Abstract
Advanced Material Characterization of Thermoplastic Composites at the Forming State
Amirth N.1, Marchese G.2, Getti C.1, Sisca L.1, Airale A.1, Palenzona M.1, Romeo A.1, Ferraris A.1, Carello M.1 and Monti M.2
1Department of Mechanical and Aerospace Engineering Department, Polytechnic University of Turin, Turin, Italy
2Proplast, Rivalta Scrivia, Alessandria, Italy
Fiber reinforced composites have been increasingly used in the last decades due to the performance-to-weight ratio, which is higher than the other structural materials. In the fiber composite field, beside the thermosetting matrices, the use of thermoplastic (TP) polymers has risen up a great interest by the industrial world, since they are more suitable for the high production volumes typical of mass production. The accurate structural design of a TP composite component needs to take into account the modification in the fiber direction of the laminate induced by the thermoforming process. Advanced processing simulations can be used to predict the local variation of the microstructure, which is actually present in the produced component.
The present work aims to establish a methodology for an exhaustive characterization of TP composite laminate at the forming state for advanced finit element (FE) process simulation, which is particularly interesting because of the lack of industrial standards. This research presents the experimental protocols for tensile, shear (trellis frame and bias extension tests), friction and bending state of the laminate. Corresponding FE material cards are created by integrating finite element analysis at every step. The final scope is to attain a more accurate processing simulation by analysing the testing variations to obtain accurate input parameters, thereby simplifying the product development phase of general lightweight thermoplastic components.
Structure and Properties of New Polyolefin Thermoplastic Elastomers
Bertini F., Canetti M., Pierro I., Zanchin G., Ricci G. and Leone G.
Institute for Macromolecular Studies ISMAC, National Research Council CNR, Milan, Italy
Thermoplastic elastomers (TPE) are attractive materials because they combine the processing advantages and recycling potential of thermoplastics with the flexibility and low modulus of elastomers. This paper reports the synthesis and characterization of polyolefin TPE from α-olefin chain-walking polymerization. The polymers were characterized by 13C NMR for quantification of the total branching level and branch-type distribution. The numerous combinations of monomer insertions and chain-walking paths afford polymers with unique microstructure and properties, depending on the monomer length. The thermal properties and crystallinity of the polymers are strongly controlled by their microstructure: the presence of long branches interferes on the crystallization and melting behavior. A comprehensive investigation of the mechanical behaviour of the polymers by means of uniaxial stretching until failure, step-cycle and creep tensile tests was carried out. Overall, the polymers exhibit a broad spectrum of tensile properties, depending on their microstructure and crystallinity. 1-Octene and 1-decene polymers behave as elastomers with excellent mechanical properties, i.e., high elongation at break (up to 1500%) and good strain recovery, while the 1-octadecene polymer behaves as plastomers.
Production by Rapid Prototyping of Samples for Testing of Self-Produced Starch-Based Bioplastics
Cardorani P., Paciotti D. and Santulli C.
School of Architecture and Design, University of Camerino, Ascoli Piceno, Italy
In this work, thermoplastic biopolymers were developed from corn starch, hydrochloric acid, water, agar fibers, isinglass and glycerol, with different proportions of the ingredients. 3D printing allowed rapid realization of normalized samples to perform mechanical and chemical tests. It has moreover highlighted the need of a controlled drying at the moment in which extrusion takes place for the correct solidification of experimented materials. Samples for Charpy impact tests (according to ASTM D256 standard), Shore hardness tests (ASTM D2240) and tensile tests (ASTM D638) were realized. Following this, printing tests of basic geometrical shapes have been realized, including cube, cylinder and parallelepiped, both in a full structure and in an empty one.
The material was printed in a Delta WASP 40 70 printer, which is a 3D printer for dense fluid materials, such as clay, therefore using the LDM (Liquid Deposition Modeling) technique. To allow the above printer extruding a fluid material instead of the typical filament, hardware and software of a RepRap printer were both modified. The objective was to replace the “extruding block” of FDM or FFF technique (Filament Deposition Modeling or Fused Filament Fabrication), with a syringe containing and expelling the material, deciding, according to the engine steps, controlled by the software, its descent velocity to expel from the syringe nozzle the right amount of material necessary to compose the different layers of the final model.
