Impact properties of laminated angle ply composites

The impact properties of laminated composites have been studied as a function of fiber orientation angle, lamination configuration and specimen geometry. The energy absorbing mechanisms havebeen identified. The impact properties of laminated composites are influenced significantly by the fiber orientation angle, lamination configuration and specimen geometry. All off-axis composites (0° < θ < 90°) fail by brittle inter-fiber cleavage mode with little or no interlayer delamination. The longitudinal composites (θ = 0°), both unidirectional and crossplied, fail by a combination of failure modes which take place in a sequential manner—fiber failure and interfacial splitting followed by a layer-to-layer delamination. The presence of 0° layer(s) in transverse composite (θ ±90°) improves their impact performance.     

A 5 in. Si(Li)/Pb sampling calorimeter telescope for observation of cosmic gamma rays in the GeV region

A 5 in. diameter Si(Li)/Pb sampling calorimeter with a depth of 28 radiation lengths (30 unit cells × 0.93 radiation lengths) has been constructed. The energy and angular resolutions of the calorimeter have been investigated using CERN SPS positron beams with energies of 10 to 147.8 GeV. The calorimeter shows good linearity over this energy region and the energy resolution is expressed well by σ_E (rms)/E = (16.9 ± 0.9)%/ √E[GeV], where E represents the incident beam energy. The angular resolution of the calorimeter for a single event is 0.3° (rms) at 80 GeV/c. The agreement between these results and Monte Carlo simulations is good.

We are showing a new design of the Si(Li)/Pb sampling calorimeter telescope (SSCT) with an angular resolution (point source localization capability) of about 0.04° (rms) for bright galactic gamma-ray sources. We believe that this telescope is a suitable detector for future observations of cosmic gamma rays in the GeV region, especially when used to search for point sources.     

A large solid-angle array for heavy ions from APEX

A large solid-angle array of Low Pressure Multi-Wire Proportional Counters (LPMWPCs) has been constructed as part of the ATLAS Positron Experiment (APEX). Eight three-element trapezoidal counters span 360° in φ and 20–68° in laboratory θ. Angle sensitivity in θ is provided by a transmission-line delay cathode, while the 24-fold segmentation provides angle sensitivity in φ. Details are given on the design of the counters and associated hardware. Performance of the counters is described, based on tests with scattered heavy ions ranging from ⁵⁸Ni to ²³⁸U.     

Formation of second phase particles in aluminum-copper alloy films

The formation of second phase particles in Al+3% Cu alloy films was examined in order to find differences of the precipitation in thin films from that occurring in bulk alloys. Compared to bulk alloys in the thin film material the formation of Guinier-Preston zones is retarded. In well quenched thin films 60 h at 100°C or 6 h at 130°C are necessary to produce G.P. zones. θ′ particles are nucleated after approximately 100 h at 120°C without formation of θ″. The stable θ-Al₂Cu precipitate was found at temperatures as low as 150°C on the film surface. The results show that excess vacancies cannot be retained in thin films and that the film surfaces provide preferential nucleation sites for the equilibrium precipitate θ-CuAl₂.     

Performance of the ATLAS electromagnetic calorimeter barrel module 0

The construction and performance of the barrel pre-series module 0 of the future ATLAS electromagnetic calorimeter at the LHC is described. The signal reconstruction and performance of ATLAS-like electronics has been studied. The signal to noise ratio for muons has been found to be 7.11±0.07. An energy resolution of better than (sampling term) has been obtained with electron beams of up to 245 GeV. The uniformity of the response to electrons in an area of Δη×Δφ=1.2×0.075 has been measured to be better than 0.8%.     

Performance of transmission dynode photomultipliers in magnetic fields up to 1.5 T

The performance of commercially available photomultiplier tubes with 1, 2, 8 and 16 parallel transmission dynodes is examined in homogeneous magnetic fields B with strengths up to 1.5 T and axial as well as nonaxial orientations. The samples with 16 dynodes allow an operation with gains G ≥ 10³ and time resolutions σ ≤ 230 ps in such strong fields and for tilting angles θ ≤ 50°. The dependence of relative gain G/G(B = 0) and time resolution σ on B and θ is less expressed for the PMs with the smaller numbers of dynodes and a more compact design. The influence of B(θ) on the transit time is discussed qualitatively.     

