Investigation of carbon fiber reinforced polymer (CFRP) sheet with subsurface defects inspection using thermal-wave radar imaging (TWRI) based on the multi-transform technique

A combined theoretical and experimental approach is reported using thermal-wave radar imaging (TRWI) for carbon fiber reinforced polymer (CFRP) with subsurface defects inspection. The multi-transform technique (Fourier transform, FT; Hilbert transform, HT; and cross-correlation, CC) is applied to extract the characteristics of thermal-wave signal. Experimental results indicate that the multi-transform technique of thermal-wave signal is available for detecting the subsurface defect. For the shallow defect (defect depth ≤1 mm), the delay time image of CC exhibits high contrast, and the phase image of FT has high SNR at the right frequency component. For the deep defect (defect depth 2.0 mm), the phase images of HT have both high contrast and large SNR value.     

Non-destructive investigation of sluices using radar and ultrasonic impulse echo

Radar and ultrasonic impulse echo have been successfully applied for the assessment of two almost 100 year old sluices. The interior condition of the side walls has been investigated with radar enabling the detection of detachments of the faced brickwork as well as the determination of moisture content. With ultrasonic impulse echo working joints were found in the concrete slab of the sluice heads. The results of these investigations gathered comparative data to reduce the number of cores which had to be taken.     

Study of molybdenum precipitation in steels using thermoelectric power measurement

The precipitation of molybdenum in iron has been investigated using thermoelectric power measurement. We found an increase of the thermoelectric power of iron with the molybdenum content and a coefficient of its influence has been determined. A correlation between secondary hardening due to the precipitation of Mo₂C carbides and thermoelectric power variations has been established.     

Non-destructive testing in the high-temperature regime by using a magneto-optical film

The plane of a polarized light beam is rotated when the beam is transmitted through a magneto-optical film (MOF). Magnetic flux leakage (MFL) occurs around a crack when the specimen is magnetized and affects the magnetic domains. Therefore, a crack can be detected using a polarized lighting system and MOF. The crack detection ability depends on the domain width and saturation magnetization of the MOF. Also, crack detection at high temperatures is essential. The physical properties of the MOF at high temperatures were examined, and a nondestructive testing (NDT) method for detecting cracks at high temperatures was proposed in this paper.     

Artificial neural networks for modelling the mechanical properties of steels in various applications

The application of artificial neural networks (ANNs) in predicting some key properties of steels is discussed in detail. This paper reports on the effectiveness of three back-propagation artificial neural network models that predict (i) the impact toughness of quenched and tempered pressure vessel steel exposed to multiple postweld heat treatment (PWHT) cycles, (ii) the hardness of the simulated heat affected zone in pipeline and tap fitting steels after in-service welding and (iii) the hot ductility and hot strength of various microalloyed steels over the temperature range for strand or slab straightening in the continuous casting process. Predicted and actual experimental values for each model are well matched and highlight the success of applying ANNs in predicting mechanical properties. The capability of ANNs in predicting multiple outputs (hot ductility and hot strength) is also demonstrated.

The sensitivity, which is a measure of the response of an output across the range of an individual input variable, of key input variables (individual alloys and/or process steps) for each model is shown to be in agreement with findings of both the experimental investigation and reports in the literature. Although this paper shows that ANNs can be employed for optimizing steel and process design parameters, some difficulty can arise when inter-relationships exist between input variables. An understanding of the inter-relationships between input variables is essential for interpreting the sensitivity data and optimizing design parameters. It is argued that artificial neural network models can be developed that have the capacity to eliminate the need for expensive experimental investigation in areas, such as welding (new and repair), inspection and testing, and manufacturing processes.     

Corrosion cracking of high-strength structural steels at large depths in the Black Sea

The results of testing various high-strength structural steels for corrosion cracking (CC) in deep zones of the Black Sea, naturally polluted with hydrogen sulfide, are considered. Selecting materials and electrochemical protection means for deep-sea constructions in the Black Sea, one should take into account the possible CC of these steels.     

