Journal articles: 'Graded density'

1

Brothers, A. H., and D. C. Dunand. "Density-Graded Cellular Aluminum." Advanced Engineering Materials 8, no. 9 (September 2006): 805–9. http://dx.doi.org/10.1002/adem.200600074.

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Winter, R. E., M. Cotton, E. J. Harris, D. J. Chapman, and D. Eakins. "A novel graded density impactor." Journal of Physics: Conference Series 500, no. 14 (May 7, 2014): 142034. http://dx.doi.org/10.1088/1742-6596/500/14/142034.

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Balaba, I. N., S. V. Limarenko, A. V. Mikhalev, and S. V. Zelenov. "Density Theorems for Graded Rings." Journal of Mathematical Sciences 128, no. 6 (August 2005): 3350–64. http://dx.doi.org/10.1007/s10958-005-0272-2.

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Aslam, Tariq D., Michael A. McBride, Nirmal Rai, Daniel E. Hooks, Jamie A. Stull, and Brian J. Jensen. "Modeling atomically mixed graded density impactors." Journal of Applied Physics 131, no. 22 (June 14, 2022): 225901. http://dx.doi.org/10.1063/5.0085223.

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Graded density impactors (GDIs) are multi-material composite impactors used in gas gun experiments to tailor the drive conditions imparted to a sample test material. Previous graded density impactors generally rely on thin, but discrete, layers of different materials. The thinner and the greater number of layers will result in smoother compression. Taken to the limit of very thin layers would be pure material 1 at one surface, such as the front surface of an impactor, smoothly transitioning at the atomic scale to pure material 2 on the back surface. Such an impactor can initially shock, then smoothly compresses a material during a dynamic experiment. This type of experiment can serve to explore a larger region of thermodynamic space than a single or even multi-shock experiments. An overview of how graded density impactors are made is reviewed and sample results are given. A strategy for modeling these kinds of impactors is presented. The length scales of constituent mixing are given from the experimental build through electrochemical-deposition. Equation of state models for pure constituents and their subsequent mixtures are presented. It is demonstrated that the time scales for pressure and temperature equilibration, for atomically mixed GDIs, are short enough to be a justifiable closure for the resulting multiphase flow. Furthermore, we present simulation results of dynamic shock followed by a ramp compression, utilizing a silver/gold graded density impactor, onto a tantalum sample.

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He, Si-Yuan, Yi Zhang, Ge Dai, and Jia-Qiao Jiang. "Preparation of density-graded aluminum foam." Materials Science and Engineering: A 618 (November 2014): 496–99. http://dx.doi.org/10.1016/j.msea.2014.08.087.

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6

Witthayaweerasak, Juthamat, Pemika Lertjittham, and Nipat Aui-aree. "Correlation between relative afferent pupillary defect and visual field defects on Humphrey automated perimetry: A cross-sectional clinical trial." PLOS ONE 17, no. 5 (May 26, 2022): e0267469. http://dx.doi.org/10.1371/journal.pone.0267469.

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Purpose To evaluate the correlations between relative afferent pupillary defect (RAPD) magnitude, assessed using the clinical plus scale and neutral density filters, and visual field parameters in patients with unilateral or asymmetrical bilateral optic neuropathy or retinopathy. Methods Fifty-two patients with RAPD, graded by the swinging flashlight test and neutral density filters, were analyzed in this cross-sectional trial. The RAPD clinical plus scale was divided into grade 1+, initial weak constriction; grade 2+, initial stall then dilatation; grade 3+, immediate dilatation; and grade 4+, fixed amaurotic pupil. Patients with positive RAPD underwent a visual field examination with Humphrey automated perimetry that included visual field index (VFI), mean deviation (MD), and pattern standard deviation (PSD). Spearman’s rank correlation coefficients and linear regression were used to analyze the association between RAPD grades and visual field parameters. Results RAPD clinical plus grades were correlated with interocular VFI (r = 0.55, P < 0.001) and MD (r = 0.48, P = 0.004) differences. Average interocular VFI differences were estimated as follows: 16.75 × RAPD plus grade– 7.53. RAPD, graded by neutral density filters, was correlated with VFI (r = 0.59, P < 0.001), MD (r = 0.54, P < 0.001), and PSD (r = 0.34, P = 0.01). Conclusions The RAPD plus scale and neutral density filter grading systems were associated with quantitative visual field defect parameters, with VFI showing the strongest association. RAPD clinical grading could substitute more sophisticated central visual field evaluation methods as a low-cost, low-tech, and widely available approach.

