Optimization of Design Parameters in Ionography

It has been shown that good quality radiographic images can be formed by allowing the X-ray beam transmitted through an object to fall on an ionization chamber in which a layer of gas or liquid is confined between conducting surfaces. The ions formed by X-ray absorption in this layer are collected on an insulating foil lying over one of the electrodes, and the resulting charge distribution on the foil can then be developed by one of the toner techniques common in Xerography.

There are many parameters which can be varied both in the design of the ionography chamber and in the development process. This paper considers the choice of these various parameters with a view to optimizing sensitivity and resolution and discusses in detail the efficiencies of different ionographic absorbers relative to selenium, the absorber used in Xeroradiography.     

Evaluation of a Non‐destructive High‐voltage Technique for the Detection of Pinhole Leaks in Flexible and Semi‐rigid Packages for Foods

This study evaluated the capabilities of a high‐voltage technique for the detection of pinhole leaks by using flexible pouches and semi‐rigid cups for foods. This evaluation was performed by measuring the discharge voltage when high voltages ranging from 0.25 to 10 kV were applied to sample packages. The results showed that package contact surface area, film thickness, food type and electrical conductivity are significant factors affecting the detection of pinhole leaks in flexible pouches by a high‐voltage leak detection (HVLD) system within the ranges tested (p < 0.05). For plastic cups with plastic‐laminated and foil‐laminated lids, the headspace inside a cup had the greatest effect followed by dielectric constant of lid films, electrical conductivity of foods and pinhole diameter (p < 0.01). In general, the HVLD system can detect pinholes as small as 10 µm in both plastic‐laminated and foil‐laminated pouches and lid cups, even at worst‐case scenario conditions, including liquid, semi‐solid and solid foods with 0.85 a_w. Because of high voltages applied, however, delamination in foil‐laminated films occurred when an applied voltage was greater than 3.5 kV, which resulted in increased oxygen permeability. Statistical z‐test analysis of results from blind studies showed that the HVLD technique is significantly effective in determining defective pouches and cups with pinhole leaks as small as 10 µm (p < 0.05). Therefore, it can be concluded that the HVLD technique is a promising non‐destructive and on‐line method to detect pinhole defects, which may be applicable to a wide range of hermetically sealed packages. Copyright © 2013 John Wiley & Sons, Ltd.     

Low‐cycle fatigue life behaviour of BS 460B and BS B500B steel reinforcing bars

This paper investigates the low‐cycle fatigue resistance of BS 460B and BS B500B steel reinforcing bars and proposes models for predicting their fatigue life based on plastic‐strain (?_ap) and total‐strain (?_a) amplitudes. Constant‐amplitude, strain‐controlled low‐cycle fatigue tests were carried out on these bars under cyclic load with a frequency of 0.05 Hz. The maximum applied axial strain amplitude (?_s,max) ranges from 3 to 10% with zero and non‐zero mean strains. The strain ratios (R = ?_s,min/?_s,max) used are R =?1, ?0.5 and 0. Hysteresis loops were recorded and plastic and total strain amplitudes were related to the number of reversals (2N_f) to fatigue failure and models for predicting the number of reversals to fatigue failure were proposed. It is concluded that the predicted fatigue life of these bars is very accurate when compared with the measured experimental fatigue life results for wide range of values of strain ratios. It is also observed that based on plastic‐strain amplitude, BS B500B consistently has a longer life (higher number of cycles to failure) than those of BS 460B for all R values; however, at low plastic‐strain amplitudes they tend to behave similarly, irrespective of R value. Other observations and conclusions were also drawn.     

Practical mathematical model to predict the performance of insulating packages

Thermal insulation is used in a variety of applications to protect temperature‐sensitive products from thermal damage. Several factors affect the performance of insulating packages. These factors include the packaging material, the geometry of the package, the geometry of the product, and the degree of contact between the product and the package. In this study, a comprehensive model which includes all of these factors was developed to predict the performance of the insulating package. First, an equation was derived for the calculation of the thermal resistance of a multilayered wall. The wall resistance was then used in a mathematical model which included the aforementioned factors. Basic heat transfer principles covering conduction, convection and radiation were applied to the model and the package heat penetration rate was calculated. Based on this model, several factors affecting the performance of the insulating package were discussed. Examples of the use of this model for ice requirement calculations were also included. Copyright © 2007 John Wiley & Sons, Ltd.     