Research on the fiber lay-up orientation detection of unidirectional CFRP laminates composite using thermal-wave radar imaging

A depth dynamic-resolution thermal-wave radar imaging (TWRI) was used to detect fiber lay-up orientations in the unidirectional CFRP laminate composite. A phase characteristic of thermal wave radar (TWR) signal was proposed and calculated by discrete fractional Fourier transform (DFrFT). The DFrFT phase distribution contour line was approximated as an ellipse and fitted by a non-standard elliptic equation. The ellipse ration angle dependent on the DFrFT phase (defined as Ellipse Angle Curve, EAC) was found to be sensitive to the fiber lay-up orientations of CFRP composite. An inverse methodology was developed to quantitatively characterize the fiber lay-up orientation angle through reconstructing DFrFT phase distribution. A cost function that minimized the square of DFrFT phase difference between TWRI inspection and numerical calculations was constructed, and a hybrid algorithm that combined the simulation annealing (SA) with Nelder–Mead simplex research (NM) method was employed to solve the cost function and find the global optimal solution of the fiber layer-up orientation angle. Experimental investigation of a 7-layer CFRP laminates [0°/45°/90°/0°]_s validated the feasibility of estimating carbon fiber layer-up orientations by TWRI.     

Non-destructive testing of fired tunnel walls: the Mont-Blanc Tunnel case study

The investigation of fired tunnel walls typically relies on visual inspection and a comprehensive study of core samples. Visual inspection is limited to surface diagnosis, while core samples only provide a detailed image of the damaged zone at a single point. In order to gain an extensive view of the entire depth of the damaged zone as well as specific material properties, both the seismic refraction method and ground-penetrating radar investigation may be carried out. In the case of the Mont-Blanc Tunnel, these non-destructive methods have been tested in three zones: heavily damaged, moderately damaged, and sound. On the radargrams generated, several layers can be roughly identified; seismic refraction then confirms and characterises the existence of layers with contrasting mechanical properties.     

Influence of alloying on the passive behaviour of steels in bicarbonate medium

The electrochemical behaviour of passive films on carbon steel, chromium steel and high speed steel (HSS) was studied in 0.5 M NaHCO₃. The influence of the presence of 10 mM potassium chloride on passive film stability, and of the heat treatment of chromium steel and HSS on the respective film properties, was also investigated. Polarization curves showed that the alloy composition exerts a significant influence on the onset of passive film formation, chromium and HSSs passivating more easily as a result of the higher alloying content. Values of passive current, obtained both potentiodynamically and at fixed potential, were higher for HSS than for carbon and chromium steels, which was attributed to the contributions of Mo and W to the passive film composition. The presence of chloride ion delays the passivation of chromium and HSSs, but does not interfere with passive film stability, as shown by the chronoamperometric profile and passive current values. In the case of carbon steel, with no alloying elements, chloride ion diminishes film stability but does not influence passive film formation. Heat treatment, which alters the microstructure, does not alter the properties of the passive films except for a small effect on those formed potentiodynamically on HSS.     

Analysis of thin-wire ground penetrating radar systems for buried target detection, using a hybrid MoM-FDTD technique

A hybrid method combining the finite difference time domain (FDTD) method and the method of moments (MoM) in the frequency domain is proposed to model the electromagnetic behavior of a realistic ground penetrating radar (GPR) system. The GPR is a non-destructive testing (NDT) technique. It consists of a broadband thin-wire vee-dipole antenna located in the vicinity of a lossy ground containing unexploded ordnances. In the solution of the problem, we identify two sub-problems, namely, the antenna problem and the ground buried object problem. Capabilities of the MoM for solution of the governing thin-wire electric field integral equation of the antenna problem and general FDTD solution of Maxwell's equations posed by the scattering of arbitrary shape objects in multilayered media are combined to efficiently and accurately simulate the electromagnetic operation of the system. The proposed simulation technique is validated against the original MoM solution of the problem. It is shown that the proposed hybrid technique exhibits superior performance based on both computation time and numerical accuracy compared with the conventional FDTD and MoM solution techniques. It is also shown that the position and size of the target, as well as the electromagnetic characteristics of the target, can be determined using a simple signal processing technique.     

Physical simulation of hot rolling in the ferrite range of steels

Hot rolling of low carbon steel is usually performed in the austenite range. Demands for lowering the energy consumption, for thinner gauges and new compact strip mills create recent interest in ferritic rolling. An overview on industrial ferritic rolling is given. The effects of low temperature deformation on the work hardening and softening mechanisms are described by means of flow curves.     

