Monte Carlo modeling of a cosmic ray imaging system for non-destructive evaluation of a reinforced concrete column

A detailed knowledge of the condition of reinforced concrete columns is essential for the planning of maintenance of a large building. We performed a Monte Carlo simulation to examine how well cosmic-ray muon radiography technique works on non-destructive testing of reinforcing concrete and we found that this technique can be an efficient tool for obtaining information such as the size and depth of reinforcing bars beneath concrete. We examined a concrete column with a cross-sectional size of 559×559 mm², reinforced with steel bars of 52 mm diameter, in order to estimate the positioning accuracy. Using simulations of 6 million muons/sr, we found that the precision for bar size measurement is 4.1 mm and that for bar location is 2.5 mm. We describe a possible inexpensive imaging system capable of determining the size and depth of an object and discuss the technique and the benefits of cosmic-ray radiography.     

高温合金小直径棒材超声检测信号的余弦变换分析及识别

将离散余弦变换（DCT）用于直径为φ26mm的变形高温合金棒材超声检测信号的特征分析，提取缺陷回波的离散余弦变换幅度谱作为特征矢量，并对提取的特征利用人工神经网络进行训练和分类，实验和距离可分性测度计算结果表明，与离散傅里叶变换提取的谱类别特征相比，离散余弦变换使缺陷信号的谱类别特征有明显增强。     

不同截面尺寸贝氏体非调质钢的组织和性能

研究了经920 ℃空冷,300 ℃回火后不同直径贝氏体非调质钢棒料的组织和力学性能。结果表明,不同直径贝氏体钢试棒,经空冷+回火后的组织均为贝氏体铁素体和残留奥氏体,属于无碳化物贝氏体组织,ϕ30 mm以下棒料热处理后组织变化较小,直径大于ϕ50 mm棒料,心部组织有所粗化,并伴随粒状贝氏体量的增加。热处理后,随棒料直径的增加,其强度、硬度有降低的趋势。直径大于ϕ50 mm棒料的冲击吸收能量随直径的增加有降低的趋势。ϕ70 mm棒料R/2处抗拉强度为1226 MPa,心部冲击吸收能量(KV₂)为61.3 J。较大直径的贝氏体非调质钢具有良好的强韧性。     

Neural and Neural Gray-Box Modeling for Entry Temperature Prediction in a Hot Strip Mill

In hot strip mills, initial controller set points have to be calculated before the steel bar enters the mill. Calculations rely on the good knowledge of rolling variables. Measurements are available only after the bar has entered the mill, and therefore they have to be estimated. Estimation of process variables, particularly that of temperature, is of crucial importance for the bar front section to fulfill quality requirements, and the same must be performed in the shortest possible time to preserve heat. Currently, temperature estimation is performed by physical modeling; however, it is highly affected by measurement uncertainties, variations in the incoming bar conditions, and final product changes. In order to overcome these problems, artificial intelligence techniques such as artificial neural networks and fuzzy logic have been proposed. In this article, neural network-based systems, including neural-based Gray-Box models, are applied to estimate scale breaker entry temperature, given its importance, and their performance is compared to that of the physical model used in plant. Several neural systems and several neural-based Gray-Box models are designed and tested with real data. Taking advantage of the flexibility of neural networks for input incorporation, several factors which are believed to have influence on the process are also tested. The systems proposed in this study were proven to have better performance indexes and hence better prediction capabilities than the physical models currently used in plant.     

35CrMnSi低合金钢淬火直径与微观组织的关系

对不同直径的35CrMnSi低合金钢棒进行900 ℃油冷淬火+230 ℃回火处理,通过分析钢棒直径与横截面硬度、横截面中心显微组织的关系,探索了35CrMnSi低合金钢油冷淬火临界直径。结果表明,由于贝氏体的存在使淬火马氏体量与硬度的相关性不再符合SAE J406标准提供的对应关系,其中Ø60 mm钢棒马氏体含量仅约40%,但轴线中心硬度接近于按SAE J406标准90%马氏体对应的硬度,轴线中心强度和韧性考核证明符合超高强度钢强韧性要求,可以判定35CrMnSi低合金高强度钢淬火临界直径不小于Ø60 mm;Ø90 mm钢棒轴线中心粒状贝氏体和上贝氏体对硬度影响有限,450 HV10(46 HRC)的硬度远高于SAE J406标准50%马氏体对应的硬度,同样证明若用SAE J406标准淬火马氏体量预测35CrMnSi钢的淬火临界直径远低于实际值。     

