Ana Pavlovic

CYCLIC STRESS ANALYSIS OF POLYESTER, ARAMID, POLYETHYLENE AND LIQUID CRYSTAL POLYMER YARNS

Mooring ropes used in offshore oil platforms are exposed to a set of extreme environmental conditions that can be crucial to their behaviour in service. Considering the elevated mechanical demands on these ropes imposed by both the undersea environment and the station keeping of the vessel, this paper is focused on the experimental determination of the yarns fatigue behavior. In order to be able to foresee and compare their general wear rate, a diagram that correlates the force to which the specimens are submitted to the number of cycles for failure for each material is achieved. The analyzed fibers are Polyester, Aramid, Polyethylne and Liquid Crystal Polymer (henceforth quoted as PET, AR, PE and LCP, respectively), and this work followed a pattern composed by a fixed test frequency and an established maximum stress for the diagrams.

Multi-agent team for engineering: a machining plan in intelligent manufacturing systems

This paper explores the modelling of technical expertise in metal-cutting processes in a form suitable for the development of computer-aided process planning (CAPP) in intelligent manufacturing systems using agent-oriented software technologies. Focusing on the selection of tools and cutting parameters in the design of machining operations, the ontology for the knowledge domain was first introduced, and then in that context identify and analyse some of the challenges that CAPP presents to the multi-agent system architect. In particular, interactions between operation design and setup design was investigated, issues arising from global impacts of local decisions in plan construction were examine, and differences between software agents and humans in comparable planning roles were discuss. The analysis leads to several multi-agent design patterns that help capture domain-specific know-how and integrate it into efficient team behaviour. A pattern is illustrated with a concrete scenario.

Increasing the Energy Efficiency in Solar Vehicles by Using Composite Materials in the Front Suspension

The pursuance of energy efficiency is a constant endeavour in modern mobility. Accordingly, several institutions worldwide have been investing time and resources in developing solar powered vehicles, directing their efforts towards a continual search of technical solutions aiming at attaining the highest energy efficiency levels. This work investigates and compares the mechanical behaviour of a front suspension wheel hub, subjected to its operational forces, when made by three different materials: aluminium, carbon or basalt fiber reinforced composites. Despite of investigating the sole mechanical response of materials, the comparison focuses on the feasibility of applying light and stiff composites in structural parts in order to improve the energy efficiency in vehicles due to weight reduction whilst granting safety.

Numerical modelling of ballistic impacts on flexible protection curtains used as safety protection in woodworking

Numerical control boring and routing machines use curtains made from resistant, but flexible materials to protect end-users from the projection of wood chips and tool pieces. These curtains allow the work piece to gently pass through, but firmly stop every small sharp piece or fragment ejected at the highest speed by fast drilling tools. Nowadays, curtains are commonly made in flexible thermoplastic materials as polyamide, polyurethane, polyvinyl chloride or similar materials. Safety issues to be addressed related to the risk of projection of parts during processing are defined by EN 847-1 and EN 847-2 standards, both collecting practical experiences from manufacturers and users. The effectiveness of these curtains was investigated by technical observations, experiments and even numerical simulations, but conclusive results are not available at the moment. This independent research, where ballistic impacts on flexible curtains were simulated using finite element (FE) methods, aims at verifying the effectiveness of specific protective barriers when realized and used in accordance with the UNI EN 848-3 standard. Numerical simulations were permitted to verify the congruity of the main barrier’s characteristics (materials, shape, depth, mass, cost, etc.) in relation to the projectile parameters (shape, mass, speed, direction, etc.) identifying their mutual influence. Outcomes from this research provide useful information toward the definition of a new way for the design of efficient curtains. A comparison between numerical simulations and experimental results coming from ballistic tests was also realized, permitting to validate this predictive methodology.

Simulation of hydraulic check valve for forestry equipment

Modelling and simulating complex systems, such as forestry equipment, are often the only way for their full analysis and design. This problem may lead to a stiff set of equations that are followed by numerical problems. In this paper two alternative approaches are investigated. The first one refers to the use of a variable step of integration by continuous models adjusted to the fastest processes. The second one refers to the approximation of fast transitions by ideal instantaneous mode-transitions and hybrid models. These two approaches are analysed in the framework of bond graph. The classical bond graph is adopted for description of the continuous models, and the switched bond graph is preferred for description of the hybrid models. The model of check valve is used as a working example for illustration of results. Matlab/Simulink tools are used for modelling and simulation.

Modelling the viscoelasticity of ceramic tiles by finite element

This research details a numerical method aiming at investigating the viscoelastic behaviour of a specific family of ceramic material, the Gres Porcelain, during an uncommon transformation, known as pyroplasticity, which occurs when a ceramic tile bends under a combination of thermal stress and own weight. In general, the theory of viscoelasticity can be considered extremely large and precise, but its application on real cases is particularly delicate. A time-depending problem, as viscoelasticity naturally is, has to be merged with a temperature-depending situation. This paper investigates how the viscoelastic response of bending ceramic materials can be modelled by commercial Finite Elements codes.

