy after THP shows higher hardness and notched tensile strength than as-received alloy. The enhanced high hardness does not induce a significant notched embrittlement effect.

Abstract: The fractal dimension is a basic parameter to indicate the random self-similar shape and phenomena. The damage process is the result of co-effect of all the cracks, which shows a good collective behavior and random statistical complexity. The collective evolution of short fatigue cracks was experimentally studied through cylindrical specimens with annular notches with respect to the variation of nominal strain amplitudes. The maximum between-class variance method (Otsu's method) was adopted for the denoised image binarization and the fractal dimensions were obtained. The results show that: the collective behavior of short fatigue cracks possesses good fractal characteristics; as the evolution of the short fatigue cracks, fractal dimensions underwent two stages: a primary stage of high growth speed, a relatively stable stage of almost to zero growth speed; the critical cut-off point at about 30% of the fatigue life according to the experimental results can be used to represent a threshold value of the MSC and PSC of short fatigue cracks.

Abstract: The effect of energy input of welding thermal cycles with different t_(8/5) on the cryogenic toughness of the coarse-grained heat-affected zones(CGHAZs) in steel 9Ni was invested. The CGHAZ specimens for different energy input welding thermal cycles were prepared by GLEEBLE3500 thermal simulative experimental machine. The fracture morphology of welding thermal cycle specimens with different t_(8/5) was observed by using SEM. The microstructure, prior austenite grain and the appearance of packet in HAZ were observed by using OM. The block width was measured by using EBSD. The cryogenic toughness of the welding thermal cycle specimens becomes better with increasing t_(8/5). With increasing t_(8/5)，the appearance of granular bainite makes the space of martensite diminish, which refines the packet and block sizes. The refinement of martensite packet is the reason of the improvement of cryogenic toughness in steel 9Ni.

Abstract: Both experimental and numerical analyses into the shear toughness parameter for Sn/3.0Ag/0.5Cu and 63Sn/37Pb solder ball joints are performed. The ball shear tests are conducted at the loading speeds of 200μm/s and 300μm/s using ball joint specimens with diameters of 300, 600 and 760 μm. The failure behavior of the solder joints is quantified in terms of their fracture toughness. The results show that the shear toughness increases with an increasing solder ball diameter. Furthermore, it is shown that the Sn/3.0Ag/0.5Cu solder ball has a greater ductility than the eutectic 63Sn/37Pb solder ball. It is found that the shear toughness with great differentiability is relatively insensitive to the loading speed, and is therefore a suitable parameter with which to evaluate the ductility of solder ball joints in ball shear tests. Finally, the finite element analysis is further employed in the simulation with the software of MSC, Marc. Numerical predictions have good agreements compared with experiment ones.

Abstract: Stability of rectangular triaxial weave fabric (TWF) composite plate with simply supported edges that is subjected to uniformly distributed biaxial compressive forces, Nx and Ny, is investigated for various load intensities and aspect ratios. TWF unit cell is discretized using 2D composite finite element of non-conforming types adopting Lagrange and Hermite interpolation functions for in-plane and out-of-plane degree of freedoms, respectively. In addition, homogenized and segmentation methods are used for the material descriptions of the plate. For the solution, eigenvalue analysis is employed in obtaining the critical buckling loads of the assembled global stability governing equation. In general, TWF plate’s aspect ratio plays somewhat greater role on biaxial stability than that of load intensity.

Abstract: In this paper, a constitutive relationship of the concrete core restrained by L-Shaped steel tube is put forward based on referring to the constitutive relations of core concrete in concrete-filled square steel tube columns, which takes the restraint of steel tube to concrete as an equivalent confinable effect coefficient . Load-deformation relationship of L-Shaped concrete-filled steel tubular column subjected to axial compression is analyzed by finite element analysis (using ABAQUS software). The predicted load versus deformation relationship cures are in good agreement with those of tests based on the finite element analysis, loads carried by steel tubes and concrete respectively during the loading process, as well as interactions between them are analyzed. Finally, influences of length-width ratio and width-thickness ratio on the interaction between steel tubes and concrete are investigated.