Experimental Study on Young′s Modulus of Concrete

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Deterioration of dynamic mechanical property of concrete with mineral admixtures under fatigue loading

The dynamic mechanical property of concrete is one of the key parameters, which greatly influences durability of infrastructures subjected to continuous heavy loading, such as girder and track slab of high-speed railway foundation structure. This paper reports serials of experiments designed to investigate the deterioration of dynamic mechanical properties of different concretes under fatigue loading condition. Four parameters including relative dynamic elastic modulus (RDEM), relative dynamic shear modulus (RDSM), relative compressive strength (RCS) and water absorption (WA) of concrete were evaluated to assess the dynamic properties and microstructures of concretes. Results show that the fatigue stress levels and fatigue cycle durations significantly influence the dynamic mechanical properties of concrete including dynamic elastic modulus and dynamic shear modulus. Addition of proper mineral admixture can improve the dynamic mechanical characteristics of concrete and increase its resistance against the fatigue loading effect. Keeping the amount of mineral admixture in concrete constant, its dynamic mechanical property with fly ash is lower than that with fly ash and silica fume. The water absorption in concrete, which is an indirect parameter reflecting capillary porosity, increases evidently after bearing fatigue-loading. There is a close correlation between the deterioration of dynamic mechanical property and the increasing of water absorption of concrete. This indicates that the damage of microstructure of concrete subjected to fatigue loading is the indispensable reason for the decay of its dynamic mechanical performance.     

Synthesis of A Novel Photosensitive Prepolymer with Trimethylolpropane Triglycidylether and Acrylic Acid as Starting Materials

A novel photosensitive prepolymer of trimethylolpropane triglycidylether triacrylate was synthesized by utilizing trimethylpropane triglyridylether anti acolic acid as two starting materials, triphenyl phosphine as catalyst and p- hydroxyanisole as inhibitor. The optimum synthesis conditions were that the conceutration of triphenyl phosphine wets 0. 85wt% of reactants, the conceutration of p-hydroxyanisole was 0. 3wt% of reactants, and the reaction temperature was at 90-110℃ . Benzil dimethyl ketal of a UV-cured initiator was added to the synthesized trimethylolpropane triglycidylether triacrylate to prepare a kind of UV-cured coating. The mechanical properties of the UV-cured films were determined, giving 28.43 MPa of tensile strength, 965 . 59 MPa of Young‘ s modulus and 4.10% of elongation at tear.     

Cold resistant properties of high modulus polyurethane

Six kinds of polyurethane (PU) elastomers were prepared based on different polyesters, polyethers and chain extenders. The structure, mechanical properties and cold resistant properties of PU were systematically investigated by FTIR, XRD, DMTA, universal testing machine and flex ductility machine. The results show that T _g of soft segment is the main factor of the cold resistant properties of polyurethane elastomer. Compared with the same relative molecular mass of the polyester and the polyether, the polyether flexibility is better, the glass transition temperature (T _g) is lower and the cold resistant properties is remarkable, for example the cold resistant properties of PU based on poly (tetramethylene glycol), 1, 4-BG and MDI achieves the fifth level. The physics performances of polyurethane elastomers, such as breakdown strength, Young’s modulus and the cold resistant properties, are all superior.     

温度对C50纤维混凝土力学性能的影响

结合武汉市某工程大体积混凝土实测温度,试验研究了高温高碱环境对纤维自身力学性能的影响,及不同养护温度下混凝土的力学性能发展趋势.试验结果表明:聚丙烯纤维在10%浓度的NaOH溶液中浸泡24 h且经历室温—65℃—室温循环,纤维自身力学性能下降约10%;处理后的纤维掺入混凝土中对标准养护的试块强度无不良影响;不同养护温度下纤维混凝土力学性能发展趋势差异明显,65℃养护1 d龄期的轴心抗压强度、弹性模量、劈裂抗拉强度可达标准养护28 d龄期相应参数的97%,74%,74%,4 d龄期轴心抗压强度、劈裂抗拉强度有一定增长趋势.因此,大体积混凝土实体结构强度评定需考虑水化温度作用的影响.     

