Decoupling fracture modes in non-standard test specimens: state of the art

We call here as non-standard an interfacial fracture specimen that features an asymmetry w.r.t. the crack plane (e.g., bimaterial joint). Such specimens generally undergo mixed-mode (I/II) fracture even if they are loaded in pure mode (I or II). Aiming, however, to characterize the pure-mode fracture of them, several attempts have been made to decouple mode I and mode II. Ouyang et al. [1] focused on the bimaterial case. They stated that mode decoupling is achieved when the differential equation of the mode I (mode II) fracture is only governed by the interfacial normal (shear) stress and relative transverse (axial) displacement. A similar statement was recently made by Bennati et al. [2], who provided a more general decoupling condition covering the case where both adherents feature bending-extension coupling. The same topic was also investigated by Maimí et al. [3], who provided a different decoupling condition from that by Bennati et al. Wang et al.’s [4] “strain-based” decoupling condition is the same with that by Ouyang et al. based on an assumption (i.e., matching the axial strains of the two adherents) simpler than solving the mathematical problem. In parallel, individual authors sometimes adopt different decoupling criteria (e.g., matching the bending rigidities of the two adherents), usually without justifying their choice, though. The present work brings together and reviews the scattered—and sometimes overlapping—contributions, aiming to elucidate the confusion observed

Toughening and healing of continuous fibre reinforced composites by supramolecular polymers

\u3cp\u3eInterleaves comprising self-healing materials based on hydrogen bonded supramolecular polymers (SP) were successfully incorporated in the mid-plane of unidirectional (UD) carbon fibre reinforced polymers (CFRPs). The fracture toughness of these hybrid composites and their healing capability were measured under mode I loading. The fracture toughness appeared to have increased considerably since the maximum load (P\u3csub\u3emax\u3c/sub\u3e) of the hybrid composite had increased approximately 5 times, and the fracture energy I (G\u3csub\u3eIC\u3c/sub\u3e) displayed a dramatic increase by almost one order of magnitude when compared to the reference composite without the SP. Furthermore, the double cantilever beam (DCB) hybrid composites displayed a healing efficiency (H.E.) value for the mode I interlaminar characteristics around 60% for the P\u3csub\u3emax\u3c/sub\u3e and the G\u3csub\u3eIC\u3c/sub\u3e after the first healing cycle, dropping to 20-30% after the seventh cycle. During the mode I interlaminar fracture toughness tests the acoustic emission (AE) activity of the samples was also monitored. It was found that AE-activity strongly reduced due to the presence of the SP. Moreover, optical microscopy not only showed that the epoxy matrix at the interface is partly infiltrated by the SP, but it also revealed that cross-sections of both fractured surfaces were covered with the SP comprising pulled-out carbon fibres, indicating a strong interfacial adhesion. Finally it was shown that the SP fractured surfaces were partially covered with pulled-out carbon fibres emanating from the edges of the SP film in which the epoxy system exists.\u3c/p\u3

Toughening and healing of continuous fibre reinforced composites by supramolecular polymers

Interleaves comprising self-healing materials based on hydrogen bonded supramolecular polymers (SP) were successfully incorporated in the mid-plane of unidirectional (UD) carbon fibre reinforced polymers (CFRPs). The fracture toughness of these hybrid composites and their healing capability were measured under mode I loading. The fracture toughness appeared to have increased considerably since the maximum load (Pmax) of the hybrid composite had increased approximately 5 times, and the fracture energy I (GIC) displayed a dramatic increase by almost one order of magnitude when compared to the reference composite without the SP. Furthermore, the double cantilever beam (DCB) hybrid composites displayed a healing efficiency (H.E.) value for the mode I interlaminar characteristics around 60% for the Pmax and the GIC after the first healing cycle, dropping to 20-30% after the seventh cycle. During the mode I interlaminar fracture toughness tests the acoustic emission (AE) activity of the samples was also monitored. It was found that AE-activity strongly reduced due to the presence of the SP. Moreover, optical microscopy not only showed that the epoxy matrix at the interface is partly infiltrated by the SP, but it also revealed that cross-sections of both fractured surfaces were covered with the SP comprising pulled-out carbon fibres, indicating a strong interfacial adhesion. Finally it was shown that the SP fractured surfaces were partially covered with pulled-out carbon fibres emanating from the edges of the SP film in which the epoxy system exists

Mode II fracture toughening and healing of composites using supramolecular polymer interlayers

