Assessment of fiber distribution in steel fiber mortar using image analysis

A new test method was introduced to measure fiber distribution in steel fiber reinforced mortar by using image analysis technique. Through specimen preparation, image acquisition, fiber extraction, and measurement of related fiber parameters, quantitative analysis of fiber distribution could be obtained by two parameters, namely dispersion coefficient and orientation factor. Effect of boundaries, size and steel fiber content on fiber distribution was discussed. Results showed that, steel fiber distribution was affected by boundary effect, which would be weakened with the increase of specimen size. If the length and width remained constant, the specimen height had a significant effect on orientation factor of fiber, while its influence on dispersion coefficient was not so obvious. With the increase of steel fiber content, dispersion coefficient decreased slightly, and orientation factor deviated from 0.5.     

Effect of C/Mo Duplex-coating on Thermal Residual Stresses in SiC_f/Ti_2AlNb Composites

Three-dimensional finite element physical models considering the layered distribution of materials at the interface were developed to study the effect of the coating system on distributions of thermal residual stresses in SiC_f/Ti₂AlNb composites.Two coating systems were comparatively studied,namely C coating and C/Mo duplex-coating.The thermal residual stresses after 1 080 ℃/1 h solution treatment and 800 ℃/20 h ageing treatment in the composites were also analyzed.The expe...     

Bond-slip constitutive relationship between bars and mortar for block masonry

Ten specimens were tested in this paper in order to study the bond behavior and the process of force transfer when bars adhered to mortar. The development of the bond stress between bars and mortar was calculated. Test results show that the maximum bond-stress is not influenced by the bar bond length and increases as the increased splitting strength of mortar for block. The local bond stress-slip curve was obtained. Then,based on the regressive analysis of test data,two bond shearing stress-slip constitutive models between bars and mortar were proposed. The models can be used in the numerical simulation or finite element analysis and provide references for the improvement of the corresponding design codes.     

Modeling and finite element analysis of rod and wire steel rolling process

Two thermomechanical coupled elastic-plastic finite element （FE） models were developed for predicting the 12-pass continuous rolling process of GCrl 5 rod and wire steel. The distances between stands in the proposed models were set according to the actual values, and the billets were shortened in the models to reduce the calculation time. To keep the continuity of simulation, a technique was developed to transfer temperature data between the meshes of different models in terms of nodal parameters by interpolation functions. The different process variables related to the rolling process, such as temperature, total equivalent plastic strain, equivalent plastic strain rate, and contact friction force, were analyzed. Also, the proposed models were applied to analyze the reason for the occurrence of an excessive spread in width. Meanwhile, it was also utilized to assess the influence of the roll diameter change on the simulated results such as temperature and rolling force. The simulated results of temperature are found to agree well with the measured results.     

Comparison of closure measurements with finite element model results in an underground coal mine in central Utah

Quantitative analysis of mine-wide subsidence at the kilometer scale and details of stress distribution about an advancing longwall face are estimated using an adaptation of the finite element method. The method is well suited to the tasks at hand. For greater realism, variability of strata properties is taken into account as are the effects of joints and cleats on elastic moduli and strengths. Evolution of pillar stress and entry closure remote from the face is readily quantified in a series of analyses that simulate face advance. Computed results compare favorably with the evolution of closure measurements about an instrumented pillar in a two-entry headgate. The appropriateness of the finite element method is confirmed. This method is based on first principles that avoid empirical schemes of uncertain applicability and numerical models ‘‘calibrated" by fitting computer output to mine measurements.     

Numerical simulation of Liquid Steel Solidification in Slab Molds

A mathematical model was proposed to calculate the stress distribution of the solidification shell in a slab mold based on the local heat flux calculated by using the measured temperature of the copper plate. Solidification equations to liquid steel were built and discreted by the finite element method. ANSYS commercial software was used to solve these discrete equations, the stress and strain distributions were obtained and the taper of the mold was decided according to these calculating results.     

