摘要: In order to reveal the failure properties of AFRP sheet-reinforced beams under 4-point bending, a 3-D finite element model of RC beam, including rebar, interface and sheet elements, was established by using MIDAS FEA finite element software. The stress and displacement of each of components in beam were solved by cycling calculations. In terms of Code for Design of Concrete Structures, the initial cracking loads of RC beams strengthened with prestressed and non-prestressed AFRP were further obtained, which are relatively conformed to the existing experiment. The results show that, compared with the beams strengthened with prestressed and non-prestressed AFRP, the initial cracking load of the former has considerable increase.
摘要: Structure information of barium hexaferrite is very important in designing higher efficient synthetic methods and in tailoring the magnetic properties of barium hexaferrite by doping. The structure information of M-type barium hexaferrite has helped to find new efficient routes of hydrothermal and co-precipitation methods in synthesizing barium hexaferrites and in altering their magnetic properties by doping.
摘要: Owing to its high mechanical strength, chemical inertness, low frictional coefficient, high wear and corrosion resistance properties and so on, carbon nanotubes (CNTs) films have emerged as a potential material for biomedical applications. In order to investigate the blood compatibility properties of CNTs films synthesized on the silicon (Si) substrate using thermal chemical vapor deposition, the blood compatibility was evaluated in vitro by the platelet adhesion and the activated partial thromboplastin time (APTT). The experimental results demonstrated that the Si-CNTs films reduced thrombus formation by minimizing the platelet adhesion, activation , aggregation and had a tendency to retard the intrinsic coagulation activities of blood due to a higher APTT compared to Si, lower temperature isotropic pyrolytic carbon (LTIC) and Polydimethylsiloxane (PDMS) materials. Further, we found that hydrophobic surfaces are more prone to direct cellular motility in comparison with hydrophilic surfaces. It is concluded that CNTs films on the Si substrate were effective for improvement of blood compatibility.
摘要: Springback during unloading affects the dimensional accuracy of sheet metal parts. This paper proposes a finite element model to predict springback with contact evolution between the sheet and dies. The underlying formulation is based on updated Lagrangian elastoplastic materials model. The solutions validated with experimental data of NUMISHEET’93 show more accurately. The effects of the variable blank holding force (VBHF) on springback results are investigated based on genetic algorithms (GAs) for the determination of the parameters in blank holding operations. It has been found that the GAs based optimization technique is very effective in solving this kind of problem. The difficulty of choosing correct starting values for the constants in the traditional optimization techniques has been completely overcome and the GAs technique provides a better chance to converge to the global minimum.
摘要: The numerical simulation by nonlinear finite element method(FEM) was adopted to analyze the behavior and the influences of the volume fraction of steel fibers and the strength of steel fiber reinforced concrete on the load capacity and the deformation performance of reinforced concrete shearwalls.The effect of steel fiber on the FEM was determined. The results show that with the increase of the volume fraction of steel fibers, the crack load, bearing capacity and ductility coefficient of steel fiber reinforced concrete shearwalls increase gradually. With the increase of the strength of steel fiber reinforced concrete, the bearing capacity and ductility coefficients of steel fiber reinforced concrete shearwalls decrease.
摘要: With the development of oil exploration and electronics technology, the automation control technologies of hydraulic disc brake system (HDBS) have become more and more widely used. After analysis the braking performance of HDBS, The optimizing schemes for hydraulic disc brake, such as PWM high speed on/off valve and pressure switch are used in the constant weight auto-drilling system. It has been tested successfully both on the integrated braking facility in lab and in the oil field. And it proved that the PWM valve have great prospects on the braking system.
摘要: Based on the property that micro-cells strength is consistent with lognormal distribution function, this paper presented a new statistical damage softening constitutive model simulating the full process of strain softening for rock. Through discussing the characteristics of random distributions for rock micro-cells strength, lognormal distribution assumption is tested by Kolmogorov-Smirnov test in statistics, and the reasonable method of geometry boundary condition is selected to determine model parameters that can be easily applied to the situations under different complex conditions. Gabbro experiment comparative analyses show that the new damage softening constitutive model is rational and convenient in engineering.
摘要: Thin plates and small thin-walled tubes of zircaloys are used as fuel cladding materials of nuclear reactors. In order to prevent buckling of plate or tube specimens of zircaloys under cyclic strain loading, a set of self-invented clamps were used for strain fatigue tests of small thin-walled tubes of Zr-4 and Zr-1Nb at elevated temperature. Depending on axial control strain, a new strain fatigue test method named as (equivalent strain)-SF(strain fatigue) was developed for thin funnel-like plate specimens of N18 zircaloy with double side notches. A series of monotonic tension tests for the three kinds of zircaloys at different temperatures and strain fatigue tests for Zr-4 and Zr-1Nb at 375°Cand for N18 at 20°C,300°Cand 500°C were carried out. Monotonic and cyclic constitutive relations and Manson-Coffin life-estimating expressions for these zircaloys are given. ES-SF method has no Poisson effect and has better accuracy to predict strain fatigue behavior.
摘要: Based on low cycle fatigue critical damage, a numerical procedure for predicting stable fatigue crack propagation behavior of materials and structures was developed, which was named as LFF (LCF: Low Cycle Fatigue + FCP: Fatigue Crack Propagation + FEA: Finite Element Analysis) in this work. In the LFF method, stress and strain amplitude of nodes located at the plastic zone in the crack growing direction and fatigue damage of these nodes were firstly computed from a finite element code ANSYS. Then, by assuming a discontinuous step of propagation in the process of fatigue crack propagation, the stable fatigue crack propagation behavior of materials and structures could be estimated. Experiments on low cycle fatigue and fatigue crack propagation for Cr2Ni2MoV, TA12 and TC4 alloys were employed to certificate the applicability and validity of the LFF method. The results show that the LFF method is suitable for the estimation of stable fatigue crack propagation of a CT specimen with a straight crack under mode Ⅰloading and with a slant crack under mixed mode Ⅰ and Ⅱ loading.