Synthesis of a novel UV-curable prepolymer polypropyleneglycol diglycidyl ether diacrylate

A novel UV-curable prepolymer polypropyleneglycol diglycidyl ether diacrylate （PPGGEA） was synthesized by utilizing polypropyleneglycol diglycidyl ether （PPGGE） and acrylic acid （AA） as starting materials, N, N-dimethylbenzylamine as catalyst and p-hydroxyanisole as inhibitor. The optimum synthetic conditions were in the following： the concentration of N, N-dimethylbenzylamine was 0.80 wt% of reactants, the concentration of p-hydroxyanisole was 0.3 wt% of reactants, the reaction temperature was 90-110 ~C, and the molar ratio of PPGGE to AA was 1：2.2. Meanwhile, 1-hydroxycyclohexyl phenyl ketone of a UV-cured initiator was added to the synthesized PPGGEA to prepare a kind of UV-cured coating. The mechanical properties of the UV-cured films were determined, giving 29.99 MPa of tensile strength, 834.27 MPa of the Young＇s modulus and 5.66% of elongation at tear.     

老化前后沥青与沥青混合料指标相关性分析

为分析老化前后沥青与沥青混合料指标相关性，开展了相应室内试验研究：在不同老化阶段进行沥青针入度、延度、软化点试验；在中、低温条件下，对不同老化时期AC-13沥青混合料进行半圆弯拉试验，分析混合料力学强度、弹性模量、断裂能演化规律；将老化前后沥青三大指标与沥青混合料力学指标进行相关性回归分析。试验结果表明，老化初期对混合料强度、弹性模量影响较大，且老化对弹性模量影响较为敏感；混合料对低温断裂能作用明显，中温断裂能显著高于低温断裂能；混合料老化前后的强度、弹性模量与沥青三大指标具有较高线性相关性，针入度可对中低温下混合料力学性能进行预测。     

Experimental study on the mechanical properties of rocks at high temperature

The mechanical properties of marble, limestone, and sandstone as well as the stress-strain curve, the varying characteristics of the peak strength, the peak strain and elastic modulus were studied by using the MTS810 Rock Mechanics Servo-controlled Testing System under the action of temperatures rang- ing from room temperature to 800℃ . Results show that (1) the peak strength and elastic modulus of marble fluctuate at the temperature from normal to 400 ℃ ; and they decrease gradually over 400℃ . (2) With th...     

热处理对34CrNi3Mo铸钢力学性能的影响

为研究不同热处理工艺对34CrNi3Mo铸钢力学性能的影响,对比了"喷水淬火+高温回火"、"油淬+高温回火"、"双液淬火(水-油)+高温回火"和"双液淬火(水-油)+两次高温回火"4种热处理工艺条件下34CrNi3Mo铸钢的力学性能。结果表明:采用"喷水淬火+高温回火"处理的试样不仅比"油淬+高温回火"处理的试样强度好、硬度高,而且塑性和冲击韧性也更好。当对铸件进行"双液淬火(水-油)+高温回火"后,可以实现铸件外强内韧的特性;双液淬火(水-油)后2次高温回火会使铸件的强度、硬度更高,但塑性、韧性下降。     

Stress-strain model of corroded concrete under uniaxial compressive loading

The prism specimens of corroded concrete were subjected to uniaxial compressive load to develop the stress-strain model. Compared to the un-corroded concrete, the mechanical properties of corroded concrete, such as peak strength, Young’s modulus, and residual deformation, et al are degraded. The concrete, which were subjected to the aggressive media in the environment, were resulted in randomly distributed pre-loading flaws and defects. The propagation of these corrosion flaws during the procedure of loading was the main reason of degradation of corroded concrete properties. By the application of the statistic theory of continuum damage, the compressive stress-strain curve of corroded concrete was simulated. The initial damage factor was introduced to represent the corrosive effects of different media. The present damage constitutive model agreed well with the test results.     

混凝土单轴动态抗拉特性的试验研究

在应用过程中,混凝土结构肯定要受到动态荷载的作用,而混凝土材料的动态力学特性与静态情况下有非常大的区别.为了考察动态荷载作用下混凝土的抗拉特性,本文应用MTS试验机,对C40混凝土在应变速率为10-5/s～10-2/s范围内进行单轴动态拉伸试验,系统研究了不同应变速率下混凝土的抗拉强度、弹性模量、峰值应变等抗拉力学特性,并分析了应变速率对混凝土抗拉强度、弹性模量等的影响规律.试验结果表明:混凝土抗拉强度、弹性模量会随应变速率的增加而增加,泊松比离散性比较大,规律不明显,动态受拉应力应变曲线与静态相似.这些成果可以为混凝土的结构设计提供技术参数.     

