Regular and Inverse interval Estimation of Individual Observations Using Uniform Confidence Bands

Bowden and Graybill construct uniform confidence bands under the familiar simple linear regression model, and use those bands to write joint confidence intervals for expected Y given X = X_o for all X_o in a specified finite range X_a ≤ X_o ≤ X_b . Their approach is extended here to provide joint confidence intervals for individual observations on Y given X, and also for individual X given Y (the inverse interval estimation problem), in both cases using uniform confidence bands constructed for X_a ≤ X ≤ X_b . We show that Bowden and Graybill's tables can be used in these applications, and give supplementary tables to cover additional cases which more commonly arise in these new contexts. Asymptotic results are also given, allowing the user to generate additional “table” values.

The relative efficiencies of the uniform and Scheffé procedures for inverse interval estimation of individual X given Y are extensively compared. It seems that one need not pay a price in efficiency for the convenience of the uniform procedure.     

中厚板轧机支承辊中心疏松压实过程的有限元模拟研究

基于 Gleeble 热模拟压缩实验和 Arrhenius 方程建立了 70 Cr3Mo 的本构模型,运用 Deform-3 D 软件对支承辊的多工步锻造过程进行了有限元模拟,得到了镦粗和拔长过程中压下量和中心疏松密度的关系,对比研究了平板镦粗和锥板镦粗对中心压实的影响。     

粉末冶金高速压制技术的研究进展

主要介绍了高速压制技术的特点和研究进展.高速压制技术是一项低成本、高效率成型高密度粉末冶金零件的新技术,由于具有良好的性价比而备受关注.其压制速度快,可使材料性能更加优良、生产更加经济化,具备用中小型设备生产超大零件的能力,具有广阔的应用潜力.     

Study of Laboratory and Field Tests Related to Soil Compaction Based on Proficiency Testing Schemes

The main objective of the paper is to present some understandings of laboratory and field tests related to soil compaction and useful for quality control purposes. The methodology of this study is different of other similar works because it is based on proficiency testing schemes （PTS）, involving several operators and test devices. The study was performed in the following test methods： laboratory Proctor compaction test; determination of density and unit weight of soil in place by the sand-cone method; and determination of density and water content of soil and soil-aggregate by nuclear methods. The paper describes the procedures followed for the PTS implementation. The statistical analysis is presented, firstly focusing on the repeatability and reproducibility of the test results. Secondly, beyond this analysis, the paper describes some studies related to practical aspects of the test methods： the influence of the manual or mechanical compaction devices in the modified Proctor test results; the comparison between direct transmission and the backscatter modes in the case of the wet density measurements obtained by the in situ nuclear method; the relationship concerning test results obtained by the nuclear and conventional methods used in the field quality control.     

Research on the Shear Behaviour of Plain Weave Prepreg at Lateral Compaction Stage

Abstract:  An investigation of the shear behaviour of plain weave prepreg at lateral compaction stage was undertaken by the picture-frame test. A unit cell of weave prepreg was modelled and three moments were assumed in the unit cell: (i) the moment of shear force that picture frame applies on the unit cell; (ii) the friction moment at crossover of yarns; and (iii) the compaction moment between the yarns. Through moment balance, a relationship between the load and the shear rate was deduced. A plain sheet shearing film resin model was established to obtain the friction moment at crossover. To get the compaction moment, a constitutive equation of a single prepreged yarn was deduced and a transverse viscosity coefficient equation was given. Moreover, through an equivalent cross-sectional area model, the lateral contact thickness between the yarns was obtained. The comparison between the experimental and theoretical results shows that the presented model can describe the shear behaviour of weave prepreg at lateral compaction stage well.     

基于修正Drucker-Prager Cap模型的金属粉末成形本构模型参数确定方法

针对修正Drucker-Prager Cap模型参数复杂且难准确获取的问题,提出一种采用相对简单实验操作结合联合仿真反演优化确定模型参数的方法,用于金属粉末成形的数值模拟。首先通过实验分析与理论推导,确定重点反演优化参数,即偏心距参数R;采用联合仿真反演优化方法,借助ABAQUS有限元及二次开发平台与MATLAB优化算法,对参数R进行反演计算,进而完成相关硬化参数的确定;以金属粉末Distaloy AE为例,讨论参数R不同函数表达形式的反演结果对粉末压制成形过程数值模拟的影响。研究结果表明,偏心距参数R2及其关联的硬化参数比R1在压制力、脱模力、相对密度和残余应力数值模拟方面具有更高的准确性。     

