ASTM D5420 is a standard test method for impact resistance of flat, rigid plastic specimen by means of a striker impacted by a falling weight (gardner impact). This test consists of a fixed weight impacting a striker resting on top of a supported specimen dropped from various heights. The energy required to cause 50% of the specimens to fail is employed by this test method to determine the relative ranking of materials. The equipment required for this test is the very same equipment used to measure the impact resistance of coatings under the ASTM D2794. Micom offers ASTM D5420 as part of its polymer testing services.
Use and factors to be considered for ASTM D5420
When developing and selecting materials for specific applications, the knowledge of how the deformation of a polymer depends on their composition and structure is imperative. The fluid and elastic properties of plastic or, better put, their viscoelasticity makes them sensitive to changes in weight velocities falling on their surface. Different polymers behave differently to changes in the velocity impact and it is crucial to be aware of their behavior.
Typical Experimental parameters for ASTM D5420 testing
- It is possible to use different striker diameters and specimen support plate geometries to obtain various types of failure. There are predefined strikers and specimen support plate dimensions in table 1 of ASTM D5420. In this table, we find 5 types of geometry offering different test conditions:
- GA: Causes a moderate level of stress and can be employed for most polymers
- GB: The test conditions of this geometry are identical to the geometry used for the Gardner Variable Height Impact Test
- GC: Provokes a punch shear of failure on account of the support plate hole that is similar to the diameter of the striker
- GD: Causes a transition from ductile to brittle failure by changing the conditioning and test temperature in a controlled manner (can be employed for most plastics)
- GE: The test conditions are the same as those in test method ASTM D4226. The impactor head configuration H.25 (0.48 in 6 0.04 in. (1.22 cm 6 0.10 cm)) is employed
- The selection of a test method and striker is arbitrary considering the nature of impact testing. The end use environment of the material shall be considered for the choosing but the selection of any other possibilities is permitted.
- Number of specimens/product: 20 if, for a given sample, the estimate mean-failure height is known. If the latter is unknown, six or more additional specimens are necessary.
- Exposure temperature: Impact properties of polymers can be fairly sensitive to temperature. The specimen can be exposed at any reasonable temperature representing the end use conditions.
- Relative humidity: Just like the temperature, the relative humidity shall represent the end use conditions as much as possible especially if the material tested is known to be hygroscopic.
- Width of flat test specimens: at least 25 mm (1 in.) greater than the diameter of the hole in the support plate.
- Thickness of specimen: to be specified
Should you need guidance in deciding which geometry or other elements should be used for your precise needs, feel free to contact us today.