Search results for "TLE"
showing 10 items of 2417 documents
Grain-boundary modelling of hydrogen assisted intergranular stress corrosion cracking
2018
Abstract A novel hybrid strategy for modelling intergranular hydrogen embrittlement in polycrystalline microstructures is proposed. The technique is based on a grain-boundary integral representation of the polycrystalline micro-mechanics, numerically solved by the boundary element method, coupled with an explicit finite element model of the intergranular hydrogen diffusion. The intergranular interaction between contiguous grains in the aggregate is modelled through extrinsic cohesive-frictional traction-separation laws, whose parameters depend on the concentration of intergranular hydrogen, which diffuses over the interface according to the Fick’s second law, inducing the weakening of the i…
Building large molecular models with plastic screw-on bottle caps and sturdy connectors
2016
An improved method of connecting atoms formed with screw-on bottle caps is described. Fishing line (artificial polymer), steel wire, and countersunk bolts with nyloc nuts are proposed as sturdy connectors. Advantages and disadvantages of each method are described. The molecular models are stable while handling, can be built in a relatively short time at low cost, and can be useful at every level of education. The method is an alternative to professional model kits, in particular in construction of large models for long-term usage.
Effects of Nylon 6,6 Nanofibrous Mats on Thermal Properties and Delamination Behavior of High Performance CFRP Laminates
2014
none 8 no Nylon 6,6 electrospun nanofibrous membranes interleaved in Carbon Fibre Reinforced Plastic (CFRP) laminates have been proposed as a means to provide a higher threshold value to delamination on structural sites where composites are more prone to develop such failure. A model, highly crosslinked thus inherently brittle, epoxy matrix was selected for its high Young’s modulus and glass transition temperature exceeding 250 °C. The influence of the Nylon 6,6 nanofibres on the curing behaviour of the matrix and on the thermal and dynamic mechanical properties of the cured resin was investigated. These properties were related to the features of the epoxy resin and of the resin impregnated…
Orientation induced brittle – Ductile transition in a polyethylene/polyamide 6 blend
2014
Abstract Polyamide/polyolefin blends are of scientific and technological interest but, on the other hand, the different chemical nature of the two components makes them incompatible, resulting in unsatisfactory physical properties and making compatibilization necessary. In particular, although the two components are ductile, the binary blends can show brittle behaviour. It is also known that the effect of the elongational flow (and then of the induced orientation) on polymer blends is a decrease of elongation at break with increase of the degree of orientation. In this work, the effect of orientation on the mechanical properties of a low density polyethylene/polyamide 6 incompatible blend w…
Model of delamination propagation in brittle-matrix composites under cyclic loading
2001
A model of interlaminar fatigue crack growth based on damage accumulation ahead of the crack is proposed. Linear cumulative assumption is used for damage estimation, and a quadratic failure criterion is applied for complex interlaminar loading. Model parameters are determined from mode I and mode II fatigue tests, and used to predict mixed-mode delamination propagation rate. Comparison of theoretical prediction with mixed-mode test results for different brittle graphite FRP at several mode- and load ratios show reasonable agreement.
Coating fragmentation by branching cracks at large biaxial strain
2007
The fragmentation behaviour of a thin brittle coating attached to a ductile substrate subjected to equibiaxial quasi-static in-plane tension is studied. The experimentally observed cracking patterns are related to repetitively branching coating cracks. The fragmentation process is modelled by the rate equation approach. It is established that fragmentation by branching cracks leads to a qualitatively different fragment distribution compared to binary fragmentation. The fragmentation model is applied to identify crack branching and coating/substrate stress transfer parameters.
Nonthrombogenic, Biodegradable Elastomeric Polyurethanes with Variable Sulfobetaine Content
2014
For applications where degradable polymers are likely to have extended blood contact, it is often important for these materials to exhibit high levels of thromboresistance. This can be achieved with surface modification approaches, but such modifications may be transient with degradation. Alternatively, polymer design can be altered such that the bulk polymer is thromboresistant and this is maintained with degradation. Toward this end a series of biodegradable, elastic polyurethanes (PESBUUs) containing different zwitterionic sulfobetaine (SB) content were synthesized from a polycaprolactone-diol (PCL-diol):SB-diol mixture (100:0, 75:25, 50:50, 25:75 and 0:100) reacted with diisocyanatobuta…
Mechano-activated processes on metal oxide interfaces at room temperature
1997
Solid state bonding of metal with oxide at room temperature have been studied. The properties of Al/SiO 2 , Al/glass, Al/MgO, Mg/SiO 2 , In/glass interfaces as well as to ascertain the mechanism of formation of interfaces. Structure, composition and mechanical properties were investigated using auger-spectroscopy (AES), secondary-ion mass-spectrometry (SIMS), electron microscopy and precision microindentation. The results showed marked adhesion not all over contact area but only at zones of the maximum shear stress. The effect of mechanoactivation is considered from the viewpoints of both structure formation and physico- chemical interaction of nonequilibrium systems. As a result of relaxat…
Microhardness of different resin cement shades inside the root canal
2012
Objectives: To compare microhardness along the root canal post space of two resin cements in different shades and a dual-cure resin core material. Study Design: Root canals of 21 bovine incisors were prepared for post space. Translucent posts (X•Post, Dentsply DeTrey) were luted using one the following resin luting agent: Calibra (Dentsply DeTrey) in Translucent, Medium and Opaque shades, RelyX Unicem (3M ESPE) in Translucent, A2 and A3 shades and the dual-cure resin core material Core•X flow. All materials were applied according to manufacturers’ instructions and were all photopolymerized (Bluephase LED unit, Ivoclar Vivadent, 40s). After 24 hours, roots were transversally cut into 9 slice…
Deformation behavior of nanostructured ZnO films on glass
2012
Abstract Nanostructured ZnO films on glass substrate were studied by nanoindentation, scanning electron and atomic force microscopy. The films were obtained by a straightforward mechanoactivated oxidation method. The morphology of the obtained films was grained with a grain size in the range 50–100 nm and the thickness was approximately 2 μm. A detailed deformation behavior of ZnO films, critical parameters and indentation induced plastic deformation mechanisms were determined in correlation to bulk ZnO, Si single crystal and commercial ZnO films. In comparison to a single crystal ZnO, nanostructured films exhibit increased hardness (9 GPa); however, the Young's modulus is decreased (120 GP…