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A high-quality brake material was developed by using different rare earth oxide modified resin-based brake materials and designing the composite material through an orthogonal optimization test. The effect of rare earth oxide on the properties of the resin-based brake material, such as the friction and wear, thermal decay resistance, and recovery, was explored using the constant-speed friction test, Chase friction test and worn surface morphological observation. The results show that rare earth lanthanum oxide can be added to improve the friction and wear properties of the brake material compared to cerium oxide and yttrium oxide. At 100-350°C, the friction coefficient of the developed brake material fluctuates in the range of 0.40-0.50, and the material has high friction coefficient, good thermal decay resistance and favourable wear resistance. The friction coefficient of the optimal formulation can reach the GF level, so its tribological properties are very good and better than the brake pads of automobiles at home and abroad. [ABSTRACT FROM AUTHOR]

Highlights • The low-cycle fatigue behavior of Cr18Mn18N0.6 austenitic steel is studied under strain controlled condition. • Cyclic softening that is affected by the ratio of tensile strength over yield stress is found. • Relationships such as stress-life and strain-life are analyzed with theoretical equations. • Dislocation structures with twins during fatigue test are observed via transmission electron microscopy. • Cr18Mn18N0.6 austenitic steel possesses a higher low-cycle fatigue resistance compared with conventional steel alloys. Abstract Low-cycle fatigue characteristics (e.g. cyclic stress-strain curves, strain-life curves, stress-life curves, and transition fatigue life) of austenitic stainless steel Cr18Mn18N0.6 used for supercritical turbogenerator retaining rings were studied under an axial strain controlled condition with total strain amplitudes ranging from 0.005 to 0.0085 at working temperature 100 °C. Cr18Mn18N0.6 was found to be cyclic softening during low-cycle fatigue with the extent and rate of cyclic softening increasing with strain amplitude. Stress amplitude decreased more rapidly for larger applied total strain amplitude. The transition fatigue life of Cr18Mn18N0.6 was found to be about 2177 cycles. Fatigue crack initiated from a relatively flat zone at the specimen surface due to persistent slip band and surface roughening. Cr18Mn18N0.6 austenitic stainless steel was found to possess a high low-cycle fatigue resistance compared with conventional steel alloys like 304 stainless steel. [ABSTRACT FROM AUTHOR]

Radius and area function of a spherical indenter are calibrated by performing spherical nanoindentation tests on fused silica with known properties. The spherical indenter is made of ruby with a relatively large radius of 200 μm in nominal value. Hertzian relation was found to be successful in characterizing radius of spherical indenter under purely elastic deformation condition. Oliver and Pharr's method is dependent on the measurement accuracy of residual displacement, which cannot be measured within acceptable precision under very little plastic deformation with values of residual displacement being only several nanometers. Area function calibrated with Oliver and Pharr's method on a brittle material like fused silica was found to be smaller than true value, leading to measured elastic modulus larger than true value. A softer material that can produce sufficient plastic deformation with large residual displacement is recommended as the standard material for area function calibration. [ABSTRACT FROM AUTHOR]

Scaling relationships among indentation variables such as the maximum indentation displacement, contact depth, the ratio of load over contact stiffness, and the ratio of permanent displacement over the maximum displacement were investigated via Berkovich indentation of fused silica. Load-displacement curves were characterized by power-law functions for both loading and unloading. The power exponents can be assumed to be constant for loading and unloading. Hardness, elastic modulus, and yield stress were measured to be 9.8 GPa, 73.3 GPa, and 5.5 GPa, respectively, for fused silica that can be assumed to be elastic-perfectly plastic. The empirical algorithm for estimating yield stress was verified for fused silica. The experimental results accorded well with theoretical prediction and dimensional analysis. The expressions obtained can be used to check indentation data, and general implications of the relations are discussed. [ABSTRACT FROM AUTHOR]

