Method B - Width/Depth:
Measure the width or depth of the scratch
(grooves) using an optical measuring device.
Method C - Image Analysis:
The scratch mark intensity may also be evaluat-
ed by using Image Analysis techniques.
NOTE: Detailed descriptions are recommended
when depicting scratch or mar damage. Items
that might be described include surface topogra-
phy, material deformation, material removal, and
color changes. The following examples have
been used to describe damage in plastics:
-
scratch is shallow (or deep)
-
scratch is smooth, with a well defined shape
(or rough and deformed)
-
scratch includes plastic flow of the material (or
cutting, tearing, cracking, chipping, crazing)
-
scratch includes visible ripple marks at the
bottom (i.e. chevron or parabolic shaped)
-
strain whitening is visible (or no change in
color)
INFLUENCES ON RESULTS
For comparable and reproducible tests, it is rec-
ommended the operations be performed under
conditions covered by an established test proce-
dure. The following factors are known to affect
the scratch resistance of materials, and could
potentially impact your test results:
Test methodology
Test conditions (i.e. temperature or humidity)
Scratching speed
Geometry and condition of scratch tip or
indenter tool
Applied load
Material (i.e. filler type; additives; lubricant;
polymer type)
Surface roughness and grain direction
Type and thickness of surface treatment
Elastic properties of the specimen
Method of scratch assessment
Length of time between scratch and evaluation
Plastics
The properties of plastic materials can greatly
influence the evaluation of scratch and mar
resistance. It is important to be aware of the fol-
lowing factors and take them into consideration:
1. Many plastics have elastic recovery upon
removal of applied stress.
2. Many plastics have visco-elastic properties
and the stresses in the plastics may relax dur-
ing loading.
3. Plastics may change structure during material
flow, which can also change the mechanical
properties of plastics.
Irregular Surfaces
The existence of 'chatter' in a scratch path may
indicate a non-uniform composition or the pres-
ence of surface irregularities. An irregular sur-
face may also cause a scratch pin to 'bounce' on
the specimen surface, resulting in additional
impact force at landing points and additional
damage to the surface.
MAINTENANCE
Taber recommends annual factory calibration at
which time the unit will be thoroughly checked.
Care of the Scratch Tips
The precision cutting edge of the scratch (mar)
tips is fragile, and must be handled with care.
Depending on the material being tested, tips can
provide months of satisfactory service.
» Do not scrape the cutting edge of the scratch
tip against a hard surface, such as steel.
Doing so may prematurely dull the tool.
» The spline-shaft fingers must not be allowed
to drop against the specimen or platform.
Carefully lower them against the specimen
just prior to making a test.
The scratch tip will eventually become dull
through use. It is recommended that several
spare tips be kept on hand for replacement and
standardization purposes.
5
710 Operating Instructions ver 1.1
Summary of Contents for 710
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