On the Effects of Stress State and Microstructure Induced Anisotropies on Ductile Fracture
Abstract
A major challenge that is currently facing the mechanics of materials community
is the accurate prediction of fracture in advanced ductile materials. The intertwined
effects of intrinsic and extrinsic factors make ductile fracture one of the most complex
phenomena in materials mechanics. Intrinsic factors include large plastic deformations,
induced anisotropies, microstructural evolution, and stress state effects.
Extrinsic factors relate to the effect of boundary conditions and to the onset of plastic
instabilities, either material (e.g., shear bands) or structural (e.g., necking). This
dissertation sheds light on three fundamental topics - effect of non proportional loadings,
anisotropic ductile fracture and failure by shear localization. First, by means
of a simple fracture model, a generic shape of the fracture strain versus average triaxiality
locus and previously published experimental results are rationalized. Then,
a more elaborate ductile fracture model is utilized to carry out three-dimensional
finite element simulations of damage accumulation to failure in initially crack-free
specimens under certain symmetry considerations. The results reveal an emerging
competition between intrinsic and structural effects imparted by plastic anisotropy.
Finally, full 3D simulations are carried out when the triads of loading and plastic
anisotropy are misoriented. The simulations reveal, for the first time, failure by
shear band formation in initially round notched bars, reminiscent of experimental
observations in Al or Mg alloys. These insights have practical and theoretical
consequences and will aid the implementation of improved models of ductile fracture
with accurate predictive capabilities and the design of safer structural components in
the aerospace, automotive and energy industries.
Subject
ductile fractureanisotropy
shear localization
shear bands
fracture
non-proportional loadings
path dependent
void shape
void orientation
Citation
Thomas, Nithin (2016). On the Effects of Stress State and Microstructure Induced Anisotropies on Ductile Fracture. Doctoral dissertation, Texas A & M University. Available electronically from https : / /hdl .handle .net /1969 .1 /159104.