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Spa rnins E.,Ecole Polytechnique Federale de Lausanne | Andersons J.,Institute of Polymer Mechanics | Michaud V.,Ecole Polytechnique Federale de Lausanne | Leterrier Y.,Ecole Polytechnique Federale de Lausanne
Smart Materials and Structures | Year: 2015

The interfacial shear strength (IFSS) between nickel-titanium (NiTi) shape memory alloy wires, characterized by a nonlinear stress-strain behavior, and epoxy matrix was determined by pull-out tests. Tests were carried out at several temperatures and levels of pre-strain in the wires, to evaluate the effects of embedded wire length and of crystalline state of the alloy. The IFSS between the twinned NiTi and epoxy was estimated at 24 MPa, and found to increase to 47 MPa for completely detwinned and preloaded martensitic NiTi. This increase in IFSS values was attributed to microcracking of the superficial TiO2 layer and the resulting roughening of the NiTi wire surface. © 2015 IOP Publishing Ltd.

Kerch G.,Latvia University of Agriculture | Korkhov V.,Institute of Polymer Mechanics
European Food Research and Technology | Year: 2011

The mechanical (tensile strength, elongation at break, mechanical work of deformation) and barrier (water vapor permeability and water vapor uptake) properties of chitosan films produced with acetic and lactic acids have been studied as a function of storage time, molecular weight of chitosans, concentration of plasticiser and the storage temperature. It was demonstrated that mechanical properties of chitosan-based films can be improved to a great extent during storage at low temperatures in freezer and refrigerator. Transition of chitosan molecules during storage in the solid state to more extended conformations and free volume changes are considered as mechanisms for the improvement of mechanical and barrier properties of chitosan films. The best mechanical properties are achieved for chitosan films produced with acetic acid and plasticized by the addition of 20% of glycerol. Sharp decrease in water vapor permeability has been demonstrated for thinner chitosan films and related to more dense packing and orientation of linear chitosan macromolecules. © 2010 Springer-Verlag.

Aniskevich K.,Institute of Polymer Mechanics | Starkova O.,Institute of Polymer Mechanics | Aniskevich A.,Institute of Polymer Mechanics
Journal of Applied Polymer Science | Year: 2012

To go ahead in understanding the nature of rubber reinforcement and evaluate the kinetics of filler clusters destruction during stretching of filled rubber, the styrene-butadiene rubber both unfilled and filled with various contents of silica particles with and without surface treatment was tested under quasistatic loading up to failure. The Klueppel-Schramm model was used for description of strain softening, evaluation of both the rubber and filler network parameters as the functions of the filler volume content. It was found that an elastic modulus as a function of filler volume content follows Guth-Gold equation, confirming the hydrodynamic nature of the rubber reinforcement; the effectiveness factor depends on filler surface treatment. Hydrodynamic amplification factor increases with increase of filler volume content, its value depends on filler particles surface treatment. The decrease of hydrodynamic amplification factor during stretching correlates with the increase of viscoelastic strain. Taking into account the viscoelastic strain improves the description of the stress-strain response of filled rubber for loading-unloading process with the parameters obtained for active loading. © 2011 Wiley Periodicals, Inc.

Concrete, because of its strength and durability, has been a mainstay of construction for thousands of years. The problem is that, while it is very strong, it is not particularly efficient and it is no friend to the environment; the cement industry is one of the primary producers of CO2 worldwide. The material is also prone to cracking as it dries, a feature which significantly reduces the lifespan of concrete structures and makes them less aesthetically pleasing. "Primekss is far more successful than it used to be […] the project has directly created at least 40 jobs since 2010." In recent years, however, the market has changed thanks to an innovative product developed by a consortium of partners from Belgium and Latvia. It all began with research conducted by the University of Latvia's Institute of Polymer Mechanics, which suggested that randomly-dispersed fibres scattered in a special, improved concrete mixture would allow it to bear double the load of other concrete. Latvian SME Primekss Ltd, an expert in concrete coverings, saw an opportunity here to develop a new, more efficient product that might fill a gap in the market. With the help and support of the EUREKA Network, Primekss and the Institute of Polymer Mechanics joined forces with Belgian SME Sprl Xavier Destree to engage in INNODISP CONCRETE, a project that ran between 2008 and 2010 with €230,000 in funding. Its aim was to create an improved concrete that could achieve the same construction goals as regular concrete when 20% less was used – but in practice, the researchers achieved even better with a 50% reduction in volume. On top of this, the new product – PrimeComposite – reduces and often eliminates the need for joints, which are always a weak spot in concrete constructions. It is also lean, crack-free and immune to shrinkage. As project leader, Primekss played a significant part in the day-to-day activities on INNODISP CONCRETE, as CEO Janis Ošlejs recalls: "Our role was to work together with the other partners to come up with systems and recipes for making better concrete – as well as providing a place for field tests and application of the product." Although this work had its share of challenges, it resulted in lasting partnerships that persist today, and big changes for the SMEs involved. "Primekss is far more successful than it used to be," Ošlejs enthuses. "The project has directly created at least 40 jobs since 2010." But the biggest success story is in the product itself, which continues to exceed competitors and has achieved sales of more than €100m to clients throughout Europe, South Africa, Kazakhstan, the USA, India, Russia and many other countries. Going forward, Primekss will further investigate and develop the impact of its innovative material – and it will facilitate this goal by applying, once again, for EUREKA funding. "EUREKA has been a very important part in the success of this project. Its support and funding have helped us focus on the development of the product, and we are really grateful to the Network for this assistance." Explore further: Green concrete proves more durable to fire

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