Comparison of flat film to total package water vapour transmission rates for several commercial food wraps

The barrier properties of a package are the sum of material and seal permeations. Although addressed for hermetically sealed and modified atmosphere packages, little consideration of total package permeation has been given to commercial food wraps. Standard protocols were used to compare the water vapour transmission rates (WVTRs) of materials and packages for seven commercial food wraps: aluminum foil; poly(vinylidene chloride) (PVdC) film; three poly(ethylene) (PE) films; an adhesive‐modified PE film; and plasticized poly(vinyl chloride) (PVC) film. Water ingress for a complete package was compared to calculated material permeation based on film WVTRs. Film‐to‐glass adhesion strength was also measured. Model systems (desiccant) were compared to foods at ambient and refrigeration temperatures. Aluminum foil had the lowest material WVTR (0.10 g/h/m²), closely followed by PVdC (0.13 g/h/m²). These WVTRs were approximately five‐fold lower than the PEs (～0.65 g/h/m²), which were nearly 10‐fold lower than PVC (4.9 g/h/m²). The adhesive‐modified PE film had the lowest difference between material and package transmission rates (0.7 E‐03 g/h), approximately half that of the PVdC film (1.1 E‐03 g/h), which was significantly lower than the remaining films (2.3 E‐03 –3.9 E‐03 g/h). The adhesive PE film had the strongest film–glass adhesion. Ambient food product test results were similar to model system (desiccant) results, but refrigerated trials showed significantly different relative package transmission rates. This was attributed to the reduced adhesion of most wraps at refrigeration temperatures. Copyright © 2002 John Wiley & Sons, Ltd.     

Experimental and numerical investigation of the effect of temperature on mixed‐mode fracture behaviour of AM60 Mg alloy

The aim of present paper is to experimentally investigate mixed‐mode fracture behaviour of AM60 Mg alloy at low and elevated temperatures. For this purpose, mode I, 45° mixed‐mode, and mode II tests were conducted using a modified version of Arcan device at three different temperatures. An elastic‐plastic finite element model was used to extract necessary geometric parameters. Crack resistance curves (J‐R) and critical J‐integral of the material were extracted. The results indicated that, for all loading modes, maximum critical J‐integral value was observed at ambient temperature and decreased by either increasing or decreasing the temperature. It was observed that effect of temperature on fracture behaviour is much larger at temperatures above 0°C rather than sub‐zero temperatures. By changing the loading angle to go from mode I to mode II, a decreasing trend was observed in the values of critical fracture parameters at all temperatures. Finally, the surfaces were examined using scanning electron microscopy (SEM).     

FGA formation mechanism for X10CrNiMoV12‐2‐2 and 34CrNiMo6 for constant and variable amplitude tests under the influence of applied mean loads

The aim of the present work is to clarify the fine granular area (FGA) formation mechanism in two steels (tempered 34CrNiMo6 and X10CrNiMoV12‐2‐2) causing grain refinement in the early state of fatigue for internal crack initiation and propagation in the very high cycle fatigue regime at pure tension‐compression loading (R = ?1) and for applied mean stresses (R ≠ ?1). Fatigue tests were performed with constant and variable amplitude at several R values using ultrasonic fatigue testing setups. Failed specimens were investigated using high‐resolution scanning electron microscopy and focused ion beam technique with special attention paid to the crack origin and the surrounding microstructure. To prove models for FGA formation proposed in literature, a numerical model to evaluate effective R values and contact stresses between the fracture surfaces depending on the crack length has been realised. The aim of these investigations is to estimate the influence of crack closure effects on FGA formation. FGA formation due to repeating contact of the fracture surfaces according to the model postulated by Hong et al correlates well with the findings for numerical simulations.     

