Preliminary Validation of a Continuum Model for Dimple Patterns on Polyethylene Naphthalate via Ar Ion Beam Sputtering
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This work reports the self-organization of dimple nanostructures on a polyethylene naphthalate (PEN) surface where an Ar ion beam was irradiated at an ion energy of 600 eV. The peak-to-peak roughness and diameter of dimple nanostructures were 29.1~53.4 nm and 63.4~77.6 nm, respectively. The electron energy loss spectrum at the peaks and troughs of dimples showed similar C=C, C=O, and O=CH bonding statuses. In addition, wide-angle X-ray scattering showed that Ar ion beam irradiation did not induce crystallization of the PEN surface. That meant that the self-organization on the PEN surface could be due to the ion-induced surface instability of the amorphous layer and not due to the partial crystallinity differences of the peaks and valleys. A nonlinear continuum model described surface instability due to Ar ion-induced sputtering. The Kuramoto-Sivashinsky model reproduced the dimple morphologies numerically, which was similar to the experimentally observed dimple patterns. This preliminary validation showed the possibility that the continuum equation used for metal and semiconductor surfaces could be applied to polymer surfaces where ion beam sputtering occurred.Keywords:
Dimple
Polyethylene naphthalate
Biological hydroxyapatite (BHAp) derived from thermally-treated fish bones was successfully produced. However, the obtained biological HAp was amorphous and thus making it unfavorable for medical application. Consequently, this research exploits and engineers the crystallinity of BHAp powders by addition of CaCO3 and investigates its degree of crystallinity using XRD and IR spectroscopy. On XRD, the HAp powders with [Ca]/[P] ratios 1.42, 1.46, 1.61 and 1.93 have degree of crystallinity equal to 58.08, 72.13, 85.79, 75.85% and crystal size equal to 0.67, 0.74, 0.75, 0.72 nm, respectively. The degree of crystallinity and crystal size of the obtained calcium deficient biological HAp powders increase as their [Ca]/[P] ratio approaches the stoichiometric ratio by addition of CaCO3 as source of Ca2+ ions. These results show the possibility of engineering the crystallinity and crystal size of biological HAp by addition of CaCO3. Moreover, the splitting factor of PO4 vibration matches the result with % crystallinity on XRD. Also, the area of phosphate-substitution site of PO4 vibration shows linear relationship (R2 = 0.994) with crystal size calculated from XRD. It is worth noting that the crystallinity of the biological HAp with [Ca]/[P] ratios 1.42 and 1.48 fall near the range 60-70% for highly resorbable HAp used in the medical application.
Crystal (programming language)
Stoichiometry
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The purpose of this study is to investigate friction characteristics according to micro-dimple patterns. The surface texturing of micro-dimple patterns was tested to examine the friction of pin-on-disk using flat-on-flat contact geometry. The patterns of both dimple circle and groove pattern were adopted to carry out the effect of those ones. In the low loads, such as 13.8N and 27.7N, the friction coefficients of groove pattern were lower than those of dimple circle pattern. In many other comparisons of normal loads, the groove pattern had lower friction forces, which showed the effect of surface texturing. The relationship between sliding time and friction forces showed that the increase of friction forces of groove pattern were relatively lower than those of dimple pattern. In conclusion, the dimple patterns of dimple-circle pattern and groove pattern strongly contributed to reducing the friction between contacting materials.
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Groove (engineering)
Inclination angle
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It covers the tribological behaviour of sliding surfaces, one of which has bowtie-shaped micro-dimples. Against the other fixed, textured wall, one wall is smooth and moving at a constant speed. For the formation of hydrodynamic pressure and tribological behaviour, the effects of bowtie-shaped dimples and orientated bowtie-shaped dimples have been compared with circular-shaped dimples. Additionally, the impact of sliding speed, dimple area density, and dimple depth on tribological behaviour was examined. The findings show that compared to a circular-shaped dimple, an atypical bowtie-shaped and orientated bowtie-shaped dimple generates a higher net hydrodynamic pressure in the fluid domain and offers improved stability between the sliding surfaces. It has been demonstrated that geometrical factors like dimple depth and area density as well as operational factors like sliding speed have a substantial impact on the hydrodynamic average pressure and tribological behaviour of sliding surfaces. The experimental results support the conclusions from the analysis and CFD.
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Metallurgical structures and ductile fracture surfaces of spheroidized carbon steels and quenched and tempered steels were investigated and following results were obtained.1) The fibrous rupture surfaces of tensile specimens of steels used were, micro-fractographically, consisted of dimples. Among them, in the center of rupture surface, they were “equi-axed” dimple.2) The dimple size was found to distribute as “logarithmically normal distribution” and in the large dimple, second phase particle or its trace was observed. On the other hand, in the small dimple any particle or its trace was not observed. So, in this paper, we call temporarily the former “primary dimple” and the latter “secondary dimple”3) The depth of dimple was observed to be about 1.0 or 1.5 times the diameter of dimple, but it is more reasonable to suggest dimple to be funnel shape, so the ratio of the depth of dimple to the diameter will be larger than the value mentioned above.4) A close correlation between the dimple size and the mean free ferrite path of spheroidized carbon steel was found, but any relation between some kinds of metallurgical factors of quenched and tempered steel and dimple size was not observed.5) On the basis of the existence of primary dimple and secondary dimple, a ductile rupture model was presented that primary dimple corresponds to the void nucleated around a second particle before rupture and secondary dimple will be formed when unstable fracture occurs between neighboring primary dimples at final rupture.
