Browsing by Author "Saiful Alam, Md."

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Characterization of tensile failure behavior of natural single fibre composite by acoustic emission technique
(Department of Materials and Metallurgical Engineering (MME), 2012-07) Saiful Alam, Md.; Gulshan, Dr. Fahmida
In the present days among the different non-destructive testing methods Acoustic Emission is a suitable tool for detecting and evaluating and for better understanding the damage mechanism and failure behavior in composites during mechanical loading. Methodology was developed for natural single fibre tensile test with Acoustic Emission (AE) to assess or monitor the tensile failure behavior of natural single fibre especially for bamboo single fibre. Series of experiment performed with this methodology. Before the final failure of fibre during tensile test few (one or two) load drop observed from the time vs load graph. From AE parameter such as Amplitude, Energy, duration etc. significant information of corresponding to that load drops found. These AE signals from the load drop may occur from the failure such as debonding between two elementary fibre or from join of elementary fibre at edge. The value of load at first load drop was not found consistent for different sample (for a particular sample the value is 8N, Stress: 517.51 MPa). Final breaking of fibre gives saturated level AE amplitude of preamplifier (99.9 dB) for all samples. Therefore it was not possible to think up exact AE energy value for final breaking. The other AE signal of AE may occur for the micro failure mechanism. Same methodology was used for tensile test of three single fibres, which gives clear indication of load drop before the final breaking of first and second fibre. Moreover, tensile test of single fibre composite (bamboo single fibre/epoxy) was performed to identify the individual fibre and matrix failure mechanism in composites using AE technique. Experimental data from AE for SFC test shows that many of them have a clear correlation between acoustic emission amplitude and failure mechanisms in single fibre composite.
Microstructure, dielectric and magnetic properties of Bi1-xGdxMnO3 ceramics
(Department of Physics (PHY), 2015-12) Saiful Alam, Md.; Abdul Basith, Dr. Mohammed
The nominal compositions of Bi1-xGdxMnO3 (x = 0.00-0.12) ceramics were synthesized by conventional solid state reaction technique and their morphological, dielectric and magnetic properties were investigated. The field emission scanning electron microscopy images and their respective histograms demonstrate that due to the substitution of Gd, the average grain size was reduced with a narrow size distribution. Particularly, for 12 % Gd substitution the average size was reduced up to around ~200 nm which is much smaller than that of undoped BiMnO3 ceramic. The substitution of Gd also generated significant amount of oxygen vacancies and the oxygen vacancies were gradually increased with Gd doping concentration. Compared to the undoped BiMnO3, the dielectric constant was stable in Gd doped BiMnO3 ceramics over a wide range of high frequencies (104 to 108 kHz) by suppressing the dispersion at low frequencies. The substitution of Gd in place of Bi also reduced the dielectric constant, particularly at low frequencies. The reduction of dielectric constant at low frequencies in Gd doped BiMnO3 ceramics may be associated with the large amount of oxygen vacancies which was generated upon the substitution of Gd. The magnetization versus magnetic field hysteresis loops were recorded using a Vibrating Sample Magnetometer (VSM) at room temperature. Due to the substitution of Gd, the magnetic parameters like remanent magnetization and coercive fields were enhanced nominally. The enhanced magnetic properties might be associated with the high magnetic moment of Gd3+ ion as well as the structural distortion in the perovskite with change in Mn–O–Mn bond angle. An asymmetric shift both in the field and magnetization axes of magnetization versus magnetic field curves was observed. This indicates the presence of exchange bias effect in these compounds notably at room temperature. Finally, the temperature dependent zero field cooled (ZFC) and field cooled (FC) magnetization curves demonstrate a ferromagnetic to paramagnetic transition around ~ 45 K in BiMnO3. Below this phase transition temperature, there was a splitting between ZFC and FC curves which indicates the presence of a spin glass like state in undoped BiMnO3. Due to the substitution of 4 % Gd in BiMnO3, the ferromagnetic to paramagnetic transition was remain unchanged, however, the ZFC and FC curves were coincided with each other.
Retrofitting of footings
(Department of Civil Engineering, 2003-09) Saiful Alam, Md.; Seraj, Dr. Salek M.
Footing is onc of thc most important structural e1cmcnts in the field of construction. Punching shear is a govel11ing factor to be considered in the dcsign of footings. Depth of footing is a major concern of punching strcngth calculation. Hence the increase of footing depth is expectcd to contributc to thc punching strength of existing footings. A total of twelve model footings were cast and tested in the laboratory in an effort to ascertain the effect of concrete overlay on the punching shear capacity of footings. In this regard model footings wcrc prepared with different combinations of concrete overlay, compressive reinforcement, dowel bars. Test program was carried out to gather basic infol111ation on real punching behavior of footings subjected to conccntrated loading. The punching strength of footings with ovcrlay has been found to be significantly higher than that of footings without ovcrlay and having lesser thickness. It has been observed that footings having concrcte overlay could attain punching capacity very near to the capacity of footings having similar thickness, but cast monolithically. The code specified strengths of thc specimens wcre calculated in accordance with ACI 318-95, BS 8110-85, CAN3-A23.3-M84 and CEB-FIB. It appears that most of the codes do not recognize the role of percentage of longitudinal stcel on the punching shear strength. Overlay on old concrete provide additional punching strength; dowel bars and compressive rcinforccmcnt did not increasc the punching strength, but these contributed significantly in other ways. Dowels provided bonding between old concrete and overlay. Hence, the samples of overlay with dowel behaved monolithic-ally at the time of failure. On the other hand, overlay without dowel bars was separated during failure. Compressive reinforcement showed some significance for the samples without overlay to reduce the deflection. But it was not very significant for the samples with overlay.