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Any given material or component can be tested in
many different ways by many different instruments so how do you
know which instrument is right for testing your material? In order
to determine which instrument will accomplish your testing needs,
there are several key factors that one must determine before choosing
an impact test instrument.
If you have any questions or need help determining
what system may be appropriate for you, send our Applications Engineer
your question or call us
at 1.800.564.8378 option 2 (US) or call your local
Instron office.
Raw Material or End Product?
First, one should categorize the test specimen as
a raw material or an end product. Raw materials can be tested on
all Dynatup® systems while the size of certain end components
may narrow your selection. For instance, standard ASTM and ISO specimens
can be tested on all Dynatup Drop Towers; an I-beam component would
most likely fall into the 8100 Series of drop towers.
Raw Materials
Metals, Plastics, Films, Ceramics, Composites
When testing raw materials, some knowledge of the
materials' strengths is useful in determining which instrument is
appropriate. For example, most plastic and film testing is performed
by Dynatup 9200 Series and the Mini-Tower. Heavy metals
testing such as welded plates and metal pipe testing is usually
reserved for 8100 Series machines as well as some high-strength
ceramics.
While IZOD and Charpy tests can be performed with basic pendulum
test instruments, more and more people are realizing the limitations
of such tests and are switching to drop tower style test instruments
that can do those tests in addition to penetration and real-life
simulation tests. So while the initial cost of a drop tower style
system may be higher than that of a pendulum tester, the actual
return on investment and testing flexibility is much higher with
a drop tower instrument.
Specification Testing or Research Testing?
Generally, if testing is going to concentrate on
a particular ASTM, ISO, EN, or other industry specification, the
specification itself will reveal the necessary capabilities the
machine must possess regarding impact energy, geometry, etc. However,
if one is performing research testing with no feel for what the
test should do or how the results should look, one should determine
the following:
- Impact Energy: How much kinetic
energy do I need to hit this material with to cause failure?
Sometimes, experimental data from similar materials is useful
in determining this value.
- Impact Velocity/Strain Rate:
Is this material going to behave differently depending on how
fast I hit it?
In some materials, dropping a 5 kg weight from 1 meter produces
very different results than a 1 kg weight from 5 meters. This
is called strain rate sensitivity, and, if one wishes to investigate
this on a particular specimen, a high velocity machine (e.g.
Dynatup 9250HV) is useful.
- Temperature: Is this material
going to be used at the same temperature that I test at?
Temperature can mean the difference between a specimen failing
in a brittle (glass shattering) or ductile (plastic) mode. All
materials will have a ductile-to-brittle transition point and
this point may be critical in material selection and product
design. To accurately determine a material's response to impact,
one must recreate the appropriate environments that will be
encountered in service. The Dynatup 9200 Series machines along
with the Mini-Tower may be used in conjunction with Dynatup
environmental chambers for testing specimens while inside the
chamber.
Impact Geometry: Is this material going to behave differently
depending on the striker's geometry and how the specimen is supported?
Every material will behave differently depending on the geometry
of the striker, how the specimen is clamped, and the geometry
of the clamping. If testing to an ASTM, ISO, EN or other industry
specification, the specification will define what the geometry
should be. If one is not sure how to hold the specimen, they
can consult with Dynatup as to how to test their samples.
- Safety and Ergonomics: What safety
features are in place to protect the user? For example, are there
protective enclosures to contain shattered test specimens? Will
the instrument stop automatically if the operator opens such safety
enclosures or works within the test area?
Does the operator have to manually lift very heavy weights?
What keeps the falling mass or striker from inadvertently moving?
These are very important questions when selecting any test instrument.
Safety should be paramount.
Product Testing
When testing finished products, most of the criteria
above still applies but with more emphasis on the impact geometry
and temperature. A finished product should be tested with an emphasis
on reproducing real-life impact scenarios and at real-life temperatures.
For instance, when testing baseball bats, great care is taken in
reproducing the support at the lower end of the bat to simulate
the grip of the player and it is important to strike the bat near
the center of percussion or “sweet-spot” for accurate
results.
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