Cristiano Fragassa

Effect of PVDF nanofibers on the fracture behavior of composite laminates for high-speed woodworking machines

The use of light composites when designing fast moving parts for machine tools is emerging as a very efficient solution for improving productivity. Nevertheless, several aspects of these materials have to be carefully considered in woodworking. This paper aims to investigate the effect of interleaved nanofiber on mode I interlaminar properties and the failure modes that occur in this mode. For this purpose, woven carbon/epoxy laminates with and without Polyvinylidene difluoride nanofibers in the mid-plane were subjected to mode I interlaminar loading and the results were compared with each other. Acoustic emission technique was also utilized for better understanding of the failure modes that occurred in the virgin and nanofibers-modified specimens. Mechanical data and acoustic emission parameters associated with pattern recognition analyses were used for investigation of the interlaminar properties and the occurred failure modes. The mechanical results showed that the electrospun nanofibrous mat was able to increase the GIC by 98%. The acoustic emission results highlighted that different failure modes were the origin of different interlaminar failure behaviors. Different percentages of the failure modes in the modified specimens compared with the virgin ones were observed. Furthermore, the number of occurred interlaminar failure modes diminished in the modified composite layers.

Effect of natural fibers and bio-resins on mechanical properties in hybrid and non-hybrid composites

The aim of the present experimental investigation was to perform a comparative analysis concerning the influence on mechanical properties of natural fibers and/or bio-resins in reinforced thermoset composites. Flax and basalt fibers were selected as natural reinforcements, as single constituents or in hybrid combination. Glass synthetic fibers were used for comparison. Eco-friendly matrixes, both epoxy or vinylester, were considered and compared with composites based on traditional resins. Samples were fabricated by hand lay-up and resin infusion techniques. Cures were accelerated and controlled by applying heat and pressure in autoclave. Tensile, flexural and impact tests were carried out according to ASTM standards.

A Brief Review on Determinant Aspects in Energy Efficient Solar Car Design and Manufacturing

In the past decades, sustainable means of transportation have become an important issue once they are potentially able to supply modern transport needs whilst not harming the environment. Accordingly to this general interest, solar vehicles have been developed by several institutions worldwide to participate in international class races, promoting this research field. As the competitiveness increased, solar technologies evolved toward noteworthy solutions for a modern and sustainable mobility. Hence, this work intends to provide a general overview on solar vehicles, particularly regarding the main design and manufacturing features that allowed to increase energy efficiency, considering the relevance of this factor for solar cars. Due to the huge amount of information available, a limited number of aspects was selected for further analysis, mainly related to design and engineering, such as: weight reduction, aerodynamics and kinematics, mechanics and advanced materials.

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.

Utjecaj uzdužnog pomaka na nelinearne glavne parametarske rezonancije tračne pile

The transverse vibrations of axially moving Timoshenko beam, as suitable mathematical models for woodworking bandsaws, are investigated. Special attention is paid to the influence of longitudinal displacement effect, as opposed to most models which can be usually encountered in the literature. This influence is introduced through the integro-partial differential equations. The expressions for the mode shapes in the case of hybrid supports with different torsion spring stiffness on the support points are also derived. The influence of mean beam velocity and axial tension on its natural frequencies and mode shapes is also investigated. Based on the nonlinear model, the amplitudes of the steady-state response are calculated for the case of principal parametric resonance. Developed program solution was tested on a number of earlier known examples. Present theoretical considerations, with the help of the program solution, is also used to analyse an example from industrial practice.

Material selection in machine design: The change of cast iron for improving the high-quality Iin woodworking

This paper analyzes the possibility to substitute the gray iron, traditionally used for the production of relevant parts in woodworking machines, with ductile iron or vermicular iron. A large experimental campaign to determine the mechanical beavior of ductile and vermicular irons respect to tensile, fatigue, and fracture loads was conducted and the microstructures were also analyzed. Results show that ductile or vermicular cast iron in parts and components of machine tools could provide additional stiffness and resistance for the high precision woodworking respect to Gray Iron. A balanced utilization of these alternative irons would permit to take a full advantage by each specific property (as strength, hardness, weight, etc.).

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.

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.

Aerodynamic Effects of Manufacturing Tolerances on a Solar Car

In the case of solar vehicles, since the primary necessity is to optimise the energy efficiency during motion, many efforts are addressed by designers in searching the perfect aerodynamics. It means, in particular, the minimization of the drag force at cruising speeds and an elaborated vehicle’s Computer-Aided Design (CAD) are the principal result of this activity. Despite, these efforts can be nullified by geometrical tolerances emerging from manufacturing. In this paper, the effects of tolerances introduced by composite manufacturing processes are investigated combining 3D scanning technology and Computational Fluid Dynamics (CFD). After the solar car manufacturing, a reverse engineering process is executed with the aim to scan the vehicle’s body and compare it to the initial theoretical design. Geometric deviations are found and their aerodynamic consequences are evaluated in terms of aerodynamic losses.