Simulation of dynamic instabilities during high rate deformation of ductile bars and plates
Author
Summary, in English
In this thesis, some of the phenomena occurring in plates and cylindrical bars subjected to dynamic loading are investigated. Numerical simulations using a dynamic finite element code are performed for a number of different sized specimens with various initial surface imperfections. Typically imposed loading velocities are in the range 10m/s<v_0<50m/s. The specimens are either subjected to tensile or to compressive loading.
Effects of inertia are examined by introducing an artificial volume load, representing the hydrostatic pressure that follows a homogeneous deformation of a cylindrical bar where no necking is accounted for. The influence of elastic unloading is studied by comparing the necking patterns obtained for cylindrical bars, using two different material models,
J_2-flow theory and J_2-deformation theory. The deformation developments for the specimens of interest are visualized using a contour plot method denoted q-plot.
In the case of dynamic buckling of plates, the visualized results using the q-plot method are compared with that obtained using a direct geometrical method, denoted geo-plot. Ductile fracture is simulated by using cohesive elements, included in the original finite element mesh after a prescribed state of deformation is reached. Fracture is controlled by
the cohesive law, whereas the constitutive relation for the bulk material is chosen as J_2-flow
theory.
Effects of inertia are examined by introducing an artificial volume load, representing the hydrostatic pressure that follows a homogeneous deformation of a cylindrical bar where no necking is accounted for. The influence of elastic unloading is studied by comparing the necking patterns obtained for cylindrical bars, using two different material models,
J_2-flow theory and J_2-deformation theory. The deformation developments for the specimens of interest are visualized using a contour plot method denoted q-plot.
In the case of dynamic buckling of plates, the visualized results using the q-plot method are compared with that obtained using a direct geometrical method, denoted geo-plot. Ductile fracture is simulated by using cohesive elements, included in the original finite element mesh after a prescribed state of deformation is reached. Fracture is controlled by
the cohesive law, whereas the constitutive relation for the bulk material is chosen as J_2-flow
theory.
Department/s
Publishing year
2005
Language
English
Document type
Dissertation
Publisher
Division of Mechanics, Lund University
Topic
- Applied Mechanics
Keywords
- numerical simulation
- non-linear
- wave propagation
- multiple necking
- necking
- buckling
- fracture
- Mechanical engineering
- Maskinteknik
- finite elements
- cohesive elements
- dynamic
- J2-flow theory
- J2-deformation theory
- viscoplastic
- background inertia
Status
Published
Supervisor
ISBN/ISSN/Other
- ISBN: 91-628-6427-0
- ISRN: LUTFD2/TFME--05/2005--SE(1-94)
Defence date
17 March 2005
Defence time
10:15
Defence place
Room M:B of the M-building at Lund Institute of Technology, Lund University, Lund, Sweden
Opponent
- Peter Olsson (Professor)