A damping analysis of composite laminates using the closed form expression for the basic damping of Poisson's ratio

Various methods have been presented to obtain the effective damping of a symmetric laminated composite. In this paper, modified classical lamination theory based upon the elastic–viscoelastic correspondence principle was utilized by developing the basic damping of Poisson's ratio for accurately predicting the damping of laminated composite beams. The analysis involves an extension of the elastic–viscoelastic approach. Futhermore, Ni and Adams' theory was used for verifying the modified classical lamination theory. Six typical laminated composites with [±θ]_s,[0/θ]_s,[0/±θ/90]_s,[90/±θ/0]_s,[0/90/±θ]_s and [90/0/±θ]_s, stacking sequences were employed for this study. Numerical results have shown that damping values were in some difference among prediction methods over the particular range of fiber orientation.     

Lattice rotation and stability of 22.5° ND rotated cube orientation in cold rolled polycrystalline AA 5182 aluminum alloy

AA 5182 aluminum alloy with a strong cube texture was cold rolled to different reductions at an angle of 22.5° to the prior rolling direction. The texture evolution at this new rolling direction was investigated by X-ray diffraction. The rotation paths and stability of the 22.5° ND rotated cube orientation were determined based on the variation in the three-dimensional orientation distribution function (ODF) with rolling reduction. The results show that most of the grains with the 22.5° ND rotated cube orientation are directly rotated to the β fiber along different rotation paths, but there are a few grains moving through the cube orientation to the β fiber. The {0 0 1}<1 1 0> oriented grains possess the lowest stability during rolling, and the stability increases as the initial orientation changes from the {0 0 1}<1 1 0> orientation to the {0 0 1}<1 0 0> orientation along the ₁ axis.     

Performance of an electromagnetic liquid krypton calorimeter based on a ribbon electrode tower structure

The NA48 collaboration is preparing a new experiment at CERN aiming to study CP violation in the K⁰- system with an accuracy of 2 × 10⁻⁴ in the parameter e(ε′/ε). Decays in two π⁰'s will be recorded by a quasi-homogeneous liquid krypton calorimeter. A liquid krypton calorimeter has been chosen to combine good energy, position and time resolution with precise charge calibration and long-term stability. The prototype calorimeter incorporating the final design of the electrode read-out structure is presented in this paper. An energy resolution of 3.5%/√E with a constant term smaller than 0.5% has been obtained. The time resolution was found to be better than 300 ps above 15 GeV.     

Étude électrique de couches minces de polymère obtenues dans une décharge luminescente II: Caractérisation électrique sous champ alternatif

The aim of this study was to investigate the electrical characteristics under alternating stress of a metal-polymer-metal structure, the dielectric of which was a thin layer created by a glow discharge in styrene.

The study, carried out in the 250 Hz–100 kHz range between −90° and 150°C, indicates two different domains for the variations of ε_r and ε_r'. Using bi-logarithmic coordinates the variation of the a.c. conductivity σ_ac(Ω) obeys the law σ_ac(Ω)∝Ω for temperatures lower than 50°C.

In order to explain this result, two hypotheses are proposed: that dipolar fluctuations occur and that a hopping process takes place.     

Impact parameter dependent k-shell ionization probabilities in ion-atom collisions with different asymmetry

We present experimental probabilities P_κ(θ) for target K-shell ionization in 1.26 MeV/u He → Te, Dy; N → In, Nd collisions up to very large scattering angles (θ 170°). The P_κ(θ) are nearly constant for θ > 10°. Groups of collision systems with about the same sum of projectile and target nuclear charge (Z_P + Z_T = united atom system) and collision velocity were s probabilities are within these groups of collision systems nearly proportional to the square of the projectile nuclear charge even up to Z_p/Z_T = 0.7. The calculations in the semiclassical approximation (SCA) by Trautmann et al. are compatible with the experimental results when the recoil effect is included and wave functions of the united atom system are used.     

Modification of Microstructure for Improved Oxidation Resistance in γ-Based Ti-Al-X Alloys

The effect of microstructural refinement on the oxidation behavior of γ + laves Ti-45Al-15Cr and γ + σ Ti-40Al-27Nb was investigated. A fine, uniform γ + laves microstructure in Ti-45Al-15Cr resulted in protective alumina scale formation over most of the sample surface at 800°C and 1000°C in air. In contrast, the oxidation resistance of this same alloy was severely degraded by a coarse γ + laves microstructure. The oxidation behavior of Ti-40Al-27Nb at 1200°C in air was poor. Refinement of the γ + σ microstructure in this alloy was not effective in improving oxidation resistance. The mechanistic reasons for these effects, and the implications for improved oxidation resistance through microstructural refinement are discussed.     

