Deformation mechanisms speed-dependent

The deformation behavior of many pharmaceutical materials is time-dependent and the nature of this time dependency is often related to the mechanism of compaction for a given material. It is thought that time dependency or speed sensitivity arises from the viscoelastic or viscoplastic characteristics of a material. In contrast, studies have shown that brittle materials are much less speed dependent that ductile materials because yielding and fragmentation are not as dependent on the rate of compression. It is also believed that the particle size and size distribution of the powder or granules have an important role in the speed sensitivity due to the fact that this property affects the predominant mechanism of deformation (6,58-60). 

The assessment of RBCs deformability can also be performed by active methods, through the application of external force fields, such as acoustic, optical, electrical, and magnetic ones. Acoustic radiation force has been reported for fast and direct measurement of the mechanical properties of cells in a microfluidic chip. This method is based on the formation of an acoustic standing wave within a straight microchannel that moves the cells to the acoustic pressure nodes, with a movement speed dependent on the compressibility (Hartono et al., 2011). 

Like deformation mechanisms, the damage mechanisms and destruction causes of a structure depend greatly on the temperature and the applied stress (or reciprocally on the speed of the imposed deformation). 

At room temperature, well below Tg, a brittle failure is generally observed. The ductile behavior appears when yielding becomes a competitive mechanism of deformation. At high speeds the brittle stress is not too much affected but ductile-brittle transition to higher temperatures. 

According to IK-spectroscopy inorganic filler is inert in the relation to polymeric matrix because the identical spectra of absorption of initial unfilled polymer and the polymer filled with inorganic filler are the same. Hence, mechanical behavior of PCM is defined by structural organization of composite materials, its dependence on conditions of formation and test on PCM (in our case, speed of deformation). 

Figure 53.3 summarizes injury mechanisms associated with torso impact deformation. For low speeds of deformation, the limiting factor is crush injury from compression of the body (C). This occurs at C = 35-40% depending on the contact area and orientation of loading. For deformation speeds above 3 m/sec, injury is related to a peak viscous response of VC = 1.0 m/sec. In a particular situation, injury can occur by a compression or viscous responses, or both, as these responses occur at different times in an impact. At extreme rates of loading, such as in a blast-wave exposure, injury occurs with less than 10 15% compression by high-energy transfer to viscous elements of the body. 

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