高弹模CFRP粘贴法修复钢桥板疲劳裂纹

针对钢桥中钢板疲劳裂纹进行了一系列疲劳裂纹修复试验研究,以确定不同修复方法下结构的疲劳性能。高弹模CFRP(碳纤维增强复合材料)修复法是通过粘贴高弹模CFRP布来增大结构刚度,以延长结构疲劳寿命,且碳纤维材料基本不会产生疲劳裂纹,具有较好的抗疲劳效果。采用数值模拟和试验研究相结合的方法,首先对修复钢板的应力分布和特点进行了详细的分析,然后通过3组对比疲劳试验,确定了不同修复方法对损伤钢板疲劳寿命的增强效果。最后利用修复试验值与各国规范规定的S-N曲线进行比较,分析已修复钢板的疲劳性能。研究结果表明:在止裂孔上覆盖粘贴高弹模CFRP布可有效减小孔边应力集中,具有延长结果疲劳寿命的效果,修复后的裂纹钢板的疲劳寿命是仅用止裂孔修复的裂纹钢板疲劳寿命的8倍以上。仅用止裂孔法修复损伤钢板不足以满足各国规范规定的疲劳强度要求,而在止裂孔法上进一步采用高弹模CFRP布修复后的损伤钢板的抗疲劳性能更优,其疲劳强度等级高于美国规范AASHTO中的A类细节等级。

高弹模PVA纤维超高强混凝土拉压比试验研究

本文在超高强混凝土(C100)中掺入高弹模PVA纤维,通过立方体抗压强度与劈裂抗拉强度试验,研究PVA纤维对超高强混凝土增强增韧效果和拉压比性能的影响。立方体试件尺寸为100×100×100 mm,PVA纤维掺量为0%、0.17%、0.25%、0.34%、0.5%。试验结果表明,掺入PVA纤维后,超高强混凝土立方体试件裂缝开展路径较多,裂而不散,坏而不碎,抗压韧性显著增强;掺入PVA纤维后,超高强混凝土立方体抗压强度提高2.9%～8.2%,劈裂抗拉强度提高21.8%～46.7%;掺入PVA纤维的超高强混凝土拉压比为0.0562～0.0661,拉压比值提高15.30%～35.61%。掺入PVA纤维可使超高强混凝土脆性大、韧性小的缺点得到显著改善。

低模高弹体泊松比试验测试方法

[目的]在轴向承载时,低模高弹体存在侧向形变大、均匀性差等问题,常规电阻式应变测试方法难以准确获取材料的泊松比。为了消除试件侧向变形的不均匀性影响,准确获取高分子材料的泊松比值,[方法]基于弹性力学理论,推导了圆柱形低模高弹体在侧向刚性约束时的压缩模量、弹性模量与泊松比的表达式,建立了试验的理论模型。在理论分析的基础上,提出了由钢制套筒侧向约束轴向加载的泊松比测试方案,并开展了天然橡胶及HW-050型浮力材料的钢制套筒约束试验研究,验证了该试验测试方法的有效性及合理性。最后利用ABAQUS软件对浮力材料模型试验过程进行仿真,分析不同钢筒壁厚对试验的影响规律。[结果]研究结果表明,该试验测试方法可被用于准确测量低模高弹体材料的泊松比值,适用于低模量、高弹特性材料的力学性能研究。[结论]研究工作可为相关试验测试提供参考。

高轴压比PVA纤维超高强混凝土短柱延性的试验研究

试验旨在研究在较高轴压比条件下,高弹模PVA纤维对超高强混凝土短柱抗震延性的改善作用。制作剪跨比为2.0的短柱试件,强度为103.6～112.1MPa,PVA纤维的体积含纤率分别为0.17%、0.33%、0.5%。采用简支梁加载图式进行低周反复荷载试验。观测试件在荷载作用下的开裂和破坏的发展过程,研究不同PVA纤维含量短柱的破坏形态、滞回特性,得到短柱的开裂荷载和峰值荷载。试验结果表明:未掺PVA纤维的试件,在高轴压作用下,发生脆性特征明显的剪切破坏,延性很差。随着PVA纤维含量的增加,试件的破坏形态向具有一定延性特征的弯剪破坏转变,并且开裂荷载和峰值荷载得到大大提高,提高的幅度分别为12.8%～31.1%、13.2%～29.9%;同时抗震延性得到大大改善,位移延性和极限弹塑性位移角分别增加了19.5%～33.6%、42.3%～53.8%。最后给出满足一定位移延性和极限弹塑性位移角的抗震设计要求的最小PVA纤维体积含纤率的建议值。

