高炉炉缸炭砖环裂机制初探

热力学计算表明,高炉炉缸仅存在纯的碱金属蒸气,不存在碱金属的氧化物和碳酸盐,并且碱金属蒸气压很低,不是对炉缸炭砖进行侵蚀的直接原因,而当前大多文献认为环裂是碱蒸气侵蚀的结果.炭砖传热性能较差时炭砖内部热应力较大,诱发炭砖产生微裂纹,纯的碱金属蒸气通过炭砖的微裂纹不断向炭砖低温区流动和扩散,微裂纹是环裂产生的诱因.在炉缸...     

转炉托圈裂纹产生机理分析及修复方案

详细地介绍了托罔的传动及冷却原理,针对转炉托圈出现裂纹的现象,从裂纹产生的机理、材质、加工及现场使用情况进行了初步的原因分析,找出存在的问题.制定了修复方案,采取了预热、保温及消除应力的具体措施,取得了明显的效果.     

Three-Dimensional Discrete Element Models for Asphalt Mixtures

The main objective of this paper is to develop three-dimensional (3D) microstructure-based discrete element models of asphalt mixtures to study the dynamic modulus from the stress-strain response under compressive loads. The 3D microstructure of the asphalt mixture was obtained from a number of two-dimensional (2D) images. In the 2D discrete element model, the aggregate and mastic were simulated with the captured aggregate and mastic images. The 3D models were reconstructed with a number of 2D models. This stress-strain response of the 3D model was computed under the loading cycles. The stress-strain response was used to predict the asphalt mixture’s stiffness (modulus) by using the aggregate and mastic stiffness. The moduli of the 3D models were compared with the experimental measurements. It was found that the 3D discrete element models were able to predict the mixture moduli across a range of temperatures and loading frequencies. The 3D model prediction was found to be better than that of the 2D model. In addition, the effects of different air void percentages and aggregate moduli to the mixture moduli were investigated and discussed.     

基于离散元的花岗岩热敏感性及裂纹扩展研究

在一定应力状态下,热诱导产生的应力场和初始应力场相叠加,导致岩石中裂纹萌生,对岩石的力学性质造成影响。基于离散元方法,在不同初始应力状态下,对含有不同倾角预制裂纹模型的热裂过程进行研究。对相关热特征值进行分析,并根据Det.（σ_ij ）准则,结合第二不变量的演化过程,对热裂纹的扩展路径进行理论分析。结果表明：高应力状态下,热敏感性较强（起裂温度较低,裂纹扩展温度区间靠前,裂纹扩展剧烈）,峰值温度较低,而峰值热应力较高;不同角度的预制裂纹也会影响相关热特征值,在同一初始应力状态下,随着预制裂纹角度的增加,热敏感性降低;热裂纹首先在预制裂纹尖端形成,随着温度的升高,应力第二不变量的分布发生改变,热裂纹在第二不变量最大处扩展。研究结果对深部热力破岩和岩石工程稳定性具有一定借鉴意义。     

Theoretical Modeling of Signal Loss versus Crack Opening for a Novel Crack Sensor

The degradation of concrete structures is always accompanied by the formation of cracks. Crack monitoring is hence useful in assessing the “health condition” of the structure. In our previous investigation on an optical-fiber crack sensor, we have successfully demonstrated the possibility of crack detection and monitoring without requiring prior knowledge of crack locations. Also, a single fiber can be employed to monitor a number of cracks. In practical applications, the signal loss versus crack opening relationship of the sensor needs to be properly “designed” to satisfy performance requirements on sensitivity to small cracks and/or the total number of detectable cracks (which is limited by the maximum loss at each crack). In this paper, a theoretical model for the signal loss versus crack opening relationship is developed through a combination of mechanical and optical analyses. Using concrete beams with embedded sensors, crack monitoring experiments are conducted. Test results are found to be in reasonably good agreement with predictions from the model. With the verified model, simulations are carried out to study the effect of various parameters on sensor performance. The potential application of the theoretical model to generate sensor design guidelines is hence demonstrated.     