To study the effect of solid body contact deformation on the real contact area, various models are established. These contact models include a contact model between an elastic rough solid and a rigid flat one (E-R model), an elasto-plastic rough solid and a rigid flat one (P-R model), an elasto-plastic rough solid and an elastic flat one (P-E model), an elasto-plastic rough solid and an elasto-plastic flat one (P-P model). The effects of thermo-mechanical coupling and the heat flux coupling are considered in the model which is solved by ABAQUS software. The results show that the real contact area is not only determined by the normal load, but also affected by the contact deformation mode of solid body. The real contact area from the purely elastic model (E-R model) is much smaller than that from the other elasto-plastic model. But the real contact area obtained from the P-R model is the largest. No matter what kind of the solid body contact deformation is, at the moment of the abrupt change of sliding speed and of the hot spotting coming into being, the real contact area increases noticeably, and then varies in a small range during the constant frictional sliding process. [ABSTRACT FROM PUBLISHER]

Molecular and density distributions of the lubricant, pentaerythritol tetraheptanoate (PEC7), confined to a nanogap were investigated using molecular dynamics (MD) simulations at various temperatures, initial film thicknesses and pressures. All of the simulated film thicknesses were less than 10 nm. The PEC7 molecular orientation and density profiles were analyzed, and the simulated densities were compared with empirical bulk fluid densities. The results show that the PEC7 atoms tend to form two or three layers near every confining wall, but the PEC7 molecules orient randomly throughout the film. The lubricant density profiles are found to fluctuate frequently, and the distances between the layers of lubricant atoms are irregular. Furthermore, the equivalent density is lower for films with a thinner initial film at the same pressure and temperature, but the compressibility is similar for films with different initial film thicknesses. The simulated densities with an initial film thickness of 9.32 nm are in agreement with the values obtained from the Tammann–Tait equation, with deviations less than 5%. The MD simulation can not only predict the bulk compressibility of the lubricant but also provide information on the density and molecular distribution within a thin film, which cannot be obtained from experiments. [ABSTRACT FROM AUTHOR]

Dual tree complex wavelet transform (DT-CWT) exhibits superiority of shift invariance, directional selectivity, perfect reconstruction (PR), and limited redundancy and can effectively separate various surface components. However, in nano scale the morphology contains pits and convexities and is more complex to characterize. This paper presents an improved approach which can simultaneously separate reference and waviness and allows an image to remain robust against abnormal signals. We included a bilateral filtering (BF) stage in DT-CWT to solve imaging problems. In order to verify the feasibility of the new method and to test its performance we used a computer simulation based on three generations of Wavelet and Improved DT-CWT and we conducted two case studies. Our results show that the improved DT-CWT not only enhances the robustness filtering under the conditions of abnormal interference, but also possesses accuracy and reliability of the reference and waviness from the 3-D nano scalar surfaces. [ABSTRACT FROM AUTHOR]

Abstract: Partner selection is a major issue in the formation of a virtual enterprise. In practice, in the partner selection process, the information about the candidates and their performances are incomplete and uncertain. Vague sets theory is one of the methods used to deal with uncertain information. In this paper, a new method based on vague sets is proposed to deal with the partner selection problem in the formation of a virtual enterprise while the factors of satisfaction degree, due date, cost and the precedence of tasks are taken into account. On the basis of the agreement index of satisfaction degree, the formulated partner selection problems are interpreted so as to maximize the minimum agreement index. To solve the problem, an improved particle swarm optimization (PSO) algorithm is proposed. Finally, the simulation of a numerical example demonstrates that the method is effective. [Copyright &y& Elsevier]