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Trivedi, Vijaylaxmi, and Kei-Ichi Watanabe. "Hilbert-Kunz density function for graded domains." Journal of Pure and Applied Algebra 226, no. 2 (February 2022): 106835. http://dx.doi.org/10.1016/j.jpaa.2021.106835.

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Wang, Xiaokai, Zhijun Zheng, and Jilin Yu. "Crashworthiness design of density-graded cellular metals." Theoretical and Applied Mechanics Letters 3, no. 3 (2013): 031001. http://dx.doi.org/10.1063/2.1303101.

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Zhong Yanhong, 钟艳红, 周斌 Zhou Bin, 归佳寅 Gui Jiayin, 杜艾 Du Ai, 吴广明 Wu Guangming, 张志华 Zhang Zhihua, and 沈军 Shen Jun. "Fabrication of multilayer graded density carbon aerogel target." High Power Laser and Particle Beams 23, no. 3 (2011): 657–60. http://dx.doi.org/10.3788/hplpb20112303.0657.

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10

Li, Jingde, Guowei Ma, Hongyuan Zhou, and Xiuli Du. "Energy Absorption Analysis of Density Graded Aluminium Foam." International Journal of Protective Structures 2, no. 3 (September 2011): 333–49. http://dx.doi.org/10.1260/2041-4196.2.3.333.

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Zelenov, S. V. "The Zelmanowitz density theorem in the graded case." Russian Mathematical Surveys 56, no. 3 (June 30, 2001): 599–600. http://dx.doi.org/10.1070/rm2001v056n03abeh000405.

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Malik Shoeb Ahmad, Dr. "Low Density Polyethylene Modified Dense Graded Bituminous Macadam." International Journal of Engineering Trends and Technology 16, no. 8 (October 25, 2014): 366–72. http://dx.doi.org/10.14445/22315381/ijett-v16p273.

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13

Lee, Jae-Chul, and Sung-Hoon Ahn. "Bulk density measurement of porous functionally graded materials." International Journal of Precision Engineering and Manufacturing 19, no. 1 (January 2018): 31–37. http://dx.doi.org/10.1007/s12541-018-0004-4.

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14

Matsumoto, Yoshihisa, A. H. Brothers, and David C. Dunand. "Density-Graded Aluminum Foams by the Corrosion Method." Materials Science Forum 539-543 (March 2007): 1903–8. http://dx.doi.org/10.4028/www.scientific.net/msf.539-543.1903.

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Optimum corrosive density-grading of T6- and solution-treated alloys was studied using NaOH solutions. Rough corroded strut surfaces in aluminum foams were found to transform to smooth metallic surfaces with an increase in pH from 10 to 13. For instance, during immersion in pH13 solutions, pits with large curvatures appeared on strut surfaces, and corrosive mass losses increased. Strut diameters also decreased, and open cell windows became wider, without an increase in visible damage. Processing parameters such as pH, corrosion rate, and the surface state of the struts were examined to optimize final structure. An experimental method for grading of relative density continuously between 10% and 5% is described.

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Barzegari, Mohamad Reza, Jiaolian Yao, and Denis Rodrigue. "Mechanical Properties of Density Graded Foams: Tensile Properties." Cellular Polymers 32, no. 6 (November 2013): 323–42. http://dx.doi.org/10.1177/026248931303200601.

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16

Yang, Jie, Shi Long Wang, Zhi Jun Zheng, and Ji Lin Yu. "Impact Resistance of Graded Cellular Metals Using Cell-Based Finite Element Models." Key Engineering Materials 703 (August 2016): 400–405. http://dx.doi.org/10.4028/www.scientific.net/kem.703.400.

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A varying cell-size method based on Voronoi technique is extended to construct 3D graded cellular models. The dynamic behaviors of graded cellular structures with different density gradients are then investigated with finite element code ABAQUS/Explicit. Results show that graded cellular materials have better performance as energy absorbers. Graded cellular structures with large density near the distal end can protect strikers, and those with low density near the distal end can protect structures at the distal end. It is concluded that graded cellular materials with suitable design may have excellent performance in crashworthiness.

