文档类型

Small range 文档类型:"1"

Totally found 4571 items.

  • [会议] Environmental effects in biaxially orientated Polymethyl Methacrylate
    Environmental stress cracking (ESC) is commonly found in polymers when submerged in an environment under applied stress. In such conditions, a crack may initiate and propagate from a material defect until it reaches a critical size and causes catastrophic failure. It is known that materials with a denser molecular structure are less prone to ESC, hence amorphous polymers often suffer greatly from this effect. A fracture mechanics approach was employed to investigate the fracture mechanism and crack growth in both air and environment. Two different grades of PMMA (amorphous and biaxially stretched PMMA) were tested in solvents with similar solubility parameters as this is known to hasten crazing. Time for crack initiation and crack speed were obtained and plotted against their corresponding fracture toughness. Thus, the ESC resistance of each material can be compared and component life expectance can also be predicted. To validate the experimental results, scanning electron microscopy (SEM) was used to examine the fracture mechanism of ESC.
    关键词: Environmental stress cracking;Biaxially orientated PMMA;Fracture mechanics;Crazing
  • [会议] Environmental effects in biaxially orientated Polymethyl Methacrylate
    Environmental stress cracking (ESC) is commonly found in polymers when submerged in an environment under applied stress. In such conditions, a crack may initiate and propagate from a material defect until it reaches a critical size and causes catastrophic failure. It is known that materials with a denser molecular structure are less prone to ESC, hence amorphous polymers often suffer greatly from this effect. A fracture mechanics approach was employed to investigate the fracture mechanism and crack growth in both air and environment. Two different grades of PMMA (amorphous and biaxially stretched PMMA) were tested in solvents with similar solubility parameters as this is known to hasten crazing. Time for crack initiation and crack speed were obtained and plotted against their corresponding fracture toughness. Thus, the ESC resistance of each material can be compared and component life expectance can also be predicted. To validate the experimental results, scanning electron microscopy (SEM) was used to examine the fracture mechanism of ESC.
    关键词: Environmental stress cracking;Biaxially orientated PMMA;Fracture mechanics;Crazing
  • [会议] Deep hole drilling of polymethyl methacrylate with small diameters by actively compensating the hole straightness deviation
    Deep hole drilling is very demanding in terms of process control and precision of the used machine tools. In particular for drilling of polymethyl methacrylate (PMMA) with small drill diameters below 1 mm specific aspects have to be considered compared to regular drilling. Instances are the low glass temperature and the poor heat transmission from the material's viewpoint and the hole straightness deviation and the inability of proper process monitoring from the process viewpoint. Furthermore it hast to be evaluated individually if other manufacturing technology are possibly more suitable for the desired application. In this paper the problems are discussed which occur when drilling polymethyl methacrylate with small diameters. On this basis the results of initial drilling tests are discussed and presented whereby the used concept for live condition monitoring of the process is introduced.
    关键词: Micro Manufacturing;Deep Hole Drilling;Polymethyl Methacrylate
  • [会议] Properties of Porous Magnesium Using Polymethyl Methacrylate (PMMA) as a Space Holde
    Porous magnesium has been recognized as a promising biodegradation metal for bone substitute application because of its excellent biocompatibility, low density, ability to biodegrade in vivo and excellent mechanical properties. In the present work, porous magnesium was fabricated by powder metallurgy using spherical polymethyl methacrylate (PMMA) as a space holder. To determine the optimum sintering temperature for porous magnesium fabrication, the porous magnesium was fabricated using double step sintering process at various sintering temperature (550℃, 585℃ and 620℃) in first stage of research. The porous magnesium fabricated was then characterized for morphology, porosity, density and compressive strength. Density of porous magnesium increases and the porosity decreases with increasing sintering temperature. The mechanical characterization indicated that porous magnesium sintered at 620℃ exhibited the highest compressive strength and density with optimum range of porosity of 39.37%. For second stage of research, porous magnesium with porosities of 39.38 - 40.82% was produced with different sizes of PMMA particles (38-63 μm, 63-90 μm and 90-125 μm). The compressive yield strength ranges between 19.95 MPa to 23.28 MPa and increases with decreasing PMMA particles size and porosity. These results proven that the PMMA has a potential to be used as space holder in porous magnesium for biomedical application.
    关键词: -
  • [会议] Thermal Shock Behavior and Bonding Strength of MoSi_2-BaO-Al_2O_3-SiO_2 Gradient Porous Coating with Polymethyl Methacrylate Addition for Porous Fibrous Insulations
    In order to improve the thermal shock behavior of high temperature resistant coating on porous fibrous referactory insulations, the MoSi_2-BaO-Al_2O_3-SiO_2 (MoSi_2-BAS) gradient porous coatings were designed by preparing a dense surface layer and a porous bonding layer with the method of brushing and subsequent sintering at 1773 K. The porous bonding layer was obtained by adding polymethyl methacrylate (PMMA) as pore former. As the content of PMMA increases, the MoSi2-BAS coatings changed from a dense structure into a gradient porous structure. The interface bonding strength and thermal shock resistance of the MoSi_2-BAS coatings were investigated. The result shows that the as-prepared coating with gradient porous structure exhibited excellent thermal shock resistance, which remained gradient structure without cracking after thermal cycling 100 times between 1773 K and room temperature. And the interface bonding strength of the gradient porous coating reached 1.5±0.08 Mpa, which was much better than that of the dense coating.
    关键词: polymethyl methacrylate;porous insulation;gradient porous coating;BAS glass
  • [会议] Structural Changes in Polymethyl Methacrylate during Laser Machining
