A Review on Topology Optimization Strategies for Additively Manufactured Continuous Fiber-Reinforced Composite Structures

Topology Optimization (TO) recently gained importance due to the development of Ad- ditive Manufacturing (AM) processes that produce components with good mechanical properties. Among all additive manufacturing technologies, continuous fiber fused filament fabrication (CF4) can fabricate high-performance composites compared to those manufactured with conventional technolo- gies. In addition, AM provides the excellent advantage of a high degree of reconfigurability, which is in high demand to support the immediate short-term manufacturing chain in medical, transportation, and other industrial applications. CF4 enables the fabrication of continuous fiber-reinforced compos- ite (FRC) materials structures. Moreover, it allows us to integrate topology optimization strategies to design realizable CFRC structures for a given performance. Various TO strategies for attaining lightweight and high-performance designs have been proposed in the literature, exploiting AM’s design freedom. Therefore, this paper attempts to address works related to strategies employed to obtain optimal FRC structures. This paper intends to review and compare existing methods, analyze their similarities and dissimilarities, and discuss challenges and future trends in this field

Ultra-High-Molecular-Weight Polyethylene Rods as an Effective Design Solution for the Suspensions of a Cruiser-Class Solar Vehicle

Ultra-high-molecular-weight polyethylene (UHMWPE) is a subgroup of the thermoplastic polyethylene characterized by extremely long chains and, as result, in a very tough and resistant material. Due to remarkable specific mechanical properties, its use is gradually being extended to multiple fields of application. This study describes, perhaps for the first time, how the UHMWPE can represent a valid material solution in the design and optimization of suspensions for automotive use, especially in the case of extremely lightweight vehicles, such as solar cars. In particular, in this design study, UHMWPE rods permitted to assure specific kinematic trajectories, functionalities, and overall performance in an exceptionally light suspension systems, developed for an innovative multioccupant solar vehicle. These rods reduced the weight by 88% with respect to the classic design solutions with similar functions, offering, at the same time, high stiffness and accuracy in the movements. An experimental campaign was conducted to evaluate the ratcheting behaviour and other mechanical properties needed for a proper design and use

Toward a sustainable mobility: A solar vehicle for a new quality of life

The vehicular mobility causes 15% of greenhouse gases emission: one million tons of carbon anhydrite per hour. In addition, it produces CO, NOx, fine powders, carcinogenic and mutagenic elements: These substances will disappear in the presence of solar vehicles. And solar mobility would also mitigate indirect effects: fuel used to transport fuel, energy for the distillation of hydrocarbons, gas leaks, even fracking, explosions, rivers and oceans. In contrast, electric and hybrid vehicles do not allow this improvement in the quality of life. In almost all modern countries, the energy mix is strongly unbalanced towards fossil fuels: massive electrification would not make mobility sustainable, but rather risks worsening its effect on the environment by shifting the problem of emissions from cities to power plants. The Sun, indeed, can guarantee long-Term sustainable mobility: for every circulating solar vehicle CO2 production is really zero. From July to today, our solar racing car has travelled 3000 km, avoiding to emit half a ton of CO2: reporting these data to a conventional use, each solar vehicle would avoid the release of 1.5 tons of CO2 per year: like planting 10 large trees for each month in our garden. This study describes how to transform a solar super-car into an ordinary vehicle for urban and everyday mobility

INNOVATION IN SOLAR VEHICLES: FROM THE IDEA TO THE PROTOTYPE IN LESS THAN 24 MONTHS

The article aims to describe the integrated path used for the conceptual, functional and constructive design of an exclusive solar vehicle. The project was based on the massive implementation of concurrent engineering and quality tools, rarely used in such an integrated way. New and attractive design, 3D CAD modelling, details design, structural and fluid dynamic validations, in-scale rapid prototyping, functional tests, multi-objective optimization, parts manufacturing and assembly. Thanks to this approach, the solar prototype presents high technological contents, especially in terms of materials, structures and processes, together with their optimizations. Furthermore, large CNC-machined multi-material molds, hybrid manufacturing solutions: everything was used to speed up phases permitting to move from the initial idea to the final prototype in 24 months. Since June 2018, the solar vehicle is on the road, transporting 4 people, weighing less than 300kg, reaching speeds of 120km/h and able to run hundreds of km without fuel

First assessment on suspension parameter optimization for a solar-powered vehicle

Optimization of suspension parameters with respect to comfort and road holding is a challenging issue for solar-powered cars, due to in-wheel electric engines on very light vehicles, carrying payloads which can exceed their total mass. The solar-powered car considered in this study was designed and manufactured for racing by the University of Bologna; with a mass of 300 kg and a payload of 320 kg due to four occupants, using 5 m2 of monocrystalline silicon photovoltaic panel on the roof, 64 kg of lithium-ion batteries and two electric engines coupled directly to the rear wheels, it can achieve either a range of 600 km at cruising speed, or velocity peaks of 120 km/h. In this contribution, equivalent vertical stiffness and equivalent damping coefficients are optimized for both axles, achieving results that in terms of comfort and road holding are comparable to those of standard passenger cars

