查看更多>>摘要：Single sensor scanning (hereafter SSS) used to inspect cracks on paramagnetic materials can measure the distribution of the root mean squared value (RMS) of the magnetic field around crack tips quantitatively when sheet type current is induced on the specimen. The vertical direction magnetic field alternates to the surface of the crack tips because the sheet type induced current on the specimen is distorted by the existence of the crack in an SSS system. The RMS distribution of the magnetic field, which can be measured by using SSS, depends on the crack size and shape, so it can be used to evaluate a crack size quantitatively. An algorithm of quantitative nondestructive testing and evaluation of cracks of various shapes and sizes on the aluminum alloy, A17075 is proposed in this paper.
查看更多>>摘要：The defect initiation and crack propagation in wheel may result in the damage of the railway vehicle or derailment. Therefore, it is important to evaluate the characteristics of the wheel tread. In the present paper, the characteristics of wheel tread based on contact positions, running distance and brake pattern are evaluated. To evaluate the damage for railway wheels, the measurement for the replication of wheel surface is carried out. The result shows that the damaged wheel tread is remarkably depended on the contact positions between wheel and rail. It should be noted that the replication test can be applied in new evaluation method of wheel damage.
查看更多>>摘要：Ultra High Strength Steel-Fiber Reinforced Concrete (UHS-SFRC) is characterized by very high compressive and tensile strength that is about 8 times of ordinary concrete, and high ductility owing to the addition of steel fibers. This paper investigates the relationship existing among the direct tensile strength, flexural tensile strength and splitting tensile strength of UHS-SFRC. Differently from ordinary concrete, it is found that the first cracking strengths in UHS-SFRC obtained through direct tensile test and splitting tensile test are similar, while the strength obtained from flexural tensile test is significantly larger than those from other tests. Based on the experimental results, relationships between the direct tensile strength and flexural tensile strength, between the first cracking strengths in direct tensile test and in flexural tensile test, and between the first cracking strength in direct tensile test and the flexural tensile strength are proposed.
查看更多>>摘要：The behavior of plasticity induced fatigue crack closure (PICC) in middle tension specimen was analyzed by the elastic-plastic finite element method. For the constant-K (CK) loading cases, the opening stress intensity factor K_(op) are independent of crack length. The level of K_(op)increases with the maximal applied stress intensity factor K_(max) for given load ratio R and increases with R for fixed K_(max). The K_(op) in plane strain state is much smaller than that in planestress state. The results under CK loadings can be deduced to constant amplitude cyclic loading case during which the load ratio, maximal load level, crack length and specimen thickness are all the factors affecting the crack closure effect. The phenomena revealed in the analysis are beneficial in understanding the driving force mechanism of the fatigue crack growth.
查看更多>>摘要：This study investigated the stress-induced crack propagation and precipitation in Ti-51.45at.%Ni thin films. Tensile tests were carried out on CSS-44100 electron universal testing machine. The strain rate was 1.1×10~(-4) s~(-1). The surface micrographs of the NiTi thin film were obtained using scanning electron microscopy (SEM). The precipitates were determined by X-ray diffraction (XRD) experiments (D8 GADDS). The results showed that a series of parallel cracks grew in the film and the cracks were equally spaced. The fracture toughness of the film was estimated, K_(Ic)=0.96MPa·m~(1/2). The minimum crack spacing was about 87μm, The stress-strain curve can be divided into two stages. The first linear stage corresponded to the elastic deformation of the parent phase. In the following stage, the serrations were considered to be the stress relaxation due to the cracks propagating and the precipitate grain transformation. During tension the (102) peak intensity of Ni_sTi phase increased with elongation increased. The precipitate orientation was same.
查看更多>>摘要：This paper primarily presents the automation computational analysis techniques to determine the dynamic stress intensity factor for the stiffened damaged aircraft fuselage subjected to triangle blast load. 3-dimention panel models can be created using parameterization and the dynamic stress intensity factor can be obtained in the procedure of the blast automatically. A typical stiffened curved panel model which consists of 7 frames and 8 stringers is calculated. The calculation results show that the peak SIF value of the crack in the panel with strips under blast load is always smaller than that without strips for all longitudinal crack lengths; the strips can slow down the crack growth markedly and the effect of the strips on SIF is most obvious when the crack tips are close to the edge of strips; the blast load time has effect on the SIF peak value, and the effect is most significant when the load time is about 25 milliseconds for the panel with strips.
查看更多>>摘要：A mechanical model of the pressure-sensitive dilatant material is established in order to investigate the viscous effect in quasi-static growing crack-tip field. The constitutive equations on the pressure-sensitive dilatant material are deducted. Through asymptotic analysis, it is shown that in the stable creep growing stage, the elastic-deformation and the visco-deformation are equally dominant in the near-tip field, as r~(-1/(n-1)) . The asymptotic solutions of separative variable in the crack-tip field of plane stress mode II quasi-static are aslo obtained. According to numerical calculation, the curves of stress, strain and displacement in terms of various parameters are given. The asymptotic solutions of quasi-static growing crack-tip field gained here can conveniently degenerate the incompressible case, when the Poisson ratio v →0.5, named as HR field. The conclusions can provide the references for further studying the dynamic growing crack-tip field in the pressure-sensitive dilatant material.
查看更多>>摘要：Polycrystalline Cubic Boron Nitride (PCBN) is a superhard material which is used in machining of hardened steels and other abrasive and aerospace grade alloys. In these applications the tools are subjected to high operating temperatures, abrasive and impact loading. Impact loading can lead to the sudden fracture and hence failure of the tool. In this work the static and dynamic fracture toughness of PCBN is determined via a combined experimental-numerical approach. The results show that the fracture toughness of PCBN varies with loading rate.
Dan Mihai ConstantinescuMarin SanduEniko VolceanovMatei-Constantin Miron...
673-676页
查看更多>>摘要：Static loading and impact tests of ceramic alumina tiles have shown a very interesting behaviour of tough, brittle, and high energy absorbing materials. Strain gauges techniques and data acquisition were used in previous research for static and low velocity impact testing. A static-dynamic equivalence was done through a calibration procedure of the measuring system. The research is continued in this paper by using the digital image correlation method with the complete displacement and strain history acquired till the failure of the ceramic tiles of different compositions, proving the capacity of such materials to be used for particular purpose applications.
查看更多>>摘要：The influence of concrete meso-structure and coarse aggregate size on early age crack is studied. In this study, concrete is regarded as a three-phase material based on shrinkage property. The mortar matrix and interfacial transition zones undergo shrinkage and no spherical coarse aggregate particles are considered to restain the shrinkage by particle interaction. The results show that concrete meso-structure plays an important role in the safety of concrete, different aggregate distribution in concrete leads to different initial cracks and propagation due to shrinkage. With the increase of maximum aggregate size, the value of shrinkage deformation becomes unstable and varies in a wide range; relevant shrinkage cracking becomes easier too.
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