机械设计制造相关问题分析

本文论述了机械设计生产时期对于物质的选取以及标准的使用等内容。

铝合金焊接结构件抗断裂性能的优化

本文提出了将析出强化、屈服强度、机械硬化和力学建模等过程组合起来,能有效改善时效硬化Al-Mg-Si合金制成的汽车焊接件的承载能力。

Kinetics for static recrystallization after hot working of 0.38C-0.99Cr-0.16Mo steel

The restoration mechanisms for static recrystallization of work-hardened austenite were investigated by using double-pass compression tests performed on medium-carbon steel containing chromium and molybdenum. The softening fraction was defined by 2% offset method. The results show that Avrami exponent of about 0.21 is insensitive to deformation temperature, indicating that the action of steel grade should be considered. The time of 50% recrystallization (t0.5) decreases noteworthily with the increase of deformation temperature. Apparent activation energy for static recrystallization of 195 kJ/mol, which is close to that of vanadium microalloyed steel, is obtained by calculating. The increasing trend of the driving force for recrystallization is opposite to that of the deformation temperature, which is attributed to the number of operative slip system increasing as temperature increasing.

Effect of Mg addition on mechanical and thermoelectrical properties of Al-Al_2O_3 nanocomposite

The effects of Mg addition on mechanical thermo-electrical properties of Al.Mg/5%Al2O3 nanocomposite with differentMg contents （0, 5%, 10% and 20%） produced by mechanical alloying were studied. Scanning electron microscopy analysis （SEM）,X-ray diffraction analysis （XRD） and transmission electron microscopy （TEM） were used to characterize the produced powder. Theresults show that addition of Mg forms a predominant phase （Al.Mg solid solution）. By increasing the mass fraction of Mg, thecrystallite size decreases and the lattice strain increases which results from the atomic penetration of Mg atoms into the substitutionalsites of Al lattice. The microhardness of the composite increases with the increase of the Mg content. The thermal and electricalconductivities increase linearly with the temperature increase in the inspected temperature range. Moreover, the thermalconductivity increases with the increase of Mg content.

Field application of non-blasting mechanized mining using high-frequency impact hammer in deep hard rock mine

A non-blasting mechanized mining experiment was carried out with a high-frequency impact hammer,and the daily mining performance was recorded to explore the applicability of the high-frequency impact hammer in deep hard rock mines.Before the field application,the scope of the excavation damage zone was monitored,and rock samples were obtained from the ore body to be mined to carry out a series of laboratory experiments.Field application results show that the overall excavation efficiency reaches 50.6 t/h,and the efficiency of pillar excavation after excavating stress relief slot reaches 158.2 t/h.The results indicate that the non-blasting mechanized mining using high-frequency impact hammer has a good application in deep hard rock mines,and the stress relief slot is conducive to mechanical excavation.In addition,the high-frequency impact hammer also exhibits the advantages of high utilization rate of labor hours,small lumpiness of spalling ore,little dust,and little excavation damage.Finally,according to the field application and laboratory experiment results,a non-blasting mechanized mining method for hard rock mines based on high-frequency impact hammer is proposed.

Influence of the Main Technological Variables of Cyclical Mechanic-Thermal Processing on the Strain Hardening of Steel Parts

The main objective of the present work was to determine the influence of the most important technological variables of CMTP （cyclical mechanic-thermal processing） on the strain hardening in the surface layers of steel parts. For this, it was designed a full factorial plan at two levels of five independent variables that include the whole processing in two and three cycles, the cold-forming degree and force during the plastic deformation （burnishing）, and the temperature and time at the given temperature during the aging. Each cycle is composed of plastic deformation at room temperature plus aging. As dependent variables, the degree and penetration depth of strain hardening were evaluated. Based on the appropriately used set of experimental data, it had been fitted an exponential model for each dependent variables and also a two-degree polynomial fitting of in-depth evolution of microhardness profile was obtained. The amount of cycles and the cold-forming degree are the technological variables of CMTP that influence the most on strain hardening, although other variables also are significant. The microhardness profile highlights that during the CMTP, the strain hardening decreases from the outer bound to the transition zone of the surface layers, where it disappears.

The Effect of Vanadium Content on Mechanical Properties and Structure of Self-Hardening Steel X 160C rMo 12-1

The aim of this research was to examine the influence of vanadium on the structure, hardness and tensile strength of X I60CrMo 12-1 self-hardened steels. It is known that vanadium affects the process of solidification of this alloy in a way that narrows temperature interval of crystallization. Vanadium, as an alloying element, moves liquidus and solidus lines toward higher temperatures, approximately for 25 to 30 ~C. In addition, vanadium forms V6C5 carbides, which, are partly distributed between present phases in the steel; carbide （Cr,Fe）7C3 and austenite. The presence of vanadium enables the formation of （Cr, Fe）23C6 carbide and its precipitation into austenite during the cooling process. In local areas around fine carbide particles, austenite is transformed into martensite, i.e., vanadium reduces remained austenite and improves steel air-hardening. Vanadium concentration over 2.5% significantly improves the impact toughness. The basic problem in the application of high alloyed Cr-Mo steels is to increase their impact toughness and thereby sustain a relatively high value of hardness. Recent studies, concerning to the chemical composition and heat treatment regime, show that it is possible to get a martensitic structure with a very small amount of retained austenite. Investigations are directed toward the testing of the influence of alloying elements such as molybdenum, manganese and especially vanadium. Vanadium has great influence to the crystallization process. With increasing of its content, the eutectic point moves toward lower carbon concentrations and the temperature interval of solidification is narrowing.

Application of nanoindentation to investigate chemomechanical properties change of cement paste in the carbonation reaction

Nanoindentation technique was adopted to investigate the chemomechanical properties change of hardened cement paste before and after carbonation.It was found that the mean elastic modulus and mean hardness obviously increase after the carbonation reaction.Specifically,the probability of the elastic modulus showed a sharp reduction for the elastic modulus at the range of 7-34 and 83-160 GPa,in comparison of a large increase for the elastic modulus between 34-83 GPa.For the same reason,the probability of the hardness showed a large decrease when the hardness fell within 0.15-1.75 and 4.15-8.20 GPa and a dramatic increase for the hardness at the range of 1.75-4.15 GPa.In addition,low density C-S-H was affected by the carbonation degradation more seriously than high density C-S-H.The carbonation reaction led to distinct decrease of the number and size of unhydrated cement paste particles.