In this paper an attempt to determine the relationship between the electrical resistivity and the tensile strength and hardness of cast iron of
carbon equivalent in the range from 3.93% to 4.48%. Tests were performed on the gray cast iron for 12 different melts with different
chemical composition. From one melt poured 6 samples. Based on the study of mechanical and electro-resistive determined variation
characteristics of tensile strength, hardness and resistivity as a function of the carbon equivalent. Then, regression equations were
developed as power functions describing the relationship between the resistivity of castings and their tensile strength and hardness. It was
found a high level of regression equations to measuring points, particularly with regard to the relationship Rm=f(ρ). The obtained
preliminary results indicate the possibility of application of the method of the resistance to rapid diagnostic casts on the production line,
when we are dealing with repeatable production, in this case non variable geometry of the product for which it has been determinated
before a regression equation.
The paper describes the influence of graphite shape, size and amount to electrical properties of different cast irons. Experiments of electrical resistivity measurements were conducted during solidification of four different melts in different time intervals from melt treatment by inoculation and nodularization. Metallographic analyses were made in order to determine the shape, size, distribution and amount of graphite and correlate results with electrical resistivity measurements. It was found out that nodular graphite is giving the lowest electrical resistivity and is decreased during solidification. Electrical resistivity of lamellar cast iron is increased during solidification since lamellas interrupt metal matrix severely There is no significant difference in resistivity of vermicular cast iron from nodular cast iron. Smaller size of graphite and lower amount of graphite and higher amount of metal matrix also decrease resistivity.
The Lithuanian national standard of electric resistance is maintained as the basis for calibration and measurement capabilities published in the key comparison database of the International Bureau of Weights and Measures (BIPM). The stability and uncertainty of the resistance value measurements, performed since 2004 using the calibrated values of the standard resistors to predict their future behaviour as well as influence of environmental conditions, are discussed. Also discussed is the recovery of a standard resistor which had undergone a mechanical disturbance. It is concluded that the standard resistors operated by the Lithuanian National Electrical Standards Laboratory feature stable drift of resistance, which is well predicted by means of linear regression.
Wider application of silicon carbide (SiC) is anticipated for increasing the durability of various structural facilities. For this study, SiC was fabricated with decreased electrical resistivity for precision electrical discharge machining. Two-step reaction sintering by infiltration of molten Fe-Si alloy was applied for SiC fabrication. The procedure included first sintering at 973 K in Ar gas atmosphere and second sintering by spontaneous infiltration of molten Fe-75%Si alloy at 1693 K in vacuum. The sintered structure porosity became very low, forming 3C-type SiC. Results confirmed that molten Fe-75%Si alloy infiltration occurred because of reaction sintering. The electrical resistivity of the sintered SiC infiltrated by molten Fe-75%Si alloy can be improved to be two orders of magnitude lower than that by molten Si, consequently maintaining the high performance of SiC.
The durability of roads is dependent on the proper screening of the variations in subsurface geological characteristics and conditions through geo-engineering investigations and good construction practices. In this study, electrical resistivity tomography (ERT) technique was used to investigate the subsurface defects and potential failures along the substrate of Etioro-Akoko highway, Ondo State, southwestern Nigeria. Results of the inverse model resistivity sections generated for the two investigated traverses showed four distinct subsurface layers. The shallow clayey topsoil, weathered layer, and partially weathered/fractured bedrock have resistivity values ranging from 4–150 ohm-m, 10–325 ohm-m, and 205–800 ohm-m, with thickness values of 0–2 m, 0.5–12.5 m, and less than few meters to > 24 m, respectively. The fresh bedrock is characterised by resistivity generally in excess of 1000 ohm-m. The bedrock mirrored gently to rapidly oscillating bedrock troughs and relatively inclined deep penetrating multiple fractures: F1–F’1, F2–F’2 and F3–F’3, with floater in-between the first two fractures. These delineated subsurface characteristic features were envisaged as potential threats to the pavement of the highway. Pavement failures in the area could be attributed to the incompetent clayey sub-base/substrate materials and the imposed stresses on the low load-bearing fractured bedrock and deep weathered troughs by heavy traffics. Anticipatory construction designs that included the use of competent sub-base materials and bridges for the failed segments and fractured zones along the highway, respectively, were recommended.
The main scientific goal of this work is the presentation of the role of selected geophysical methods (Ground-Penetrating Radar GPR and Electrical Resistivity Tomography ERT) to identify water escape zones from retention reservoirs. The paper proposes a methodology of geophysical investigations for the identification of water escape zones from a retention fresh water lake (low mineralised water). The study was performed in a lake reservoir in Upper Silesia. Since a number of years the administrators of the lake have observed a decreasing water level, a phenomenon that is not related to the exploitation of the object. The analysed retention lake has a maximal depth between 6 and 10 m, depending on the season. It is located on Triassic carbonate rocks of the Muschelkalk facies. Geophysical surveys included measurements on the water surface using ground penetration radar (GPR) and electrical resistivity tomography (ERT) methods. The measurements were performed from watercrafts made of non-metal materials. The prospection reached a depth of about 1 to 5 m below the reservoir bottom. Due to large difficulties of conducting investigations in the lake, a fragment with an area of about 5,300 m 2, where service activities and sealing works were already commenced, was selected for the geophysical survey. The scope of this work was: (1) field geophysical research (Ground-Penetrating Radar GPR and Electrical Resistivity Tomography ERT with geodesic service), (2) processing of the obtained geophysical research results, (3) modelling of GPR and ERT anomalies on a fractured water reservoir bottom, and (4) interpretation of the obtained results based on the modelled geophysical anomalies. The geophysical surveys allowed for distinguishing a zone with anomalous physical parameters in the area of the analysed part of the retention lake. ERT surveys have shown that the water escape zone from the reservoir was characterised by significantly decreased electrical resistivities. Diffraction hyperboles and a zone of wave attenuation were observed on the GPR images in the lake bottom within the water escape zone indicating cracks in the bottom of the water reservoir. The proposed methodology of geophysical surveys seems effective in solving untypical issues such as measurements on the water surface.