高密度聚乙烯材料的注塑自增强工艺研究

本工作研究了在注塑机上进行体型聚乙烯试样的自增强成型工艺,探讨了自增强效果与注塑工艺之间的关系。 试验材料的自增强效果强烈地依赖于熔体的流动条件。在一个低熔体温度的范围内,发现有一个对应最大自增强效果的注塑温度。自增强效果随注塑压力的升高而增强。注塑速度和模具温度对自增强效果的影响很小。在其他可以类比的工艺条件下,试样的力学性能依试样形状的不同,表现出极不同的结果。     

Instrumented Borehole Drilling for Subsurface Investigation

The successful application of instrumented borehole drilling techniques in offshore exploration has encouraged its further use on-shore as a ground investigation tool. The drilling of holes for grouting tubes creates the potential for obtaining supplementary ground information, which may be valuable to the succeeding tunnel construction. The instrumented drilling system was therefore investigated to determine its power to discriminate between ground strata. The configuration of the drilling system in terms of plant, equipment, and testing procedures was standardized and applied at a site in Kennington Park in London. The general characteristics of the measured drilling parameters are given and qualitative and quantitative methods of interpreting the drilling parameters are demonstrated. The possible soil–machine interactions that are responsible for the measured drilling characteristics are examined. A new method of data interpretation is proposed for identifying soil formation changes. Previously published correlations and analyses of drilling were examined and tested by comparing the trend-lines of drilling data in London clay against known undrained strength data. The degree of correlation was found to be limited.     

采用吊垂式拉伸试验机探讨超塑性变形速度的提高方式

在吊锤式拉伸试验机上研究了2024铝合金在自由延伸过程中每个时期的应变速度与显微组织的变化,发现经过恒速应变后,金属的超塑性变形会出现应变速度不断加快,实际应变速度比恒速应变速度可提高1.25个数量级.并提出:材料在低温、高应变速度下难以获得理想的超塑性效果;在提高超塑性成形速度的同时,适当升高变形温度,可使工件超塑性恒温锻造的应变速度提高8～10倍.     

Full-Scale Testing of Procedures for Assembling Trunnion-Hub-Girder in Bascule Bridges

To simulate a trunnion-hub-girder (THG) assembly for bascule bridges, two full-scale laboratory tests were conducted for quantifying stresses at previously observed failure locations and for identifying a favorable assembly procedure. One assembly procedure, AP#1, cools the trunnion for a shrink fit into the hub, followed by cooling of the trunnion-hub assembly to shrink fit it into the girder. Using AP#1, development of cracks on the hub was observed in one THG assembly, and, in yet another assembly, the trunnion got stuck in the hub before full insertion could take place. Large hoop stresses and low temperatures were observed at the trunnion-hub interface when the trunnion-hub assembly was cooled for insertion into the girder. Since fracture toughness of THG parts decreases with temperature, allowable crack lengths were small. In an alternative assembly procedure, AP#2, where the hub is shrink fitted into the girder first, followed by cooling the trunnion and shrink fitting it into the hub-girder assembly, the allowable crack length was determined to be double the allowable crack length of AP#1. Hence, for the given full-scale geometry and interference values, assembly procedure AP#2 was found to be better than AP#1.     

材料拉力试验机专用夹持器结构的改进

分析了材料拉力试验机的几种专业夹持器存在的问题,介绍了夹持器的改进设计及工作原理.     

A proposed framework for conducting data-based test analysis.

