Cold Consolidation of Ball-Milled Titanium Powders Using High-Pressure Torsion

Pure Ti (99.5 pct) powders after processing with ball milling (BM) were consolidated to disc-shaped samples with 10-mm diameter and 0.8-mm thickness at room temperature using high-pressure torsion (HPT). A relative density as high as 99.9 pct, high bending and tensile strengths of 2.55 to 3.45 and 1.35 GPa, respectively, and a moderate ductility of 8 pct with an ultrafine grained structure are achieved after cold consolidation with HPT, which exceed those of hot consolidation methods. X-ray diffraction (XRD) analysis showed that a phase transformation occurs from α phase to ω phase during HPT under a pressure of 6 GPa as in bulk pure Ti, whereas no phase transformation is detected after processing with BM alone. It was confirmed that the strength and ductility are improved by a combined application of BM and HPT when compared with other severe plastic deformation methods applied to Ti and Ti-6 pct Al-4 pct V, so that no alloying elements are required for the achievement of a comparable strength and ductility.     

Incremental Feeding High-Pressure Sliding for Grain Refinement of Large-Scale Sheets: Application to Inconel 718

Metallurgical and Materials Transactions A - This study updates a process of high-pressure sliding (HPS) recently developed as a severe plastic deformation process under high pressure for grain...     

The Relationship Between Crack-Tip Strain and Subcritical Cracking Thresholds for Steels in High-Pressure Hydrogen Gas

Threshold stress intensity factors were measured in high-pressure hydrogen gas for a variety of low alloy ferritic steels using both constant crack opening displacement and rising crack opening displacement procedures. Thresholds for crack extension under rising displacement, K _THi, for crack extension under constant displacement, $ K_{\text{THi}}^{*} $ , and for crack arrest under constant displacement K _THa, were identified. These values were not found to be equivalent, i.e. K _THi < K _THa <  $ K_{\text{THi}}^{*} $ . The hydrogen assisted fracture mechanism was determined to be strain controlled for all of the alloys in this study, and the micromechanics of strain controlled fracture are used to explain the observed disparities between the different threshold measurements. K _THa and K _THi differ because the strain singularity of a stationary crack is stronger than that of a propagating crack; K _THa must be larger than K _THi to achieve equivalent crack tip strain at the same distance from the crack tip. Hydrogen interacts with deformation mechanisms, enhancing strain localization and consequently altering both the nucleation and growth stages of strain controlled fracture mechanisms. The timing of load application and hydrogen exposure, i.e., sequential for constant displacement tests and concurrent for rising displacement tests, leads to differences in the strain history relative to the environmental exposure history and promotes the disparity between $ K_{\text{THi}}^{*} $ and K _THi. K _THi is the only conservative measurement of fracture threshold among the methods presented here.     

Quantification of Shear Strain Development in the Through-Thickness Direction During Sliding Wear

Metallurgical and Materials Transactions A - Quantifying strain in a deformation mechanism like wear can be critical to enhancing knowledge on structure–property correlation, especially for...     

大型球磨机滑履轴承安装技术

根据大型球磨机滑履轴承的安装工艺要求以及大型中心传动球磨机滑履轴承设备的安装特点,总结了其安装规律,阐述了安装技术要领及相应的安装程序,为今后同类设备的安装提供了一定的经验。     

Probabilistic Analysis of Circular Tunnels in Homogeneous Soil Using Response Surface Methodology

A probabilistic analysis of a shallow circular tunnel driven by a pressurized shield in a frictional and/or cohesive soil is presented. Both the ultimate limit state (ULS) and serviceability limit state (SLS) are considered in the analysis. Two deterministic models based on numerical simulations are used. The first one computes the tunnel collapse pressure and the second one calculates the maximal settlement due to the applied face pressure. The response surface methodology is utilized for the assessment of the Hasofer-Lind reliability index for both limit states. Only the soil shear strength parameters are considered as random variables while studying the ULS. However, for the SLS, both the shear strength parameters and Young’s modulus of the soil are considered as random variables. For ULS, the assumption of uncorrelated variables was found conservative in comparison to the one of negatively correlated parameters. For both ULS and SLS, the assumption of nonnormal distribution for the random variables has almost no effect on the reliability index for the practical range of values of the applied pressure. Finally, it was found that the system reliability depends on both limit states. Notice however that the contribution of ULS to the system reliability was not significant. Thus, SLS can be used alone for the assessment of the tunnel reliability.     

