Applied Mechanics and Materials Vols. 110-116

Abstract: In recent years SS316LN microalloyed stainless steel is preferred for use as jacket material for Nb₃Sn superconductor strands/wires. In the present investigation, microalloyed SS316LN is prepared in a vacuum induction melting furnace; Niobium and Molybdenum in their ferroalloy stage are considered as alloying element. This microalloyed steels are cast in water cooled copper mould. The tensile strength and elongation are measured and the fracture surface is studied under scanning electron microscope. It is observed that, there is a reduction of tensile strength and decrease in hardness of the steels prepared with addition of either/both the alloying elements; however there is an increase in ductility, which is helpful for cold rolling operation. From the micrographs it is observed that nitride precipitates are formed along the grain boundary, but formation of chromium carbide precipitates is reduced.

Abstract: In this work, we are reporting on the simulation of the beryllium selenide (BeSe) nanowires (NWs) by computational package Q-Espresso / PWSCF according to the ab-initio calculations. Structural and electronic properties, including cohesive energy and Density Of State (DOS) BeSe NWs in two phases on the zinc–blende (ZB) and wurtzite (WZ), using density functional theory based on pseudo-potential approximation and generalized gradient approximation (GGA) up to 20 angstrom in diameter has been calculated. Due to dangling bonds (DBs) in the side surface NWs, cohesive energy is obtained less than the amount of this energy in bulk state of this compound, but with increasing diameter of NWs, the amount of this energy will approach to the bulk state. Comparison of cohesive energy with beryllium selenide NWs in two phases, we find these NWs in WZ phase is more stable and have good compatibility for this result with other results in NWs of similar compounds. The value of energy gap in these NWs on various diameters is obtained less than the amount of the bulk state. It is observed that by increasing the diameter of NWs, the cohesive energy approaches to its value in bulk state.

Abstract: SnO2 powder was prepared by soft chemical method. The Structure and Morphological characteristics of SnO₂ powder was analyzed by X-Ray Diffraction (XRD), Atomic Force Microscopy (AFM), UV, FTIR and Scanning Electron Microscopy (SEM) techniques. Its gas sensing properties are analyzed towards toxic gas at ppm level. Sensitivity of a SnO₂ oxide based sensor towards an analyte gas can be enhanced by using the metals in different geometries viz, thick film. The gas sensing properties were studied towards reducing gas like ethanol and it is observed that SnO₂ shows high response to ethanol at relatively lower operating temperature. The SnO₂ nanomaterial shows better sensitivity towards ethanol at an operating temperature 2500C. Ethanol vapour has been one of the most extensively studied gases for metal oxide gas sensors.

Abstract: The present paper describes the development of a genetic algorithm (GA) based methodology for determination of optimal number of actuators and their locations in smart fiber reinforced polymer composite shell structures. Finite element (FE) based state space representation of the system has been used to determine the optimal placement of actuators in order to maximize the controllability. Spillover from residual modes has also been considered while maximizing controllability. Even though the developed methodology needs a large computational time, it will be useful in off-line determination of optimal actuators locations in large structures.

Abstract: The effect of holding time variation and sintering temperature on the mechanical properties and sinterability of yttria stabilized tetragonal zirconia doped with 1 wt. % MnO₂ was investigated. Samples were sintered at 1150-1500 °C with holding times varying from 12 and 120 minutes. Comparing to the MnO₂-doped Y-TZP, longer holding time resulted in enhanced densification of the undoped Y-TZP samples. In the case of MnO₂-doped Y-TZP however, Bulk density, Young’s modulus, Vickers hardness and fracture toughness results show the beneficial effect of MnO₂ in enhancing the densification of Y-TZP ceramics.

Abstract: Hydroxyapatite (HA) is among the leading ceramic materials for hard tissue replacement implants. Despite the excellent bioactivity of HA, low toughness has limited the application of these materials to non-load bearing areas. The sinterability of nanocrystalline hydroxyapatite (HA) powder via new heating profile for conventional pressureless sintering was studied. The starting nanocrystalline HA powder was synthesized by wet chemical precipitation method. After uniaxial pressing followed by isostatic pressing, HA powder compacts are sintered over the temperature range of 1000°C to 1300°C. Different holding time of 1 minute and 120 minutes was applied as a heating profile of HA samples. The results revealed that new heating profile was effective in producing a HA body with high density of 98% when sintered at 1200°C. Subsequently, mechanical properties such as fracture toughness and hardness, of HA compacts increased with decrease in grain size. HA showed the highest hardness of 9.51 GPa and fracture toughness of 1.41 MPa.m1/2 when sintered at 1100 °C. XRD analysis indicated that decomposition of HA phase during sintering at high temperatures do not occur. Short holding time leads to finer microstructure of HA and subsequently better mechanical properties.

