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Purpose The purpose of this paper is to report the tribological behavior of dimples textured rolling element bearings (REBs) under variable load and starved lubrication. Design/methodology/approach The pattern parameters include line-diameter of dimples (200 µm, 250 µm, 300 µm), depth of dimples (10 µm, 20 µm, 30 µm). Dimple patterns were prepared on the raceways of the shaft washers of cylindrical roller thrust bearings (CRTBs). A vertical wear test rig was used to obtain their coefficients of friction (COFs) under stepped load (1200–6000 N, with a manually increase of 1200 N every 3600 s) and starved lubrication. The wear losses and worn surfaces were characterized. The tribological performance between stepped load and fixed load (4000 N) was compared. The influence mechanism of dimples on the friction and wear properties of CRTBs under stepped load and starved lubrication was also discussed. Findings Compared with the data of smooth ones, the average COFs of the dimples textured bearings are almost all reduced under stepped load and starved lubrication, while their mass losses almost all get higher. The depth−diameter ratio and the effective volume coefficient of dimples are the important factors. In this work, compared with the smooth group, when the line-diameter of dimple is 250 µm and the depth is 20 µm, i.e. the depth−diameter ratio is 0.08, its average COF is reduced by 46.8% and its mass loss is reduced by about 7%, showing wonderful friction-reducing effect and good wear resistance. Originality/value This work can provide a reference for the raceway design of REBs.

Purpose The purpose of this paper is to reveal the friction and wear performance of grooves textured cylindrical roller thrust bearings with different groove dimensions under starved lubrication. Design/methodology/approach The groove dimensions include: width of grooves (WOG, 50 µm, 100 µm and 150 µm), depth of grooves (DPOG, 7 µm, 11 µm and 15 µm) as well as groove deflection angle (GDA, 45°). A fiber laser marking system was used to prepare groove patterns on the raceways of shaft washers. The friction and wear properties of grooves textured bearings were researched through a vertical universal wear test rig using a customized roller bearing tribo-pair under starved lubrication. Static finite element analyses were conducted to reveal their surface stresses. Through the comprehensive comparison and analyses, the influence mechanism of grooves on the tribological behavior of cylindrical roller thrust bearings was proposed and discussed. Findings When grooves textured bearings run under starved lubrication, their average coefficients of friction (COFs) and wear losses are all significantly reduced and much lower than those of smooth group. The influence of DPOG on the COF curves is significant, while the influence of WOG on the COF curves is a little weak. The influence of groove dimensions on the surface stresses of grooves textured bearings is weak, whether the WOG or DPOG. In this work, when the WOG is 100 µm and the DPOG is 15 µm, its average COF and wear loss are both the lowest, 0.0066 and 0.61 mg, respectively. Compared with the data of smooth group, its friction coefficient is reduced by 75.3% and its mass loss is reduced by 95.8%, showing a significant improvement in this condition. Originality/value This work can provide a valuable reference for the raceway design and reliability optimization of rolling element bearings.

This study presents the influence of initial deflection angle (IDA) on the tribological properties of gray cast iron (GCI) rings with curve distributed pits in the radial direction (CDPRD). The thermal behavior of pits textured GCI rings with different initial deflection angles (0°, 30°, 45°, 60°, 75°) and fixed deflexional angle of adjacent pits (DAAP, 10°) were researched, through APDL programming. A pin-on-disc wear test rig was used to reveal the anti-wear performance of samples under dry sliding, at a rotating speed of 200 rpm, with a normal load of 70 N. An electronic balance and an optical microscope (OM) were used to obtain their wear losses and worn surfaces, respectively. The results show that: comparing with the smooth GCI ring, there are evident high temperature regions between two adjacent pits groups, called “temperature barrier and separation effect”. Among all textured samples, the von Mise’s stress of IDA45 is the most stable, and its temperature is almost the lowest. The friction coefficient curve and the wear loss of IDA45 are also the lowest, and much lower than the loss of smooth GCI ring, indicating the excellent anti-wear performance. This work can provide a valuable reference for the surface design of journal bearings.

