Enhanced fracture energy and effects of temperature at spalling in ceramics: continuum damage modelling |
| |
| Authors: | J Najar V V Silberschmidt M Müller-Bechtel |
| |
| Institution: | Lehrstuhl A für Mechanik, Technische Universit?t München, Boltzmannstr. 15, D-85748 Garching, Germany, DE
Tecasim 6mBH, Im Eichsfeld 3, D-65428, Rüsselsheim, Germany, DE
|
| |
| Abstract: | Summary Enhanced fracture energy losses at spalling and the temperature dependence of the spalling strength of alumina ceramic bars
are analysed on the basis of the experimental tests conducted both in room temperature and within the temperature range up
to 1500°C at strain rates of some 500 s−1. The experimental method and the measurements are first shortly outlined. The mechanical response of ceramic bars is modelled
then as a heterogeneous distribution of brittle-elastic mesoelements undergoing continuum damage at the known strain history,
corresponding to that registered in the experiments. The mesoelements are characterised by the values of initial damage randomly
fluctuating within a given band-width superposed on a deterministic distribution, which corresponds to the fabrication conditions
of the ceramic bars. The model has been tested in the evaluation of room-temperature experiments, its parameters: the average
value of the initial damage, Young's modulus of the undamaged material and the energy absorption capacity in continuum damage
are taken from the calibration fitting the experimental data. The registered energy losses at spalling, which exceed the static
values of fracture energy by almost an order of magnitude, can be explained thus by the enhancement of the dissipation due
to bulk damage, which is computed on the basis of the above parameters. The temperature change of the Young's modulus of the
matrix material is taken as corresponding to the measured change of the uniaxial wave velocity in the bar, and corrected by
the temperature change of the mass density. The analysis of the model shows that the drop in the spalling strength of the
specimens with the increase of the temperature is phenomenologically related to the falling energy absorption capacity within
the continuum damage mechanism. An explanation of this phenomenon is attempted, based on the grain-size-related mechanisms
of the microfracture from pre-existing intergranular flaws distributed over the bulk of ceramics.
Received 7 May 1999; accepted for publication 14 June 1999 |
| |
| Keywords: | spall ceramics strength fracture energy size effect continuum damage inhomogeneity |
| 本文献已被 SpringerLink 等数据库收录！ |
|