Experimental Analysis of AM Metal Lattices for Structural Design of Lightweight Components
De Pasquale G.
Department of Mechanical and Aerospace Engineering, Polytechnic University of Turin, Turin, Italy
The work is about lightweight materials with lattice structure fabricated with SLM and EBM processes with Ti6Al4V alloy.
Static characterization provided force-displacement curves able to validate the equivalent properties predicted by FEM and homogenization-based models. Lattice samples are built with parametric variation of cell dimensions, strut thickness, and cell staggering. The EOS M290 and the Arcam Q10 machines are used for SLM and EBM processes respectively. Samples are treated thermally in TAV furnace and subjected to ultrasonic cleaning. Then, they are encapsulated into polymer and cut before detections with optical microscope. The servohydraulic testing machine is used for static characterization of load-displacement curves. The stiffness variation during the successive layer collapse is also monitored, revealing progressive structural softening. Failure mechanisms and cracks direction propagation under compressive load are also studied. Three main collapse modes are observed. Mode 1 is associated with buckling of the strut intersections, mode 2 is related to brittle fracture of horizontal struts under shear forces, and mode 3 is the combination of first two modes. Dynamic tests and simulations are conducted to measure resonance frequency shift and global stiffness loss during localized ruptures of lattice struts. Resonance variation is the order of 25% are efficiently predicted for further applications in monitoring of lattice wellness through FFT analysis.
Tension-Tension Fatigue Resistance of Fibre Rope Terminations to Be Used in Dynamic Applications
Holschemacher D.
Professorship of Materials Handling and Conveying Engineering, Technische Universität Chemnitz, Chemnitz, Germany
Mechanical components made from high-strength synthetic fibres become more important because of their potential for lightweight construction. High-strength fibre ropes are, due to their high specific strength, predestined to be used in dynamically loaded applications in conveying engineering. Subject of present investigations are ropes and rope-like structures. A problem to be solved is the realization of end connections. The requirements imposed on the design of those connections are high. Among other things, rope end connections must endure static and dynamic loads, exhibit the same temperature stability as the rope and have the same degrees of freedom. Every rope can, irrespective of design, material and diameter, only be loaded with the force that can be borne by the end connection. Admittedly, the state of knowledge regarding needed rope end connections and for adequate force transmission is insufficient. This is a weak point in rope structure which leads to high oversizing of the rope. Connecting mechanisms known from steel wire ropes cannot be transferred to the fibre ropes because of fibre’s higher sensibility to bending and compressing forces and their creep behaviour.
Main subject of the presented work is the development of a test method suitable for high-strength fibre ropes, and further a competitive investigation of the performance of common rope end connections for high-strength fibre ropes under tension-tension loading.
Dynamic Mechanical Analysis of Bovine Meniscus: a Map of the Compressive Modulus in Longitudinal and Radial Directions
Lagazzo A., Giuliani F. and Barberis F.
Department of Civil, Chemical and Environmental Engineering DICCA, University of Genoa, Genoa, Italy
The storage modulus (E’) displays lower values in correspondence of the regions with higher vascularization (red zone). This differences are also evident considering the loss factor Q-1 = E”/E’, that, in the peripheral region, is about three time higher than the one measured in the internal zone without vascularization (white zone).
References
1. Baker, BE, et al. Am J Sports Med. 1985;13:1–4.
2. Nguyen AM et al., J Orthop Res. 2012; 30(1):95-102
Determination of Mechanical Properties of Acrylamide Based Polymers Obtained by Gamma Radiation
Mahmudi N.
