3-Sctratch Hardness Test (Group:hardness test)
There is no older definition
(new definiton)
One of the oldest
hardness testing methods is the hardness scale according to Mohs, which is
based on a series of minerals using the principle: “Who scratches whom?” The
scale according to Mohs provided comparison values (see table 1). Thus, the
Mohs hardness 5 (apatite) is, for example, harder than the Mohs Hardness 4
(fluorite)
The advantages of
scratch hardness testing is:
-It is an
easy-to-handle method.
Disadvantages
include:
-It is appliciable
to metallic materials to a limited degree only.
-The differentiation
of the hardness values is inadequate for metals.
(Konrad Herrman, Hardness Testing: Principles
and Applications, pg:95)
4-Elastoviscoplasticity (material behaviour)
(old definiton)
The elasto viskoplastic rheological model consisits of a slider and a dashpot in parallel and this combination is in series whit a Hookean spring. Fort he uniaxial model the behaviour is purely elastic until the stress exceeds the yield stress . Onece in the plastic region the viscous component becomes active and for raidly applied loads the stress can exceed the pşastic limit. If unloading takes place form the yielded state the strain path followed is different form that of loading and permanent deformation takes place. Elastoviskoplastic behaviour is also loading path dependent since it has been demonstrated by experiments that if two loading paths reach the same point on the yield surface by different routes .
(The Finite element method in heat transfer analysis ; Roland Wynne Lewis ; pg.198 , 1996)
(new definiton) (better)
The
deformation of solid materials is usually purelly elastic when the stresses are
below a certain critical level, called the yield stres. When the stresses are
above this threshold, a combination of elastic and plastic deformation ocur,
where the latter type of deformation is recognized by being permanent.
(Hans Petter Langtangen, Computational Partial Differential Equations: Numerical Methods and
Diffpack, pg: 522)
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