Mechanical compression experiments modeling

The theoretical approach for determining the deformation behaviour of a network due to swelling or due to a mechanical force (stress-strain measurements, compression experiment) is based on a hypothetical phantom network. A phantom network is, by definition, a network with the fictitious property that chains and junctions can move freely through one another without destroying the cormectivity of the network. Usually, the network chains behave as Gaussian chains. Within the phantom network model, three network types can be distinguished ... 

In spite of these representative first-order descriptions, experiments, theory, and material models do not typically agree to second order. Compressibility (derivatives of pressure with volume) shows complex behaviors that do not generally agree with data obtained from other loadings. Mechanical yielding and strength behavior at pressure show complexities that are not... 

Thakurta G, Borst CL, Schwendeman DW, Gutmann RJ, Gill WN. Pad porosity, compressibility and slurry delivery effects in chemical-mechanical planarization modeling and experiments. Thin Solid Films 2000 366 181-190. 

FIGURE 17.30 Mechanical properties of baked cellular products, (a) The Young (compression) modulus En as a function of product density (p of wafers kept in air of various water activities (indicated near the curves). (After results by G. E. Attenburrow et al. J. Cereal Sci. 9 (1989) 61.) (b) Compression and decompression (indicated by arrows) of the crumb of a model wheat bread (p/pm 0.35), giving the stress a versus the Cauchy strain c- Complete densification would presumably be reached at c 0.7. The solid line shows the first compression and decompression, the broken line the second compression. The bread was 4 hours old. (c) Same experiment, same bread, but now 7 days old. (After results by C. J. A. M. Keetels et al. J. Cereal Sci. 24 (1996) 15.)... 

Numerical simulations of compressible flows developing in both space and time with precise control of initial and boundary conditions are ideally suited in the quest to recognize and understand the local and global nature of the flow instabilities driving the combustor performance — which are the main focuses of this work. Numerical experiments can be used to isolate suspected fundamental mechanisms from others which might confuse issues. The extensive space/time diagnostics available based on the simulation database can be exploited to develop analytical and conceptual bases for improved modeling of the turbulent flame. 

In respect of the classical mechanics, E is an "ideal" coefficient, like the elasticity modulus in Hooke s model. Most of the practical compressions/dilatation experiments carried out with adsorption layers are comparable to the screening of elastic properties in material science. In analogy to the coefficients of the 3D-elasticity theory, we have to consider complex coefficients in surface rheology. The surface elasticity coefficient written as a complex modulus therefore has the form... 

William Harvey [77] taught that the heart is the only pump that propels blood around the closed circulatory loop. Liebau [78], on the other hand, based on experiments with fluid mechanical models of his own design, concluded that blood could be propelled around the loop without the benefit of cardiac and venous valves. Liebau demonstrated with his simplest model, consisting of two tubes with different elastic properties, free of valves, making a closed water-filled loop, that periodic compression at an appropriate, fixed site caused steady net fluid flow around the loop, but could not explain the reason why this occurred. The explanation, developed in 1998 [57], was that Liebau worked with an asymmetric loop to which he provided energy by periodic compression at some site. This was termed impedance defined flow, in view of the nonuniform distribution of impedances around the loop. (Compression at a symmetric point, if any, generates no steady net flow, either experimentally or theoretically.)... 

Non-linear viscoelastic mechanical behaviour of a crosslinked sealant was interpreted as due to a Mullins effect. The Mullins effect was observed for a series of sealants under tensile and compression tests. The Mullins effect was partially removed after a mechanical test, when a long relaxation time was allowed, that is the modulus increased over time. Non-linear stress relaxation was observed for pre-strained filler sealants. Time-strain superposition was used to derive a model for the filled sealants. Relaxation over long periods demonstrates that the Mullins effect is caused by non-equilibrium with experimental conditions being faster than return to the initial state. If experiments were conducted over times of the order of a day there may be no Mullins effect. If a filled elastomer were only required to perform its function once per day then each response might be linear viscoelastic. 

In conjunction with the above experiments, hydrodynamic computer models have been developed to provide a detailed description of the liner motion [18]. The effect of the compressibility of the liner fluid becomes particularly important in thick liners moving at high velocity. If the turnaround time is much less than the transit time of a sound wave through the liner, compression waves will be set up which modify the motion and can cause severe shock loading of the driving mechanism. It is desirable to operate a reactor under conditions where these waves are not significant, and this sets an upper limit on the final pressure to which the plasma may be compressed. 

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