Viscoelastic Analysis of Constant Creep Tests on Silicate-Grouted Sands at Low Stress Levels

This paper presents the mechanical properties of silicate-grouted sands subjected to creep loadings at low stress levels. Uniaxial compressive tests were performed in order to determine the stress levels of constant creep tests. The uniaxial compressive strength rapidly increased with time over the first 7 days of curing and then approached a constant level. A series of creep tests were performed for three stress levels and viscoelastic theory was employed to assess the creep behavior. During the loading process elastic, plastic, and viscoelastic strains existed together. The recoverable portions contained elastic and time-dependent viscoelastic strains, and both were approximately linear. Test results showed that the magnitude of the instantaneous recoverable strains was independent of the unloading time. A constitutive model to predict the permanent deformation was developed.     

影响MnSiB贝氏体耐磨铸钢力学性能的因素

研究了成分、铸造工艺及空冷工艺对新型空冷贝氏体耐磨铸钢力学性能的影响。结果表明,硅能显著提高贝氏体铸钢的冲击韧性。与低硅贝氏体铸钢相比,在相同硬度的前提下,添加硅能使贝氏体铸钢的韧性提高１倍以上。通过透射电镜观察发现,韧性提高的主要原因是较高的硅含量能抑制贝氏体中碳化物的析出,即用高韧性的残余奥氏体代替脆性的渗碳体。研究还表明,钢中碳含量、铸造工艺及空冷工艺对贝氏体铸钢的强韧性影响极大。采用中低碳、高硅及适当的铸造工艺和空冷工艺可使贝氏体铸钢有优良的强韧性配合：ＨＲＣ≥４５,ａｋ＝３０～５０Ｊ／ｃｍ２（１０ｍｍ×１０ｍｍ×５５ｍｍ,Ｕ型缺口）。     

Geological and Physical Factors Affecting the Friction Angle of Compacted Sands

This study evaluated the effects of physical characteristics and geologic factors on the shear strength of compacted sands from Wisconsin that are used as granular backfill for mechanically stabilized earth walls and reinforced soil slopes. Physical properties and shear strength were determined for 30 compacted sands collected from a broad range of geological deposits. Relationships between strength/deformation behavior, geologic origin, and physical properties were used to categorize the sands into four friction angle groups. Sands with the lowest friction angle are derived from weathering of underlying sandstones, and tend to be medium-fine, well-rounded, and poorly graded sands. Sands with the highest friction angle are from recent glacial activity and tend to be coarser grained, well-graded, and/or angular sands. A multivariate regression model was developed that can be used to predict friction angle (?′) of compacted sands from comparable geological origins based on effective particle size (D10), maximum dry unit weight (γdmax), and Krumbein roundness (Rs).     

Factors Affecting the Creep Behavior of Grouted Sand

The creep behavior of Fontainebleau sand grouted with a chemically unstable silicate grout was compared with the creep behavior of the same sand grouted with two chemically stable grouts, a microfine cement-based grout and a mineral-based grout. Unconfined and confined creep experiments were performed to highlight drained creep behavior. The duration of the tests was between 100 and 200 days. Results were compared in terms of creep slope, and creep limit strength. Test results have shown that the method with which sand was prepared plays an important part in creep strains of grouted sand. Creep strains were considerably reduced by applying a confining stress. The creep behavior of sands was modified by the grouting treatment: depending on the nature of the grout, the grouted sand has exhibited creep strains of different degrees. The creep slopes of grouted sand were proportional to the creep slopes of pure grout. Creep characteristics of grouted sand may also be deduced from the creep behavior of pure sand and the creep behavior of pure grout.     

Some Factors Affecting on the Structure-formation and Mechanical Properties of As-Cast High Toughness Nodular Cast Iron

Using sand moulds for step-shape casting tests and different silicon percentage of nodular cast iron it was possible to separate structural variations produced during freezing from those occurring at Ac1 transformation temperature. The results show that an increase in silicon content leading to different variation in the matrix structure> leads to a changing mechanical properties of nodular cast irons. Tensile strength and elongation of obtained as-cast nodular cast iron with the composition of 3.9%C, 3.2%Si, 0.5%Mn are maximum of about 524.5N/mm2 and 19.8% accordingly. In the same nodular cast iron, but only with 0.1% Mn the silicon addition first increases after decreases elongation, impact toughness and hardness. But tensile strength changes to the opposite side.     

Engineering Properties of Grouted Sands

A comparison of the behavior of uncemented and grouted sands is presented. Four sands (Fontainebleau sand and three types of alluvial deposits of the Seine River) were tested. Specimens of grouted sands were prepared in the laboratory by injection of very fine cement or mineral grouts. An initial series of unconfined uniaxial compression tests and tensile tests was performed to highlight the effect of some key factors (mainly the cement-to-water ratio of the grout and the relative density of the granular skeleton) on the strength of the grouted sands. Subsequent triaxial tests showed that when a soil is impregnated by either a very fine cement grout or a mineral grout, both stiffness (secant stiffness or small-strain stiffness) and strength of the soil improve. Similar trends were observed for the behavior of both uncemented and grouted sands. The behavior of grouted sands can be roughly reproduced by applying a linear elastic, perfectly plastic model with a nonassociated Mohr–Coulomb yield criterion whose parameters can be easily determined. Finally, preliminary recommendations are proposed relative to improvements ratios of the parameters of this simple constitutive model that is still commonly used in geotechnical engineering.     

