Summary of Test
ASTM D638 is one of the most widely used standards for determining the tensile properties of reinforced and unreinforced plastics. The method evaluates material characteristics such as tensile strength, elongation, yield strength, and modulus using standardized “dog bone” specimens typically less than 14 mm thick. ASTM D638 testing is performed using a universal testing machine (UTM) equipped with the appropriate grips, load cell, and extensometer. Before conducting testing, users should review the complete ASTM D638 standard to ensure proper specimen preparation, test setup, speed selection, and reporting procedures.
Note: Testing with ASTM D638 is not recommended for thin films or elastomers.
For films under 1 mm thickness, use ASTM D882. For elastomers, use ASTM D412.
Recommended Equipment
The capacity of the Testing Machine needs to be sufficient to load customer materials until failure. A 5kN machine is usually sufficient for most non reinforced plastics. A 10kN dual column system is recommended for a variety of materials. 50kN systems can be used to test a wide range of reinforced plastics, composites and metals.
Software or suitable electronics are required to operate the machine and to take the measurements. Basic systems will provide the raw data, and stress-strain charts. Using these sources of data, you can determine and calculate all of the analysis listed above. However, fully PC based systems have the capability to calculate all of these automatically. For example, our MTESTQuattro testing software has built in support for ASTM D638 and all of these calculations are provided immediately after performing the test.
An extensometer is required when measuring modulus, yield, and modulus. Why? For two reasons: 1) The linear region of plastics is very small and happens suddenly so grip separation is just not accurate enough. 2) Dumbbell specimens do not have uniform widths so there will be errors when both the wide and narrow sections of the dumbbell shaped specimen elongate at different rates.
Testing Procedure
- Prepare a dog-bone specimen (Type I, II, III, IV, or V) according to the dimensions defined in the standard.
- Secure the specimen in tensile grips with proper sample alignment.
- Install an extensometer if strain measurement is required.
- Run test at crosshead speed specified by ASTM D638 until specimen failure occurs.
- Use test software to calculate tensile properties and generate stress-strain curve.
Sample Geometries:
- Type I — General-purpose rigid plastics
- Type II — Molded plastics and thicker materials
- Type III — Thicker rigid sheet materials
- Type IV — High-elongation materials
- Type V — Small specimens and limited material samples
Just Ask!
Questions about running ASTM D638 on your system?