Fracture behavior of epoxy asphalt pavement on steel bridges based on optical fiber sensing technology and numerical simulation

The distributed optical fiber sensing technology was used to investigate the fracture behavior of the Epoxy Asphalt Mixture. The spatial distribution and variation of the strain development with crack propagation were acquired using the brillouin optical time-domain reflectometer through the loading experiments of the composite beam structure. In addition, a finite element model of the composite beam structure was developed to analyze the mechanical responses of the epoxy asphalt mixture using the extended finite element method. The experimental results show that the development of crack propagation becomes instable with the increase of the load, and larger loads will generate deeper cracks. Moreover, the numerical results show that the mechanical response of the crack tip changes with the crack propagation, and the worst areas that subjected to crack damage are located on both sides of the composite beam structure.     

Numerical study on deformation and failure of reinforced sand

In order to investigate the deformation and failure of reinforced sand, and the reinforcing mechanism of flexible and rigid reinforcement, a set of plane strain compression tests of dense Toyoura reinforced sand with planar reinforcement of a wide range of stiffness were analysed by a nonlinear finite element method. The analysis was incorporated into an energy-based elasto-plastic constitutive model for sand to develop a stress path-independent workhardening parameter based on the modified plastic strain energy concept. Numerical results indicate that the global stress-strain relations of sand specimens are reinforced by using relatively flexible and rigid reinforcement, and an unreinforced sand specimen can be reasonably simulated by the current finite element method. It is also found that the reinforcing mechanism and progressive failure with a development of shear bands in reinforced sand can be reasonably examined by the finite element method.     

Oxidation behaviors of Ni-Cr-Al superalloy foams at 1 000 ℃ in air

The oxidation behaviors of Ni-16Cr-xAl （x=4.5%, 9.0%, mass fraction） superalloy foams in air at 1000℃ were investigated. The effects of AI content on the resistance to high temperature oxidation were examined. The oxidation mechanisms of the foams were discussed. The results show that the resistance to the oxidation of the Ni-16Cr-xA1 based alloy at 1 000 ℃ increases with the content of A1 increasing from 4.5% to 9.0%. Complex oxide products are formed on the surface of the superalloy foams after the oxidation. Cr203 and A1203 are the predominant oxides for the scales of the foams with 4.5% A1 and 9% A1, respectively. Excellent high temperature oxidation resistance and superior pore conformation stability for the Ni-16Cr-xA1 based superalloy foam with 9% A1 can be mainly attributed to the formation of relatively continuous and protective A1203 oxides on the surface of the foam.     

Long-term Behavior of Fiber Reinforced Concrete Exposed to Sulfate Solution Cycling in Drying-immersion

The damage process and corrosion ion distribution in concrete, which was exposed to 60 and 170 drying-immersion cycles of sulfate solution, were systematically investigated. The effects of plain concrete, plain concrete mixed with 4 and 8 kg/m~3 modified PP fiber and high-performance concrete(HPC) mixed with 0.8 kg/m~3 fine PP fiber on the damage process were also studied. The experimental results showed that thenarditeinduced surface scaling, as well as gypsum-and ettringite-induced cracks, were the main degradation forms of concrete under attack of sulfate solution and drying–immersion cycles. The relative dynamic modulus of elasticity of concrete initially increased, then reached stability and finally decreased to failure. The sulfate diffusion coefficients of plain and HPC were 10~(-12) and 10~(-13) m~2/s, respectively. The concentration of sodium ion increased with depth, then maintained stability and finally decreased rapidly with concrete depth. The content of calcium ion on the concrete surface was 110%-150% of that in the interior of specimens. Although fiber worsened the surface scaling of concrete, better resistance capacity of sulfate ion penetration into concrete was observed in plain concrete with 4 kg/m~3 modified PP fiber and HPC.     

Experimental Study on Young′s Modulus of Concrete

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Prediction of mechanical properties of 50CrVA tempered steel strip for horn diaphragm based on BPANN

50CrVA cold-rolled spring steel strip was used to fabricate the diaphragm of the automotive horn. The material parameters which were taken into account in the design of the diaphragm involve elongation, elastic limit, Young’s modulus, yield strength and tensile strength. The tempering process was carried out in order to enable the diaphragm to possess the excellent mechanical properties, such as high elastic limit, high fatigue strength and perfect stress relaxation resistance. As a nonlinear information processing system, the backpropagation artificial neural network (BPANN) was applied to predict and simulate the relationship between the mechanical properties of the diaphragm and the tempering process parameters. Experimental results show that a BPANN with 3-8-5 architecture is capable of predicting the relationship between the mechanical properties of the diaphragm and the tempering temperature successfully and lays the profound foundations for optimizing the design of the diaphragm. BPANN simulation results show that the tempering temperature ranging from 380 to 420 °C contributes to enhancing the comprehensive mechanical properties of the diaphragm including high Young’s modulus, high elastic limit and high fatigue strength.     

