Strain direct

The direct strains in the global X and Y directions will be given by (see Appendix C for details)... 

Alternatively, the x-direction strain at buckling can be calculated from Equation (3.117) and the uniaxial stress-strain relation as... 

In order to apply the crack nucleation approach, the mechanical state of the material must be quantified at each point by a suitable parameter. Traditional parameters have included, for example, the maximum principal stress or strain, or the strain energy density. Maximum principal strain and stress reflect that cracks in rubber often initiate on a plane normal to the loading direction. Strain energy density has sometimes been applied as a parameter for crack nucleation due to its connection to fracture mechanics for the case of edge-cracked strips under simple tension loading. ... 

Extended defects interrupt the continuity of the crystal, generating crystal subgrains whose dimensions depend, in a complex fashion, on the density of extended defects per unit area. Table 4.1 gives examples of reported dislocation densities and subgrain dimensions in olivine crystals from the San Carlos perido-tite nodules (Australia). Assuming a mean dislocation density within 1.2 X 10 and 6 X 10 cm , Kirby and Wegner (1978) deduced that a directional strain pressure of 35 to 75 bar acted on the crystals prior to their transport to the surface by the enclosing lavas. 

Initiating particles may also be formed by processes other than direct strain of covalent bonds. It appears that the mechanical energy transferred to the... 

Strain, usually refers to the direct strain (aligned with the major axis) of a deformable film. The axial extensional strain resulting from bonding two layers. 

M. Pyo, C.C. Bohn, E. Smela, J.R. Reynolds, and A.B. Brennan, Direct strain measurement of polypyrrole actuators controlled by the polymer/gold interface, Chem. Mater., 15 (4), 916 922 (2003). 

Another model-free method for active damage detection is based on directional transducers. For passive sensing. Section 16.9 has already discussed the use of directional strain rosettes (both piezo and optical) to effectively detect an acoustic source without the need for a structural model. For active sensing, directional transmission as well as reception of guided wave can be achieved with phased-array transducers. 

V12 = major Poisson s ratio (load in 1 -direction, strain in 2-direction)(please note that this is different from V21, which is the minor Poisson s ratio)... 

Quasi-static direct methods are both versatile and well suited to investigating fully the piezoelectric response of polymers. Direct methods of this type are especially appropriate for amorphous polymers. TSC measurements (68) are used to measure the remanent polarization imparted to a polymer, and direct strain or charge measurements are used to investigate the piezoelectric coefficients with respect to the electric field, frequency, and stress. 

Osteocytes and osteoblasts are essential for mechanosensing and mechanotransduc-tion, and cell response depends on strain and loading frequency (Kadow-Romacker et al., 2009 Mosley et al., 1997). We explored the use of piezoelectric materials as a mean of directly straining bone cells by converse piezoelectric effect. 

According to the theory of elasticity, for one directional strain where the stress is teiow the yield point, Eqs. 6.1a and 6.1b apply. Therefore... 

AR Series Rheometers These are a group of rheometer systems that measure viscoelastic data for both fluids and solids. The AR series is a sequel to the former rheometrics rheometers with updated performance and efficiency. The instruments feature sensitive low-torque performance, accurate stress, direct strain control, and intuitive software. There are three AR series models in addition, TA offers the ARES-G2 rheometer, which is a research instrument. Each instrument has different features and torque ranges. The newest of the group, the ARG-2 instrument, has a magnetic drive that provides enhanced low-torque precision and accuracy. 

It is a nondimensional measure, often expressed in percentage of original length, and mistakenly called elongation instead of direct strain. The direct strain under tension is correlated to the direct stress in the elastic range up to o, by the Young modulus E. 

Changes in dimensions ean be quoted as either an absolute or relative metrie. For example expansion is an absolute metric, typically quoted in pm or mm, whieh gives the movement in a specified direction strain is a relative metric, typically quoted as a percentage or fraction, which relates the expansion to an initial fixed dimension. Both of which can have their uses. However, the direction in which the expansion or strain is measured should be clearly specified, e.g., in-plane (x-y direction, parallel to the plane of the film) strain and out-of-plane (z-direction, perpendicular to the plane of the film) strain. In addition, how the strains have been calculated, e.g., relative to the as-synthesized passive length or relative to the stable length after precycling, should be clearly specified. Furthermore, it should be clearly stated whether the metric quoted is a reversible or irreversible expansion or... 

However, the software of advanced stress controlled instruments allows for running an experiment at variable strain amplitudes. In this operation mode, several iterative cycles have to be measured before the actual measurement. In these iterations, the applied torque is adjusted to produce the desired strain amplitude [27]. In contrast to the classical way of amplitude adjustment, new operating modes of stress controlled rheometers (termed Direct Strain Oscillation or Continuous Oscillation) use a feedback control to compare the current strain signal y(t) at time t to the desired pure sinusoidal signal yd t) = y o sin(control loop then adjusts the torque accordingly in order to minimize the difference Yd t + At) — y (t -I- At)I for the next step at t -I- At. This deformation control enables a stress controlled rheometer to mimic a strain controlled experiment [27]. This holds true even beyond the linear regime where nonlinear contributions to the strain wave are compensated for and are then transferred into the stress wave, as the control loop tries to make the appropriate adjustments to the torque within minimum time. 

LAOS measurements for two samples, a polyisoprene melt (abbreviated PI-84k, Mw = 84,000 g/mol, PDI = 1.04) and a 10 wt% solution of poly isobutylene (abbreviated PIB, Af = 1.1 xlO g/mol) in oligoisobutylene, were conducted on four different rheometers. The first two were separated motor transducer(SMT)-rheometers, namely the ARES-G2 (TA Instruments) and the ARES-LS (TA Instruments) with a IKFRTNl transducer. The DHR-3 (TA Instruments) and the MCR501 (Anton Paar) are in principle stress controlled instruments, but can be used for strain controlled experiments when using the deformation control feedback option (called continuous oscillation for DHR-3 and direct strain oscillation for MCR501). 

Chan HK, Mohraz A (2012) Two-step yielding tmd directional strain-induced strengthening in dilute colloidtil gels. Phys Rev E 85 041403... 

Lhuger J, Wollny K, Huck S (2002) Direct strain oscillation a new oscillatory method enabling measurements at very small shear stresses and strains. Rheol Acta41 356-361... 

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