超高性能混凝土制备关键技术及其工程应用实践

超高性能混凝土具备超高强、超高韧和超高耐久性等显著特性,可大幅促进土木工程的轻量化、高层化、大跨化和高耐久化,具有广阔的应用前景。然而,大规模应用超高性能混凝土过程中仍面临着原材料取材苛刻、施工粘度大、自收缩大等技术瓶颈。简要介绍了超高性能混凝土超高强、低粘度、低收缩、高韧性和高弹模的制备关键技术,及其应用于预制桥面板和板梁湿接缝的工程实践。

Numerical Analysis for High⁃Throughput Elastic Modulus Measurement of Substrate⁃Supported Thin Films

Micro/nano-thin films are widely used in the fields of micro/nano-electromechanical system(MEMS/NEMS)and flexible electronics,and their mechanical properties have an important impact on the stability and reliability of components.However,accurate characterization of the mechanical properties of thin films still faces challenges due to the complexity of film-substrate structure,and the characterization efficiency of traditional techniques is insufficient.In this paper,a high-throughput determination method of the elastic modulus of thin films is proposed based on the strain variance method,the feasibility of which is analyzed by the finite element method(FEM),and the specific tensile configuration with array-distributed thin films is designed and optimized.Based on the strain difference between the film-substrate region and the uncoated region,the elastic modulus of multiple films is obtained simultaneously,and the influences of film width,spacing,thickness,and distribution on the measurement of elastic modulus are elucidated.The results show that the change in film width has a more obvious effect on the elastic modulus determination than film spacing and thickness,i.e.,the larger the film width is,the closer the calculation results are to the theoretical value,and the change in calculation results tends to be stabilized when the film width increases to a certain length.Specifically,the simultaneous measurement of the elastic modulus of eight metal films on a polyimide(PI)substrate with a length of 110 mm and a width of 30 mm can be realized,and the testing throughput can be further increased with the extension of the substrate length.This study provides an efficient and low-cost method for measuring the elastic modulus of thin films,which is expected to accelerate the development of new thin film materials.

碳纤维复合材料在水库溢流坝闸墩补强加固中的应用

在阐述碳纤维复合材料(CFRP)的主要力学性能及其作用的基础上,结合某水库溢流坝坝顶闸墩应用碳纤维复合材料进行裂缝补强加固的工程实践,得出了碳纤维复合材料在修复加固水工混凝土结构方面具有高强、高效、施工简便、质量保证、防水、防腐效果好及适用面广等优点,表明用碳纤维复合材料对水工结构进行补强加固是十分有效的,并将在该领域中发挥重要的作用。

Properties of failure mode and thermal damage for limestone at high temperature

The mechanical properties of limestone such as the stress-strain curve, the variable characteristics of peak strength and the modulus of elasticity of limestone were studied under the action of temperatures ranging from room temperature to 800 °C.Our results show that:1) the temperature has not clear effect on the mechanical properties of limestone from room temperature to 600 °C.However, the mechanical properties of limestone deteriorate rapidly when the temperature is above 600 °C.In this case, the peak stress and modulus of elasticity decrease rapidly.When the temperature reaches 800 °C, the entire process, showing the stress-strain curve is displayed indicating an obvious state of plastic-deformation;2) the failure mode of limestone shows the breakdown of tensile strength from room temperature to 600 °C, as well as the compress shearing damage over 600 °C;3) combining our test results with the concept of thermal damage, a thermal damage equation was derived.

High Energy ^-pp and pp Elastic Scatterings in QCD Inspired Model

We propose QCD inspired model to calculate ^-pp and pp elastic scatterings at high energies in this paper. A calculation for total cross section of ^-pp and pp is performed in which the contributions from gluon-gluon, quark-quark, and gluon-quark interactions are included. Our results show that the QCD inspired model gives a perfect fit to experimental data of total cross section both for ^-pp and pp elastic scatterings at the whole energy region where experimental data existed at FNAL and CERN.

Experimental study on biaxial mechanical behavior of concrete suffered high temperature and constitutive model

Biaxial compression tests on plain concrete suffered high temperature ranging from 200 ℃ to 600 ℃ were carried out using the large-scale dynamic-static tri-axial concrete test system at the State Key Laboratory of Coastal and Offshore Engineering with designated stress ratios of 0, 0.25, 0.5, 0.75 and 1, respectively. The measured strength and strain were reported and the changes in both biaxial compressive failure envelopes and strains at peak stresses were analyzed. The regressive equation of initial elastic modulus in the biggest principal compressive stress direction was derived from test results. With the published results from previous biaxial tension-compression experiments, a three-parameter failure criterion has been proposed. A biaxial nonlinear elastic incremental constitutive model was developed for the compressive stress directions by using the equivalent uniaxial strain values deduced from test results. Analytical results obtained from the proposed biaxial constitutive model achieve good agreement with the experimental results.