Size determination of ultramicropores and small mesopores using a calculation procedure based on the tangents of comparison plot

Pore size distribution (PSD) curves of synthesized hollow silica spheres with ultrmicropores and small mesopores were obtained from calculations based on the BJH, KJS, SF, MP, NLDFT models and Prof. Zhu’s method. Comparisons indicate that Zhu’s method not only gives reasonable small mesopore size but also could be further extended to the ultramicropores region for the PSD evaluation.     

纤维对水泥土加固效果影响的试验研究

将短切玄武岩纤维和水泥掺入取自长春地区的黄土中,进行无侧限抗压强度试验.主要研究纤维掺量、纤维长度对纤维水泥土无侧限抗压强度特性的影响.试验结果表明:同一纤维质量掺入比下,随着纤维长度的增加,纤维水泥土抗压强度大体呈上凸型曲线形式,曲线最终趋于无纤维掺入的水泥土强度,说明纤维分布均匀性和纤维分布密度对强度影响较大;同一...     

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)     

重型龙门数控机床-基础系统承载变形

为了研究重型龙门数控机床混凝土基础对整机刚度的影响规律,首先提出一种可计算空间网状布筋的加筋复合基础本构模型,应用该模型建立了横观各向同性的混凝土基础边界元方程,采用有限元法建立了整机结构模型,从而建立了上下结构有限元-边界元耦合系统模型.然后,通过实例,采用光纤光栅实验法获取各部件布点处应变值,对布点处曲率二次积分确定部件的变形曲线,同时进行了承载作用下的变形仿真分析,验证了理论模型的正确性.最后,基于上述力学模型,分析了布筋情况对系统承载变形的影响,给出了基础建设的一些建议.     

Influences of polypropylene fiber and SBR polymer latex on abrasion resistance of cement mortar

Influences of polypropylene (PP) fiber and styrene-butadiene rubber (SBR) polymer latex on the strength performance, abrasion resistance of cement mortar were studied. The experimental results show that the flexural strength, brittleness index (σ_F/σ_C) and abrasion resistance can be improved significantly by the addition of PP fiber and SBR polymer latex. The relationship between the flexural strength and abrasion resistance was analyzed, showing a good linear relationship between them. The reinforced mechanism of PP fiber and SBR polymer latex on cement mortar was analyzed by some microscopic tests. The test results show that the addition of SBR polymer latex has no significant influence on the cement hydration after 7 d curing. Adding SBR polymer latex into cement mortar can form a polymer transition layer in the interfaces of PP fiber and cement hydrates, which improves the bonding properties between the PP fiber and cement mortar matrix effectively.     

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.     

配筋率对连续板抗火性能的影响

采用理论分析与有限元分析相结合的方法,研究了钢筋混凝土连续板配筋率及负筋长度对楼板抗火性能、裂缝分布及破坏模式的影响.发现配筋率过大或过小都会降低结构的抗火性能,建议最佳取值为0.598%;负筋长度对裂缝分布规律、楼板的破坏形态、变形以及破坏铰的位置有很大的影响,负筋的长度为板计算跨长的1/3时,楼板的抗火性能最佳.     

Bending characteristic of a cantilevered magnetostrictive film-substrate system

The bending problem of a film-substrate cantilever with arbitrary film-to-substrate thickness ratio is solved exactly by employing the force equilibrium equation, and then the optimization and application of the bending characteristic of the magne-tostrictive cantilever is discussed. Furthermore, the influence of geometrical and physical parameters of the two cantilever components on the maximum free-end deflection of the cantilever is addressed. The results indicate that as the substrate thickness is kept constant, the greater film-to-substrate stiffness ratio will induce a larger deflection, while for the case of fixed total cantilever thickness, the optimal cantilever deflection is independent of the physical parameters of the materials such as Young’s modulus and Poisson’s ratio.