Characteristic bending length in micropolar materials with periodic internal structure

This paper describes the laboratory experiments conducted on specimens with artificially created internal structure produced by drilling a regular pattern of circular holes in an alumnium matrix. The specimens are subjected to four-point bending and the protocol is described in detail with emphasis given on the top-edge and bottom-edge axial-strain measurement and processing in the zone of pure bending. An increase in stiffness is observed with the reduction in the characteristic specimen dimension (size effect), which may be explained by the micropolar theory of elasticity. A methodology is suggested for establishment of the effective Young’s modulus and the characteristic bending length of a homogenised substitute micropolar material, which is entirely based on a known closed-form pure-bending solution. The results are compared with those obtained using an alternative protocol from the literature.