The Young's moduli prediction of random distributed short-fiber-reinforced polypropylene foams using finite element method

The elastic moduli of short-fiber-reinforced foams depend critically on the fiber content and fiber length, as well as on the fiber orientation distribution. Based on periodic tetrakaidecahedrons, the finite element models with short-fiber reinforcement were proposed in this paper to examine the effects of the fiber content and fiber length on Young's modulus. The fiber length distribution and fiber orientation distribution were also considered. The proposed models featured in a three-dimensional diorama with random short-fiber distribution within or on the surfaces of the walls and edges of the closed-cells of polypropylene (PP) foams. The fiber length/orientation distributions were modeled by Gaussian prob-ability density functions. Different fiber volume fractions, different lengths, and different distributions were investigated. The predicted Young's moduli of the PP foams with short-glass-fiber or short-carbon-fiber reinforcement were compared with other theoretic and experimental results, and the agreement was found to be satisfactory. The proposed finite element models were proved to be acceptable to predict the Young's moduli of the grafted closed-cell PP foams with short-fiber reinforcement.     

热处理工艺对27SiMn钢组织及力学性能的影响

为得到热处理工艺对27SiMn钢显微组织及力学性能的影响,制定了9种热处理工艺,并对其进行显微组织观察和力学性能测试.实验结果表明,27SiMn钢淬火＋回火后的显微组织与回火温度和时间有关,当回火温度低、时间短时,显微组织为回火屈氏体＋马氏体;当回火温度高、时间长时,显微组织为回火屈氏体＋回火索氏体.同时,回火温度和时间对27SiMn钢的力学性能有很大影响,当回火温度为450℃,时间为45 min时力学性能最高,抗拉强度为1 175 MPa。当热处理温度为490℃,时间为75 min时力学性能最差,抗拉强度为975 MPa.综合分析27SiMn钢热处理最优工艺为900℃淬火＋475℃回火75 min。     

Mechanical Property Evaluation on the Bending and Compressing Behaviour of Nano-beam

Based on quasicontinuum(QC) multiscale simulation method,a series of simulation models were set up for bending and compressing rod-shaped microstructure of single crystal Cu.The effects of structural parameters on typical mechanical properties were analyzed,such as elastic modulus,elastic limit,yield strength,and Poisson's ratio.According to the analysis of displacement,inner stress and strain energy,the mechanisms of deformation and failure were also revealed.The experimental result shows that the mechanical properties exhibit obvious size effect during the bending and compression process.In the bending simulation,when the span-thickness ratio is more than 10,the elastic modulus rises slightly with the increase of strain.And the smaller the beam is,the faster the elastic modulus grows.Meanwhile,when the spanthickness ratio keeps constant the elastic modulus will decrease with the growth of the beam sizes.However,in the compression model,the size effect on Poisson's ratio is not remarkable.The dimensional change in one direction cannot influence the mechanical parameters greatly.Mechanical twins and dislocation contribute to the compression behaviour greatly.Meanwhile,the stress concentration can also be found in the inner partial area and the strain energy decreases abruptly after the crush of beam microstructure.     

FRC路面配合比设计

从普通水泥混凝土路面的基本要求可知：混凝土路面要有较高的弯拉强度,较低的弹性模量和良好的耐疲劳和抗冲击性能,而纤维混凝土（简称FRC）比普通混凝土具有更优良的动、静力学性能.为了发挥FRC的力学性能,必须有合理的设计配合比.文章以常见的剪切钢纤维和杜拉纤维（Durafibre）为例,设计路面的材料配合比.     