故宫石质螭首健康状况无损检测及评估预研究

目的通过无损检测方法评估故宫石质螭首风化和安全程度。方法首先在现场选取6个螭首进行无损检测,获取各项风化指标(表面风化程度、裂缝大致情况、孔洞、回弹强度、酥粉质量)和安全等级指标(裂缝性质、裂缝数量等具体值,超声波波速、回弹强度)。在实验室模拟风化、破损试验,建立超声波波速、回弹强度与抗折强度的曲线关系。最后通过德尔菲法建立评价体系,采用加权平均法获得各螭首的风化等级、安全等级。结果石材的抗折强度、超声波波速和回弹强度的曲线关系式为fk=0.0004V~(0.4393)R~(2.9302)。确定了6个螭首的风化程度和安全状况水平,其中构件2的表面风化程度最弱、最安全;构件6的安全情况最差,急需采取有效防范措施。结论该无损检测和健康程度评估研究方法是一种简单、快速、可量化的评价方法,其成果可用于石质文物健康状况的检测和评估工程,以获得其风化等级、安全等级,并作为文物管理决策的依据。     

Enhancement of the GPR method of railway trackbed investigation by the installation of radar detectable geosynthetics

For several years ground penetrating radar (GPR) surveys have been used to provide a rapid method of investigating the depth of the ballast/sub-grade interface.At the same time, rail industry geotechnical engineers are increasingly recognising the benefits of geosynthetic products specifically developed to suit the variety of needs and subgrade conditions encountered during repair and construction of the trackbed. This paper describes the recent development of a specialised geosynthetic, namely Terram PW5, which is uniquely designed to enhance remote monitoring by GPR. The benefits of providing a geosynthetic which is clearly detectable by radar are firstly, that it is easy to confirm after construction that the geosynthetic has been installed, and secondly that it facilitates the measurement of the depth of ballast above the geosynthetic at any time after construction. Terram Ltd and IMC Geophysics Limited have collaborated to develop a GPR detectable geosynthetic, and also a method of GPR detection, which improves the accuracy of depth of ballast measurement. A further application of radar detectable geosynthetics is monitoring trackbeds which are susceptible to subsidence, such as those running over karstic landscapes or old mine-workings, where gradual downward deflection of the reflecting stripe may be used to identify developing cavities.Other possible developments will be briefly discussed, regarding additional geotechnical monitoring functions which may be implemented by means of suitably designed geotextiles.     

靶控输注异丙酚不同麻醉深度对兔脑神经元型一氧化氮合酶mRNA水平的影响

目的: 研究异丙酚不同麻醉深度对兔脑神经元型一氧化氮合酶(nNOS)mRNA水平的影响。方法: 30只日本大耳兔,随机分为3组:对照组,浅麻醉组,深麻醉组,每组10只。浅麻醉组、深麻醉组予以异丙酚靶控输注,达到所需麻醉状态后1h断头处死。对照组行耳缘静脉注射空气造成空气栓塞后致死。动物处死后0～4℃分离取脑,原位杂交法测定小脑皮质、大脑顶叶皮质nNOSmRNA表达水平。结果: 与对照组比较,异丙酚麻醉状态下明显抑制兔大脑顶叶皮质、小脑皮质nNOSmRNA表达水平(P<0.05)。随麻醉深度的加深,小脑皮质nNOS表达水平进一步明显降低(P<0.05),但大脑顶叶皮质nNOS表达水平并未进一步降低(P>0.05)。结论: 异丙酚可能通过抑制nNOS活性,降低NO、环磷酸鸟苷(cGMP)水平,从而发挥麻醉作用。异丙酚对nNOS活性的抑制存在脑区差异。     

Location of steel reinforcement in concrete using ground penetrating radar and neural networks

Ground-penetrating radar is becoming increasingly popular for use as a non-destructive assessment method for investigating reinforced concrete structures. The amount of data collected however can be very large and take a significant level of subjective experience to interpret. This study focuses upon the use of a neural network approach to automate and facilitate the post-processing of ground penetrating radar results. The radar data is reduced to a simplified data set by using an edge detection routine. Signal reflections from reinforcing bars displaying a hyperbolic image format are detected using a multi-layer perceptron (MLP) network with a single hidden layer containing 8 nodes to recognise a simplified hyperbolic shape. Training and testing of the network was carried out making use of an emulsion analogue tank, simulating the properties of concrete, and using real concrete specimens. The results showed that the use of a MLP neural network approach could be quite effective in automating the identification and location of embedded steel reinforcing bars from a radar investigation. Accurate estimation of depth, or cover, requires a reliable knowledge of the dielectric properties of the concrete, and recent work using a specially-developed wideband horn antenna for direct determination of in situ properties is also outlined.     

