Plastic Buckling of Cones Subjected to Axial Compression and External Pressure

2012 ◽  
Vol 135 (1) ◽  
Author(s):  
J. Błachut ◽  
A. Muc ◽  
J. Ryś
Keyword(s):  
Axial Compression ◽  
Wall Thickness ◽  
True Strain ◽  
Safety Margin ◽  
External Pressure ◽  
Perfectly Plastic ◽  
Test Models ◽  
Failure Loads ◽  
Elastic Perfectly Plastic ◽  
Strain Modeling

The paper provides details about tests on six steel cones. Test models were machined from 250 mm diameter billet. All cones had substantial and integral top and bottom flanges in order to secure well defined boundary conditions. Experimental data were obtained for: (i) two cones subjected to axial compression, (ii) two cones subjected to external pressure, and (iii) the remaining two models subjected to combined action of external pressure and axial compression. Apart from axisymmetric modeling of tested cones, true geometry with true wall thickness was also used in calculations. Theoretical failure loads were obtained for: (i) elastic perfectly plastic, (ii) engineering stress–strain, and (iii) true stress–true strain modeling of steel. The latter approach coupled with measured geometry and wall thickness secured safe predictions of the collapse loads in all cases. Comparisons of experimental collapse loads with estimates given by ASME and ECCS design codes are included. It is seen here that the ASME and ECCS rules provide a safety margin of about 100% against the collapse (except 50% for axial compression in the case of the ECCS).

Plastic Buckling of Cones Subjected to Axial Compression and External Pressure

2011 ◽  
Author(s):  
J. Blachut ◽  
A. Muc ◽  
J. Rys´
Keyword(s):  
Axial Compression ◽  
Wall Thickness ◽  
Failure Load ◽  
Thickness Distribution ◽  
True Strain ◽  
Cone Angle ◽  
External Pressure ◽  
Large Radius ◽  
Perfectly Plastic ◽  
Failure Loads

The paper provides details about buckling tests on six steel cones and the corresponding numerical estimates of failure load (asymmetric bifurcation and/or collapse). Test models were machined from 250 mm billet. The wall thickness was 2 mm, small-end radius was 74.0 mm and the large radius end was 100 mm. The semi-cone angle was 14 deg. Cones had substantial, and integral top and bottom flanges. Experimental failure loads were obtained for: (i) the first two cones subjected to axial compression, (ii) subsequent two cones subjected to external pressure, and (iii) the remaining two models subjected to combined action of external pressure and axial compression. The magnitude of test pressure was about 5 MPa, and the axial failure load was approximately 230 kN. Good repeatability of experimental failure loads was obtained. Numerical estimates of failure loads were obtained for elastic perfectly plastic, engineering stress-strain, and true stress–true strain modelling of steel. Apart from axisymmetric modelling of shells, true geometry with true wall thickness distribution was adopted in calculations. Some of the numerical estimates of buckling loads are close to test data but other are not. The reasons for these discrepancies are highlighted in the paper.

Buckling of Unstiffened Steel Cones Subjected to Axial Compression and External Pressure

2012 ◽  
Vol 134 (3) ◽  
Author(s):  
J. Błachut ◽  
O. Ifayefunmi
Keyword(s):  
Axial Compression ◽  
Wall Thickness ◽  
Degrees Of Freedom ◽  
Static Stability ◽  
Stability Domain ◽  
External Pressure ◽  
The Other ◽  
Elastic Behavior ◽  
Geometrical Parameters ◽  
Perfectly Plastic

This is the first study into elastic-plastic buckling of unstiffened truncated conical shells under simultaneously acting axial compression and an independent external pressure. This is both a numerical and experimental study. Domains of combined stability are obtained using the finite element method for a range of geometrical parameters. Cones are clamped at one end and free to move axially at the other end, where all the other degrees of freedom remain constrained. Shells are assumed to be from mild steel and the material is modeled as elastic perfectly plastic. The FE results indicate that the static stability domains remain convex. The failure mechanisms, i.e., asymmetric bifurcation and axisymmetric collapse are discussed together with the spread of plastic strains through the wall thickness. Also, the combined stability domains are examined for regions of purely elastic behavior and for regions where plastic straining exists. The latter is not convex and repercussions of that are discussed. The spread of plastic strain is computed for a range of the (radius-to-wall-thickness) ratios. Experimental results are based on laboratory scale models. Here, a single geometry was chosen for validation of numerically predicted static stability domain. Parameters of this geometry were assumed as follows: the ratio of the bigger radius, r2, to the smaller radius, r1, was taken as (r2/r1) = 2.02; the ratio of radius-to-wall-thickness, (r2/t), was 33.0, and the cone semiangle was 26.56°, while the axial length-to-radius ratio was (h/r2) = 1.01. Shells were formed by computer numerically controlled machining from 252 mm diameter solid steel billet. They had heavy integral flanges at both ends and models were not stress relieved prior to testing. Details about the test arrangements are provided in the paper.