不同包装材料对酱肉挥发性风味物质的影响

目的 研究酱肉在PET/AL/PE铝箔包装、PET/PE透明包装条件下不同时间段的挥发性风味物质的变化。方法 采用顶空固相微萃取–气相色谱–质谱连用法(SPME–GC–MS)并结合相对气味活度值(ROAV)、主成分分析(PCA)对酱肉挥发性风味物质变化进行分析。结果 研究发现,酱肉中挥发性物质主要为酯类、醇类,其中苯甲酸乙酯、乙酸芳樟酯、癸酸乙酯、正己酸乙酯、(+)–柠檬烯、壬醛、正己醛、(–)–4–萜品醇、桉叶油醇、芳樟醇、乙基麦芽酚、茴香脑的ROVA值大于1,为关键风味物质。PCA分析得出,2–甲基丁酸乙酯、(E,E)–2,4–壬二烯醛、正己酸乙酯、2,5–辛二酮、(1R)–2,6,6–三甲基双环[3.1.1]庚–2–烯、3–甲硫基丙醛、异丁酸乙酯、茴香脑为特征性挥发性风味物质。另外,通过对在PET/AL/PE铝箔和PET/PE透明包装下,酱肉各类风味物质含量、主体香味物质和异味物质ROVA值、主成分分析的比较,说明不同包装材料对酱肉挥发性风味物质的成分、含量均有影响。结论 从长期检测的结果看出,PET/AL/PE铝箔包装比PET/PE透明包装可显著地阻止脂肪氧化,较少生成异味物,可更好地保护酱肉的香味,为酱肉的贮藏保鲜提供了依据。     

Strong and Tunable Electrical Anisotropy in Type‐II Weyl Semimetal Candidate WP2 with Broken Inversion Symmetry

A transition metal diphosphide, WP₂, is a candidate for type‐II Weyl semimetals (WSMs) in which spatial inversion symmetry is broken and Lorentz invariance is violated. As one of the prerequisites for the presence of the WSM state in WP₂, spatial inversion symmetry breaking in this compound has rarely been investigated. Furthermore, the anisotropy of the WP₂ electrical properties and whether its electrical anisotropy can be tuned remain elusive. Angle‐resolved polarized Raman spectroscopy, electrical transport, optical spectroscopy, and first‐principle studies of WP₂ are reported. The energies of the observed Raman‐active phonons and the angle dependences of the detected phonon intensities are consistent with results obtained by first‐principle calculations and analysis of the proposed crystal symmetry without spatial inversion, showing that spatial inversion symmetry is broken in WP₂. Moreover, the measured ratio (R_c /R_a ) between the crystalline c‐axis and a‐axis electrical resistivities exhibits a weak dependence on temperature (T) in the temperature range from 100 to 250 K, but increases abruptly at T ≤ 100 K, and then reaches the value of ≈8.0 at T = 10 K, which is by far the strongest in‐plane electrical resistivity anisotropy among the reported type‐II WSM candidates with comparable carrier concentrations. Optical spectroscopy study, together with the first‐principle calculations on the electronic band structure, reveals that the abrupt enhancement of the electrical resistivity anisotropy at T ≤ 100 K mainly arises from a sharp increase in the scattering rate anisotropy at low temperatures. More interestingly, the R_c /R_a of WP₂ at T = 10 K can be tuned from 8.0 to 10.6 as the magnetic field increases from 0 to 9 T. The so‐far‐strongest and magnetic‐field‐tunable electrical resistivity anisotropy found in WP₂ can serve as a degree of freedom for tuning the electrical properties of type‐II WSMs, which paves the way for the development of novel electronic applications based on type‐II WSMs.     