The authors argue that the current state of applied data-based test analytic practice is unstructured and unmethodical due in large part to the fact that there is no clearly specified, widely accepted test analytic framework for judging the performances of particular tests in particular contexts. Drawing from the extant test theory literature, they propose a rationale that may be used in data-based test analysis. The components of the proposed test analytic framework are outlined in detail, as are examples of the framework as applied to commonly encountered test evaluative scenarios. A number of potential extensions of the framework are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Shear resistance in stainless steel plate girders with transverse and longitudinal stiffening

This paper summarizes and presents main results of the investigation conducted in the Department of Construction Engineering of the UPC dealing with shear behaviour of stainless steel plate girders. Initial shear buckling stress together with ultimate shear capacity of these structural elements have been evaluated with special attention paid to the effect of including stiffeners, both transverse and longitudinal. The studies conducted, both numerical and experimental tests, have permitted the development of new and simple design expressions to determine more accurately the initial shear buckling stress in stainless steel web panels and the ultimate capacity of plate girders considering the presence of a rigid or non-rigid end post.     

On the High Temperature Testing of Superplastic Materials

The simplest test in characterizing the behavior of superplastic materials is the uniaxial tensile test. Since superplasticity is achieved at relatively high temperatures, heat involvement adds so many unpredictable problems to the simplest testing technique. In spite of the vast number of research activities directed towards studying the various aspects of superplastic deformation, there is a lack of a standardized testing procedure that can tackle the various issues associated with high temperature testing. In this work, we attempt to shed some light on the controversial issues associated with high temperature superplastic testing. The effects of various testing procedures and parameters on the accuracy of the results are investigated. We address the issues related to gripping and test sample geometry, heat and temperature effects, and comment on the available testing and analysis procedures. We hope that this study highlights the urgent need to develop a standardized testing approach that takes into account all the important issues affecting high temperature testing. This article was presented at the AeroMat Conference, International Symposium on Superplasticity and Superplastic Forming (SPF) held in Seattle, WA, June 6–9, 2005.     

Two-sample tests of the equality of two cumulative incidence functions

Typically, differences in the effect of treatment on competing risks are compared by a weighted log-rank test. This test compares the cause-specific hazard rates between the groups. Often the test does not agree with impressions gained from plots of the cumulative incidence functions. Here, we discuss two-sample tests of the equality of two cumulative incidence functions. The first test, based on a suggestion of Lin [1997. Non-parametric inference for cumulative incidence functions in competing risks studies. Statist. Med. 16, 901-910], compares the maximum difference between the two cumulative incidence functions. A Monte Carlo method is used to find p-values for the test. The second test, based on a suggestion of Pepe [1991. Inference for events with dependent risks in multiple endpoint studies. J. Amer. Statist. Assoc. 86, 770-778], compares the integrated difference between the functions. A new variance estimator is proposed for this statistic. A small simulation study is used to compare the various tests. The methods are illustrated on a bone marrow transplant study.     

Effect of cathodic polarization and sulfate reducing bacteria on mechanical properties of different steels in synthetic sea water

At the slow strain rate tensile tests done using the specially designed facility, the decrease in the elongation to fracture, reduction of area, fracture energy and no effect on the strength have been stated for the low alloy ferrite‐pearlite and sorbite steels, polarized in synthetic sea water at potentials corresponding to the cathodic protection (? 800 to ? 1400 mV_SCE). Presence of SRB promotes the plasticity loss, being especially pronounced at potentials ? 1100 to ? 1200 mV_SCE. At higher cathodic polarization, the plasticity estimated in inoculated and in sterile water equalizes. The effects have been correlated with the contents of absorbed and of permeable hydrogen. The promotion of hydrogen charging and the plasticity loss by SRB at the low and medium applied cathodic polarization has been accounted for the observed production of S^?2 ions and inhibition of deposit formation. The negligible effect of SRB at the high cathodic polarization has been suggested to be a result of the suppression the SRB growth due to the high alkalization of the near surface solution. The same amount of hydrogen produces the less detrimental effect on the sorbite than on the ferrite‐pearlite steel. However, at the similar cathodic polarization, the sorbite steel absorbs the highest amount of hydrogen and reveals the most pronounced degradation. Cathodic protection of constructions subjected to the action of SRB in the sea water should provide the conditions, under which no fragment of marine construction could be polarized by potential corresponding to the maximum degradation of the plastic properties of steels (? 1100 to ? 1200 mV_SCE).