1,720,974 research outputs found
Simulating fracture in bonded composite joints using cohesive zone models
No full textThe cohesive zone model (CZM) is a powerful tool for the simulation of fracture in bonded assemblies. In this chapter the CZM is used to study the enhancement of bond toughness in adhesive joints with laser-irradiated substrates. The chapter first discusses the implementation of an interface element, incorporating the Park-Paulino-Roesler (PPR) potential-based cohesive model, in the framework of a finite element commercial code (ABAQUS Standard). The PPR model is then applied to the simulation of debonding in T-peel joints with laser-treated substrates when these undergo failure with large plastic deformations. © 2011 Woodhead Publishing Limited. All rights reserved
Numerical simulations and experimental measurements of the stress intensity factor in perforated plates
No full textA numerical procedure, which combines two hybrid finite element formulations, was developed to analyse the stress intensity factors in cracked perforated plates with a periodic distribution of holes and square representative volume elements. The accuracy of the method in predicting the stress intensity factor was verified by a comparison with experimental measurements, carried out by a photoelasticity method, and by commercial finite element software. Several simulations were executed by varying both the crack length and the hole diameters, and the effects of the holes on the stress intensity factor are illustrated. The method shows high accuracy and efficiency, as small differences were observed when compared with the traditional finite element method, notwithstanding a strong reduction in degrees of freedom and mesh complexity
Simulation of debonding in Al/epoxy T-peel joints using a potential-based cohesive zone model
No full textIn this work, a cohesive zone model of fracture is employed to study debonding in plastically deforming Al/epoxy T-peel joints. In order to model the adhesion between the bonded metal strips, the Park-Paulino-Roesler (PPR) potential based cohesive model (J Mech Phys Solids, 2009; 57:891-908) is employed, and interface elements are implemented in a finite element commercial code. A study on the influence of the cohesive properties (i.e. cohesive strength, fracture energy, shape parameter and slope indicator) on the predicted peel-force versus displacement plots reveals that the numerical results are mostly sensitive to cohesive strength and fracture energy. In turn, these parameters are tuned until a match between experimental and simulated load displacement curves is achieved. © 2011 Published by Elsevier Ltd
Measurement of laser shock peening induced residual stress by nanoindentation and comparison with XRD technique
Full text linkLaser shock peening (LSP) is an innovative surface treatment technique successfully used to improve fatigue performance of metallic components. It is based on the application of high intensity laser and suitable overlays with the aim to generate high pressure shock waves on the surface of the mechanical part to be treated. Shock waves generate severe plastic deformations and, consequently, compressive residual stresses (RS). An accurate measurement of these latter is crucial for predicting the resistance of treated parts under service loads and to assess the effectiveness of LSP process. In this paper, a non-destructive method, based on the nanoindentation technique and finite element analysis (FEA), was developed to measure the RS generated by LSP process on AA-7050-T451 samples. In particular, the methodology is based on the analysis of the nanoindentation peak load variation generated by the presence of residual stresses on a component. Obtained results were compared, for validation, with the measurements carried out by the most consolidated X-ray diffractometer (XRD) technique. The results showed a satisfactory agreement between the two techniques, revealing nanoindentation as a promising and reliable method for characterizing RS induced by LSP
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
On the effect of pulsed laser ablation on shear strength and mode I fracture toughness of Al/epoxy adhesive joints
No full textThe present work describes an experimental study about the shear strength and the mode I fracture toughness of adhesive joints with substrates pre-treated by pulsed laser ablation. An ytterbium-doped pulsed fiber laser was employed to perform laser irradiation on AA6082-T4 alloy. Morphological and chemical modifications were evaluated by means of surface profilometry, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Thick adherend shear tests were carried out in order to assess the shear strength while the mode I fracture toughness was determined using the double cantilever beam. For comparison, control samples were prepared using classical surface degreasing. The results indicated that laser ablation has a favorable effect on the mechanical behavior of epoxy bonded joints; however, while a + 20% increase was recorded for shear strength, a remarkable threefold enhancement of fracture toughness was observed with respect to control samples. XPS analyses of treated substrates and SEM observations of the fracture surfaces indicated that laser pre-treatment promoted chemical and morphological modifications able to sustain energy dissipation through mechanical interlocking. As a result cohesive failure within the adhesive bond-line was enabled under predominant peel loading
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