Stiffness compatibility of coralline hydroxyapatite bone substitute under dynamic loading

When hydroxyapatite bone substitutes are implanted in human bodies, bone tissues will grow into their porous structure, which will reinforce their strength and stiffness. The concept of mechanical compatibility of bone substitutes implies that their mechanical properties are similar to the bone tissues around, as if they were part of the bone. The mechanical compatibility of bone substitutes includes both static and dynamic behavior, due to the mechanical properties of bone depending on the strain rate. In this study, split Hopkinson pressure bar technique (SHPB) was employed to determine the dynamic mechanical properties of coralline hydroxyapatite, bones with and bones without organic components, and their dynamic stress-strain curves of the three materials were obtained. The mechanical effects of collagens in bone were assessed, by comparing the difference between the Young’s moduli of the three materials. As the implanted bone substitute becomes a part of bone, it can be regarded as an inclusion composite. The effective modulus of the composite was also evaluated in order to estimate its mechanical compatibility on stiffness. The evaluated result shows that the suitable porosity of HA is 0.8, which is in favor of both static and dynamic stiffness compatibility. Supported by the Tianjin Natural Science Foundation (Grant No. 05YFJMJC10500)     

锯片基体材料的非调质生产工艺

为了降低锯片基体生产成本并提高产品质量,以特定Si-Mn系试验钢为研究对象,采用TM CP工艺对新型锯片基体材料进行了研究.利用扫描电子显微镜、拉伸试验机等试验设备对基体材料的组织和力学性能进行了分析测试.结果表明,当轧后冷速为32.3℃/s时,可以获得以细小束状贝氏体为主的显微组织,且该冷速下基体材料的抗拉强度、屈服强度可以分别达到1 315与1 030 M Pa,冲击吸收功可以达到53.9 J,同时试验钢的弹性模量与弹性极限分别为198.5 GPa和915.4 M Pa.此外,经过8万次循环载荷作用后,试验钢的三点弯曲永久变形高度为0.21 mm,试验钢表现出较好的综合机械性能.采用非调质工艺生产的Si-Mn系贝氏体钢可以用作锯片基材.     

多层氧化石墨烯单轴拉伸行为的分子动力学模拟

为探索氧化官能度、堆叠层数和温度对多层氧化石墨烯力学特性及变形行为的影响规律,本文采用分子动力学方法模拟了多层氧化石墨烯的单轴拉伸试验过程。结果表明:双层氧化石墨烯呈现各向同性特征,弹性模量和极限强度与氧化官能度的变化呈负相关;弹性模量受温度影响较小,而极限应力和极限应变受温度影响显著;氧化石墨烯的力学性能基本参量的变化对堆垛层数不敏感。研究结果揭示了影响多层氧化石墨烯力学特性的关键因素,可为介观尺度多层氧化石墨烯材料的应用提供指导。     

Molecular dynamics simulation of the test of single-walled carbon nanotubes under tensile loading

Molecular dynamics (MD) simulations were performed to do the test of sin-gle-walled carbon nanotubes (SWCNT) under tensile loading with the use of Bren-ner potential to describe the interactions of atoms in SWCNTs. The Young’s modulus and tensile strength for SWCNTs were calculated and the values found are 4.2 TPa and 1.40―1.77 TPa, respectively. During the simulation, it was found that if the SWCNTs are unloaded prior to the maximum stress, the stress-strain curve for unloading process overlaps with the loading one, showing that the SWCNT’s de-formation up to its fracture point is completely elastic. The MD simulation also demonstrates the fracture process for several types of SWCNT and the breaking mechanisms for SWCNTs were analyzed based on the energy and structure be-havior.     

基于纳米压痕技术的电子玻璃微观力学性能研究

为了研究不同电子玻璃的微观力学性能,采用先进的纳米压痕技术记录钠钙硅、无碱硼铝硅和碱铝硅等典型电子玻璃的载荷-位移曲线,利用Oliver-Pharr方法和经典的弹塑性变形理论,计算玻璃的硬度和弹性模量. 玻璃的硬度主要与结构的键合度相关,平均非桥氧数越高,外力作用下越容易致密化,硬度越小;弹性模量主要取决于质点间的化学键强度,化学键力越强,变形越小,弹性模量越大;九点法测得的弹性模量与硬度的变化趋势不完全相同,借助硬度-弹性模量-能量耗散之间的本征关系,评价玻璃样品的微观均匀性,其中无碱硼铝硅玻璃的恢复阻力大,局部能量耗散大,不容易引起整体破坏,力学性能最好;与浮法工艺相比,溢流下拉法制备样品的局部力学性能波动较小,微观均匀性较好.