Faculty of Natural Sciences and Mathematics, University of Tetovo, Tetovo, Republic of Macedonia
Different monomers such as AAm, MAAm, HEMA and the MBA crosslinker were used for obtaining polymers with desired different mechanical properties. Different MBA amounts and doses of irradiation condition the mechanical properties, the swelling degree in equilibrium and elastic module. There was determined the swelling kinetics, such as swelling ratio ks, transport exponent n, diffusion coefficient D and diffusion constant k related to the structure of polymer crosslinked network. The study revealed that different crosslinked networks can be obtained by using different amount of crosslinker MBA which alters the swelling characteristics of the hydrogel. Elastic properties of hydrogels were determined by using a Zwick Z010. The molecular weight between crosslinks and the effective cross-link density of hydrogels νe were calculated from swelling, while stress-strain curves of hydrogels from compression tests were evaluated to calculate shear modulus values G, the average molecular weight between junctions and the effective crosslink density. A comparative analysis between the cross-link density or average molecular weight of hydrogels by using swelling tests and mechanical measurements has been made. Results have shown that simple compression analyses can be used for the determination of the effective cross-link density of hydrogels without the need for some polymer-solvent based parameters as in the case of swelling based determinations.
Mechanical Fixation in Anterior Cruciate Ligament Reconstruction: an in Vitro Laboratory Study at Time Zero
Monaco E., Labianca L., Fabbri M., Lanzetti R. M., Del Duca A., Rota P. and Ferretti A.
Orthopaedic Department and “Kirk Kilgour” Sports Injury Center, Sant’Andrea Hospital, Sapienza University of Rome, Rome, Italy
Group A: TightRope-RT with the All-inside GraftLink technique
Group B: EndoButton CL and BioRCI
Group C: Rigidfix and Intrafix
Group D: Transfix and Deltascrew
Group E: Swing Bridge and Evolgate
After a preconditioning with a tensile load of 90 N, 1000 cycles between 0 and 150 N were applied to the complex before the final load to failure. Stiffness and strength were evaluated at the final pullout, displacement (slippage) at first, 100th, 500th, and 1000 cycles. Test were performed using a Z010 Zwick Roell tensile machine. Data were recorded with testXpert 8.1 software (Zwick Roell).
Investigation of Wood-Based Materials Under Impact Bending Load to Evaluate the Suitability of Materials for Use in Mechanical Engineering
Müller C.
Professorship of Materials Handling and Conveying Engineering, Technische Universität Chemnitz, Chemnitz, Germany
In the present work wood-based materials are compared under static bending load and impact bending load. Several thermal stress conditions are applied to selected materials, furthermore one relevant notch geometry is tested.
The objective of these tests is to investigate the suitability of distinct wood materials for security-relevant applications with the occurrence of impact loads. For this purpose the basics of instrumented impact testing and wood-based materials are acquired. The state of the technology and a comprehensive analysis of original studies are subsequently presented. On this basis an own impact pendulum was developed to allow force-acceleration measurement with high sample rates. The apparatus is validated by several methods and the achieved signals are tested for plausibility. A general approach of testing for adequate sample size is implemented and applied to the tested samples. Based on the characteristic values of the static bending and impact bending tests a classification model for material selection and comparison is proposed. The classification model is an integral approach for mechanical performance assessment of wood-based materials. In conclusion a method for impact testing of components (in future studies) is introduced.
Numerical and Experimental Investigation on Induction-Welded Thermoplastic Composites Joints: Mechanical Performance and Optimum Processing Parameters
Palmieri B.1 and Galise F.1,2
1Department of Chemical, Materials and Industrial Production Engineering, University of Naples Federico II, Naples, Italy
2Fiat Research Center, Pomigliano D’Arco, Naples, Italy
Development of thermoplastic matrix composite materials has increased considerably, due to the possibility for recycling, reparability and weldability. Among the welding techniques, induction welding has allowed obtaining joints with high mechanical features.
Usually polymers cannot be heated by electromagnetic induction because they are neither electrically conductive nor electromagnetic. So, it is necessary apply susceptors, such as carbon fiber; in this case, the basic condition for the generation of eddy currents is the presence of closed electrical loops.
Induction heating of fiber reinforced composites represents a very complex Multiphysics process, which is characterized by the electromagnetic and heat transfer physics phenomena.
In this paper numerical simulations and experimental tests of the process were carried out to optimize the process parameter such as temperature, current and holding time.
Finally, the performance of the welded joint was evaluated by Single Lap Shear (SLS) test according to ASTM D5868 standard method.