Identification of Statistically Homogeneous Soil Layers Using Modified Bartlett Statistics

Stationarity or statistical homogeneity is an important prerequisite for subsequent statistical analysis on a given section of a soil profile to be valid. The estimation of important soil statistics such as the variance is likely to be biased if the profile is not properly demarcated into stationary sections. Existing classical statistical tests are inadequate even for simple identification of stationarity in the variance because the spatial variations of soil properties are generally correlated with each other. In this paper, a modified Bartlett statistical test is proposed to provide a more rational basis for rejecting the null hypothesis of stationarity in the correlated case. The accompanying rejection criteria are determined from simulated correlated sample functions and summarized into a convenient form for practical use. A statistical-based soil boundary identification procedure is then developed using the modified Bartlett test statistic. Based on the analysis of a piezocone sounding record, two advantages can be discerned. First, the proposed procedure provides a useful supplement to existing empirical soil classification charts, especially in situations where inherent variability tends to complicate interpretation of soil layers. Second, various key assumptions in geostatistical analysis such as stationarity and choice of trend function can be verified more rigorously using the framework of hypothesis testing.     

Prediction of Transformation Strain Using Microtexture Data

The transformation strain, resulting from austenite-to-bainite transformation induced under both external stress and without stress, is estimated by employing two different mathematical models. These models use actual fractions of individual variants in every prior austenite grain, which are calculated using electron backscattered diffraction (EBSD) scans after reconstruction of prior austenite microstructure. The strains predicted by models match closely with the experimentally determined macrostrain obtained using dilation data.     

Roles of Friction-Induced Strain Hardening and Recrystallization in Dry Sliding Wear of AZ31 Magnesium Alloy

Dry sliding wear tests were performed on AZ31 alloy using a pin-on-disc configuration under the loads of 5–360 N and sliding speeds of 0.1–1.5 m/s. Friction and wear characteristics of AZ31 alloy were investigated as a function of the load and sliding speed. Wear mechanisms for AZ31 alloy were characterized by scanning electron microscopy. The wear behavior in mild and severe wear regimes was described in terms of plastic deformation and microstructure evolution in subsurface, and surface hardness change and temperature rise of worn surfaces. The results revealed that surface strain hardening caused by large plastic deformation played an important role in maintaining a low slope of wear rate in mild wear regime, while surface thermal softening originating from dynamic recrystallization and surface melting were responsible for a rapid wear in severe wear regime.     

Study of Fatigue in Metals Using Ultrasonic Technique

Abstract

An investigation of the basic mechanisms associated with cyclic and fatigue stressing was undertaken employing as a research tool a megacycle frequency internal friction method (ultrasonic wave attenuation). The materials used were plain high-carbon and alloy steels (SAE 1095 and SAE 4340). The behaviour of lattice imperfections, dislocations and interstitial atoms (carbon) in particular, was studied in more detail, since these are reported to have a strong influence on the fatigue characteristics of iron-base alloys.

Initially, static stressing conditions were studied. Using a dislocation loop pinning model, the conditions for the break-away of a dislocation loop from interstitial atoms in annealed and in cold-worked material were investigated. These findings were applied to the experimental results obtained on cyclic stressing and an interpretation is offered in terms of the formation of active dislocation loops and their immobilization by interstitial atoms.

The results are discussed with reference to improving fatigue characteristics of iron-base alloys and a similarity with the work of Mason (19) on non-ferrous metals is noted.     

深过冷技术制备均质过偏晶合金及其形成机制的研究

采用熔融玻璃净化和循环过热相结合的方法使Ni 40 % (质量分数 )Pb合金获得 2 92K大过冷度 ,成功制备出大体积均质过偏晶合金。根据BCT模型和组织演化结果分析表明 :过冷粒状晶是在内应力的作用下 ,枝晶发生全面碎断 ,随后在枝晶段表面和应变能的驱动下使晶界移动发生再结晶的结果 ,即枝晶碎断 再结晶机制 ;试样基体上弥散分布的细密铅颗粒是由于快速凝固阶段溶质截留效应而形成的 ,少量较大尺寸铅颗粒的形成主要与慢速凝固阶段分布于枝晶骨架间残余富铅液相的聚合有关。     