High‐cycle and very‐high‐cycle fatigue behaviour of a titanium alloy with equiaxed microstructure under different mean stresses

The fatigue behaviour of a titanium alloy Ti‐6Al‐4V with equiaxed microstructure (EM) under different values of tensile mean stress or stress ratio (R) was investigated from high‐cycle fatigue (HCF) to very‐high‐cycle fatigue (VHCF) regimes via ultrasonic axial cycling. The effect of mean stress or R on the fatigue strength of HCF and VHCF was addressed by Goodman, Gerber, and Authors' formula. Three types of crack initiation, namely, surface‐with‐RA (rough area), surface‐without‐RA, and interior‐with‐RA, were classified. The maximum value of stress intensity factor (SIF) at RA boundary for R < 0 keeps constant regardless of R in HCF and VHCF regimes. The SIF range at RA boundary for R > 0 also keeps constant regardless of R in VHCF regime, but this value decreases linearly with the increase of R for surface RA cases. The microstructure observation at RA regions gives a new result of nanograin formation only in the cases of negative stress ratios for the titanium alloy with EM, which is explained by the mechanism of numerous cyclic pressing.     

A direct estimate of JIc from the load versus load-line displacement record

The purpose of this study is to examine the current standard fracture toughness test procedure to determine if there could be an easier method to get a J_Ic value from the test record. The current method for determining J_Ic involves a detailed computational and construction procedure. The objective in this study is to simplify the analysis for the determination of J_Ic. The results of this study show that the load and displacement record for a fracture toughness test can be used to directly estimate a J_Q value, a provisional value for fracture toughness, J_Ic. The J value taken at the maximum load point can be used along with an adjustment factor to estimate a J_Q value. This J_Q estimate is close to the one obtained from the construction procedure of ASTM Standard E 1820. When a unit‐sized specimen is tested, that is, a specimen with a width of 50 mm and a thickness of 25 mm the maximum load point provides a direct estimate of J_Q. Other sizes require a size adjustment factor, which is simply a square root relationship between the width of the test specimen and a unit width. The proposed new method of estimating J_Q is simple in concept and requires a minimum number of calculations. It appears to produce values of J_Q which are comparable to those obtained from the ASTM E1820 construction procedure and may produce less scatter.     

基于有限元分析的笔记本纸浆模制品包装改进设计

目的在跌落工况下验证笔记本纸浆模制品对产品的保护性,并进行改进设计。方法使用Creo对笔记本电脑及缓冲包装结构进行初步设计,根据实际的物理跌落试验工况建立跌落仿真模型,通过ABAQUS/Explicit进行仿真分析,得到产品跌落加速度曲线和产品应力应变云图。根据仿真结果进行缓冲包装设计改进,对改进后的方案再次进行仿真分析并进行试验验证。结果初步设计方案的正面跌落加速度达到160.1g,超过规定值120g,且键盘面板塑性应变达到4.95%,存在较大变形风险。纸浆模制品缓冲结构改进后,跌落时正面、侧面和底面的跌落加速度分别为118.5g、98.2g、101.2g,均处于规定值范围内。键盘面板塑性应变降低至0.14%,符合要求。此外,仿真数据与实测结果基本吻合,仿真过程能较好地反映包装制品与产品的跌落碰撞过程。结论通过有限元分析法进行跌落仿真分析,相较于传统的试验法,能快速、准确地找到包装方案的风险点,可为产品的缓冲包装结构改进设计奠定良好基础。     

Fast kd‐tree‐based hierarchical radiosity for radiative heat transport problems

In this paper we present a new efficient approach for radiative heat transfer simulations for various applications in engineering, combining existing approaches from different fields of computer science and heat transfer. For these application fields we assume radiative exchange between gray, diffuse surfaces in a radiatively nonparticipating medium. To solve the complex space–time behavior of radiation in 3D domains we use the hierarchical radiosity method. Here, the basic idea is to hierarchically subdivide surfaces forming a quad‐tree structure until a refinement criterion is reached. The fundamental underlying operation of the radiosity method is visibility detection which can be solved efficiently by using a space partitioning approach for the input surfaces. For this reason we choose a kd‐tree which is the best known acceleration structure for visibility detection on irregularly distributed surfaces. These approaches dramatically decrease the complexity of the radiation problem from n³ to O((k² + n)logk), where k is the number of input surfaces and n is the number of refined surfaces. We validate the approach for several non‐trivial examples and demonstrate that the scheme is second‐order accurate. Copyright © 2011 John Wiley & Sons, Ltd.     

