Nonrecoverable deformation

The plastic properties of a material are often determined by an indentation test [28]. Both static and dynamic test methods are available, but all generally determine the pressure necessary to cause permanent and nonrecoverable deformation. 

Hardness Measurements. Hardness was measured on two scales, the Rockwell R scale, and the Shore D scale. The Rockwell test measures nonrecoverable deformation after a %-inch sphere has been pressed into a molded sheet of the plastic and the load released. In the Shore... 

Creep - Nonrecoverable deformation in a part subjected to a continuous load. Creep is dependent on temperature, and the duration and amount of the load. 

Brittle fractures and potentially more dangerous because there occurs no observable deformation of the material. In a ductile failure, on the other hand, large nonrecoverable deformations occur before rupture actually takes place and serve as a valuable warning. A material thus absorbs more energy when it fractures in a ductile fashion than in a brittle fashion. 

Viscoelasticity is the property of materials that exhibit both viscous and elastic characteristics when undergoing deformation. To model this material behavior, viscoelasticity utilizes spring constants ( i and E2), dashpots (viscosity, v), and St. Venant sliders (a slider to account for nonrecoverable deformation) elements. The properties of these elements may be selected to cover a wide range of elastic and time-dependent viscous behavior. Viscoelastic models can be divided into both the number of elements employed and whether the elements are in a series or parallel arrangements. These elements may be linear or nonlinear and are combined as necessary for the model to describe the behavior of the sediment imder study. These models describe short-term behavior reasonably well, but tend to not yield reliable predictions of deformation for extended time periods. 

Buchdahl R, Nielson L E and Merz E H (1951), Rheology of thermoplastics. II. Recoverable and nonrecoverable deformations of polystyrene between 90" C and 240°C, as a function of molecular weight . Journal of Polymer Science, 6, 403-422. 

The values of Young s modulus for isotropic glassy and semicrystalline polymers are typically two orders of magnitude lower than those of metals. These materials can be either brittle with fracture at strains of a few percent or ductile leading to large but nonrecoverable deformation. Young s modulae for elastomers are t3q)ically four orders of magnitude smaller than, say, steel— which is how recoverable extensions up to %1000% are possible. 

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