1.1 This test method covers the determination of the effective tensile properties of ordered cellular additively manufactured (AM) materials when tested under defined conditions of pretreatment, temperature, humidity, and testing machine speed. 1.2 This test method can be used for testing materials of any total specimen thickness up to 13 mm [0.50 in.]. However, for testing thin specimens, including film less than 1.3 mm [0.05 in.] in thickness, additional precautions are required to prevent improper failure. 1.3 This test method implements digital image correlation (DIC) as the primary strain measurement system to provide equivalent global strain responses. The utilization of conventional strain gauges would not sufficiently capture the strain effects involved in the effective properties. The ordered cellular AM materials provide portions of samples when there is insufficient material with which to bond to the conventional gauge and, when there is sufficient material, localized strain effects dominate the measured results. The DIC system allows for the displacement tracking on a 50 microstrain uncertainty level from any point on the visible surface sample to any other visible surface point for global response, as well as providing quantitative full-field strain response of the various stress concentrations in the ordered cellular material. NOTE 1This test method is not intended to cover precise physical procedures. It is recognized that the constant rate of crosshead movement type of test leaves much to be desired from a theoretical standpoint, wide differences may exist between rate of crosshead movement and rate of strain between individual unit cells of the ordered structure, and t the testing speeds specified disguise important effects characteristic of materials in the plastic state. Further, it is recognized that variations in the thicknesses of test specimens, which are permitted by these procedures, produce variations in the surface-volume ratios of such specimens, and that these variations may influence the test results. Hence, when directly comparable results are desired, all samples should be of equal thickness. Special additional tests should be used when more precise physical data are needed. 1.4 UnitsThe values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in non-conformance with the standard. 1.5 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.
5.1 Effective tensile properties may vary with specimen preparation such as print build orientation and location within the print envelope and with speed and environment of testing. Consequently, when precise comparative results are desired, these factors shall be carefully controlled. 5.2 It is realized that a material cannot be tested without also testing the method of preparation of that material. Hence, when comparative tests of materials per se are desired, the greatest care shall be exercised to ensure that all samples are prepared in exactly the same way unless the test is to include the effects of sample preparation. Similarly, for reference purposes or comparisons within any given series of specimens, care shall be taken to secure the maximum degree of uniformity in details of preparation, treatment, and handling. 5.3 When uniaxial tensile force is applied to an ordered cellular array, the array stretches in the direction of the applied force, that is, axially, but it also deforms in both dimensions lateral to the applied force. If the array is homogeneous and isotropic and the material remains elastic under the action of the applied force, the lateral strain bears a constant relationship to the axial strain. This constant, referred to as the effective Poissons ratio, is defined as the negative ratio of the transverse (negative) to axial strain under uniaxial stress when measured across whole unit cells.
Keywordsadditive manufacturing; effective modulus; effective stress; lightened structures; ordered cellular materials; tensile properties
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Draft Under Development