Characterization of Graded Subsurface Zones in Industrial Case-Hardening Using a Non-Destructive Testing System

For process monitoring and quality assurance of case-hardened components, the determination of the case-hardening depth in the manufacturing process after hardening of the subsurface layer is a quality verification that is often required in industry. Currently, these quality assurance tests can only be realized with destructive measures. During case-hardening, the essential microstructural formation, and thus the key component properties are developed during the heat treatment in the cooling section. The testing technique used in the present study is based on the analysis of harmonic signals of eddy current testing. The aim of this project was to achieve an early identification of incorrect cooling processes in the case of a known transformation behaviour of the components during cooling. The data collected in the industrial hardening process show that an evaluation of the carburizing process on the basis of the case-hardening depth can be carried out non-destructively during component cooling and in the cooled state with the use of eddy current technology.

Tilt angle and lifetime of sunspot groups

We use the Catalog of Solar Activity (CSA) to study the latitudinal variations of tilt of solar active regions. The tilt angles β are computed taking into account changes of the heliographic grid with latitude ϕ. We show that when sunspot groups of different sizes and lifetimes are included, a classical representation of the Joy’s law as a linear function of latitude (β∝ϕ) is only the first approximation valid within a limited range of latitudes (−25○ ≤ ϕ ≤ +25○). Outside this range, the functional dependence β = f(ϕ) becomes non-linear. Separating the dataset on large long-living groups (LLG) and small short-living groups (SSG) reveals two quite different dependencies in β = f(ϕ): non-linearity in tilt is only present in LLGs and the steepness of linear section of β = f(ϕ) fit is higher for LLGs. This suggests a difference in the physical properties of two populations of solar groups, which could be hypothesized as an indication of different localization of subsurface zones of their formation in the framework of a distributed dynamo. However, since CSA contains the coordinates of sunspots averaged over the lifetime (or disk passage) of each group, one cannot ruled out that the difference in tilts of SSG and LLG groups may be affected by the evolution of tilt angles during the lifetime/disk passage of the groups.

Influence of cutting parameters on the formation of white etching layers in BTA deep hole drilling

In this study, the influence of cutting speed and feed rate on surface integrity in Boring Trepanning Association (BTA) deep hole drilling of AISI 4140+QT is investigated. Microstructure and micro-hardness in the subsurface zones of bores are analyzed, using metallographic and micromagnetic methods. It was found that when using high feed rates and cutting speeds, white etching layers (WEL) form at the surface of the bores. These layers are up to three times harder than the substrate material and have a maximum thickness of approx. {t_{\mathrm{WEL}}}\approx 12\hspace{0.1667em}\text{\textmu m}. WEL were usually followed by a transitional layer, so that elevated hardness was observed until a depth of {d_{\mathrm{surf}}}=35\hspace{0.1667em}\text{\textmu m} below the surface. Magnetic Barkhausen noise (MBN) analysis proved to be applicable for the fast and reliable detection of WEL. The presented results contribute to gaining a deeper understanding of the complex interrelations between the design of the BTA process, the resulting microstructure in the machined component and the properties of the conditioned surface. Based on discovered correlations, a dynamic process control will be developed for BTA deep hole drilling, which will allow reliably tailoring surface integrity of components to specific demands, like an optimized fatigue performance.

Generation of tailored subsurface zones in steels containing metastable austenite by adaptive machining and validation by eddy current testing

In order to withstand high mechanical and tribological loads, it is important that the components not only have a high core ductility but also a hard surface. Typically, a suitable microstructure is created by heat treatment processes before the workpiece is machined. However, these processes are time and energy consuming and can lead to component distortion. It would therefore be of great advantage if no additional heat treatment process would be required to produce a hardened subsurface zone. Since turning is often already integrated as a machining process in production lines, it would be advantageous to create a hardened subsurface within this process. As there is no possibility to measure the hardness directly during the turning process, a soft sensor was developed to determine the properties of the subsurface directly during the machining process. Steels with metastable austenite are of particular interest in this context, as metastable austenite can be converted into martensite by deformation. The amount of martensite produced in the subsurface can be adjusted provided that suitable turning parameters can be found. For this purpose, a process parallel material removal simulation was used to determine the actual conditions governing the process. It was found that there is a correlation between the martensite content and the amplitude of the 3rd harmonic of eddy current testing. Therefore, an eddy current sensor accompanying the process can be used as a basis for controlling the turning process for tailored martensite volume content adjustment.

TECHNOGENIC LAYER IN THE AREA OF UNDERGROUND NUCLEAR EXPLOSIONS CONDUCTING BY THE EXAMPLE OF SEMIPALATINSK TEST SITE

Results of seismic investigation of the underground nuclear explosions area at the Semipalatinsk test site are considered. Using refracted waves method subsurface zones of surrounding geological media disintegration were revealed. These zones are characterized by decrease of P and S waves velocity on the value of 0,5-1,5 km/s and increase of Poisson coefficient on 0,07. Estimation of the induced fracturing was done; parameter of crack density measures up to 0,45.

ELECTRICAL RESISTIVITY METHOD APPLIED TO STUDY GROUNDWATER CONTAMINATION AROUND THE ALAGOINHAS CEMETERY, BAHIA, BRAZIL

ABSTRACT. To investigate the subsurface geological and hydrological conditions around the area of the Alagoinhas county cemetery – Bahia State, Brazil, 38 vertical electrical soundings using Schlumberger electrode array were performed to a maximum AB/2 spacing of 300 m. The electrical resistivity data were automatically inverted by computer, using a least square fit criterion to the error of the model with respect to the observed data and the help of public domain softwares RESIST V1.0 and RES1D. Geological constraints of lithological well logs were used to control the data interpretation, by fixing the number of layers and an initial model suggested by the interpreter. Represented as maps, sounding curves and geoelectrical cross-sections, the results allow: (i) to map the static water table depth, which in the more plain areas, are around 27m depth; (ii) to suggest that the subsurface zones of low true resistivity (<300Ω.m) are contamination plumes above the aquifer top, whose sources are related to the cemetery; and (iii) to detect electrical heterogeneities in the aquifer vadose zone, indicatives of the travel of the invading contamination.Keywords: electrical methods, resistivity, Alagoinhas, water contamination.RESUMO. Para investigar as condições geológicas e hidrológicas da subsuperfície na área do entorno do Cemitério Municipal de Alagoinhas, Bahia, foram realizadas 38 sondagens elétricas verticais centradas em pontos acessíveis da área. As sondagens foram executadas usando o arranjo Schlumberger de eletrodos, até espaçamentos máximos de eletrodos de corrente AB/2 de 300 m. Os dados de resistividade elétrica foram invertidos automaticamente em computador usando critérios de ajuste de mínimos quadrados para o erro domodelo comrespeito aos dados observados, usando os programas de domínio público RESIST V1.0 e RES1D. Informações geológicas de poços foram usadas no controle da interpretação, efetuada com o envolvimento do intérprete através da fixação do número de camadas e de um modelo inicial para a inversão. Apresentados na forma de mapas, curvas de sondagens e seções geoelétricas transversais, os resultados permitiram: (i) mapear o nível estático da água subterrânea que, nas partes mais planas da área, situa-se em torno de 27m de profundidade; (ii) indicar que as zonas subsuperficiais de baixas resistividades verdadeiras (<300 Ω.m) são plumas de contaminação na parte superior do aquífero, cuja fonte é associada ao cemitério; e (iii) detectar heterogeneidades elétricas na zona vadosa do aquífero apontando feições indicativas de rotas de invasão do contaminante.Palavras-chave: métodos elétricos, resistividade, Alagoinhas, contaminação da água.