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beyond their yield point.
10. Ductibility is a polymer's ability to be stretched, pulled, or rolled into a shape
without destroying its structural integrity.
11. Notch Sensitivity is a measure of the ease with which a crack propagates
through a plastic part from a pre-existing notch, crack, or sharp corner.
12. Lubricity is a function of the load bearing characteristics of a material under
relative motion. It refers to the ability of a plastic material to slide against itself or
other plastic materials.
MECHANICAL PROPERTIES
While mechanical properties are established through the use of individual, very
specific tests performed under critical laboratory conditions, a finished plastic
product is seldom exposed to such rigorous conditions. Mechanical forces on a
plastic part are actually a combination of stresses, all working with or against each
other. These facts must be taken into consideration when you are trying to decide if a
plastic material is right for you.
1. Stress: There are two types of stress: direct and shear. While direct stress is
reflected in forces that act perpendicular to a surface, shear stress is reflected in
forces that act parallel to that same surface. When stress exists, strain is also
present.
2. Strain is a ratio measure between a change in dimension of a stressed plastic
versus the original dimension of the plastic before being stressed. Strain
measurements are usually represented as a percentage.
3. Modulus of Elasticity (or Young's Modulus) is a constant in Hooke's Law which
measures the “slope” of the original portion of the stress/strain curve.
4. Poisson's Ratio is a constant used for determining the stress and deflection
properties of plastic structures such as rotating discs or plates.
5. Ultimate Strength is the maximum stress a material can withstand when
subjected to a load.
6. Flexural Strength is a property from which we can determine the bending
capabilities of a plastic. A specimen is placed across two beams and a force is
directed from the opposing side.
7. Yield Strength represents the amount of stress required to begin to
permanently deform the material.
8. Creep is defined as increased strain over a period of time in the presence of
constant stress occurring from a constant load.
9. Impact Strength measures the ability of a plastic part to absorb energy from
impact. Impact strength is determined by a plastic specimen's basic shape, size,
thickness, as well as the type of plastic used to make the specimen.
9. Fatigue Endurance is the ability of a polymer to endure repeated stress as the
result of cyclic action, i.e., the snap action latch device, or any component subjected
to vibration.

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