Performance of metal meshes as a function of incidence angle

An inductive mesh was measured for transmission as a function of frequency, incidence angle, and polarization. The experimental data agree well with Chen's waveguide theory for meshes as long as an adequate number of modes are included in the calculations. To simplify calculations of mesh transmission a lumped circuit model has been developed to fit Chen's theory. This model predicts transmission for the two major polarizations and a variety of angles to within 1%.     

Influence of the ion incidence angle of alumina surface cleanness,roughness and topography

Polycrystalline ceramic specimens of 96% sintered alumina and mechanically polished 99.5% alumina were bombarded by Ar^ü ions at an applied voltage of 7 kV at various incident angles from 0 to 1.4 rad (0 to 80°) and at a beam current of about 70 A. The influence of the incidence angle on alumina surface cleanness, roughness and topography was investigated.     

Fractography of unidirectional graphite-epoxy as a function of moisture,temperature and specimen quality

The tensile failure surfaces of (0°)₈ T300/5208 graphite-epoxy specimens were examined using both optical and scanning electron microscopy. Fractography was used to determine how moisture content and temperature as well as specimen preparation technique, prepreg batch and cure condition affected the failure mode. A distinctive low-energy failure morphology was found in defective specimens and also in those whose edges were poorly prepared. This morphology was predominant in failures at elevated temperature or moisture content for specimens which had been made from one suspect batch of prepreg. This finding combined with unusual end-tab failures from such specimens indicated that this batch was indeed defective, but that such defective batches could in the future be identified by tests under hot, wet conditions. For specimens made from good prepreg, temperature or moisture appeared to decrease flaw sensitivity and thus increase strength, even though moisture also seemed to increase interfacial debonding between filament and matrix. When combined, moisture and temperature appeared to degrade performance by increasing interfacial debonding and making the epoxy matrix more prone to fracture.     

Stages of surface erosion under ion irradiation

Initial stages of surface erosion have been studied for NaCl and LiF single crystals bombarded by Ar⁺ ions with 20 keV. For irradiation with doses D=10¹⁰-10¹¹ ions/cm², exoelectron emission has been used, whereas for higher doses, we have used electron microscopy. Two stages of initial surface erosion have been identified; for small doses, there is slow development of atomic-scale roughening, which reaches its peak when areas damaged by closest incident ions start to overlap, and then, beginning with D=10¹⁶ ions/cm², there is rapid etching, deep into the crystal, followed by the emergence of secondary microscopic structure, i.e. caverns, concentric closed steps and terraces. Ion-induced surface structure of alkali halide crystals has been shown to depend strongly on the presence of foreign particles on the surface, as well as on segregation. Topography of thin carbon films and some metals have been discussed.     

Development of a general surface contour by ion erosion. Theory and computer simulation

An analytical treatment of the development of a general contour under ion bombardment is proposed. The derived equations relate the properties of the eroded material through its yield variation upon the angle of incidence,S (θ). New specific angles (θs ₁ andθs ₂) are introduced which limit regions where the evolution process of the surface may be different. The theory allows prediction of the number of angular points which will appear in each region. A computer simulation program is used to describe the evolution of sine-type surfaces. With infinite time, such profiles in relief above a horizontal plane, tend towards the steady state which exists in a horizontal plane. The model is compared to one previously described.     

Effect of incidence angle on laser scanner intensity and surface data

We present a comprehensive experimental set of data on the dependence of the laser intensity on the angle of incidence to the target surface. The measurements have been performed in the laboratory for samples with a Nd:YAG laser and terrestrial laser scanner. The brightness scale data were also compared with data acquired by airborne laser scanning (ALS). The incidence angle effect is evident for all the targets. The effect is significant for incidence angles >20 degrees, and stronger for bright targets. However, effects due to some of the other surface properties, such as roughness, were also detected. We also found a set of gravel samples for which the incidence angle effect was minor even up to 40 degrees . The data provide an important reference for the interpretation and applications, e.g., full-waveform data processing of a laser scanner and ALS intensity calibration.     

Nano-structural characteristics of Ti/glass and Ti/Mo films as a function of deposition rate and angle of incidence

Titanium films of 90 nm thickness were deposited under UHV condition at different deposition rates, ranging from 0.3 to 10.2 Å s^− 1, at room temperature on glass and Mo substrates at two incidence angles of 8.5° and 45°. The samples were analyzed using XRD and AFM techniques. The grain sizes were obtained from AFM images, while the crystallite sizes and preferred orientation of the films were obtained from XRD profiles. Results show that Ti/glass films at 8.5° angle of incidence show (002) preferred orientation, while at 45° incidence angle, at lower deposition rates, films show an almost amorphous structure, which develops to a strong (002) preferred orientation for deposition rate of 1.6 Å s^− 1, and again at much higher deposition rate of 10.2 Å s^− 1 it changes to an amorphous structure. Ti/Mo films deposited at 45° incidence angle showed (101) preferred orientation.     

