Characterization of the size effect in grinding and the sliced bread analogy

The size effect is a well known phenomenon in grinding. The specific energy increases with decreasing depth of cut. A comprehensive explanation is therefore required to explain the size effect. In this paper, the size effect in grinding is reviewed and the proposition investigated that the size effect correlates with chip surface area. This effect is shown to be too large to ignore. It was found that the chip surface area created in grinding may increase by nearly 20% when the depth of cut is reduced by half. The effect of the density of the cutting edge distribution on the wheel surface is taken into account and is shown to be as important as the kinematic conditions of grinding. The density of the cutting edge distribution is influenced by the dressing conditions. A grinding power model is presented taking dressing effects into accounts. Grinding performance is comprehensively explained by the size effect and bluntness of the grinding wheel grains. The size effect is explained by the 'sliced bread analogy'. The characterization of the influence of grinding and dressing conditions on the size effect in grinding provides a basis to achieve improved control of the process.     

减排和宣传的时延与低碳参考双重效应影响下供应链决策研究

考虑减排效果和低碳宣传效果的时延效应与消费者具有的低碳参考效应,针对由单个投入碳减排的制造商和单个投入低碳宣传的零售商组成的两级供应链,构建基于产品减排水平、低碳信誉和低碳参考的微分博弈模型。研究分散决策和集中决策下供应链的最优努力投入策略,并分析时延和参考双重效应相关参数对供应链决策和利润的影响。研究发现,集中决策下的最优努力投入高于分散决策的相应值,但集中决策下整体利润并非总是高于分散决策的相应值,两者利润差取决于减排效果和宣传效果的延迟时间;减排效果和宣传效果的延迟时间与参考效应的记忆参数和敏感参数均是制造商和零售商投入减排努力和低碳宣传努力的主要因素;减排效果和宣传效果的延迟时间存在相应阈值,影响产品的减排、低碳信誉和低碳参考的策略选择与供应链成员的利润优势。     

Intralaminar and interlaminar fracture in graphite/epoxy laminates

Various matrix failure modes (intralaminar and interlaminar) in T300/934 graphite/ epoxy laminates are studied. The intralaminar mode is considered by using centre-notchedtension. surface-notched-tension, three-point-bend and compact-tension specimens where transverse fracture toughness and 0° split initiation are investigated. The interlaminar fracture is studied by using double-cantilever-beam and cracked-lap-shear specimens for mode 1 and mode 2 respectively. A simple method for the prediction of split initiation is given and it is seen that the predicted and experimental results agree well. In addition to testing the dry specimens. a few hygrothermal conditions are also used to assess the influence of environment on various failure modes. The effect of environment shows a mixed trend on fracture toughness depending on damage mechanisms involved in the failure modes. The moisture and temperature show a deleterious effect on interface-controlled failure modes, but a beneficial effect on the modes controlled by matrix cleavage.     

Electroplastic effect in nanocrystal and amorphous alloys

The influence of the structural and phase state in nanocrystalline and amorphous alloys, as well as the pulsed current modes, on the electroplastic effect is studied under their tension. The decreasing grain size to nanoscale, the emergence of secondary phases, and amorphization in alloys cause the attenuation or disappearance of the electroplastic effect. The application of current pulses upon tension of alloys with a reversible thermoelastic martensitic transformation suppresses the step down of stress on the tensile diagrams caused by the electroplastic effects, but activates the jump up of stress attributed to the shape memory effect.     

Micromechanical modeling of intrinsic and specimen size effects in microforming

Size effect is a crucial phenomenon in the microforming processes of metallic alloys involving only limited amount of grains. At this scale intrinsic size effect arises due to the size of the grains and the specimen/statistical size effect occurs due to the number of grains where the properties of individual grains become decisive on the mechanical behavior of the material. This paper deals with the micromechanical modeling of the size dependent plastic response of polycrystalline metallic materials at micron scale through a strain gradient crystal plasticity framework. The model is implemented into a Finite Element software as a coupled implicit user element subroutine where the plastic slip and displacement fields are taken as global variables. Uniaxial tensile tests are conducted for microstructures having different number of grains with random orientations in plane strain setting. The influence of the grain size and number on both local and macroscopic behavior of the material is investigated. The attention is focussed on the effect of the grain boundary conditions, deformation rate and the grain size on the mechanical behavior of micron sized specimens. The model is intrinsically capable of capturing both experimentally observed phenomena thanks to the incorporated internal length scale and the crystallographic orientation definition of each grain.     

