1,721,077 research outputs found
PROGETTO DI UNA SOSPENSIONE POSTERIORE IN MATERIALE COMPOSITO PER VEICOLI ELETTRICI
No full textIl lavoro descrive la progettazione e la modellazione agli elementi finiti di un sistema di sospensione per veicoli elettrici leggeri caratterizzato da molle flessionali, da una barra di torsione con funzionalità antirollio e da braccetti con snodi flessibili, il tutto in composito rinforzato mediante fibra di carbonio.
Il sistema consente la regolazione rapida dell’assetto del veicolo e l’ottenimento di differenti caratteristiche dinamiche variando il rapporto tra le rigidezze delle molle e della barra di torsione.
Inoltre, mantiene una funzionalità residua che consente la marcia anche in caso di rottura di uno degli elementi elastici
Delamination localisation and length estimation in composite laminate beam by VSHM and pattern recognition methods
Full text linkThe 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
On the Notch Effect in Low Temperature Carburized Stainless Steel under Fatigue
No full textThe present paper describes the fatigue behaviour of carburized notched AISI 316 austenitic stainless steel specimens. Rotary four point bending fatigue tests have been performed using carburized smooth specimens with two different values of surface rugosity and notched specimen with two different stress concentration factors Kt, of 3.55 and 6.50 and the effects of carburizing on fatigue strength and notch sensitivity were discussed. Results show a general improvement of the fatigue life due to the treatment for all the series with an apparent notch sensitivity lower than one in the case of blunt notches due to secondary effects that were singled out
NUMERICAL ANALYSIS OF THE EFFECT OF MEMBRANE PRELOADS ON THE LOW-SPEED IMPACT RESPONSE OF COMPOSITE LAMINATES
No full textThis article presents a comprehensive study on the mechanical behaviour of composite laminated plates undergoing a low-speed impact of an external body while they are subjected to in-plane preloads. The effect of such preloading was investigated by means of finite-element analysis of several impact events on laminates with three different span-to-thickness ratios. Tensile and compressive preloads, both uniaxial and biaxial, were considered; in the case of compression, the impact on buckled specimens was also studied. The results obtained show that the span-to-thickness ratio is a fundamental parameter in determining the effect of initial strains. Under a tensile preload, the impact-caused peak stresses were higher than in the case of no preload, and their increment was higher in thicker laminates. Under compression, the most dangerous influence of initial
stresses was found at medium span-to-thickness ratios for preloads comparable with the buckling load, whereas, in other cases, negligible or even beneficial effects were observed. These results can justify some experimental findings from the existing literature, even if they were obtained without modelling the material degradation due to damage. Also, they allow us to conclude that the explanation of other phenomena strictly related to damage, as well as an accurate prediction of the extent of damage, requires a failure model
An integrated approach based on acoustic emission and mechanical information to evaluate the delamination fracture toughness at mode I in composite laminate
No full texthis paper addresses a new method based on the combination of mechanical behavior and acoustic emission (AE) information of composite materials during mode I delamination. The method is based on a special purpose function, called sentry function, which is defined as the logarithm of the ratio between mechanical energy and acoustic energy (f=Ln(Es/Ea)). The sentry function is used to study the delamination process and to evaluate the delamination fracture toughness in mode I. The relationship between cumulative fracture toughness energy release rate (GI) and the integral of the sentry function during crack propagation showed a transition point with two sensitive regions below and above it. This behavior can be followed to obtain the critical strain energy release rate value (GIc). Results obtained by means of the sentry function are compared with results obtained by a methodology proposed by other author
Falling weight impact and indentation damage characterisation of sandwich panels for marine applications
No full textOn three configurations of laminates for nautical use, impact and indentation properties have been compared, in the understanding that these represent two different and significant cases in the laminate service, namely contact with fal- ling body and ramming. All the laminate configurations were fabricated using the same stacking sequence of E-glass mats (of weight 225 and 600 g/m2) as skins, while the core was obtained with different types of rigid PVC foams in the case of A laminate (HEREX C-75) and in that of B and C laminates (COLTH C-55). The latter laminates are also protected with Gelcoat on the outer side. The resin used for A and B laminates was a conventional vynilester (DISTITRON VE 100 SC), while for C laminate a polyester-based including some non-oil derived components was used (ENVIREZ 1807). Laminates of each of the three configurations have been impacted from 1, 1.5 and 2 meters with a 1.25 kg mass using a 12.7 mm hemispherical nose, therefore yielding impact energies of 12.25, 18.37 and 24.5 Joules respectively. Subsequently, other laminates have been quasi-statically indented at with 0.05 mm/s cross-head speed, using the same indentor, until the maximum average displacement obtained during low velocity impact for each configuration and each energy was obtained. The results obtained show that strain rate has an effect on the performance of these laminates. In particular, the improved resistance to penetration appears to occur at the expense of damage dissipation due to vibrations. Quasi-static indentation does not appear to fully reproduce the effect of low velocity impact loading for these sandwich structures, showing significant differences in the hysteresis cycles, both during loading and during the damping phase, which need to be combined with the variable effect of damage on the laminates
Low-Velocity Impact on preloaded and curved laminates
No full textDynamic Deformation, Damage and Fracture in Composite Materials and Structures, Second Edition reviews various aspects of dynamic deformation, damage and fracture, mostly in composite laminates and sandwich structures, and in a broad range of application areas including aerospace, automotive, defense and sports engineering. This book examines low- and high-velocity loading and assesses shock, blast and penetrative events, and has been updated to cover important new developments such as the use of additive manufacturing to produce composites, including fiber-reinforced ones. New microstructural, experimental, theoretical, and numerical studies with advanced tools are included as well. The book also features four new chapters covering topics such as dynamic delamination, dynamic deformation and fracture in 3D-printed composites, ballistic impacts with fragmenting projectiles, and the effect of multiple impacting
Validation of a Continuum Damage Model for predicting the axial-crush response of CFRP composite material
No full textIn this work, the validation of the Finite Element (FE) analysis code PAM-Crash for the simulation of crashworthy composite structures is proposed. The investigation follows the principles of the Building Block Approach (BBA): FE analyses are supported at an increasing level of geometrical complexity by experimental campaigns. The investigation starts with multiple sets of coupon level testing on carbon fiber-epoxy UD material, followed by the quasi-static axial crushing of a self-supporting specimen. Tests performed include: tension, compression, in-plane shear and delamination modes I and II. A continuum damage mechanics (CDM) model is implemented starting from elementary load cases, then scaling up to the self-supporting specimens. The phenomenological meso-model for the intra-ply post-failure behaviour is based on the studies of Ladevèze, as later revised by Johnson and Pickett. In addition, a cohesive zone model is used to account for the delamination phenomena. Influence of different simulation strategies and simulation settings are discussed within the body of this work: a model comprising a single multilayered shell element, a staked set of shells representing the single constituent ply connected by inter-ply cohesive elements, and lastly, an intermediate solution using sub laminate groups. Influence of mesh size, friction coefficients and crushing velocity are also discussed. Results show that the CDM model alone is not able to correctly simulate the complex load cases, but calibration strategies of the material card are necessary to fit the experimental data. The required manual tuning limits the predictive quality of the model, as the characterisation effort alone is unable to describe the energy absorption characteristic of the different physical phenomena occurring during crushing. In addition, due to the different features of the proposed numerical approach, the contribution on Specific Energy Absorption (SEA) of the different crushing modes is discussed. A sensitivity analysis of different card parameters on simulation results is finally discussed in order to propose a framework for future investigation
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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