Determination of temperature distribution in the cutting zone using hybrid analytical-FEM technique

In this study, the temperature distribution in the cutting zone was determined by integrating thermal analytical and simulation models of orthogonal cutting process with uncoated and coated carbide tools. Primarily, 2D FEM simulations were run to provide numerical solutions of temperatures occurring at different points through the chip/tool contact region and the coating/substrate boundary under defined cutting conditions. In addition, an analytical model for heat transfer in the cutting tool and its partitioning, proposed in References [W. Grzesik, P. Nieslony, Physics based modelling of interface temperatures in machining with multilayer coated tools at moderate cutting speeds, Int. J. Mach. Tools Manufact. 44 (2004) 889–901; W. Grzesik, P. Nieslony, A computational approach to evaluate temperature and heat partition in machining with multilayer coated tools, Int. J. Mach. Tools Manufact. 43 (2003) 1311–1317], was employed to generate the input data to computations of the tool–chip interface temperature. The changes of the temperature distribution fields resulting from varying heat flux transfer conditions are the main findings of the FEM simulations. Finally, the analytically and numerically predicted average temperatures were validated against the tool-work thermocouple-based measurements and discussed in terms of relevant literature data.     

Effects of molybdenum additions on the structure, depth, and austenite grain size of the case of carburized 0.13% carbon steels

Carbon (0.13%) steel samples containing about 0.48% molybdenum (Mo) singly and in combination with nickel (Ni) were carburized in a natural Titas gas atmosphere at a temperature of 1223 K (950 °C) and at a pressure of about 0.10 MPa (15 psia) for time periods ranging from 1–4 h followed by slow cooling in the furnace. Their microstructure was studied by optical microscopy. The austenite grain size of the case and the case depths were determined. It was found that Mo and Ni alone and in combination decrease the thickness of the cementite network near the surface of the carburized case of the steels. However, Ni is found to be more effective than Mo in decreasing the thickness of cementite network. Both Mo and Ni enhance the formation of Widmanstätten cementite plates at the grain boundary and within the grains near the surface of the carburized steels. However, Ni alone is more effective than Mo in the formation of Widmanstätten cementite plates. In the presence of Ni, Mo is much more effective in the formation of Widmanstätten cementite plates than Mo in absence of Ni. It was also revealed that both Mo and Ni increased the case depth. Ni is more effective than Mo in increasing the case depth. The combined effect of Mo and Ni is much greater than that of either Mo or Ni alone in increasing case depth. Mo as Mo carbide (Mo₂C) particles refined the austenite grain size of the carburized case. Ni in solution was not found to have any effect in restricting grain growth of austenite, but the presence of Ni enhances the austenite grain size refining effect of Mo in the carburized case.     

A quantitative analysis of the effect of laser transformation hardening on crack driving force in steels

A mechanical model of a laser transformation hardening specimen with a crack in the middle of the hardened layer is developed to quantify the effects of the residual stress and hardness gradient on crack driving force in terms of J-integral. It is assumed that the crack in the middle of the hardened layer is created after laser transformation hardening. Using a Double Cantilever Beam model, the analytic solutions, which can be used to quantify the effects of the residual stress and the hardness gradient resulting from laser transformation hardening on crack driving force, are obtained. A numerical example shows the crack driving force decrease is very sensitive to the residual compressive stress increase.     

Ultrasonic detection of defects in strongly attenuating structures using the Hilbert–Huang transform

Non-destructive testing of polymer materials meets specific problems caused by a high attenuation of ultrasonic signals. When the expected flaws are close to the interfaces, the signals reflected by the flaws may be hidden in the tail of much stronger signals caused by front reflection from the sample and by interfaces between the adjacent layers. For improved detection of defects in plastic pipes, a new approach based on a combined application of non-linear deconvolution and the Hilbert–Huang transform is proposed.The first step of the algorithm is the elimination of strong ultrasonic echo signals reflected by interfaces. The second step is processing of ultrasonic signals using the Hilbert–Huang method. In order to improve visualization of defects we have proposed a new presentation of the Hilbert–Huang spectrum based on calculation of the product of the amplitude and the instantaneous frequency of analytic signal and displaying this product in a three-dimensional plot. The experimental investigations demonstrated a good performance of the proposed technique in the case of highly attenuating plastic pipes.