CTU Open Journal Systems (Czech Technical University, Prague / České vysoké učení technické v Praze)
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Measurement of tensile properties of selected rovings
Get PDFThis article is focused on measuring the tensile properties of chosen fibre materials, such as flax, alkali resistant glass or viscose. All selected materials were tested both pure and impregnated using epoxy resin. In this article, the tensile strength and the Young’s modulus were observed. Young’s modulus was measured using Digital Image Correlation. The suitability of the location of small speckle pattern targets, which are used for measurements of deformations, was first verified on the viscose fiber samples. Targets were applied directly to the roving and further to the sleeves made of epoxy resin used to fix samples in the test equipment. After the evaluation, the selected location was then applied to the selected types of rovings. Finally, the measured results were compared
Modulus estimation of polymers via nanoindentation – impact of surface roughness, peak force and testing speed
Get PDFNanoindentation is widely used to study small-scale structures in materials. The impact of varying testing conditions on the measurement’s accuracy is of high interest, and their influence on the characterization of polymeric materials is still quite scarce. Therefore, this study investigates varying loading and unloading rates paired with maximum loads ranging from 0.5 to 20 mN on Polyethylene samples with varying surface finishes after wet grinding. The indentation Data was analyzed using the Oliver & Pharr Method, and the resulting Modulus was compared with those obtained from macroscopical tensile tests. The hardness was compared to Shore hardness measurements. A correlation between the measured modulus values and the surface Quality was explored. The results prove the already established rule that the best surface finish (Sa = 0.07 μm) leads to the smallest standard deviation. However, they show that the modulus characterization is less influenced by surface roughness than hardness evaluations
Finite element analysis of nanoindentation pile-up and correction of projected contact area
Get PDFThis paper deals with the pile-up phenomenon that can occur during nanoindentation. Finite Element (FE) simulation of X5CrNiCuNb16-4 steel nanoindentation with pyramidal Berkovich indenter was done, and stress and strain beneath the indenter leading to pile-up behavior were analyzed in detail. Pile-up also influences the projected contact area, which should be corrected to include the pile-up into the Oliver-Pharr analysis. Accurate calculation of the projected contact area requires knowledge of its boundary. Few methods of boundary approximation were used, including approximation by the triangle and the semi-ellipse. For more precise approximation, the expression for parabolical approximation was derived. These methods were compared with the projected contact area calculated by finite element method. The most precise results were obtained using semi-elliptical and parabolical correction, which can be used for the determination of the projected contact area and its boundary
Local cohesion of splats in hybrid plasma spray coating as observed by in-situ experiment
Get PDFHybrid plasma spraying combines spraying of dry coarse powders and liquids (suspensions and/or solutions). Introduction of secondary miniature phase from the liquid may provide new coating functionality but also may have a significant influence on the local coating cohesion – increasing or decreasing it, depending on the materials combination and deposition conditions. In this study, cohesion of dissimilar splats within the early-stage experimental hybrid thermal barrier coating (TBC) was evaluated by in-situ SEM three-point bending (3PB) observation coupled with high-resolution strain mapping. Loading was carried out on the annealed sample simulating in-service thermal exposure. Observed coating failure confirmed that the coating exhibits a rather high intersplat cohesion lowering its strain-tolerance, which was presumably the reason for the relatively low thermal cycling resistance of the deposit
Micromechanical characterization of γ-irradiated cement paste exposed to different relative humidity conditions
Get PDFIn this study, well-hydrated cement paste samples made from Portland cement CEM I-42.5R were gamma irradiated with a 200 TBq 60Co source, resulting in a total absorbed dose of 13.82MGy. During irradiation, the samples were stored under specific relative humidity (RH) conditions of 11 %, 33 %, 76 %, 96 %, and water. Grid nanoindentation was performed on polished sample surfaces to assess the nanoindentation Young’s modulus of both irradiated and non-irradiated control samples. An increase in Young’s modulus by 9.3 % was observed for irradiated samples at low RH (11 %). Samples stored at medium RHs (33 %, 76 %) showed negligible differences in micromechanical properties. However, a significant decrease in Young’s modulus, approximately 15 %, was measured for samples stored at high RHs (96 %, water)
APPLICATION OF NEURAL NETWORKS IN SILICONE BREAST IMPLANT DIAGNOSTICS ON MAGNETIC RESONANCE IMAGING
