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Analysis of the deformation and failure of blast loaded unstiffened and striffened plates Rudrapatna, Nagaraja
Abstract
A numerical investigation into the deformation and failure of clamped unstiffened and stiffened mild steel plates is carried out. Studies indicate that with increasing load intensity, simple plate structures under blast loading exhibit the three general modes of failure: mode I (large inelastic deformation), mode II (tensile tearing and deformation) and mode III (shear rupture). The failure analysis of plate structures subjected to blast loading is still considered a difficult task. These problems are highly nonlinear due to the combined effect of large deformation, material plasticity and high strain-rates. The present work develops a semi-numerical model for failure prediction which is aimed at providing a simple tool for preliminary design/analysis of such structures. Analytical failure models have been incorporated in an existing finite element code which handles the large deformation, elastic-plastic transient behaviour of unstiffened and stiffened plate structures. The finite element formulation employs existing super finite plate and beam elements. An interactive failure model is proposed to predict the tearing and rupture of thin steel plates and stiffened plate structures under blast loading. The model accounts for the membrane and bending strains as well as the transverse shear stress experienced by the structure under the applied load. The interaction between the tensile tearing and shearing mode of failure is considered via an interaction relation between the strain and stress ratios. Two interactive failure criteria are considered, either Linear (LIC) or Quadratic (QIC) based on the way the ratios are added. The bending strain is estimated by assuming that a plastic hinge line develops at the boundary, while the membrane strain is calculated using the finite element prediction of the deformed profile. The total strain, composed of membrane and bending components, is then divided by a specified rupture strain for the material, to obtain the strain ratio. Since the finite element formulation is based on Kirchhoff plate bending theory, there is no direct prediction of shear strains (stresses). In order to achieve a continuous estimation of the shear force and stress along the plate boundary, a series of very stiff springs are introduced there. The use of high stiffness values effectively simulates the clamped boundary condition of the problem. The estimated shear stress is then compared to the ultimate shear strength of the material to form a stress ratio. A node release algorithm is developed to simulate the progression of rupture. The analysis is continued in the post-failure phase to account for the deformation which continues during the free flight of the torn plate. The predicted failure modes using the above model for blast loaded plate structures are presented and compared with previously published experimental data. The Quadratic Interaction Criterion predicts consistently better results than the Linear Interaction Criterion as compared to the experimental results. The results clearly indicate the influence of shear on the failure mechanism not only for mode III, but also for mode II. The results confirm the importance of the interaction effects of tensile and bending strain on tearing and shear failure.
Item Metadata
Title |
Analysis of the deformation and failure of blast loaded unstiffened and striffened plates
|
Creator | |
Publisher |
University of British Columbia
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Date Issued |
1997
|
Description |
A numerical investigation into the deformation and failure of clamped unstiffened and
stiffened mild steel plates is carried out. Studies indicate that with increasing load
intensity, simple plate structures under blast loading exhibit the three general modes of
failure: mode I (large inelastic deformation), mode II (tensile tearing and deformation)
and mode III (shear rupture). The failure analysis of plate structures subjected to blast
loading is still considered a difficult task. These problems are highly nonlinear due to the
combined effect of large deformation, material plasticity and high strain-rates. The
present work develops a semi-numerical model for failure prediction which is aimed at
providing a simple tool for preliminary design/analysis of such structures.
Analytical failure models have been incorporated in an existing finite element
code which handles the large deformation, elastic-plastic transient behaviour of
unstiffened and stiffened plate structures. The finite element formulation employs
existing super finite plate and beam elements.
An interactive failure model is proposed to predict the tearing and rupture of thin
steel plates and stiffened plate structures under blast loading. The model accounts for the
membrane and bending strains as well as the transverse shear stress experienced by the
structure under the applied load. The interaction between the tensile tearing and shearing
mode of failure is considered via an interaction relation between the strain and stress
ratios. Two interactive failure criteria are considered, either Linear (LIC) or Quadratic
(QIC) based on the way the ratios are added. The bending strain is estimated by assuming that a plastic hinge line develops at the boundary, while the membrane strain is calculated
using the finite element prediction of the deformed profile. The total strain, composed of
membrane and bending components, is then divided by a specified rupture strain for the
material, to obtain the strain ratio.
Since the finite element formulation is based on Kirchhoff plate bending theory,
there is no direct prediction of shear strains (stresses). In order to achieve a continuous
estimation of the shear force and stress along the plate boundary, a series of very stiff
springs are introduced there. The use of high stiffness values effectively simulates the
clamped boundary condition of the problem. The estimated shear stress is then compared
to the ultimate shear strength of the material to form a stress ratio.
A node release algorithm is developed to simulate the progression of rupture. The
analysis is continued in the post-failure phase to account for the deformation which
continues during the free flight of the torn plate. The predicted failure modes using the
above model for blast loaded plate structures are presented and compared with previously
published experimental data.
The Quadratic Interaction Criterion predicts consistently better results than the
Linear Interaction Criterion as compared to the experimental results. The results clearly
indicate the influence of shear on the failure mechanism not only for mode III, but also
for mode II. The results confirm the importance of the interaction effects of tensile and
bending strain on tearing and shear failure.
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Extent |
8903330 bytes
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Genre | |
Type | |
File Format |
application/pdf
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Language |
eng
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Date Available |
2009-04-03
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Provider |
Vancouver : University of British Columbia Library
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Rights |
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.
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DOI |
10.14288/1.0050233
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URI | |
Degree | |
Program | |
Affiliation | |
Degree Grantor |
University of British Columbia
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Graduation Date |
1997-05
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Campus | |
Scholarly Level |
Graduate
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Aggregated Source Repository |
DSpace
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Item Media
Item Citations and Data
Rights
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.