Papers by Keyword: Mass Loss

Abstract: The effectiveness of the use of structures made of wood-polymer composites lies in ensuring their stability and durability both under wide temperature and humidity fluctuations and under biological action. Therefore, the object of research was the change in the properties of wood-polymer composites under biological influence and its protection when using synthetic resins capable of penetration by microorganisms. It has been established that in the process of biological action, the process of stability of wood-polymer composite consists in the use of materials with low biodegradation. Experimental studies on the determination of the biological stability of wood-polymer composites show that the maximum mass loss in the case of biodegradation of samples of wood-polymer composites based on starch was up to 15% and refers to biodegradation. The mass loss of samples of wood-polymer composites based on PVA glue did not exceed 5%, made from sawdust and synthetic resin was less than 1.5%, which refers them to bioresistant materials. The study of the compressive strength after biodegradation showed that the product from wood-polymer composite on starch and PVA glues is brittle. So, the lowest compressive strength was shown by the sample on starch with an average value of 0.1 MPa, a slightly better value was shown by the sample on PVA glue D3 – 0.98 MPa and the sample on PVA glue D4 – 1.92 MPa. However, for samples based on synthetic resins, the compressive strength is much higher and is: for wood-polymer composite based on epoxy resin, the average value is 3.1 MPa and polyester resin – 2.4 MPa.

Abstract: Aluminum alloys are known for their wide application in the automotive, river and marine boat constructions, but also in hydraulic systems (radiators/oil coolers). Their use is made by manufacturing parts directly from the semi-finished state, with or without certain volumetric heat treatments and surface hardening, depending on the functional role and the physical-mechanical characteristics pursued. Some of these parts work in hydrodynamic conditions, where cavitation manifests itself through erosion, such as: propellers of boats and barges, pump rotors in water cooling systems of automobiles. Visual analyzes performed on sailboat and powerboat propellers, after identical durations and operating conditions, showed cavitation erosion damage, different depending on the type of aluminum alloy. As a result, the paper presents and analyzes the behavior and resistance to erosion by vibratory cavitation of 4 types of aluminum alloys in the state of rolled semi-finished products. To highlight the differences in the destruction of structures under the cyclic stresses of cavitational microjets, macro and microscopic images of the eroded structure are used, as well as the curves with the values of the parameters specific to cavitation, recommended by the ASTM G32 -2016 norms and used in the research laboratory's custom. The analysis of the results shows that the resistance of the structure to cavitation erosion is dependent on the type of alloy, the degree of brittle intermetallic compounds and the mechanical properties specific to toughness.

Abstract: There are concerns towards the vulnerability of geopolymer concrete towards fire. High-temperature conditions instigate physical alterations and chemical reactions in concrete, which progressively breaks down the gel structure of cement. Consequently, the breakdown leads to an increase in tendency of drying shrinkage, changes to colors of aggregates and losses in load-bearing capacity and durability. In the present study, geopolymer concrete samples were exposed to fire at 1000°C at varying heating duration to investigate the effects on mass loss, residual strength and its microstructure properties. Samples with three grades of strength, GEO20, GEO40 and GEO60, were prepared. Six heating durations ranging from 30 to 180 minutes were adopted. Overall, mass losses were less than 3%, ranging from 1.65% as obtained by the low-strength concrete to 2.93% as obtained by the high-strength concrete. For the most part, as heating duration increased, residual strengths decreased, except for when residual strengths of low and medium-strength concrete initially increased at the heating duration of 30–60 minutes, where the exposure to fire facilitated geopolymerization. Analysis of the microstructure reveals that structural integrity of the matrix at high-temperature conditions is adequate. The study investigated the geopolymer concrete is able to resist the exposure to fire and must be seriously considered as an alternative to ordinary-Portland-cement-based concrete for the future of sustainable construction.