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17

Ding, Yuanyuan, Yuxuan Zheng, Zhijun Zheng, Yonggang Wang, Siyuan He, and Fenghua Zhou. "Blast Alleviation of Sacrificial Cladding with Graded and Uniform Cellular Materials." Materials 13, no. 24 (December 9, 2020): 5616. http://dx.doi.org/10.3390/ma13245616.

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Graded cellular material is a superb sandwich candidate for blast alleviation, but it has a disadvantage for the anti-blast design of sacrificial cladding, i.e., the supporting stress for the graded cellular material cannot maintain a constant level. Thus, a density graded-uniform cellular sacrificial cladding was developed, and its anti-blast response was investigated theoretically and numerically. One-dimensional nonlinear plastic shock models were proposed to analyze wave propagation in density graded-uniform cellular claddings under blast loading. There are two shock fronts in a positively graded-uniform cladding; while there are three shock fronts in a negatively graded-uniform cladding. Response features of density graded-uniform claddings were analyzed, and then a comparison with the cladding based on the uniform cellular material was carried out. Results showed that the cladding with uniform cellular materials is a good choice for the optimal mass design, while the density graded-uniform cladding is more advantageous from the perspective of the critical length design indicator. A partition diagram for the optimal length of sacrificial claddings under a defined blast loading was proposed for engineering design. Finally, cell-based finite element models were applied to verify the anti-blast response results of density graded-uniform claddings.

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18

Fan, Tao, and Xiaohua Shao. "Functionally Graded Piezoelectric Energy Harvester Using Thin Cylindrical Shell." International Journal of Structural Stability and Dynamics 17, no. 08 (October 2017): 1750085. http://dx.doi.org/10.1142/s0219455417500857.

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Presented herein is a functionally graded piezoelectric energy harvester using a thin cylindrical shell. The torsional mode for the thin cylindrical shell is studied and the effects of the functionally graded parameters on the power density are discussed. The analytical expressions for the power density are derived. From the results obtained, it can be observed that the functionally graded constant has obvious influences on the peak value of the power density. Moreover, larger values of the power density may be obtained by increasing the elastic parameter and the mass density. This work is expected to be useful in the analysis and design of energy harvester as well as new kinds of energy systems.

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Thompson, Avery. "A graded-density shell facilitates inertial confinement fusion reactions." Scilight 2021, no. 51 (December 17, 2021): 511103. http://dx.doi.org/10.1063/10.0009065.

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20

Brothers, Alan H., and David C. Dunand. "Mechanical properties of a density-graded replicated aluminum foam." Materials Science and Engineering: A 489, no. 1-2 (August 2008): 439–43. http://dx.doi.org/10.1016/j.msea.2007.11.076.

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21

Zhong, Yanhong, Bin Zhou, Jiayin Gui, Ai Du, Zhihua Zhang, and Jun Shen. "Fabrication of multilayer graded density peeled-carbon-aerogel target." Fusion Engineering and Design 86, no. 2-3 (March 2011): 238–43. http://dx.doi.org/10.1016/j.fusengdes.2011.01.001.

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Li, Lang, Bin Han, Si-Yuan He, Zhen-Yu Zhao, Rui Zhang, Qian-Cheng Zhang, and Tian Jian Lu. "Shock loading simulation using density-graded metallic foam projectiles." Materials & Design 164 (February 2019): 107546. http://dx.doi.org/10.1016/j.matdes.2018.107546.

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23

Shen, Qiang, Ying Hu Liu, Jing Zhou, Guo Qiang Luo, and Lian Meng Zhang. "Preparation of Mg-W Graded Materials by Spark Plasma Sintering." Key Engineering Materials 368-372 (February 2008): 1869–71. http://dx.doi.org/10.4028/www.scientific.net/kem.368-372.1869.

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A new kind of functionally graded materials (FGM) with density gradient has come to show great potentials as flier-plates for creating quasi-isotropic compression waves. In order to meet the demand of lower density in the front face and wider density range for such flier-plate, Mg with a density of 1.74g/cm3 and W of 19.3g/cm3 are selected to make Mg-W system density graded materials. Mg-W alloys with various mass fractions of Mg and W were sintered by spark plasma sintering (SPS) technique at low temperatures, and the processing of densification is mainly investigated. It is found that, up to 92wt%W, the Mg-W alloys can be fully densified at 873K due to the conglutination of Mg particles. The Mg-W alloys still exist as a mechanical mixture of Mg and W. Finally, the Mg-W density graded materials with a density change from 1.74g/cm3 to 10.55g/cm3 have been successfully prepared.

