Advanced Materials Research Vols. 139-141

Abstract: Large oil storage tank (oil tank for short) shells are vulnerable to buckling damage when suffering the seismic loads. Numerical simulation analysis was taken to estimate the effects of the weld form, number and their location to axial buckling stress of cylindrical shells, considering not only the characteristic of welding processes, but also the effects probably caused by magnitude of residual stress and deformation on elephant foot buckling to oil tanks. It is revealed that the existence of circumferential welds had obvious negative effect on axial buckling critical stress compared with the structure without welds, while the effects of weld number and location were not as much; longitudinal welds had no visible effect on axial buckling critical stress; controlling the residual stress and deformation range caused by circumferential welds should be the key point during the tanks welding process.

Abstract: The frequency domain power spectra of acoustic emission (AE) signals from different metal-acid reaction processes such as 6111 Al-alloy-hydrochloric acid (HCl) and 7070 Al-alloy-HCl for evolving hydrogen gases were obtained by fast Fourier transform (FFT) program and used for chemical analysis of different metal materials. Averaged power spectra from these processes and their corresponding characteristics were extracted. The characteristic AE frequency signals could be used for chemical pattern recognition of different metal materials like 6111 and 7050 aluminum alloys from the metal-acid reaction processes, that the principal component analysis (PCA) with appropriate frequency selection procedure gave a satisfactory classification with a correct rate of 78.1%. The back-propagation (BP) algorithm of artificial neural network (ANN) could give better recognition of AE signals for 6111 and 7050 alloys with a correct rate of 100%. Moreover, the AE energetic parameters are linearly correlated with the pH value of the acidic buffer solution, which opens a new possibility for quantitatively analytical application of AE signals on metal materials.

Abstract: In the present research, the influences of different extrusion ratios (15, 30, 45, 60, and 75) and extrusion temperatures (300°C, 330°C, 360°C, 390°C, 420°C) on the mechanical properties and microstructure of homogenized AZ80 alloy have been investigated through the tensile tests and via metallographic microscope observation. The results show that the alloy’s grain is small and small amounts of black hard and brittle second-phase β (Mg17Al12) are precipitated uniformly along the grain boundary causing the gradual increase of the alloy’s tensile strength at 330°C. When the extrusion temperature is up to 390°C, the grain size increases significantly, but the second phase precipitation along grain boundaries transforms into continuous and uniform-distribution precipitation within the grain. In this case, when the extrusion ratio is 60, the alloy’s tensile strength reaches its peak 390Mpa. As the extrusion temperature increases, inhomogeneous precipitation of the second-phase along grain boundaries increases, causing the decrease of the alloy’s strength. At the same temperature, the tensile strength increases firstly and then decreases as extrusion ratio increases. With the gradual increase of the refinement grain, the dispersed precipitates increase and the alloy’s tensile strength and plasticity reach their peaks when the extrusion temperature is 390°C. As the grain grows, the second phase becomes inhomogeneous distribution, and the alloy’s strength and plasticity gradually decrease.

Abstract: Products from pyrolysis of wood-based composites contain lots of valuable chemicals. The nitrogen compounds make such pyrolysis products different from those of general biomass. In this study, we characterized pyrolysis liquids and solid residues of waste wood-based composites such as particle board (PB) and medium density fiberboard (MDF). The study focuses mainly on the evolution of nitrogen compounds. Thermogravimetric analysis helped us to determine the optimum pyrolysis temperature. FTIR analysis was used to observe functions of nitrogen compounds in the solid residues. Components of pyrolysis liquids were analyzed by gas chromatography mass spectroscopy (GC-MS). Changes of FTIR spectrum indicate that C-N groups are reduced during pyrolysis process. Results from GC-MS analysis show that pyrolysis liquids are influenced a lot by the nitrogen compounds transferred from urea formaldehyde. Such changes will guide the utilization of pyrolysis products from waste wood-based composites.

