Hd. Espinosa et Ns. Brar, DYNAMIC FAILURE MECHANISMS OF CERAMIC BARS - EXPERIMENTS AND NUMERICAL SIMULATIONS, Journal of the mechanics and physics of solids, 43(10), 1995, pp. 1615
Failure mechanisms in ceramics are investigated by means of bar impact
experiments and numerical simulations of the wave propagation event.
Stress histories are measured by embedding manganin stress gauges in t
he ceramic bars. The fracture event is examined by high speed photogra
phy. A violent radial expansion, in a region dose to the impact surfac
e, followed by a cloud of debris is observed. Numerical simulations of
the inelastic wave propagation event are performed with a multiple-pl
ane microcracking model. The simulations show that when the impact str
ess exceeds a material threshold, the stress wave in the bar has a rel
atively short duration which is controlled by the rate of unconfined c
ompressive damage. A nonzero inelastic strain rate at the wave front i
s required in the simulations to properly capture the measured stress
attenuation with propagation distance. This feature is related to a he
terogeneous material microstructure which is a common occurrence in ce
ramics. Furthermore, the simulations predict a radial expansion of the
bar as a result of not only compressive but also tensile damage. The
radial velocity histories on the bar surface are functions of wave pro
pagation distance and damage rate. Tensile damage is induced by stress
release from the rod surface and is restricted to the bar core, due t
o wave focusing, and to the bar free end. In the latest case, reflecti
on of the compressive pulse produces bar spallation. The two dimension
al distribution of tensile and compressive damage is assessed by means
of contour plots of volumetric strain and the second invariant of the
inelastic strain tenser.