UO2芯块运输容器核临界安全分析

目的 在开展二氧化铀（UO₂）芯块运输容器设计时,应进行临界安全分析,优化容器设计,并通过得出的临界安全指数（CSI）限定可运输货包的数量,确保在任何可信的运输情景下的核临界安全。方法 文中采用蒙特卡罗软件SuperMC对符合要求的国际临界安全手册中6类49个基准实验案例进行建模计算,获得本案例的次临界上限值,再基于运输容器经受正常运输条件与运输事故条件试验的结果,计算得出正常运输条件与运输事故条件下的单货包与货包阵列的最大中子增殖系数keff值。结果 该案例的次临界限值（USL）为0.91974;UO₂芯块运输容器在正常运输条件与运输事故条件下单货包的最大keff值分别为0.286 08,无限阵列货包的最大keff值为0.798 34。结论 UO₂芯块运输容器在正常运输条件与运输事故条件下的最大keff值均小于0.919 74,临界安全指数为0,容器设计临界安全性能可确保可运输安全。     

R-curve behavior and roughness development of fracture surfaces

We investigate the idea that the fractal geometry of fracture surfaces in quasibrittle materials such as concrete, rock, wood and various composites can be linked to the toughening mechanisms. Recently, the complete scaling analysis of fracture surfaces in quasibrittle materials has shown the anisotropy of the crack developments in longitudinal and transverse directions. The anomalous scaling law needed to describe accurately these particular crack developments emphasizes the insufficiency of the fractal dimension, usually used to characterize the morphology of fracture surfaces. It is shown that a fracture surface initiating from a straight notch, exhibits a first region where the amplitude of roughness increases as a function of the distance to the notch, and a second one where the roughness saturates at a value depending on the specimen size. Such a morphology is shown to be related to an R-curve behavior in the zone where the roughness develops. The post R-curve regime, associated with the saturation of the roughness, is characterized by a propagation at constant fracture resistance. Moreover, we show that the main consequence of this connection between anomalous roughening at the microscale and fracture characteristics at the macroscale is a material-dependent scaling law relative to the critical energy release rate. These results are confirmed by fracture experiments in Wood (Spruce and Pine).     

Zirconium Temperature Measurements from the Melting Point to 4100 K Involving the Use of Blackbody Models in the Liquid State

The temperature (2128–4100 K) dependence of specific enthalpy Eat atmospheric pressure is obtained under conditions of fast (microseconds) pulsed electric heating of zirconium foil samples. The enthalpy dependence of the spectral density of radiation at the wavelength of 0.855 m is measured for flat surfaces and for two blackbody models made of zirconium foil. The temperature is calculated by Planck's formula. The temperature plateau on the curve of the dependence of Ton Ein the melting of zirconium is used for calibration, and the value of the plateau temperature is taken to be equal to the equilibrium melting point of 2128 K. The blackbody models are assembled of separate flat strips of zirconium. The objective of this study is to develop and experimentally verify a blackbody model suitable for both metals and graphite and to derive the temperature dependence of the thermal properties of liquid metals and liquid carbon at high temperatures under conditions of fast pulsed heating. A Tektronix TDS 754C four-channel digital oscilloscope was used in the measurements.     