The results of the mechanical test performed were used to experimentally validate the numerical model, as well as to optimize the process parameters. Moreover, the extension of the welded area, measured after the mechanical test performed, was correlated with the results of the numerical model; in addition, the optimal process parameters were identified studying the mechanical performances obtained from the SLS tests.
Testing High Performance and Lightweight Additively Manufactured PA12 Lattices
Rosso S.1, Curtarello A.1, Boscolo Bozza D.2, Meneghello R.2, Concheri G.1 and Savio G.1
1Department of Civil, Environmental and Architectural Engineering - Laboratory of Design Tools and Methods in Industrial Engineering, University of Padua, Padua, Italy
2Department of Management and Engineering -Laboratory of Design Tools and Methods in Industrial Engineering, University of Padua, Vicenza, Italy
In the last decades, Additive Manufacturing (AM) technologies allowed to produce customized and optimized parts in a layer-wise fashion, bringing freedom in shape and complexity, reducing waste and enabling to economically produce small batches. The possibility of putting material only where it is needed is fully exploited by topology optimization at a macroscale level and by lattice structures at a mesoscale level.
Current methods for geometric modeling of lattice structures implemented in commercial CAD software show critical issues such as scalability, robustness and automation. Recent researches proposed a novel approach based on direct polygonal mesh modeling to overcome the aforementioned limits. To obtain smooths surfaces, the method exploits subdivision algorithms to avoid stress concentration at struts nodal points.
In this work, numerical tests were carried out to analyze stress concentration factor and surface curvature, which is closely linked to stress concentration. Then, static and fatigue tests were numerically simulated and compared with the results of experimental tests both on PA 12 bulk material and lattice structures specimens based on cubic cells, produced by two different AM technologies: selective laser sintering and high-speed sintering.
Results show that wider and continuous surface curvatures, obtained by the proposed geometric modeling approach, result in a lower stress concertation factor, improving fatigue life as experimental results confirm.
Dynamic Response of Hybrid Natural Fiber Reinforced Polypropylene Laminates
Russo P.1, Papa I.2 and Lopresto V.2
1Institute for Polymers, Composites and Biomaterials, National Research Council, Pozzuoli-Naples, Italy
2Department of Chemical, Materials Engineering and Industrial Production, University of Naples Federico II, Naples, Italy
The development of innovative eco-friendly lightweight structures is an issue of considerable interest [1]. Research has been conducted into to use of different types of natural fibres such vegetable [2] and mineral fibers [3]. This work deals with the low-velocity impact behavior of polypropylene basalt composite laminates including a core of hybrid poly(lactic acid)/flax woven fabric (BFB) taking polypropylene/basaltfabric samples obtained under the same processing conditions and having similar thickness as the reference material.
Preliminary results show that the presence of the hybrid core can positively affect the penetration performances: surprisingly, samples resist to the completed penetration obtaining only a confined delamination on the front side and a detachment of the last layer of the specimens (fig. 1).
Image of penetrated BFB sample a) front; b) back.
References
[1]. Witik, R.A., Payet, J.,Michaud, V., Ludwig C., Manson, J.-A.E.,“Assessing the life-cycle costs and environmental performance in lightweight materials in automobile applications” Composite Part A, 42, 1694-1709(2011).
[2]. I. Papa, P. Russo et al., Ultrasonic damage investigation on woven jute/poly (lactic acid) composites subjected to low velocity impact, September 2016, Composites Part B 115 (2017) 282-288, DOI 10.1016/j.compositesb.2016.09.076
[3]. Lopresto V et al. Mechanical characterization of basalt fibre reinforced plastic. Composites Part B Engineering, 2011, Vol. 42, pp. 717-723.
DIY Bioplastics: Challenges and Opportunities in the Assessment of Their Mechanical Properties
Santulli C.
School of Architecture and Design, University of Camerino, Ascoli Piceno, Italy
The production of DIY bioplastics is aimed at evaluating the expressive and functional possibilities of materials to be molded, but also in prospective applications such as use in different techniques of rapid prototyping. These materials can have an interest for designers to obtain more customized products and to establish a closer relationship with material manufacturing, a practice often referred to as “material tinkering”.