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Yin, Hanfeng, Jinle Dai, Guilin Wen, Wanyi Tian, and Qiankun Wu. "Multi-Objective Optimization Design of Functionally Graded Foam-Filled Graded-Thickness Tube Under Lateral Impact." International Journal of Computational Methods 16, no. 01 (November 21, 2018): 1850088. http://dx.doi.org/10.1142/s0219876218500883.

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Foam-filled thin-walled structure has been widely used in vehicle engineering due to its highly efficient energy absorption capacity and lightweight. Unlike the existing foam-filled thin-walled structures, a new foam-filled structure, i.e., functionally graded foam-filled graded-thickness tube (FGFGT), which had graded foam density along the transverse direction and graded wall thickness along the longitudinal direction, was first studied in this paper. Two FGFGTs with different gradient distributions subjected to lateral impact were investigated using nonlinear finite element code through LS-DYNA. According to the parametric sensitivity analysis, we found that the two design parameters [Formula: see text] and [Formula: see text], which controlled the gradient distributions of the foam density and the tube wall thickness, significantly affected the crashworthiness of the two FGFGTs. In order to seek for the optimal design parameters, two FGFGTs were both optimized using a meta-model-based multi-objective optimization method which employed the Kriging modeling technique as well as the nondominated sorting genetic algorithm II. In the optimization process, we aimed to improve the specific energy absorption and to reduce the peak crushing force simultaneously. The optimization results showed that the FGFGT had even better crashworthiness than the traditional uniform foam-filled tube with the same weight. Moreover, the graded wall thickness and graded foam density can make the design of the FGFGT flexible. Due to these advantages, the FGFGT was an excellent energy absorber and had potential use as the side impact absorber in vehicle body.

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Long, Luping, Yingbiao Peng, Wei Zhou, and Wensheng Liu. "Study on Hypervelocity Impact Characteristics of Ti/Al/Mg Density-Graded Materials." Metals 10, no. 5 (May 25, 2020): 697. http://dx.doi.org/10.3390/met10050697.

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An improved shielding structure of a bumper that constructed from Ti/Al/Mg density-graded materials was presented. Two types of Ti/Al/Mg density-graded materials with the same areal density were prepared by diffusion bonding and powder metallurgy, respectively. The characteristics of hypervelocity impact including penetration holes in the bumper, damage patterns on the rear wall and micrographs of the crater were investigated. The results show that damage mechanism of Ti/Al/Mg density-graded materials is closely related to the interface bonding strength and matrix strength. The penetration holes of Ti/Al/Mg density-graded material obtained by diffusion bonding exhibit typical ductile characteristics. The Ti/Al/Mg density-graded material prepared by powder metallurgy shows significant mechanical synergistic response under high strain compression and appears fragile characteristic. The shielding performance of Ti/Al/Mg bumper is increased by 20.4% compared with aluminum bumper. A theoretical analysis suggests that a Ti-Al-Mg bumper can fully break the projectile and greatly increase the entropy during the impact process. Larger projectile kinetic energy is converted into the internal energy during the impact process, thereby causing an obvious increase in shielding performance.

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Erdal, M., Serkan Dag, Y. Jande, and C. M. Tekin. "Manufacturing of Functionally Graded Porous Products by Selective Laser Sintering." Materials Science Forum 631-632 (October 2009): 253–58. http://dx.doi.org/10.4028/www.scientific.net/msf.631-632.253.

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Selective laser sintering (SLS) is a rapid prototyping technique which is used to manufacture plastic and metal models. The porosity of the final product obtained by SLS can be controlled by changing the energy density level used during the manufacturing process. The energy density level is itself dependent upon manufacturing parameters such as laser power, hatching distance and scanning speed. Through mechanical characterization techniques, it is possible to quantitatively relate the energy density levels to particular strength values. The present study is directed towards manufacturing functionally graded polyamide products by changing the energy density level in a predetermined manner. The mechanical properties of the functionally graded components are characterized by means of tensile testing. Both homogeneous and functionally graded specimens are produced and tested in order to examine the influence of the energy density level on the mechanical response and on the ultimate tensile and rupture strengths. Selective laser sintering is shown to possess the potential to produce functionally graded porous specimens with controlled variations in physical and mechanical properties.

