关键词： Uncertainty analysis   Interval parameters   Surrogate model   Hilbert-Huang transform (HHT)   Local mean decomposition (LMD)   Multibody dynamics  

摘要： Studying multibody dynamic systems, a common way to evaluate the effects of uncertainty parameters is the response surface method, which works by building a polynomial surro -gate model at each time instant through a set of input and corresponding output responses. However, a dynamic response always becomes a more and more complicated function of uncertainty parameters with the increase of time;as a result, the fitted surrogate model often fails to provide an accurate approximation at later time instants. This paper suggests that a dynamic response is composed of several vibration components and one trend com-ponent. Therefore, it is better to decompose the response into its multiple components, and then fit the amplitude and phase of each vibration component, as well as the trend compo-nent, using polynomial functions. By combining the response surface method with signal decomposition techniques, such as Hilbert-Huang transform and local mean decomposi-tion, this study proposes a novel methodology to develop a high-accuracy surrogate model for interval uncertainty analysis. The proposed methodology will degenerate to the con-ventional response surface method when the dynamic response is a trend component. Three mechanical systems-a Duffing oscillator, a single pendulum and a slider-crank model-are used to confirm the effectiveness of the proposed methodology. This method-ology provides a new technical pathway to improve the accuracy of dynamical uncertainty analysis. (c) 2021 Elsevier Ltd. All rights reserved.

关键词： vibration sensor   condition monitoring   predictive maintenance   self-powering device   triboelectric effect  

摘要： This article showcases a compact self-powered contact-mode triboelectric (TE) phenomenon-based vibration sensor for predictive maintenance of industrial machinery. The sensor has a suspended proof-mass that oscillates under external vibration and causes contact-separation between Teflon and zinc oxide (ZnO) films creating tribo signals, which are used for both sensing and powering mechanisms. For these sensors to be implemented in real-time applications, the sensor must be cost-effective, reliable, and repeatable. Hence, the active layer (ZnO film) is fabricated by an efficient process of microwave-assisted thermal decomposition followed by the established screen printing method. The sensor operates up to 400 Hz and is highly robust with no significant decay in signal strength even after 120 000 cycles tested at elevated stress values. The device produces a maximum voltage (V) of +/- 30 V, short circuit current of +/- 3 mu A, and can deliver a maximum power density of 0.5 W m(-2), at 8 M omega load resistance. In the frequency domain, the device generates a maximum V at 55 Hz and can charge 1 mu F capacitor to 3.5 V in 25 s. To demonstrate the functionality of the sensor in a real application, it is implemented on a lab-scale vacuum pump to capture the system faults by analyzing the harmonic signatures. Thus, in this article, we have showcased end-to-end development of the sensor from material synthesis to device testing along with its signal processing techniques and proved that the sensor can readily be implemented in industrial environments as is. This article thus emphasis bridging the lab-to-market gap for TE devices as a self-powering sensor.

关键词： Axial dispersion   Twin-screw granulator   Mixing dynamics   Dispersion model   Residence time distribution  

摘要： Wet granulation is a size enlargement process in which fine powders are agglomerated into larger granules via the presence of a liquid binder. Among various types and modes of granulation processes, twin-screw granulation is a popular continuous wet granulation technique. The typical residence time that powders spend in a twinscrew granulator are in the order of seconds, hence, the rigorous mixing of solid and liquid particles across particle sizes and equipment geometry becomes even more important. This study aims to improve the mechanistic understanding of the effect of process and screw parameters on the mixing dynamics inside a twin-screw granulator using dispersion coefficient as a key metric. The dispersion coefficient quantifies the dispersion and is directly proportional to the extent of mixing occurring inside the granulator. An analysis of the experimentally obtained dispersion coefficient is performed to understand the effect of key process and design parameters such as feed rate, screw speed, number of kneading elements and, stagger angle. A semi-mechanistic model that incorporates these parameters was developed to estimate and predict the dispersion coefficient. The model accurately predicts the dispersion coefficient values and the goodness-of-fit values (R-2) for the test set and full data set were found to be equal to 0.920 and 0.932 respectively. This model was further tested by predicting the complete RTD curves using the predicted dispersion coefficients. The average goodness-of-fit value (R-2) for the prediction of RTD curves for all the experimental runs was calculated to be equal to 0.698. (C) 2021 Elsevier B.V. All rights reserved.

