Chapter 5A Flashcards
What are the main types of properties tested in plastics?
Mechanical, physical, thermal, environmental, and optical.
Why are tests conducted on plastics?
To maintain control of manufacturing processes and to characterize the products.
What are the main agencies that establish testing specifications?
American Society for Testing and Materials (ASTM)
International Organization for Standardization (ISO).
SIRIM
What are the three types of mechanical forces that affect materials?
Compression, tension, and shear.
Define stress and strain.
Stress: Pressure applied over an area.
Strain: The change in length relative to the original length.
What is tensile strength, and how is it measured?
The ability of a material to withstand forces pulling it apart. Measured as the maximum force divided by the cross-sectional area of the narrow section.
- Machine pulls the specimen (dumbbell).
- Records both for and elongation on a stress/strain diagram.
Describe the compressive strength test.
Measures how much force is required to rupture or crush a material by loading a specimen between two plates.
- Load the specimen between two plates.
- The specimen is then compressed at a uniform rate.
- The maximum load is recorded along with tress-strain data.
-Specimen (block or cylinder).
- Stress can be reported at arbitary strain (1-10%).
What is flexural strength?
Measures the stress a material can bear before it breaks during bending.
- The specimen lies on a support span
- The load is applied to the center by the loading nose producing three-point bending at specific rate.
- Most plastic do not breaks when deflected, not easy to calculated.
- 5% strain occurs in the samples.
What are the methods to measure impact strength?
To measure the resistance of the material against impact.
-Falling mass test and pendulum test
What is the falling mass test used for?
To determine the impact resistance of a flat rigid plastic when struck by a falling mass. Or sample slide down a through and strike a meatal anvil.
If damage, fail the test.
Pendulum test
Use the energy of a swinging hammer to strike the sample.
- Charpy and Izod.
Describe the Charpy test.
- specimen supported at both ends but not held down
-A hammer strikes at center of sample, measuring the energy absorbed.
-Specimens can be notched or unnotched.
What are the basic categories of materials in stress-strain diagrams?
Brittle and ductile materials.
What do the points A, B, and C on a stress-strain curve represent?
Yield point (A), break point (B), and ultimate strength (C).
How is toughness defined in a stress-strain curve?
It is the area under the curve, representing the energy needed to break the sample.
