Search

The paper focuses on the buckling of circumferentially corrugated cylindrical shells under uniform external pressure, along with the effects of corrugation on the buckling. The buckling of unstiffened and corrugated cylindrical shells are studied using a numerical method. The nonlinear numeric compares well with the existing experiment. Then, the buckling of triangle, half-circle, and sine corrugated shells are, respectively, presented, which demonstrates that the sine-shaped corrugation leads to best buckling pressure. Subsequently, several sine-shaped corrugated cylindrical shells with different corrugation amplitudes are evaluated. On this basis, preferred mass and volume equivalent corrugated shells are, respectively, used to make a comparison with the unstiffened cylindrical shell. Finally, the effects of diameter, thickness, and material properties on the buckling of preferred corrugated shells are, respectively, investigated. The results show that the circumferentially sine-shaped corrugation with the half period-to-amplitude ratio of 4.4 can enhance the buckling pressure of shell by more than four times. [ABSTRACT FROM AUTHOR]

The paper is devoted to a kind of egg-shaped shell with varying wall thickness subjected to uniform external pressure. The numerical buckling performances of several such shells are presented, which are compared with corresponding equivalent egg-shaped shells with uniform wall thickness. It is indicated that the buckling capacity of egg-shaped shells with varying wall thickness is greatly improved; furthermore, such shells are less sensitive to initial geometric imperfections than those with uniform wall thickness. To validate the proposed numerical approach, three nominally identical egg-shaped shells is tentatively fabricated, accurately measured, slowly tested, and numerically studied. A good agreement between experiments and computations are obtained. [ABSTRACT FROM AUTHOR]

Astract This study examined the buckling of spherical caps with four different geometric imperfections: local inward dimple, increased-radius, force-induced dimple, and linear buckling mode. The influence of imperfection amplitude, meridional position, and meridional extent on cap buckling was numerically explored and partially validated using experiments. The numerical and experimental data were well consistent. Results indicated that, in the case of small-sized imperfections, the linear buckling mode-shaped imperfection presented a relatively conservative cap buckling prediction compared with those of the other three imperfections. This finding contradicts previous findings that the force-induced dimple imperfection is the most unstable imperfection. Highlights • Buckling of imperfect caps are numerically explored and experimentally validated. • Effect of imperfection amplitude, meridional position and extent on buckling is studied. • The linear buckling mode-shaped imperfection is relatively conservative. [ABSTRACT FROM AUTHOR]

This study focused on the buckling of stainless steel spherical caps under uniform external pressure. Caps with a circular arc meridian have a nominal base diameter of 146 mm, nominal uniform wall thickness of 1 mm and nominal height of 37 mm. Six nominally identical laboratory-scale caps were fabricated, measured precisely and tested slowly. The buckling performances of such caps were studied experimentally and numerically, and the results show good agreement with each other. Furthermore, the buckling of 13 mass-equivalent caps of various heights were numerically analysed to identify the cap with the best load-carrying capacity. The results suggest that a spherical cap with height-to-base diameter ratio of 0.274 supports the highest buckling load. Such a cap can be applied as an end-closure for cylindrical pressure hulls or as a manhole cover for manned cabins in deep-sea vehicles. [ABSTRACT FROM AUTHOR]

Abstract This study examined the buckling of spherical caps fabricated under different conditions of wall-thickness reduction. The spherical caps were fabricated using photosensitive resin and had a base diameter of 150 mm and height of 41.1 mm; they were subjected to uniform external pressure. In total, 42 spherical caps—6 with full thickness reduction and 36 with partial thickness reduction—were fabricated through rapid prototyping; after their external surface and wall thickness were measured, all caps were tested to collapse to experimentally and numerically evaluate their buckling properties, namely buckling pressures and collapse modes. Moreover, the effects of site, magnitude, and range of the thickness reduction on the buckling properties were evaluated. Herein, the experimental and numerical results are comparatively presented in tables and figures. Highlights • Spherical caps of various site, range, and magnitude of thickness reduction were built. • Buckling pressures and collapse modes of 42 such caps were obtained experimentally. • A semianalytical formula for evaluating their load-bearing capacity is identified. [ABSTRACT FROM AUTHOR]

