Estimation of Length Limits for Integral Bridges Built on Clay

In this paper, the maximum length limits for integral bridges built on clay are determined as a function of the ability of steel H-piles supporting the abutments to sustain thermal-induced cyclic displacements and the flexural capacity of the abutment. First, H-pile sections that can accommodate large plastic deformations are determined considering their local buckling instability. Then, a low-cycle fatigue damage model is used to determine the maximum cyclic deformations that such piles can sustain. Next, nonlinear static pushover analyses of two typical integral bridges are conducted to study the effect of various geometric, structural, and geotechnical parameters on the performance of integral bridges subjected to uniform temperature variations. Using the pushover analyses results, design guidelines are developed to enhance and determine the maximum length limits for integral bridges built on clay. It is recommended that the maximum length of concrete integral bridges be limited to 210 m (689 ft) in cold climates and 260 m (853 ft) in moderate climates and that of steel integral bridges be limited to 120 m (394 ft) in cold climates and 180 m (590 ft) in moderate climates.     

Axial offset control of PWR nuclear reactor core using intelligent techniques

Improved load following capability is one of the main technical performances of advanced PWR (APWR). Controlling the nuclear reactor core during load following operation encounters some difficulties. These difficulties mainly arise from nuclear reactor core limitations in local power peaking, while the core is subject to large and sharp variation of local power density during transients. Axial offset (AO) is the parameter usually used to represent of core power peaking, in form of a practical parameter. This paper, proposes a new intelligent approach to AO control of PWR nuclear reactors core during load following operation. This method uses a neural network model of the core to predict the dynamic behavior of the core and a fuzzy critic based on the operator knowledge and experience for the purpose of decision-making during load following operations. Simulation results show that this method can use optimum control rod groups maneuver with variable overlapping and may improve the reactor load following capability.     

TRADE‐OFF BETWEEN APPROXIMATION ACCURACY AND COMPLEXITY FOR TS FUZZY MODELS

This paper proposes a transformation method that serves the trade‐off between the modelling complexity and accuracy of multi‐variable Takagi‐Sugeno fuzzy inference operator‐based modelling (TS fuzzy modelling). The relation between the number of fuzzy rules and the modelling accuracy is defined in the paper. The proposed transformation method is capable of finding the minimal number of fuzzy rules for a given accuracy of a given TS fuzzy model. A case study, focusing on a benchmark problem of fault diagnosis, developed in the framework of EC‐founded Research Training Network DAMADICS, of an actuator in a sugar factory, is presented to provide feasibility of the proposed method.     

A torsional resonance mode AFM for in-plane tip surface interactions

Changing the method of tip/sample interaction leads to contact, tapping and other dynamic imaging modes in atomic force microscopy (AFM) feedback controls. A common characteristic of these feedback controls is that the primary control signals are based on flexural deflection of the cantilever probes, statically or dynamically. We introduce a new AFM mode using the torsional resonance amplitude (or phase) to control the feedback loop and maintain the tip/surface relative position through lateral interaction. The torsional resonance mode (TRmode™) provides complementary information to tapping mode for surface imaging and studies. The nature of tip/surface interaction of the TRmode facilitates phase measurements to resolve the in-plane anisotropy of materials as well as measurements of dynamic friction at nanometer scale. TRmode can image surfaces interleaved with TappingMode™ with the same probe and in the same area. In this way we are able to probe samples dynamically in both vertical and lateral dimensions with high sensitivity to local mechanical and tribological properties. The benefit of TRmode has been proven in studies of water adsorption on HOPG surface steps. TR phase data yields approximately 20 times stronger contrast than tapping phase at step edges, revealing detailed structures that cannot be resolved in tapping mode imaging. The effect of sample rotation relative to the torsional oscillation axis of the cantilever on TR phase contrast has been observed. Tip wear studies of TRmode demonstrated that the interaction forces between tip and sample could be controlled for minimum tip damage by the feedback loop.     

Influence of tool material on dynamics of drilling of GFRP composites

Drilling trials have been carried out on glass Fibre reinforced plastics (GFRP) with plain high speed steel (HSS), TiN coated HSS and tipped tungsten carbide drills. Most of the defects in drilling of composites are due to thrust force experienced by the workpiece. The parametric influence on cutting force was experimentally evaluated. The experimental results show that the defects toleranced drilling can be attained by proper selection of cutting parameters and tool material. This is substantiated by monitoring flank wear, hole shrinkage and acoustic emission during drilling.     

