混凝土四重球弹性模量随龄期发展预测模型

混凝土的抗压强度和弹性模量随龄期不断增长.然而,与抗压强度相比,弹性模量随龄期的增长并不明显,相关的研究也较少.本文在混凝土弹性模量双重球和三重球预测模型的基础上,考虑了水泥浆体与骨料间的界面过渡区效应,建立了混凝土弹性模量四重球理论模型,且模型能够较好的反映界面过渡区在混凝土弹性模量发展中的作用.分析表明,对混凝土弹性模量发展起到主要作用的参数按重要程度依次为骨料体积分数、骨料粒径及界面过渡区效应.     

粉末冶金法制备Ti-Mg合金的探索研究

<正>钛合金具有良好的生物相容性、高比强度、高耐蚀性,可用于制作外科植入件。然而,钛合金的弹性模量(100 GPa)与人体骨骼的弹性模量(20~40GPa)相差较大,易产生"应力屏蔽"。为了降低钛合金的弹性模量,拟采用粉末冶金的方法将弹性模量较低的材料均匀分散在弹性模量较高的基体材料中。为此,日本大学的科研工作者选择了弹性模量为45GPa的镁作为添加元素。从Ti-Mg系的平衡相图来     

新型Ti-Al金属间化合物多孔材料的弹性模量表征

基于新型Ti-Al金属间化合物多孔材料的孔隙微观结构特点,采用三维八面体结构模型,首次通过能量法推导出该多孔材料的弹性模量理论计算公式,并分析孔棱横截面形状和剪力对相对弹性模量的影响规律。结果表明,与现有模型相比,本文模型推导弹性模量理论公式过程更简单,且因考虑了孔棱横截面形状及孔棱内力(含轴力、剪力、弯矩)对相对弹性模量的影响,所得结果更为精确且偏于安全。孔棱横截面形状和剪力对相对弹性模量的影响均随相对密度的增加而增大,当相对密度较小时两者均可忽略不计。新型Ti-Al金属间化合物多孔材料的弹性模量表征为该材料的工程实际应用提供了可靠的理论依据。     

脊椎固定器用钛合金弹性模量自调整功能的控制原理

<正>脊椎固定器在较狭窄的手术视野中应能够随着脊椎侧弯的程度进行简单的形变,且不应产生大的回弹。然而为了抑制应力屏蔽效应,又要求其具有低的弹性模量。为此,大阪大学H.H.Liu研发了通过具有高弹性模量的变形诱发ω相来控制的自调整型Ti-9Cr-0.2O合金,在变形区可以获得高弹性模量,未变形区仍维持低弹性模量。为改善合金弹性模量的自调整特性,探讨了变形诱发ω相的形成机理。     

轻质钢的研究进展(二)——铁素体—奥氏体双相轻质钢和奥氏体轻质钢

首先主要阐述了富Al铁素体—奥氏体双相轻质钢和奥氏体轻质钢的微观组织特征、力学性能和强韧化机制。尽管添加Al可以降低钢的密度和提高比强度,但是它会使钢的弹性模量显著降低。针对这一不利属性,介绍了一种切实可行的提高轻质钢(以及碳钢)弹性模量的措施,即利用凝固过程中原位自生高弹性模量的硬质颗粒(如Ti C和Ti B2等)来增强钢的基体。所形成的颗粒增强钢基复合材料可以具有较常规碳钢和富Al轻质钢更高的弹性模量和比弹性模量。     

三点弯曲法测试硬质合金弹性模量

通过确定荷载范围和修正仪器变形引起的系统误差,用三点弯曲法在电子万能试验机上测定了硬质合金的弹性模量。结果表明:硬质合金弹性模量(y)与Co含量(x)存在稳定的线性关系,其关系式为y=0.13x2-14.24x+708.41,即弹性模量随着Co含量的增加而减小。三点弯曲法测试的硬质合金弹性模量结果稳定、精确,与振动法测试的结果相吻合。这种测试方法简单易行,适合于硬质合金的力学性能表征。     

层状岩石倾角对弹性模量的影响研究

层理倾角对互层复合岩体的力学特性和物理参数等具有显著的影响,为研究层状岩石倾角对互层复合岩体弹性模量的影响,首先推导出水平状互层复合岩体平行于层理方向和垂直于层理方向的弹性模量,进而推导了层理倾角与互层复合岩体弹性模量关系的解析解,并通过不同层理倾角页岩的单轴抗压实验验证了解析解的正确性。     

