Applied Mechanics and Materials Vol. 440

Abstract: In order to evaluate the effective thermal conductivity (ETC) of hollow fibers, three theoretical models (the parallel/series model, quadrate model and cylindrical model) and finite element method carried out by ANSYS simulation were studied. The results showed that different theoretical models gave quite different effective thermal conductivities. The results from theoretical models and simulations were completely identical in the case when models had regular structures and the heating surface was the same kind of material. The ETC of hollow fibers from all of theoretical models and simulations decreased exponentially with the increase of air volume content. In addition, the ETC of hollow fibers from the first theoretical model were a bit higher than the results from simulation, whereas those from the second theoretical model were smaller than the results from simulation, and those from the third theoretical model were identical to the results from simulation.

Abstract: ZrN films were prepared by magnetron sputtering on die steel substrates. The objective of this study was to investigate the effect of nitrogen flow rate on the microstructure ,morphology, nanohardness properties determined by X-ray diffraction, field-emission scanning electron microscope, nanoindentation, and pin-on-disk, respectively. The XRD shows that ZrN has (111) and (200) preferred orientation under lower nitrogen flow rates. The surface of coatings revealed smaller grains and uniform dense under lower nitrogen flow rates. With increasing the nitrogen flow rates, this result showed ZrN films lead to poor mechanical properties and hardness values. However, films consisted of up high ernitrogen flow rate had much lower friction coefficient.

Abstract: Two types of non-Newtonian fluids, magneto rheological (MRF) and shear thickening (STF) fluids, respectively were chosen as candidates for energy dissipation study in smart body armour. A series of magneto rheological fluids was synthesized on a basis of synthetic oil and carbonyl iron. The shear modules for the MRF containing 75 wt% of carbonyl iron, obtained in a magnetic field of 230 kA/m were as follows: complex shear modulus G* - 1.2 MPa, storage modulus G-1.2 MPa and loss modulus G 0.35 MPa. The studies revealed also that the silica fumed, dispersed in polypropylene glycol or polyethylene oxide, demonstrates shear thickening properties. The best combination of the properties (high viscosity, obtained at high shear rate) represents the material composed of the silica fumed (SF) and PEO300. Change of the volume fraction of the SF and variation of the molecular weight of the oligomer enables tailoring of the STF properties. Ballistic tests revealed that the structures containing PE bags with MRF (in magnetic field) or STF can enhance the protective performance of body armours providing their flexibility.

Abstract: A feasible and effective method of thermal hydrolysis to prepare poly (lactic acid) (PLA) oligomers with different controlled molecular weight from PLA is presented in this paper. The thermal hydrolytic reaction was carried out by immerging PLA resin pellets in boiling distilled water for a certain period of time. Ester groups in PLA chains are hydrolytically degraded in the presence of water and thermal, so PLA oligomers with different molecular weight were prepared. The structures and properties of PLA oligomers were characterized by FT-IR, GPC, DSC, etc. The results showed that thermal hydrolytic reaction could effectively reduce the molecular weight of PLA, which declines with the increase of the thermal hydrolytic reaction time. Meanwhile, the content of terminal hydroxyl group, glass transition temperature, melting point of PLA oligomers prepared from thermal hydrolytic reactions exhibit gradual changes with the extension of the thermal hydrolytic time.

Abstract: The influences of Stark Effect and quantum wells thickness on the optical properties of InGaN laser diodes have been studied. The results indicated that the Stark Effect greatly affects the optical properties of InGaN laser diodes, when the quantum wells thickness increases, the Stark Effect leads to deteriorating of the optical proprieties of the InGaN laser diodes. The polarization in the active layer of the InGaN laser diodes has been estimated by the blue shift of the spectral lines. The results shown that the better properties of InGaN laser diodes can be obtained with smaller quantum wells thickness, where more carriers can be restricted in the quantum wells, which leads to a larger recombination rate, which in turn increases the output power of the laser diodes, decreases the threshold current of the laser diodes.

Abstract: Several nitroxides are used for study of their inhibiting effect on styrene polymerization. These nitroxides contain different nitroxyl moieties within molecules. Molecules with multinitroxyl centers within a single molecule possess stepwise radical killing reactivity. Each of these nitroxyl centers exhibits slightly different inhibitory capabilities in terminating the growth of polymer chains. A kinetic model is developed to calculate individual inhibition constants for each molecule's nitroxyl center and to characterize their kinetic behavior.

Abstract: This work proposes the investigation of nanosized Titanium Aluminum Nitride (TiAlN) on the Stainless Steel (316L) substrate. A chromium interlayer has been applied over the modified surface which will act as an interlayer between the substrate and hard composite coating. The composite coating was prepared by Magnetron Sputtered-Physical Vapour Deposition (PVD) on chromium coated lapped and textured surfaces of stainless steel substrate. Scratch test was performed to characterize the adherence of the coatings on the substrate. TiAlN surface coating over the textured surface exhibits higher adherence than the lapped surface coating surface. The tribological performance of the wear resistant coatings on lapped and textured surfaces was experimentally investigated by pin on disc tribometer at dry sliding contact conditions under various normal loads. The testing results were compared and the results showed that TiAlN coating on textured surfaces exhibited lower friction coefficient and wear rate than lapped coating surfaces under same testing conditions. Sliding wear characteristics such as coefficient of friction and specific wear rate were investigated.

Abstract: Natural fibre based composites are gaining more importance now-a-days due to their specific properties. The aim of this work is to present a comparison of machinability of jute fabric and glass fabric reinforced polymeric composite. Drilling was carried out in a Vertical Machining Centre using HSS twist drill of 6 mm diameter. The quality of hole is compared based on the delamination factor obtained by digital image processing technique, on both sides. Factorial design based experiments were conducted at different levels of speed and feed rate. Analysis Of Variance is done to study the influence of natural fibre on delamination. Results show that natural fibre reinforced composite has better machinability than synthetic fibre reinforced composite.

Abstract: In this study, electro-active artificial muscle was developed based on sulfonated poly (styrene-b-(ethylene-co-butylene)-b-styrene) (S-SEBS). The S-SEBS membrane was prepared by a solution casting method using THF as solvent. The physical properties were tested in terms of ion-exchange capacity, water uptake and linear expansion. Fourier transform infrared (FT-IR) was used to study the composition of S-SEBS. The results showed that the S-SEBS exhibited electro-active property with blocking force about 2.3gf/g.