1,721,005 research outputs found
The role of unconscious inference in models of delusion formation (CHAPTER 3)
No full textIn this chapter we discuss the role of conscious and unconscious inference in theories of delusion formation. Two competing accounts aim to shed light on the formation of delusions: according to explanationism, the delusional belief is offered as an explanation for anomalous experience; according to the endorsement theory, the delusional belief is an acknowledgement that the anomalous experience is veridical. Whereas explanationists argue that the delusional belief is inferred from experience, endorsement theorists argue that there need be no inference from the experience to the delusional belief. Here we put pressure on the idea that the two accounts can be distinguished on the basis of whether inference is involved in delusion formation and argue that they are both compatible with the increasingly influential idea that Bayesian inference is responsible for the adoption of the delusional belief. One of the models of delusion formation focusing on Bayesian inference is the Coltheart model (Coltheart, Menzies, and Sutton, 2010) which we discuss in detail in the chapter. We show that, given its features, the model does not fit neatly under either explanationism or the endorsement theory
Mode I translaminar fracture toughness of high performance laminated biocomposites reinforced by sisal fibers: Accurate measurement approach and lay-up effects
Full text linkThe present work performs a systematic experimental analysis of the translaminar fracture behavior of high performance biocomposites constituted by green epoxy reinforced by sisal fibers, by varying the main influence parameters as fiber concentration and lay-up. Despite the corrective function properly introduced to take into account the anisotropy as well as the use of the equivalent crack length, the study shows that the LEFM does not give accurate estimations of the fracture toughness, because the extension of the near tip damaged zone is higher than the singular dominated one. Accurate estimations can be obtained instead by the proposed modified area method that takes into account both the local damage and the fiber bridging that occurs during crack propagation, that lead to R-curves whose asymptotic values constitute the true fracture toughness of the biocomposites examined. The constancy of the damage mechanisms observed by varying the fiber concentration, allows the user to compute the fracture toughness of a generic laminate from the specific fracture energy of the unidirectional lamina. Finally, the relatively high fracture toughness of the examined laminates allows to state that they can advantageously replace not only other composites having lower toughness, but also metals as steel, aluminum and titanium
RESISTENZA ALLA FRATTURA TRANSLAMINARE DI BIOCOMPOSITI RINFORZATI CON FIBRE DI AGAVE
No full textData la crescente attenzione nei confronti dell’ambiente, le sempre più restrittive norme in materia di
salvaguardia ambientale e di riciclo dei materiali hanno portato ad un notevole interesse dei ricercatori
verso i biocompositi, materiali costituiti da rinforzi di origine naturale e matrici a basso impatto
ambientale. Nonostante molteplici studi siano stati indirizzati a tali materiali innovativi, allo stato
attuale poche ricerche hanno riguardato l’analisi della tenacità alla frattura di laminati biocompositi. Il
presente lavoro propone pertanto uno studio sperimentale del comportamento alla frattura
translaminare in modo I di laminati biocompositi in fibre di agave e matrice epossidica green,
valutando in particolare l’effetto della variazione percentuale volumetrica del rinforzo e della sequenza
di impacchettamento (unidirezionali, cross-ply, angle-ply ecc.). Le prove di resistenza alla frattura a
trazione in modo I sono state eseguite su campioni con configurazione Compact Tension (CT) al fine
di determinare sia il fattore critico di intensificazione delle tensioni, sia la Critical Strain Energy
Release Rate (CSERR). In particolare, i diversi provini CT sono stati ottenuti attraverso laminazione
manuale e successivo processo di compression-moulding, a partire da tessuti unidirezionali di tipo
stitched appositamente prodotti in laboratorio. Al fine di individuare il metodo ottimale per una
accurata valutazione sperimentale della CSERR, sono stati confrontati i risultati ottenuti con diversi
metodi tra cui l’Area Method ed il Compliance CalibrationThe recent attention toward the environmental protection, as well as to the restrictive regulations in term of material recycling, have led to a noticeable interest of the scientific research for biocomposites, i.e. materials constituted by natural fibers and eco-friendly matrix. Although various research works have been focused on such innovative materials, only a few articles have been devoted to the their fracture strenght (thoughness).
The present work regards the experimental study of the translaminar fracture behavior (in mode I) of biocomposite laminates constituted by green epoxy matrix reinforced by optimized agave sisalana fibers, varying the main influence parameters as the fiber concentration and the lay-up (unidirectional, cross-ply, angle-ply etc.).
The fracture tests in mode I, have been performed by using Compact Tension (CT) specimens, in order to determine both the critical Stress Intensity Factor (SIFc) and the so called Critical Strain Energy Release Rate (CSERR).
