1.1 This test method covers a procedure for the determination of moisture absorption or desorption properties in the through-the-thickness direction for single-phase Fickian solid materials in flat or curved panel form. Also covered are procedures for conditioning test coupons prior to use in other test methods; either to an essentially moisture-free state, to equilibrium in a standard laboratory atmosphere environment, or to equilibrium in a non-laboratory environment. Also included are procedures for determining the moisture loss during elevated temperature testing, as well as moisture loss resulting from thermal exposure after removal from the conditioning environment, such as during strain gage bonding. While intended primarily for laminated polymer matrix composite materials, these procedures are also applicable to other materials that satisfy the assumptions of 1.2.
1.2 The calculation of the through-the-thickness moisture diffusivity constant in Procedure A assumes a single-phase Fickian material with constant moisture absorption properties through the thickness of the specimen. The validity of the equations used in Procedure A for evaluating the moisture diffusivity constant in a material of previously unknown moisture absorption behavior is uncertain prior to the test, as the test results themselves determine if the material follows the single-phase Fickian diffusion model. A reinforced polymer matrix composite material tested below its glass-transition temperature typically meets this requirement, although two-phase matrices such as toughened epoxies may require a multi-phase moisture absorption model. While the test procedures themselves may be used for multi-phase materials, the calculations used to determine the moisture diffusivity constant in Procedure A are applicable only to single-phase materials. Other examples of materials and test conditions that may not meet the requirements are discussed in Section 6.
1.3 The evaluation by Procedure A of the moisture equilibrium content material property does not assume, and is therefore not limited to, single-phase Fickian diffusion behavior.
1.4 The procedures used by this test method may be performed, and the resulting data reduced, by suitable automatic equipment.
1.5 This test method is consistent with the recommendations of CMH-17 Rev G (1), which describes the desirable attributes of a conditioning and moisture property determination procedure.
1.6 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system are not exact equivalents; therefore, each system must be used independently of the other. Combining values from the two systems may result in nonconformance with the standard.
1.6.1 Within the text the inch-pound units are shown in brackets.
1.7 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.
Procedure A is designed to produce moisture diffusion material property data that may be used as follows:
To determine approximate exposure times for coupon conditioning in Procedures B-E, Y, Z;
As input to moisture prediction analysis computer codes; or
For making qualitative decisions on material selection or performance under environmental exposure to various forms of moisture.
Procedures B-E are designed to condition test coupons to a specified environmental condition or equilibrium state prior to other material property testing (including but not limited to mechanical testing).
Procedures Y-Z are designed to determine the loss of moisture content due to removal of a test coupon from the conditioning chamber (such as for strain gage bonding) or due to heating of the test coupon prior to and during mechanical loading.
A single pair of tests on thin and thick specimens using Procedure A provides the moisture diffusivity constant, Dz, and the moisture equilibrium content, Mm, at the given moisture exposure level and temperature. Multiple tests at differing temperatures are required to establish the dependence of Dz on temperature. Multiple tests at differing moisture exposure levels are required to establish the dependence of Mm on moisture exposure level.
Note 1—For many polymer matrix composites the moisture diffusivity is usually only weakly related to relative humidity and is often assumed to be a function only of temperature, usually following an Arrhenius-type exponential relation with inverse absolute temperature. For many of these materials, moisture equilibrium content is only weakly related to temperature and is usually assumed to be a function only of relative humidity. (1)
Vapor-exposure testing shall be used to condition the specimen when the in-service environmental condition is a vapor such as humid air. Immersion in a liquid bath should be used to simulate vapor exposure only when apparent absorption properties are desired for qualitative purposes. Properties determined in the latter manner shall be reported as apparent properties.
Note 2—For many polymer matrix composites the moisture absorption properties under atmospheric humid conditions are generally not equivalent to exposure either to liquid immersion or to pressurized steam. These latter environments may have different material diffusion characteristics.