Buckle Propagation Analysis of Deep-Water Petroleum Transmission Pipelines with Axial Tension

2014 ◽  
Vol 1008-1009 ◽  
pp. 1134-1143 ◽  
Author(s):  
Sun Ting Yan ◽  
Yin Fa Zhu ◽  
Zhi Jiang Jin ◽  
Hao Ye
Keyword(s):  
Plastic Hinge ◽  
External Pressure ◽  
Isotropic Hardening ◽  
Rigid Plastic ◽  
Perfectly Plastic ◽  
Fitting Procedure ◽  
Plastic Materials ◽  
Buckle Propagation ◽  
Elastic Perfectly Plastic ◽  
Hinge Model

Quasi-static finite element simulation is carried out on buckle propagation phenomenon of offshore pipelines under external pressure. Arc-length method and volume-controlled static analysis by employing hydrostatic fluid element F3D4 are employed to calculate the steady buckle propagation pressure. After verifying the validity of numerical model, emphasis is on the influence of tension on propagation pressure considering isotropic hardening elastoplastic and elastic-perfectly plastic materials. Parametric study is conducted to include the effect of diameter-thickness ratio, after which two empirical equations are derived by curve fitting procedure. Finally, some comments on the results obtained through rigid-plastic hinge model are presented and a modified plastic hinge model including effect of material anisotropy is derived. The results can serve as a reference for more reasonable design of buckle arrestors.

The Effect of Shape, Thickness and Boundary Imperfections on Plastic Buckling of Cones

2011 ◽  
Author(s):  
O. Ifayefunmi ◽  
J. Błachut
Keyword(s):  
Boundary Conditions ◽  
Axial Compression ◽  
Wall Thickness ◽  
Thickness Distribution ◽  
Radial Pressure ◽  
External Pressure ◽  
Combined Loading ◽  
Small Radius ◽  
Worst Case ◽  
Buckling Strength

Three types of imperfections are analysed in the current paper, and they are: (i) Initial geometric imperfections, i.e., deviations from perfect geometry, (ii) Variations in the wall thickness distribution, and (iii) Imperfect boundary conditions. It is assumed that cones are subject to: (a) axial compression only, (b) radial pressure only, and (c) combined loading, i.e., axial compression and external pressure acting simultaneously. Buckling strength of imperfect cones is obtained for all of the cases above. It is shown that the buckling strength is differently affected by imperfections, when cones are subjected to axial compression or to radial external pressure. The response to imperfections along the combined stability envelope is also provided, and these results are first of this type. The finite element analysis, using the proprietary code is used as the numerical tool. Cones are assumed to be from mild steel and the material is modelled as elastic perfectly plastic. Geometrical imperfection profiles are affine to eigenshapes. A number of them are tried in calculations, as well as the effect of them being superimposed. The results indicate that imperfection amplitude and its shape strongly affect the load carrying capacity of conical shells. Also, it is shown that the buckling loads of analyzed cones are more sensitive when subjected to combined loading as compared to their sensitivity under single load conditions. At the next stage, uneven thickness distribution along the cone slant was considered. Variation of wall thickness was assumed to vary in a piece-wise constant fashion. This appears to have a large effect on the buckling strength of cones under axial compression only as compared with that of cones subjected to radial external pressure only. Finally, the effect of variability of boundary conditions on failure load of cones was investigated for two loading conditions, i.e., for axial compression and for radial pressure, only. Results indicate that change of boundary conditions influences the magnitude of buckling load. For axially compressed cones the loss of buckling strength can be large (about 64% for the worst case (beta = 30 deg, the cone not restrained at small radius end). Calculations for radial pressure indicate that the loss of buckling strength is not as acute — with 34% for the worst case (beta = 40 deg, relaxed boundary conditions at the larger radius end). This is an entirely numerical study but references to accompanying experimental programme are provided.

Effect of Imperfections on Buckling of Thin Cylinders Under External Pressure

1956 ◽  
Vol 23 (4) ◽  
pp. 569-575
Author(s):  
L. H. Donnell
Keyword(s):  
Axial Compression ◽  
External Pressure ◽  
Finite Deflection ◽  
Failure Loads ◽  
Deflection Theory

Abstract The buckling of thin cylinders under external pressure is studied by finite-deflection theory, assuming the same type of imperfections as had been assumed in a previous study of buckling under axial compression (3). Unlike the axial compression case only a small elastic postbuckling reduction in resistance is found, and this only for long cylinders. However, if reasonable imperfections are assumed, failure loads initiated by yielding are found to be of the same order as those indicated by experiments.