Abstract: The impact-echo method is commonly used for detection of flaws in concrete elements based on the shift in the thickness frequency of a plate-like member. However, there is a need to develop this efficient technique for other applications. This paper investigates the feasibility of using the impact echo-method for identifying corrosion of steel reinforcement in concrete structures. For this purpose, 180 reinforced concrete cubes were cast and tested. The main parameters studied were the amount of recycled aggregate (i.e. 0%, 25%, 50% and 100%), nanosilica (1.5% and 3%) and the steel bar diameter (12 and 20mm). Different levels of corrosion were electrochemically induced by applying impressed voltage technique for 2, 5, 10 and 15 days. The impact-echo results were correlated against the actual corrosion levels obtained by the mass loss method. The experimental results showed that the response of impact echo in terms of frequency peaks is found to be sensitive to the high and moderate levels of corrosion. However, no clear trend was observed at the initial stage of corrosion. It is demonstrated that the impact-echo testing can be effectively used to qualitatively detect the damage caused by corrosion phenomenon in reinforced concrete structures.

Abstract: In this paper, the effect of Sc addition (0.06 wt%) on the corrosion behavior of medium strength Al-Zn-Mg alloy is investigated by mass loss measurements, electrochemical experiment, intergranular corrosion and exfoliation corrosion tests. The results indicate the addition of Sc reduces the relative weight loss and enhances pitting performance as a result of grain refinement. The improved intergranular corrosion and exfoliation corrosion resistance caused by minor Sc addition are mainly attributed to the delay in both the initiation and advance stages of local corrosion.

Abstract: In this paper, a report is given on an experimental study of the combustion characteristics of six bundle lithium-ion batteries in a calorimeter. Several parameters including mass loss, heat release rate, surface temperature and heat flux distribution were measured to evaluate the hazards. The experimental results show that the lithium-ion batteries undergo fierce combustion processes. The total mass loss of six lithium-ion batteries fire is 67.8g, and the effective heat of the fire is 7.06 kJ/g. The highest temperature of the batteries fire is 816.9 °C and the maximum heat flux is 0.68 kW/m².The results provide scientific basis for the development of fire protection measures during the usage, storage and distribution of primary lithium batteries.

Abstract: The conjugate problem of aerodynamic heating of a blunted cone moving in the atmosphere at angle of attack at supersonic speed is considered. Three modifications of a thermal protection material based on coal-plastic with different proportions of a phenol-formalhyde binder and a carbon cloth are investigated. The effect of the material composition on the surface temperature and the mass loss characteristics is analyzed.

Abstract: One of the most harmful effects of cavitation, with strong influence on the life of the hydraulic machines is the destruction caused by erosion Since its discovery, over 150 years ago, evaluating the degradation is achieved by mass of material removed by erosion in a given time, which in the case of rotors and blades of hydraulic machines and marine propeller blades are equivalent by amount of electrode consumption for filling the voids left by the removal of material. Laboratory research on cavitation, from the beginning until now, evaluates the intensity of cavitation erosion rate, defined as a mass of material removed by erosion at a certain time of attack.The purpose of this paper is to develop and validate a technique based on vibroacoustic signal analysis of corroded samples, and that through their natural frequencies deviations to emphasize mass loss.The experimental measurement of the vibroacustic response of corroded specimens is carried out by using a condenser microphone. The vibration responses, in free-free conditions of the specimens, are analyzed using algorithm based on Fast Fourier Transform (FFT). The results are compared with other indicators of cavitation corrosion, such as lost mass and mass loss rate.

Abstract: The concrete dam under dead load, water pressure load and wind load is in high stress state for a long time, whose safety is in a dangerous station to a certain extent. The static calculation of the dam was done by ANSYS. In order to know the static characteristics of the dam, and to provide a theoretical basis for dam health diagnosis and routine maintenance, the variation of the dam stress and displacement caused by the stiffness degradation and mass loss was studied. The influence degree of the dam mass loss and stiffness degradation on stress and displacement were discussed. The results show that stress along the dam height (Y direction) is higher than it along the horizontal direction (X direction), the maximum stress difference is to about 4 times. The influence degree of dam stress and displacement caused by stiffness degradation is more serious than those by mass loss.

Abstract: This paper deals with the effect of calcium leaching on the microstructure and rupture strength of cement asphalt (CA) mortar. It is conducted by an accelerated experiment method with species obtained from construction site. Results show that the leaching process mainly contains a total leaching of CaOH2 (CH) and some other cement hydrations. The leaching is proved by the “portlandite dissolution front” on the cross-section of species using a reagent of phenolphthalein. As time goes, the species are continually leached, and then the loss of mass and porosity ratio are obviously increased. Fick’s law can describe the relationship between leaching depth and time very well. The loss of mass and increasing of porosity ratio respond to the shrinking of mechanical properties of CA mortar.