Search results for "Elasticity"

Effect of moisture on elastic and viscoelastic properties of epoxy and epoxy-based carbon fibre reinforced plastic filled with multiwall carbon nanot…

2016

Abstract In this study, we investigated the peculiarities of moisture absorption and moisture-induced effects on the elastic and viscoelastic flexural properties of epoxy resin and carbon fibre reinforced plastic (CFRP) filled with multiwall carbon nanotubes (MWCNTs). Short-term cyclic creep-recovery tests of moistened epoxy and CFRP filled with MWCNTs revealed improvements in creep resistance for both materials. The addition of MWCNTs to the epoxy resin suppressed the moisture absorption by the material, causing a reduction in the diffusion coefficient by 31% and equilibrium moisture content by 15%. The addition of MWCNTs reduced the flexural strength of moistened epoxy and CFRP samples by…

Influence of hydrogen bonding on the viscoelastic properties of thermoreversible networks: analysis of the local complex dynamics

1995

Abstract The viscoelastic properties of thermoreversible polybutadiene networks in which junctions are formed by binary contacts between polar stickers (phenylurazole) are investigated by a dynamic mechanical spectroscopy within the frequency range 0.0079–79.5 Hz (0.05–500 rads−1). Time-temperature superposition is applicable in the terminal flow region and the glass transition regime, whereas thermorheologically complex behaviour is observed within the rubbery plateau region. For the terminal relaxation zone the polar stickers enhance the relaxation time and broaden the relaxation time spectrum. The thermorheologically complex behaviour within the rubbery plateau region results from the oc…

A method for determination of time- and temperature-dependences of stress threshold of linear-nonlinear viscoelastic transition: Energy-Based Approach

2011

A methodology for determination of time- and temperature-dependences of stress threshold of linear–nonlinear viscoelastic transition is proposed and validated by example of uniaxial creep of epoxy resin. Energy approach is applied for characterization of the region of linear viscoelasticity (LVE) and the threshold of LVE is given in the stress–strain representation as the master curve independent of time and temperature. Time- and temperature-dependences of the stress threshold are calculated by extending LVE theory and time–temperature superposition principles (TTSP) to the energy relations. Reasonable agreement between experimental data and calculations is obtained. It is shown that numbe…

1980

Compression creep and stress-relaxation tests have been performed on PMMA at several deformations after the sample yielding. At large loading rates, the behaviour observed was found significantly affected by the temperature rise due to the plastic deformation. Creep and stress-relaxation data taken holding the samples at constant temperature after the material loading could be collected into single curves by means of a time shift factor proportional to the loading rate. Retardations- und Relaxationsuntersuchungen bei Druckbeanspruchung von PMMA wurden bei verschiedenen Deformationen oberhalb des Fliespunktes durchgefuhrt. Bei hohen Beanspruchungsgeschwindigkeiten wurde festgestellt, das das…

Pulsatile protein release and protection using radiation-crosslinked polypeptide hydrogel delivery devices

2011

Abstract In the recent years recombinant technology has identified numerous protein based therapeutics. Their effective delivery, though, can be challenging due to the poor stability of most proteins along their pathway to the target site in the body. Hydrogels have been identified as good candidates for protein encapsulation and delivery thanks to both material and manufacturing process advantages. In this work we propose high energy irradiation as a synthetic methodology of choice to engineer hydrogel-based delivery devices for encapsulation and pulsatile release of proteins, triggered by pH, and for prevention of their denaturation when encapsulated. In particular, maleic anhydride funct…

Physicochemical and Rheological Characterization of Different Low Molecular Weight Gellan Gum Products and Derived Ionotropic Crosslinked Hydrogels

2021

A series of four different low molecular weight gellan gum products was obtained by alkaline hydrolysis with the aim to investigate the impact of the molecular weight on the rheological properties of the polysaccharide aqueous dispersions and on the physicochemical characteristics of derived ionotropic crosslinked hydrogels. In particular, thermo-rheological analysis was conducted on aqueous dispersions to study the influence of molecular weight on the thermogelation properties typical of the native polysaccharide while strain sweep experiments were conducted to establish if aqueous dispersion shows a viscoelastic behavior. The effect of different Ca2+ on the rheological properties of hydro…

Application of time-temperature superposition to energy limit of linear viscoelastic behavior

2009

The energy approach for evaluation of the limits of linear viscoelastic (LVE) behavior is considered. The approach of Foux and Bruller based on the Reiner-Weissenberg dynamic theory of strength is developed for the temperature effect. Value of the stored energy at the limit of LVE is considered as the material characteristic independent on loading conditions and temperature. Time–temperature superposition principle is extended for the energy calculations. Curves of the stored energy calculated for different temperatures are shifted to each other in the logarithmic time axes similarly as creep compliance and relaxation modulus curves in creep and tension tests, respectively. Temperature is c…

Entry and exit in a vertically differentiated industry

2011

This paper presents a duopoly model of firm rivalry in a vertically differentiated industry when market dynamics is explicitly accounted for. It shows how the interplay between demand (degree of product differentiation, demand elasticity) and cost (fixed and quality costs) factors determine firms’ relative strength when quality is irreversible. The main strategic choices are product quality, price and the timing of entry and exit. Further, firms incur sunk quality costs at time of entry and operating fixed costs of maintaining quality. Although the low quality firm may outlast its rival in the declining phase, both firms wish to be the “quality leader”.

Price discrimination and market power in export markets: The case of the ceramic tile industry.

2005

This paper combines the pricing-to-market equation and the residual demand elasticity equation to measure the extent of competition in the export markets of ceramic tiles, which has been dominated by Italian and Spanish producers since the late eighties. The findings show that the tile exporters enjoyed substantial market power over the period 1988-1998, and limited evidence that the export market has become more competitive over time.

Group Buying of Competing Retailers

2010

Under group buying, quantity discounts are offered based on the buyers' aggregated purchasing quantity, instead of individual quantities. As the price decreases with the total quantity, buyers receive lower prices than they otherwise would be able to obtain individually. Previous studies on group buying focus on the benefit buyers receive in reduced acquisition costs or enhanced bargaining power. In this paper, we show that buyers can instead get hurt from such cooperation. Specifically, we consider a two-level distribution channel with a single manufacturer and two retailers who compete for end customers. We show that, under linear demand curves, group buying is always preferable for symme…