Finite element analysis (FEA) is a computerized method that
models how products behave, using a virtual environment. When using FEA, the performance
of a material or product can be tested under a variety of conditions. The
variables that can be manipulated include pressure, vibration, heat and fluid
flow. The results of these tests can determine precisely whether the product
will work the way it was designed, or if adjustments are necessary.
For example, the exact strength and flexibility of plastics
can easily be determined with FEA techniques. The FEA process subdivides the
product or part into thousands (or even hundreds of thousands) of simple-sized
units in a simple way, such as cubes. The areas that are expected to have a
high stress are generally divided into a higher mesh density of smaller units,
compared to those areas that experience little stress.
The mathematical equations are used to test the displacement
of each unit, from which the voltage and voltage can be calculated. The
cumulative effect of the performance of each unit is also calculated, which
results in an evaluation of the expected strength and function of the product.
Finite element analysis is ideal for determining which material is best for a particular
design or application.
Stress responses can be modeled for different factors, such
as mechanical stress and vibration, loading, acceleration, material fatigue,
torque, movement, fluid flow, heat transfer and electrostatics.
One of the key elements of FEA is the stress-strain curve or
graph, which is distinctive for each material. This is a reflection of the
amount of strain (tension) caused by the tension / compression load (tension or
pressure). The shape of this curve depends on several conditions, including the
composition of the material, the temperature of the material and the loading
speed. The final curve reveals the critical properties of the material: will it
deliver the properties it must have for its intended use?
Plastics can be non-reinforced or reinforced. The pieces of
plastic reinforced with glass are analyzed with linear techniques FEA. The
linear FEA assumes a "small displacement" of the part being analyzed
and uses an appropriate equation to solve the calculations more quickly.
Non-reinforced plastics (more flexible) have a very non-linear tension-strain
line up to the yield point and must be analyzed with derivative equations for
non-linear materials, not linear materials.
This is an important distinction: some molders use what they
know and can afford. Non-linear FEA software is more expensive, requires more
configuration time and requires more time to run. The molders sometimes do not
personally analyze the stress-strain curve of the plastic they are evaluating
and, instead, rely on the Young's modulus value published in the data package
of a plastic supplier. This can provide very misleading results because the
value of the module represents only one point in the voltage-voltage curve. A
non-linear FEA analysis incorporates all the real tension-voltage information
to provide accurate results.
The FEA analysis can also be used to predict the strength of
the dotted line. The dotted line occurs where the flow fronts come together.
The flow fronts will push any smoke, trapped air or contamination of the
surface of the mold in front of it, which may be trapped in the dotted line,
weakening the bond of the plastic along that line. Of course, it is also important
to use the best science of injection molding to eliminate any contamination
during the process. The FEA can be used to model the directions "in
flow" and "cross flow" to obtain a better understanding of how
the piece will react / react. Knowing the locations of the dotted line in
advance also allows engineers to better design the strength characteristics of
the piece.
Designers/engineers must understand the material they are
evaluating to make the most of the FEA simulation. This requires going beyond
the unique published values in a plastic supplier specification sheet. The
stress-strain plots, at different temperatures and deformation rates, must be
evaluated to choose the most suitable properties for the piece being designed.
Technosoft Engineering is a global provider of engineering
design, integrated services, engineering documentation and IoT for several EPCM engineering and manufacturing and
service verticals in the oil and gas industry.
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