This test method measures the system material properties of an insulated formed heat shield under in-vehicle conditions. While the material properties of the individual components can often be determined via existing test methods, the system properties of the entire composite is typically much harder to ascertain (especially for multi-layer shields). System material properties include thermal conductivity in the lateral or in-plane (x) direction, thermal conductivity through the thickness or perpendicular (y), surface emissivity on the top and bottom sides of the shield and specific heat of the shield material.

All properties are determined for the entire shielding material specimen as a composite of the entire structure. Properties are determined using a testing apparatus that allows for two-dimensional heat flow through the specimen. Due to this, the material property results from this test method may not agree with one-dimensional heat flow type testing methods, but is representative of most heat shield materials performance tested with a centralized heat source. Therefore, material property results from this test method may be more suited for multi-dimensional analytical studies.

This standard sets forth the general guidelines to construct and operate the testing apparatus to acquire a satisfactory set of test data. Designs conforming to this standard are included and must not be deviated from for sensitivity reasons that will be discussed in more detail later. Test parameters that cannot be deviated from include, but are not limited to; specimen size, distance between the source and the specimen, source diameter and environmental conditions around the apparatus.

This method ultimately determines the shield material properties by using the test data along with an analytical scheme, see Section 8.1.

This test method will evaluate both isotropic and anisotropic insulated shielding materials. This may also include multi-layer shielding structures which include embossed/corrugated solids, porous, fibrous, granulated and coated materials.

Limitations

This test method does have limitations in the type of insulated shielding materials that can be evaluated. However, many of the limitations apply to materials that would not typically be suitable in a heat shielding function or the properties can be derived by simpler one-dimensional hot plate methods (SAE J1361, ASTM C 177).

Limitations include:

a) Materials where the radiant transmissivity through the material cannot be assumed as zero. Materials of this type are classified as translucent or transparent.

b) Materials that do not have an insulating characteristic in at least one axis; (i.e., single wall stamped metal shielding). This includes shielding materials where lateral thermal conductivity (x) and thermal conductivity through the thickness (y) are the same and considered high (in the order of 25 W/m-C) when compared to metallic materials. These types of single sheet metallic shields are not included in the standard because the properties of these materials are typically well known and do not require a procedure to determine them.

c) Materials where the lateral thermal conductivity (x) is less than the thermal conductivity through the thickness (y).

d) Testing exposes the shielding material to temperatures up to 250°C. Materials with limits below this level should not use this method.

Safety

This method involves a test apparatus that exposes the operator to very high temperatures. 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.

The attached Appendix A provides a detailed discussion of the analytical technique used in calculating the insulated shielding material properties from the test data. The Appendix A also presents the theoretical sensitivity study of the analytical method.

This test method requires two specific pieces of test instrumentation. A portable emissometer as outlined in ASTM C1371 and a radiosity meter or infrared camera with the ability to set the emissivity to 1.0.

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