Fracture mechanics of laser sintered cracked polyamide for a new method to induce cracks by additive manufacturing

This paper presents an experimental investigation on specimens manufactured by Selective Laser Sintering (SLS), with the purposes of giving designers advice when designing 3D printed parts, and laying the basis for a step forward in the field of fracture mechanics of 3D complex parts. The aim is to investigate the effect of building direction in Polyamide (PA) 3D printed samples and to assess whether a crack can be initiated directly from the sintering process for fracture mechanics study purposes. Six different configurations of Mode I Compact Tension (CT) specimens were manufactured and tested; the experiments were monitored by Digital Image Correlation (DIC) and fractured surfaces were analyzed using microscopy. Results showed that samples with better mechanical performance are those in which all the layers contain a portion of the crack. On the other hand, those with layers parallel to the crack plan offer a preferential pathway for the crack to propagate. DIC and fractography investigations showed that, under certain conditions, small-radius geometries, or too-close surfaces may glue depending on printer resolution. Experiments also showed that SLS is capable of printing specimens with internal cracks that can be used to study fracture mechanics of complex parts or parts with internal cracks

Feasibility study of adhesive bonding reinforcement by electrospun nanofibers

Abstract In previous works, the authors showed that the interleaving of an electrospun nylon nanofibrous mat at the interface between adjacent plies of a composite laminate increases the delamination strength. In particular, the nanomat acts a net-like reinforcing web, enabling a ply-to-ply bridging effect. This reinforcing property of the nanomats can be potentially used in other applications which need to improve the fracture resistance of interfaces, such as adhesive bonding. The present work analyses the feasibility of an electrospun polymeric nanomat as adhesive carrier and reinforcing web in industrial bonding. Thus the adhesive is used to pre-impregnate a nylon nanofibrous mat that is then placed at the interface between two metal pieces and then cured. The aim of the work is first to assess the effectiveness of this procedure, by comparison of the mode-I fracture toughness measured with DCB (Double Cantilever Beam) tests with and without the reinforcement in the adhesive layer. For this purpose, a 2024-T3 aluminum alloy will be bonded using a general purpose, one-part epoxy resin with low viscosity

Caratterizzazione microstrutturale e meccanica di giunti in composito AA6061/20%vol.Al2O3p ottenuti mediante Friction Stir Welding

Nel presente articolo vengono descritti i risultati delle caratterizzazioni microstrutturali e meccaniche effettuate su giunti in composito AA6061/20%vol.Al2O3p, ottenuti mediante Friction Stir Welding (FSW). Le analisi microstrutturali hanno evidenziato un sostanziale affinamento ed arrotondamento delle particelle di rinforzo nella zona FSW, indotto dall’utensile, oltre ad una diminuzione delle dimensioni dei grani della matrice, probabilmente conseguente a fenomeni di riscristallizzazione dinamica nel corso della saldatura. Non sono stati evidenziati fenomeni di segregazione del rinforzo, porosità o altri difetti microstrutturali tipici di processi di saldatura per fusione. I profili di microdurezza interparticellare hanno mostrato una diminuzione delle stessa in corrispondenza del cordone, che è stata correlata ad un probabile sovrainvecchiamento della matrice, generato dal calore sviluppato per attrito. Le prove di trazione hanno fornito un’efficienza del giunto pari a circa il 72%, rispetto alla resistenza a trazione. Le prove di fatica oligociclica hanno mostrato che il composito saldato resiste ad un numero di cicli inferiore fino ad un ordine di grandezza rispetto al composito base. Le analisi frattografiche hanno evidenziato meccanismi di frattura sostanzialmente analoghi per il composito saldato e non

In‐plane shear strength of single‐lap co‐cured joints of self‐reinforced polyethylene composites

The present study introduces the analysis of single‐lap co‐cured joints of thermoplastic self‐reinforced composites made with reprocessed low‐density polyethylene (LDPE) and reinforced by ultra‐high‐molecular‐weight polyethylene (UHMWPE) fibers, along with a micromechanical analysis of its constituents. A set of optimal processing conditions for manufacturing these joints by hot‐press is proposed through a design of experiment using the response surface method to maximize their in‐plane shear strength by carrying tensile tests on co‐cured tapes. Optimal processing conditions were found at 1 bar, 115 °C, and 300 s, yielding joints with 6.88 MPa of shear strength. The shear failure is generally preceded by multiple debonding‐induced longitudinal cracks both inside and outside the joint due to accumulated transversal stress. This composite demonstrated to be an interesting structural material to be more widely applied in industry, possessing extremely elevated specific mechanical properties, progressive damage of co‐cured joints (thus avoiding unannounced catastrophic failures) and ultimate recyclability