Search Results (8)

In this study, polysulfone/polyvinylpyrrolidone (PSf/PVP, 20 wt%/5 wt%)-based ultrafiltration (UF) membranes reinforced with different ratios (0.5 and 1 wt%) of cellulose nanocrystals (CNCs) and cellulose nanofibres (CNFs) were prepared by the phase inversion method. The effect of CNC, CNF, and CNC-CNF reinforcement on the morphology, roughness, crystallinity, porosity, average pore size, mechanical properties, and filtration performance of PSf/PVP-based membrane was investigated. Distilled water and surface water (lake water) fluxes of the membranes were determined at 3 bar using a dead-end filtration system. The distilled water flux of the fouled–hydraulic cleaned membranes was determined, and scanning electron microscopy (SEM) images of the fouled–cleaned membranes were examined. The flux recovery ratio (FRR) and fouling parameters were calculated to examine the fouling behaviour of the membranes. The mechanical properties of the membranes were modelled by the Mori–Tanaka, finite element, Voigt–Reuss, self-consistent scheme, and Halpin–Tsai methods using Digimat and/or analytically. In addition, the von Mises equivalent stress distributions of the nanocomposites were presented. Among the investigated membranes, PSf/PVP/CNC-0.5 had the highest distilled water flux (475.5 ± 17.77 L/m².h), PSf/PVP/CNF-1 exhibited the stiffest behaviour with an elasticity modulus of 70.63 ± 3.15 MPa, and PSf/PVP/CNC-1 had the best organic matter removal efficiency. The finite element was the most successful modelling method for estimating the mechanical properties of nanocellulose-reinforced flat sheet membranes. Full article

The response of any engineering design components to stresses should be predictable, While the response of a material to complex loading, such as high strain rates experienced during service, is difficult to represent with simple tests, the Taylor impact test is one of a number of tests devised for high strain rate complex loading. To expedite the acceptance of LPBF Ti6Al4V (ELI) for use in demanding structural applications, there is a need to develop numerical models based on the internal microstructural state variables to predict the performance of the alloy over a wide range of high strain rates using such complex tests. This paper documents the numerical simulation of Taylor impact tests for direct metal laser-sintered and post-processed Ti6Al4V (ELI—Extra Low Interstitial) alloy. A microstructural variable-based constitutive model was used to predict the mechanical properties (stresses and evolution of plastic strains) of the material. The corresponding material parameters of the model were based on the specific microstructure obtained upon post-process heat treatment. The model was first implemented as a user material subroutine in the explicit finite element program ABAQUS using the VUHARD subroutine. Subsequently, the symmetrical Taylor impact tests of Laser Powder Bed Fusion (LPBF) Ti6Al4V (ELI) parts were numerically simulated using the VUHARD subroutine at different impact velocities. The equivalent von Mises stress and plastic strain obtained from numerical simulations were compared with the analytical solutions based on the strain rates obtained. It was shown that the instantaneous and average absolute errors between the numerical and analytical values of the model were generally less than 5%. The mushroom end, commonly observed in a Taylor test specimen, was also seen in the numerical model. Full article

Based on a V-shaped microactuator with a pair of beams, modifications were made to the length and width of a microactuator to observe the effects. A theoretical approach and numerical characterization of the modified microactuator were performed. Its performance was compared to a similar microactuator with equal beam widths, and a V-shaped microactuator. The proposed microactuator, fed at 2 V, compared to the V-shaped actuator, showed a 370.48% increase in force, but a 29.8% decrease in displacement. The equivalent von Mises stress level increased (until 74.2 MPa), but was below the silicon ultimate stress. When the modified microactuator was applied to the proposed microgripper, compared to the case using a V-shaped actuator, the displacement between the jaws increased from 0.85 µm to 4.85 µm, the force from 42.11 mN to 73.61 mN, and the natural frequency from 11.36 kHz to 37.99 kHz; although the temperature increased, on average, from 42 °C up to 73 °C, it is not a critical value for many microobjects. The maximum equivalent von Mises stress was equal to 68.65 MPa. Therefore, it has been demonstrated that the new modified microactuator with damping elements is useful for the proposed microgripper of novel geometry, while a reduced area is maintained. Full article

Creep tests were carried out on notched plate specimens of nickel-based superalloy GH4169 with different stress concentration coefficients. It was found that the duration of the first stage of the creep curve increases with the increase of stress concentration coefficient, while the fracture ductility decreases with the increase of stress concentration coefficient. To predict the life of notched plate specimens, four constitutive models were used to analyze the stress and strain of the notches. It was found that the average Von Mises equivalent stress (AVES) on the minimum notch section first decreases and then increases with the creep time, resulting in a minimum value. The minimum average Von Mises equivalent stress (MAVES) is considered as the characteristic stress of notched specimens in this paper. The creep life equation is fitted according to the results of creep tests of smooth specimens, and then the predicted life of notched specimens is obtained by substituting the minimum average Von Mises equivalent stress of notched specimens into the creep equation. The prediction results of the four constitutive models are within 2 times the dispersion band, and the three-stage model is within the 1.5 times dispersion band. Full article