25t转炉托圈裂纹的焊修工艺

山东冶金机械厂在对２５ｔ转炉托圈裂纹的焊修中，采用手工电弧焊，焊接顺序为先修轴头再修盖板。焊前钻止裂孔，加拘束连接板，预热；焊接时采取多层多道、分段焊接的方法；焊后分别进行去应力退火和整体回火处理，使焊补焊缝及表面质量达到Ⅱ级。     

Visualization and Analysis of Microstructure in Three-Dimensional Discrete Numerical Models

A computer program has been developed to allow for the virtual slicing of irregularly spaced and irregularly shaped three-dimensional image data. The program was used to virtually slice three-dimensional particle assemblies from discrete element method (DEM) simulations, allowing, for the first time, direct comparison to two-dimensional slices extracted from solidified physical specimens. Based on slices obtained from the numerical specimens, it is possible to compare quantitatively numerical microstructure directly to its physical analog, which should lead to greatly improved calibrations of granular mechanics models, and could facilitate the calibration of models across all scales of interest rather than solely at specimen boundaries. Improved confidence in the ability of the DEM to realistically simulate the microstructure of granular assemblies (through improved multiscale calibration) should result in increased confidence in microstructural parameters measurable in numerical simulations but inaccessible in the laboratory. Algorithm development within the framework of the open-source Visualization Toolkit is described and performance of the algorithm is quantified for two platforms. Results from virtual slices of a test assembly with regular particle packing are verified against known analytical solutions. A slice of a more complex assembly comprised of nearly 40,000 spheres is quantified statistically and compared to an analogous slice from a physical specimen of uniform sand.     

Discrete threshold versus continuous strength models of perceptual recognition.

Tested discrete-threshold models of letter and word recognition against models that assume that decision criteria are applied to measures of continuous strength. Some of the predictions for discrete-threshold were generated from J. Grainger and A. M. Jacobs' (see record 1995-16120-001) dual-readout model (DROM) and some predictions for continuous strength were generated from a revised version of the activation-verification model (K. R. Paap et al; see record 1982-31874-001). Exp 1 used a 2-alternative forced-choice task, followed by an assessment of confidence and then a whole report if a word was recognized. Factors were manipulated to assess the presence or magnitude of a neighbourhood-frequency effect, a lexical-bias effect, a word-superiority effect, and a pseudoword advantage. Discrepancies between DROM's predictions and the obtained data are noted. Both types of models were also used to predict the distribution of responses across the levels of confidence for each. The predictions based on continuous strength were superior. Exp 2 used a same-different task and confidence ratings to enable the generation of receiver operating characteristics (ROCs). The shapes of the ROCs are more consistent with the continuous strength assumption than with a discrete threshold. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Structural Integrity Assessment by Models of Ductile Crack Extension in Sheet Metal

Methods for analytical and numerical simulation of ductile crack extension are used for the prediction of tolerable loads and residual strength of a structure. They cover a wide range from relatively modest phenomenological approaches which allow quick and inexpensive analyses to elaborate micromechanical models, in particular an analytical flaw assessment model, a finite element model which uses the crack tip opening angle as controlling parameter, a cohesive zone model and a ductile damage model. The various phenomenological and micro‐mechanical models constitute elements of an overall concept of damage analysis designated as Structural Integrity Assessment Method (SIAM). The contribution gives an overview over the respective concepts and equations and explains the application of these models by examples of numerical simulations of crack extension in metal sheets. The models are compared with respect to their capabilities, advantages, limitations and drawbacks.     

Al-Mg合金汽车材深冲开裂问题的工艺研究

Al-Mg合金因性能良好常用于汽车材料,但加工工艺的不当容易导致产品出现冲压开裂状况。本文证实了临界加工率的存在,并分析其导致材料开裂的原因。临界加工率条件下进行完全再结晶退火(350℃×4h),晶粒尺寸增长至正常尺寸的6倍,同时抗拉强度、延伸率均出现下降,提高退火温度(450℃×4h),材料晶粒增长至原尺寸的10倍,抗拉强度下降约20MPa,延伸率降低4%。高于临界加工率下进行350℃×4h或450℃×4h完全再结晶退火,材料组织与性能基本不产生变化。     

部分预应力混凝土结构的裂缝闭合问题的探讨

就配筋系列砼结构裂缝问题进行阐述，并对部分预应力砼结构的概念、性能、优点及经济效益等作了论述，为今后有效控制砼构件裂缝作了初步的探索。     

The Integration of Continuous and Discrete Latent Variable Models: Potential Problems and Promising Opportunities.

