ASTM D790-17 pdf free download.Standard Test Methods for Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating Materials.
1.1 These test niethods are used to determine the flex ural properties of unreinforced arid reinforced plastics, including high modulus Composites and electrical insulating materials utilizing a three-point loading system to apply a load to a simply supported beam (specimen). The method is generally applicable to both rigid and semi-rigid materials, hut flexural strength cannot be determined for those materials that do not break or yield in the outer surface of the test specimen within the 5.0 strain limit.
1.2 Test specimens of rectangular cross section are inject ion molded or. cut from molded or extruded sheets or plates. or cut from molded or extruded shapes. Specimens must be solid and uniformly rectangular. The specimen rests on two supports and is loaded by means of a loading nose midway between the supports.
1 .3 Measure deflection in one of two ways using crosshead position or a deflectometer. Please note that studies have shown that deflection data obtained with a deflectomeer will differ from data obtained using crosshead position. The method of deflection measurement shall be reported.
4. Summary of Test Method
4.1 A test specimen of rectangular cross section rests on two supports in a flat-Wise position and is loaded by means of a loading nose located midway between the supports. Unless testing certain laminated materials (see 7 for guidance). a support span-to-depth (of specimen) ratio 16:1 shall be used. The specimen is deflected until rupture occurs in the outer surface of the test specimen or until a maximum strain (see 5.1.6) of 5.0 is reached, whichever occurs first.
4.2 Procedure A is designed principally for materials that break at comparatively small deflections and it shall be used for measurement of flexural properties, particularly flexural mxiulus, unless the material specification states otherwise. Procedure A employs a strain rate of 0.01 mrnlrnm/min (0.01 in./in./min) and is the preferred procedure for this test method.
4.3 Procedure B is designed principally for those materials that do not break or yield in the outer surface of the test specimen within the 5.0 % strain limit when Procedure A conditions are used. Procedure B employs a strain rate of 0.10 mm/mm/min.
4.4 Type I tests utilze crosshead position for deflection measurement.
4.5 Type II tests utilize an instrument (deflectometer) for deflection measurement.ASTM D790 pdf download.