Integrated ANN–GA for estimating the minimum value for machining performance

In this study, we proposed a new approach in estimating a minimum value of machining performance. In this approach, artificial neural network (ANN) and genetic algorithm (GA) techniques were integrated in order to search for a set of optimal cutting condition points that leads to the minimum value of machining performance. Three machining cutting conditions for end milling operation that were considered in this study are speed (v), feed (f) and radial rake angle (γ). The considered machining performance is surface roughness (R _a). The minimum R _a value at the optimal v, f and γ points was expected from this approach. Using the proposed approach, named integrated ANN–GA, this study has proven that R _a can be estimated to be 0.139?µm, at the optimal cutting conditions of f?=?167.029?m/min, v?=?0.025?mm/tooth and γ?=?14.769°. Consequently, the ANN–GA integration system has reduced the R _a value at about 26.8%, 25.7%, 26.1% and 49.8%, compared to the experimental, regression, ANN and response surface method results, respectively. Compared to the conventional GA result, it was also found that integrated ANN–GA reduced the mean R _a value and the number of iterations in searching for the optimal result at about 0.61% and 23.9%, respectively.     

Determination of displacements around fatigue cracks using image analysis of in‐situ scanning electron microscope images

A technique to in‐situ measure the displacements in the vicinity of the crack tip during fatigue crack propagation has been developed. High‐resolution images of the crack tip were taken continuously throughout the fatigue load cycles with a scanning electron microscope (SEM), and an image analysis program was used to determine the displacements at different positions with respect to the crack tip. The displacements were then used to determine crack shapes and compliance curves. The measured crack shapes show a general √r dependence versus the distance to the crack tip. However, close to the crack tip the crack shape is clearly affected by plastic deformation, even in cases when small scale yielding prevails. The compliance curve measurements close to the crack tip can be used to determine the global stress level when the crack surfaces are separated, so that the exact opening and closure stresses can be determined.     

A notch stress intensity approach to assess the multiaxial fatigue strength of welded tube-to-flange joints subjected to combined loadings

Full penetration T butt weld joints between a tube and its flange are considered, subjected to pure bending, pure torsion and a combination of these loading modes. The model treats the weld toe like a sharp V‐notch, in which mode I and mode III stress distributions are combined to give an equivalent notch stress intensity factor (N‐SIF) and assess the high cycle fatigue strength of the welded joints. The N‐SIF‐based approach is then extended to low/medium cycle fatigue, considering fatigue curves for pure bending and pure torsion having the same slope or, alternatively, different slopes. The expression for the equivalent N‐SIF is justified on the basis of the variation of the deviatoric strain energy in a small volume of material surrounding the weld toe. The energy is averaged in a critical volume of radius R_C and given in closed form as a function of the mode I and mode III N‐SIFs. The value of R_C is explicitly referred to high cycle fatigue conditions, the material being modelled as isotropic and linear elastic. R_C is thought of as a material property, independent in principle of the nominal load ratio. To validate the proposal, several experimental data taken from the literature are re‐analysed. Such data were obtained by testing under pure bending, pure torsion and combined bending and torsion, welded joints made of fine‐grained Fe E 460 steel and of age‐hardened AlSi1MgMn aluminium alloy. Under high cycle fatigue conditions the critical radius R_C was found to be close to 0.40 mm for welded joints made of Fe E 460 steel and close to 0.10 mm for those made of AlSi1MgMn alloy. Under low/medium cycle fatigue, the expression for energy has been modified by using directly the experimental slopes of the pure bending and pure torsion fatigue curves.     

Effect of residual stresses on crack behaviour in single edge bending specimens

Residual stresses due to manufacturing processes, such as welding, change the load bearing capacity of cracked components. The effects of residual stresses on crack behaviour in single edge bending specimens were investigated using Finite element analyses. Three parameters (J, Q and R) were used to study the crack behaviour. The J‐integral predicts the size scale over which large stresses and strains exist, the constraint parameter Q describes the crack‐tip constraint as a result of geometry, loading mode and crack depth and the constraint parameter R is used to describe the constraint resulting from residual stresses. To carry out a systematic investigation on the effect of residual stresses on the J‐integral and crack‐tip constraints, models under different combinations of residual stresses and external loads with different crack depths were analysed. It has been shown that the crack‐tip constraint R increased by tensile residual stresses around the crack‐tip. On the other hand, the constraint parameter R decreased and tended to zero at high external load levels.