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Naryanappa, K. M., M. Krishna, S. C. Sharma, and H. N. Narasimha Murthy. "Numerical Study of Functionally Graded Materials." Advanced Materials Research 29-30 (November 2007): 311–14. http://dx.doi.org/10.4028/www.scientific.net/amr.29-30.311.

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One-dimensional comprehensive mathematical model coupling particle movement and thermal conduction in the casting mould system is developed. A formula for pressure in liquid metal during the centrifuge process is derived. The model takes into consideration the propagation of solidification front and movement of particles due to centrifugal acceleration which takes place either in the same or in opposite direction to that of the solidification front depending on the relative density difference between the particles and melts. In the force balance expression, repulsive force term is incorporated for the particles that are at the vicinity of the solid/liquid interface to calculate the particle segregation pattern in the casting region The effects of various process parameters such as, rotational speed of the mold, size of the reinforcing material, relative density difference between the particle and melt, initial pouring temperature of the liquid melt, mold pre-heating temperature, heat transfer coefficient between the casting/mold interface are studied. It is noted that for a given set of operating conditions, the thickness of the particle rich region in the composite decreases with increase in rotational speed, particle size, relative density difference between the particle and melt, initial pouring temperature and initial mold temperature. With decrease in the heat transfer coefficient between the casting/mold interface, the solidification time increases which, in turn, results in more intense segregation of solid particulates. Again, with increase in the initial volume fraction of the solid particulates, both the solidification time as well as the final thickness of the particulate rich region increase.

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Sweeney, Alison M., David L. Des Marais, Yih-En Andrew Ban, and Sönke Johnsen. "Evolution of graded refractive index in squid lenses." Journal of The Royal Society Interface 4, no. 15 (February 9, 2007): 685–98. http://dx.doi.org/10.1098/rsif.2006.0210.

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A lens with a graded refractive index is required for vision in aquatic animals with camera-type eyes. This optical design entails a radial gradient of protein density, with low density in external layers and high density in internal layers. To maintain the optical stability of the eye, different material properties are required for proteins in different regions of the lens. In low-density regions of the lens where slight protein aggregation causes significant light scattering, aggregation must be minimized. Squid lens S-crystallin proteins are evolutionarily derived from the glutathione S-transferase protein family. We used biochemistry, optical modelling and phylogenetics to study the evolution and material properties of S-crystallins. S-crystallins are differentially expressed in a radial gradient, suggesting a role in refractive index. This gradient in S-crystallin expression is correlated with their evolutionary history and biochemistry. S-crystallins have been under positive selection. This selection appears to have resulted in stabilization of derived S-crystallins via mutations in the dimer interface and extended electrostatic fields. These derived S-crystallins probably cause the glassy organization and stability of low refractive index lens layers. Our work elucidates the molecular and evolutionary mechanisms underlying the production and maintenance of camera-like optics in squid lenses.

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Raphael, Johanna, Tedi Kujofsa, and J. E. Ayers. "Comparison of Buffer Layer Grading Approaches in InGaAs/GaAs (001)." International Journal of High Speed Electronics and Systems 29, no. 01n04 (March 2020): 2040002. http://dx.doi.org/10.1142/s0129156420400029.

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Metamorphic semiconductor devices often utilize compositionally-graded buffer layers for the accommodation of the lattice mismatch with controlled threading dislocation density and residual strain. Linear or step-graded buffers have been used extensively in these applications, but there are indications that sublinear, superlinear, S-graded, or overshoot graded structures could offer advantages in the control of defect densities. In this work we compare linear, step-graded, and nonlinear grading approaches in terms of the resulting strain and dislocations density profiles using a state-of-the-art model for strain relaxation and dislocation dynamics. We find that sublinear grading results in lower surface dislocation densities than either linear or superlinear grading approaches.

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30

LIAO, Zhongyuan. "Graded-density Lattice Structure Optimization Design Based on Topology Optimization." Journal of Mechanical Engineering 55, no. 8 (2019): 65. http://dx.doi.org/10.3901/jme.2019.08.065.

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Xiong, Hong Qi, Li Jun Zhang, Jun Liang Li, H. Tao, and R. Yuan. "Fabrication of W-Mo Functionally Graded Material with Density Gradient." Materials Science Forum 308-311 (May 1999): 628–33. http://dx.doi.org/10.4028/www.scientific.net/msf.308-311.628.