Improved dynamic cutting force model in ball-end milling. Part I: theoretical modelling and experimental calibration

An accurate cutting force model of ball-end milling is essential for precision prediction and compensation of tool deflection that dominantly determines the dimensional accuracy of the machined surface. This paper presents an improved theoretical dynamic cutting force model for ball-end milling. The three-dimensional instantaneous cutting forces acting on a single flute of a helical ball-end mill are integrated from the differential cutting force components on sliced elements of the flute along the cutter-axis direction. The size effect of undeformed chip thickness and the influence of the effective rake angle are considered in the formulation of the differential cutting forces based on the theory of oblique cutting. A set of half immersion slot milling tests is performed with a one-tooth solid carbide helical ball-end mill for the calibration of the cutting force coefficients. The recorded dynamic cutting forces are averaged to fit the theoretical model and yield the cutting force coefficients. The measured and simulated dynamic cutting forces are compared using the experimental calibrated cutting force coefficients, and there is a reasonable agreement. A further experimental verification of the dynamic cutting force model will be presented in a follow-up paper.     

Direct probing of solvent-induced charge degradation in polypropylene electret fibres via electrostatic force microscopy

Electrostatic force microscopy was used to directly probe solvent‐induced charge degradation in electret filter media. Electrostatic force gradient images of individual polypropylene electret fibres were used to quantify the extent of charge degradation caused by the immersion of the fibres into isopropanol. Electrostatic force gradient images were obtained by monitoring the shifts in phase and frequency between the oscillations of the biased atomic force microscopy (AFM) cantilever and those of the piezoelectric driver. Electrostatic force microscopy measurements were performed using non‐contact scans at a constant tip‐sample separation of 75 nm with varied bias voltages applied to the cantilever. Mathematical expressions, based on the capacitance of the tip‐sample system, were used to model the phase and frequency shifts as functions of the applied bias voltage to the tip and the offset voltage due to the fibre's charge. Quantitative agreement between the experimental data and the simplified model was observed.     

用复合振子模型计算纳米尺度滑动摩擦力的研究

以光滑界面摩擦为研究对象,探讨用复合振子模型计算纳米尺度滑动摩擦力的原理和方法,推导出滑动摩擦力和摩擦因数的计算公式,并用原子力显微镜探针在硅试样和云母试样上做扫描实验进行验证。实验值与理论计算值的对比结果表明,两者所反映的规律基本一致,表明所提出的理论和方法可行。研究表明,滑动摩擦力与接触面积成线性增长关系,并随宏观振子横向刚度的增大而减小,由于可通过改变摩擦表面的几何形貌来改变宏观振子的横向刚度,因此这一结论将为摩擦控制提供一种新途径。     

高强度钢干式铣削替代半精磨的试验研究

采用硬质合金刀片(YW1)和涂层刀片(YB415)进行了高强度钢的干式铣削代替半精磨试验研究。根据试验结果,确定适合加工该型号高强度钢的刀具材料和切削用量。以这两种刀片在不同切削用量条件下的耐用度、加工表面粗糙度和主切削力作为刀具加工性能的评价依据,同时研究了刀片的磨、破损机理和卷、排屑稳定性。试验结果表明:涂层刀片干铣削高强度钢的加工性能优异,工件加工表面质量达到半精磨水平。     

Computational models of a nano probe tip for static behaviors

It is difficult to predict the measurement bias arising from the compliance of the atomic force microscope (AFM) probe. The issue becomes particularly important in this situation where nanometer uncertainties are sought for measurements with dimensional probes composed of flexible carbon nanotubes mounted on AFM cantilevers. We have developed a finite element model for simulating the mechanical behavior of AFM cantilevers with carbon nanotubes attached. Spring constants of both the nanotube and cantilever in two directions are calculated using the finite element method with known Young's moduli of both silicon and multiwall nanotube as input data. Compliance of the nanotube-attached AFM probe tip may be calculated from the set of spring constants. This paper presents static models that together provide a basis to estimate uncertainties in linewidth measurement using nanotubes. In particular, the interaction between a multiwall nanotube tip and a silicon sample is modeled using the Lennard-Jones theory. Snap-in and snap-out of the probe tip in a scanning mode are calculated by integrating the compliance of the probe and the sample-tip interacting force model. Cantilever and probe tip deflections and points of contact are derived for both horizontal scanning of a plateau and vertically scanning of a wall. The finite element method and the Lennard-Jones model provide a means to analyze the interaction of the probe and sample and measurement uncertainty, including actual deflection and the gap between the probe tip and the measured sample surface.