1,720,957 research outputs found
Comparison and validation of computational methods for the prediction of the compressive crush energy absorption of CFRP structures
No full textThe crushing response of fiber-reinforced composite structures under compressive loading is investigated experimentally and then simulated using two damage models implemented in ESI Virtual Performance Solution explicit solver. The conventional Ladevèze continuum damage is compared to the recently implemented Waas-Pineda model, which uses non-local damage approach: virtual cracks are embedded with prescribed traction-separation laws and direct input of modal fracture energies. Initially, characterization tests of a unidirectional carbon fiber/epoxy tape are carried out to implement material card data and elementary simulations are performed for calibration. In a second stage, quasistatic crush compression of reference coupons are used for validation and numerical results are compared to experimental data in terms of specific absorbed energy. Results show that the Waas-Pineda model is easier to set up than the Ladevèze one and it also better reproduces the experimental results. The Ladevèze model underestimates the sustained crush stress since some damage modes could not be well identified from coupon testing of brittle material
Influence of simulation parameters in the combined loading compression testing of CFRP specimens
Full text linkIn this paper a sensitivity study of a FEM model representing a carbon/epoxy composite material tested in Combined Loading Compression (CLC) is presented and the results are compared to experimental results. The present study aims to simulate the failure of composite materials when subjected to compression and crush loading conditions. This is required as a first step of a Building-Block Approach towards full-scale modelling of complex structures. In the experimental part of the work, a laminate panel was manufactured with carbon unidirectional prepreg (Deltapreg UTS-300-DT120-37EF) in a cross-ply, balanced and symmetric stacking sequence, cured in autoclave at 120°C and 5 bar for 90 min. A number of six samples, extracted from the panel, were tested in compression following ASTM D6641/D6641M-16. Numerical simulations have been implemented by means of the commercial software, ESI-VPS PAM CRASH. Boundary conditions, specimens' dimensions and material properties emulated real test conditions. A sensitivity study was performed on critical simulation parameters: the effect of mesh size and number of shell surfaces representing the composite stacking sequence was initially investigated. Furthermore, the specimen failure mode was inspected by the application of TIED links between the composite plies. Numerical results have been compared with experimental data and the comparison provided references for testing scale-up in the Building-Block Approach
Numerical simulation of the compression crushing energy of carbon fiber-epoxy woven composite structures
Full text linkThe crashworthiness of composites is investigated in an experimental campaign and simulated using the explicit
Finite Element solver ESI-VPS. Two damage models, derived from Ladev`eze and Waas-Pineda, are implemented
in modified forms, to work with woven-fabrics. The former uses conventional continuum damage formulations,
while the latter introduces a traction-separation law to simulate cracks with prescribed fracture energies. The
Waas-Pineda approach aims to simplify the material card definition and make the calibration more straight-
forward. Characterization tests are carried out on specimens manufactured with plain weave carbon fiber-epoxy
tape. Notched coupons are analysed, as these tests are representative of the conditions observed during crushing
of a composite structure. Innovative procedures to calibrate the damage models are introduced to remove, where
possible, the need for iterative tuning. Once implemented, the calibrated material cards are validated against
quasi-static crushing of corrugated specimens with two different layups. In the Waas-Pineda model, mesh ob-
jectivity is obtained only after correction of the modal fracture energies, instead, the Ladev`eze model formulation
is already consistent at different scale lengths. In addition, a sensitivity analysis shows a modest influence of
friction coefficient and interlaminar fracture toughness on sustained load. Results demonstrate that it is possible
to obtain adequate results from both damage models when the proposed calibration strategy is used, but vali-
dation on test results is still advised to ensure the mesh discretization is suitable for the selected problem
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
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Numerical Investigation of Al-Reinforced CFRP Composite under Low-Velocity Impact
Full text linkFibre-reinforced composite materials are widespread in lightweight, high-performance applications. However, polymeric composites generally exhibit a brittle behaviour, which makes them susceptible to impact damage. Even low-velocity impacts can produce delaminations, which cause a substantial reduction of the compressive mechanical properties. Metallic layers have been embedded in composite laminates with the aim to improve their fracture behaviour: aluminium plies can be employed to increase the indentation resistance of Carbon Fibre Reinforced Polymers (CFRP) specimens. For this reason, hybrid fibre-metal laminates are expected to be a viable solution to reduce the damage caused by low-velocity impacts. In this work, CFRP specimens reinforced with aluminium plies were modelled using the finite element method and a cohesive zone model. Cohesive elements based on a traction-separation formulation were embedded at each ply-to-ply interface to enforce delamination damage. Different configurations of the Al reinforcements were studied by varying the position of the aluminium layers between the CFRP plies
- …