Numerical and Experimental Study on Ultimate Strength of Stiffened Column Under Axial Compression

2020 ◽  
Author(s):  
Hongyuan Mei ◽  
Deyu Wang ◽  
Qi Wan
Keyword(s):  
Ultimate Strength ◽  
Axial Compression ◽  
Strain Curve ◽  
High Strength ◽  
Tensile Tests ◽  
True Stress ◽  
Stress Strain ◽  
Test Fixture ◽  
Perfectly Plastic ◽  
Elastic Perfectly Plastic

Abstract Six specimens with one Tee-bar stiffener and its attached plating were tested under axial compression to investigate the ultimate strength. The specimens have one longitudinal span and the simply supported boundary conditions at the end edge of loading were produced based on a horizontal test fixture. The initial geometrical imperfections were measured and tensile tests of high tensile steel used in the specimens with different thickness were conducted. The results calculated by FE analysis with true stress-strain curves, average measured thickness and measured initial geometrical deformation could reach a good agreement with experimental results. The ultimate strength calculated with elastic/perfectly plastic curve is approximately 10% larger than that with true stress-strain curve. The reason is that the proportional limit stress of material is significantly lower than 0.2% proof stress for the high strength steel used in specimens. And the occurrence of buckling is earlier than the time that the material enters into plastic stage. As a result, the ultimate strength assessed with elastic/perfectly plastic curve doesn’t always the lowest result and it should be adopted carefully.

Nonlinear Analysis of Anchored Tanks Subject to Equivalent Seismic Loading

2002 ◽  
Author(s):  
D. Redekop ◽  
P. Mirfakhraei ◽  
T. Muhammad
Keyword(s):  
Nonlinear Behavior ◽  
Seismic Loading ◽  
Material Behavior ◽  
Seismic Action ◽  
The Finite Element Method ◽  
Perfectly Plastic ◽  
Liquid Storage ◽  
Failure Loads ◽  
Elastic Perfectly Plastic ◽  
Hydrodynamic Effects

The finite element method is applied to the problem of the nonlinear behavior of anchored cylindrical liquid-storage tanks subject to horizontal seismic loading. The tank alone is modelled with assumptions of fixed conditions at the base and free conditions at the top. Geometric nonlinearity is considered and the material behavior is taken as elastic-perfectly plastic. The loading consists of a constant hydrostatic pressure to which is added an equivalent static pressure representing hydrodynamic effects arising from seismic action. The latter loading is increased until failure occurs. As an indication of the validity of the approach a comparison with a test result is given. A parametric study is then conducted. Nonlinear failure loads are calculated in each case, and these are compared with previously determined elastic buckling loads.

Buckling of Truncated Cones With Localized Imperfections

2012 ◽  
Author(s):  
J. Błachut
Keyword(s):  
Axial Compression ◽  
Wall Thickness ◽  
External Pressure ◽  
Buckling Load ◽  
Buckling Loads ◽  
Conical Shells ◽  
Buckling Strength ◽  
Shape Deviations ◽  
Combined Action ◽  
Axisymmetric Shape

The paper shows that both the inward and outward bulge-type axisymmetric shape imperfections can significantly lower the buckling strength of steel conical shells. The FE results are provided for: (i) axial compression, (ii) external pressure, and (iii) combined action of both loads. Sensitivity of buckling loads to outward bulges has not been generally known or expected. It is shown that the sensitivity of buckling load depends not only on the shape, amplitude but also on the position of the imperfection along the slant. Geometry of recently tested cones was also used in order to assess the influence of measured shape deviations on the buckling strength. The amplitudes of imperfections in these machined models were small (up to 5 % of wall thickness). As a result their influence on the buckling strength was found to be negligible.

Buckling of Unstiffened Steel Cones Subjected to Axial Compression and External Pressure

2010 ◽  
Author(s):  
J. Blachut ◽  
O. Ifayefunmi
Keyword(s):  
Axial Compression ◽  
Wall Thickness ◽  
Degrees Of Freedom ◽  
Static Stability ◽  
Stability Domain ◽  
External Pressure ◽  
The Other ◽  
Combined Loading ◽  
Elastic Behavior ◽  
Geometrical Parameters

The paper considers buckling of unstiffened truncated conical shells under simultaneously acting quasi-static axial compression and an independent external hydrostatic pressure. This is both numerical and experimental study. Domains of combined stability were obtained using the finite element method for a range of geometrical parameters. Cones are clamped at one end and free to move axially at the other end, where all the other degrees of freedom remain constrained. Shells are assumed to be from mild steel and the material is modeled as elastic perfectly plastic. The FE results indicate that the static stability domains remain convex. The failure mechanisms, i.e., asymmetric bifurcation and axisymmetric collapse are discussed together with the spread of plastic strains through the wall thickness. Also, the combined stability domains are examined for regions of purely elastic behavior and for regions where plastic straining exists. The latter is not convex and repercussions of that are discussed. The spread of the latter is computed for a range of the (radius-to-wall-thickness)-ratios. Experimental results are based on laboratory scale models. Here, a single geometry was chosen for validation of numerically predicted static stability domain. Parameters of this geometry were assumed as follows: the ratio of bigger radius, r2, to smaller radius, r1, was taken as (r2/r1) = 2.02; the ratio of radius-to-wall-thickness, (r2/t), was 33.0, and the cone semi-angle was 26.56°, whilst the axial length-to-radius ratio was, (h/r2) = 1.01. Shells were CNC-machined from 252mm diameter solid steel billet. They had heavy integral flanges at both ends and models were not stress relieved prior to testing. Details about the test arrangements are provided in the paper. In particular, the development details and experience of the test rig for independent/combined loading of cones are given. The current contribution complements Ref. [1].

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