The materials obtained have very variable properties, which can span from thermosetting to thermoplastic characteristics, and their mechanical assessment is by no means obvious. Conversely, a preliminary mechanical characterization, often based on hardness and Charpy impact testing, is important to qualify the obtained material and to decide how to possibly evolve to a semi-industrial production. On the other side, this evaluation may suggest ways to improve the material by modifying its composition and addressing molding or more generally production issues.
In this work, spent ground coffee was integrated in different amounts, either on its own, or with other ligneous waste, such as sawdust, in biopolymer matrices produced through a trial-and-error iterative approach. The matrices were obtained either by a starch-based polymer, plasticized through polyols e.g., glycerol, or by a milk whey based matrix subjected to acid hydrolysis. Difficulties observed in proceeding to mechanical characterization of this wood-like polymer material are also reported.
Characterization of Foams Used in Mechanized Tunnelling with TBM-EPB Technology
Sebastiani D.1, Vilardi G.2, Bavasso I.2, Di Palma L.2 and Miliziano S.1
1Department of Structural and Geotechnical Engineering, Sapienza University of Rome, Rome, Italy
2Department of Chemical Engineering Material and Environment, Sapienza University of Rome, Rome, Italy
Currently, TBM-EPB technology is the most common method to perform mechanized tunnel excavation in soil, particularly in urban environment. The development of technologically improved machines and the injection of chemicals under the form of foams made this technology very effective in many geological contexts.
This technology requires the continuous injection of foam to modify the excavated soil features. The characteristics of the injected foam affect the effectiveness of the injection and consequently the excavation performances. This paper describes the most significant results obtained in years of laboratory activities on the factors affecting the quality of the foam, from the chemical composition up to the foam generation modes.
Among several laboratory activities, half-life time (hlt) tests were performed on more than 25 commercial products in standard condition of temperature, pressure and generation modes, employing a modern and effective laboratory foam generation system and setting different values of Foam Expansion Ratio (FER) and chemicals dosages. Based on the obtained results a classification scheme of the products is proposed according to their ability to generate stable foam.
The proposed classification defines 5 classes, from Class I to V, useful to assess the stability of a foam, to select a product able to guarantee the generation of adequate stable foams and to evaluate the direct correlation between chemical composition and stability of generated foam.
Sustainable Mineral Coating of AR-Class Fibres in Textile Reinforced Mortar (TRM) Composites for Structural Purposes
Signorini C.1, Nobili A.2 and Siligardi C.2
1Department of Sciences and Methods for Engineering DISMI, University of Modena and Reggio Emilia, Reggio Emilia, Italy
2Department of Engineering Enzo Ferrari DIEF, University of Modena and Reggio Emilia, Modena, Italy
We present experimental results concerning the effect of silica-based mineral nano-coating on the mechanical performance of AR-glass fabric employed in TRM composites for structural strengthening.
Indeed, TRM exhibits interesting advantages over Fibre Reinforced Polymer (FRP) composites, in light of the inorganic matrix that is less sensitive to high temperature, UV-ray exposure and aging. In contrast, mechanical performance is generally poor and inconsistent, unless fabric-to-matrix bond is improved through interphase strengthening. To this aim, a silica nano-film is applied to the AR-glass fabric by sol-gel deposition. Two different lime mortars are considered as embedding matrix with different ultimate compressive strength. Mechanical performance is assessed according to ICC (AC434) guidelines through uni-axial tensile tests on prismatic laminates. Remarkable strength and ductility enhancements are observed and discussed. Digital Image Correlation confirms that interphase bond is improved, for crack pattern analysis shows diffused micro-cracks, in contrast to a few large macro-cracks which precede failure in the uncoated specimens.
Lightweight Metallic Matrix Composites: Development of New Composites Material Reinforced with Carbon Structure
Valente M., Marini D., Genova V., Marra F. and Pulci G.
Department of Chemical Engineering, Materials, Environment, Sapienza University of Rome – INSTM Reference Laboratory for Engineering of Surface Treatment, Rome, Italy
Carbon nano/micro-structures used as fillers in metallic lightweight alloys matrix composites are receiving considerable attention in scientific research and industrial applications.
Aluminium and magnesium are the most studied light metals used as matrices in metal composites materials principally for their low density (respectively 2.7 g/cm3 and 1.7 g/cm3) and low melting temperature (around 660 °C for both metals).
