The standard ASTM D5023 describes Dynamic Mechanical testing of thermoplastics, thermosetting resins, and composites. Rectangular bar specimens are tested in flexure using three-point bending and forced vibration to determine key viscoelastic properties like elastic and loss moduli.
The Standard test method ASTM D5023 is used for conducting Dynamic Mechanical Analysis (DMA) of Plastics in Flexure. It enables determination of viscoelastic properties of a wide variety of plastics materials, using forced-vibration techniques, at a frequency range from 0.01 Hz to 100 Hz. The test involves application of three-point bending loads on specimens of rectangular cross section, under dynamic, fixed frequency, mechanical linear displacement forces. Viscoelastic properties such as elastic (storage), loss (viscous) and complex moduli along with tan delta can be studied as a function of frequency, time, or temperature. The test is applicable to thermoplastic and thermosetting resins as well as polymer composites. The test is useful for studying functional properties of resins, effectiveness of cure (thermosetting resin system), and damping behaviour of resins at various conditions. The data from this test facilitates quality control, research and development, and process optimization during production.
The ASTM D5023 test apparatus includes a loading frame with cylindrical loading nose, a device for dynamic linear strain application at various frequencies and amplitudes, a three-point bend fixture with adjustable span, instrumentation for measuring force (stress), deflection (strain), frequency, and temperature and environmental chamber with heating and cooling provisions. The test set-up can be integrated with an automatic control panel and data processing system.
Rectangular bar shaped specimens of specified dimension are made from the test polymer. They can be cut directly from sheets, plates, or can be moulded. Sufficient overhang at the ends of the three-point loading fixture must be ensured. The specimens must be conditioned as specified, prior to testing.
The test specimen rests on two end supports and is loaded at mid-point by means of a cylindrical loading nose. Under three-point bending conditions, mechanical linear displacement is induced at fixed frequencies and at a constant temperature or with a linear rate of temperature variation. The elastic modulus and loss modulus are measured.
Specimens should be sufficiently long, so that overhang at each end is at least 10% of the support span, but not less than 6.4 mm on each end. This prevents the sample slipping through during bending. Normally, the support span to sample depth ratio shall be 16 (tolerance +4 or −2). Typically, for a 50 mm support span a test specimen placed flat would be of 64 mm × 13 mm × 3 mm size. This provides the required span to depth ratio.
The elastic and loss moduli are typically reported in Megapascals (Mpa) or in N/mm2 .
The standard method ASTM 5023 recommends a reporting structure for the results, which include details of material, sample preparation, testing conditions and procedure as well as tabulation and graphical representations.