The main focus of current research in polymeric matrix brake composites is on searching out a replacement for copper, which has been recently proved to be a hazard to human health and the environment. In this paper, rare earth lanthanum oxide was explored for the replacement of copper in composites. The mechanism of the role of lanthanum oxide in brake composites to replace copper was analyzed. Four series of polymeric matrix brake composites with various amounts of copper (15, 10, 5 and 0 wt %) and rare earth lanthanum oxide (0, 5, 10 and 15 wt %) were developed, in which the copper was gradually replaced by lanthanum oxide in the formula. These series were characterized in terms of physical, thermo-physical and mechanical properties. The results show that lanthanum oxide can be successfully used as a replacement for copper in brake composites. Brake composites with 15 wt % lanthanum oxide that are copper-free are considered optimal, where tribo-properties are considered best. Compared with the addition of copper in brake composites, lanthanum oxide is more conducive to the formation of compacted friction films and transfer films, which is beneficial to the tribological properties of the brake composites. The addition of La2O3 to the brake composites can cause the reaction between La2O3 and Al2O3 to form LaAlO3, and the reaction between Al2O3 and BaSO4 can produce Ba18Al12O36 and Al2SO4 during the friction and wear processes, which can effectively improve the tribological properties of the brake composites at elevated temperature. This research was contributive to the copper-free, metal-free and eco-friendly brake composites. [ABSTRACT FROM AUTHOR]

In this work, a new and effective treatment on bamboo fiber (BF) is presented, and its effect on the interfacial bonding properties of the BF/resin matrix was studied. The interfacial functionary mechanism of rare earth solution (RES) modification to improve the interfacial bonding properties between BF and the resin matrix was analyzed. The hardness and elastic modulus of the interfacial zone between BF and the resin matrix were measured using nanoindentation. Fourier-transform infrared spectroscopy (FT-IR) was used to analyze the change in the surface functional group of BF in the modification process. The surface chemical composition of BF before and after the modification was characterized by X-ray photoelectron spectroscopy (XPS). The results show that the RES modification significantly increases the hardness and elastic modulus of BF and its interfacial zone with the resin matrix. The hydroxyl concentration on the surface of RES-treated BF decreases, which reduces the hydrophilicity of BF. Rare earth ions react with oxygen in the hydroxyl group at the C2 position in the glucosylic ring of cellulose. The RES-modified BF bonds with the resin matrix to form a rare earth complex, which significantly enhances the interfacial adhesion between BF and the resin matrix. [ABSTRACT FROM AUTHOR]

Microscratch tests were carried out on polyamide (PA) and polypropylene (PP) by Berkovich indenter to study influence of sliding velocity on microscratch response of carbohydrate polymers. Both penetration depth and residual depth decrease nonlinearly with the increase of sliding velocity. Elastic deformation is dominant in the total deformation during scratching of polymers. Both residual and contact scratch widths decrease nonlinearly with sliding velocity. The elastic recovery rate increases with sliding velocity. Both scratch hardness and lateral hardness increase nonlinearly with sliding velocity. Scratch hardness also increases nonlinearly with the increase of strain rate due to strain rate hardening effect. Scratch friction coefficient of PA decreases with increasing sliding velocities, and can be regarded to be constant under large sliding velocities. Nevertheless, scratch friction coefficient of PP increases with sliding velocity. Residual scratch grooves, scratch friction coefficient, and lateral force under different sliding velocities can be used to reveal the different friction mechanisms of PA and PP. • Microscratch responses of two carbohydrate polymers were investigated by Berkovich indenter. • Strain rate sensitivity was investigated by adjusting sliding velocity. • Friction mechanisms of two polymers were compared. • Effects of sliding velocity on scratch variables were quantified under different normal loads. • Friction coefficient, residual groove, and lateral force can be used to study friction mechanism. [ABSTRACT FROM AUTHOR]

Cu-free resin-based brake material filled with waste foundry resin-bonded sand (waste sand) was prepared using the hot-pressing method. The changes in the physical and chemical properties of Cu and waste sand during braking were investigated, and their role in resin-based composites was discussed. The effects of the content of waste sand on the hardness, impact strength, indentation hardness, elastic modulus, friction coefficient, wear rate, micro-scratch friction coefficient, scratch depth, residual depth, and wear mechanism of resin-based brake material were investigated. Cu-contained composites generate Cu 2 O when braking at high temperatures, which adversely affects the friction and wear properties. Compared to Cu, waste sand was found to be more favorable for the overall friction and wear properties of resin-based composites. This suggests that waste sand can be used as a substitute for Cu in brake material. Waste sand is beneficial for improving the friction coefficient and stability of brake material through the formation of a friction layer. This layer can significantly impact the wear mechanism of brake material, particularly at high temperature (250–350 ℃). The brake material with 10–15% waste sand indicates excellent heat-fade resistance. • Waste foundry sand have been successfully replaced copper in brake material. • The role of waste foundry sand and copper in brake material were comparatively studied. • The effects of waste sand on mechanical and tribological properties of brake material were investigated. • The brake material containing 10–15% waste foundry sand show excellent heat-fade resistance. [ABSTRACT FROM AUTHOR]