Anelastic relaxation peak associated with the presence of incoherent θ phase in Al-4wt.%Cu alloy

Internal friction measurements have been made for Al-4wt.%(1.76at.%)Cu alloy aged at various temperatures. A relaxation peak was observed at around 400 °C (ƒ = 1.6 Hz) after the speciment had been aged within the temperature range 330–450 °C. X-ray diffraction analysis showed that the incoherent θ phase is formed after aging within this temperature range and that it grows and becomes coarsened at increasing aging temperatures according to electron microscopy observations. Consequently the 400 °C internal friction peak observed for the first time is associated with the presence of θ phase in the alloy. Examination of the experimental results showed further that this peak is not due to a process occurring inside the θ phase but is associated with the stress-induced relaxation along phase boundaries between the θ particle and the matrix phase.

The activation energy of this peak is found to be 1.0 eV. The relaxation time and the relaxation strength of this peak calculated on the basis of an equivalent inclusion model are in accord with experimental results.     

LED Lighting Configurations for Visual Inspection of IC Packages

This article discusses configurations of light-emitting diode (LED) light sources for visual inspection of integrated circuit (IC) packages. A package visual inspection (PVI) system with multiple LED light sources used for inspection of IC packages was designed. The image contrast changes of the sample IC packages are explained using the Torrance-Sparrow (TS) model. A few conclusions on appropriate lighting configurations for inspection of various IC packages are achieved. The TS model can be used to represent the specular lobe component. The contrast between two surfaces with different surface roughness values increases with increasing θ_i (incident light angle). Lighting C (θ_i = 75°) is recommended for packages with high surface roughness heights and resin materials. Lighting B (θ_i = 60°) is recommended for packages with moderate surface roughness heights and metal materials. If the background is white, the use of light sources A (θ_i = 15°) and B simultaneously is recommended. Light sources A and C are recommended to be chosen for packages with low surface roughness values and transparent materials. The experimental results with the actual gray-level values of the images are compared to support the conclusions. The PVI system is part of an inspection machine. All images of the sample IC packages reported in this article were obtained from an actual production line. Therefore, the results are close to those of the actual inspection situation in the manufacturing industry.     

Emission probability measurement of γ-ray of Rh

¹⁰⁵Rh becomes a stable ¹⁰⁵Pd after β⁻-decay with a half-life of 35.36 h. The energies of especially strong γ-rays emitted from ¹⁰⁵Rh are 306.1 and 318.9 keV, and the emission probabilities are evaluated to be 5.1±0.3% and 19.1±0.6% by de Frenne et al. To improve the certainty, the γ-ray emission probabilities were determined from the disintegration rate and absolute γ-ray intensities measured using a 4πβ(ppc)-γ(HPGe) coincidence apparatus with two-dimensional data-acquisition system. The results for the 306.1 and 318.9 keV γ-rays were 4.76±0.05% and 16.99±0.17%, respectively.     

Infrared Transmission Curves of Pb0.1 Ca0.9La2S4 Pellets Densified by Pressureless Sintering

Highly sinterable submicron Pb_0.l Ca_0.9La₂S₄(PCLS) powders were prepared by sulfidizing calcium and lanthanum alkoxides al 500°C under CS, atmosphere for 8 hours and then in pure H₂S atmosphere at 600-800°C for 8 hours. After sintering the pellets were used as infrared transmitting window material of 8-14 μm wavelength. The CdS was added from 3 to 7 wt.% lo improve the sinterability by forming liquid phase during sintering. For sulfidization of lanthanum alkoxide, sulfide powder with LaS₂ phase was formed at 500°C, and a pure Th3P4 phase formed follow by 700°C heat treatment. A powder with β-La₂S₃phase formed at 800°C, and a pure Th₃ P₄phase formed follow by 900°C heat treatment. The powder with β-La₂S₃ phase was sintered to full density at 1350°C by adding 3 wt.% CdS. The PCLS powder with Th3P4 phase sintered to full density at 1400°C by also adding 3 wt.% CdS. The pellet exhibited 45% transmittanceat 13 μm when sintered from the powder with p-La₂S₃phase. The transmittance at 2.5 μm for the pellet sintered from the PCLS powder with Th₃P₄ type structure was 3 times higher than that from the p-La₂S₃ powder.     