重庆江北商圈道路(下穿车行道)工程设计特点

江北商圈道路下穿道工程是重庆市江北区的主要交通枢纽,解决通向渝中区和江北国际机场的交通要道。主要采用477m"单层双跨刚架"顶板高弹薄壁管内模钢筋混凝土结构.重点介绍该工程的主要设计构造以及设计特点.

Higher mode effects in hinged wall with BRBsin base-frame structures using distributed parameter models

To investigate the effect of higher modes on the displacement and inner forces in HWBB(hinged wall with buckling-restrained braces in base)-frame structure,distributed parameter models for both the HWBB-hinged frame structure and the HWBB-MRF(moment resisting frame)structure are built.The hinged wall is simplified as a flexural beam.BRBs(bucking-restrained braces)are simplified to a rotational spring.MRF is simplified to a shear beam.Vibration equations of distributed parameter models are derived.Natural periods,natural modes of vibration,inner forces and displacements of the distributed parameter models are derived based on the vibration equations using numerical methods.The effect of the relative stiffness ratio and the rotational stiffness ratio on the higher mode effects is investigated.For elastic structures,the global displacement and shear in MRF are predominantly controlled by the first mode,while the shear and bending moment in the wall are significantly affected by higher mode effects.The effect of the yielding of BRB on the inner forces distribution in the HWBB-hinged frame is investigated.The results indicate that the first mode will no longer contribute to the inner forces and the contribution from higher modes to inner forces increases after the BRBs yield.Displacement is not sensitive to higher mode effects and it is controlled by the first mode after the BRBs yield.Parameter analysis demonstrates that the displacement amplitudes are reduced with the increase in the flexural stiffness of the wall before the flexural stiffness reaches a certain value.The first three periods decrease with the increase in the rotational stiffness.With the increase in the rotational stiffness ratio,the contribution from the first mode decreases while contributions from both the second mode and third mode increase.

Grain size effect on cyclic deformation behavior and springback prediction of Ni-based superalloy foil

In order to clarify the influence of grain size on cyclic deformation response of superalloy sheets and springback behavior,cyclic loading-unloading and shearing tests were performed on the superalloy foils with 0.2 mm in thickness and diverse grain sizes.The results show that,the decline ratio of elastic modulus is weakened with increasing grain size,and the Bauschinger effect becomes evident with decreasing grain size.Meanwhile,U-bending test results determine that the springback is diminished with increasing grain size.The Chaboche,Anisotropic Nonlinear Kinematic(ANK)and Yoshida-Uemori(Y-U)models were utilized to fit the shear stress-strain curves of specimens.It is found that Y-U model is sufficient of predicting the springback.However,the prediction accuracy is degraded with increasing grain size.

Effects of strain rates on mechanical properties of limestone under high temperature

The experimental tests for limestone specimens at 700 °C in uniaxial compression were carried out to inves- tigate the mechanical effects of loading rates on limestone by using a MTS810 rock mechanics servo- controlled testing system considering the loading rate as a variable. The mechanical properties of limestone such as the stress-strain curve, variable characteristics of peak strength and the modulus of elasticity of limestone were studied under the strain rates ranging from 1.1 10à5 to 1.1 10à1 sà1. (1) Sharp decreases were shown for the peak strength and elastic modulus of limestone from 1.1 10à5 to 1.1 10à4 sà1 at 700 °C as well as a downward trend was shown from 1.1 10à4 to 1.1 10à1 sà1 with the rise of the strain rate. (2) The peak strain increased from 1.1 10à5 to 1.1 10à4 sà1, however, there was no obvious changes shown for the peak strain of limestone from 1.1 10à4 to 1.1 10à1 sà1. These results can provide valuable references for the rock blasting effect and design of mine.

Higher Order Multipole Potentials and Electrostatic Screening Effects on Cohesive Energy and Bulk Modulus of Metallic Nanoparticles

Higher order rnultipole potentials and electrostatic screening effects are introduced to incorporate the dan gling bonds on the surface of a metallic nanopaticle and to modify the coulornb like potential energy terms, respectively. The total interaction energy function for any rnetallic nanoparticle is represented in terms of two- and three-body potentials. The two-body part is described by dipole-dipole interaction potential, and in the three-body part, triple-dipole （DDD） and dipole-dipole-quadrupole （DDQ） terrns are included. The size-dependent cohesive energy and bulk modulus are observed to decrease with decreasing sizes, a result which is in good agreement with the experimental values of Mo and W nanoparticles.