Numerical and analytical investigation of the size-dependency of the FPZ length in concrete

The main objective of this paper is to study the size effect on the fracture characteristics in concrete structures. The numerical investigation is based on a mesoscale modeling approach. Analytically, two size effect laws are investigated: the classical Ba?ant SEL and a new size effect law based on the enrichment of the stress field on the crack tip. The mesoscopic approach is used to study the evolution of the tangential stress along the crack path in order to investigate the fracture process zone variation during the cracking process. In addition, different analytical governing equations are used to evaluate the size-dependency of the FPZ length.     

Modeling quantum and structure noise of phosphors used in medical X-ray imaging detectors

The noise properties of granular phosphors used in X-ray imaging detectors are studied in terms of a noise transfer function, NTF. This study is performed in high-exposure conditions where the contribution of structure noise to total screen noise is considerable. An analytical model, based on the cascaded linear systems methodology presented in the literature, is developed. This model takes into account the quantum noise and structure noise. Furthermore, it considers the effect of the K X-rays reabsorption on the phosphor material and the effect of screen thickness on the NTF. The model was validated against experimental results obtained by a set of Zn₂SiO₄:Mn phosphor screens prepared by sedimentation. The model may be used to evaluate the effect of screen thickness and the effect of the characteristic X-rays on NTF in high-exposure conditions where structure noise is considerable.     

Numerical Study on the Effects of Gravity and Surface Tension on Condensation Process in Square Minichannel

A volume of fluid (VOF) method is adopted to simulate the condensation of R134a in a horizontal single square minichannel with 1 mm side length. The effect of gravity, surface tension and gas-liquid interfacial shear stress are taken into account. The result denotes that condensation is first appeared at the corner of channel, and then the condensation is stretched at the effect of surface tension until the whole channel boundary covered. The effect of gravity on the distribution of the liquid film depends on the channel length. In short channel, the gravity shows no significant effect, the distribution shape of steam in the cross section of the channel is approximately circular. In long channel, due to the influence of gravity, the liquid converges at the bottom under the effect of gravity, and the thickness of the liquid film at the bottom is obviously higher than that of the upper part of the channel. The effect of surface tension on condensation is also analysed. The surface tension can enhance the condensation heat transfer significantly when the inlet mass flux is low. Whilst, at high mass flux, the enhancement of surface tension on heat transfer is unobvious and can be neglected.     

高温管道内流体流量及温度识别研究

建立了高温管道稳态导热模型,通过有限体积法进行求解,对管道外表面温度分布随流体温度流量的变化规律进行了研究。根据Levenberg-Marquardt算法,提出了由管道外壁面温度分布同时识别管内流体流量及温度的计算方法,通过数值模拟研究了随机测量误差对识别结果的影响,证明了算法的有效性,给出了减小随机误差对识别结果影响的方法。     

Influence of ageing, inclusions and voids on ductile fracture mechanism in commercial Al-alloys

The objective of the paper is to study the effect of ageing, inclusions and voids on the mechanism of fracture and resultant toughness. It has been found that the voids are initiated at only a fraction of the larger inclusions present. The initiation of voids at small particles in the ductile fracture process appears to have little effect on fracture toughness. The strain hardening capacity has a marked effect on void size, and is an indicator of fracture toughness in the commercial Al alloy.     

Changes in crystallinity and thermal effects in ground vaterite

The fractional conversion of vaterite into calcite promoted by grinding and its influence on the thermal behaviour of the samples is studied. The occurrence of a complex exothermal effect in the DSC curves is ascribed to the recovery of crystallinity of calcite and vaterite, on the basis of X-ray line profile analysis.     

Formation of PFZ and Its Effect in a RSP AI-Li Alloy

The formation of precipitation free zone (PFZ) and its effect in a RSP AI-Li alloy has been studied.The results show that PFZ is easy to form when aged at 190℃,but there is no equilibrium phase ongrain boundaries.The growth of PFZ in the alloy is different from that in conventional AI-Li alloys,The effect of PFZ is of great importance because of its large volume fraction in the alloy.It offsets thebeneficial effect of RSP,and is thought to be an important factor that leads to the poor toughnessand low ductility of RSP AI-Li alloy sheet.     

Modelling of creep effect on moisture warping and stress developments in concrete pavement slabs

Abstract

One of the major reasons for the fatigue failure in concrete pavements attributes to the curling and warping deformations and the traffic loads, while creep effect can reduce such deformation and consequently the stress generated in slabs. The literature on the influence of creep effect on slab warping and stress generation is found rare. In this study, a test set-up was designed to measure the flexural creep of concrete beams exposed to sealed and drying conditions. The measured creep properties were then incorporated in finite element analysis to model the creep effect on warping deformation and stress generated in slabs under the conditions of bounded and unbounded with base. It is found that creep effect is significant in slab bonded with base, it reduces warping deformation and stress by 36 and 45%, respectively. The total stress is reduced by 34%. Therefore, it is of importance to take into account creep effect when conducting deformation and stress analysis in concrete pavement slabs.     