The research and application of new wall materials have been attracting increasing attention owing to the continuous promotion of sustainable development in the building industry. An alkali-activated slag ceramsite compound insulation block (AASCCIB) is used as the research object. Based on the finite element method, the effects of different numbers of hole rows and hole ratios on the thermal and mechanical performances of AASCCIBs are analyzed using ANSYS CFX. On this basis, the AASCCIB with the optimal comprehensive performance is determined by a multi-objective optimization analysis. Finally, the improvement effect of the AASCCIB wall on the indoor thermal environment relative to an ordinary block (OB) wall is quantitatively analyzed using ANSYS CFX. The results show that the von Mises equivalent stress and heat transfer coefficient of the AASCCIB decrease with the increase in the hole ratio when the hole shape and number of hole rows are constant. ${\mathrm{AASCCIB} \mathrm{B}}_1$ has the optimal comprehensive performance among six AASCCIBs, with the heat transfer coefficient and average von Mises equivalent stress of 0.446 W/(m²∙K) and 9.52 MPa, respectively. Compared with the indoor lowest and average temperatures of the building with the OB wall, those of the building with the AASCCIB wall increased by at least 1.39 and 0.82 °C on the winter solstice, respectively. The indoor temperature difference decreased by at least 0.83 °C. In addition, the indoor highest temperature, average temperature, and temperature difference decreased by at least 1.75, 0.79, and 1.89 °C on the summer solstice, respectively. Full article

In this study, a cladding layer and nitriding layer were prepared on nodular cast iron, to provide guidance for remanufacturing of nodular cast iron. Their microstructure and composition and the tribological properties under dry and starved lubrication conditions were studied. Meanwhile, the contact stresses at different friction stages were simulated through the finite element method. The micro-hardness of the cladding layer and nitriding layer were 694 HV_0.5 and 724.5 HV_0.5, which were 4 times and 4.2 times higher than that of the substrate. For dry friction conditions, the wear resistance of the cladding layer and nitriding layer were 113.2 times and 65.5 times that of the substrate. For starved lubrication conditions, the friction coefficients of the cladding layer and nitriding layer were lower than that of the substrate. In addition, their average friction coefficients and wear resistance were gradually reduced with the increase in load. Contact simulation showed that the maximum equivalent stress gradually increased with the friction coefficient during the dry friction, and the peak value of von Mises stress on the nitriding layer was larger than that of the cladding layer, and the nitriding layer was more likely to yield and peel off. Full article

Thermal barrier coating (TBC) plays a vital role in the gas turbine combustor liner (CL) to mitigate the internal heat transfer from combustion gas to the CL and enhance the parent material lifetime of the CL. This present study examined the thermal analysis and creep lifetime prediction based on three different TBC thicknesses, 400, 800, and 1200 μm, coated on the inner CL using the coupled computational fluid dynamics/finite element method. The simulation method was divided into three models to minimize the amount of computational work involved. The Eddy Dissipation Model was used in the first model to simulate premixed methane-air combustion, and the wall temperature of the inner CL was obtained. The conjugate heat transfer simulation on the external cooling flows from the rib turbulator, impingement jet, and cross flow, and the wall temperature of the outer CL was obtained in the second model. The thermal analysis was carried out in the third model using three different TBC thicknesses and incorporating the wall data from the first and second model. The effect of increasing TBC thickness shows that the TBC surface temperature was increased. Thereby, the inner CL metal temperature was decreased due to the TBC thickness as well as the material properties of Yttria Stabilized Zirconia, which has low thermal conductivity and a high thermal expansion coefficient. With the increase in TBC thickness, the average temperature difference between the TBC surface and the inner metal surface increased. In contrast, the average temperature difference between the inner and outer metal surfaces remained nearly constant. The von Mises equivalent stress, based on the material property and thermal expansion coefficient, was determined and used to find the creep lifetime of the CL using the Larson–Miller rupture curve for all TBC thickness cases in order to analyze the thermo-structure. Except in the C-channel, the increasing TBC thickness was found to effectively increase the CL lifespan. Furthermore, the case without TBC was compared with the damaged CL with cracks due to thermal stress, which was prevented by increasing TBC thickness shown in this present study. Full article

The friction wear and thermal fatigue cracking of the brake shoe and friction-induced self-excited vibration (frictional flutter) of the disc brake can easily occur during emergency braking of a deep coal mine hoist with at high speed and with a heavy load. Therefore, tribo-brake characteristics between the brake disc and brake shoe during emergency braking of a deep coal mine hoist are investigated in the present study. Scaled parameters of the disc brake of a deep coal mine hoist are determined by employing the similarity principle. Friction tests between friction disc and brake shoe are carried out to obtain the coefficient of friction in the case of high speed and large specific pressure between the friction disc and brake shoe. Coupled thermo-mechanical finite element analyses of the brake disc and brake shoe are established to investigate temperature and stress fields of the brake disc and brake shoe during emergency braking, which is validated by the engineering failure case. Effects of braking parameters on flutter characteristics between the brake disc and brake shoe are explored by employing a double-degrees-of-freedom vibration mechanism model. The results show that the maximum temperature, equivalent Von Mises stress and contact pressure are all located at the average friction radii of contact surfaces of the brake disc and brake shoe during emergency braking. The cage crashing accident in the case of high speed and heavy load in a typical coal mine shows crack marks and discontinuous burn marks at central locations of brake shoe and brake disc surfaces, respectively, which indicates frictional flutter characteristics between brake disc and brake shoe. During emergency braking, flutter time duration decreases with increasing initial braking speed and damping parameter; the flutter amplitude and frequency of the disc brake increases with increasing normal braking load and stiffness, respectively. Full article