Micromechanical force

Micromechanical force measurement apparatus (Taylor, 2006 Taylor et al., 2007) Particle adhesive forces Yes Adhesive forces vs. time (min) 15 psi >5 pm Adhesive forces between hydrate—hydrate particles, hydrate particle-surface... 

A micromechanical force apparatus has been developed at CSM to measure directly the adhesive forces between hydrate particles or between a hydrate particle and a surface (Yang et al., 2004 Taylor et al 2007). Similar micromechanical force apparatus designs have been applied to measure adhesive forces between ice particles (Hosier, 1957 Hosier and Hallgren, 1961 Fan, 2003). This apparatus... 

Figure 6.9 A schematic of the micromechanical force measurement (left) and video images of hydrate particles during each stage of the adhesive force measurement. (From Taylor, C.J., Adhesion Force between Hydrate Particles and Macroscopic Investigation of Hydrate Film Growth at the Hydrocarbon/Water Interface, MS Thesis, Colorado School of Mines, Golden, CO (2006). With permission.)...

Nevertheless, as response data have accumulated and the nature of the porous deformation problems has crystallized, it has become apparent that the study of such solids has forced overt attention to issues such as lack of thermodynamic equilibrium, heterogeneous deformation, anisotrophic deformation, and inhomogeneous composition—all processes that are present in micromechanical effects in solid density samples but are submerged due to continuum approaches to mechanical deformation models. 

Irrespective of the analysis approach, the representative volume element must be carefully defined and used. In fact, the representative volume element is crucial to the analysis and is the micromechanics analog of the free-body diagram in statics and dynamics. The representative volume element is of higher order than the free-body diagram because deformations and stresses are addressed in addition to forces. 

For a consideration of filler-network breakdown at increasing strain, the failure properties of filler-filler bonds and filler clusters have to be evaluated in dependence of cluster size. This allows for a micromechanical description of tender but fragile filler clusters in the stress field of a strained mbber matrix. A schematic view of the mechanical equivalence between a CCA-filler cluster and a series of soft and hard springs is presented in Figure 22.9. The two springs with force constants... 

The commercial composite materials being marketed today are optimized in order to make the interfacial properties acceptable in the sense that they will not fail at such low levels as to detract from the overall composite behavior. Considering a unidirectional specimen, where the fibers are all aligned parallel to each other, commercial systems can be described by a rule of mixtures661 relationship (Fig. 10). Properties of the matrix and fiber can be linearly combined based on the volume fraction of each constituent. For example, the longitudinal tensile modulus is the sum of the proportion of each component. The interface in these systems is considered ideal in that it efficiently transmits forces between fiber and matrix without failure. Using this model as a basis for micromechanical analysis and discussion, the magnitude of the forces present at the interface can be predicted. 

Our reason for stressing the concept of representative volume element is that it seems to provide a valuable dividing boundary between continuum theories and molecular or microscopic theories. For scales larger than the RVE we can use continuum mechanics (classical and large strain elasticity, linear and non-linear viscoelasticity) and derive from experiment useful and reproducible properties of the material as a whole and of the RVE in particular. Below the scale of the RVE we must consider the micromechanics if we can - which may still be analysable by continuum theories but which eventually must be studied by the consideration of the forces and displacements of polymer chains and their interactions. 

Fig. 6 Micromechanical model of a section of a semi-crystalline polymer with lamellae oriented perpendicular to the principal stress direction showing the long period L and the thicknesses of crystalline (Lc) and amorphous layers (La) the latter are composed of loose segments, entangled chains and more or less extended tie molecules. Large forces can be transferred at those points (o) where highly extended tie molecules (eTM) enter crystalline lamellae...

Other valuable extensions of contact-mode SFM probe micromechanical properties of the sample. Variation of the repulsive force or upward deflection of the cantilever are registered while a Z-modulation is applied either to the sample or the cantilever base (Fig. 6). The dZ/dZc signal contains information about the local stiffness dF/d.8 of the sample, where S=Zt-Zc is the indentation depth. Micromechanical applications will be discussed in Sect. 2.2. 

Micromechanical experiments made so far can be roughly divided into two parts (i) design of special techniques to measure and evaluate separately different contributions in the net force, such as adhesion, friction, deformation, and (ii) imaging of various heterogeneous surfaces such as blends, composites and microphase separated structures by conventional SFM s to collect statistical information and understand the origin of the mechanical contrast. Many of the micromechanical experiments were discussed elsewhere [58, 67, 68, 381, 412-414]. Here we will focus on recent advances in analytical applications of the active probe SFM. 

Abstract When subjected to a mechanical loading, the solid phase of a saturated porous medium undergoes a dissolution due to strain-stress concentration effects along the fluid-solid interface. Through a micromechanical analysis, the mechanical affinity is shown to be the driving force of the local dissolution. For cracked porous media, the elastic free energy is a dominant component of this driving force. This allows to predict dissolution-induced creep in such materials. 

H. B. Chan, V. A. Aksyuk, R. N. Kleiman, D. J. Bishop, and F. Capasso, "Quantum mechanical actuation of microelectro mechanical systems by the Casimir force," Science, 291, 1941-4 (2001) "Nonlinear micromechanical Casimir oscillator," Phys. Rev. Lett., 87, 211801 (2001). 

The determination of the elementary propagation rate constant is connected with considerable difficulties. Measurements can rarely be made in the gaseous phase, and in the condensed phase the consequences of attractive intermolecular forces cannot be excluded. The reaction studied depends on the medium. Therefore the micromechanism of propagation must be known in detail, and suitable kinetic methods must be applied. Even then, the elementarily of the measured constant will not be guaranteed at the present state of the art. 

Figure 6.2 Typical evolution at various voltages of SACE glass gravity-feed drilling using a cylindrical tool (cathode) of 0.4 mm diameter with a force of 0.8 N acting on it. The electrolyte (30 wt% NaOH) level above the workpiece is about 1 mm. Reprinted from [131] with the permission of the Journal of Micromechanics and Microengineering.

Treating cells with CD to disassemble their actin cytoskeleton has been described many times in the literature. When cells were studied by scanning force microscopy (SFM) after CD exposure, a significant reduction of membrane stiffness was reported for various cell types [41,42]. Since the acoustic impedance also decreases, it seems reasonable to propose that the QCM may serve as a micromechanical probe to study membrane stiffness. Further experiments will be presented below that support this point of view. 

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