Instability Of Tubular Structures Under Pressure And Axial Loading

Hyperelastic membrane structures are widely used in many modern engineering applications and our everyday life.Advanced benefits include foldable,lightweight and inflatable in which enables a great potential in extra-terrestrial and biomedical applications.Many biological organs in human bodies are hyperelastic membrane structures.They have specific bulging phenomenon under internal pressure and axial loading,which may affect the functions of biological tissue and efficiency.Similarly,localized bulging of an inflated hyperelastic membrane tube shares the same mathematical and mechanical features with a variety of other strain localization phenomena in engineering structures and materials,especially the strain localization which can cause harm to engineering safety and functions of biological tissue.This thesis investigated large deformation and localized instability of hyperelastic smooth cylindrical tubes with two cases of fixed axial force and length.An experimental study was carried out on localized bulging of inflated hyperelastic tubes with a range of wall thicknesses and tube lengths.Theoretical and numerical models were developed and their predictions were generally close to experimental results.The instability of textured hyperelastic tube(origami-inspired tube)under internal pressure and axial force was also studied.The hyperelastic origami-inspired textured tubes were fabricated with 3D printing and dip processing.Experimental and numerical analyses were conducted to investigate the instability features of the textured tube.A detailed numerical parametric analysis was also carried out to study the influence of tube parameters m and n on the non-linear behavior and load capacity of the origami-inspired tube.The buckling response of elastoplastic deep-subsea pipelines with conventional,origami-inspired textured,and novel curved-crease(CC)surface geometries was also investigated.The static nonlinear behaviors of hyperelastic cylindrical tube were studied with series of experiments in which a novel test system was built.Air pressuring measurement system including a high-speed camera and Data Acquisition(DAQ)was developed for the inflation tests in which the tubes were subjected to axial loading and internal pressure.The hyperelastic textured tubes used in the experiments were considered as an isotropic,homogeneous and hyperelastic rubber,modeled as a Mooney-Rivlin incompressible material described by two material constants.Material samples of the inflated tubes were consistently manufactured under the same condition and tested by a non-contact strain measurement.In the subsequent experimental study of localized bulging in smooth tube guided by newly emerged analytical results,the Gent-Gent material model was used.The material parameters were determined by flat latex sheet inflation test.A hyperbaric chamber device for studying instability of subsea pipelines was discussed.Experimental results of buckling propagation obtained from prior hyperbaric chamber testing were used to validate the numerical model of the conventional subsea pipeline.The buckling response of textured and curved-crease pipelines were then studied numerically with this validated model.The experimental results of localized instability shown in the thesis have a good agreement with numerical results.This may explain certain instability phenomena in biological tissue and other material and structures.This work provides a framework for explaining the mechanism of localized instability,and designing novel tubular structures with increased capacity for resisting propagation.