Strain relaxations

The most characteristic features of viscoelastic materials are that they exhibit a time dependent strain response to a constant stress (creep) and a time dependent stress response to a constant strain (relaxation). In addition when the... 

The basic viscoelastic theory assumes a timewise linear relationship between stress and strain. Based on this assumption and using mechanical models thought to represent the behavior of a plastic material, it can be shown that the stress, at any time t, in a plastic held at a constant strain (relaxation test), is given by ... 

Assuming axi-symmetrical deformation, simulation of the complete micromirror surface has been found to have a "palm-tree" shape, with t5q)ical maximum deformation less than 2 nm. This shape can be explained by strain relaxation in the thin aluminum layer constituting the mirror surface (Zamkotsian and Dohlen, 1999). 

That characteristic of vulcanised elastomers or thermoplastics in showing a gradual increase in deformation under constant load with passage of time also known as strain relaxation or drift. Crepe Rubber... 

GaP has a much larger mismatch with CdS (-7%) compared with InP. Yet a fair degree of epitaxy was obtained for CD CdS on the (111) GaP surface [58]. In this case, a mixture of cubic and hexagonal CdS with a large density of stacking faults, presumed due to strain relaxation arising from the large mismatch, was obtained. 

A ,Ga)As buffer layer is grown before epitaxy of (Ga,Mn)As. To control strain in the film, strain-relaxed thick (In,Ga)As ( 1 /zm) with the lattice constant a0 greater than the subsequent (Ga,Mn)As layer can be employed. The Mn composition x in the Gai - Mn As films can be determined from measurements of a0 by x-ray diffraction (XRD), once the dependence a0(x)is calibrated by other means, such as electron probe micro-analysis (EPMA) or secondary ion mass spectroscopy (SIMS). 

Fluorescence EXAFS studies of a (In,Mn)As thin layer (10 nm) grown on a GaSb buffer layer and of (In,Mn)As quantum dots (QDs) on GaAs were also performed. The results show that in the thin (In,Mn)As layer, the In-site substitutional Mn and the NiAs-type MnAs coexist, whereas the majority of Mn atoms are substituted into the In-sites of InAs in (In,Mn)As QDs. It is argued that the difference of the strain deformation between the thin layer (with strain) and thick layer and QDs (strain relaxed) is responsible for the differences in the local structure of the Mn atoms (Ofuchi et al. 2001b). 

For shear strains greater than approximately 2 the ratio cr(r)/> 0 for a concentrated polystyrene solution was reduced at all observable times. For the large strains, relaxation proceeded more rapidly at short times, but at longer times the residua] stress decayed with about the same time dependence as that in the linear viscoelastic region. 

Polyurethanes under tension are very "notch" sensitive and when used as a spring, a nick will propagate and cause failure. Under long-term tension, polyurethanes will suffer from creep (strain relaxation) and set. 

Softer materials normally have better compression set results than the harder grades. This is due to the chains being able to move more readily over each other. Compression set values can also be improved by introducing some degree of permanent cross-linking at the prepolymer stage. If polyurethane is placed under a constant stress, it will creep slowly over the course of time due to strain relaxation. 

Recently, it has been demonstrated [53] that at room temperature the Ge(0 01) surface does not show a uniform simple reconstruction, but instead an ordered striped pattern consisting of p(2 x 1) and c(4 x 2) domains (see Fig. 4). This striped pattern corresponds to a minimum free energy and can be fully explained in terms of a well-established strain relaxation theory [54]. With increasing temperature the p(2 x 1) domains grow at the expense of the c(4 x 2) domains. It requires extremely clean and defect-free surfaces to observe this phenomenon, which is probably the reason why it hasn t been observed before. In contrast to Ge(00 1) it is inherently difficult to prepare clean Si(00 1) surfaces with defect densities low enough for this pattern to develop. 

TABLE 2 Deformation potentials (eV) of zincblende GaN and AIN. The values obtained without internal strain relaxation are also listed in parentheses. 

K. Shimada, T. Sota, K. Suzuki [ Mater. Res. Soc. Symp. Proc. (USA) vol.482 (1998) p.869 private communication for results without internal strain relaxation ]... 

They took the standard energy functional in DFT theory but, rather than simply solving this, they sought a way of achieving the solution of the Kohn-Sham DFT equations, geometry relaxation and volume and strain relaxation simultaneously. 

S. C. Jain and M. Willander, Introduction Strain, Stability, Reliability and Growth Mechanism of Strain Relaxation Strain, Growth, and TED in SiGeC Layers Bandstructure and Related Properties Heterostructure Bipolar Transistors FETs and Other Devices... 

The experimentally determined redox potentials are given as solid points while the line corresponds to the calculated potentials. Based on Eq. 11.1, where F is the Faraday constant (F = 96.5 kJ mol1) and n = 1, the slope of the line should be 96.5 kJ mol-1 V"1, if differences in AS are neglected and strain relaxation is the only contribution to the variation in redox potential. 

Relaxation processes are universal. They are found in all branches of physics mechanical relaxation (stress and strain relaxation, creep), ultrasonic relaxation, dielectric relaxation, luminescence depolarisation, electronic relaxation (fluorescence), etc. Also the chemical reaction might be classified under the relaxation phenomena. It will be readily understood that especially in polymer science this time-dependent behaviour is of particular importance. 

The linear regression (Fig. 47) has a slope of 61 kJ mol iV i and a correlation coefficient of = 0.78. The deviation of the slope from the theoretical value of 96 kJ mol-iV i is caused by influence of different factors (entropy contributions, electronic effects and the force field parametrization etc.). The calculated value of the slope is ca 65% of the theoretically expected one. This indicates that strain relaxation is a major component, and from the linear variation it follows that the neglected factors vary roughly linearly with strain energy effects. The mean error of calculated reduction potentials is 100 mV (Fig. 48). 

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