    The focus of the article is an issue of laser machining of polymethyl methacrylate materials. Specifically, it deals with evaluation of structural changes in polymers as due to the effect of concentrated energy there appears vaporization of the material in the place of cut as well as heat transfer into the material around the place of cut and thus to the heating. As a result of the raised temperature, different structural changes may occur in the material; some high-molecular substances begin to break down into low-molecular substances, and depoly-merization or degradation of the material may occur. All these changes may result in a change of the final properties of the product. For experimental machining and subsequent study using the "Fourier Transform Infrared" vibration spectroscopy, PMMA was chosen as it is one of the most feasible polymeric materials in this technology.
    关键词: Laser Technology; Structural Changes; Polymeric Material; Vibration Spectroscopy
  • [会议] Properties of Porous Magnesium Using Polymethyl Methacrylate (PMMA) as a Space Holde
    Porous magnesium has been recognized as a promising biodegradation metal for bone substitute application because of its excellent biocompatibility, low density, ability to biodegrade in vivo and excellent mechanical properties. In the present work, porous magnesium was fabricated by powder metallurgy using spherical polymethyl methacrylate (PMMA) as a space holder. To determine the optimum sintering temperature for porous magnesium fabrication, the porous magnesium was fabricated using double step sintering process at various sintering temperature (550℃, 585℃ and 620℃) in first stage of research. The porous magnesium fabricated was then characterized for morphology, porosity, density and compressive strength. Density of porous magnesium increases and the porosity decreases with increasing sintering temperature. The mechanical characterization indicated that porous magnesium sintered at 620℃ exhibited the highest compressive strength and density with optimum range of porosity of 39.37%. For second stage of research, porous magnesium with porosities of 39.38 - 40.82% was produced with different sizes of PMMA particles (38-63 μm, 63-90 μm and 90-125 μm). The compressive yield strength ranges between 19.95 MPa to 23.28 MPa and increases with decreasing PMMA particles size and porosity. These results proven that the PMMA has a potential to be used as space holder in porous magnesium for biomedical application.
    关键词: -
  • [会议] High color gamut of perovskite QDs/PMMA-based white light-emitting diode
    Inorganic perovskite quantum dots (P-QDs) is a new kind of optoelectronic materials in recent years. Because the high quantum yield (QY), the narrow full width at half-maximum (FWHM) and spectrum tenability of novel P-QDs, making them have more potential on the display application. However, P-QDs not only have poor water resistance and heat resistance, but also easily exchange halogen ions to cause wavelength variations. Therefore, the above problems must be solved before use. In this study, red and green P-QDs were synthesized by thermal injection method and then mixed with polymethyl methacrylate (PMMA) in different ratios. Controlling the P-QD concentrations and the thickness of the fluorescent films to form white light. The results show that the fluorescent film can avoid the ion exchange reaction effectively. Moreover, the CIE of P-QD/PMMA device locates at (0.29, 0.31), and the NTSC and sRGB are 131 and 183 %, respectively.
    关键词: perovskite quantum dots;polymethyl methacrylate;full width at half-maximum;display;fluorescent film;white light
  • [会议] High color gamut of perovskite QDs/PMMA-based white light-emitting diode
    Inorganic perovskite quantum dots (P-QDs) is a new kind of optoelectronic materials in recent years. Because the high quantum yield (QY), the narrow full width at half-maximum (FWHM) and spectrum tenability of novel P-QDs, making them have more potential on the display application. However, P-QDs not only have poor water resistance and heat resistance, but also easily exchange halogen ions to cause wavelength variations. Therefore, the above problems must be solved before use. In this study, red and green P-QDs were synthesized by thermal injection method and then mixed with polymethyl methacrylate (PMMA) in different ratios. Controlling the P-QD concentrations and the thickness of the fluorescent films to form white light. The results show that the fluorescent film can avoid the ion exchange reaction effectively. Moreover, the CIE of P-QD/PMMA device locates at (0.29, 0.31), and the NTSC and sRGB are 131 and 183 %, respectively.
    关键词: perovskite quantum dots;polymethyl methacrylate;full width at half-maximum;display;fluorescent film;white light
  • [会议] PHOTOSENSITIVITY OF MONOLAYER GRAPHENE-BASE FIELD EFFECT TRANSISTOR
    The optical properties and device physics of monolayer graphene under light is investigated in this study. In order to understand the change of the electronic behavior of graphene under light, it was necessary to study from the most fundamental layer with high quality. Thus, it became mandatory to develop a highly efficient, low-cost fabrication process for synthesis of high-quality monolayer graphene. The high-quality monolayer graphene was grown on a copper foil using a low-pressure chemical vapor deposition (LP-CVD) method at temperature of 1035℃ for 10 minutes. Acetylene was used as the precursor gas for the synthesis of monolayer graphene. Thin Pt/Au films were, then, deposited on a silicon dioxide/silicon (SiO_2/Si) substrate using electron beam (EB) lithography which served as source and drain electrodes of a transistor. The synthesized graphene was, then, transferred to a SiO_2/Si substrate using PMMA (polymethyl methacrylate)-assisted method. The quality of the synthesized graphene was validated using Raman spectroscopy. No significant D peak was observed in the Raman spectra of the synthesized graphene. This result validated the high quality of the transferred graphene. Next, the photo-sensitivity of G-FET was investigated under light source of color temperature of 2856 K at room temperature. The electron transfer characteristic of the fabricated G-FET was measured under dark and light illumination conditions. Finally, the graphene-based field effect transistor G-FET demonstrated an external photo responsivity of about 200 μA/W with a maximum photocurrent attained to be 0.2 μA at an incident luminance power of 1 mW. The active detection region of this sample was 1000 × 60 μm~2.
    关键词: -
意见反馈
返回顶部