Heat processes in mixtures of polymers with cyanuric acid after plastic deformation under high pressure according to calorimetric data

Mixtures of cyanuric acid with different polymers are subjected to plastic deformation under pressure of 1 GPa, and the DSC method is used to establish that endothermal processes with enthalpies that can reach 50 J g^-1 occur in deformed mixtures under heating in the range of 50–250°C. The occurrence of endothermal processes is related to the destruction of intermolecular bonds formed at the acid–polymer interface and due to formation of double electric layers and appearance of interphase electrostatic attraction.     

Thermal effects in mixtures of aluminum with polyvinyl chloride after plastic deformation under high pressure

PVC and mixtures of PVC with aluminum of different compositions were subjected to plastic deformation under a pressure of 0.5–3.0 GPa using setups of Bridgman anvil type. DSC data showed that ΔC _p in the polymer was doubled and T _c increased by 20°C. Chemical reactions occurred on the interfaces of freshly opened metal surface/polymer phase under pressure treatment in the mixtures. They were accompanied by formation of volatile and soluble products. When metal-polymer mixtures were heated under pressure after deformation, chemical reactions occurred in them starting at 40°C and reaching the maximum intensity in the temperature range of polymer transition from the vitreous to highly elastic state. Thermogravimetric studies of mixture samples of different compositions were carried out.     

Melting of high- and low-density polyethylene in mixtures with aluminum after plastic deformation under high pressure

Mixtures of low- and high-density polyethylene with aluminum were subjected to plastic deformation at a pressure of 0.5–4.0 GPa. DSC analysis showed that heating of samples at 110 and 140°C results in addition to the melting of polymers in the melting of ultrafine polymer crystallites at 40°C and also in chemical interaction at 80°C at the polymer–metal phase interface; crystallization of the polymer phase in deformed mixtures occurs at 14–18° higher than that of the initial polymers. Enthalpies of thermal processes in baric dependences reached extremum values at the pressures at which restructuring of the electron subsystem occurs in the deformed mixtures.     

A calorimetric study of the process of formation of a supramolecular high-density polyethylene structure in mixtures with different oxides after plastic deformation under high pressure

Mixtures of ultrahigh-molecular-weight polyethylene with 95 wt % oxides of different elements were subjected to plastic deformation under the pressure of 1 GPa at a high pressure device of the Bridgman anvil type and thermal effects were studied using the DSC technique. Thermograms contained exothermic peaks with a maximum at 50–90°C related to cold crystallization of the polymer. The process of polymer fusion was described by two peaks with the maximums at T ₁ = 125–128°C and T ₂ = 136–139°C. The low-temperature peak was related to fusion of a structure with high amounts of defects formed on the oxide surface.     

A study of the mixtures of polystyrene and polyvinyl fluoride with aluminum after plastic deformation under high pressure using DSC and thermogravimetry

Mixtures of powdered polystyrene and polyvinyl fluoride with aluminum exposed to plastic deformation under pressure of 1 and 4 GPa, have been studied by DSC and thermogravimetry. It has been established that, in the deformed mixtures at temperatures up to 200°C, exothermal processes take place. Interaction between polymer decomposition products and aluminum has been studied, as have its oxidation and nitrogenation.     

高温塑性变形中孔隙性缺陷自修复机理

通过物理模拟研究20MnMo材料内部孔隙性缺陷的修复过程,建立了孔隙性缺陷高温修复的修复再结晶机理。将孔隙性缺陷修复分为3个阶段:修复再结晶晶粒形核准备、修复再结晶晶粒形核、修复再结晶晶粒长大和改建,其中修复再结晶形核主要存在3种方式。孔隙性缺陷修复再结晶机理的提出对深入研究塑性变形中缺陷修复以及塑性变形对性能的影响作用具有重要理论意义,对缺陷修复规律在生产实际中应用具有重要的实用价值。     

Structure evolution of pure iron upon low-temperature deformation under high pressure

Structure evolution of iron (99.97% purity) deformed by shear under pressure at 80 K in a medium of liquid nitrogen has been investigated. It has been found that, along with dislocation slip, twinning and development of deformation microbands become operative mechanisms of low-temperature deformation. This led to specific type of inhomogeneity of the structure in which, up to ultimately attained degrees of deformation, low-angle misorientations are retained and, unlike room-temperature deformation, no homogeneous submicrocrystalline (SMC) structure is formed. Twinning contributes to the refinement of structure elements that are more than 1 μm in size; the further refinement occurs by the dislocation-disclination mechanism and goes to the steady-state stage.     

