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.     

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.     

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.     

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.     

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.     

Evaluation of tempering induced changes in the hardness profile of case-carburised EN36 steel using magnetic Barkhausen noise analysis

The effect of tempering on the magnetic Barkhausen noise (MBN) signal profile was studied in case-carburised EN36 steel using a range of magnetic excitation frequencies and a number of frequency ranges for analysis of the MBN signal. The MBN level generally increases with tempering due to coarsening of the microstructure. With higher values of excitation frequency, f_EX, the MBN profile exhibits a single peak, but with low values of f_EX, double peaks are observed. The MBN peak obtained with higher f_EX was found to correlate well with hardness changes in a region, down to 100 μm below the surface. The analysis of the MBN signal produced with low f_EX, in narrow frequency ranges selected by software frequency filtering, showed variations in the extent of changes in the relative height of the two MBN peaks in the profile. After taking into account the skin depth-frequency relation for the MBN signal, variations in the values of the two MBN peaks in different analysing frequency ranges were found to correlate well with hardness variations at different depths down to 425 μm below the surface. An empirical relationship has been established between the hardness-depth profile and the MBN measurements.     

Difference in the detection limits of flaws in the depths of multi-layered and continuous aluminum plates using low-frequency eddy current testing

We examined the difference in the detection limits of flaws in the depths of multi-layered and continuous aluminum plates using low-frequency eddy current testing. The detection limits were measured by using a magneto-resistive sensor. Comparing the frequency of an applied magnetic field, the detection limit at 50 Hz is deeper than that at 1 kHz. Comparing the sample structure, the detection limit in the multi-layered samples is deeper than that in the continuous samples. These results are likely due to the differences in the skin depth and conductivity of the sample.     

污水深度处理后回用于循环冷却水的试验研究

本文介绍了将污水经深度处理后回用于循环冷却水的中试试验过程，确定了该试验工艺路线的技术可行性，它的实施将产生良好的社会效益。     

GPR evaluation of the damage found in the reinforced concrete base of a block of flats: A case study

Ground-penetrating radar (GPR) is a non-destructive geophysical technique that is used to analyse soils and structures by providing continuous images of the interior of the media being analysed. In this paper, we present the methodology and results of a study of the reinforced concrete base of a large block of flats, where flow water and flooding are common in the wet and dry seasons. There are also a large number of cracks and fissures in the soil under the base. The damaged building is located in Valencia (Spain). The measurements were taken during two different seasons to include a period when flooding occurred and a period without flooding. The aim of the study was to determine whether the base would remain watertight in future and to analyse the depth of the damage observed on the surface. The results provided us with a detailed map of the damage and the zones that require more detailed analysis. Such damage affects the whole concrete slab. In addition to this analysis, several measurements were carried out to determine the possible causes of the inundations by locating potential wet areas and zones with high water content. A water table and a well were detected, which could be the cause of the humidity damage.     

SCC evaluation of type 304 and 316 austenitic stainless steels in acidic chloride solutions using the slow strain rate technique

The stress corrosion cracking (SCC) of the commercial austenitic stainless steels type 304 and 316 was investigated as functions of strain rate, test temperature and pH in acidic chloride solutions using a slow strain rate technique. From the comparison between the parameters such as time to failure (t_f), maximum stress (σ_m) and strain at t_f (ε_f) obtained in inert and corrosive environments, the relationships between t_f^Cl(corrosive)/t_f^W(inert), σ_m^Cl/σ_m^W and ε_f^Cl/ε_f^W versus strain rate were divided into three regions for type 304 and 316 specimens: the strain rate-dominated, SCC-dominated and corrosion-dominated regions, respectively. Furthermore, it was found that the relationship between t_f^Cl/t_f^W and σ_m^Cl/σ_m^W in the SCC-dominated region became a good straight line for the type 304 and 316 specimens irrespective of strain rate, test temperature and pH. This suggests that σ_m^Cl/σ_m^W became the parameter for predicting t_f. The results obtained were compared with those obtained from the constant load method and are discussed in terms of the formation of slip steps, dissolution current and film formation rate.     

Evaluating the deterioration of electrodes when increasing the number of pulses in the welding time using galvanised IF and HSLA steels and assigning mechanical properties in the spot welds

ABSTRACT

Resistance spot welding is the most important method in the industry of self-supporting or monocoque body joinery because of its automation, its speed, the flexibility of welding parts with a complicated shape, and it is economical because it does not require a filler metal, and it is also possible to apply pre-heating and post-heating pulses to improve the weldability of the spot weld, which is defined as the ability of the structure to adequately protect passengers against injuries in the event of a collision, and this mainly depends on the integrity and mechanical performance of the weld button. In order to extend the lifetime of vehicles, galvanized steels are produced. However, zinc coatings have increased the difficulty of weldability, with higher currents being required in the process, since there is less resistance at the weld interface due to improved electrical conductivity. This work investigates the effect of galvanizing on the reduction of the lifetime of the electrodes, for this reason, it follows that there is a loss in the mechanical properties in the weld buttons as the number of spot welds increases. The main aim of this study is to correlate the electrode wear with the mechanical properties of the weld buttons. The experiment procedure consists of making 1,000 spot welds; and every twenty-fifth spot weld after the first was examined by means of stereoscopy, hardness tests, unbuttoning tests and shear stress tests. In terms of electrode wear, the face was evaluated using impressions on carbon paper, optical microscopy and X-ray spectroscopy.