Calculation of Drag Force on an Object Settling in Gas-Solid Fluidized Beds

Gas-solid fluidized beds can be used for dry beneficiation of minerals. Estimation of the drag force on separated materials is important for the design and operation of separators. Previous research was based on the empirical correlation or on the hypothesis that fluidized beds behave as a Newtonian fluid. However, much experimental evidence showed that the hypothesis of Newtonian fluid was suspect. The drag forces on spheres passing through fluidized beds were calculated using the Bingham fluid model. The plastic viscosity and yield stress of a fluidized bed can be obtained by measurement of the terminal settling velocity of spheres. The relationship between drag coefficient (C D ), sphere size (d o ), settling velocity (u t ), bed bulk density ( ρ b ), plastic viscosity (µ), and yield stress ( τ 0 ) is expressed as C D = 24/ Re m (1 + 0.15 Re 0.687 m ), Re m = d o u t ρb /(µ + τ0 d o /3 u t The calculated results agree well with the experimental data.     

The development of compression damage zones in fibrous composites

Recent experimental work (Narayanan S, Schadler LS. Mechanisms of kink band formation in graphite/epoxy compsites: a micromechanical experimental study. Comp Sci Technol 1999; 59:2201-13) suggests that kink bands in unidirectional continuous carbon fiber reinforced polymer composites initiate from damage zones formed under axial compressive loads. A damage zone consists of a cluster of locally crushed fibers and broken fibers, that are often fractured at an angle, θ > 0°, normal to the fiber axis. Typically, under compressive loads, fiber breaks in damage zones form roughly along a plane at an angle φ, normal to the fiber axis. These damage zones produce stress concentrations which can lead to instabilities in the nearby fiber and matrix and initiate microbuckling and kink bands. This paper extends a micromechanical influence function technique based on earlier shear lag fiber composite models. Our modified technique calculates the fiber axial and matrix shear stress concentrations due to multiple angled and crushed fibers in arbitrary configurations. Modeling reveals that angled or ‘shear’ breaks (θ > 0°) can lead to higher shear stress concentrations in the matrix than transverse breaks (θ=0°). Also we find that the damage zone is more likely to form at an angle φ, which is greater than that of its individual fiber breaks, θ. When φ is slightly greater than θ, the shear stress in the surrounding matrix regions within the damage zone achieves a maximum, potentially weakening the matrix and interface and consequently leading to kink band formation. Monte Carlo simulations incorporating this stress analysis predict that the initiation and propagation of crushed and angled breaks progress roughly along an angle, φ ≈ 17° in a linear elastic system. When possible, our model results are compared to strain measurements of fiber composites under compression obtained by Narayanan and Schadler using micro-Raman spectroscopy (MRS).     

Prediction for delamination initiation around holes in symmetric laminates

The purpose of this paper is to present an analytical technique for predicting the delamination initiation load and delamination location for balanced symmetric laminates containing a hole. Basically, this approach includes two phases. First, the stress distribution around the hole region is calculated by the authors' recently developed efficient method. Second, the delamination initiation load and delamination location are predicted by using an average stress failure hypothesis together with the Hashin-Rotem delamination criterion. A computer program was developed to calculate the delamination initiation load and location for notched laminates with different ply orientations, different material properties and different stacking sequences. Numerical results for (θ/ – θ/0°)_s and (0°/90°)_s composite laminates generated by the current approach are compared with existing solutions. The results show that the present method is very efficient and useful for the purpose of engineering design.     

Tungsten chemical vapor deposition using tungsten hexacarbonyl: microstructure of as-deposited and annealed films

Tungsten (W) films were deposited on Si(100) from tungsten hexacarbonyl, [W(CO)₆], by low-pressure chemical vapor deposition (CVD) in an ultra-high vacuum (UHV)-compatible reactor. The chemical purity, resistivity, crystallographic phase, and morphology of the deposited films depend markedly on the substrate temperature. Films deposited at 375°C contain approximately 80 at.% tungsten, 15 at.% carbon and 5 at.% oxygen. These films are polycrystalline β-W with a strong (211) orientation and resistivities of >1000 μΩ cm. Vacuum annealing at 900°C converts the metastable β-W to polycrystalline -W, with a resistivity of approximately 19 μΩ cm. The resultant -W films are porous, with small randomly oriented grains and nanoscale (<100 nm) voids. Films deposited at 540°C are high-purity (>95 at.%) polycrystalline -W, with low resistivities (18–23 μΩ cm) and a tendency towards a (100) orientation. Vacuum annealing at 900°C reduces the resistivity to approximately 10 μΩ cm, and results in a columnar morphology with a very strong (100) orientation.