Abstract: There are two approaches to design high energy absorbing materials and structures: one is to optimize the structures by using ordinary materials. The other is to design new energy absorbing materials. The efficiency of energy absorbing structures is continuously improved by developing various types of structural geometries and selecting appropriate energy absorbing materials like polymeric foams or metallic foams. Because of composite materials which are used in these kinds of structures, too many useful properties are achieved, for example, light weight, high energy absorption, high stiffness, fracture toughness. In this study, different composite sandwich structures are modeled by ABAQUS FE software. The model is validated by the results in existed literature. Different materials as core and as face sheets in the composite sandwich structure are investigated. Internal energy and displacement of the structure during the impact analysis in low velocity are calculated. By changing variables and parameters such as dimensions of the structure, different properties and sequences of the layers in the face sheets and different core materials, the optimum state of the structure for gaining the highest internal energy is determined. By increasing the size of the structure and using the stiffer fibers, the absorbed energy is increased. The effect of stiffer core in increasing absorbed energy is more significant. The layer sequencing does not affect any changes in the absorbed energy.

Abstract: The Al-Zn-Mg-Cu aluminum alloys are primarily used in the aerospace industry as structural components. This study aim to improve properties of Al-5.6% Zn-2.5%Mg-1.6%Cu such as impact toughness, thermal stability and corrosion resistance by using quenching in 30% polyethylene glycol and addition 0.1%Zr to this alloy. Results showed that the addition 0.1% Zr to base alloy improve impact toughness by (40%) when quenching in water, and by (60 %) when quenching in 30%PAG corresponding to the base alloy when aging at 150 °C. Also results showed that the thermal stability improved when we addition 0.1% Zr by (20%). An improvement of corrosion resistance when addition 0.1% Zr (B alloy) by (326 %), at aging time 150°C in comparison to the base alloy.

Abstract: This paper developed a novel elongation type of Pneumatic Artificial Muscle (PAM), which is mainly composed of the expandable internal rubber tube surrounded by the external cylindrical helical spring and the two ends are closed. The PAM is not only the actuator of the flexible joint but also the core components to make up of the flexible joint. Therefore, the mechanical properties of the PAM directly influence the performance of the flexible joint. A mathematical model on the axial deformation and bending stiffness of elongation type of PAM was built applying theoretical analysis and experimental research methods. The results show that the axial deformation of PAM and the air pressure supplying to the PAM are nonlinearly related due to the generic nonlinear of deformation of the rubber tube; the bending angle of the PAM is proportional to moment; Similarly, the bending angle of the PAM is also proportional to its length. Furthermore, it indicates that the air pressure indirectly affects the bending stiffness of PAM as the air pressure directly influences the elongation of PAM. Finally, this paper provides a powerful framework for the dynamic analysis and motion accuracy control of the flexible joint or the robot which is composed by the artificial muscles.

Abstract: There were very limited number of references published discussing the burning characteristic of aluminized propellant without any additive substance. This paper describes the performance characteristics of basic formulations of aluminized ammonium perchlorate based propellant. Four sets of propellant formulations namely by p60, p66, p74 and p80 had been formulated and manually prepared without adding any additives. The propellant consists of ammonium perchlorate (AP) as an oxidizer, aluminum (Al) as fuel and hydroxy-terminated polybutadiene (HTPB) as fuel/binder. For each mixture, HTPB binder composition was fixed at 15% per-weight. By varying AP and Al, the effect of oxidizer-fuel (O/F) ratio on the whole propellant can be determined. The propellant strands were manufactured using press-molding method and burnt in a strand burner over a range of chamber pressure from 6 atm to 31 atm. Based on theoretical evaluation using NASA CEC71 program, p66 has been selected for testing in ballistic evaluation motor (BEM) to ascertain its characteristics performance. The results from burning rate test shows that the increasing of O/F ratio and combustion pressure lead to the increase in burning rate. The highest burning rate achieved was 12mm/sec at combustion pressure of 31atm for propellant p80 which has O/F ratio of 4.0. While for the BEM, the propellant efficiency obtained for p66 was 95.44%.