• Pop-in or serrations cannot be detected at large loading rates. • Indentation hardness decreases with a constant elastic modulus under small loads. • Fracture toughness can be obtained from the total indentation energy. • Area of shear band scales with contact and residual areas. • Scaling relationships among indentation variables of Zr-based BMG were quantified. Berkovich nanoindentation experiments were conducted on Zr 55 Cu 30 Al 10 Ni 5 bulk metallic glass under a constant loading rate. Indentation hardness decreased linearly with contact depth, which defied the direct application of conventional indentation size effect model for crystalline material. Elastic modulus remained invariant under small loads, but decreased linearly under large loads. The scaling relationships between indentation variables such as contact depth, permanent depth, the maximum indentation displacement, plastic energy, the total work of indentation and their ratios were investigated. The area of shear band circle, the projected contact area at the maximum load, and the residual projected area were all found to be proportional to one another. A new methodology to determine fracture toughness was proposed based on the total work of indentation, provided that the critical indentation displacement at the onset of fracture corresponds to zero value of elastic modulus extrapolated from curve fitting. [ABSTRACT FROM AUTHOR]

Rockwell C diamond indenter with a spherical tip of radius of 108 μm was used to slide on bulk polycarbonate under linearly increasing normal load from 5 mN to 20 N in order to investigate deformation and damage of ductile polymers during scratching. The peak value of the ratio of residual depth over penetration depth corresponds to a critical normal load, which can be used as the piecewise point for the subsection functions describing variation of tangential load, penetration depth and residual depth with normal load. The true adhesion interfacial friction coefficient was found to be 0.3 for contact between PC and diamond by three-dimensional model. Residual groove widths were found to be proportional to the square root of normal load, and provided useful information to characterize the radius of spherical tip. Values of fracture toughness of PC obtained by scratch-based methodologies under sufficiently large normal loads associated with brittle fracture and crack plane, are in excellent agreement with literature values. The material is under triaxial compressive stress state, making the flow and shear stresses much larger than the ones for uniaxial tensile test. • True adhesion friction coefficient can be obtained by three-dimensional model rather than two-dimensional model. • Fracture toughness of polycarbonate can be measured by scratch-based methodologies. • Scratch-based approaches of assessing fracture toughness of PC are only applicable under large loads. • The radius of spherical tip can be characterized by residual scratch groove widths. • Flow and shear stresses during scratching are larger than the ones for uniaxial tension. [ABSTRACT FROM AUTHOR]

Fracture toughness can be measured by microscratch test from objective force and depth measurement, which is much convenient than indentation approach and conventional means, since initial notch or pre-crack is not required. Micro-scratch test was conducted on copper under a spherical probe of radius 105 μm and constant applied normal load with the aim of characterizing fracture toughness of copper by sliding technique with a sphere. Scratch variables such as normal load, lateral load, friction coefficient, and penetration depth were analyzed, and different methodologies for calculating fracture toughness were compared. Linear elastic fracture mechanics was found to be inapplicable to scratch of elastic-plastic material with sufficient plasticity under a spherical probe, while energetic size effect law can be successfully applied to characterize fracture toughness by microscratch test with a sphere abrading metallic material. • Fracture toughness of copper was obtained from scratch test with a spherical indenter. • Correlations among scratch variables for a sphere sliding on copper were examined. • Spherical indentation and scratch test with a spherical indenter were compared. • Different methodologies for computing fracture toughness by scratch test were compared. • The energize size effect law is applicable to characterize fracture toughness of metallic material by scratch test. [ABSTRACT FROM AUTHOR]

