Contact Damage Research Articles

Enhanced Scratch Performance of Plasma Sprayed Hydroxyapatite Composite Coatings Reinforced with BN Nanoplatelets

In recent years, research on hydroxyapatite (HA) coatings has been driven by the demands of clinical applications. However, the intrinsic brittleness of HA limits its potential in the use for the load-bearing implant. To improve mechanical properties of the HA coating itself, a HA composite coating reinforced with hexagonal boron nitride nanoplatelets (BNNP) was fabricated using plasma spray, and its scratch behavior was investigated in this research. Typical brittle fractures such as microcracks both in and beyond the residual groove and material chipping were observed in the HA coating, while stronger and tougher BNNP/HA coatings exhibited a dominant role in protecting them from scratch damage through resisting plastic deformation and brittle microfracturing. Moreover, easier grain sliding within a splat and splat sliding at the splat boundaries due to the presence of BNNPs, and the nature porosity at different length scales of the as-sprayed HA composite coatings would provide significant self-lubricating effects to reduce the lateral force during scratching and alleviate the contact damage. Therefore, the addition of BNNPs renders HA coating with low scratch friction and enhanced tolerance to surface damage, which is naturally beneficial for the long-term durability and reliability of the implants.

Incomplete contact between a coated elastic substrate and rigid foundation perturbed by a rigid disc

This paper investigates an axisymmetric and frictionless contact problem of a coated elastic substrate pressed onto a rigid foundation with a rigid disc by remoted uniform compressive stress. Such an incomplete contact problem is formulated as a three-parts mixed boundary values problem (MBVP). By means of Hankel transform technique and a new solution derived for a multilayered elastic solid subjected to surface displacement (dislocation), the MBVP is converted to a system of triple integral equations. A series expansion method characterized by expressing the unknown surface displacement as Bessel function series is adopted to solve the triple integral equations. Explicit analytical expressions for contact stress, resultant contact force and Mode-I stress intensity factor are obtained. The accuracy of the present solutions is verified by comparing to the results available in the literatures for the simple cases of a single layer and a homogeneous half space. Numerical studies are also performed to investigate the contact mechanics of coated material under incomplete contact. Results from this study are valuable for the design of coating to protect engineering machine components against third-body abrasive particles or solid contaminants induced contact damage.

Effects of aging and transformation of anatase and rutile TiO2 nanoparticles on biological phosphorus removal in sequencing batch reactors and related toxic mechanisms

The effect of nanomaterials aging, namely the transformation of comprehensive characteristics after experiencing real or complex environmental behaviors, on their ecotoxicology is still lacking. Moreover, the mechanisms by which NPs influence biological phosphorus (P) removal during sewage treatment require further elucidation. Therefore, we used both pristine and aged anatase (TiO2-A) and rutile (TiO2-R) NPs to investigate the mechanisms by which NPs affect P removal in a SBR. At 0.1 mg/L, the four types of NPs (pristine and aged) had no significant effect on sludge purification after acute (72-h) exposure under simulated sunlight. However, at 50 mg/L—regardless of the crystalline phase of the NPs—SOP and COD removal efficiency dropped steeply to approximately 42.2–82.4 % (p < 0.05) and 69.8–83.3 % (p < 0.05), respectively, especially in the pristine TiO2-NPs groups because of decrease of richness and diversity of genus level of PAOs and enzyme activity of both PPK and PPX, and the sluggish transformation of PHA and glycogen. Aging reduced the ability of NPs toxicity. The toxicity mechanisms of TiO2-NPs included lipid peroxidation and contact damage, or leakage from bacterial cytoplasmic membrane, which are closely related to photooxidation capacity and aqueous solution stability—i.e., nanoscale effects—and the impacts of aging or inclusion.

Flexural strength improvement for structural glass: a numerical study

Glass is generally known as a fragile material. It is sensible to the cracks created from manufacturing or contact damage. The strength of a perfect glass without crack could reach 10 GPa. By mean of strengthening such as thermal tempering, glass can be safely use for building as architectural elements and very limited to the structural elements. The authors have been developing glass strengthening methods and structural design for large scale glass beam. Some influencing factors are considered: material, premature crack effect, geometry of sample and bolt. The mechanical behaviour of glass is modelled as elastic-plastic material, which show significant results in glass-bolt contact problem. The crack length, size and position provide information of a critical angle that allow to govern the crack effect in the beam connection.

