On the Nonlinear Analysis Methodologies for Thin Spherical Shells Under External Pressure with Different Finite-Element Codes

1989 ◽  
Vol 33 (04) ◽  
pp. 318-325
Author(s):  
Dario Boote ◽  
Donatella Mascia
Keyword(s):  
Finite Element ◽  
Numerical Procedure ◽  
External Pressure ◽  
Experimental Investigations ◽  
Nonlinear Analyses ◽  
Spherical Shells ◽  
Double Curvature ◽  
Load Carrying ◽  
Material Load ◽  
Structure Collapse

Submersible structures consist merely of simple and double curvature thin-walled shells. For this kind of structure, collapse occurs due to the combined nonlinear action of buckling and plasticity of material. Load-carrying capacity may then be assessed mainly by two approaches: experimental investigations and step-by-step numerical procedures. In nonlinear analyses, the results obtained are influenced by the magnitude of the load increment adopted. Solution procedures are then required in order to choose adequate parameters for material failure description as well as elastic nonlinearity. The aim of this paper is to carry out a suitable numerical procedure whose reliability does not depend on the finite-element code adopted.

Research of Reinforce Stress on the Pressure Structure of Submersible Vehicle

2014 ◽  
Vol 496-500 ◽  
pp. 590-593
Author(s):  
Guan Nan Chu ◽  
Qing Yong Zhang ◽  
Guo Chun Lu
Keyword(s):  
Residual Stress ◽  
Finite Element ◽  
Stress Distribution ◽  
Hoop Stress ◽  
External Pressure ◽  
Finite Element Models ◽  
Cylinder Pressure ◽  
Simulation Experiments ◽  
Element Analysis ◽  
Load Carrying

In order to improve the load-carrying properties of pressure structure, a new method to improve the external bearing limit is put forward and residual stress is used. Based on finite element analysis, finite element models of cylinder pressure structure of submersible vehicle are established to produce hoop residual stress in the process of outward expansion. According to a lot of data of simulation experiments, the result indicates that hoop residual stress is compressive on the outer surface of the pipe and the hoop stress keeps tensile on the inside surface. This kind of stress distribution is helpful to the cylinder structure and can improve its bearing capacity of external pressure. Moreover, the rules of the residual stress are got. The influences of physical dimension, yield strength of material and the expansion rate to the stress distribution are analyzed. The measures to produce the stress distribution are also presented.

Experimental Investigations and Finite-Element Modeling of Thermoplastic Effect during Tensile Tests of Metal Material

2013 ◽  
Vol 634-638 ◽  
pp. 2835-2838
Author(s):  
Wei Qing Wang ◽  
Li Yang ◽  
Shi Gui Lv
Keyword(s):  
Plastic Deformation ◽  
Finite Element ◽  
Temperature Field ◽  
Surface Temperature ◽  
Strain Rate ◽  
Numerical Procedure ◽  
Infrared Camera ◽  
Tensile Tests ◽  
Experimental Investigations ◽  
Finite Element Software

During plastic deformation of materials, part of the plastic work is converted into heat, and the temperature field will be changed, this phenomenon is well known as thermoplastic effect. Based on the analysis of thermoplastic effect, the surface temperature of Q235 steel during quasi-static tensile tests was measured by using an infrared camera, and the surface temperature field and it versus time for different strain rate were obtained. A numerical procedure was devised to model the thermoplastic effect during the tensile tests by using ANSYS software. The results showed that, the heat loss during deformation process will be smaller as the strain rate increase, and the temperature increase on the specimen surface generated by the plastic deformation will be higher. The simulation results matched well with the experiment results showed that it was a good way to analyse the thermoplastic effect by the commercial finite element software.

Penetrations in Shells Under External Pressure

1970 ◽  
Vol 92 (2) ◽  
pp. 269-274
Author(s):  
R. C. DeHart ◽  
L. F. Greimann
Keyword(s):  
Finite Element ◽  
Stress Distribution ◽  
Stress Condition ◽  
External Pressure ◽  
Experimental Stress ◽  
Spherical Shells ◽  
Premature Failure ◽  
Resistant Structure ◽  
Theoretical Results ◽  
Stress Analyses

Penetrations, in the pressure-resistant structure of a submersible, disturb the stress condition in the shell and may cause a premature failure. In this paper, two types of finite-element solutions are used to predict the stress distribution near view port openings in spherical shells under external pressure. Results of experimental stress analyses are also given and compared to the theoretical results.