钢的晶界区弹性模量计算

基于弹性作用应力引起的非平衡晶界偏聚理论模型和动力学方程,在Misra和Shinoda的试验结果基础上计算多晶体材料钢的晶界区弹性模量。对郑磊的文章参数选择进行修正并重新计算,求得883K下2.6Ni-CrMo-V钢的晶界区拉伸弹性模量为3.50MPa;同时基于非平衡晶界偏聚和贫化的模型,分别计算773K下某钢晶界区的拉伸和压缩弹性模量,所得结果为1.395和1.076MPa,与2.6Ni-Cr-Mo-V钢的计算结果在数量级上是一致的,进一步证明非平衡晶界偏聚和贫化的理论模型作为晶界区弹性模量的计算可靠性。     

炉料弹性模量对高炉内炉料运动行为与应力分布的影响

采用三维离散元法对不同弹性模量条件下,5000m3高炉内的炉料的运动行为进行了研究.发现,当弹性模量取0.06GPa时,炉料颗粒的变形量超过了自身半径的1/2,炉身处发生严重的混料现象,炉缸内焦炭颗粒发生堆积,无焦空间减小,而且计算在100步以后自动终止.而当弹性模量在10～0.6GPa范围内变化时,炉身段料层倾角随弹...     

合金元素、加工与热处理对医用β型钛合金力学性能的影响及微观分析

研究了不同合金添加元素（Mo,Sn,Zr,Nb）、加工以及热处理对近β型医用钛合金力学性能和显微组织的影响规律,讨论了保持医用钛合金强度、弹性模量和塑性优良匹配的影响因素和解决办法。研究发现：Ti-Nb-Zr-Mo-Sn合金中增加Zr,Mo,Sn元素含量使合金强化,而增加Mo,Nb元素含量和热加工率利于降低弹性模量;经过固溶处理后强度和弹性模量降低,经时效处理后合金产生弥散强化和细晶强化使强度和弹性模量增加;热轧态和固溶状态下产生应力诱发马氏体而导致较低的屈强比和允许应变,利于二次加工和实际应用。     

Elastic Modulus of 304 Stainless Steel Coating by Cold Gas Dynamic Spraying

 304 stainless steel coating was deposited on the IF steel substrate by cold gas dynamic spraying (CGDS), and the elastic modulus of the 304 stainless steel coating was studied. The elastic modulus of cold sprayed 304 stainless steel coating was measured using the three-point bend testing and the compound beam theory, and the other mechanic parameters (such as the equivalent flexural rigidity and the moment of inertia of area) of the coatings were also calculated using this compound beam theory. It is found that the calculated results using the above methods are accurate and reliable. The elastic modulus value of the cold sprayed 304 stainless steel coating is 1179×105 MPa, and it is slightly lower than the 304 stainless steel plate (about 2×105 MPa). It indicates that the elastic modulus of the cold sprayed coatings was quite different from the comparable bulk materials. The main reason is that the pores and other defects are existed in the coatings, and the elastic modulus of the coatings also depends on varies parameters such as the feed stock particle size, porosity, and processing parameters.     

大变形条件下弹模对边坡应力变形的影响

据弹塑性大变形理论,在平面应变的条件下,用控制力的方法来控制边坡的收敛性,定性分析了弹性模量影响下边坡的应力、应变规律,对大变形和小变形对边坡塑性应变差异做了对比。计算结果表明:对于均质土坡,弹性模量对塑性区范围影响不大,对坡脚的沉降、水平位移有明显的影响。     

A Finite Element Model to Predict the Effect of Porosity on Elastic Modulus in Low-Porosity Materials

The effect of porosity on elastic modulus in low-porosity materials is investigated. First, several models used to predict the reduction in elastic modulus due to porosity are compared with a compilation of experimental data to determine their ranges of validity and accuracy. The overlapping solid spheres model is found to be most accurate with the experimental data and valid between 3 and 10 pct porosity. Next, a FEM is developed with the objective of demonstrating that a macroscale plate with a center hole can be used to model the effect of microscale porosity on elastic modulus. The FEM agrees best with the overlapping solid spheres model and shows higher accuracy with experimental data than the overlapping solid spheres model.     

Spherical Indentation on an Elastic Coating/Substrate System: Determining Substrate Modulus

A vast amount of indentation studies on coating/substrate systems focused on extracting the mechanical properties of the film, by either avoiding or subtracting off the substrate effect. However, in engineering and biomedical applications, very often the substrate properties, in particular the substrate modulus, need to be measured from an indentation test and the protective layer cannot be removed. For the model system of an elastic film deposited on an elastic substrate, we establish the general approach of spherical indentation focusing on the substrate property determination. Indentation data are taken from different indentation depths which reflect different degrees of film and substrate effects. An effective reverse analysis algorithm is established such that, from an indentation test if either the film modulus or film thickness is known, the other variable can be measured along with the substrate modulus. Error sensitivity of the proposed formulation is analyzed in a systematic way.     

