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European Journal of Wood and Wood Products - For the purposes of structural design, cross-laminated timber (CLT) panels are typically chosen from tables detailing standardized layups. While this is...  相似文献   
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The fabrication of cellulose-spider silk bio-nanocomposites comprised of cellulose nanocrystals (CNCs) and recombinant spider silk protein fused to a cellulose binding domain (CBD) is described. Silk-CBD successfully binds cellulose, and unlike recombinant silk alone, silk-CBD self-assembles into microfibrils even in the absence of CNCs. Silk-CBD-CNC composite sponges and films show changes in internal structure and CNC alignment related to the addition of silk-CBD. The silk-CBD sponges exhibit improved thermal and structural characteristics in comparison to control recombinant spider silk sponges. The glass transition temperature (Tg) of the silk-CBD sponge was higher than the control silk sponge and similar to native dragline spider silk fibers. Gel filtration analysis, dynamic light scattering (DLS), small angle X-ray scattering (SAXS) and cryo-transmission electron microscopy (TEM) indicated that silk-CBD, but not the recombinant silk control, formed a nematic liquid crystalline phase similar to that observed in native spider silk during the silk spinning process. Silk-CBD microfibrils spontaneously formed in solution upon ultrasonication. We suggest a model for silk-CBD assembly that implicates CBD in the central role of driving the dimerization of spider silk monomers, a process essential to the molecular assembly of spider-silk nanofibers and silk-CNC composites.  相似文献   
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The initiation, growth, and stability of buckling driven debonding in structural assemblies of stiff blocks, compliant joints, and adhesively bonded composite layers are analytically investigated. The model is developed with focus on masonry walls externally strengthened with composite materials where static and, mainly, dynamic loads may induce compression in the strengthening layers triggering a buckling driven debonding near the joints. The model introduces the interfacial nonlinearity (debonding) through a cohesive interface approach. The geometrical nonlinearity is introduced through the kinematics of intermediate class of deformation (large deflections, moderate rotations, small strains), and the material nonlinearity of the masonry construction is introduced through the constitutive law for the mortar joints. A numerical study of the debonding process in strengthened masonry walls is presented. The study uses the periodicity of the wall for sub-structuring and examines configurations that include composite strips or sheets, strengthening on one face of the wall or on both faces, and compliant mortar materials. Emphasis is placed on the localized debonding near the joint, its stability characteristics, and the possibility to detect the debonding process before it reaches the point of instability.  相似文献   
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This paper studies the interactive, simultaneous, and unstable multiple debonding mechanisms in masonry walls strengthened to resist out-of-plane flexure using composite materials bonded on their tensed and compressed faces. This structural form combines rigid blocks and brittle joints sandwiched between adhesively bonded composite layers. It characterizes masonry walls strengthened to resist dynamic and seismic out-of-plane loads, but also armor plates with ceramic tiles, electronic packaging, and sandwich panels with embedded inserts. The study focuses on the stability of the interactive debonding mechanisms and on the potential evolution of coupled and simultaneous debonding processes. It uses a cohesive interface approach and a geometrically nonlinear high order model. A numerical study that examines the coupled debonding processes in masonry wall samples strengthened with composite materials on the two outer faces is presented. The study examines the instabilities involved with the processes, the order in which the tension driven debonding and the buckling driven one nucleate, and the interaction between them. It also examines the impact of the properties of the cohesive interface, the presence of pre-existing debonded regions, the arching effect, and the accumulation of damage at the interfaces. This effort aims to gain insight into the debonding processes and their impact on the performance, functionality, and safety of the strengthened element.  相似文献   
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Creep properties of specimens taken from the core of AZ91D magnesium alloy ingots (9 pct Al, 1 pct Zn) were examined in the temperature range of 120 °C to 180 °C and stress range of 40 to 115 MPa. Solution-treated and aged creep specimens were also tested. The creep rates observed were about three orders of magnitude lower than those of pure magnesium, and elongations to fracture were seen to be at least twice those of pure magnesium. A minimum creep rate was reached after approximately 2/3 of the creep life of the specimens (except for the aged specimens, in which the minimum creep rate appears at the beginning of the test). A qualitative model for the creep process in proposed on the basis of the creep tests and optical, scanning electron, and transmission electron microscopy. This model proposes that dislocation motion on additional slip systems is the primary creep mechanism and that cracking acts as a stress relief mechanism. Structural instability dictates the amount of hardening and, hence, creep resistance.  相似文献   
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In the light of the outstanding importance of hydrocarbons for global energy, the controversy over peak oil has become both pressing and emotionally charged. Two conflicting parties – alarmists and optimists – hold irreconcilable positions. The shaping of the future energy policy is presently based on modeling results and geological considerations only. We show that the existing predictions of the energy crisis are increasingly mixed-up with value-judgments. The value analysis of those forecasts allows us to suggest that at least part of the estimations are implicit reflections of predictors’ ends and values, and do not demonstrate a real ability to anticipate future conditions. Paradoxically, the question of oil reserves depletion is better understood when predictions are viewed as an instrument to impose the predictors’ values and intervene in the currently bustling oil market. The intervention in the oil prices may occur in either direction becoming a tool to justify values rather than an instrument for the acquisition of knowledge.  相似文献   
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