Modeling for prediction of restrained shrinkage effect in concrete repair

A general model of autogenous shrinkage caused by chemical reaction (chemical shrinkage) is developed by means of Arrhenius' law and a degree of chemical reaction. Models of tensile creep and relaxation modulus are built based on a viscoelastic, three-element model. Tests of free shrinkage and tensile creep were carried out to determine some coefficients in the models. Two-dimensional FEM analysis based on the models and other constitutions can predict the development of tensile strength and cracking. Three groups of patch-repaired beams were designed for analysis and testing. The prediction from the analysis shows agreement with the test results. The cracking mechanism after repair is discussed.     

Effects of cooling rate on the microstructure and tensile behavior of a Sn-3.5wt.%Ag solder

The tensile behavior and microstructure of bulk, Sn-3.5Ag solders as a function of cooling rate were studied. Cooling rate is an important processing parameter that affects the microstructure of the solder and, therefore, significantly influences mechanical behavior. Controlled cooling rates were obtained by cooling specimens in different media: water, air, and furnace. Cooling rate significantly affected secondary dendrite-arm size and spacing of the Sn-rich phase, as well as the aspect ratio of Ag₃Sn. The Sn-rich dendrite-arm size and spacing were smaller for water-cooled specimens than for air-cooled specimens. Furnace cooling yielded a nearly eutectic microstructure because the cooling rate approached equilibrium cooling. The morphology of Ag₃Sn also changed from spherical, at a fast cooling rate, to a needlelike morphology for slower cooling. The changes in the microstructure induced by the cooling rate significantly affected the mechanical behavior of the solder. Yield strength was found to increase with increasing cooling rate, although ultimate tensile strength and strain-to-failure seemed unaffected by cooling rate. Cooling rate did not seem to affect Young’s modulus, although a clear coorelation between modulus and porosity was obtained. The mechanical behavior was correlated with the observed microstructure, and fractographic analysis was employed to elucidate the underlying damage mechanisms.     

拉伸变形纯铜的显微组织特征

为了研究多晶体中晶粒取向对其形变显微组织的影响，采用透射电镜定量表征了拉伸变形无氧高纯铜(0FHC)的显微组织，研究了形变显微组织与晶粒取向之间的相关性．结果表明：在晶粒内部形变显微组织均匀一致，而在不同晶粒之间则存在明显差异；根据位错组态的不同可将形变组织分为3种类型，即I型组织、Ⅱ型组织、Ⅲ型组织；不同类型形变显微组织与晶粒取向间存在明显的相关性．     

碳纤维的性能缺陷及改进方法

碳纤维的实际强度远小于其理论计算值 ,导致碳纤维材料强度下降的最主要的因素是缺陷。本文介绍了碳纤维理论强度的计算和缺陷的分类、表征及来源 ,以及减少缺陷 ,提高碳纤维力学性能的方法。     

掺粘土混凝土徐变试验

根据新疆乌拉泊水库副坝防渗墙掺粘土混凝土不同龄期的室内徐变试验结果，拟合了该混凝土材料弹性模量、徐变度及应力松驰系数等的计算式，可用于观测应力计算。     

高温炉管断裂的两种机制

通过对过热炉管受热冲击影响的事件考察，指出了在高温炉管的断裂中存在着超温引起过早的蠕变断裂，通常有明显的变形和热冲击导致快速的脆性断裂两种不同的机制。在失效成因的分析中，讨论了Manson—Haferd参量外推技术、热应力沿壁厚的分布和热冲击产生应力峰值问题，给出了热冲击的安全曲线。     

相关统计技术在力学检测中的应用

通过对Q235A热轧圆盘条抗拉强度过程能力指数和化学成分进行统计分析．确定了抗拉强度和化学成分的相关性．建立和验证了两者之间的多元回归函数关系．并通过回归方程来词整钢材的化学成分，从而提高过程能力指数。     

Reduction Annealing for Cast Iron Powder and Its Effect on Sintered Antifriction Material Properties

The effect of reduction annealing for powder obtained from cast iron shavings on powder specimen properties is studied. An approximate mechanism is suggested for the oxidation-reduction process during annealing of cast iron powder. An increase in annealing temperature leads to an increase in carbon gasification rate and change in absolute powder weight. Prior reduction annealing for cast iron powder improves its compactability, and increases the mechanical properties of sintered material. The best mechanical properties were obtained for specimen made from cast iron powder reduced at 1000°C. Alloying an iron-cast iron charge with 3 mass% of nickel-chromium alloy leads to a marked improvement in the mechanical properties of a sintered composite.     

Influence of Precipitates Size and Distribution on Room Temperature Mechanical Properties and Accelerated Creep of X20CrMoV121

The effect of microstructure on creep resistance of the low carbon chromium steel X20CrMoV121 after 100‐hours of static‐load test at a temperature of 580 °C and constant stress of 170 MPa was investigated. The specimens for the experiments were extracted from steam pipes of a steam power plant and heat treated. The effect of isothermal annealing on the microstructure and hardness as well as the kinetics of the precipitation of the carbide particles were determined.     

Optimisation of post-weld heat treatment — A simple, practical method

The authors have evolved an empirical method for characterizing resistance to ductile fracture using two parameters Γ _f andηf that can be determined from tensile test data of smooth cylindrical specimens. This method stipulates that the post-necking regime during tensile deformation is dominated by microvoid growth and coalescence processes, and therefore the energy absorbed in this regime can be used to estimate the resistance of the necked region to ductile fracture. The test procedure employed is simple and does not require gauge-length extensometry, a distinct advantage at non-ambient temperatures. The tests are carried out in a screw-driven machine at a constant crosshead speed, with online computerized acquisition of load-time data; it is also necessary to have a prior precise calibration for the (nonlinear) elastic deformation of the load train. The method of computing Γ _f and η_f, from tensile data is described, and its engineering application demonstrated by characterizing the effect of ageing of two dissimilar metal welds, namely Alloy 800/2.25Cr-lMo steel and Alloy 800/9Cr-1Mo steel. From these results, it has been established that this procedure of estimating the ductile fracture toughness from tensile tests can be used as a simple, practical method for optimisation of post-weld heat treatment of weld joints.