Search

A wide variety of scientific aims have been formulated for future explorations of space and planets. In order to achieve these aims, a need for robotic systems and mission set-ups with increasing complexity arises. The H2020 EU-funded project SIROM (Standard Interface for Robotic Manipulation of Payloads in Future Space Missions), aims to realize an integrated interface for mechanical, data, electrical and thermal connectivity that allows a reliable, robust and multi-functional coupling. The present paper reports an overview of classifications of power, data and mechanical interfaces and thermal transfer methods in current robotic and space applications. Eventually, the paper presents ideas for innovation and development of standard multi-functional interface with the most promising developments expected in the next few years.

The present work aims for investigate the influence of electrospun Nylon 6,6 nanofibrous mat on the behavior of composite laminates. The main idea is that nanofibrous interleaved into particular ply-to-ply interfaces of a laminate can lead to significant improvements of mechanical properties and delamination/damage resistance. Experimental campaigns were performed to investigate how nanofibers affect both the static and dynamic behavior of the laminate in which they are interleaved. Fracture mechanics tests were initially performed on virgin and 8 different configuration of nanomodified specimens. The purposes of this first step of the work are to understand which geometrical parameters of the nanointerleave influence the behavior of the laminate and, to find the optimal architecture of the nanofibrous mat in order to obtain the best reinforcement. In particular, 3 morphological parameters are investigated: nanofibers diameter, nanofibers orientation and thickness of the reinforce. Two different values for each parameter have been used, and it leads to 8 different configurations of nanoreinforce. Acoustic Emission technique is also used to monitor the tests. Once the optimum configuration has been found, attention is focused on the mechanism of reinforce played by the nanofibers during static and dynamic tests. Low velocity impacts and free decay tests are performed to attest the effect of nanointerlayers and the reinforce mechanism during the dynamic loads. Bump tests are performed before and after the impact on virgin and two different nanomodified laminates configurations. The authors focused their attention on: vibrational behavior, low velocity impact response and post-impact vibration behavior of the nano-interleaved laminates with respect to the response of non-nanomodified ones. Experiments attest that nanofibers significantly strength the delamination resistance of the laminates and increase some mechanical properties. It is demonstrated that the nanofibers are capable to continue to carry on the loads even when the matrix around them is broken.

The effect of Nylon 6,6 electrospun nanofibers interleaved in composite laminate material is numerically simulated to investigate the damage evolution a nanomodified laminate interface. DCB and ENF mechanical test results from a previous work of the authors are used as benchmark for numerical simulations: carbon fiber/epoxy matrix 0/90 prepreg laminate are simulated and mechanical properties are determined for both virgin and nanomodified configurations. Numerical simulation with finite element software Abaqus using implicit time integration were performed to build a numerical model to simulate both the tests taking into account the presence on nanofibers. Nanofibrous interlayer was simulated using a bilinear damage law corresponding to resin a nanofibrous materials behavior. Virgin and nanomodified configuration for experimental and numerical results are compared and it is shown that numerical results are in good agreement with experimental ones

Polymeric nanofibers are promising to significantly influence the develops of many fields in material science and engineering, and they lead the way into nanotechnology. This work deals with nanofibers and their interaction with epoxy resin-based composite materials. For such kind of material, when subjected to impact and fatigue loads, delamination is often the dominating failure mode. Several methods have been developed over the years to enhance delamination resistance of laminates, like matrix toughening, optimization of stacking sequence, laminate stitching, braiding, edge cap reinforcement, critical ply termination, and so on. Palazzetti et al. successfully proposed to use a polymeric electrospun nanofibers interleave in composite laminates: the objective of the present study is to characterize a composite material made by epoxy resin reinforced with polymeric electrospun nanofibers. For this purpose a modified VARTM (Vacuum Assisted Resin Transfer Molding) process has been implemented to manufacture 0.6 mm thick specimens where a layer of nanofibers is placed in the middle. Four different thicknesses are manufactured: 25, 50, 75 and 100 m. Weight increasing is negligible due to the very low density of nanobifrous sheet. Epoxy resin and Nylon 6,6 provided by DuPont company are materials used in this work. Electrospun process is performed inside the laboratories of University of Bologna by a selfdesigned semi-automatic machine. The VARTM process was erformed using a closed mould and permitted to obtain dimensionally accurate specimens with no voids in them. Specimens were tested on tensile test and DMTA, performed to determine the effect of nanofibers on static and dynamic behavior of epoxy resin. From tensile tests, the tensile strength and the stiffness were determined; storage and loss modulus were obtained from DMTA tests in order to calculate the dissipation factor (tan()). Tests were performed on both virgin and nanoreinforced specimens, for each nanolayer thickness, and the results were compared. It is shown that the presence of nanofibers significantly change the behavior of the specimen under the tests. In tensile, maximum load sensibly increased due to the nanofibers and no decrease in stiffness was registered. DMTA showed in important increase in damping factor for nanomodified specimens: it was observed that nanomodified resin is much more capable to store energy, compared to virgin one. Effect of nanolayer thickness was also discussed: for both the test it was observed that properties change proportionally to the nanofibrous thickness with a mixture-rule-like law.