混浊海水声吸收与温度、盐度、压强关系

混浊海水的声吸收和声散射特性对水声探测设备工作性能的影响较大。通过经验公式仿真分析了温度、盐度和压强对低频段、低悬浮泥沙颗粒浓度混浊海水声吸收的影响。结果表明:温度和盐度对混浊海水声吸收的影响较大,而压强对混浊海水声吸收的影响可以忽略。构建并研制了一套混浊海水声吸收特性测量系统,实验研究了温度对混浊海水声吸收的影响,声吸收系数随温度的变化规律与仿真结果吻合较好。此研究成果可对混浊海水中的声传播建模、声纳探测系统设计及声纳性能的评估等提供一定参考。     

Nano-precipitate and its aging behavior in a B2-NiAl strengthened ferritic ODS alloy

The effect of aging on a mechanical alloyed (MA) ferritic oxide dispersion strengthened (ODS) alloy was investigated focusing on the B2-NiAl nano-precipitates. The matrix of the alloy is decorated with a high volume fraction of B2-NiAl precipitates and dispersed nano-oxide particles. Due to the coarsening effect of Al on oxides and the changed Zener drag effect on grain growth, the bimodal grain structure was formed. With the extension of the aging time, the size of nano-precipitate increases and its morphology changed from near spherical to rodlike. The temporal evolution of nano-precipitates upon aging treatment is consistent with the modified Lifshitz–Slyozov–Wangner (LSW) theory. In addition, the quantitative calculation reveals the weakening effect caused by nano-precipitates coarsening during aging is the main reason for the decrease in alloy strength.

     

Bullwhip and anti-bullwhip effects in a supply chain

The anti-bullwhip effect, coined by Li et al. in 2005 based on the findings in a simulation study, is the contrary effect of the well-known bullwhip effect. Although there is ample empirical evidence that suggests both effects exist, current literature has not yet provided an integrated framework to address how the two effects are related with each other. By extending the classic work of Lee, Padmanabhan, and Whang of 1997 to a multi-stage supply chain, we derive closed-form formula to analytically describe how the two effects originate initially and then evolve over time and space in the supply chain. Our results show both the bullwhip effect and the anti-bullwhip effect can occur when facing different end-customer demands. However, the magnitude of these effects gradually decreases when moving upstream. We also show the impact of long lead-time on increasing the magnitude of information transformation at the next stage and simultaneously decreasing the magnitude at higher stages. These analytical results provide a theoretical explanation to most simulation findings of Li et al.'s 2005 work and can be used by researchers and practitioners to examine the empirical data and design innovate marketing strategies to convert the unwelcome bullwhip effect into the anti-bullwhip effect.     

Numerical simulation of forced flow in boundary layer and of heat transfer by non-Newtonian fluid in view of the temperature dependence of viscosity

Differences are determined in the degree of the effect made by the temperature dependence of viscosity of fluid on heat transfer and friction. The effect of the temperature factor depends on the direction of heat flux and on the index of nonlinearity of the medium; in so doing, the rheology makes no effect on relative heat transfer and friction. The temperature dependence of viscosity of fluid is self-similar relative to the Prandtl number and makes no effect on friction. Criterional equations are obtained for the calculation of local and average values of Nusselt number and coefficients of friction under conditions of laminar forced convection in the vicinity of a cooled plate.     

Driver age and vehicle engine size effects on fault and severity in young motorcyclists accidents

This paper reports a study of the combined effect of driver age and engine size on accident severity and at-fault risk of young riders of two-wheelers. Data from the national accident database of Greece are used to calculate accident severity and relative fault risk rates. The induced exposure technique is applied due to the lack of exposure data. A log-linear analysis is then used to examine first- and second-order effects within three-variable groups. Accident severity modelling revealed a significant second-order interaction between severity, driver age and two-wheeler engine size. On the contrary, no second-order effects were identified in fault risk modelling. Moreover, a significant effect of driver age on accident fault risk was identified. The effect of engine size was not significant.     

Power losses in bent and elongated polymer optical fibers

This study performs experimental and numerical investigations into the power losses induced in bent, elongated polymer optical fibers (POFs). The theoretical analysis is based on a three-dimensional elastic-plastic finite-element model and makes the assumption of a planar waveguide. The finite-element model is used to calculate the deformation of the elongated POFs such that the power loss can be analytically derived. The effect of bending on the power loss is examined by considering seven different bend radii ranging from 10 to 50 mm. The results show that bending and elongation have a significant effect on the power loss in POFs. The contribution of skew rays to the overall power loss in bent, elongated POFs is not obvious at large radii of curvature but becomes more significant as the radius is reduced.