Elastoplastic analysis of the enhancing mechanism of tensile performance of ductile thin-walled circular tubes with internal support

Abstract

Composite components with internal support, such as concrete-filled steel tubes (CFST), are widely applied in a variety of industries. Various experimental and numerical studies have revealed that internal supports could effectively enhance the tensile performance of ductile tubes. However, stress–deformation relations and strengthening mechanisms of thin-walled circular tubes under tension, (especially in plastic stages) have not been studied based on plastic increment theory. In this study, based on circumferential deformation coordination and generalized Hook’s law, the effects of internal support on yield strength and axial deformation of tubes were analyzed and the yield strength calculation equation of filled tubes was derived under true triaxial conditions. Based on plastic increment theory and isotropic linear hardening hypothesis, the differential relationship between the pressure increment of internal support and the axial plastic strain increment of steel tubes was established. The effects of elastic modulus, radius–thickness ratio and axial plastic strain on strength increase were also evaluated. Comparative analyze showed that the value of stress increase on filled tubes predicted by the proposed model was consistent with the results obtained from CFST tensile test and flexible support-filled thin-walled circular tube (FTWCT) test. In conclusion, a theoretical model was established for the first time for tensile strength enhancement mechanism of FTWCTs in plastic large-deformation stage, which was important in predicting the performance of ductile thin-walled structures under extreme loads.