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Shen, Qiang, Chuan Bin Wang, Lian Meng Zhang, J. S. Hua, H. Tan, and Fu Qian Jing. "Preparation and Quasi-Isentropic Characteristics of Graded Density Flier-Plates." Key Engineering Materials 249 (September 2003): 287–90. http://dx.doi.org/10.4028/www.scientific.net/kem.249.287.

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Cox, G. A., and J. R. Maw. "Modelling the equation of state of a graded density impactor." Journal of Physics: Conference Series 500, no. 14 (May 7, 2014): 142007. http://dx.doi.org/10.1088/1742-6596/500/14/142007.

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Liu, Hu, and Bing Feng Ng. "Dynamic response of density-graded foam subjected to soft impact." Composite Structures 284 (March 2022): 115145. http://dx.doi.org/10.1016/j.compstruct.2021.115145.

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Chen, J. S., L. S. Huang, J. F. Hu, G. Ju, and G. M. Chow. "FePt–C graded media for ultra-high density magnetic recording." Journal of Physics D: Applied Physics 43, no. 18 (April 21, 2010): 185001. http://dx.doi.org/10.1088/0022-3727/43/18/185001.

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Liu, Yuanqing, Jun Li, Duo Chen, and Jiansheng Yuan. "Numerical Simulation of Current Density Distributions in Graded Laminated Armatures." IEEE Transactions on Magnetics 43, no. 1 (January 2007): 163–66. http://dx.doi.org/10.1109/tmag.2006.887653.

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Shen, Yang, Ai Du, Xiaoguang Li, Xiuguang Huang, Junjian Ye, Zhiyong Xie, Xueling Wu, Jun Shen, and Bin Zhou. "Preparation and optimization of aerogel flyer-plates with graded density." Materials & Design 110 (November 2016): 225–32. http://dx.doi.org/10.1016/j.matdes.2016.07.142.

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He, Si-yuan, Yi-nan Lv, Shi-ting Chen, Ge Dai, Jia-gui Liu, and Meng-ke Huo. "Gradient regulation and compressive properties of density-graded aluminum foam." Materials Science and Engineering: A 772 (January 2020): 138658. http://dx.doi.org/10.1016/j.msea.2019.138658.

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Zheng, Jie, Qinghua Qin, and T. J. Wang. "Impact plastic crushing and design of density-graded cellular materials." Mechanics of Materials 94 (March 2016): 66–78. http://dx.doi.org/10.1016/j.mechmat.2015.11.014.

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Kuipers, Tim, Jun Wu, and Charlie C. L. Wang. "CrossFill: Foam Structures with Graded Density for Continuous Material Extrusion." Computer-Aided Design 114 (September 2019): 37–50. http://dx.doi.org/10.1016/j.cad.2019.05.003.

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Fritzsche, A. K., M. K. Murphy, C. A. Cruse, R. F. Malon, and R. E. Kesting. "Characterization of asymmetric hollow fibre membranes with graded-density skins." Gas Separation & Purification 3, no. 3 (September 1989): 106–16. http://dx.doi.org/10.1016/0950-4214(89)80020-9.

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Kelly, M., H. Arora, A. Worley, M. Kaye, P. Del Linz, P. A. Hooper, and J. P. Dear. "Sandwich Panel Cores for Blast Applications: Materials and Graded Density." Experimental Mechanics 56, no. 4 (August 4, 2015): 523–44. http://dx.doi.org/10.1007/s11340-015-0058-5.

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Yao, Jiaolian, Mohamad Reza Barzegari, and Denis Rodrigue. "Density Graded Linear Medium Density Polyethylene Foams Produced under a Temperature Gradient with Expancel Microbeads." Cellular Polymers 30, no. 4 (July 2011): 157–86. http://dx.doi.org/10.1177/026248931103000401.

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Kujofsa, Tedi, and John E. Ayers. "Threading Dislocations in S-Graded ZnSxSe1-x/GaAs (001) Metamorphic Buffer Layers." International Journal of High Speed Electronics and Systems 23, no. 01n02 (March 2014): 1420005. http://dx.doi.org/10.1142/s0129156414200055.

