Applied Mechanics and Materials Vols. 152-154

Abstract: In this text, the effect of electromagnetic stirring (EMS) on the quantities of the martensite stainless steel ingots was investigated by static casting experiment. The results of the experiment show that to compared with the traditional cast, the EMS can obviously improve the quantities of the martensite stainless steel ingots. By the EMS technique, the ratio of equiaxed grains greatly increased and when the current remains content, the ratio of equiaxed grain increases first and then decreases as the stirring frequency increasing. There is a maximum value at the 5Hz. With the EMS the carbon and the chromium in the ingots are better distributed. The segregation of C and Cr is inhabited. And also with the EMS, the grains of the martensite stainless steel ingots become finer and more homogeneity; consequently the appearance and distribution of the troostite in the ingots obviously changed: without the EMS the troostite distributes in net shape or block shape and with the EMS, the troostite distributes in the matrix dispersedly.

Abstract: Hybrid poplar boards were subjected to thermo-mechanical densification combined with heat treatment. Hydroscopicity and hygroscopicity of the treated samples were measured. The results showed that dimensional stability of the samples was influenced by compression set significantly. The higher the compression set, the greater the swelling of the samples. On the contrary, the influence of densification temperature and duration was not significant. Thermal modification significantly reduced hydroscopicity and hygroscopicity of the samples. Both higher treatment temperature and longer holding time resulted in better dimensional stability.

Abstract: To investigate the validity of steel slag as aggregates in road surface dressing, a series of tests for asphalt concrete mixed with asphalt cement and steel slag aggregates particles are performed using Marshall method. Through the statistical analysis of the test data, and comparison the data with those of asphalt macadam mixture, the asphalt concrete mixed with asphalt cement and steel slag aggregates have very large stiffness, high resistance to deformation and high resistance to cracking. If meeting the requirements of the code in china for asphalt macadam mixture, steel slag can be applied in road surface dressing instead of stone aggregates, but also bring remarkable economic effect and has broad application prospect.

Abstract: Oscillography impact properties were studied in four different temperatures. The research indicated that impact energy of sampled 4145H DC met the standard of“SYT5144-2007 Drilling collar” and “API SPEC7” in four different temperatures. With temperatures getting down, impact energy, crack propagation energy, and crack propagation energy/impact energy ratio decreased, cracking energy/impact energy ratio increased, crack propagation rate increased and dynamic fracture toughness decreased. In drilling, crack growth rate in DC was slow; the DC was not liable to fracture in normal temperature. On the contrary, crack growth rate was fast, as a result, the DC was easy to fracture in low temperature. The results provide reliable experiment resources for research on 4145H DC fracture. The research results provide reliable guidance for DC production and use in drilling and offer basic experimental evidence to the analysis of 4145H DC fracture mechanism.

Abstract: Non-agglomerated ammonium dimolybdate (ADM) monocrystals with large diameter and high dispersion has been prepared through reaction-evaporation-crystallization (REC) process using ammonium tetramolybdate and ammonia solution as reactants. The as-prepared ADM monocrystals were systematically characterized by x-ray powder diffraction, transmission-reflection optical microscope, Fourier transform infrared spectroscopy and TG-DSC thermal analysis. It is shown that the as-prepared ADM samples are disperse monocrystals with well grain distribution and geometric shape, which can well meet the quality requirements for the subsequent production of molybdenum powders.

Abstract: Nano-Cr2O3 was added to vitrified bond CBN grinding tools to improve their properties. Effects of nano-Cr2O3 on properties and microstructures of vitrified bond CBN grinding tools were investigated. The samples were characterized by differential thermal analysis (TG-DTA), scanning electron microscopy (SEM) and related detecting techniques. Results show that the refractoriness of vitrified bond firstly decreases and then increases with the addition of nano-Cr2O3, but the fluidity has the opposite change. Compared with basic vitrified bond, the refractoriness and fluidity of vitrified bond (4 wt.% nano-Cr2O3) are reduced by 25°C and increased by 5.4%, respectively. The bending strength of CBN grinding tools can be enhanced obviously with the addition of nano-Cr2O3, and it has the maximum bending strength (59.27MPa) when adding 4 wt.% nano-Cr2O3. SEM result shows that CBN grinding tool has the most dense structure and the least pore when adding 4 wt.% nano-Cr2O3.

Abstract: Age forming is the best forming method of integral panel parts of aircrafts, which have large amount of springback and the springback’s accuracy, is hard to control, so a method which can make an accurate prediction of the springback after forming is needed. This article which is based on creep test data and CPT, fits the creep constitutive equation and obtained the material parameter. The numerical simulation is adopted to process age forming simulation on springback of T-specimen of aluminum 2124, and the simulation result is compared with the test result to do revision of the material parameter; the revised material parameter is applied into the numerical simulation of age forming of the integral panel which is of high strength. Through tests which can confirm the error ranges from -1mm to +1mm, this method’s accuracy is proved.

Abstract: This paper proposed a method and process of stress relaxation forming based on initial geometric springback compensation-finite element optimization-revision by experiment iteration. Obtained material parameters of 2124 aluminum alloy by a series of foundation craft experiments; springback law on the structure of 2124 aluminum alloy by foundation experiment of autoclave forming of T test specimens, that use to compensate the mold surface with the geometric springback. The precision of the geometric springback compensation of the mold surface is about 3 mm; while after the finite element iteration optimization on the mold surface with the initial geometric springback compensation, the deviation of that between the testing date and the theory appearance of specimens can reach the magnitude about ±1.2 mm. Next use the mold “frequency domain” revision algorithm based on experiment iteration to revise local mold surface of the stress relaxation forming. The testing date shows the precision control in ±0.5 mm that satisfied with the application of engineering.

Abstract: Semi-infinite elastic solid is a classical mechanics subject. Recently, the subject has been researched on various ways. Under different loading conditions, various solutions were given by researchers. But their results are more complicated and expressed in implicit equations. Due to the limitations of their results, the explicit function of stresses filed at given conditions is given by the use of numerical analytical method, 3D finite-element method and 3D fitting equation software. The applicability of the proposed approach has been verified by the use of Boussinesq’s solution. The result shows that the proposed approach presented in this paper can not only be applied to deal with semi-infinite elastic solid subject, but also be suitable for damage evaluation and life prediction of semi-infinite elastic solid under special conditions.

Abstract: Tensile properties of rolled and annealed copper thin foils were investigated based on the grain size and thickness. Yield strength was higher in the thinner foil than in the thicker foil at as-rolled state. Difference of yield strength between the thinner foil and the thicker foil becomes small at annealed state. Tensile strength was higher in the thinner foil than in the thicker foil at as-rolled state, but it was reversed at annealed state. Strain to fracture or elongation increased with increasing thickness in the annealed state. A knife edge type of fracture was characterized in both the as-rolled state and the annealed state. A higher tensile strength and strain to fracture of the annealed thicker foil was attributed to the higher number of grains per thickness. From this work, it was concluded that mechanical properties of thin foils were dependent upon the number of grains per thickness.