Abstract: Solidification cracking and hydrogen cracking are some defects generated in the fusion welding of ultrahigh carbon steels. However, friction stir welding (FSW) of such steels, being a solid-state technique, has been demonstrated to alleviate such problems encountered in traditional welding. FSW include different process parameters that must be carefully defined prior processing. These parameters included but not restricted to: tool feed, tool RPM, tool geometry, tool tilt angle. These parameters form a key factor behind avoiding warm holes and voids behind the tool and in achieving a defect-free weld. More importantly, these parameters directly affect the microstructure of the weld and hence the final mechanical properties of weld. For that, 3D finite element (FE) thermo-mechanical model was developed using DEFORM 3D to simulate FSW of carbon steel. At points of interest in the joint, tracking is done for history of critical state variables such as temperature, stresses, and strain rates. Typical results found include the ability to simulate different weld zones. Simulations predictions were successfully compared to experimental FSW tests. It is believed that such a numerical model can be used to optimize FSW processing parameters to favor desirable defect free weld with better mechanical properties.
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.