Abstract This study focused on the nonlinear elastic buckling of mass equivalent egg-shaped shells with variable and constant wall thicknesses under uniform external pressure. The shells were made of photosensitive resin and had a nominal mass of 570 g, a nominal major axis of 260.36 mm, and a nominal minor axis of 181.32 mm. Four egg-shaped shells were fabricated using the aforementioned parameters and using the rapid prototype technique—stereo lithography appearance. Two shells had a constant wall thickness, whereas the remaining shells had a variable wall thickness along the meridian. The geometry of all shells was accurately measured, and the shells were slowly pressurised to destruction, thus yielding good repeatability. On the basis of the measured results, the buckling performance of the tested shells was further studied numerically. The experimental data were found to be in agreement with the numerical predictions. The results revealed that the average collapse pressure for the egg-shaped shells with variable wall thickness was approximately 24% higher than that for the egg-shaped shells with constant wall thickness, thus indicating that the load-carrying capacity of the egg-shaped shells was significantly improved when variable thickness was used. Highlights • Egg-shaped shells with variable wall thicknesses are developed by keeping stress constant. • Rapid prototyping egg-shaped shells are measured for geometry and tested to destruction. • Load carrying capacity of egg-shaped shell is improved by 24% using wall variable thickness. [ABSTRACT FROM AUTHOR]

This paper focuses on spherical shells under uniform external pressure. Ten laboratory scale models, each with a nominal diameter of 150 mm, were tested. Half of them were manufactured from a 0.4-mm stainless steel sheet, whereas the remaining five shells were manufactured from a 0.7-mm sheet. The geometry, wall thickness, buckling load, and final collapsed mode of each spherical shell were measured, as well as the material properties of the corresponding sheet. The buckling behaviors of these shells were demonstrated analytically and numerically according to experimental data. Analyses involved considering the average geometry, average wall thicknesses, and average elastic material properties. Numerical calculations entailed considering the true geometry, average wall thicknesses, and elastic-plastic modeling of true stress–strain curves. Moreover, the effects of purely elastic and elastic-perfectly plastic models on the buckling loads of spherical shells were examined numerically. The results of the experimental, analytical, and numerical investigations were compared in tables and figures. [ABSTRACT FROM AUTHOR]

This study investigated the buckling behavior of steel and steel–composite cylinders under external pressure. The steel cylinders had a length-to-diameter ratio of 2.01 and a thickness-to-diameter ratio of 0.0094. The external surfaces of the steel cylinders closed using two heavy bungs were blasted with grit. The steel–composite cylinders were fabricated by wrapping [55 ∘ / − 55°] 4 composite layer on the steel cylinders. The total thickness-to-diameter ratio of the steel–composite cylinders was 0.0170. Three nominally identical steel cylinders and three nominally identical steel–composite cylinders were designed, fabricated, geometrically measured, and hydrostatically tested. Linear eigenvalue and nonlinear RIKS analyses were performed to evaluate the buckling behavior of fabricated cylinders. The experimental and numerical data agreed well with each other. The average ultimate strength of the steel–composite cylinders was 2.853 MPa, which is 1.838 times that of steel cylinders. These findings indicate that the steel cylinders can be considerably strengthened by wrapping composite materials. Furthermore, the steel–composite cylinders were slightly less sensitive to large imperfections compared with steel cylinders. • Buckling behavior of steel and steel–composite cylinders were experimentally explored. • Wrapping CFRP layers considerably enhanced the loading capacity of steel cylinder. • RIKS method could reasonably estimate buckling of steel and steel–composite cylinders. • Effect of initial geometric imperfection size on ultimate strength were numerically explored. • Numerical and experimental data exhibited satisfactory agreement. [ABSTRACT FROM AUTHOR]

This study investigated the buckling performances of stainless steel toroidal shell segments under uniform external pressure. The toroidal shell segments used in this study exhibited a nominal section radius of 70.5 mm, nominal wall thickness of 1.346 mm, and nominal rotation radius of 138 mm. A total of 12 toroidal shell segments were manufactured using roll bending and were measured geometrically, tested hydrostatically, and evaluated numerically. Six of the shell segments had a 45° rotation angle, whereas the other six had a 90° rotation angle. Moreover, the buckling of geometrically perfect toroidal shell segments was explored under various rotation angles ranging from 30° to 360°. • Twelve steel toroidal shell segments were machined via roll bending of male and female dies. • All machined toroidal shell segments were studied experimentally and evaluated numerically. • The effects of toroidal shell segment completeness on the buckling were explored numerically. • Currently used empiric guidelines yield a very conservative assessment for small angle segments. [ABSTRACT FROM AUTHOR]