The measurement of specimen surface temperature in high-speed tension and torsion tests

A radiometric technique has been developed capable of measuring specimen surface temperatures as low as 25°C with a time resolution of ∼1 μs. The application of this technique to SHPB tests at strain rates of the order of 1000/s in both tension and torsion is described. In the torsion test results are obtained both during uniform deformation, using a single element radiometer, and during localised deformation and the onset of fracture, using a 12-element radiometer. In the tension test the same 12-element radiometer was used to obtain the surface temperature distribution along each half of the broken specimen immediately after fracture. The proportion of work converted to heat, β, has been calculated using the temperature data from torsion tests and was found to vary with increasing plastic strain from approximately 0.2 to approaching 0.7.     

基于屈服面的曲线梁桥地震动最不利输入方向

曲线梁桥由于线形、刚度及质量的不规则分布,需要研究其地震动最不利输入方向。Bresler屈服面给出了钢筋混凝土构件在轴压力与双向弯矩组合作用下的截面屈服条件,本文据此将地震中桥墩截面最易发生屈服的方向定义为最不利地震动输入方向。在应用反应谱法得到两个正交方向地震反应的基础上,提出了基于Bresler屈服面的地震动最不利输入方向的一种新算法,该法考虑了水平面内双向地震动共同作用及曲线梁桥振型间的相关性。进一步,给出基于时程分析法的地震动最不利输入方向确定算法。最后,以某闭合圆环匝道桥为对象,分析了各墩的地震动最不利输入方向,同时验证了方法的准确性。     

Estimation of high‐temperature fracture parameters for small punch specimen with a surface crack

An outline of a newly proposed methodology for evaluating creep crack growth (CCG) parameters using cracked small‐punch (SP) specimens is explained. Three‐dimensional finite element analyses were performed to calculate the stress intensity factor along the crack front for a surface crack formed at the centre of a SP specimen. Effects of crack ratio, (a/t); crack aspect ratio, (a/c); and thickness of the specimen, (t), on the fracture parameters were studied. It was observed that the minimum variation of K‐value along the crack front can be achieved when a/c was 0.50 except the location very near the intersection of the crack and free surface. This condition is similar to the case of constant K‐values along the crack front of the conventional compact tension specimen. Thus, it can be argued that the SP specimen with a surface crack is a suitable specimen geometry for CCG testing. The proposed CCG test method was found to be practically applicable for the crack geometry of 0.10 to 0.30 of a/t with constant aspect ratio of 0.50. An estimation of the K and C_t‐parameter under the small scale creep condition was derived. Future work for further development of the suggested CCG testing is discussed.     

Dynamic study of ion etching in a high resolution SEM

On-line studies of surface topographical development have been made by mounting a saddle-field ion source into a standard scanning electron microscope. Preliminary results obtained during operation in both dynamic and static modes are presented.     

Elastic constants of silver as a function of temperature

The temperature dependence of the elastic constants of silver single crystals has been determined over the range 300–1173 K with the piezoelectric ultrasonic composite oscillator technique (PUCOT). From a comparison of the present results with those available from the literature, it is deduced that the PUCOT and hence other standing-wave techniques are adequate for measuring compliances, but these techniques may have complications for computations of stiffnesses.     

Measurement of critical temperature as a function of field

The critical temperature has been measured for various magnet conductors as a function of the perpendicular applied magnetic field. The isothermal environment was provided by a variable temperature cryostat which fits into the bore of a 10 telsa solenoid. The temperature gradient across the sample volume was measured to be less than 25 millikelvins. The superconducting to normal state transition was measured resistively, using sample current densities from 0.01 to 2 A cm^?2. The maximum applied magnetic field was 10 T and varied less than 0.5% in the sample volume. The critical transport current range of the samples measured from tens to thousands of amperes in the presence of a 10 T perpendicular magnetic field at 4.2 K.     

Conduction mechanism in anthracene as a function of temperature

Conduction mechanism in anthracene single crystal grown by Bridgman method was carried out. The investigations consisted of dark- and photo-current variation with respect to (i) applied electric field and (ii) temperature. The applied electric field ranged from 0·5 to 2·5 kV/cm and the temperature range was between 300 K and 450 K. Photo and dark current variations with temperature indicate, based on activation energy determination, that a band model can be applied to the conduction process. The band gap is calculated to be 1·6 eV. The band model consists of a recombination centre 0·37 eV above the valence band edge and a trap level 0·55 eV below the conduction band edge to which electrons are first thermo-optically excited and then they are thermally excited into the conduction band.