This study presents the influence of Zr/ZrN coatings on the tribological performance of pits textured grey cast iron parts under dry sliding. A laser marking system and a physical vapor deposition equipment were applied to manufacture pits textured grey cast iron rings combined with Zr/ZrN coatings. A pin-on-disc wear test rig was used to reveal the wear behavior of samples under dry wear condition, at a rotating speed of 200 r/min, with a normal load of 70 N. The wear losses and the worn surfaces of all rings were obtained by an electronic balance and a three-dimensional surface profilometer, respectively. The results show that Zr/ZrN coatings can significantly increase the surface roughness and surface hardness of grey cast iron rings. As a result, Zr/ZrN coatings increase the friction coefficients of all coated GCI rings, and reduce the wear losses of some ones. In this work, when surface texturing combines with Zr/ZrN coatings, the final tribological properties of coated grey cast iron rings may be either improved or deteriorated, depending on surface characteristics, texturing parameters and loads. Compared with the uncoated smooth grey cast iron ring, Zr/ZrN coatings cannot effectively improve the wear behavior of pits textured samples. Among all coated grey cast iron rings, when the diameter of the pit is 0.8 mm, and the distance between pits is 1.25 mm, the pits textured grey cast iron ring can provide the optimal anti-wear performance. This work would provide a valuable reference for the surface design of journal bearings and roller bearings.

Novel lignin-based polyurethane (LPU) and LPU-nanosilica composite films were prepared using in situ polymerization. The effects of various nanosilica contents on the structure and properties of the LPU matrix films were investigated by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), dynamic thermomechanical analysis (DMA), tensile test, and contact angle measurements. The results showed that hydrogen bonding and cross-linking occurred between the -N-H and -C=O functional groups in the LPU-nanosilica films. Morphological and surface energy analyses showed uniform dispersion of amine modified silica nanoparticles in the LPU matrix at low concentrations. The incorporation of silica nanoparticles considerably improved the thermal stability and mechanical properties of the LPU films because of the introduction of silicon-oxygen bond between the LPU matrix and nanosilica. Overall, the introduction of small amounts of silica nanoparticles could improve the properties of the renewable LPU films, which are useful in the development of biomaterials.

To explore the effect of dents on the tribological behavior of the “washers-cage-rollers” system of rolling element bearings (REBs), the friction and wear properties of dents textured thrust cylindrical roller bearings (81107TN) with different diameters of dents (DAOD, 200, 250, 300 μm), depth of dents (DPOD, 4, 8, 12 μm) as well as circumferential interval angle (CFIA, 1.5°, 2.0°, 2.5°) were researched under dry wear. The surface stresses of REBs and the influence mechanism of dents were also compared and discussed. The results show that: due to the nylon film formed and left on the raceways, the coefficients of friction (COFs) of dents textured bearings are all higher than the average COF of smooth ones, while their wear losses may become higher or lower, depending on the combination of pattern parameters. The influence of the DPOD on the tribological performance of textured bearings is more significant than that of the DAOD. The results show that, when the DAOD and DPOD are 250 and 8 μm, respectively, compared with the smooth ones, the mass losses of bearings can be reduced by up to 49.22% under dry wear, which would be an important reference for the optimal design of the “washers-cage-rollers” system of REBs.

Efficient production of furfural from cornstalk in 2-Methyltetrahydrofuran/aqueous (MTHF/H2O) biphasic system via parameter regulation (e.g., VMTHF/VH2O, temperature, time, and H2SO4 concentration) was proposed. The resulting solid residues achieved from the different MTHF/H2O system conditions for furfural production were also to prepare glucose by adding cellulases to increase the high-value applications of cornstalk. A maximum furfural yield (68.1%) was obtained based on reaction condition (VMTHF:VH2O = 1:1, 170 °C, 60 min, 0.05 M H2SO4). Among these parameters, the concentration of H2SO4 had the most obvious effect on the furfural production. The glucose yields of the residues acquired from different MTHF/H2O processes were enhanced and then a maximum value of 78.9% based on the maximum furfural production conditions was observed. Single factor may not be sufficient to detail the difference in glucose production, and several factors affected the hydrolysis efficiency of the residues. Overall, the MTHF/H2O system effectively converted cornstalk into furfural and glucose via a simple and environment-friendly process, thus was an ideal manner for the food industries.

Biochar is a low-cost carbon-rich material derived from the thermochemical degradation of biomass. Due to its unique chemical structure, biochar with a large surface area and tailored surface functional groups can be easily prepared by activation and/or functionalization, and shows great potential to be used as a versatile catalyst and/or catalyst support in many chemical processes. However, the application of biochars as versatile catalysts and/or catalyst supports for biomass upgrading has not been systematically overviewed so far. In this work, the formation of pyrochar and hydrochar is proposed, and the activation and/or functionalization of biochar are also included. Subsequently, the application of biochar-based catalysts in biomass upgrading, including biochar-based solid acids for biomass hydrolysis and dehydration, biochar-based catalysts for biodiesel production, and biochars as catalyst supports for biomass pyrolysis, gasification, and bio-oil upgrading, are discussed in detail.