关键词： mechanical properties   molecular dynamics   polyurethane-modified asphalt  

摘要： In this study, the mechanical performance of polyurethane (PU)-modified asphalt was investigated. To this end, the molecular dynamics method was adopted to study the influence of the PU modifier on the compatibility, mechanical properties, and structure of asphalt. Using the Materials Studio software, a four-component molecular model of asphalt, a PU molecular model, and an asphalt-PU mixed system model were constructed, and the molecular density and glass transition temperature (Tg) were used to verify the performance of the aforementioned models. Molecular dynamics simulations of the three molecular models were conducted under different temperatures, and the solubility parameter (delta), interaction energy, mechanical properties, and radial distribution functions (RDFs) were obtained. The results showed that at 413.15 K (140 degrees C), the difference between the solubility parameters of the asphalt and PU molecules ( increment delta) is the smallest, and their interaction reaches the most optimal phase state. The effects of the PU modifier on the Young's modulus, bulk modulus, and shear modulus of asphalt were studied. Finally, the RDF analysis showed that the PU modifier has a direct effect on the degree of swelling and dispersion between the aromatic-aromatic and saturate-saturate components in the asphalt, reducing the aggregation of both molecules. This verifies the PU modification effect.

关键词： compatilibization   crystallization kinetics   Macaiba shell   PCL   tensile properties  

摘要： Biocomposites based on macaiba shell (MS) and Polycaprolactone (PCL) were melting processed in this work;seeking better compatibility between PCL, MS was chemically treated with maleic anhydride (MA) and sodium hydroxide (NaOH), in addition, PCL-g-MA was used as compatibilizer. The biocomposites' performance was evaluated through Fourier transform infrared (FTIR), thermogravimetry (TG), contact angle, water absorption, scanning electron microscopy (SEM), the tensile experiments were executed according to ASTM D638 and the nonisothermal crystallization kinetics was performed from differential scanning calorimetry (DSC) scans using Pseudo-Avrami, Ozawa, and Mo models. Chemical treated and compatibilized biocomposites presented better tensile behavior with no significant changes in the thermal stability. Higher HDT was verified on PCL/MS biocompounds due to the MS hardening effect, whereas higher contact angle and water absorption were computed for PCL/MS most due to new ways origin for the water get in as provided by MS. Related to crystallization kinetics Ozawa as displayed in the Appendix S1 failed to fit PCL/MS kinetics whereas Pseudo-Avrami and Momay be safely used form processing purposes. Summing up, PCL/MS biocomposites were carefully investigated and gathered information may be promptly used in sundry applications as well as be added to the literature database.

关键词： Molecular dynamics  

摘要： A series of polyamic acid (PAA) solutions and corresponding polyimide (PI) films with different chemical structures were prepared through a partial pre-imidization process, and the rheological behavior of PAA solutions and thermal mechanical properties of PI films were investigated in detail. The FT-IR spectra indicate that the pre-imidization degree (pre-ID) of PI could be accurately controlled by adjusting the amount of dehydration reagents. The PI films with a certain pre-ID exhibit better mechanical properties and lower coefficient of thermal expansion. The viscosity curves of PAA solution with varying shear rate show that the PAA solutions with high pre-ID have low shear sensitivity, which exhibits a lower viscosity at the low shear rate, but retains almost the same viscosity at high shear rate. Chain conformation variations with pre-IDs and solvent content were investigated by molecular dynamic (MD) simulation. The MD results indicate that a sudden increase in cohesive energy density leads to gel at a certain pre-ID and the mobility of molecular chain decreases greatly with solvent volatilization. It is supposed that the molecular chain orientation induced by the pre-imidization will be preserved in the subsequent thermal imidization process. Therefore, the PI films with a certain pre-IDs exhibit more excellent thermal mechanical properties, especially for the PI with rigid-rod segments.

关键词： Metallic Materials   Characterization and Evaluation of Materials   Structural Materials   Surfaces and Interfaces   Thin Films   Nanotechnology  

摘要： The present study has focused on the detailed dilatometric and electron microscopic analysis of the formation of austenite and its decomposition in two Cerium (Ce) modified steels containing 0.6 and 0.03 wt pct Ce. Despite a long incubation time, the austenite formation is very fast in the high-Ce steel (0.6 wt pct Ce) during heating. Whereas, the low-Ce steel (0.03 wt pct Ce) promotes early nucleation of austenite but shows a significant delay in the completion of the transformation. Similar trend has been observed for the decomposition of austenite during cooling;the low-Ce steel shows early start of transformation with a sluggish kinetics. The role of Ce on the overall transformation kinetics of austenite during the heating-cooling cycle has been investigated and discussed from thermodynamic viewpoint and nucleation probability. Engineering stress-strain curves have shown a better combination of strength and ductility in the low-Ce steel compared to the high-Ce one. Coarse and spherical Ce2O3 particles (average dia. similar to 4 mu m) in grain interior along with the brittle and grain boundary elongated Ce-C/Ce-Fe intermetallic phases (length similar to 8 mu m and width similar to 3 mu m) are responsible for the lower strain hardening as well as an early failure of the high-Ce steel. Finally, the microstructure-tensile property correlation has been established using chemical composition and fractographic analysis. (C) The Minerals, Metals & Materials Society and ASM International 2021