Micro-scratch tests have been carried out on borosilicate K9 glass using a Rockwell C diamond indenter with a spherical tip radius 105 μm in order to study deformation/damage regimes and microcracking patterns of K9 glass with increasing normal load. The abrupt changes of test data together with optical microscopy observation can be used to determine three transition loads corresponding to initiation of sub-surface median crack, onset of surface ring crack, and lateral cracks reaching the surface, respectively. Based on linear elastic fracture mechanics, fracture toughness obtained from scratch test under a low driving speed and a suitable fitting range of nominal size is found to be 0.85 MPa•m1/2 for K9 glass, which is close to 0.82 MPa•m1/2 obtained from Vickers hardness technique, making micro-scratch a powerful means to assess fracture toughness of material, and opening new application of scratch test as a quantitative method. [ABSTRACT FROM AUTHOR]

Lateral-force microscopy is a powerful tool to study the frictional properties of two-dimensional materials. However, few works distinctly reveal the correlation between the tip radius with the tip–sample distance and the frictional properties of the two-dimensional (2D) materials. We performed molecular-dynamics simulations to study the atomic-scale friction of a typical two-dimensional single-layer molybdenum disulfide (SLMoS2). The effects of tip radius and tip–sample distance on the frictional properties were analyzed and discussed. The frictional force–sliding-distance curves show typical stick–slip behaviors, and the periodicity can be used to characterize the lattice constants of SLMoS2. Sub-nanoscale stick-slip movements occur in one-lattice sliding periods along with only the armchair (AC) direction and only when the tip radius is smaller than 3 Å with 1.47 Å tip-sample distance. At the same tip–sample distance, a smaller tip can provide a more detailed characterization and higher-precision frictional properties of SLMoS2. A larger tip is capable of providing comparative frictional properties of SLMoS2 at a proper vertical tip–sample distance, compared with the small tip. [ABSTRACT FROM AUTHOR]

The single-layer molybdenum disulfide (SLMoS2) nanosheets have been experimentally discovered to exist in two different polymorphs, which exhibit different electrical properties, metallic or semiconducting. Herein, molecular dynamics (MD) simulations of nanoindentation and uniaxial compression were conducted to investigate the phase transition of SLMoS2 nanosheets. Typical load–deflection curves, stress–strain curves, and local atomic structures were obtained. The loading force decreases sharply and then increases again at a critical deflection under the nanoindentation, which is inferred to the phase transition. In addition to the layer thickness, some related bond lengths and bond angles were also found to suddenly change as the phase transition occurs. A bell-like hollow, so-called residual deformation, was found to form, mainly due to the lattice distortion around the waist of the bell. The effect of indenter size on the residual hollow was also analyzed. Under the uniaxial compression along the armchair direction, a different phase transition, a uniformly quadrilateral structure, was observed when the strain is greater than 27.7%. The quadrilateral structure was found to be stable and exhibit metallic conductivity in view of the first-principle calculation. [ABSTRACT FROM AUTHOR]

Using numerical simulations, we study the atomic-scale frictional behaviors of monovacancy-defective graphene and single-layer molybdenum-disulfide (SLMoS2) based on the classical Prandtl–Tomlinson (PT) model with a modified interaction potential considering the Schwoebel–Ehrlich barrier. Due to the presence of a monovacancy defect on the surface, the frictional forces were significantly enhanced. The effects of the PT model parameters on the frictional properties of monovacancy-defective graphene and SLMoS2 were analyzed, and it showed that the spring constant of the pulling spring cx is the most influential parameter on the stick–slip motion in the vicinity of the vacancy defect. Besides, monovacancy-defective SLMoS2 is found to be more sensitive to the stick–slip motion at the vacancy defect site than monovacancy-defective graphene, which can be attributed to the complicated three-layer-sandwiched atomic structure of SLMoS2. The result suggests that the soft tip with a small spring constant can be an ideal candidate for the observation of stick–slip behaviors of the monovacancy-defective surface. This study can fill the gap in atomic-scale friction experiments and molecular dynamics simulations of 2D materials with vacancy-related defects. [ABSTRACT FROM AUTHOR]