影响HRB335钢筋力学性能的因素分析

分析了影响HRB335钢筋力学性能的因素，通过加强小方坯质量控制，改善了HRB335钢筋的力学性能。     

Geotechnical Properties of Cemented Sands in Steep Slopes

An investigation into the geotechnical properties specific to assessing the stability of weakly and moderately cemented sand cliffs is presented. A case study from eroding coastal cliffs located in central California provides both the data and impetus for this study. Herein, weakly cemented sand is defined as having an unconfined compressive strength (UCS) of less than 100 kPa, and moderately cemented sand is defined as having UCS between 100 and 400 kPa. Testing shows that both materials fail in a brittle fashion and can be modeled effectively using linear Mohr-Coulomb strength parameters, although for weakly cemented sands, curvature of the failure envelope is more evident with decreasing friction and increasing cohesion at higher confinement. Triaxial tests performed to simulate the evolving stress state of an eroding cliff, using a reduction in confinement-type stress path, result in an order of magnitude decrease in strain at failure and a more brittle response. Tests aimed at examining the influence of wetting on steep slopes show that a 60% decrease in UCS, a 50% drop in cohesion, and 80% decrease in the tensile strength occurs in moderately cemented sand upon introduction to water. In weakly cemented sands, all compressive, cohesive, and tensile strength is lost upon wetting and saturation. The results indicate that particular attention must be given to the relative level of cementation, the effects of groundwater or surficial seepage, and the small-scale strain response when performing geotechnical slope stability analyses on these materials.     

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.     

Updated Liquefaction Resistance Correction Factors for Aged Sands

Data from over 30 sites in 5 countries are analyzed to develop updated factors for correcting liquefaction resistance for aged sand deposits. Results of cyclic laboratory tests on relatively undisturbed and reconstituted specimens suggest an increase in the correction factors of 0.12 per log cycle of time and an average reference age of 2 days for the reconstitute specimens. Laboratory and field test results combined with cyclic resistance ratio (CRR) charts suggest an increase in the correction factors of 0.13 per log cycle of time and an average reference age of 23 years. A reference age of 23 years seems appropriate for the commonly used CRR charts derived from field liquefaction and no liquefaction case history data. Because age of natural deposits is often difficult to accurately determine, a relationship between measured to estimated shear-wave velocity ratio (MEVR) and liquefaction resistance correction factor is also derived directly from the compiled data. This new MEVR-liquefaction resistance correction factor relationship is not as sensitive to MEVR as in the relationship derived indirectly in a previous paper.     

Ti／Mn基Laves相贮氢合金贮氢性能的影响因素

介绍了影响Ti/Mn基Laves相贮氢合金贮氢性能的一些因素,这些因素包括锆部分取代钛,Cr、V、Fe、Cu、Ni、Co、Mo等元素部分取代锰,非化学计量,非金属杂质元素与杂质气体。同时也介绍了热处理、熔炼方式、氟化处理对Ti/Mn基Laves相贮氢合金贮氢性能的影响。     

反应熔渗法制备C/C-SiC复合材料及其影响因素的研究进展

本文比较了C／C－SiC复合材料的三种主要制备方法，主要介绍了反应熔渗法制备工艺，以及液Si渗入C／C多孔体，液Si与固体C反应和C／C－SiC复合材料性能的主要影响因素，提出了尚待解决的关键问题。     

热滑伤判断条件及其影响因素

为了研究冷连轧高速生产过程中的热滑伤问题,在首次引入滑伤指数新概念的基础上,给出了判断冷连轧过程中是否发生热滑伤的不等式,并定量分析了热轧来料温度、总压下率、轧制速度、压下规程以及乳化液流量密度等因素对热滑伤的影响.同时提出了防止热滑伤的措施,把此措施用于实际生产中,并取得了较大的经济效益.     

Factors Affecting Engineering Productivity

Engineering performance has a major impact on subsequent project phases, such as procurement and construction, and thus, has the potential to affect the overall project outcome. This study utilizes metrics and a database from the Construction Industry Institute (CII) benchmarking and metrics program to investigate relationships between factors thought to affect direct engineering labor productivity during detailed engineering. Collaborating with industry practitioners, quantitative assessments were analyzed with industry input through various CII committee meetings and industry forums. Significant correlations are found between engineering productivity and project size, project type, project priority, and phase involvement. Correlations are also found between degree of modularization, funded front-end planning effort, and quality management and engineering productivity. These findings extend and, in some cases, contradict previous research.     

Factors Affecting International Construction

A construction company’s decision to expand into international markets must be based on a good understanding of the opportunities and threats associated with international business, as well as the development of company strengths relative to international activities. These factors were evaluated in this study by surveying the executives in charge of international construction of large United States based contractors. The information was collected by means of two rounds of a Delphi survey, the results of which were used as input in an analytic hierarchy process (AHP). The findings indicate that track record, specialist expertise, project management capability are the most important company strengths; loss of key personnel, shortage of financial resources, and inflation and currency fluctuations are the most important threats relative to international markets; and increased long term profitability, the ability to maintain shareholders’ returns, and the globalization and openness of the markets are the most important opportunities available in international works. This study is of relevance to practitioners as it systematically highlights the factors that affect international construction for the benefit of executives of medium-to-large size construction companies who are considering expanding into overseas markets. It is of relevance to researchers too as it demonstrates the successful use of the combined Delphi and AHP.