Abstract: The structure of the woven fabric liner of spherical plain bearing with self-lubricating is introduced, according to the microstructure and the actual weave pattern of the liners, the fibre yarns undulation and the distance between two fibre yarns are taken into account. A general elastic properties analysis model adjusting to the stain woven fabric liner is built. The elastic properties of the fabric liner are obtained using the method of micromechanical through getting the material and geometric parameters of the fiber yarns in the basis of stiffness average. The parameter expression of the compliance matrix and nine elastic constants are obtained and the theory model of fabric liner is validated by the experiment. The calculation results are in good agreement with the experimental data.

Abstract: This research develops a robust experimental procedure to monitor the evolution of early fatigue damage in AZ31 magnesium alloy with the acoustic nonlinearity parameter , and demons- trats its reliability by measuring the linear relationship between amplitudes of the second-harmonic waves and fundamental waves squared. Using this system, of two sets of specimens with different stress level is measured. The experimental results show that there is a significant increase in linked to fatigue degree in the early stages of fatigue life and reaches the maximum about 55%of fatigue life, when the stress level is ±60%of the yield stress, can characterize the early fatigue damage of magnesium alloy. However, when the stress level is ±70%of the yield stress, there is a regular fluctuation in linked to fatigue degree, this experimental results can’t be explained.

Abstract: A formula of equivalent strain for FCC single crystal superalloy was derived based on Hill’s yield criterion and was used for design of biaxial tension-torsion strain paths and loading levels of specimens. biaxial tension-torsion non-proportional cyclic loading process for single crystal nickel-based superalloy at the temperature of 680°C and 850°C was simulated by FEM analyzes; and influence degree of factors, such as strain range, strain path angle, tension-torsion loading phase angle, cycle characteristics and temperature etc., to low cycle fatigue damage of single crystal nickel-based superalloy were analyzed by using analysis of variance based on orthogonal experiments. The results show that if Hill’s equivalent stress range is used as a fatigue damage parameter, the factors produce effects on low cycle fatigue damage of single crystal nickel-based superalloy. The factors are listed in the order of significance as followed: temperature, strain range, tension-torsion loading phase angle, strain path angle and axial loading strain ratio.

Abstract: Dual phase (DP) steel is increasingly utilized in automotive industry to match the requirement of both performance and lightweight of autobody for economical and ecological considerations. Most of autobody structures are manufactured by stamping process which imports prestrain effects into original material and alters its static and cyclic mechanical behaviors. In this study, mechanical behavior of prestrained DP steel was researched. Firstly, microstructure of commercial DP steel with different prestrain levels was examined with optical microscope of 500X magnification. Then, static tensile experiments and strain-controlled fatigue experiments were carried out at room temperature. Test results of differenet prestrain levels were compared. Static stress-strain relationship and local strain-life model were determined using linear regression method. Furthermore, fatigue performance and notch fatigue resistance capability were compared with prestrain level based on Neuber factor. Finally, explanation of the change with prestrain was presented with crack closure theory.

Abstract: The cold rolled strip undergoes great transforming of micro-organization and change in properties in continuous annealing furnace. At the same time, it is acted upon by all kinds of forces, such as tensile and compressive stresses, bending stress, thermal stress. and thus it would affect stability of the steel strip. The finite element model of steel strip and guide rollers are established, and the ANSYS software is used to study the effects on transverse stress distribution under different strip shapes that contains center buckle, double edge wave, compound buckle, quarter buckle and quality shape. Profile of guide rollers such as different crowns and straight lengths are also be researched which is intended to provide a reliable base in theory for getting reasonable profile of guide rollers and homogenizing the tensile stress to improve shape quality.

Abstract: Using the model of generalized micropolar magneto-thermo-elasticity, reflection and refraction of longitudinal displacement wave at interface of two welded micropolar elastic media are studied. The model can be applied to the coupled theory as well as to five generalizations, such as L-S theory, G-L theory, H-I theory, G-N theory of type (II) and C-T theory. And if some parameters in this model are taken as given values, we can easily deduce the known models of Kelvin-Voigt model and other generalized micropolar/magneto/thermo/viscoelastic theory model. Using continuous conditions at the interface, the amplitude ratios of reflected and refracted micropolar magneto-thermoelastic longitudinal displacement waves, longitudinal microrotational waves and the coupled transverse and microrotational waves are studied for incident longitudinal displacement wave. The numerical results show that the effect of magnetic field is very significant on the amplitude ratios.