关键词： Furan epoxy resins   Hydrogen bonds   Molecular dynamics simulation  

摘要： The hydrogen bonds (H-bonds) are employed for the thermal and mechanical property enhancement of epoxy networks;however, the formation and evolution of H-bonds, especially in emerging bio-based furan epoxy, cannot be deeply understood at the atomic level in the traditional experimental method. Herein, molecular dynamic (MD) simulation is employed to clearly investigate the H-bonds, free volume and its distribution, mean square displacement, as well as their further influence on thermomechanical behaviors of selected model epoxy resins. The model epoxy resins composed of 2,5-bis [(2-oxiranylmethoxy)-methyl]-furan (BOF), 1,4-bis [(2-oxiranylmethoxy)-methyl]-benzene (pBOB) and 2.5-bis(2-oxiranylmethoxy)-methyl)-cyclopentadiene (BOC), which were cured by 4,4'-diamino diphenyl methane (DDM), respectively. These three epoxy molecules have very similar structure with the only difference in ring blocks of monomers from furan, benzene to cyclopentadiene. Wherein, BOC is artificially designed to further explore the influence of the oxygen atom of furan rings, with ensuring the consistency with the rotation and planarity of BOF. From contrastive simulation results, BOF-DDM has the highest Young's modulus among all these systems due to the least free volume leading by the maximum H-bonds. However, for DDM crosslinking networks, H-bonds seem to have limited influence on T-g of BOF-DDM, and the effect of molecular weight and steric hindrance on T-g is more decisive, which is different from the most relevant reports on furan-based epoxy. Our study gives the significant insight of H-bonds behavior of furan rings, and it is expected to effectively guide the design of epoxy resins.

关键词： Styrene  

摘要： The statistical anionic copolymerisation of the biobased monomer beta-myrcene with styrene in cyclohexane was investigated via in situ near-infrared (NIR) spectroscopy, focusing on the influence of the modifiers (i.e., Lewis bases) tetrahydrofuran (THF) and 2,2-di(2-tetrahydrofuryl)propane (DTHFP) on the reactivity ratios. With increasing [modifier]/[Li] ratio, the reactivity ratios in the system myrcene/styrene are adjustable from r(S) MUCH LESS-THAN r(Myr)via r(S) approximate to r(Myr) to r(S) >> r(Myr). The bidentate modifier DTHFP affects the reactivity ratios much more than THF: minute amounts only (0.35 equivalent relative to Li) are required to randomize the copolymer, and one equivalent to invert the reactivity ratios. Using these reactivity ratios, copolymer composition profiles are obtained, which upon increasing the modifier concentration vary from tapered, block-like copolymers to random to inversely tapered copolymers. H-1-NMR spectroscopy was used to determine the microstructure of the myrcene units in the copolymers. With increasing [modifier]/[Li] ratio, the content of 1,4-units decreases and the content of 3,4- and 1,2-units increases. DTHFP as a modifier minimizes the content of 1,2-units. The glass transition temperatures also depend on the [modifier]/[Li] ratio, but less strongly than in the copolymer poly(styrene-co-isoprene). Although all copolymers have the same composition (33%(mol) myrcene, corresponding to 39.6%(weight) and 45%(vol)), very similar molecular weights (about 90 kg mol(-1)) and low dispersities (1.06 to 1.10), different morphologies could be obtained. Lamellar, cylindrical and gyroid structures were identified by TEM and SAXS measurements. The mechanical properties vary in a wide range from hard and brittle to soft and flexible. The gyroid structure showed the highest Young's modulus and no viscoelastic deformation.

关键词： Hydrogenation  

摘要： A newly proposed borophane structure is characterised mechanically and thermally in this work by using a reactive molecular dynamics study. A full hexagonal lattice of borophene is connected with other hexagonal lattices by placing hydrogen atoms as the connecting bridges. It is found that hydrogenation improves the Young's modulus of armchair borophene significantly. However, this noticeable increase is not found in the case of thermal conductivity. There are only slight variations of thermal conductivity upon hydrogenation. The increase of temperature was then found to decrease the Young's modulus and thermal conductivity. The presence of a vacancy defect also diminishes the Young's modulus of borophene remarkably, yet this reduction is less significant when borophene is hydrogenated which shows the stabilising effect of hydrogenation on the mechanical properties of borophene. The removal of a single boron atom was also found to provide an insignificant reduction in thermal conductivity. Given the mechanical and thermal stabilities of the proposed borophane structure, this structure can also be used as an alternative to the recently synthesised H1B1 hydrogen boride sheet. It is expected that this work will provide meaningful insights for the design of on-board hydrogen storage applications.