Response of an underwater cylindrical composite shell to a proximal implosion

An experimental investigation is conducted to study the dynamic underwater response of a cylindrical composite shell under near critical hydrostatic pressure, to the implosion of another shell in proximity. A primary cylindrical composite shell is imploded in proximity to a secondary shell which is similar in all respects except for the secondary shell having a smaller length. Length differences of 10% and 20% are chosen to simulate variations in collapse pressures occurring in shells from real life manufacturing defects and/or degradation during operational use. The response of the secondary shell is investigated to understand if and how its collapse occurs in addition to studying the Fluid-Structure Interaction (FSI) phenomenon. The pair of shells are subjected to underwater hydrostatic loading using a large pressure vessel suitable for high-speed photography in conjunction with 3D Digital Image Correlation (DIC). 3D-DIC is employed to obtain full-field displacement measurements of both the shells, and local dynamic pressure histories are also simultaneously recorded. The primary shell always imploded first, causing a dynamic loading on the secondary shell. In cases of implosion of the secondary shell, although the transient radial deformations occurred in mode 2, the failure itself occurred with a localized failure of the shell walls. It is observed that there exists an inner critical stand-off distance for the secondary shell to fail catastrophically upon the implosion of the primary shell, and an outer critical stand-off distance beyond which the secondary shell does not implode. A critical stand-off distance is found to exist only in the case of the 10% smaller secondary shell length. If the secondary shell stand-off distance is more than the outer critical distance or when length of the secondary shell is 20% smaller, the secondary shell responds with bending and breathing modes and no visible damage is recorded. When the stand-off distance is in between the inner and the outer critical distances, the relative orientation of the incipient modal shapes of the two shells is the factor governing the collapse of the secondary shell. A method is also developed to decouple full-field 3D-DIC measurements into bending and breathing deformation measurements

Underwater implosion pressure pulse interactions with submerged plates

An experimental and analytical investigation is conducted to study the underwater interaction of implosion pressure pulses with large plates. Two plates with stiffnesses significantly apart are investigated experimentally in a large-diameter pressure vessel for their Fluid-Structure Interaction (FSI) phenomena during proximal implosions of low stiffness metallic shells. High-speed photography, in conjunction with 3D Digital Image Correlation (DIC) measurements, is employed to obtain full-field displacements of the plates. Local dynamic pressure histories are also simultaneously recorded to investigate the incident, reflected and transmitted fluid pressures across the plates during dynamic loading. The lesser stiffness plate showed higher deflection, allowed a weaker reflected pressure pulse and allowed a stronger transmitted pressure pulse as compared to the higher stiffness plate. The peak deflections of the plates occurred during the underpressure phase of the implosion event. Four analytical modeling iterations with increasing complexities starting from Taylor\u27s FSI model are considered to assess the response of water backed plates to dynamic pressure pulse loadings. Each iteration is analyzed individually in an experimental context to understand its role as a building block in a final analytical model. The final model developed is based on the classical plate-bending equation and fluid velocity corrected for ‘afterflow’ effects and performed better than Taylor\u27s original model in predicting pressure-time history of the plates’ reflected pressure and transmitted pressure. The plates’ mid-point deflection profiles are also better predicted using this model. Furthermore, the model showed that the response of a plate during a dynamic implosion pressure pulse interaction is weakly dependent on its bending stiffness. Instead, it is observed that for a large plate, its areal mass density is the dominant factor in determining the reflected pressure, the transmitted pressure and the plate mid-point deflection profiles

Dynamic response of pre-loaded structures subjected to combined extreme environments

A series of experiments was performed on Hastelloy X plates which were subjected to a combination of extreme temperatures, in-plane tensile loading, and transverse shock loading. To achieve these conditions a shock tube apparatus was used in conjunction with a novel hydraulic pre-loading fixture and propane flame torches. In order to understand the effects of shock load magnitude on the deformation behavior of the plates, two series of experiments were carried out at peak shock pressures of 1.7 MPa and 3.1 MPa, respectively. Both series of experiments were conducted over a range of temperatures from room temperature to 900 °C. High speed photography and Digital Image Correlation (DIC) were used to obtain three-dimensional, full-field deformation information. Side view images were also captured to validate the DIC results. The addition of a tensile pre-load reduced the maximum deflection for all temperatures. However, a higher magnitude of the tensile pre-load did not further reduce the maximum out-of-plane deflection of the plate for temperatures higher than 400 °C. The specimen deformation increased with increasing temperature until 800 °C. However, at 900 °C, due to anomaly in material constitutive behavior, the specimen deflection was observed to be lower than at 800 °C. An indentation mode of deformation was observed in some instances of the 3.1 MPa peak shock pressure experiments, particularly at higher temperatures