The present investigation is devoted to the nonlinear elastic collapse properties of externally pressurized egg-shaped shells under local geometrical imperfections. The shells have nominal major axis, nominal minor axis, and nominal wall thickness of 256 mm, 180 mm, and 2 mm, respectively. Nine resin egg-shaped shells are manufactured, measured accurately, tested hydrostatically, and analysed numerically. Of these, three each have nominally identical perfect geometries, nominally identical geometries with local flat imperfections, and local dimple imperfections. Furthermore, the effect of local and eigenmode imperfection depths on the collapse pressures of egg-shaped shells are studied numerically using nonlinear elastic buckling analysis. Both experimental and numerical data are presented and compared through graphs and tables. • Collapse of imperfect egg-shaped shells are evaluated experimentally and numerically. • Local flat and dimple imperfections are concentrated in the experiment. • Sensitivity threshold of egg-shaped shells to local imperfections is obtained. [ABSTRACT FROM AUTHOR]

This study examined the buckling of unstiffened cylindrical shells under external pressure. Six stainless steel cylindrical shell specimens were tested, with a length-to-radius ratio, L/R, ranging from 1 to 7. The wall thickness, diameter, axial length, and geometry of each specimen and the material properties of the corresponding sheets were measured. All cylindrical specimens were subjected to external pressure in a pressure chamber; the buckling load and final collapsed mode were recorded. This paper presents a comparison among theoretical calculations, finite element (FE) results, and experimental data for externally pressurized cylindrical shells. In the numerical calculations, true geometry, average wall thicknesses, and elastic–perfectly plastic modeling were considered. Deviation between theoretical and FE results was 0%to − 22%, and it increased with the length-to-radius ratio. Experimental results are consistent with FE results, with deviation of 2–9%, and final collapsed modes of all shells are consistent. [ABSTRACT FROM AUTHOR]

This study explored the elastic buckling of egg-shaped shells made of stereolithography resin. The shells had identical nominal geometry parameters with the thickness of 2 mm, the major axis of 232 mm, and the minor axis of 160 mm, respectively. Five near-perfect laboratory-scale models were fabricated using stereolithography appearance (SLA), a rapid prototyping technique. Each model was scanned by a three-dimensional optical scanner, measured using a micrometer, and tested in a pressure chamber. The buckling behaviours of egg-shaped shells with deterministic geometric imperfections were experimentally, analytically, and numerically analysed. The perfect egg-shaped shell was also compared with the fabricated egg-shaped models. A good agreement among them was obtained. The remarkable experimental results of egg-shaped shells were presented in this paper by using 3D printing technologies, which shows the high machining accuracy of 3D printing technologies and provides a new solution for the limitation of experimental study into non-typical shells of revolution. Also, the study could provide a new non-typical shell structure and its stability evaluation approach for space vehicles, pressure tanks, and pressure hulls. [ABSTRACT FROM AUTHOR]

This paper focuses on the buckling of titanium alloy spherical pressure hulls subjected to uniform external pressure. Hulls were spherical shells with 1000 mm median radius and had uniform wall thickness of 25–80 mm. The linear and nonlinear buckling of geometrically perfect hulls were examined numerically and verified analytically in linear range. The nonlinear buckling of hulls with eigenmode geometrical imperfections were evaluated numerically using the modified Riks method, in which imperfection size ranged from 2 to 10 mm. The critical buckling load of geometrically perfect and imperfect hulls was obtained based on elastic-perfectly plastic material modelling, in which the yield strength varied from 800 to 1300 MPa. A semi-analytical formula to predict the load carrying capacity of hulls was derived based on the numerical computations, which was verified against previous laboratory experiments conducted years ago and numerical benchmark study. Results of analytical, numerical, and experimental investigations were given in tables and figures. [ABSTRACT FROM AUTHOR]

