Scale stress effects

Electrodeposits are usually in a state of internal stress. Two types of stress are recognised. First order, or macro-stress, is manifest when the deposit as a whole would, when released from the substrate, either contract (tensile stress) or expand (compressive stress) (Fig. 12.12). Second order or microstress, occurs when individual grains or localities in the metal are stressed, but the signs and directions of the micro-stresses cancel on the larger scale. The effects of first order stress are easily observed by a variety of techniques. 

Lastly, we studied the effect of 7-stress on the effective time to steady state and the corresponding magnitude of the peak hydrogen concentration. We found that a negative T -stress (which is the case for axial pipeline cracks) reduces both the effective time to steady state and the peak hydrogen concentration relative to the case in which the T -stress effect is omitted in a boundary layer formulation under small scale yielding conditions. This reduction is due to the associated decrease of the hydrostatic stress ahead of the crack tip. It should be noted that the presented effective non-dimensional time to steady state r is independent of the hydrogen diffusion coefficient D 9. Therefore, the actual time to steady state is inversely proportional to the diffusion coefficient (r l/ ). 

The above equations describe the large-scale motion. Lij represents the interactions among the large scales. The effect of small scales appears through the residual stress tensors (i.e., Cij and Rij). In particular, Cij represents the interactions between the large and small scales, and Rij reflects the interactions between subgrid scales. The tensors Lij, Cij and Rij are known as the Leonard stress, cross-term stress and the residual Reynolds stress, respectively. 

Field observations indicate that the stress condition affects the flow characteristics of fractured rock mass (Barton et al., 1995 Ito and Hayashi, 2003 Pusch, 1989). Many laboratory investigations on single fractures also prove that the normal closure and shear dilation can significantly change the transmissivity of fractures (Makurat et al., 1990 Olsson et al., 2001). When it comes to the block scale stress-permeability relationship, the analytical models based on the orthogonal and/or persistent fracture model are available (Bai and Elsworth, 1994). However, analytical solutions do not generally exist for more realistic fracture systems. Furthermore, to the authors knowledge, block-scale study about the effect of shear dilations of fractures on the... 

Abstract A new upscaling method has been developed using 3D numerical tools (RESOBLOK 3DEC). This method has been successfully compared with standard analytical approaches in the case of a simple fracture network. This method has been applied to determine the equivalent permeability, stiffness and Biot tensor of a real fracture rock-mass at different scales. The effects of the fracture network properties and of the state of stress on the result have been investigated. 

While some of the effects of, and issues with, stress under aqueous corrosion conditions are fairly well recognized, those associated with high temperatures have received less attention. However, these stress effects play a critical role in determining whether a scale is truly protective with respect to the substrate on which it has grown. 

Mechanical Load. Static mechanical load by strain leads to stretching of random-coil polymer chains in the direction of sample elongation and chain compression in the orthogonal directions. The value of the residual dipolar and quadrupolar couplings is increased by the mechanical load, and moreover, the distribution of the correlation times is also modifled. Therefore, many NMR parameters sensitive to the residual dipolar couplings and slow motions can be used for characterization of the local strain-stress effects in heterogeneous elastomers (158,160,161,179). Dynamics mechanical load leads to sample heating where the temperature distribution in dynamic equilibrium is determined by the temperature-dependent loss-modulus and the thermal conductivity of the sample. Because transverse relaxation rate (approximated by the T2 relaxation) scales with the temperature for carbon fllled SBR, a T2 map provides a temperature map of the sample. Such temperature maps have been measured for carbon-black filled SBR cylinders for different filler contents and mechanical load (180). 

At the macroscopic scale, the effect of the creep hold time is characterized by stronger damage while holding in compression than in tension during tests in air (Fig. 6.18(a)) [69,70]. Intergranular creep damage is rather rarely observed and is only present under tensile stress and therefore cannot explain hold time effects. These effects are explained by oxidation mechanisms active in steels with 9% Cr loaded under air at... 

Extension of Time Scale Channel Charge Buildup and Bias Stress Effects. 105... 

The relaxation and creep experiments that were described in the preceding sections are known as transient experiments. They begin, run their course, and end. A different experimental approach, called a dynamic experiment, involves stresses and strains that vary periodically. Our concern will be with sinusoidal oscillations of frequency v in cycles per second (Hz) or co in radians per second. Remember that there are 2ir radians in a full cycle, so co = 2nv. The reciprocal of CO gives the period of the oscillation and defines the time scale of the experiment. In connection with the relaxation and creep experiments, we observed that the maximum viscoelastic effect was observed when the time scale of the experiment is close to r. At a fixed temperature and for a specific sample, r or the spectrum of r values is fixed. If it does not correspond to the time scale of a transient experiment, we will lose a considerable amount of information about the viscoelastic response of the system. In a dynamic experiment it may... 

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