The functionally graded porous (FGP) linings reinforced by graphene platelets (GPLs) are applied to rehabilitate damaged pipes in practical engineering. The lining is susceptible to local buckling under a crown-concentrated loading. Insufficient expansion and deformations of the host pipe may induce ovalization of the lining during installation, which poses a significant threat to the long-term stability of the pipe-lining system. Therefore, this study explores the instability mechanism of encased FGP-GPLs oval linings under a crown concentrated load. The cross-sectional distributions of pores and GPLs in the lining are established by combining the Halpin-Tsai micromechanical rule and the Gaussian random field, respectively. A displacement expression is proposed to express the deflection of the oval lining. The load-displacement equilibrium paths and buckling loads are predicted by employing the principle of minimum potential energy and nonlinear thin-walled shell approaches. The theoretical solutions are systematically compared with alternative closed-form solutions and numerical results. Good consistency confirms the effectiveness of the theoretical method. Finally, the impacts of porosity coefficient, GPLs content, and ovality on the load-displacement equilibrium paths are evaluated. It is found that the critical buckling load increases 54.45% by mixing 1% GPLs, and decreases by 39.20% as the ovality increases from 0% to 10%, respectively.
Zhang et al. (Sun,) studied this question.