Braced Excavations: Temperature, Elastic Modulus, and Strut Loads

Relationships between strut loads, earth pressures, temperatures, and the measurements provided by strain gauges are presented in this paper. A braced excavation up to 20-m deep, 9–20 m wide, and >650-m long constructed in competent glacially derived sand, silt, and clay soils (including glacial till) provided a significant amount of data for analysis. The excavation was supported by soldier piles and lagging with pipe struts and was covered with decking during construction. A direct correlation between incremental changes in strut load and temperature was observed during the course of the project. The few existing relationships between strut load and temperature were reexamined and were found to produce back-calculated elastic modulus values that were either without comparison or inconsistent with data from field tests and published sources. The relationships derived as a result of this work are supported by limited case-history data from other published sources and are consistent with practical application of elastic deformation concepts and published soil modulus values.     

Mechanistic Corrections for Determining the Resilient Modulus of Base Course Materials Based on Elastic Wave Measurements

The mechanical performance of pavement systems depends on the stiffness of subsurface soil and aggregate materials. The moduli of base course, subbase, and subgrade soils included in pavement systems need to be characterized for their use in the new empirical-mechanistic design procedure (NCHRP 1-37A). Typically, the resilient modulus test is used in the design of base and subbase layers under repetitive loads. Unfortunately, resilient modulus tests are expensive and cannot be applied to materials that contain particles larger than 25 mm (for 125-mm diameter specimens) without scalping the large grains. This paper examines a new methodology for estimating resilient modulus based on the propagation of elastic waves. The method is based on using a mechanistic approach that relates the P-wave velocity-based modulus to the resilient modulus through corrections for stress, void ratio, strain, and Poisson’s ratio effects. Results of this study indicate that resilient moduli are approximately 30% of Young’s moduli based on seismic measurements. The technique is then applied to specimens with large-grain particles. Results show that the methodology can be applied to large-grained materials and their resilient modulus can be estimated with reasonable accuracy based on seismic techniques. An approach is proposed to apply the technique to field determinations of modulus.     

Q345钢中厚板热矫直变形抗力与弹性模量数学模型的研究

根据中厚板矫直力的理论公式和Q345钢22～40mm板500～630℃矫直的生产实测数据,以变形抗力和弹性模量数学模型中的待定系数为优化变量,以矫直力计算误差最小为目标函数,采用单纯形法对待定系数进行优化计算,建立了Q345钢中厚板矫直过程变形抗力和弹性模量数学模型,得出Q345钢中厚板在500～630℃矫直过程随温度(T)提高,变形抗力(σs)降低:σs=-1080.1+4.8547 T-0.0048115 T~2;随温度(T)提高,弹性模量(E)先增加后减少:E= (-6.4807×10~5) +2576.5 T-2.3875 T~2。结果表明,矫直力的计算值和测量值的相对误差小于5%。     

Elastic constants of martensite

The elastic constants of Fe−Ni−C martensite are increased by retained austenite. Also, nickel markedly decreases the elastic constants of such martensite. Therefore, to properly evaluate the effect of carbon on the elastic constants of Fe−Ni−C martensite, it is necessary to first correct for both retained austenite and nickel content. When these corrections are made, both the Young's modulus and the shear modulus of Fe−Ni−C martensites. decrease with increasing carbon content, in agreement with earlier work on Fe−C martensites. thus, an increased lattice stiffness cannot be used to explain the high strength of martensite.     

Estimating Subgrade Reaction Modulus for Transversely Isotropic Rock Medium

Most of the rock medium possesses intrinsic grain orientation or preferred bedding and joint directions, thus requiring the use of at least transverse isotropy to describe its elastic behavior. This paper presents a series of charts, based on extensive finite element parametric studies along with nonlinear regression analysis of FE simulation results, for estimating the subgrade reaction modulus (or initial tangent to the p-y curve) using five elastic constants of a transversely isotropic rock mass. The proper characterization of subgrade reaction modulus is critical for accurate prediction of the elastic lateral deflection of a rock socketed drilled shaft under the applied lateral loads. The sensitivity of the response of a laterally loaded drilled shaft to the degree of anisotropy and orientation of the plane of anisotropy (bedding plane direction of the rock medium) was demonstrated in this paper for an actual lateral load testing case in Ohio. It is highly recommended to use five elastic constants to estimate subgrade reaction modulus of rock medium exhibiting high degree of cross anisotropy.