196,094 research outputs found
An investigation of underground monitoring and communication system based on radio waves attenuation using ZigBee
No full textAbstract not availableMohammad Ali Moridi, Youhei Kawamura, Mostafa Sharifzadeh, Emmanuel Knox Chanda, Hyongdoo Jan
Dynamic Beamforming Strategy for Sidelobe Level Suppression in Piezoelectric Micromachined Ultrasonic Transducer (PMUT) Sparse Arrays
No full textIn this paper, we proposed a novel method to suppress the sidelobe level for a presented quasi-periodic sparse 2D array based on piezoelectric micromachined ultrasonic transducer (PMUT) technology. We applied a dynamic apodization based on Dolph-Chebyshev weights to the transducer for both transmitting and receiving for different steering angles. The apodization weights were obtained by iterative calculations in a simulation model built with Field II. Based on the calculated weights, intensity profiles were simulated and compared with that without weighting. The results showed that the side lobe level was reduced from - 14.3 dB to -38 dB when no steering angle, and from -12 dB to - 16 dB when the steering angle was 45°. It is shown that the side lobe level was largely suppressed, with the cost of an acceptable larger main lobe
Development of underground mine monitoring and communication system integrated ZigBee and GIS
No full textAbstract not availableMohammad Ali Moridi, Youhei Kawamura, Mostafa Sharifzadeh, Emmanuel Knox Chanda, Markus Wagner, Hyongdoo Jang, Hirokazu Okaw
From conventional to severe shot peening to generate nanostructured surface layer: A numerical study
No full textNumber of passes and thickness effect on mechanical characteristics of cold spray coating
No full textAbstractNowadays, with severe competitive business environment, limited material sources and high cost of manufacturing, the importance of maintenance and repair is self-evident. In this field, cold spray technology is gaining more and more attention especially in light alloy components. One of the potential applications of cold spray coating is dimensional recovery of damaged structural parts. In most cases, thick coatings are necessary to fill the damages such as cavities, worn or corroded parts. Thick coatings can be deposited in a single or multiple passes giving different thermal input and stress distribution to the substrate and coating itself. The thermal input, the amount and type of residual stress (compressive or tensile) confer appreciable or depreciable characteristics to the coating mechanical properties. In this study, single and multi-pass deposition of a 0.5mm thick Al 6082 coating on the same substrate is studied to explore the number of passes effect on mechanical characteristics. In addition, one pass deposition of 0.65 and 0.8mm thick coating is investigated to examine the thickness effect. Micro-structural observation, micro-hardness measurements and X-Ray diffraction (XRD) measurement of residual stress were performed on all groups. Adhesion test and tubular coating tensile test were also carried out to characterize the coating in different cases. Observation of fractured surface was used to investigate the failure mechanism of the cold-sprayed coating. A critical discussion on the effects of pass number and thickness on mechanical properties of coated specimens is presented
Solid-state additive manufacturing of porous Ti-6Al-4V by supersonic impact
No full textAdditive manufacturing of functional metallic parts based on layer-by-layer melting and solidification suffers from the detrimental effects of high-temperature processing such as large residual stresses, poor mechanical properties, unwanted phase transformations, and part distortion. Here we utilize the kinetic energy of powder particles to form a solid-state bonding and overcome the challenges associated with the high temperature processing of metals. Specifically, we accelerated powders to supersonic impact velocities (~600 m/s) and exploited plastic deformation and softening due to high strain rate dynamic loading to 3D print Ti-6Al-4V powders at temperatures (800 °C, 900 °C) well below their melting point (1626 °C). By using processing conditions below the critical powder impact velocity and controlling the surface temperature, we created mechanically robust, porous metallic deposits with spatially controlled porosity (apparent modulus 51.7 ± 3.2 GPa, apparent compressive yield strength 535 ± 35 MPa, porosity 30 ± 2%). When the mechanical properties of solid-state 3D printed Ti-6Al-4V were compared to those fabricated by other additive manufacturing techniques, the compressive yield strength was up to 42% higher. Post heat treatment of solid-state printed porous Ti-6Al-4V modified the mechanical behavior of the deposit under compressive loading. Additionally, the 3D printed porous Ti-6Al-4V was shown to be biocompatible with MC3T3-E1 SC4 murine preosteoblast cells, indicating the potential biomedical applications of these materials. Our study demonstrates a single-step, solid-state additive manufacturing method for producing biocompatible porous metal parts with higher strength than conventional high temperature additive manufacturing techniques
Dr. Duane M. Jackson, Morehouse College, July 2011
No full textThis video is a conversation with Dr. Duane M. Jackson. Dr. Jackson talks about his paper, "Recall and the Serial Position Effect: The Role of Primacy and Recency on Accounting Students' Performance." Jackie Daniel, AUC Woodruff Library, is the interviewer
Deformation and failure mechanisms of Ti–6Al–4V as built by selective laser melting
No full textThe ability to create complex geometries with tailored material properties has brought interest in using additive manufacturing (AM) techniques for many industrial applications. However, further understanding of the complex relationship between AM process parameters, microstructure, and resultant properties is critical for the widespread use of metal AM. In this study, selective laser melting (SLM) is used to print Ti–6Al–4V. Tensile tests with concurrent microstructural analysis using electron backscatter diffraction, electron channeling contrast imaging, and digital image correlation are performed to understand the damage and its relation to the microstructure of Ti–6Al–4V after SLM processing. We find that the as-printed Ti–6Al–4V shows hierarchical microstructures, consisting of primary, secondary, and tertiary martensite. This hierarchical structure is formed as a result of cyclic heat treatment during the layer-wise SLM process. Upon tensile deformation, strain localization within primary martensite results in microscopic ductile micro-void formation and coalescence, as well as macroscopic brittle fracture. In addition to localization inside primary , surface steps at the boundaries of these high aspect ratio grains are formed which reveal the contribution of interfacial plasticity to the overall deformation of the material
The effect of nitriding, severe shot peening and their combination on the fatigue behavior and micro-structure of a low-alloy steel
No full textFatigue strength of mechanical components can be greatly enhanced by generating compressive residual stress, increasing the hardness and reducing the grain size. It is well known that while the use of mechanical treatments is able to generate an effective field of compressive residual stresses and, if severe parameters are used, to cause grain refinement, thermochemical treatments are able to increase the surface hardness. This justifies the interest in developing combined treatments, able to achieve all the just mentioned factors.
In this study, the effect of combination of severe shot peening and nitriding on the fatigue limit of a low-alloy steel is investigated. Severe shot peening was conducted by using particular processing parameters to obtain ultra-fine/nano-structured surface layers. Micro-structural observation, micro-hardness, surface roughness and XRD measurement of residual stress were performed on single and hybrid surface treated specimens including nitrided, severely shot peened, nitrided plus severely shot peened and severely shot peened plus nitrided specimens. The fatigue limit of all series was experimentally determined and compared with the as-received specimens. Severe shot peening and Nitriding improved the fatigue limit by 11.6% and 51.3% respectively. Combination of severe shot peening and nitriding improved hardening, residual stress and nitrogen diffusion with respect to the single treatment. Nevertheless, it could not guarantee further improvement in the fatigue limit as compared with the nitrided smooth specimens. The results are critically assessed by considering the local fatigue limit concept
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