加热炉纵水管耐热滑块的焊接工艺分析

介绍了加热炉纵水管耐热滑块的可焊性对比试验 ,总结了一套行之有效的焊接方法 ,对确保焊接质量有一定参考价值。     

Feeding Mechanisms in High-Pressure Die Castings

This work focuses on understanding the feeding behavior during high-pressure die casting (HPDC). The effects of intensification pressure (IP) and gate thickness on the transport of material through the gate during the latter stages of HPDC were investigated using an AlSi3MgMn alloy. Microstructural characterization of the gate region indicated a marked change in feeding mechanism with increasing IP and gate size. Castings produced with a high IP or thick gate contained a relatively low fraction of total porosity, and shear band-like features existed through the gate, suggesting that semisolid strain localization in the gate is involved in feeding during the pressure intensification stage. When a low IP is combined with a thin gate, no shear band is observed in the gate and feeding is less effective, resulting in a higher level of porosity in the HPDC component. Although shear banding through the gate was found to reduce porosity in HPDC parts, if gates are not properly designed, deformation of the mushy zone through the gate can cause severe macrosegregation, large pores, and large cracks, which could severely reduce the performance of the component.     

Vibration Control of Wind-Excited Tall Buildings Using Sliding Mode Fuzzy Control

A sliding mode fuzzy control (SMFC) is proposed to design a controller for the third-generation benchmark problem on wind-excited buildings. A distinctive feature in vibration control of large civil infrastructure is the existence of large disturbances, such as wind, earthquake, and sea wave forces. Those disturbances govern the behavior of the structure; however, they cannot be precisely measured, especially for the case of wind excitations. Since the structural accelerations are measured only at a limited number of locations without the measurement of the wind forces, the structure of the conventional control may have the feedback loop only. The general structure of the SMFC, proposed herein, is composed of a compensation part and a convergent part. The compensation part prevents the system from diverging, and the convergent part directs the system to the sliding surface. The compensation part uses not only the structural response measurement but also the disturbance measurement, so the SMFC has a feedback loop and a feedforward loop. To realize the virtual feedforward loop for the wind-induced vibration control, a disturbance estimation filter is introduced. The structure of the filter is constructed based on an autoregressive model for the stochastic wind force. This filter estimates the wind force at each time instance based on the measured structural responses and the stochastic information of the wind force. For verification of the proposed algorithm, numerical simulation is carried out on the benchmark problem for wind-excited buildings. The results indicate that the present control algorithm is efficient for reducing the wind-induced vibration.     

3500轧机辊端联轴器改造及结构与强度分析

首先讨论了滑块式万向联轴器与十字轴式万向联轴器的优缺点,然后重点阐述采用三维CAD、装配体有限元分析方法对改造后的3500轧机辊端十字轴式万向联轴器进行结构和强度方面分析。     

Material Determination of Vehicle Part Using Strain Analysis Method

The experiment regarding material determination of a vehicle part was conducted.The experiment on stamping production of a part using the steels A, B and C was made. The strain data on the deformed parts were measured. The forming limit diagrams for the steels were examined and evaluated. The results show that three steels are unsuitable for this stamping part. The desired material properties with an optimal strain hardening exponent value were determined using experimental and analytical methods. The steel D was chosen as a desired material. The results show that the steel D is appropriate for mass production. In addition, the feasibility of the application of thinner material to this part was studied. The validity of the material selection was verified theoretically and experimentally.     

滑动式H型活塞橡胶膜密封煤气柜可行性探讨

通过对传统橡胶膜密封煤气柜分析研究,提出了独具颠覆性思维的滑动式H型活塞橡胶膜密封煤气柜构思,这种滑动式H型活塞橡胶膜密封煤气柜既具有传统一段式橡胶膜密封煤气柜全部的优点,又克服了其受力不合理、耗钢量大、无自平衡纠偏的缺点。对滑动式H型活塞橡胶膜密封煤气柜的可行性进行了探讨。     

Evapotranspiration Modeling Using Linear Genetic Programming Technique

The study investigates the accuracy of linear genetic programming (LGP), which is an extension to genetic programming (GP) technique, in daily reference evapotranspiration (ET0) modeling. The daily climatic data, solar radiation, air temperature, relative humidity, and wind speed from three stations, Windsor, Oakville, and Santa Rosa, in central California, are used as inputs to the LGP to estimate ET0 obtained using the FAO-56 Penman-Monteith equation. The accuracy of the LGP is compared with those of the support vector regression (SVR), artificial neural network (ANN), and those of the following empirical models: the California irrigation management system Penman, Hargreaves, Ritchie, and Turc methods. The root-mean-square errors, mean-absolute errors, and determination coefficient (R2) statistics are used for evaluating the accuracy of the models. Based on the comparison results, the LGP is found to be superior alternative to the SVR and ANN techniques.