Wood resource management using an endocrine NARX neural network

Planning and forecasting wood resources implies a challenging analysis, which has a direct impact on planning human resources, production timeline, as well as stock management of wooden assortments, which requires a complex data analysis taking into account all inputs that define the yield of wooden material. This paper includes an analysis of monthly time series data from 1991 to 2015 which can be characterized as long time dependence data. In recent years, artificial neural networks have become a popular tool for time dependence data treatment. Therefore, a prediction of monthly requirements of treated wood is performed by developing a new type of neural network in this research. The nonlinear autoregressive model with exogenous inputs (NARX) is used as a foundation of a new network. NARX is a type of recurrent neural network which is a very effective tool for approximation of any nonlinear function, especially ones which could occur during a nonlinear time sequence prediction. The main contribution of this paper is the introduction of an artificial endocrine factor inside the standard NARX structure. The developed ENARX model provides an extra sensitivity of the network to environmental conditions and external disturbances, as well as its improved adaptive capability. The proposed network shows better forecasting performances compared to the default NARX network, thus establishing itself as an excellent prediction tool in the field of wood science, engineering and technology.

Optimisation of tool path for wood machining on CNC machines

Peripheral pocket or contour milling in wood machining, using flat end milling tool, can be performed with different tool paths. Technology designers of multi axis CNC wood machining use their experience and intuition to choose some of the options offered by CAM systems that determine the final shape of tool path, thus the generated tool path largely depend on individual judgment. Minimum cutting force, maximum dynamic stability of the process and minimum tool wear are achieved, or some other technological requirements are met, by using optimal tool path. Tool path optimisation is based on analysis of possible tool paths and determination of cutting parameters which are dependable of chosen tool path and are affecting the main wood processing factors. Axial and radial depth of cut, engagement angle, feed and feed rate profile are identified as key parameters dependable of tool path, and their values and variations along the tool path influence the cutting speed, tool wear and cutting force. Knowledge of values and changes of those key machining parameters along the tool path is necessary for simulation and monitoring of the main cutting factors during the wood machining process. NC code transformation methodology and generation of tool path parameters necessary for calculating all elements needed for tool movement simulation from given NC programs are shown. Blank and tool mathematical description are used with tool movement information for simulation of wood machining process. Simulation of cutting parameters and their variation along the tool path, presented in this paper, can be used as bases for development of methodology for choosing the most adequate tool path for wood machining of given contour considering minimum cutting force and cutting force variation, minimum tool wear, maximum productivity or some other criteria.

Crash safety design: Basic principles of impact numerical simulations for composite materials

Along with the steady evolution of the automotive industry, the concern for developing crash-safety technologies has always been one of the major concerns within the design of a vehicle. The understanding of the response of materials to impact is a traditional but ongoing subject of investigation worldwide, powered by the challenges imposed by novel and progressively complex materials such as fiber reinforced composite plastics, with the intrinsic failure mechanisms characteristic of the combination among each matrix and reinforcement selected. Acknowledging the current importance of numerical simulations in this study, the present work aims at providing a brief summary of basic notions for which regards impact explicit numerical simulations on composite materials, particularly considering two-dimensional ‘shell’ finite elements.Along with the steady evolution of the automotive industry, the concern for developing crash-safety technologies has always been one of the major concerns within the design of a vehicle. The understanding of the response of materials to impact is a traditional but ongoing subject of investigation worldwide, powered by the challenges imposed by novel and progressively complex materials such as fiber reinforced composite plastics, with the intrinsic failure mechanisms characteristic of the combination among each matrix and reinforcement selected. Acknowledging the current importance of numerical simulations in this study, the present work aims at providing a brief summary of basic notions for which regards impact explicit numerical simulations on composite materials, particularly considering two-dimensional ‘shell’ finite elements.

Mechanical Characterization of Gres Porcelain and Low-Velocity Impact Numerical Modeling

The current investigation was conducted on gres porcelain stoneware, a robust, impermeable and aesthetically pleasing type of ceramic mainly used for flooring, characterizing its resistance to bending and low-velocity impact, both representative efforts to which flooring tiles are constantly subjected as a consequence of the fall of objects and microsubsidences. The mechanical characterization was made through experimental tests following an adapted low-velocity impact testing routine, and the model was by validated numerical simulation through the explicit code software LS-DYNA based on the Johnson–Holmquist constitutive material model. Specimens were tested before and after an annealing cycle industrially used to allow porcelain folding. The thermal treatment demonstrated to infer a decrease in mechanical resistance on the material, understood as a consequence of its elevated maximum temperature and fast cooling rate. The numerical model calibrated successfully allows predicting the behavior of gres porcelain before and after annealing against low-velocity impact.