Functionally graded materials (FGM) are some kind of composite materials that due to the continuity of mixture of constituent materials, have more effective mechanical properties than composites which leads to eliminate of interlayer stress concentration. The most application of these materials is in thin structures such as plates and shells. This research presents a Tamura-Tomota-Ozawa based model to obtain the elasto-olastic behavior of Functionality graded materials under impact loads. Also, based on this model, the ceramic phase of FGM was considered as an isotropic elastic material and the metal phase was considered as an elasto-plastic material. Several parametric study have been conducted to assess different aspects of such material behavior. The results show that the maximum displacement of the shell has increased by increasing the volume fraction index and the thickness ratio, and it has decreased by increasing the aspect ratio. It was also observed that the thickness ratio(32%), volume fraction index(30%), aspect ratios(23%) and shell curvature (16%) parameters affect the maximum displacement of the shell. The elasto-plastic response of FGM shells is similar to homogeneous shells and the TTO model can describe the mechanical behaviour of FGM shells beyond the elastic range where the FGM response is mainly governed by the plastic region of the metal phase.

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