Get PDFBreast augmentation is one of the most frequently performed cosmetic procedures worldwide, but it carries certain risks including breast implant rupture. Timely and accurate diagnostics of ruptures are crucial, as undiagnosed ruptures can lead to serious health complications. Imaging methods, such as magnetic resonance imaging (MRI), are recommended for the diagnosis of breast implants due to their high accuracy. However, current diagnostics rely heavily on the subjective interpretation and experience of the physician. This study investigates the potential of neural networks (NN) to address this limitation and improve the accuracy of rupture detection in silicone breast implants. We applied a deep learning-based neural network system trained on MRI images of breast implants to detect ruptures. The dataset included annotated MRI scans of symptomatic and asymptomatic patients with confirmed implant integrity or rupture. Several models were trained using ResNet-18, ResNet-50, and Xception networks, with various hyperparameter settings and augmentation techniques applied to enhance model performance and generalizability. The performance of the NN model was evaluated using confusion matrices and standard metrics such as true positive rate (TPR) and true negative rate (TNR). A semi-automated algorithm for the detection of intracapsular ruptures of breast implants on MRI was successfully developed. The algorithm correctly detected ruptures in 95.4% of cases and accurately identified cases without rupture in 86.7% of instances. Our findings highlight the potential of neural networks as a supportive tool in diagnosing breast implant ruptures. By semi-automating rupture detection, NNs can reduce diagnostic errors, expedite image evaluation, and optimize resource use in medical practice. The study underscores the importance of combining artificial intelligence with expert evaluation to enhance patient care and reduce costs in medical diagnostics
Surface plasma catalyzed composite industrial waste for NOx abatement in diesel exhaust
Get PDFA new approach has been proposed by catalyzing composite industry wastes with pulse discharge plasma for reducing oxides of nitrogen (NOx) in diesel exhaust. Solid wastes such as foundry sand and iron tailings were blended to form a new composite waste which is then introduced into a plasma reactor to extract the benefits of catalytic properties. The obtained NOx removal efficiency is 90% at 140 J/L in plasma catalysis as against 36% obtained with plasma alone
A practical way to apply a technique that accelerates time history analysis of structures under digitised excitations
Get PDFTime history analysis using direct time integration is a versatile and widely accepted tool for analysing the dynamic behaviour of structures. In 2008, a technique was proposed to accelerate the time history analysis of structural systems subjected to digitised excitations. Recently, this technique has been named as the SEB THAAT* (Step-Enlargement-Based Time-History-Analysis-Acceleration-Technique), and the determination of appropriate values for its parameter is introduced as the main challenge. To overcome this challenge, a procedure is proposed in this paper. The basis of the procedure is the comments on accuracy control in structural dynamics and numerical analysis of ordinary differential equations, legalised in the New Zealand Seismic Code, NZS 1170.5:2004. As the main achievement, by using the proposed procedure, we can apply the SEB THAAT and carry out the time history analysis clearly and with less parameter setting compared to the ordinary time history analysis. The proposed procedure is always applicable and, except when the behaviour is very complex, oscillatory and non-linear, the reductions in analysis run-time are considerable while the changes in accuracy are negligible. The performance can be sensitive to the problem, the integration method, the target response, and the severity of the non-linear behaviour. Compared to the previous tests on the SEB THAAT, the efficiency of applying the SEB THAAT using the proposed procedure is better, the sensitivity of the performance to the problem is lower, and a measure of accuracy is available. Compared to other techniques for accelerating structural dynamic analyses, the use of the SEB THAAT according to the proposed procedure has several positive points, including the simplicity of implementation
A new structural reconfiguration for multilevel inverters with fault tolerance capability
Get PDFKeeping electrical systems running is critical in industries especially in those that rely on static converters, for example in the case of inverters, continuous and safe of operation must be ensured even if one of the inverter’s static switch modules fails. This paper presents a method for fault detection in static converters. The study presents a 3-phase 3-level NPC (Neutral Point Clamped) inverter with IGBTs as static switches where open-circuit or closed-circuit faults are considered. In addition, leg failure and structural reconfiguration are also considered in this fault-tolerant inverter by adding a fourth 3-level leg
Transfer of master clock network technology to Czechoslovakia: Elektročas or Elektrozeit? German roots of Czechoslovak post-war timepieces 1923–1990
Get PDFIndustrial production of timepieces began in the Czech lands as early as the end of the 19th century. Public systems providing coordinated time data (information) began to be successfully distributed on a larger scale in Czechoslovakia by the company Jednotný čas in the first third of the 20th century. After that, the company changed its name several times, especially from the 1950s, to Elektročas/ZPA Pragotron. The company produced clocks for both the public and industry as well as split-flap displays for transport. Almost all clocks at Czechoslovak railway stations, airports, public spaces, public buildings, and offices came from this company. The mentioned clocks (their mechanical parts) required a lot of maintenance, as other devices depended on their correct functioning, e.g. clocks recording the observance of working hours in enterprises (punchclocks). The process of forming the company is interesting not only from the point of view of the implementation of time into the public civic space, but also from the point of view of details, e.g. the technological transfer of timekeeping technology from Germany to Czechoslovakia during the 20th century. Specifically, the technology known as uniform time (master clock networks taken over from the German company Elektrozeit by the Czech enterprise Elektročas). The topic of the article is, therefore, the analysis of the process of adoption of this technology and its later use in the second half of the 20th century in socialist Czechoslovakia