Structural equation mixture modeling (SEMM) integrates continuous and discrete latent variable models. Drawing on prior research on the relationships between continuous and discrete latent variable models, the authors identify 3 conditions that may lead to the estimation of spurious latent classes in SEMM: misspecification of the structural model, nonnormal continuous measures, and nonlinear relationships among observed and/or latent variables. When the objective of a SEMM analysis is the identification of latent classes, these conditions should be considered as alternative hypotheses and results should be interpreted cautiously. However, armed with greater knowledge about the estimation of SEMMs in practice, researchers can exploit the flexibility of the model to gain a fuller understanding of the phenomenon under study. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Discrete versus syncytial tissue behavior in a model of cardiac stimulation--II: Results of simulation

The research presented here combines mathematical modeling and computer simulation in developing a new model of the membrane polarization induced in the myocardium by the applied electric field. Employing this new model termed the "period" bidomain model, the steady-state distribution of the transmembrane potential is calculated on a slice of cardiac tissue composed of abutting myocytes and subjected to two point-source extracellular current stimuli. The goal of this study is to examine the relative contribution of cellular discreteness and macroscopic syncytial tissue behavior in the mechanism by which the applied electric field alters the transmembrane potential in cardiac muscle. The results showed the existence of oscillatory changes in the transmembrane potential at cell ends owing to the local resistive inhomogeneities (gap-junctions). This low-magnitude sawtooth component in the transmembrane potential is superimposed over large-scale transmembrane potential excursions associated with the syncytial (collective) fiber behavior. The character of the cardiac response to stimulation is determined primarily by the large-scale syncytial tissue behavior. The sawtooth contributes to the overall tissue response only in regions where the large-scale transmembrane potential component is small.     

连铸板坯角裂和边裂漏钢原因的分析

论述了板坯连铸漏钢的危害,分析了板坯角裂和边裂漏钢的原因,提出了防止措施和应注意的问题。     

长短裂纹分界点的确定及短裂纹扩展寿命的预测

采用弹塑性理论定理分析缺口根部局部应力应变场来确定长短裂纹分界点。提出的预测缺口短裂纹扩展寿命的方法 ,对提高缺口件疲劳全寿命估算的精确度具有一定的应用价值。实验结果表明 ,本文提出的处理方法更为简单合理     

Closure Effects on Fatigue Crack Detection

An experimental study of crack closure and its effects on the vibration of a simple beam shows that both frequency and damping changes due to the crack are influenced significantly, to the point of being obscured in some cases. The nonlinearity induced by crack closure is also explored. The results will be of value in the further development of models to detect crack damage in structures as well as in modeling crack closure and the mechanism of damping at a crack.     

Hydraulic Deterioration Models for Storm-Water Drainage Pipes: Ordered Probit versus Probabilistic Neural Network

A decrease in discharge capacity of storm-water drainage pipes is the result of the so-called hydraulic deterioration which reduces the cross sectional area of pipes and increases the pipe roughness. Hydraulic deterioration is caused by tree root intrusion, sediment accumulation, and encrustation, and is affected by many influential factors such as pipe size and pipe location. Predicting hydraulic deterioration is important for effective management of drainage pipes. An ordered probit deterioration model (OPDM) and a probabilistic neural network deterioration model (PNNDM) were developed in this study using the influential factors as model inputs and the hydraulic condition as model output. Their predictive performances were compared against each other using a case study from Melbourne, Australia with a sample of 417 storm-water drainage pipes subjected to closed circuit television inspection. The results show that the PNNDM is more suitable for predicting the hydraulic deterioration and outperforms the OPDM. Several input factors such as pipe size and pipe age are found significant to the hydraulic deterioration.     

锅炉高压给水泵平衡环磨损问题分析及改进

1前言新疆八一钢铁集团有限责任公司热电联产一期工程,规模为2×130t煤和高炉煤气混烧锅炉,及2×25MW抽汽凝汽供热机组。本工程主要解决八钢地区供热热源及现有低热值二次能源利用问题,完全遵循了以“热定电、热电联产、能源综合利用、保护环境”的原则,该工程被批准为国家重点技术改造,“双高一优”项目,自2002年8月23日开工到2003年10月01日,1#炉正式点火,进入调试阶段,但锅炉的高压给水泵不能正常工作,影响到锅炉的安全连续运行。2设备状况及问题在热电工程调试阶段中,3台DG150-89型的给水泵运行不到72h,给水泵的平衡环磨损严重,轴承座…