Standard requirements are absent and this is quite natural since making standard (like for compact metals) specimens by usual turning, milling etc is hardly advisable because of inevitable damage of rather porous structures BEFORE TESTING. The reasonable way is to wittingly grow (3d print) such specimens with thin external shells for a careful load application, however the matter is still in embryo stage.   

Nope, standard not yet exist for this kind of test.

Dirk - No to the best of my knowledge. You may try to follow the standard ASTM C6174-11, although it is indicated for ceramic porous materials. Otherwise I tend to use the ASTM D7264, but this is general for 3P bending composite beams.

please, find the ASTM C6174

Hello Davoud, unfortunately it is not possible to post the ASTM C6174 standard. It is a proprietary document that cannot be placed in an open access repository. You have to go to the ASTM Standards page and need to purchase the doc.

Thank you very much all for your kind responses. It seems no standards yet exist that specify evaluation methods or minimum requirements to investigate the flexural properties of metallic lattice structures manufactured via metal additive manufacturing. May be in near future more research on mechanical behaviour  of metallic lattice structures manufactured via metal additive manufacturing would help in establish new standards.