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Metamorphic semiconductor devices are commonly fabricated with linearly-graded buffer layers, but equilibrium modeling studies suggest that S-graded buffers, following a normal cumulative distribution function, may enable lower threading defect densities. The present work involves a study of threading dislocation density behavior in S-graded ZnS x Se 1-x buffer layers for metamorphic devices on mismatched GaAs (001) substrates using a kinetic model for lattice relaxation and misfit-threading dislocation interactions. The results indicate that optimization of an S-graded buffer layer to minimize the surface threading dislocation density requires adjustment of the standard deviation parameter and cannot be achieved by varying the buffer thickness alone. Furthermore, it is possible to tailor the design of the S-graded buffer layer in such a way that the density of mobile threading dislocations at the surface vanishes. Nonetheless, the threading dislocation behavior in these heterostructures is quite complex, and a full understanding of their behavior will require further experimental and modeling studies.

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Boukortt, Nour El I., Salvatore Patanè, Baghdad Hadri, and Giovanni Crupi. "Graded Bandgap Ultrathin CIGS Solar Cells (Invited Paper)." Electronics 12, no. 2 (January 12, 2023): 393. http://dx.doi.org/10.3390/electronics12020393.

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In this paper, we physically modeled passivated ultrathin Cu (In1−xGax) Se2 solar cells with different bandgap grading configurations. Firstly, we have designed the cell architecture according to the fabricated model. The novelty in this work is the modeling of passivated u-CIGS solar cells with different bandgap grading profile configurations in order to achieve high efficiency with a thickness of 500 nm. A significant influence on device performance has been observed while changing absorber doping density, electron affinity, and operating temperature (range of 10–70 °C) for the investigated samples. ZnS has been used as a buffer layer to replace the conventional CdS material in order to improve cell efficiency. The impact of the buffer doping density and electron affinity on u-CIGS cell performance is explored. The simulation results show that a high bandgap at the front and rear sides with an acceptor density of 2 × 1016 provide the best electrical cell parameters: Jsc of 31.53 mA/cm2, Voc of 742.78 mV, FF of 77.50%, η of 18.15%. Our findings can be considered guidelines for new single and/or tandem cell optimization to achieve high efficiency.

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Nia, A. Alavi, and M. Kazemi. "Experimental study of ballistic resistance of sandwich targets with aluminum face-sheet and graded foam core." Journal of Sandwich Structures & Materials 22, no. 2 (February 26, 2018): 461–79. http://dx.doi.org/10.1177/1099636218757669.

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In this research, we have investigated the ballistic resistance of sandwich structures with aluminum face-sheet and graded polyurethane foam core with different densities. The effects of graded changes of core foam density and the effect of the sequence of foam layers with different densities on energy absorption and ballistic limit of sandwich structures under the impact of hemispherical nose projectiles at high speeds (160 to 300 m/s) are studied. The results of this study showed that increasing the density and thickness of the foam core leads to increase in the ballistic limit and energy absorption; also, the ballistic limit of sandwich structures with the same mass with graded foam core for three- and five-layer panels is, respectively, 10.37 and 5.57% more than single-layer foam core with the average density in case the foam layer with less density is placed in the impact side. By using the graded foam core (laminate), the core resistance is increased and the damaged zone shape is changed, and the energy absorption of back face-sheet is increased.

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Do, Quoc-Viet, Takumitsu Kida, Masayuki Yamaguchi, Kensuke Washizu, Takayuki Nagase, and Toshio Tada. "Anomalous Strain Recovery after Stress Removal of Graded Rubber." Polymers 14, no. 24 (December 14, 2022): 5477. http://dx.doi.org/10.3390/polym14245477.

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Mechanical responses after the uniaxial deformation of graded styrene–butadiene rubber (SBR) with a gradient in the crosslink points in the thickness direction were investigated as compared with those of homogenously vulcanized SBR samples. The elongational residual strain of a graded sample was found to depend on the part with a high crosslink density. Therefore, it showed good rubber elasticity. After stress removal, moreover, the graded sample showed a marked warpage. This suggested that shrinking stress acted on the surface with a high crosslink density, which would avoid a crack growth on the surface. The sample shape was then recovered to be flat very slowly, indicating that the shrinking stress worked for a long time. This unique rubber elasticity, i.e., slow strain recovery with an excellent strain recovery, makes graded rubber highly significant.

