查看更多>>摘要：The fused region and the taper region of the optieal fibre coupler were tested by atomic force microscopy (AFM) and scanning electron microscopy (SEM), respectively. The results indicated that the surface roughness increased after fused biconical taper (FBT), that is, the fused region possessed the highest toughness (about 70nm), the taper region is in a second position (about 40nm), and the bare fibre was relatively the lowest (about 10nm). Micro crystals were observed at the fused region and the amount of the micro crystals decreased with increasing the drawing speed. Micro cracks were observed at the taper region and the micro cracks became wide and deep with increasing the drawing speed. All these changes affected not only the optical performance such as excess loss and consistence, but also the reliability and stability. Therefore a fibre device with high quality required small drawbacks.
查看更多>>摘要：In order to investigate the crack pattern and ductility of steel reinforced ultra high strength concrete composite joint subjected to reversal cycle load, six interior strong-column-weak-beam joint specimens were tested with various axial load ratio and volumetric stirrup ratio. A discussion on the crack pattern and ductility was presented. It was found that all joint specimens failed in bending with a beam plastic hinge in a ductile manner, with crack propagation different from the weak-column-strong-beam joint. The experimental results indicated that test parameters of the steel reinforced ultra high strength concrete composite joint with good seismic performance may be referred for engineering application.
查看更多>>摘要：The waterproof-adhesive layer plays an important role in cement concrete bridge pavement. The adhesive strength of the layer between the cement concrete deck and the asphalt pavement may affect the bridge's service performance directly. In the study, the direct shearing-strength experiment between the asphalt pavement, waterproof adhesive layer and the cement concrete deck was done in a laboratory. Some testing parameters were considered, including different loading speed, surface processing mode of the cement concrete deck and adhesive materials. The result shows that the coarser the surface of the cement concrete deck is, the larger the shearing strength of the adhesive material is at the same temperature. The loading speed of the shearing test has important effect on the shearing strength. The rapid loading speed can cause high shearing strength. Especially, the experiment datum indicates that the relationship between the loading speed of the test and the shearing strength can be described using the power exponent. Ultimately, the study is aimed at providing bridge engineers with an efficient testing method that attempts to increase the prediction accuracy of adhesive strength for more reliable design.
查看更多>>摘要：This paper presents a numerical simulation of the Laser Shock Peening process (LSP) using finite element method. The majority of the controlling parameters of the process have been taken into account. The laser loading has been characterised by using a repetitive time Gaussian increment pressure applied uniformly at circular impacted zone. The behavior of the subjected material is supposed to be elasto-visco-plastic coupled with damage using the Johnson Cook law with his shear failure model. The proposed model leads to obtain the surface inducing modifications, which are classified in this work into three categories: (ⅰ) the in-depth residual stress profile, ( ⅱ) the induced plastic strains profile and ( ⅲ) also the superficial damage which can be induced in few cases where the operating conditions are not well chosen. An application on a laser shock peened super alloy Ti-6Al-4V has been carried out. The comparison of the residual stresses, obtained by X-ray diffraction method and by finite element calculation, shows a good correlation.
查看更多>>摘要：Based on Jezek method of computing the elastic-plastic buckling of the member under the axial compressive load and the bending moment, the analytical expressions of calculating the ultimate load of buckling about the neutral axis with the maximum moment of inertia for an H-shaped column are derived. By degenerated into the analytical expressions of the rectangular column and compared with the values of the finite element analysis (FEA) method, it shows that the analytical method in this paper is valid, which provides a new method of theoretical study for the elastic-plastic buckling of the member.
查看更多>>摘要：Non-plane joints, such as T-joints, L-joints and π shaped joint can bring enormous potential benefits from the reduction of the fastener and the part count, which lead to the dramatic decrease of assemble cost and primary structural weight in composite structures. To understand the mechanistic character of the π joint, a 3-D finite element analysis model is established by means of software ABAQUS. The stresses on ply level and the predictions on the damage onset of 3-D woven composite π joint under tensile load are obtained. Numerical results agree well with empirical data. The effects of structural geometry parameters, such as support length, support thickness and radius of the comer, are also discussed. Results illustrated that increasing the thickness of L preform or filler radius can improve the strength of woven composite π joint effectively.
查看更多>>摘要：The magnetic field of ferromagnetic components under service load and geomagnetic field increases is induced by the residual magnetic induction and spontaneous magnetization. The stress concentration positions can be determination by detecting the magnetic field and the fracture can be avoided. The magnetic intensities of the demagnetized samples are tested by metal magnetic memory test method. By tensile test, the relationship between the magnetic memory signals and tensile load is studied, and the metal magnetic memory characteristics of the demagnetized samples under condition that the load keeps a fixed value are obtained. The test result indicates that the magnetic intensities of the samples change greatly after demagnetized; the change of the magnetic intensity of each test point are much different with different tensile displacement; in the later period of hardening phase and necking phase, the magnetic intensity about the side of the stress concentration positions increases along with the increasing of tensile displacement, however that of the other side decreases, that is the gradient of Fracture position increases obviously. Basing on this result by testing the parts of components emphatically where the fatigue failure and breakdown appear easily, the abrupt accident can be avoided.
查看更多>>摘要：Dynamic anti-plane characteristic is investigated theoretically on two dissimilar piezoelectric media with an interfacial crack subjected to time-harmonic incident anti-plane shearing in this paper. The formulations are based on the method of complex variable and Green's function. Dynamic stress intensity factors at the crack's tip are obtained by solving boundary value problems with the methods of conjunction and crack-division technique. The calculating results are plotted to show how the frequencies of incident wave, all kinds physical parameters of two dissimilar piezoelectric materials, applied electric loads and the dimension of the interfacial crack influence upon the dynamic stress intensity factor (DSIF). And some of the calculating results are compared with other published documents.
查看更多>>摘要：Crack propagation tests are conducted on TA15 titanium alloy in three stress levels to investigate the stochastic characteristics of FCG. A random variable probability FCG model, base on the Paris' law, is used to characterize the stochastic performance. Distribution significance test has been done, which shows that the random variable X can be considered reasonably to follow log-normal distribution in all the three stress levels. The probability distribution of crack size at any-specified loading cycle and the probability distribution of the random fatigue life at which a given crack size is reached are discussed. Variance analysis indicates that the standard deviations of the log fatigue crack growth rate (FCGR) under the three stress levels do not differ from each other significantly. The scatter of crack initiation life under the lowest stress level is the largest, however, the scatter for crack propagation life shows no significant difference in the three stress levels.
查看更多>>摘要：Studies about the effect of stress characteristics on multi-axial high-cycle fatigue of metals are still insufficient. Up to now, little work about the effect of different ratio of stress amplitude has been done on multi-axial fatigue under the same equivalent stress. In this paper, the effect of ratio of stress amplitude, λ = τ_o/ σ_o under the same Von-Mises equivalent stress is studied from theory and experiment. The results show that the main factor of multi-axial high-cycle fatigue failure is the maximum principal stress. For proportional loading, fatigue life raises when ratio of stress amplitude increase. The variety of fatigue life is not obvious when λ is larger than a certain value and its value closes to that of pure torsion. For non-proportional loading, when ratio of stress amplitude increases, fatigue life raise at first, then has an inflection point. The value of λ at the inflection point changes with phase difference and its value is 0.5 while phase angle is 90°. Fatigue life of uniaxial tension was lower than that of pure torsion.
NETL
NSTL