Shear elastic moduli plastics mechanical behavior

Tensile and shear forces are not the only types of loads that can result in deformation. Compressive forces may as well. For example, if a body is subjected to hydrostatic pressure, which exists at any place in a body of fluid (e.g. air, water) owing to the weight of the fluid above, the elastic response of the body would be a change in volume, but not shape. This behavior is quantified by the bulk modulus, B, which is the resistance to volume change, or the specific incompressibihty, of a material. A related, but not identical property, is hardness, H, which is defined as the resistance offered by a material to external mechanical action (plastic deformation). A material may have a high bulk modulus but low hardness (tungsten carbide, B = 439 GPa, hardness = 30 GPa). 

Considering a mass of ceramic powder about to be molded or pressed into shape, the forces necessary and the speeds possible are determined by mechanical properties of the diy powder, paste, or suspension. For any material, the elastic moduli for tension (Young s modulus), shear, and bulk compression are the mechanical properties of interest. These mechanical properties are schematically shown in Figure 12.1 with their defining equations. These moduli are mechanical characteristics of elastic materials in general and are applicable at relatively low applied forces for ceramic powders. At higher applied forces, nonlinear behavior results, comprising the flow of the ceramic powder particles over one another, plastic deformation of the particles, and rupture of... 

Therefore, the main flow properties of plastics in the widest sense are influenced by the mean molar mass. These properties include melt viscosity, modulus of elasticity and shear modulus above the glass transition range, creep behavior, stress cracking behavior, strain at break, mechanical strength, solubility and swelling behavior, etc. 

High polymers show pronounced viscoelastic and viscous (plastic) behavior under normal mechanical loads compared to most other materials, meaning the deformations that occur are in some cases elastic (reversible), and in some cases viscous and thus plastic (irreversible). A result of this is that material parameters such as modulus of elasticity, shear modulus and other important related mechanical properties of high polymers depend not only on temperature, but rather - among other things - on load application times and rates as well. 

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