Skorohod-Olevsky viscous sintering model sensitivity to temperature distribution during the sintering process

U ovom radu proučavan je uticaj neuniformnosti temperaturnog polja po uzorku na rezultate simulacije procesa sinterovanja. Kao konstitutivni model ponašanja materijala upotrebljen je modifikovan fenomenološki Skorohod-Olevski viskozni model sinterovanja. Poređeni su rezultati simulacije dobijeni korišćenjem uniformne raspodele temperature, sa rezultatima koji koriste temperaturno polje dobijeno simulacijom zagrevanj auzorka. Poređenja se odnose na uzorke različiti hveličina, kako bi se ispitao različiti nivo neuniformnosti. Dobijeni rezultati u ovoj studiji pokazuju da postoje situacije u kojima je potrebno uzeti u obzir neuniformnost raspodele temperature po uzorku, odnosno da pojednostavljenje modela korišćenjem uniformne raspodele dovodi do neprihvatljivih grešaka.This paper investigates the influence of temperature field non-uniformity on sintering simulation results using the Skorohod-Olevsky viscous sintering model. As a difference to previous studies, here a thermal transient analysis is performed to provide a detailed temperature field over the component within sintering time. Results obtained using uniform temperature distribution are compared to those obtained using a nonuniform distribution derived from a transient thermal analysis. Results are compared for different geometry sizes, that lead to different temperature non-uniformity levels. The study has shown that the temperature nonuniformity cannot always be neglected and should be considered as a possible source of modeling error

Skorohod-Olevsky viscous sintering model sensitivity to temperature distribution during the sintering process

U ovom radu proučavan je uticaj neuniformnosti temperaturnog polja po uzorku na rezultate simulacije procesa sinterovanja. Kao konstitutivni model ponašanja materijala upotrebljen je modifikovan fenomenološki Skorohod-Olevski viskozni model sinterovanja. Poređeni su rezultati simulacije dobijeni korišćenjem uniformne raspodele temperature, sa rezultatima koji koriste temperaturno polje dobijeno simulacijom zagrevanj auzorka. Poređenja se odnose na uzorke različiti hveličina, kako bi se ispitao različiti nivo neuniformnosti. Dobijeni rezultati u ovoj studiji pokazuju da postoje situacije u kojima je potrebno uzeti u obzir neuniformnost raspodele temperature po uzorku, odnosno da pojednostavljenje modela korišćenjem uniformne raspodele dovodi do neprihvatljivih grešaka.This paper investigates the influence of temperature field non-uniformity on sintering simulation results using the Skorohod-Olevsky viscous sintering model. As a difference to previous studies, here a thermal transient analysis is performed to provide a detailed temperature field over the component within sintering time. Results obtained using uniform temperature distribution are compared to those obtained using a nonuniform distribution derived from a transient thermal analysis. Results are compared for different geometry sizes, that lead to different temperature non-uniformity levels. The study has shown that the temperature nonuniformity cannot always be neglected and should be considered as a possible source of modeling error

Numerical Evaluation of the Elastic Properties of Carbon Fiber Reinforced Composite Material at Elevated and Lowered Temperatures

The effect of elevated and lowered temperatures on the elastic properties of carbon fiber-epoxy composite material was studied using multi-phase unit cell (MPUC) numerical model. Evaluation of the elastic properties of carbon fiber-epoxy composite material is based on the finite element method. Obtained results confirmed that elevated and lowered temperature has noticeable influence on elastic properties of carbon fiber-epoxy composite material. As demonstrated, this fact has considerable influence on accurate evaluation of generated thermal stresses in real laminated composite structures, exposed to extremely high or low operating temperatures

Numerical evaluation of thermal stresses generated in laminated composite structure exposed to low temperatures

This paper presents numerical calculation of thermal stresses generated in a carbon fiber-epoxy laminated composite structure which is operating at low temperatures. The thermal stress evaluation is based on the finite element method. A sample problem involving generated thermal stresses in a real laminated composite structure, exposed to low temperatures (four different temperature levels), is analyzed and discussed. Obtained results suggest that these thermal stresses remarkably decrease the strength of the laminated composite structure

Numerical evaluation of thermal stresses generated in laminated composite structure exposed to low temperatures

This paper presents numerical calculation of thermal stresses generated in a carbon fiber-epoxy laminated composite structure which is operating at low temperatures. The thermal stress evaluation is based on the finite element method. A sample problem involving generated thermal stresses in a real laminated composite structure, exposed to low temperatures (four different temperature levels), is analyzed and discussed. Obtained results suggest that these thermal stresses remarkably decrease the strength of the laminated composite structure

Numerical Evaluation of the Elastic Properties of Carbon Fiber Reinforced Composite Material at Elevated and Lowered Temperatures

The effect of elevated and lowered temperatures on the elastic properties of carbon fiber-epoxy composite material was studied using multi-phase unit cell (MPUC) numerical model. Evaluation of the elastic properties of carbon fiber-epoxy composite material is based on the finite element method. Obtained results confirmed that elevated and lowered temperature has noticeable influence on elastic properties of carbon fiber-epoxy composite material. As demonstrated, this fact has considerable influence on accurate evaluation of generated thermal stresses in real laminated composite structures, exposed to extremely high or low operating temperatures

Design and Development of Static Load Test Stand for Various Sizes of Multicopter Arms

