1. Scope 1.1 This practice provides instructions for modifying the static short beam strength test method to determine the fatigue behavior of composite materials subjected to cyclic forces applied in three-point bending. Application of this test method is limited to continuous or discontinuous-fiber-reinforced polymer matrix composites,for which the elastic properties are balanced and symmetric with respect to the longitudinal axis of the beam. 1.2 This practice supplements Test Method D 2344/D 2344M with provisions for testing specimens under cyclic loading. Several important test specimen parameters (for example, fatigue force/ (stress) ratio) are not mandated by this practice; however, repeatable results require that these parameters be specified and reported. 1.3 This practice is limited to test specimens subjected to constant amplitude uniaxial loading, where the machine is controlled so that the test specimen is subjected to repetitive constant amplitude force (stress) cycles. Either engineering stress or applied force may be used as a constant amplitude fatigue variable. 1.4 The values stated in either SI units or inch-pound units are to be regarded separately as standard. Within the text the inch-pound units are shown in brackets. 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. 1.5 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.
In most cases, because of the complexity of internal stresses and the variety of failure modes that can occur in this specimen, it is not generally possible to relate the short-beam strength to any one material property. However, failures are normally dominated by resin and interlaminar properties, and the test results have been found to be repeatable for a given specimen geometry, material system, and stacking sequence. Short-beam strength determined by this test method can be used for quality control and process specification purposes. It can also be used for comparative testing of composite materials, provided that failures occur consistently in the same mode.
KeywordsShort Beam Strength;fatigue;composite material
The title and scope are in draft form and are under development within this ASTM Committee.Back to Top