1,720,981 research outputs found
An image-based approach for structure investigation and 3D numerical modelling of polymeric foams
Full text linkPolymeric expanded materials are of great importance in many engineering applications. Despite this, as of today the development of models able to describe the mechanical behaviour of these material as a function of their microstructure is still an open challenge. In this study an image-based approach is proposed for both microstructure characterisation and 3D numerical mechanical simulations. Microstructure is investigated through different algorithms, such as Mean Intercept Length and Autocorrelation function, to determine synthetic parameters able to describe the internal structure. A novel algorithm has been developed to convert the images obtained from computed tomography into a finite element mesh with an optimized number of elements: this method preserves the original structure and can also be used to generate other fictitious structures that can be analysed. The investigation led to the identification of general relationships between foam microstructure and relevant macroscopic physical and mechanical properties. These relationships can serve as a tool to optimize foam morphology or product final properties for several different engineering applications
Influence of morpho-structural parameters on environmental stress cracking in polyethylene
Full text linkPolyethylene (PE) is widely utilized in several industries due to its versatility and mechanical strength, yet its long-term performance is often hindered by slow crack growth (SCG) and environmental stress cracking (ESC). This study quantitatively evaluates the influence of key morpho-structural parameters on SCG and ESC resistance in PE, using a linear elastic fracture mechanics (LEFM) approach to assess the effect of different comonomers on fracture toughness. Four PE materials were analyzed: two medium molecular weight, linear low-density polyethylenes (LLDPE) co-polymerized with 1-butene (Material A) and 1-hexene (Material B); a high molecular weight LLDPE copolymerized with 1-hexene (Material C); and a medium molecular weight, high-density polyethylene (HDPE) homopolymer (Material D). The results confirm that molecular weight is a dominant factor in enhancing stress cracking resistance, with the high molecular weight LLDPE (Material C) showing superior performance. Moreover, despite nearly identical structural parameters, Material B exhibited significantly higher SCG and ESC resistance compared to Material A, highlighting the critical role of the commoner type. The research identified three distinct environmental regimes influencing fracture behavior, each dependent on the applied stress intensity factor (K) and material properties. These regimes are: (1) no significant environmental effect at high K values, where fracture is dominated by the material's inherent properties; (2) partial plasticization of craze fibrils at intermediate K values, due to limited diffusion of environmental agents into the crack tip; and (3) full plasticization of craze fibrils at low K values, where extensive diffusion accelerates environmental stress cracking (ESC). By demonstrating how morpho-structural parameters and environmental conditions together influence polyethylene's resistance to SCG and ESC, this study improves our understanding of the underlying mechanisms and underscores the effectiveness of LEFM in evaluating long-term material performance. This knowledge can guide the design with polyethylene materials aimed at improving long-term durability for industrial applications
Environmental stress cracking of high-density polyethylene under plane stress conditions
Full text linkHigh-Density Polyethylene is prone to Environmental Stress Cracking if mechanically stressed in the presence of solutions containing surfactants. Even if this polymer is widely used to produce containers for industrial and household detergents, its Environmental Stress Cracking Resistance is generally evaluated under plane strain conditions irrespective of the actual stress state experienced during service life. In this work the Slow Crack Growth of thin specimens, under plane stress conditions, was studied in air and in the presence of an “active” environment. The J-integral approach was adopted to account for the extensive plastic deformations thereby occurring and the obtained results were compared to those describing the plane strain behaviour of the same polyethylene, reported in previous works. The effect of the production process was also assessed by comparing the behaviour of compression moulded and blow moulded specimens, the latter having a lower degree of crystallinity. Despite the difference in fracture resistance expected in air, the behaviour in presence of the active environment was very similar, suggesting that the production process has only negligible influence on the Environmental Stress Cracking resistance of the considered polyethylene
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
Probing athletics tracks degradation using a microscratch technique
Full text linkContinuous outdoor exposure of athletics tracks can lead to an important degradation of their mechanical and aesthetical properties. In this work, flat laboratory samples prepared from rubber blends of different colours were subjected to natural and artificial ageing, to investigate their effect on the surface properties. Compositional variations demonstrated a generalized oxidization of the outer (top) material layer, together with surfacing of inorganic additives; a small increase of the degradation temperature of the natural rubber component was reported, similar to the one previously observed on bulk track samples. The smooth surface of the present samples allowed their testing using a microscratching technique, able to mechanically probe the material within a few hundred microns below the top surface. The formation of a significantly harder outer crust layer was reported, potentially impacting the track performance since it is exactly the locus of interaction between the athlete and the sport surface. In particular, the increase in scratch hardness is accompanied by a significant reduction in the apparent friction coefficient. These surface modifications, previously unreported in the literature, are independent phenomena with respect to generalized bulk ageing. Microscratch data supported by microscopy evidenced a significantly varying sensitivity to ageing for the different colours (red, blue, green, neutral). Moreover, this sensitivity appeared strongly dependent on the applied ageing protocol (natural vs. artificial). In view of these results, care must be taken when accelerated artificial weathering is used to simulate long-term natural ageing of these materials
Effect of physical aging on scratch behavior of polycarbonate
Full text linkPhysical aging refers to relaxation of the polymer glassy state toward the amorphous state and this phenomenon affects their physical-mechanical properties. This work investigates the effect of physical aging on polymer scratch behavior and visibility. It was shown that mechanical properties were significantly modified over the aging time, especially the yield stress, in turn affecting polymer scratch behavior. As a matter of fact, the critical load for the onset of scratch visibility was shown to increase with the aging, thus improving sensitivity of polymer to scratches. Such behavior was strictly related to the yield stress increase with the aging time. The usefulness of the present work is highlighted, and some future perspectives are discussed
Recycled fillers as an alternative in bituminous mixtures for road pavements
No full textThis paper reports the results of a laboratory investigation on the use of recycled industrial fillers into bituminous mixtures for road pavements. The investigated fillers were obtained by crushing and sieving (0.00–0.63 mm) Stabilized Bottom Ashes (SBAs) from municipal waste incinerators and Electric Arc Furnace Steel Slags (EAFSSs). Moreover, a currently used calcareous filler was included in the research for comparative purposes. Two dosages of each filler were considered in the experimentation. Laboratory tests aimed at investigating compaction properties, volumetric characteristics, and mechanical performance of the bituminous mixtures. The results suggest that both the investigated recycled fillers are suitable to be used into bituminous mixtures, also demonstrating that in certain conditions those fillers increase the performance of the corresponding mixtures in comparison to the ones in which standard (calcareous) filler is used
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