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Previous studies about pure squeeze elastohydrodynamic lubrication (EHL) have disclosed a film profile with a central dimple. Two problems about pure squeeze EHL are numerically solved in this paper. One is for a very small initial impact gap, and the other is the response of a squeezed EHL conjunction under stepwise loads. None of them result in the familiar film with a central dimple, which can be attributed to the local squeeze effect generated in the periphery region. In the first problem, it has been found that when there is adequate oil present on the plate, with a decrease in the initial impact gap, a shallow circumferential dimple occurs at the periphery of the conjunction instead of the primary central dimple presented in previous studies. Correspondingly the minimum film thickness occurs at the central region. The effect of the initial impact velocity on the periphery dimple is also investigated. In the second problem, the response of a conjunction subjected to a prescribed stepwise load is studied. When the first step load is applied, a central dimple film is produced. When the applied load is increased with a second step load, a periphery dimple appears, similar to that in the first problem. The local squeeze effect for the present numerical periphery dimple has been observed in previous experiments under similar conditions.
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Conjunction (astronomy)
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Using CFD software,it was compared the performance of honeycomb on different plate pitch,dimple diameter,dimple depth and dimple horizontal pitch.It indicoded that,with the increase of Re,Nu was exponentially increased,f,Nu/Nu0,η were exponentially decreased,and f/f0 was slightly decreased overall within a certain range.The flow channel height had rarely effect on various performance.Nu/Nu0 and f/f0 were decreased with the increase of dimple pitch P,and were increased with the increase of dimple print diameter d;the increase of dimple depth Hd brought the firstly increase and following decrease of Nu/Nu0 and f/f0;η is slightly increased with the increase of P and d,and the increase of dimple depth Hd brought the decrease of η.By means of orthogonal,it fitted a flow and heat transfer performance relationship for the structure of honeycombed plate with dimpled surface.
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Honeycomb
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Crack arresting capability is experimentally examined using center cracked tension specimens and varying the placement of the dimple ahead of the crack tip. It is confirmed that the dimple gives a greater crack arrest effect than that of the stop hole method. Next, the fatigue life of smooth specimens is compared, both with and without dimples. It is indicated that the dimple has a benefit only to the repair case after the crack is initiated. Finally, stress intensity factors of a crack due to a dimple are numerically evaluated, and a guiding principle is clarified for placing dimples.
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Tension (geology)
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Dimple improves supplying the lubricating oil and it reduces friction of the sliding surface. its effect varies depending on the dimple shape and arrangement pattern, therefor generic design method of dimples has not been clarified. The purpose of this study is proposing design method of dimples based on fluid pressure under fluid lubrication. We analyzed maximum load carrying capacity and fluid pressure using the TED/CPA when single and multiple dimples were applied load and sliding velocity in oil lubrication. We changed diameter of dimple, depth, curve, number of dimples and pitch between dimples. In case of single dimple, maximum load carrying capacity increases with increasing the dimple diameter, and maximum load carrying capacity decreases with increasing the depth. There is an appropriate curve degree dependance on the depth of dimple. In case of multiple dimples, the effect of dimple overlapped and fluid pressure mutually increases. Maximum load carrying capacity increases and it per one dimple decreases as the number of dimple increases. Maximum load carrying capacity decreases with extending pitch between dimples. As a result, we proposed the method to investigate the influence of dimple shape on maximum load carrying capacity and fluid pressure.
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Abstract Crystallinity is an important parameter of thermoplastic polymers. Furthermore, crystallinity is closely related to processing conditions such as temperature and applied shear stress. However, determining the degree of crystallinity is very complicated because of the different interpretations of crystallinity according to each technique. In this paper, we analyze the crystallinity of polyethylene glycol-based composites using two instruments, i.e., X-Ray Diffraction (XRD) and wide-angle X-Ray Scattering (WAXS). The results showed that with the addition of 60 wt.% silica, the degree of crystallinity revealed by XRD was 81.24%, while WAXS showed a degree of crystallinity of 80.93%. In general, the crystallinity results obtained with WAXS were almost identical, only 0.31% different from the XRD results. This difference in results was due to more presence as a consequence of the broad amorphous halo and background instrumentation exhibited by the higher background from XRD. Thus, the instrument effect must first be removed from the XRD data and it is possible that the amorphous region of the sample will also be reduced and result in a slightly higher crystallinity. At the same time WAXS with the transmission technique will minimize the possibility of background instrumentation. Therefore, WAXS was recommended to analyze the crystallinity of polymer-based and amorphous materials.
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