A Data-Driven Framework for Buckling Analysis of Near-Spherical Composite Shells under External Pressure

2021 ◽  
pp. 1-27
Author(s):  
Mitansh Doshi ◽  
Xin Ning
Keyword(s):  
Machine Learning ◽  
Finite Element ◽  
Learning Model ◽  
External Pressure ◽  
Finite Element Simulations ◽  
Data Driven ◽  
Composite Shells ◽  
Spherical Shells ◽  
Buckling Loads ◽  
Machine Learning Model

Abstract This paper presents a data-driven framework that can accurately predict the buckling loads of composite near-spherical shells (i.e. variants of regular icosahedral shells) under external pressure. This framework utilizes finite element simulations to generate data to train a machine learning regression model based on open-source algorithm Extreme Gradient Boosting (XGBoost). The trained XGBoost machine learning model can then predict buckling loads of new designs with small margin of error without time-consuming finite element simulations. Examples of near-spherical composite shells with various geometries and material layups demonstrate the efficiency and accuracy of the framework. The machine learning model removes the demanding hardware and software requirements on computing buckling loads of near-spherical shells, making it particularly suitable to users without access to those computational resources.

Buckling Analyses of Spherical Shells by the Finite Element Method Based on the Willis-Form Equations

2019 ◽  
Vol 11 (09) ◽  
pp. 1950091 ◽  
Author(s):  
Yixiao Sun ◽  
Zhihai Xiang
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
External Pressure ◽  
Experimental Results ◽  
Spherical Shells ◽  
Buckling Loads ◽  
Geometrical Imperfections ◽  
The Impact ◽  
Previous Loading ◽  
Element Method

Buckling analysis of spherical shells under external pressure is a crucial problem in mechanical and aerospace engineering. It is widely known that the buckling loads obtained by classical methods are much higher than experimental results. The main reason for this large discrepancy is customarily attributed to initial geometrical imperfections, and the impact of inhomogeneously distributed stresses during loading process is usually ignored. In order to investigate the effect of this ignored factor, the buckling loads of several spherical shells are analyzed by the geometrically nonlinear finite element method (FEM) based on the Willis-form equations, which explicitly contain the stress gradients at previous loading step. It can be shown that the buckling loads from the Willis-form FEM are about 10% lower than the values from classical FEM. This finding may give better understandings to the differences between theoretical and experimental results for nearly perfect spherical shells and may be helpful to obtain more accurate buckling loads for shells with initial geometrical imperfections.

Discussion on Boote and Mascia: "On the Nonlinear Analysis Methodologies for Thin Spherical Shells Under External Pressure with Different Finite-Element Codes"

1991 ◽  
Vol 35 (04) ◽  
pp. 352-355
Author(s):  
G.D. Galletiy ◽  
J. Blachut
Keyword(s):  
Finite Element ◽  
Nonlinear Analysis ◽  
External Pressure ◽  
General Purpose ◽  
Spherical Shells ◽  
Geometric Imperfections ◽  
Buckling Resistance ◽  
The Subject ◽  
Initial Geometric Imperfections ◽  
Doubly Curved

The accurate prediction of the collapse pressures of thin, doubly curved elastic-plastic shells subjected to external pressure is important in many applications—not least to the occupants of submarines! As is well known, initial geometric imperfections can, in many shells, result in a substantial decrease in the shell's buckling resistance. In their paper, the authors (Boote and Mascia) discuss one imperfect hemispherical model which they analyzed with the help of two general purpose finite-element codes (MARC and ANSYS). The authors do not discuss the use of simpler programs for analyzing these shells [for example, BOSOR 5; Bushnell (1976)][Galletly etal (1987) or other work which has been published on the subject]. We have a number of comments on the subject paper, and these are given below.

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