Multiple layer separation and visualisation of inductively scanned images of reinforcing bars in concrete using a polynomial-based separation algorithm

Inductive scanning systems that exploit eddy current effects for imaging steel reinforcing bar mesh within concrete have been developed and reported by the authors in several publications. Images generated in this manner depict the different horizontal and vertical layers of the mesh within a single, 2D plane. Deeper bars appear as much fainter structures than those closer to the surface for two reasons: first, the signals they generate are weaker, and second, the image is linearly normalised with respect to the much stronger signals returned from the upper bars. This makes depth and dimensional analysis of deeper bars a severe problem. Below we describe a new suite of image processing algorithms that enables the original composite image to be visualised as separate, multiple images representing the various bar layers. This technique is termed polynomial-based layer separation (PBLS). The method also makes it possible to perform brightness-compensation of the lower bars and is a precursor to analysis that allows measurement of the diameters, orientations and depths of the bars. This information is critical for civil structures inspection teams. Knowing the spatial location of the bar peak widths in one layer, curve fitting is applied to calculate the baselines of the bars in other layers of the image. For a two-layer image, the peaks in the lower layer are removed leaving an image of the top bars, and vice versa for the bottom bars. Images of steel bar mesh processed using this PBLS system offer significant enhancements to the qualitative and quantitative properties of the original image data, and in tests described below, is significantly more robust than comparable methods of image segmentation.     

Reliability of ultrasonic testing methods for hot-rolled steel bars of medium and small diameter

This article describes research on the reliability of ultrasonic testing methods for hot-rolled steel bars of 40–60 mm diameter. Comparison of testing methods is made using direct contact with the bars along the circumferential surface using a straight beam probe (‘S’ probe), a twin crystal probe where the probe face is contoured to the bar curvature (‘SR’ probe) and a straight beam probe with a delay block. The distribution state diagrams of the echo sound pressure and the effective testing range in the cross-section of the bars are obtained. The conclusion is that methods using the SR probe and the straight beam probe with the delay block produce better quality results for steel bars with diameters equal to or smaller than 60 mm, but the S probe is not suitable.     

真空气淬压力对马氏体不锈钢硬度的影响

研究真空气淬压力对4种马氏体不锈钢(2Cr13、9Cr18、1Cr17Ni2和0Cr17Ni4Cu4Nb)硬度的影响。结果表明,在1.5、3、5 bar气淬压力下,直径φ30、φ50、φ80 mm的2Cr13钢棒材心部硬度大于45 HRC,表面硬度大于49.5 HRC。提高气淬压力,材料硬度增大。对于直径φ30 mm的2Cr13钢棒材,心部硬度与表面硬度一致;对于直径φ50和φ80 mm的棒材,心部硬度低于表面硬度。直径为φ30、φ50、φ80 mm的9Cr18、1Cr17Ni2、0Cr17Ni4Cu4Nb钢棒材,在1.5、3、5 bar 气淬压力下均淬透,材料心部硬度与表面硬度一致。     

Recognition of chatter with neural networks

Chatter deteriorates surface finish, reduces tool life, and damages machine tools. A chatter development prediction procedure is proposed for the cylindrical turning of long slender bars. The procedure uses two synthetically trained neural networks to recognize the harmonic acceleration signals and their frequency, and based on these observations, the future vibration characteristics of the system are estimated. The developed neural networks are capable of identifying 98% of the harmonic signals with over 90% certainty and estimate their frequencies with less than ±5% error from very short data sequences (only 11 sampled points). The accuracy of the neural networks is equivalent to time domain time series method based approaches; however, the proposed procedure can be implemented very quickly by using commercially available neural network hardware and software, and can use the new neural network chips to make the estimations very quickly by using parallel processors. The validity of the chatter prediction procedure is also demonstrated on the experimental data.     

Automatically tuned boring bar system

This paper introduces a boring bar system which includes an automatically tuned internal vibration absorber, called a tuned mass damper (TMD). The TMD head can be attached to boring bars with a wide range of lengths. An electromagnetic impulse force actuator is developed to measure the frequency response function (FRF) of the boring bar with an integrated power screw. A portable servo motor is attached to the power screw for adaptive tuning of the vibration damper's stiffness. The measurement and tuning cycle is automated until the negative real part of the FRF is optimized to maximize the chatter-free depth of cut. The system is experimentally validated on boring bars with a wide range of length to diameter ratios.     