In more detail, several CT specimens have been manufactured by hand lay-up and successive compression-moulding process whose parameters have been optimized in previous study of the same authors. To this aim proper stitched fabrics have been previously manufactured in laboratory. In order to detect the optimal method for an accurate experimental analysis of the CSERR, the results provided by the Area Method and the Compliance Calibration, have been compared
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
First lamina hybridization of high performance CFRP with Kevlar fibers: Effect on impact behavior and nondestructive evaluation
Full text linkThe impact behavior of a carbon-Kevlar hybrid composite, widely used in sport car manufacturing, was evaluated. To highlight the hybridization effect, comparative analyses were performed with the basic CFRP laminate having the same lay-up. Tensile, bending and low velocity impact tests, followed by nondestructive inspections, highlighted that Kevlar first lamina hybridization leads to an increment in specific impact strength, up to 55%. To assess the most reliable technique to detect the impact damage, nondestructive evaluation was performed by pulsed thermography, phased array ultrasonic technique, computed tomography and digital radiography. Phased array ultrasonic technique can be considered the most appropriate technique
Enhancement of Static and Fatigue Strength of Short Sisal Fiber Biocomposites by Low Fraction Nanotubes
Full text linkThanks to good mechanical performances, high availability, low cost and low weight, the agave sisalana fiber allows to obtain biocomposites characterised by high specific properties, potentially very attractive for the replacement of synthetic materials in various industrial fields. Unfortunately, due to the low strength versus transversal damage processes mainly related to the matrix brittleness and/or to the low fiber/matrix adhesion, the tensile performance of random short fiber biocomposites are quite low, and to date most of the fiber treatments proposed in literature to improve the fiber-matrix adhesion, have not led to very satisfactory results. In order to overcome such a drawback, this work in turn proposes the proper introduction of low fractions carbon nanotubes to activate advantageous improvements in matrix toughness as well as fiber-matrix bridging effects, that can both lead to appreciable increments of the tensile strength.
Systematic experimental static and fatigue tests performed on high quality biocomposites obtained by an optimized compression molding process, have shown that the introduction of 1% of carbon nanotubes is sufficient to gives significant improvement in both stiffness and static tensile strength, respectively by approximately 28% and 30%. Furthermore, toughening the biocomposite with 1% of nanotubes results in an appreciable enhancement in lifetime of at least 3 orders of magnitude. Biocomposites with 2% of CNTs show instead more limited improvement of 13% in stiffness, 6% in strength and 150% in lifetime. Also, a thorough analysis of the damage processes by SEM micrographs, as well as of the main fatigue data, has allowed to determine the model that can be used to predict the fatigue performance of such biocomposites
EFFETTI DI NANOTUBI SULLA RESISTENZA A FATICA DI BIOCOMPOSITI A FIBRE CORTE RANDOM
No full textIn order to comply with the recent regulations in terms of environmental protection, biocomposites reinforced with natural fibers are increasingly used in the automotive sector, for the replacement of synthetic materials in semi-structural applications as panels, filling material, coating, dashboards, etc. The good mechanical performances of these materials, mixed with low weight and low cost, also make it possible to minimize the weight of the vehicle, and therefore consumption, but also the relative production costs. These are composites with random short fiber appreciated for their good stiffness, generally well above that of the matrix alone. Due to the peculiar "transverse" damage phenomena, often also influenced by debonding and pull-out phenomena related to the limited fiber-matrix adhesion, the mechanical, static and fatigue resistance of these materials is instead generally comparable to that of the matrix alone. This prevents their use in more mechanically demanding applications. For this reason, several chemical treatments on the fibers have been proposed in the literature by various authors, although still not fully satisfactory results have been obtained in terms of improving resistance. Taking into account the positive effects of the nanotubes on the fatigue resistance of structural polymeric adhesives and polymer matrix composites reinforced with synthetic fibers, in this work the effects of nanotubes on the fatigue resistance of biocomposites reinforced with agave fibers are analyzed, the fibers are obtained with a special compression molding process. The tests carried out on green epoxy matrix biocomposites in which nanotubes with different concentrations in volume were previously dispersed, showed that the static strenght is significantly influenced by the presence of nanotubes, although more appreciable improvements are found in the fatigue performance
Analysis of the Parameters Affecting the Stiffness of Short Sisal Fiber Biocomposites Manufactured by Compression-Molding
Full text linkThe use of natural fiber-based composites is on the rise in many industries. Thanks to their eco-sustainability, these innovative materials make it possible to adapt the production of components, systems and machines to the increasingly stringent regulations on environmental protection, while at the same time reducing production costs, weight and operating costs. Optimizing the mechanical properties of biocomposites is an important goal of applied research. In this work, using a new numerical approach, the effects of the volume fraction, average length, distribution of orientation and curvature of fibers on the Young’s modulus of a biocomposite reinforced with short natural fibers were studied. Although the proposed approach could be applied to any biocomposite, sisal fibers and an eco-sustainable thermosetting matrix (green epoxy) were considered in both simulations and the associated experimental assessment. The results of the simulations showed the following effects of the aforementioned parameters on Young’s modulus: a linear growth with the volume fraction, nonlinear growth as the length of the fibers increased, a reduction as the average curvature increased and an increase in stiffness in the x-y plane as the distribution of fiber orientation in the z direction decreased
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