Abstract: Creep stresses and strain rates have been obtained
for a thin rotating disc having variable density with inclusion by
using Seth-s transition theory. The density of the disc is assumed to
vary radially, i.e. ( ) 0 ¤ü ¤ü r/b m - = ; ¤ü 0 and m being real positive
constants. It has been observed that a disc, whose density increases
radially, rotates at higher angular speed, thus decreasing the
possibility of a fracture at the bore, whereas for a disc whose
density decreases radially, the possibility of a fracture at the bore
increases.
Abstract: The main aim of the presented experiments is to
improve behaviour of sandwich structures under dynamic loading,
such as crash or explosion. Several cellular materials are widely used
as core of the sandwich structures and their properties influence
the response of the entire element under impact load. To optimize
their performance requires the characterisation of the core material
behaviour at high strain rates and identification of the underlying
mechanism. This work presents the study of high strain-rate
characteristics of a specific porous lightweight blast energy absorbing
foam using a Split Hopkinson Pressure Bar (SHPB) technique
adapted to perform tests on low strength materials. Two different
velocities, 15 and 30 m.s-1 were used to determine the strain
sensitivity of the material. Foams were designed using two types of
porous lightweight spherical raw materials with diameters of 30-
100 *m, combined with polymer matrix. Cylindrical specimens with
diameter of 15 mm and length of 7 mm were prepared and loaded
using a Split Hopkinson Pressure Bar apparatus to assess the relation
between the composition of the material and its shock wave
attenuation capacity.
Abstract: The scale dependence of the strength of virtually homogeneous rock is usually considered to be insignificant but the spectrum of discontinuities plays a very important role for the strength of differently sized rock elements and also controls the rock creep strain. Large-scale load tests comprised recording of the creep strain rate that was found to be strongly retarded and negligible for stresses lower than about 1/3 of the failure load. For higher stresses creep took place according to a log time law representing secondary creep that ultimately changed to tertiary creep and failure.
Abstract: This paper deals with a numerical analysis of the
transient response of composite beams with strain rate dependent
mechanical properties by use of a finite difference method. The
equations of motion based on Timoshenko beam theory are derived.
The geometric nonlinearity effects are taken into account with von
Kármán large deflection theory. The finite difference method in
conjunction with Newmark average acceleration method is applied to
solve the differential equations. A modified progressive damage
model which accounts for strain rate effects is developed based on
the material property degradation rules and modified Hashin-type
failure criteria and added to the finite difference model. The
components of the model are implemented into a computer code in
Mathematica 6. Glass/epoxy laminated composite beams with
constant and strain rate dependent mechanical properties under
dynamic load are analyzed. Effects of strain rate on dynamic
response of the beam for various stacking sequences, load and
boundary conditions are investigated.