A good interaction between matrix and fillers is the first step to obtain an increase of bulk properties; secondly, the manufacturing procedure of the composite is fundamental in terms of quality of fillers dispersion. In this work it is studied the influence of different surface modifications for three class of carbon fillers with aluminium and magnesium alloy (AZ63) as metallic matrices. In particular, the selected fillers are multi walled carbon nanotubes (MWCNTs), short carbon micro fibres (SCMFs) and carbon woven fabric (CWF).
SEM and EDX analysis were conducted to study the effect of surface modification. The mechanical properties of manufactured composites were evaluated by four point flexural tests according to ASTM C1161 (room temperature).
Bending tests were performed with a Zwick Roell Z 2.5 testing machine (Zwick GmbH, Ulm, Germany) equipped with a 3-point-contact extensometer, and a silicon carbide fully-articulated flexure device. The results confirm the effect and the importance of surface funzionalizing by the electroless Nickel deposition.
Rubber/Crete: Mechanical Properties from Scraps to Reuse. Tires Derived Rubber in Concrete: a Review
Valente M. and Sibai A.
Department of Chemical Engineering, Materials, Environment, Sapienza University of Rome, Rome, Italy
Obviously, up-cycling/recycling/recovery/management of waste tires is a must for taking care of our planet. Moreover, tires are worldly thrown as wastes in landfills and seas, getting rid of it through burning or dumping them, producing oil as fuels, covered again with new rubber, thermo/converted in energy, thermochemical recycling and, in addition, mechanical recycled; doing it we find three type of materials (metal, textile, rubber). The material much more promising is rubber undergoes into two types of mechanical grinding: un-refrigerated and cryo-grinding. Mechanical grinding un-refrigerated works on the separation of material and can have two types of rubber products (grinded rubber and powder rubber). Only the powder rubber has been used in aggregation with concrete. Considering work published in the last 10 years it has been demonstrated that it is possible to replace sand and little stones (in size) with rubber. This improve some technological characteristics (decreasing density, improving impact energy, improving impact load, increasing toughness, increasing ductility, increasing freeze/thaw resistance, increasing thermal insulation, increasing sound insulation, etc.), make cement much more eco-compatible (light, reuse of rubber, minor aggregate), and invalidate other technological performance (decreasing workability, increasing bleeding, decreasing mechanical strength, increasing drying shrinkage, decreasing carbonation resistance), furthermore influence considerably mechanical characteristic. In this work the behavior of principal mechanical characteristics has been analyzed and reviewed considering the different studies.
OSMOSIS: A REACH-Compliant Structural Adhesive Primer from ENBIO
Byrne L., Roche K., McDonnell K., Morgan G., Adeyemi I., Flanagan J. and Twomey B.
ENBIO Ltd., Dublin, Ireland
REACH regulations seek to eliminate the use of chromates from European industrial processes. These compounds have been shown to be carcinogenic, mutagenic and highly toxic. One of the products impacted are structural adhesive primers; vital to the space and aerospace sectors for lightweight vehicle construction.
ENBIO has received H2020 funding to investigate the use of our CoBlast process in the deposition of green, REACH-compliant adhesive primers. The CoBlast process utilises a co-incident beam of abrasive and coating media to remove a metal’s passivating layer while simultaneously depositing a primer coating on the newly-exposed reactive metal surface.
As part of this OSMOSIS (One Step Modification of Space-Integrated Surfaces) project, a range of organic and inorganic materials were deposited onto Aluminium substrates. To determine their effectiveness as adhesive primers, bonded samples were prepared using an epoxy adhesive and lap shear testing was conducted. Bond strengths were determined for:
As-bonded samples
1 week salt fog exposed samples
1 week humidity-aged (56°C, 70%RH) samples
Identical samples of current state-of-the-Art processes, namely Phosphoric Acid Anodisation (PAA) and Chromic Acid Anodisation (CAA), were also tested using identical parameters.
CoBlast-prepared surfaces were shown to achieve equivalent tensile strength to these State-of-the-Art options. Cohesive failure was also observed in samples subjected to each ageing regime.