Significance and Use
Plastics are viscoelastic and therefore are likely to be sensitive to changes in velocity of the mass falling on their surfaces. However, the velocity of a free-falling object is a function of the square root of the drop height. A change of a factor of two in the drop height will cause a change of only 1.4 in velocity. Hagan et al (2) found that the mean-failure energy of sheeting was constant at drop heights between 0.30 and 1.4 m. This suggests that a constant mass-variable height method will give the same results as the constant height-variable mass technique. On the other hand, different materials respond differently to changes in the velocity of impact. Equivalence of these methods should not be taken for granted. While both constant-mass and constant-height techniques are permitted by these methods, the constant-height method should be used for those materials that are found to be rate-sensitive in the range of velocities encountered in falling-weight types of impact tests.
The test geometry FA causes a moderate level of stress concentration and can be used for most plastics.
Geometry FB causes a greater stress concentration and results in failure of tough or thick specimens that do not fail with Geometry FA (3). This approach can produce a punch shear failure on thick sheet. If that type of failure is undesirable, Geometry FC should be used. Geometry FB is suitable for research and development because of the smaller test area required.
The conical configuration of the 12.7-mm diameter tup used in Geometry FB minimizes problems with tup penetration and sticking in failed specimens of some ductile materials.
The test conditions of Geometry FC are the same as those of Test Method A of Test Method D1709. They have been used in specifications for extruded sheeting. A limitation of this geometry is that considerable material is required.
The test conditions of Geometry FD are the same as for Test Method D3763.
The test conditions of Geometry FE are the same as for ISO 6603-1.
Because of the nature of impact testing, the selection of a test method and tup must be somewhat arbitrary. Although a choice of tup geometries is available, knowledge of the final or intended end-use application shall be considered.
Clamping of the test specimen will improve the precision of the data. Therefore, clamping is recommended. However, with rigid specimens, valid determinations can be made without clamping. Unclamped specimens tend to exhibit greater impact resistance.
Before proceeding with this test method, reference should be made to the specification of the material being tested. Table 1 of Classification System D4000 lists the ASTM materials standards that currently exist. Any test specimens preparation, conditioning, dimensions, or testing parameters or combination thereof covered in the relevant ASTM materials specification shall take precedence over those mentioned in this test method. If there are no relevant ASTM material specifications, then the default conditions apply.
Scope
1.1 This test method covers the determination of the threshold value of impact-failure energy required to crack or break flat, rigid plastic specimens under various specified conditions of impact of a free-falling dart (tup), based on testing many specimens.
1.2 The values stated in SI units are to be regarded as the standard. The values in parentheses are for information only.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. Specific hazard statements are given in Section 8. Note 1—This test method and ISO 6603-1 are technically equivalent only when the test conditions and specimen geometry required for Geometry FE and the Bruceton Staircase method of calculation are used.