This study focuses on the transfer of the healing functionality of supramolecular polymers (SP) to fibre reinforced composites through interleaving. SPs exhibiting self-healing based on hydrogen bonds were formed into films and were successfully incorporated into carbon fibre composites. The effect of the SP interleaves on in-plane fracture toughness and the subsequent healing capability of the hybrid composites were investigated under mode II fracture loading. The fracture toughness showed considerable increase since the maximum load (P max ) of the hybrid composite approximately doubled, and consequently the mode II interlaminar fracture toughness energy (G IIC ) exhibited an increase reaching nearly 100% compared to the reference composite. The healing component was activated using external heat. P max and G IIC recovery after activation were measured, exhibiting a healing efficiency after the first healing cycle close to 85% for P max and 100% for G IIC , eventually dropping to 80% for P max while G IIC was retained around 100% even after the fourth healing cycle. Acoustic Emission activity during the tests was monitored and was found to be strongly reduced due to the presence of the SP

Terminal Terrestre Yerbateros como regenerador urbano

Elabora una investigación en torno al transporte terrestre interprovincial que llega y sale de Lima, que permita diseñar un terminal con la capacidad de descongestionar la zona intervenida, mediante el agrupamiento de empresas transportistas y el ordenamiento de sus flujos vehiculares. Además, se busca comprender las necesidades básicas para garantizar el buen funcionamiento del terminal y su activación mediante la implementación de características intermodales y usos complementarios. Finalmente, se analizarán las condicionantes y problemáticas de la zona para comprender la posibilidad de regeneración y beneficios que brindaría un diseño enfocado hacia el peatón mediante la implementación de espacio público

Sustainable Development Approaches through Wooden Adhesive Joints Design

Over recent decades, the need to comply with environmental standards has become a concern in many industrial sectors. As a result, manufacturers have increased their use of eco-friendly, recycled, recyclable, and, overall, more sustainable materials and industrial techniques. One technique highly dependent on petroleum-based products, and at the edge of a paradigm change, is adhesive bonding. Adhesive bonding is often used to join composite materials and depends upon an adhesive to achieve the connection. However, the matrices of the composite materials and the adhesives used, as well as, in some cases, the composite fibres, are manufactured from petrochemical products. Efforts to use natural composites and adhesives are therefore ongoing. One composite that has proven to be promising is wood due to its high strength and stiffness (particularly when it is densified), formability, and durability. However, wood must be very carefully characterised since its properties can be variable, depending on the slope of the grains, irregularities (such as knots, shakes, or splits), and on the location and climate of each individual tree. Therefore, in addition to neat wood, wood composites may also be a promising option to increase sustainability, with more predictable properties. To bond wood or wooden composite substrates, bio-adhesives can be considered. These adhesives are now formulated with increasingly enhanced mechanical properties and are becoming promising alternatives at the structural application level. In this paper, wooden adhesive joints are surveyed considering bio-adhesives and wood-based substrates, taking into consideration the recent approaches to improve these base materials, accurately characterise them, and implement them in adhesive joints.</jats:p

Sustainable Development Approaches through Wooden Adhesive Joints Design

Over recent decades, the need to comply with environmental standards has become a concern in many industrial sectors. As a result, manufacturers have increased their use of eco-friendly, recycled, recyclable, and, overall, more sustainable materials and industrial techniques. One technique highly dependent on petroleum-based products, and at the edge of a paradigm change, is adhesive bonding. Adhesive bonding is often used to join composite materials and depends upon an adhesive to achieve the connection. However, the matrices of the composite materials and the adhesives used, as well as, in some cases, the composite fibres, are manufactured from petrochemical products. Efforts to use natural composites and adhesives are therefore ongoing. One composite that has proven to be promising is wood due to its high strength and stiffness (particularly when it is densified), formability, and durability. However, wood must be very carefully characterised since its properties can be variable, depending on the slope of the grains, irregularities (such as knots, shakes, or splits), and on the location and climate of each individual tree. Therefore, in addition to neat wood, wood composites may also be a promising option to increase sustainability, with more predictable properties. To bond wood or wooden composite substrates, bio-adhesives can be considered. These adhesives are now formulated with increasingly enhanced mechanical properties and are becoming promising alternatives at the structural application level. In this paper, wooden adhesive joints are surveyed considering bio-adhesives and wood-based substrates, taking into consideration the recent approaches to improve these base materials, accurately characterise them, and implement them in adhesive joints