This study examines the effect of shape index on the elastic buckling of Cassini oval shells under uniform external pressure. Shells are evaluated under a uniform wall thickness (2 mm) and capacity ( 3.63 × 10 6 mm 3 ), with the shape index, k c = c / a , ranging from 0 to 0.99. Several numerical computations, involving linear elastic bifurcation analysis and geometrically nonlinear elastic analysis including eigenmode imperfections, are conducted for these shells. Some of them are investigated experimentally. The results show that a Cassini oval shell with a stable character seems to be an unfavorable shape due to its low load-carrying capacity, which is at variance with previous findings regarding this problem. Notably, the k c = 0.1 Cassini oval geometry, exhibiting a high load-carrying capacity, appears to be a favorable shape in various fields such as underwater tanks, pressure hulls, and artificial capsules. [ABSTRACT FROM AUTHOR]

This paper focuses on spherical shells with openings and reinforcement under uniform external pressure. To reduce the local weakening and buckling effects of the openings on these spherical pressure shells, the opening reinforcement parameters were optimized to minimize the buckling instability. According to the result of the optimization, two laboratory-scale models were manufactured and tested. The geometry, spherical shell thickness, wall thickness, buckling load, and final collapsed mode were measured for each spherical shell with an opening; the material properties of the corresponding sheets were also measured. The buckling behavior of a simulated spherical shell with an opening was demonstrated numerically according to experimental data. Numerical calculations involved considering the real geometrical shape, average values of parameters, and elastic-plastic modeling of true stress–strain curves. Moreover, the effects of initial geometrical imperfections on the critical load of the simulated spherical shell were analyzed numerically. The scanning model was calculated according to deterministic imperfections obtained from measured geometrical shapes. The theoretical model was calculated according to the equivalent geometrical imperfection valued as the first buckling mode of linear buckling. The results of the experimental and numerical investigations were compared in tables and figures. [ABSTRACT FROM AUTHOR]

The subject of the present paper is a family of egg-shaped shells. The meridian of these shells resembles that of a goose egg. The capacity and mass of the shell were maintained constant. The ratio of the minor B to the major L axis of the shell was determined according to the experimental results of the analysis of 333 goose eggs. Fourteen B / L ratios were determined as follows: 0.4, 0.5, 0.6, 0.65, 0.66, 0.67, 0.68, 0.69, 0.70, 0.71, 0.72, 0.8, 0.9 and 1.0. The effect of the ratio on the buckling behavior of the egg-shaped shell was numerically and analytically analyzed. [ABSTRACT FROM AUTHOR]

Spherical shells are presently the most extensively used shapes for pressure hulls in the deep manned submersible. However, it is known that the spherical pressure hull has disadvantages of difficult interior arrangement/low space efficiency, and is highly sensitive to geometric imperfections. These limitations have prevented further developments of the deep manned submersible to some extent. In order to overcome these limitations, two egg-shaped pressure hulls respectively with the constant and variable thickness are proposed in this paper, where the equivalent spherical pressure hull is also presented for comparison. Buckling of these pressure hulls with geometric imperfections are further studied using numerical analyses at a given design load. It is found that, with respect to hull strength, buoyancy reserve, and space efficiency etc., egg-shaped pressure hulls could be optimally coordinated, which appear to be leading to overall better performance than the spherical pressure hull. Especially, the egg-shaped pressure hull is quite less sensitive to the geometric imperfections, making it more convenient and low costly to form the hull in manufacturing or to open holes in applications. It is anticipated that egg-shaped pressure hulls will play a key role in the future development of deep-sea manned submersibles. [ABSTRACT FROM AUTHOR]

This paper describes an experimental and numerical study of the hydroforming and buckling of an egg-shaped shell based on a petal-shaped preform. The preform was welded from 12 meridionally interconnected bent petals with a uniform thickness of 1.38 mm. Before bending, the blanked petals had a maximum width of 69.1 mm and a length of 474.6 mm. Each welding line between adjacent petals corresponded to the meridian of the target egg-shaped shell. The petal-shaped preform was filled with tap water and internally pressurized for hydroforming. The hydroformed egg-shaped shell was immersed in a pressure chamber for hydrostatic testing. After the experiment, the nonlinear finite element method was used to numerically study the hydroforming and buckling of the egg-shaped shell and the effect of internal pressure and weld seams on the buckling. • Egg-shaped shell was fabricated via free hydroforming technique. • Petal-shaped preform had 12 meridionally interconnected bent petals. • Numerical estimations agreed well with experimental observations. • Effects of hydroforming and welding on the buckling were explored. [ABSTRACT FROM AUTHOR]