The influence of output current on the tensile strength of laser-welded titanium joints

The objective of this study was to examine the influences of the laser output current on the tensile strength of laser-welded titanium bar. Titanium bars of 3 mm in diameter were perpendicularly cut to 30 mm in length for the laser welding. Two bars were fixed to each other with a jig and welded vertically with the light of a laser beam. The tensile strengths of laser-welded titanium joints increased until the output reached 250 A, but decreased as the output current exceeded 250 A. The tensile strengths were significantly lower than that of non-welded parent metal.     

Current research in Egypt on optimisation of combined mechanical strength and corrosion behaviour of steel rebar

Abstract

The effect of accelerated water cooling on the mechanical and corrosion properties of steel rebars produced from steel with composition of 0·17–0·286%C, 0·62–0·72%Mn, 0·15–0·20%Si has been assessed. The bars were rolled from continuously cast steel billets to 12, 16, 20 and 25 mm diameter. Immediately after the last rolling stand the steel bars entered the quenching box. Cooling conditions were varied by changing the number of cooling nozzles and the water flowrate. Initial bar temperature and equalised temperature were calculated using a mathematical model and recorded by pyrometers at the entry of the quenching box and the entry of the cooling bed. Corrosion resistance was determined potentiodynamically and by immersion tests in NaCl and Ca(OH)₂ solution. Equalising temperature decreased with increasing cooling time and water flowrate. Yield strength and ultimate tensile strength (UTS) increased and elongation decreased with decreasing equalising temperature, indicating that different steel grades can be obtained from billet of the same composition using accelerated cooling. Though no direct relationship was observed between mechanical properties and corrosion resistance, the results indicate that cooling conditions and process parameters for thermomechanical treatment should be selected on the basis of corrosion requirements as well as to produce the desired mechanical properties.     

Sentence-processing in echo state networks: a qualitative analysis by finite state machine extraction

It has been shown that the ability of echo state networks (ESNs) to generalise in a sentence-processing task can be increased by adjusting their input connection weights to the training data. We present a qualitative analysis of the effect of such weight adjustment on an ESN that is trained to perform the next-word prediction task. Our analysis makes use of CrySSMEx, an algorithm for extracting finite state machines (FSMs) from the data about the inputs, internal states, and outputs of recurrent neural networks that process symbol sequences. We find that the ESN with adjusted input weights yields a concise and comprehensible FSM. In contrast, the standard ESN, which shows poor generalisation, results in a massive and complex FSM. The extracted FSMs show how the two networks differ behaviourally. Moreover, poor generalisation is shown to correspond to a highly fragmented quantisation of the network's state space. Such findings indicate that CrySSMEx can be a useful tool for analysing ESN sentence processing.     

Measurement of loss of steel from reinforcing bars in concrete using linear polarisation resistance measurements

The measured weight loss data for a number of mild steel bars contained in Portland Cement concrete, together with predicted weight loss values monitored using potentiostatically controlled linear polarisation resistance (LPR) measurements are reported. Three sets of reinforced concrete specimens, each containing electrically isolated mild steel bars, were subjected to either• chloride-induced corrosion,• carbonation-induced corrosion• a control nitrogen rich environment with minimal corrosion.Each set of specimens was initially exposed to a 22-hour dry, 2-hour wet controlled environment for a duration of between 1026 and 1085 days. This was later changed to a 6-day dry, 1 day wet cycle for the carbonation exposure specimens after the initial set of gravimetric testing. The weight loss for each bar due to corrosion was recorded. Instantaneous LPR measurements were also taken on each bar at regular intervals throughout the exposure period. These resistance measurements were then integrated over the exposure period to estimate total weight loss. The results show that weight loss evaluated from experimental LPR measurements gives a significant over-estimate of the weight losses measured gravimetrically.     