一种新型Al-Cu-Li系合金的高温塑性变形研究

采用Gleeble-1500热模拟机高温压缩与高温拉伸试验,对一种新型Al-Cu-Li系合金的高温塑性变形进行了研究,并利用扫描电镜和透射电镜对该合金高温变形后的组织进行了观察。结果表明,在350℃~470℃的变形温度范围内,以1s-1~30s-1的变形速度压缩时,合金的极限压下量基本都在80%以上。以30s-1应变速度压缩时,在470℃时极限压下量陡然下降,说明变形速度很大时变形温度不宜过高。分别以0.1s-1和1s-1变形速度拉伸时,在410℃~470℃温度区间塑性较好。     

Modeling for thermal contact resistance of frictional interface under high temperature and high pressure

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P91合金钢热变形力学行为的实验

利用Gleeble-3500热模拟试验机对P91合金钢进行高温压缩实验,得到了该合金钢在不同温度1000℃、1100℃、1150℃和1200℃,不同应变速率1s-1、0.1s-1、0.01s-1和0.001s-1条件下的真应力-真应变曲线。曲线形态基本符合普通结构钢的热变形力学特征。采用包含Zener-Hollomon参数的Arrhenius双曲正弦关系描述P91合金钢的高温流变行为,确定其变形激活能Q=499.89kJ/mol。P91合金钢应力-应变曲线的典型特征是,在大应变时曲线明显上翘。采用有限元数值模拟方法,分析摩擦力对真应力-真应变曲线翘曲的影响,发现除摩擦力外,还存在其他的影响因素。     

Anomalous plastic flow of cerium near the isomorphic phase transformations under high hydrostatic pressure

Compression tests have been carried out on cerium specimens at room temperature (0.27T_m) under high hydrostatic pressures up to 1.2 GPa. A strong increase of the yield strength was observed for both isomorphic γ and α phases at pressures approaching the γ↔α isomorphic phase transformations. That increase was in good agreement with the theory of dislocations when the dependence of elastic properties and a lattice parameter of cerium on pressure was applied to calculate the effect of pressure on the yield stress controlled by the edge dislocations. An anomalous strong decrease of the yield stress was observed in both γ and α phases in the vicinity of both γ↔α phase transformations. That phenomenon was explained as an effect of pressure induced new phase atoms through spreading the cores of edge dislocations. A complete disappearance of work hardening in both γ and α phases was also observed in the wide range of pressures. The influence of hydrostatic pressure on the energy of grain boundaries of both phases was considered to be responsible for that property. The ratio of the grain boundary energy to the Peierls energy is suggested to be a criterion of the work hardening ability of f.c.c. polycrystals.     

Special features of thermal and deformation processes in welding high-strength steels with different edge preparation

Investigations were carried out into the special features of thermal and deformation processes in single- and twin-arc welding of joints with different edge reparation. On the basis of the experimental results it was established that deformation of all types when using the constricted shapes of the welding gap is lower than when using the standard welding gaps. The level of strain in the component can be additionally reduced by the application of twin-arc welding. The investigation results also show that in the final stage of welding it is necessary to correct the welding conditions in the immediate vicinity of the edge of the welded component in order to eliminate the superheating effect caused by the reflection of the heat flow from the welding edge.     

Autowave processes of the localization of plastic flow in active media subjected to deformation

Conditions have been considered for the formation of autowaves of localized plastic flow in the deformed metals upon the propagation of Lüders bands in the case of the Portevin–Le Chatelier effect, and upon the formation of a neck with taking into account the differences in the microscopic mechanisms of plastic deformation in the case of these phenomena. The laws that govern the development of the localized plastic flow of metals and the role of these laws in the development of the above effects have been investigated. It has been established that the main features of the deformation characteristic of these phenomena are determined by the differences in the properties of the active media that are formed in the material upon plastic deformation. The mechanisms of the generation of different autowave modes of the localized plastic flow upon the Lüders deformation, Portevin–Le Chatelier effect, and the formation of a neck in active media of different nature during deformation have been considered.     

The role of entrapped lubricant in asperity flattening under bulk plastic deformation

The load bearing capacity of entrapped lubricant and resulting diminished asperity flattening are studied with a new specimen design that allows for both compression and biaxial bulk deformation of the subsurface material. Numerical simulations considering the experimental compressibility curve for the trapped oil support the analysis and show how incomplete filling of the valleys affect asperity flattening depending on the asperity flank angle. Finally, the new specimen design also allows quantifying the differences in friction when bulk deformation of the subsurface material is carried out with and without trapped oil in the valleys between asperities.