Structure-thermomechanical

There are, of course, numerous options of this type, the conventional points of view tending to stress the role of thermal excitations (in basically invariant electronic structures), thermomechanical processes, or tribochemical mechanisms. 

Network properties and microscopic structures of various epoxy resins cross-linked by phenolic novolacs were investigated by Suzuki et al.97 Positron annihilation spectroscopy (PAS) was utilized to characterize intermolecular spacing of networks and the results were compared to bulk polymer properties. The lifetimes (t3) and intensities (/3) of the active species (positronium ions) correspond to volume and number of holes which constitute the free volume in the network. Networks cured with flexible epoxies had more holes throughout the temperature range, and the space increased with temperature increases. Glass transition temperatures and thermal expansion coefficients (a) were calculated from plots of t3 versus temperature. The Tgs and thermal expansion coefficients obtained from PAS were lower titan those obtained from thermomechanical analysis. These differences were attributed to micro-Brownian motions determined by PAS versus macroscopic polymer properties determined by thermomechanical analysis. 

First-order phase transitions can be detected by various thermoanalytical techniques, such as DSC, thermogravimetric analysis (TGA), and thermomechanical analysis (TMA) [31]. Phase transitions leading to visual changes can be detected by optical methods such as microscopy [3], Solid-solid transitions involving a change in the crystal structure can be detected by X-ray diffraction [32] or infrared spectroscopy [33], A combination of these techniques is usually employed to study the phase transitions in organic solids such as drugs. 

Cyclic stresses/strains, 13 481-483 Cyclic stress-strain curves, 13 491 Cyclic structures, nonaromatic, 15 5 Cyclic thermomechanical characterization, of shape-memory polymers, 22 358-362 Cyclic trimer ketone peroxides, 14 292 Cyclic trioxides, 18 448 Cyclic voltammetry, 9 580 Cyclitols, 4 710 Cyclization(s)... 

Ti-6A1-4V is probably the most widely used Ti alloy in the world. It is an alloy with a duplex structure containing solid solutions based on the a, c.p.h. A3 and / , b.c.c. A2 allotropes of Ti. In its final heat-treated form it consists predominantly of a and its high strength is partly derived from its final microstructure which is manipulated by a series of thermomechanical treatments that include hot isothermal forging just below its P transits temperature (T ). The interest is, in the first place, to predict and how the amounts of a and P vary with temperature. 

This article reviews recent developments in polymer thermomechanics both in theory and experiment. The first section is concerned with theories of thermomechanics of polymers both in rubbery and solid (glassy and crystalline) states with special emphasis on relationships following from the thermomechanical equations of state. In the second section, some of the methods of thermomechanical measurements are briefly described. The third section deals with the thermomechanics of molecular networks and rubberlike materials including such technically important materials as filled rubbers and block and graft copolymers. Some recent data on thermomechanical behaviour of bioelastomers are also described. In the fourth section, thermomechanics of solid polymers both in undrawn and drawn states are discussed with a special focus on the molecular and structural interpretation of thermomechanical experiments. The concluding remarks stress the progress in the understanding of the thermomechanical properties of polymers. 

The fibrillar structure of crystalline polymers is determined by molecular characteristics, the initial morphology and orientation conditions. Recently, a complex investigation of the effect of molecular parameters (MW, MWD and degree of branching) and orientation parameters (temperature and draw ratio) on the morphology of PE and its thermomechanical behaviour has been reported 181 185). 

These observations are valid not only for PE. The changes in the thermomechanical behaviour after annealing of oriented PP having a modulus of elasticity of E = 10-15 GPa and PA (E = 8-10 GPa)187) are similar to those of PE. The thermomechanics of the so-called hardelastic fibres, which are known to have a lamellar structure, is very similar to that of annealed PE and PP 188). 

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