High Energy Proton-Proton Elastic Scattering in Reggeon-Pomeron Exchange Model

We initially propose a Reggeon-Pomeron exchange model to describe proton-proton elastic scattering at high energies in this short paper. A calculation for total cross section of proton-proton elastic scattering at high energies is performed without any free parameters. Our new finding from this work is that the Reggeon-Pomeron model gives a perfect fit to experimental data of the total cross section at the whole energy region where experimental data exist.

Resilient Modulus of Hydraulically Bound Road Base Materials with High Volume Waste Dust

The paper presents laboratory test results on hydraulically bound road base materials containing high volume of steel slag and blast furnace slag waste dusts compared with control mixtures. These mixtures contain higher levels of （4mm-0.0 mm） dust, than would be the case in standard un bound road base mixtures. The combined influence of the steel slag and granulated blast furnace slag wastes content is to enhance the stiffness of the road base materials and save materials and cost during road construction. Triaxial repeated load tests were performed on the unbound and lightly bound materials to measure their resilient modulus. The test results show important improvements in the bond strength between the contents of road base materials. This offers the prospect of using these materials in road base materials to reduce the use of primary aggregates and thus minimize the cost of roads and highways construction.

Freezing and Thawing Durability of Ultra High Strength Concrete

Resistance to freezing and thawing of two UHSC （ultra high strength concrete） mixtures was evaluated in accordance with ASTM C 666 Procedure A. The two mixtures （plain and fiber reinforced） were developed using materials local to southern New Mexico, USA. Three different curing regimens were investigated for the mixture with fibers and one curing regimen was studied for the mixture without fibers. All curing regimens included 24 h of ambient curing followed by four days of wet curing at 50 ℃, and then two days dry curing at 200 ℃. At an age of seven days, one batch of fiber reinforced specimens was air cured at ambient conditions for the following six days and then placed in a water bath at 4.4 ℃ for 24 h prior to initiating freezing and thawing cycles. The second batch was air cured from day seven to day 12, and then wet cured for one day at 23 ℃ prior to being placed in the 4.4 ℃ water bath. The final batch was wet cured at 23 ℃ from the seventh day to an age of 13 days and then placed in the 4.4 ℃ water bath. The mixture with no fibers was air cured from the seventh day to an age of 12 days and then wet cured for one day at 23 ℃ prior to being placed in the 4.4 ℃ water bath. Higher moisture levels during curing produced greater initial dynamic elastic modulus values and durability factors at the end of the freezing and thawing tests, with the greatest durability factor being 87.5. Steel fibers were observed to improve both compressive strength and durability factor for UHSC.

Cratering process and morphological features of the Xiuyan impact crater in Northeast China

By using crater impact morphological theory and mathematics modeling,the paper studies the cratering process and morphological features of the Xiuyan Crater in Northeast China based on remote sensing imagery,digital elevation model(DEM)and drilling and measuring data.The results show that:1)Simulated calculation indicates the diameter of the transient crater was1406±12 m and the depth was 497±4 m.The diameter of the final crater was 1758±15 m and the depth was 374.5±3.5 m;the thickness of the breccia lens was 188.5±0.5 m.The data is basically the same as previous drilling data.2)Preliminary determination of the size of Xiuyan impactor:The diameter at about 55 m for an iron meteorite,and about 115 m for a stony meteorite.3)The depth-to-diameter ratio is 0.143,similar to the typical simple crater.The circularity index of the Xiuyan Crater is0.884,indicating erosion and degradation.4)The distribution pattern of radial fractures has priority in NW-SE and WNW-ESE and these fractures control the development and evolution of drainage inside the crater.

Viscoelastic plastic continuous physical model of a magnetorheological damper applied in the high speed train

In the preliminary design stage of high-speed train smart suspension,a simple,yet accurate magnetorheological(MR)damper model whose parameters have clear physical meaning is needed.Based on the working mechanism analysis and the dynamic behavior study of the MR damper,a new consecutive viscoelastic plastics(VEP)model is proposed.A methodology to find the parameters of the proposed model directly has been proposed.The comparison with experimental results indicates that the proposed model could adequately characterize the intrinsic nonlinear behavior of the MR damper,including the hysteretic behavior,roll-off phenomenon,and the variation of the hysteresis width in terms of the frequency and magnitude of excitation.The results of experimental testing prove that the accuracy of the proposed model is higher than that of the phenomenological model while only containing four undetermined parameters with clear physical meaning.Moreover,based on the proposed VEP model,a nonlinear stiffness VEP(nkVEP)model is developed with higher precision in the hysteretic region.The nkVEP model,which can reproduce the behavior of the damper with fluctuating input current,is developed.The proposed model could predict accurately the response of the MR damper in a wide range of frequency and displacement.