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Significance and Use
Test Methods A and B are used to establish the weight of the dart when 50 % of the specimens fail under the conditions specified. Data obtained by one test method cannot be compared directly with the other test method nor with those obtained from tests employing different conditions of missile velocity, impinging surface diameter, effective specimen diameter, and thickness. The values obtained by these test variables are highly dependent on the method of film fabrication.
The results obtained by Test Methods A and B are greatly influenced by the quality of film under test. The confidence limits of data obtained by this procedure can, therefore, vary significantly, depending on the sample quality, uniformity of film gage, die marks, contaminants, etc. (see Section 15).
Test Methods A and B have been found useful for specification purposes. Correlation between test results and field performance can usually be established.
The impact resistance of plastic film, while partly dependent on thickness, has no simple correlation with sample thickness. Hence, impact values cannot be normalized over a range of thickness without producing misleading data as to the actual impact resistance of the material. Data from these test methods are comparable only for specimens that vary by no more than ±25 % from the nominal or average thickness of the specimens tested.
Several impact test methods are used for film. It is sometimes desirable to know the relationships among test results derived by different test methods. A study was conducted in which four films made from two resins (polypropylene and linear low-density polyethylene), with two film thicknesses for each resin, were impacted using Test Methods D 1709 (Method A), D 3420
1.1 These test methods cover the determination of the energy that causes plastic film to fail under specified conditions of impact of a free-falling dart. This energy is expressed in terms of the weight (mass) of the missile falling from a specified height which would result in 50 % failure of specimens tested.
1.2 Two test methods are described:
1.2.1 Test Method A employs a dart with a 38.10 ± 0.13-mm (1.500 ± 0.005-in.) diameter hemispherical head dropped from a height of 0.66 ± 0.01 m (26.0 ± 0.4 in.). This test method may be used for films whose impact resistances require masses of about 50 g or less to about 2 kg to fracture them.
1.2.2 Test Method B employs a dart with a 50.80 ± 0.13-mm (2.000 ± 0.005-in.) diameter hemispherical head dropped from a height of 1.50 ± 0.03 m (60.0 + 0.25, −1.70 in.). Its range of applicability is from about 0.3 kg to about 2 kg.
1.3 Two testing techniques are described:
1.3.1 The standard technique is the staircase method. By this technique, a uniform missile weight increment is employed during test and the missile weight is decreased or increased by the uniform increment after test of each specimen, depending upon the result (fail or not fail) observed for the specimen.
1.3.2 The alternative technique provides for testing specimens in successive groups of ten. One missile weight is employed for each group and missile weight is varied in uniform increments from group to group.
1.3.3 The staircase technique and the alternative technique give equivalent results both as to the values of impact failure weight which are obtained and as to the precisions with which they are determined.
1.4 The values stated in SI units are to be regarded as standard. The values stated in parentheses are for information only.
Note 1—Tests on materials that do not break, for any reason, are not considered to be valid. It has been noted that certain materials may stretch so far as to bottom out at the base of certain test instruments without actually rupturing. Subcommittee D20.19 is currently considering methods for testing these materials. Anyone interested in participating in a Task Group should contact the Chairman of Subcommittee D20.19 through ASTM International Headquarters.
1.5 This standard does not purport to address 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.
Note 2—Film has been arbitrarily defined as sheeting having nominal thickness not greater than 0.25 mm (0.010 in.).
Note 3—This test method is technically equivalent to ISO 7765-1: 1988, with the exception of a larger tolerance on the drop height in Test Method B. Also, the ISO method does not allow the alternative testing technique described in Section 11 of this test method.
2. Referenced Documents (purchase separately) The documents listed below are referenced within the subject standard but are not provided as part of the standard.
D618 Practice for Conditioning Plastics for Testing
D883 Terminology Relating to Plastics
D1248 Specification for Polyethylene Plastics Extrusion Materials for Wire and Cable
D3420 Test Method for Pendulum Impact Resistance of Plastic Film
D4272 Test Method for Total Energy Impact of Plastic Films By Dart Drop
D6988 Guide for Determination of Thickness of Plastic Film Test Specimens
E177 Practice for Use of the Terms Precision and Bias in ASTM Test Methods
E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
ISO StandardISO7765:1988 Plastic Film and Sheeting--Determination of Impact Resistance by the Free Falling Dart Method--Part 1: Staircase Method Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036, http://www.ansi.org.
ICS Number Code 83.140.10 (Films and sheets)
UNSPSC Code 13111200(Films)