Among various failure modes in composite laminate materials, the delamination is one of the most common. Out-of-plane stresses, repeated cyclic stresses, impact, and so on, can cause layers to separate, forming a mica-like structure of separate layers, with significant loss of mechanical strength. Delamination is widely investigated, and many techniques are developed in order to improve the material strength. The aim of the present study is to investigate the infuence of electrospun nanofibers on the mechanical behaviour of composite laminate, and in particular on the delamination strength. Nanofibers, with respect to micrometric fibres commonly used in composites, are characterized by high surface to volume and aspect ratios. Moreover they also have higher strength with respect to microfbers of the same nature due to alignment of polymer chains along the fiber axis as well as to a low density of flaws and defects. The usage of nanofibers to enhance the mechanical performances of composite has been recently investigated by researchers and examples of the use of electrospun polymer nanofibers to improve the mechanical behaviour of laminates are available in the literature. The basic idea of this work is to use electrospun polymeric nanofibers as an interleaving filler placed between adjacent plies of a laminate composite material and to study the behaviour of the specimen under two specific loading conditions. Three different kinds of Nylon 6,6 are considered, and two different types of tests are performed: the Double Cantilever Beam test and the End Notch Flexure test. The specimens are manufactured by using carbon fiber/epoxy matrix laminate prepreg. The nano-modified composites are obtained by electrospinning the nanofibers directly on the ply surfaces before lay-up, thus generating a layer of fibers with a negligible thickness compared to the ply thickness. For the specified quasi-static test, one nanofiber layer is placed in the middle of the specimens. The behaviour of nanoreinforced composites is compared with the non reinforced ones. The experiments are carried out according to the ASTM standards. For the DCB tests the trend of GIC is studied depending on the thickness of nanolayer placed in the interlay. The study is repeated for the GIIC in the ENF tests. The optimum thickness of the nanofiber interlay is determined for each test. It is observed that a mat of nanofiber interleaved between the most critical plies of the composite significantly influences the delamination resistance of the same laminate. The behaviour of the laminates is different in the four tests considered, the nanofiber toughening effect being different in each one of them. By performing DMTA analysis of the resin-nanofiber system, damping effect and tensile/bending behaviours are determined in order to built up an analytical model capable to account the effect of nanofiber sheet placed in the laminates. The model is based on the lamination theory and the stiffness contributions of nanolayers are superimposed to all the other plies contributions. A new matrix formulation is presented and considerations regarding the membrane and bending behaviour are developed. In order to account the randomness of nanofibre orientation which influences the mechanical properties of composite nano-interleaved materials a probabilistic variational model is presented and discussed.

Oggetto del presente lavoro è la progettazione del sistema di sospensione anteriore di un veicolo terrestre leggero alimentato ad energia solare. Massimizzare il rapporto peso/rigidezza ha portato all’utilizzo di materiali compositi, in particolare di strutture sandwich. Si presenta in questo lavoro uno studio sistematico di ogni “feature” geometrica che caratterizza il componente, seguendo linee guide presentate in precedenti lavori. È stato inoltre condotto uno studio analitico globale e di dettaglio riguardanti le criticità geometriche del componente, con lo scopo di definire i reali valori di tensione presenti nelle zone critiche dell’elemento. La parte finale, di sperimentazione meccanica, ha confermato la bontà della fase progettuale. Con questo lavoro si intende quindi fornire al progettista un utile strumento di analisi progettuale per affrontare la realizzazione di componenti avanzati in materiale composito.

In the work polymeric electrospun nanofibers are used as interleaving filler placed between adjacent plies of a CFRP laminate in order to study the behavior of the composite material under Mode II ENF mechanical tests (End Notched Flexure, ASTM 7246). Influence of nanofibrous interlayer is investigated by comparing absorbed energy and bending stiffness respect to conventional CFRP laminates. Laminates are made of epoxy resin/carbon fiber 0/90 woven prepreg; nanofiber mats are manufactured using electrospun Nylon 6,6. For considered test (quasi-static one), one nanofibrous layer is placed in specimen’s midplane. ENF tests reveal that the nanofibrous mats strongly contribute to improve bending stiffness before the material crisis (13,3% of increment) and a measurable increment of the maximum mechanical energy that can be absorbed by the material during the crack propagation (27,4% of increment) is registered.

The focus of this work is to investigate the delamination damage in laminate composite beams, to fix a Vibration-based structural health monitoring (VSHM) method for the laminate structures. The analysis is concentrated on the vibration characteristics of the samples and, in particular, the attention is addressed on the first several natural frequencies of a composite laminate beam with a delamination damage. The core of this work is an experimental investigation on the vibration response of a composite laminate beam and its changes caused by delaminations with different sizes and in different locations of the beam. The study is divided in 3 sections: delamination detection, delamination localization, and delamination estimate. The aim is to determine how the first six harmonics frequencies change due to the delamination, and the results show that they can be successfully used to investigate the presence, the location and the dimensions of the delamination in a composite beam. A Pattern Recognition analysis is used to locate the damage, while the detection and the evaluation are done using the changes in the harmonic frequencies. A finite element analysis is performed, and the variations of the natural frequencies due to delamination are in good agreement with the experimental results.

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 bond together 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.