Anti-vibration Engineering in Internal Turning Using a Carbon Nanocomposite Damping Coating Produced by PECVD Process

Machining dynamic stability has been enhanced through a damping coating based on a novel carbon-based nanocomposite material. The coating was synthesized using a plasma enhanced chemical vapor deposition method, and deposited on to the round-shank boring bar used for internal turning and tested during machining. Comparisons between an uncoated and a coated boring bar were carried out at 0.25 mm and 0.5 mm depth of cut using a five times length to diameter ratio overhang, which are typical conditions known to generate detrimental mechanical vibrations. From sound pressure measurement it was found that the measured absolute sound level during process could be reduced by about 90% when using the tool coated with damping layer. Surface roughness measurements of the processed workpiece showed decreased Ra values from approximately 3-6 μm to less than 2 μm (and in 50% of the cases <1 μm) when comparing an uncoated standard tool with its coated counterpart. Moreover, it was found that the addition of an anti-vibration coating did not adversely affect other tool properties, such as rigidity and modularity.     

Inspection of micro-tools at high rotational speeds

Micro-tools have been widely used in industry, primarily by biomedical and electronic equipment manufacturers. The life of these cutting tools is extremely unrpedictable and much shorter than conventional tools. Also, these miniature tools, with a diameter of less than 1 mm, cannot be inspected by an operator without the aid of magnifying glass.

In this paper, evaluation of the intensity variation of a reflected laser light beam from the cutting tool surfaces is proposed as a method of estimating cutting tool surface conditions. Various encoding methods, including wavelet transformations, were proposed to obtain a small and meaningful set of data from the intensity variation readings of one tool rotation. The encoded data are classified using a simple threshold method, Restricted Coulomb Energy (RCE), and Adaptive Resonance Theory (ART2)-type neural networks. The proposed encoding and classification approaches were tested with over one hundred sets of data.

The threshold method detects only severe tool damage. The RCE neural networks and graphical presentation of the encoded sets demonstrated the feasibility of the proposed monitoring technique and encoding methods. The ART2-type neural networks were found to be the best candidate for tool condition monitoring because of their self learning capability. Wavelet transformation-based encoding and ART2-type neural networks were found to be sensitive enough to recognize wear at the cutting edge.     

回转式高速剪切下料工艺及试验

针对棒材的精密剪切下料问题,提出了一种回转式高速精密剪切下料方法。完成了回转式精密剪切下料机和送料结构的结构设计,并完成了试验平台搭建。采用数值模拟的方法对下料刀具进行了优化分析,利用回转冲击和棒料表面缺口的应力集中效应,通过变频器改变下料刀具旋转速度,控制棒料的下料效率,对直径为Φ8 mm的不锈钢棒料进行了下料试验,并和传统的冲击剪切下料结果进行了对比分析。试验结果表明,本文提出的下料方法切实可行,可满足工业中多种材料中小直径棒料的下料要求。     

Cathode Characterization with Steel and Copper Collector Bars in an Electrolytic Cell

This article presents finite-element method simulation results of current distribution in an aluminum electrolytic cell. The model uses one quarter of the cell as a computational domain assuming longitudinal (along the length of the cell) and transverse axes of symmetries. The purpose of this work is to closely examine the impact of steel and copper collector bars on the cell current distribution. The findings indicated that an inclined steel collector bar (φ = 1°) can save up to 10–12 mV from the cathode lining in comparison to a horizontal 100 mm × 150-mm steel collector bar. It is predicted that a copper collector bar has a much higher potential of saving cathode voltage drop (CVD) and has a greater impact on the overall current distribution in the cell. A copper collector bar with 72% of cathode length and size of 100 mm × 150 mm is predicted to have more than 150 mV savings in cathode lining. In addition, a significant improvement in current distribution over the entire cathode surface is achieved when compared with a similar size of steel collector bar. There is a reduction of more than 70% in peak current density value due to the higher conductivity of copper. Comparisons between steel and copper collector bars with different sizes are discussed in terms CVD and current density distribution. The most important aspect of the findings is to recognize the influence of copper collector bars on the current distribution in molten metal. Lorentz fields are evaluated at different sizes of steel and copper collector bars. The simulation predicts that there is 50% decrease in Lorentz force due to the improvement in current distribution in the molten metal.     

Q550D拉伸分层原因分析

利用光学显微镜(OM)和扫描电子显微镜(SEM)，对低合金高强钢Q550D的典型拉伸分层断口进行了微观分析。结果表明：组织为贝氏体+铁素体+颗粒状碳化物，存在一定程度的带状分布。试样拉伸变形过程中，大尺寸碳化物处的位错塞积导致萌发微裂纹和孔洞，试样出现缩颈后产生垂直拉应力导致裂纹扩展，组织的带状分布进一步促进了裂纹的扩展，最终形成宏观断口分层。