What is it about?

In this study composite and sandwich beams with homogeneous core and homogeneous or Functional Graded Materials faces under three point bending have been confronted. At first a linear static finite element analysis is performed throughout the composite and sandwich beams, which is taking into account the graded character of the faces. Computed distributions of the stress fields across the core material are given for different materials gradation of the faces; and possible crack-initiation positions have been identified. Secondly a crack in the lower face is considered parallel to the axis of gradation. When subjected to three point bending, this crack will propagate slowly perpendicular to the lower face. Stress intensity factors are calculated using Finite Element Method, and assuming linear fracture mechanics and plane strain conditions.

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Why is it important?

The main objective of this paper is to study numerically sandwich beams with homogeneous core and homogeneous or FGM faces under three point bending and to compare the results for the stress and displacement fields with those resulted of coating –substrate and homogeneous beams. In particularly the effect of the FGMs faces to the overall behavior of the sandwich beam is investigated. From our analysis possible crack-initiation positions have been identified. In particular the effect of the material gradation of the faces, on the fracture behaviour of the sandwich beam is confronted. It is proved that the FGMs faces contribute to the reduction of the maximum stresses developed in composite beams under three point bending.

Perspectives

From our analysis it was verified that the existence of homogeneous or FGM faces of the sandwich beams contribute to the decrease of the stresses in comparison with the single core beams and with the core-homogeneous face sheet or core-FGM face sheet beams. This decrease for the stresses was significant close to the interfaces between the core and the face sheets. The result for the sandwich beams with homogeneous or FGM faces are about similar. In addition the maximum vertical displacements appeared in composite beams decrease with the use of FGM or homogeneous faces. Hence the core-homogeneous face sheet and core-FGM face sheet models prevail relative to the single core model , but the sandwich beams with homogeneous or FGM faces prevail relative to the core-homogeneous face sheet or to the core-FGM face sheet. The material gradation of the faces in sandwich beams contributed to the reduction of the possibility of fracture of the core because of the decrease in the intensity of the stress fields. Initiation of small cracks according to our analyses may appear in the middle section of the bottom face sheet. Also crack initiation may appear under the introduction of load and close to the left and the right support of the beam because of the stress concentrations induced at these points.

Professor EFSTATHIOS E. THEOTOKOGLOU
National Technical University of Athens

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This page is a summary of: Numerical study of fractured sandwich beams with homogenous or FGM faces under three point bending, International Journal of Structural Integrity, February 2015, Emerald, DOI: 10.1108/ijsi-05-2014-0022.
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