芦苇秆粉末高密度材料无胶温压成形与表征

为寻求高质清洁利用农林木质剩余物的新途径,运用响应面实验设计与分析方法对芦苇秆粉末实施无胶温压成形,制备高密度木质材料,用三维立体数码显微镜、扫描电子显微镜、傅里叶红外光谱、核磁共振光谱、热重分析和热解析-气相色谱/质谱联用分析技术对试件的微观结构、物相、纤维素结晶度、热脱附挥发物进行研究。结果表明,芦苇秆粉末粒度对试件性能的影响不明显;芦苇秆粉末在压力、温度、时间的复合作用下,木质素发生软化与流展,纤维素的结晶度得以提高,粉末颗粒间发生化学反应并产生化学链接;芦苇秆粉末的最优无胶温压工艺条件:成形压力为70 MPa,成形温度为160℃,保温保压时间为30 min;在最优工艺条件下制备的木质材料塑化明显,质硬而耐磨,具有韧性断裂特征,且在40、60、90、160℃环境温度下的挥发物中,有益、有害成分的种类和芦苇杆原粉相当,但有益成分的总含量远高于原粉,表明温压成形工艺具有环境友好性,无胶温压成形可以获得高品质人工木质材料。     

粉末高速压制成形密度分布的数值模拟及影响因素分析

将研究不连续体力学行为的离散单元法应用于粉末高速压制致密化过程的研究,将粉末视为黏弹性的离散颗粒,建立粉末高速压制过程颗粒接触模型及每个颗粒的基本运动方程,推导了力与位移表达的粉末高速压制黏弹性本构关系.基于PFC软件实现了铁粉高速压制过程中粉末颗粒二维流动情况及压坯密度分布的数值模拟,模拟结果的密度分布规律与实际压制的密度分布规律较为一致;利用数值模拟结果对影响压坯密度分布的摩擦因数、高径比、双向压制因素进行了具体分析.     

粉末冶金温压工艺的技术特点及其新发展

本文概述了温压工艺的特点及其最新的发展,如流动温压、热模压制等,重点讨论了热模压制工艺的技术特点与应用,并指出以AncorMax D为代表的热模压制工艺由于工序比常规温压工艺更简单,压制温度更低,因此在将来很有可能取代常规温压工艺,成为高密度粉末冶金零件的一种非常有应用前景的方法.     

Experimental Tests and Numerical Modelling of Hexagonal Concrete Specimens

This paper describes a novel experimental investigation into concrete cracking under complex and rotating loading paths. Hexagonally shaped specimens are loaded in compression until some damage has occurred and then unloaded and rotated before being loaded again until failure. The results from tests on specimens loaded in two directions are compared with control tests undertaken under monotonic loading. The development of the test setup and sample preparation procedure for these novel experiments is described. The results show that the diffuse cracking accumulated during the initial loading direction has the effect of lowering the peak load carrying capacity of the rotated specimen relative to the peak load obtained under monotonic loading. The results of the experiments performed are subsequently used as benchmark tests for numerical simulations, to test the ability of a constitutive model, as implemented in a finite element program, to simulate cracking under complex and rotating load conditions. Numerical simulations of the experiments are performed here using a recently developed plastic-damage-contact constitutive model (Jefferson (2003) Int J Solids Str 40:5973–5999; Jefferson (2003) Int J Solids Str 40:6001–6022; Jefferson (2004) Comput Concrete 1(3):261–284). This model couples the familiar damage and plasticity model frameworks, taking advantage of their relative strengths in modelling tensile and compressive stress states, respectively. In addition, this model employs a contact function to simulate crack closure and aggregate interlock behaviour. The numerical results manage to capture the essential features of the experimental behaviour, in particular, a reduction of the peak load attained as a result of damage initiated in the original loading direction. However, the constitutive model is unable to fully capture the unloading response. A relatively high value for the specific fracture energy G _f was employed in the simulations to emulate the relatively ductile response of the experiments. This relatively ductile response of the specimens is conjectured to be due to friction on formed crack planes, and currently local plasticity on these planes is not simulated within the model framework.     

温压工艺在粉末冶金中的研究与应用

介绍了温压工艺的特点及其致密化机理，并对粉末冶金研究中温压工艺参数的选择、温压材料的性能及聚合物的加入方式和选取原则进行了讨论。在此基础上，提出了今后温压工艺的研究发展方向和应用前景。     

温压技术及其致密化机制的研究进展

综合评述了国内外温压技术的研究进展，并对其致密化机制进行了探讨。在此基础上，对今后的研究方向提出了几点建议。     

几种不同硬度和热导率的钢中的绝热剪切带特征

研究了几种不同硬度和热导率的钢铁材料在约束爆破条件下的绝热剪切带特征.研究结果表明:钢的高硬度和低热导率有利于形成相变带;反之,则倾向于形成形变带;对于具有高硬度和高热导率的钢,由于高温相变带区域的热量迅速传递到周围的基体组织而使其温度升高、硬度降低,形成的相变带会向形变带转化.     

