Strain rate- and temperature-dependent tensile properties of an epoxy-based, thermosetting, shape memory polymer (Veriflex-E)

In this study, the inelastic deformation behavior of an epoxy-based, thermally triggered shape memory polymer resin, known as Veriflex-E, was investigated. The experimental program was designed to explore the influence of strain rate on monotonic loading at various temperatures which is needed to establish the design space of SMPs in load bearing applications. Thermally actuated shape memory polymers can be thought of as having two phases separated by the glass transition temperature (T _g ). At temperatures below the T _g , Veriflex-E exhibits a high elastic modulus and positive, non-linear strain rate sensitivity in monotonic loading. The Poisson’s ratio at room temperature is independent of the strain rate, but dependent upon the strain magnitude. As the temperature is increased, the strain rate sensitivity in monotonic loading decreases. Well above the T _g , the elastic modulus drops by several orders of magnitude. In this high temperature region, the material achieves strain levels well above 100% and Poisson’s ratio is constant at 0.5 regardless of strain rate or strain magnitude.     

A thermomechanical constitutive model for an epoxy based shape memory polymer and its parameter identifications

This paper presents a three-dimensional (3D) finite deformation thermomechanical model to study the glass transition and shape memory behaviors of an epoxy based shape memory polymer (SMP) (Veriflex E) and a systematic material parameter identification scheme from a set of experiments. The model was described by viscoelastic elements placed in parallel to represent different active relaxation mechanisms around glass transition temperature in the polymer. A set of standard material tests was proposed and conducted to identify the model parameter values, which consequently enable the model to reproduce the experimentally observed shape memory (SM) behaviors. The parameter identification procedure proposed in this paper can be used as an effective tool to assist the construction and application of such 3D multi-branch model for general SMP materials.     

Dielectric and magnetoelectric properties of co-fired PbZr0.52Ti0.48O3–Co0.6Zn0.4Mn0.3Fe1.7O4–PbZr0.52Ti0.48O3 trilayer composites

In this paper we report the dielectric and magnetoelectric (ME) properties of co-fired Pb_0.52Ti_0.48O₃–Co_0.6Zn_0.4Mn_0.3Fe_1.7O₄–PbZr_0.52Ti_0.48O₃ (PZT–CZFMO–PZT) trilayer composites prepared using Mn and Zn simultaneously substituted CoFe₂O₄ (Co_0.6Zn_0.4Mn_0.3Fe_1.7O₄) as a magnetostrictive phase. For PZT–CZFMO–PZT composites, the maximum values of longitudinal and transverse ME voltage coefficient (α _E33 and α _E31 ) were observed to be comparable in magnitude contrary to the usual trend (α _E31 much greater than α _E33 ) for ME composite structures. The highest transverse ME voltage coefficient α _E31 ~64 mV/cm Oe (at an applied ac magnetic field of frequency ~1 kHz) was obtained for the composite containing the thickest layer of CZFMO. The dielectric constant spectra for PZT–CZFMO–PZT composites demonstrated very high values of resonance frequency (~47–81 MHz) and band width (~9–13 MHz).     

Fluid flow stability analysis of multilayer fiber drawing

We here investigate drawing of multi-layered Newtonian and non-Newtonian fluid fibers, drawn under isothermal and non-isothermal conditions. We first develop one-dimensional equations governing mass, momentum, and energy balances and solve them numerically to obtain steady state draw root shape, velocity, and temperature profiles. These solutions are then used to perform linear stability analysis. For the case of isothermal draw, the system displays an oscillatory instability when the draw ratio (ratio of cross-sectional areas of fiber at the entrance and exit of the drawing) is higher than a critical draw ratio (highest stable draw ratio) of about 20.21. Investigation of stability behavior under non-isothermal draw conditions is performed by considering radiative heating and convective cooling. Employing only radiative heating enhances the critical draw ratio, and simultaneous heating and convective cooling increase the critical draw ratio even further. For the case of simultaneous heating and cooling, with increasing convective cooling strength, the critical draw ratio first increases, reaches a maximum, and then gradually decreases. However, with only convective cooling, the critical draw ratio decreases with an increase in convective cooling strength. We also find that the stabilizing effect of a non-isothermal operation can be enhanced by considering fluids with higher viscosity sensitivity to temperature, increasing the maximum temperature, and for sharper attenuation of the fiber cross-sectional area with length. For the case of isothermal drawing of non-Newtonian fluid fibers, the system has a higher critical draw ratio for shear thickening fluids (power-law exponent, n>1). In contrast, the use of a shear thinning fluid (n<1) reduces the critical draw ratio. Consideration of a non-isothermal operation of non-Newtonian fluid fibers reveals that the critical draw ratio is primarily determined by the non-Newtonian behavior rather than the non-isothermal drawing.     

EFFECT OF LIPASE ENZYME ON THE RIPENING OF WHITE PICKLED CHEESE

The effect of addition of pregastric lipase enzyme on the accelerated ripening of white pickled cheese was investigated. Commercial pregastric lipase was added to milk before rennet addition at a level of 0,5, 8, 11 g per 100 L of milk and cheeses were made from this milk. Total solids, fat, total nitrogen, salt, titratable acidity, pH and free fatty acids (C₂-C_18:1) were analysed in the samples during 1–90 days of ripening period at 15 days intervals. Total solids, fat, total nitrogen, salt, titratable acidity, and pH of cheeses slightly increased during the ripening period. Free fatty acids and volatile free fatty acid contents in cheeses made from pregastric lipase added milk were affected by pregastric lipase and their contents were increased significantly (P<0.01) during the ripening period. Particularly, when cheese had a high level (11 g per 100 L milk) pregastric lipase, the amounts of butyric, caproic and caprylic acids in white pickled cheese were quite high. The relative amounts of volatile free fatty acids varied with storage time and pregastric lipase levels.