8.3.1.2 Embedded thermocouples have

8.3.1.2 Embedded thermocouples have been used to determine the temperature rise in the material near the apex of the notch during machining. Thermal stresses induced during the notching operation have been observed in transparent materials by viewing the specimen at low magnification between crossed polars in monochromatic light. The specimens used to determine temperature rise shall not be used to make determinations of impact resistance. 8.3.2 The feed rate and the cutter speed shall remain constant throughout the notching operation. 8.4 It is acceptable to notch specimens individually or in a group. In either case, however, an unnotched backup or dummy bar shall be placed behind the last specimen in the sample holder to prevent distortion and chipping by the cutter as it exits from the last test specimen.8.5 All specimens having one dimension less than 12.7 mm(0.500 in.) shall have the notch cut on the shorter side. Compression molded specimens shall be notched on the side parallel to the direction of application of molding pressure. The impact resistance of a plastic material will be different if the notch is perpendicular to rather than parallel to the direction of molding, as with or across the grain of an anisotropic bar cut from a plate.9. Conditioning 9.1 Check the materials specification for the material that is being tested. If there are no conditioning requirements stated by the materials specification, the test specimens shall be conditioned for not less than 40 h after notching and prior to testing in accordance with Procedure A of Practice D618 unless documented (between supplier and customer) that shorter conditioning time is sufficient for a given material to reach equilibrium of impact resistance.9.2 For hygroscopic materials, such as nylons, the material specifications (for example, Classification System D4066) call for testing dry-as-molded specimens. Such requirements take precedence over the above routine preconditioning to 50 % relative humidity. These specimens shall be sealed in water vapor-impermeable containers as soon as molded. When notch- ing these specimens, minimize the exposure time during notching and return the specimens to a dry container after notching to allow for full cooling of the specimens prior to testing.9.3 Test Conditions—Conduct tests in the standard laboratory atmosphere of 23 ± 2°C (73 ± 3.6°F) and 50 ± 10 % relative humidity, unless otherwise specified. In cases of disagreement, the tolerances shall be 61°C and 65 % relative humidity.10. Procedure10.1 Specimen Preparation: 10.1.1 Prepare the test specimens in accordance with the procedures in Section 7. At least five and preferably ten or more individual determinations of impact resistance shall be made to determine the average impact resistance for a particu- lar sample. The specimens shall be of nominal width only. 10.1.2 Notch the specimens in accordance with the proce- dure in Section 8. 10.1.3 Condition the specimens in accordance with the materials specification for the material that is being tested. If there are no conditioning requirements detailed in the materials specification, follow the conditioning requirements in Section 9.