The constant advance in the usage of unmanned aerial vehicles (UAVs) of all types, including electric multicopters (rotary-wing drones), requests further advancement on all project levels in order to create a competitive final product. With the usage of composite materials, mainly carbon fiber in epoxy resin, it is possible to have a very lightweight structure that is strong enough to sustain all anticipated loads. Arms are a crucial part of multicopter structures that are often made entirely of composite materials. Each multicopter arm has at least one electric motor and propeller on one and a connection with the body on the other end. A static load test stand for various sizes of arms is designed and developed in order to test prototypes within the design process and to be able to test the mechanical characteristics of each produced final part that will be later assembled with other parts. The test stand consists of a robust steel frame, part mounting clamps, a movable low-speed hydraulic cylinder with an appropriate hydraulic power pack powered by an electric motor which is controlled by a variable frequency drive, a load cell for force measurement, and a linear displacement transducer for displacement. A custom digital electronic circuit with a microcontroller is developed in order to control the actuator and obtain data from sensors. Also, custom user-friendly software with a graphical user interface is designed to control experiments and process measurements

Virtual laboratories for education in science, technology, and engineering: A review

Within education, concepts such as distance learning, and open universities, are now becoming more widely used for teaching and learning. However, due to the nature of the subject domain, the teaching of Science, Technology, and Engineering are still relatively behind when using new technological approaches (particularly for online distance learning). The reason for this discrepancy lies in the fact that these fields often require laboratory exercises to provide effective skill acquisition and hands-on experience. Often it is difficult to make these laboratories accessible for online access. Either the real lab needs to be enabled for remote access or it needs to be replicated as a fully software-based virtual lab. We argue for the latter concept since it offers some advantages over remotely controlled real labs, which will be elaborated further in this paper. We are now seeing new emerging technologies that can overcome some of the potential difficulties in this area. These include: computer graphics, augmented reality, computational dynamics, and virtual worlds. This paper summarizes the state of the art in virtual laboratories and virtual worlds in the fields of science, technology, and engineering. The main research activity in these fields is discussed but special emphasis is put on the field of robotics due to the maturity of this area within the virtual-education community. This is not a coincidence; starting from its widely multidisciplinary character, robotics is a perfect example where all the other fields of engineering and physics can contribute. Thus, the use of virtual labs for other scientific and non-robotic engineering uses can be seen to share many of the same learning processes. This can include supporting the introduction of new concepts as part of learning about science and technology, and introducing more general engineering knowledge, through to supporting more constructive (and collaborative) education and training activities in a more complex engineering topic such as robotics. The objective of this paper is to outline this problem space in more detail and to create a valuable source of information that can help to define the starting position for future research

Contamination, risk, and source apportionment of potentially toxic microelements in river sediments and soil after extreme flooding in the Kolubara River catchment in Western Serbia

Climate change is contributing to an increase in extreme weather events. This results in a higher river flooding risk, causing a series of environmental disturbances, including potential contamination of agricultural soil. In Serbia, the catastrophic floods of 2014 affected six river basins, including the Kolubara River Basin, as one of the larger sub-catchments of the large regional Sava River Basin, which is characterized by large areas under agricultural cultures, various geological substrates, and different types of industrial pollution. The main aim of this study was to establish the sources of potentially toxic elements in soil and flood sediments and the effect of the flood on their concentrations. Field sampling was performed immediately after water had receded from the flooded area in May 2014. In total, 36 soil samples and 28 flood sediment samples were collected. After acid digestion (HNO3), concentrations of the most frequent potentially toxic elements (PTE) in agricultural production (As, Cd, Cr, Cu, Ni, Pb, Zn) and Co which are closely related to the geological characteristics of river catchments, were analyzed. The origin, source, and interrelations of microelements, as well as BACKGROUND: values of the PTE of the river catchment, the pollution index (Pi), enrichment factor (Ef), and geological index (Igeo), were determined, using statistical methods such as Pearson correlations, principal component analysis (PCA), and multiple linear regression (MLRA). The content of the hot acid-extractable forms of the elements, PCA, and MLRA revealed a heavy geological influence on microelement content, especially on Ni, Cr, and Co, while an anthropogenic influence was observed for Cu, Zn, and Cd content. This mixed impact was primarily related to mines and their impact on As and Pb content. The pseudo-total concentrations of all the analyzed elements did not prove to be a danger in the catchment area, except for Cu in some samples, indicating point-source pollution, and Ni, whose pseudo-total content could be a limiting factor in agricultural production. For the Ef, the Ni content in 59% soil and 68% flood sediment samples is classified into influence classes. The similar pseudo-total contents of the elements studied in soil samples and flood sediment and their origin indicate that the long-term soil formation process is subject to periodic flooding in the Kolubara River Basin without any significant changes taking place. This implies that floods are not an endangering factor in terms of the contamination of soil by potentially toxic elements in the explored area

Dynamics based modeling of wheeled platform for humanoid robot torso

From the ancient mythology till the modern times, people were trying to build an artificial mechanical replica of themselves. Inspired by this long tradition of various engineering projects, we will hereby describe a partly humanoid robotic structure. Our robotic configuration is composed out of an anthropomimetic upper body, but instead of legs it uses a wheeled cart for the motion. In our research, this so-called semi-anthropomimetic structure has a four-wheeled cart. This work is aiming to analyze the behaviour of the robot that is exposed to different kind of external disturbances. Disturbances coming from the outside in the form of external forces (impulse and long term) simulate the interactions of the robot and its ambience. Necessary simulations were thoroughly executed (in that way analyzing robotic balance) and proper size of the cart is evaluated following the ZMP theoretical background. [Projekat Ministarstva nauke Republike Srbije, br. TR-35003 i br. III-44008