© 2018 Risheng Long et al. Inspired by the nonsmooth surface of the head of the dung beetle, grey cast iron (GCI) samples with pit textured surfaces were designed and fabricated, based on pin-on-disc friction tester. Using a tribology wear testing rig and APDL programming, the tribological behavior of smooth and textured samples was investigated and reported, both experimentally and numerically. The results show that pits can significantly change the thermal stress and temperature distribution on the surface, which will result in either positive or negative effects on the wear resistance of GCI samples, depending on the parameters. When diameter of the pit (DOP) equals 0.8 mm and distance between pits (DBP) is 1.0 mm, the pit textured surface provided the best wear resistance among all samples tested.

In order to realize the safety, high efficiency and rapidity of hard rock tunneling, we propose the drilling & hydraulic impact hard-rock tunneling (DHIHT) technology and method. Based on the LS-DYNA explicit module and APDL programming, the key parameters of DHIHT, including drilling spacing and drilling radius, were investigated. The simulation results show that: the drilling spacing should not exceed 0.20 m-larger distances weaken the actual breaking effect; the best drilling radius is about 0.035 m, larger or smaller distances would both decrease the effect of drilling-hole free surfaces. The field impact breaking experiments were conducted in Baitaizi township granite quarry, Jinzhou, Liaoning province, China. The experiment results indicate that DHIHT is a feasible method for hard-rock tunneling, but its efficiency still needs to be further optimized and improved. Keywords: Hydraulic impact breaking, Hard rock tunneling, Breaking mechanism, Numerical simulation, Technology research

© Copyright 2017 Shaoni Sun et al. To investigate the influence of surface features, in the form of pits, on the wear resistance of grey cast iron (GCI), a finite element model of the pin-on-disc friction system, with pits distributed in a curved radial d irection, was developed using APDL programming and the tribological behavior of textured surfaces was studied. The influence of relative rotation direction between the disc and the pin on the thermal behavior of the friction system under dry wear conditions was researched. GCI and C30E steel samples with pit textured surfaces were manufactured using laser marking equipment and tested using a tribology wear testing rig. The mass losses were measured and the worn surfaces were characterized. The influence of different rotation directions on the tribological behavior of the pit textured surfaces was also investigated. The simulation and test results revealed that rotation direction was a crucial parameter in determining the tribological behavior of surfaces with these features, regardless of the material. Under the conditions tested, when the pin rotated anticlockwise, the samples showed better friction and wear behavior than when the pin rotated clockwise. These results can provide important guidance for the optimization of the design of heavy-load brake systems and other similar applications.

Additional file 1: Table S1. The byproducts liberated during the dilute acid pretreatment. Table S2. Yield and contents of associated polysaccharides (absolute %, w/w) of the lignins isolated with 1.5 % NaOH at 80 °C for 2 h from the dilute acid pretreated rice straw. Table S3. Weight-average (Μ w ) and number-average (Μ n ) molecular weights, and polydispersity (Μ w /Μ n ) of the alkaline lignin fractions. Table S4. Assignments of 13C-1H cross-peaks in HSQC spectra of the alkaline lignins recovered from the integrated process. Figure S1. FT-IR spectra of the raw material, acid pretreated straw and alkali post-treated straw. Figure S2. SEM images of the raw material, acid pretreated straw and alkali post-treated straw. Figure S3. XRD patterns of the raw material, acid pretreated straw and alkali post-treated straw. Figure S4. 31P-NMR spectra of the lignins obtained from the integrated process under various processing conditions.

In order to realize the rapid hard-rock tunneling in a safe, highly effective, and economic manner, the hydraulic drilling impact hard-rock tunneling (HDIHT) technology and method were introduced based on the theories of rock mechanics and hydraulic impact. The key parameters, including drilling radius and impact distance, were researched to reveal the stress behavior during HDIHT process. The Von Mises equivalent stress and its principal stress components were analyzed, and the breaking mechanism of HDIHT was also discussed. The simulation results show that, to ensure the effectiveness of “secondary breaking” caused by drilling hole free surfaces, the impact distance should not exceed 200 mm, and the optimal drilling radius was about 35 mm.

In order to solve the problems of high knowledge forgetting rate and less continuous use in engineering drawing course for college engineering students, a continuous learning implementation way "learning through racing" is put forward to continue classroom learning, and the practical continuous learning modes for engineering drawing course are developed. Taking advanced drawing contest as an opportunity, the platform of knowledge continuity and ability raise for the students is established. After series of practices such as giving graphics lectures, carrying on rapid drawing training and setting up long-term competitive "collaborative learning" mechanism, students can well master advanced drawing skills and develop innovation design ability. Practice shows that "learning through racing" is a good way to reserve talents for the discipline competitions, innovation projects and researches in university. Keywords—engineering drawing, graphics education, continuous learning