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Chen, Zheng, Bingxue Li, Qiao Zhang, Xudong Hu, Yi Ding, Zhixiang Zhu, Peng Xiao, and Shuhua Liang. "W–Cu Composite with High W Content Prepared by Grading Rounded W Powder with Narrow Particle Size Distribution." Materials 15, no. 5 (March 3, 2022): 1904. http://dx.doi.org/10.3390/ma15051904.

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In this study, the W (10–20%)–Cu composites were simultaneously fabricated using commercial, graded commercial, and graded jet-milled W powder. The results show that the W–Cu composites prepared with the graded jet-milled W powders have the highest density and best comprehensive performance due to the combined effect of the particle gradation and jet-milling treatment. Particle gradation is employed to increase the packing density of powders, thereby increasing the relative density of the compressed W skeleton, and the rounded powder with narrow particle size distribution after jet-milling treatment is used to reduce the enclosed pores formed during the process of compacting and infiltration. W–Cu composites with a high density of 16.25 g/cm3 can be directly obtained by conventional compacting at a low pressure of 300 MPa and following infiltration.

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Liang, Pengfei, Yu Yang, Houxu Huang, Jiashun Liu, and Ning Guo. "Experimental Study on Fractal Characteristics of Particle Size Distribution by Repeated Compaction of Road Recycling Crushed Stone." Applied Sciences 12, no. 20 (October 13, 2022): 10303. http://dx.doi.org/10.3390/app122010303.

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In order to investigate the compaction characteristics of graded crushed stone under repeated utilization, it is necessary to improve the utilization rate of road recycling crushed stone and maintain its strength and stability during recycling. In the present study, repeated compaction characteristic curves of graded crushed stone were developed using repeated compaction and screening of the graded crushed stone. The correlations between the fractal dimension of particle size distribution and repeated compaction times, water content, and dry density were analyzed. The experimental results indicate that both the maximum dry density and the optimal water content increase as the repeated compaction times increase. The fractal dimension of the particle size distribution of the graded crushed stone used in this test is 2.33 to 2.57. The obtained results show that as the fractal dimension increases, the maximum dry density of the graded crushed stone increases. At a constant repeated compaction time, the fractal dimension of the particle size distribution of graded crushed stone increased and then decreased as the water content increased. In summary, the compaction performance of the structural layer of graded crushed stone can be tuned by adjusting the fractal dimension of the particle size distribution of the recycled pavement structural layer in practical applications. Moreover, the optimal graded materials can be prepared under the guidance of the fractal dimension, thereby achieving an optimized working performance of the recycled pavement structural layer.

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Teodoro, Raquel, Joabel Raabe, Danillo Wisky Silva, Rafael Farinassi Mendes, Lourival Marin Mendes, and Gustavo Henrique Denzin Tonoli. "Functionally Graded MDP Panels Using Bamboo Particles." Key Engineering Materials 668 (October 2015): 39–47. http://dx.doi.org/10.4028/www.scientific.net/kem.668.39.

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MDP (medium density particleboard) panels are normally graded in composition along their cross-section, using low-size particles and high concentration of adhesive on the particleboard surface (leading to improved physical and mechanical properties), and high-size particles in the particleboard core (interior), which provide higher porosity. Then, the aim of this study was to evaluate the impact of using different contents of bamboo particles in the particleboard core, on their physical and mechanical properties. The production of the panels was carried out using Pinusoocarpa (P) and Bambusavulgaris var. Vittata (B) particles in different contents (100% P, 100% B, 50% de B e 50% de P, 25% de B e 75% de P, 75% de B e 25% de P) in the core of the particleboards. The face of the particleboards were composed of P particles. The panels were produced with nominal density of 0.70 g/cm3, 40:60 face:core relation, 11% urea-formaldehyde adhesive in the faces and 8% adhesive for the core, specific pressure of 3.92 MPa, 160 °C temperature and pressing time of 8 min. After seasoning, the panels were submitted to evaluation of the thickness swelling (TS) and water absorption (WA) after 2 and 24 h of immersion, apparent density (AD), internal bonding (IB), modulus of rupture (MOR) and modulus of elasticity (MOE) under static bending. There was no statistical difference between the treatments for AD, IB, MOR and MOE values. Panels produced with high contents of bamboo particles (100% B, 75% B e 50% B) in the core, presented the lower WA and TS values, leading to improved dimensional stability than panels with only pinus particles. The present results show the important impact of using functionally gradation and bamboo particles on the physical properties of the MDP panels produced.

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Journal articles on the topic 'Graded density'

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