Assessment of Spatial Distribution of Porosity in Synthetic Quartz Cores Using Microfocus Computed Tomography (µCT)

The effects of particle sorting and compaction pressure on spatial distribution of porosity of synthetic quartz cores were investigated. A high-resolution X-ray computed tomography (CT) system with a microfocus X-ray source was used to acquire CT scans of 12 cores. The cores consist of a mixture of quartz powder and different proportions of quartz granulates (with a particle size range of 0.126 to 0.210 mm) that were compacted at 20.68 MPa (3,000 psi), 27.58 MPa (4,000 psi), and 34.47 MPa (5,000 psi) pressures. Calibration of core density was carried out according to the ASTM standard procedure. Computer algorithms were developed to calculate local porosity (φ) values, producing about 15 million φ values per core. The results of the analysis were represented by histograms and qualitatively compared with capillary pressure versus brine saturation measurements. As a result of changing the particle sorting (i.e., using a wider range of particle sizes), the standard deviation of the porosity distribution increases for the cores compacted under the same pressure. There were mixed trends of the effects of compaction pressure on porosity. However, they are qualitatively consistent with the capillary pressure measurements.     

纯钛高应变率拉伸力学行为的实验研究

利用MTS809材料试验机和旋转盘式间接杆杆型冲击拉伸实验装置,对多晶纯钛进行了室温环境下应变率为0.001,0.01s-1的准静态和300,1400s-1的动态拉伸实验,获得了纯钛等温和绝热拉伸应力-应变曲线;实施了应变率为300s-1的冲击拉伸复元实验,获得了纯钛在高应变率下的等温应力-应变曲线。结果表明:纯钛的拉伸力学行为具有明显的应变硬化效应、应变率强化效应和绝热温升软化效应。采用修正的KHL模型较好地表征了纯钛在准静态和动态实验应变率范围内的拉伸力学行为。     

改性沥青混合料拌和与压实温度确定方法综述

改性沥青混合料拌和与压实温度对沥青路面的设计和施工质量有很大影响,进而影响沥青路面的使用性能.介绍了4种具有代表性的确定改性沥青混合料拌和与压实温度的方法,分别为Yildirim法(Y法)、Bahia法(B法)、Shenoy法(S法)和Azari法(A法),阐明并论述了这4种方法的优缺点及适用范围.     

复合材料层合板固化压实过程有限元数值模拟及影响因素分析

根据有效应力准则和达西定律建立了描述复合材料固化压实过程层合板压缩和树脂流动的二维有限元方程, 节点自由度为位移和树脂压力, 采用向后差分方法直接耦合积分求解以提高收敛速度。数值计算结果表明: 随着层合板厚度的增加, 厚度压缩率减小, 固化压实所需时间增加, 树脂在厚度方向的不均匀性逐渐增加。对于厚度较大的层合板, 采用提高固化压力和双面吸胶两种工艺对比情况说明, 后者可以显著提高压实程度并得到相对均匀的树脂含量分布。      

Modelling of failure mode transition in ballistic penetration with a continuum model describing microcracking and flow of pulverized media

An Erratum has been published for this article in International Journal for Numerical Methods in Engineering 2002; 55(4):499–501. A new continuum model to describe damage, fragmentation and large deformation of pulverized brittle materials is presented. The multiple‐plane‐microcracking (MPM) model, developed by Espinosa, has been modified to track microcracking on 13 orientations under high pressure, high strain rate and high deformation. This model provides the elastic and inelastic response of the material before massive crack coalescence. When pulverization occurs, the constitutive response is modelled by means of a visco‐plastic model for granular material, which is a generalization to three dimensions of the double‐sliding theory augmented by a consolidation mechanism. The initialization of the granular model is governed by a yield surface at the onset of massive crack coalescence. This is accomplished by examining a representative volume element, modelled using the MPM model, in compression‐shear. The main advantage of this approach is to keep a continuum model at all stages of the deformation process and thus avoid the difficulties of crack representation in a discrete finite element code. This model has been implemented in LS‐DYNA and used to examine interface defeat of long rod penetrators by a confined ceramic plate. The numerical simulations are compared to experiments in order to identify failure modes. The model parameters were obtained independently by simulating plate and rod impact experiments. The proposed model captures most of the physical observations as well as failure mode transition, from interface defeat to full penetration, with increasing impact velocity. Copyright © 2002 John Wiley & Sons, Ltd.     

易碎岩石大粒径石料开采爆破关键参数研究

随着外海建港项目的增多,在易碎岩石中集中爆破生产大粒径规格石料成为一个难题。通过分析应力波和爆炸气体对裂隙走向和长度的影响,提出了增大最小抵抗线和填塞长度、减小孔间距的单排孔开采方案,以及关键参数的计算公式,并多次得到工程实践的验证。