THE RESEARCH OF THE RAILWAY RAIL FOR ANALYSIS OF SURFACE INITIATED ROLLING CONTACT FATIGUE CRACKS

Problems. Under the influence of dynamic loading from trains and natural conditions, the railway track deteriorates, characterized by the appearance of defects and residual deformations of the railway track, which lead to accelerated wear and malfunction of other elements of the rail. The appearance of the specified defects, failures and destructions of the elements of the rail grating is associated with the action of additional local stresses arising in the rails of the railway track. On a low-quality track grating with deviations of the parameters of the rail track, when the train is moving, there is an unaccounted interaction of the track and rolling stock with local overload of the interaction elements along the path. As a rule, the unaccounted interaction of track and rolling stock is accompanied by the impact of the wheel and the rail with overloading the contact area. When the impact of the wheel and rail strikes, stresses exceeding the endurance limit occur in the rail head. In this case, the rails are born in the head and begin to develop defects of contact-fatigue origin in the form of horizontal vertical and transverse cracks.The aim of the study. Conducting practical studies of the origin and development of contact-fatigue cracks by wear of the rails in the laboratory.Methods of implementation. An experimental unit was designed and manufactured to investigate the rails for contact damage. The unit is mounted on a mechanical single-cylinder press of the K 2322 model with a nominal force of 16 tons at a nominal stroke frequency of 120 per minute. The bulk of the experimental setup contains a wheel-rail friction unit. The force of clamping the rail to the wheel. Provides a hydraulic system. For testing, a test program was developed, which provides for two-hour tests, after which tests for the presence of defects (micro cracks) on the rail are conducted. Research on the presence of defects is carried out by the method of magnetic powder non-destructive testing.Research results. Studies have shown that contact-fatigue cracks in the rail head occurred after approximately 200 thousand load cycles. This generally coincides with the results presented in other papers, which show the occurrence of similar damage after 190-290 thousand cycles, depending on the properties of rail steel (hardness, surface roughness, etc.).Conclusions. The main cause of the origin and development of contact fatigue defects in the rail head is insufficient contact fatigue strength of the rail steel. For carrying out practical researches in laboratory conditions the methodology was developed, the experimental unit was constructed and made. Experimental studies have shown that the occurrence of defects on the surface of the rail is observed after 200-250 thousand load cycles. With the further increase in the number of load cycles, there is a rapid development of existing contact-fatigue cracks and the formation of new cracks in the contact zone.

The effect of adhesion on axisymmetric contact between a spherical punch and FGM coating

This paper investigated the axisymmetric contact problem of a functionally graded material (FGM) coating by considering the adhesion effect. The Maugis–Dugdale adhesion theory is adopted to describe the adhesion effect between the contact bodies. The Hankel integral transform is applied to obtain the singular integral equations which represent the axisymmetric adhesive contact problem of FGM coating with exponential varying modulus. The impact of the adhesion parameter, gradient index of FGM coating and thickness of coating on the contact behaviour is presented by numerically solving the singular integral equations. The results provide a method to improve the contact deformation and damage by adjusting the gradient of the FGM coating.

Inverse correlations between wear and mechanical properties in biphasic dental materials with ceramic constituents

The objective of this study is to elucidate the interdependence of competing mechanical degradation processes in biphasic dental materials with ceramic constituents in the region of high-pressure occlusal loading. It is hypothesized that wear resistance in this region correlates inversely with basic material parameters (modulus, hardness, toughness, strength) evaluated from 'standardized' test specimens. Ball-on-flat wear tests in simulation of oral function are used to quantify susceptibility to protracted sliding contact damage. Wear rates for this class of dental material tend to increase with quasistatic parameter values, so the latter do not provide a reliable guide to longevity. The generation of severe-wear facets involves cumulative quasiplastic deformation and microcrack coalescence at the grain level. It is implied that interplay between wear and fracture mechanisms should be an important consideration in future microstructural design of dental ceramics, especially in the quest to balance durability against esthetics.

Numerical analysis for investigating wheel-rail impact contact in a flange bearing frog crossing

The transition of wheel-rail contact point between the wheel tread and wheel flange in a flange bearing frog crossing (FBFC) is more complex than in a common crossing, which causes severe frictional rolling contact behavior and wheel-rail dynamic impact. This paper presents an analysis of the transient wheel-rail frictional rolling impact contact using an explicit finite element model of the dynamic interaction between the wheel and FBFC. This study adopts measured wheel geometry and an elastic-plastic material model for the simulations to provide an comprehensive understanding of the transient contact behavior of wheel-FBFC impacts. Each simulation calculates the evolution of the wheel-rail contact force, the distribution of micro-slips, and the stress during the wheel-FBFC impact. Then the contact damage mechanism is investigated and evaluated with the Zobory frictional wear model and “Layer” rolling contact fatigue model. The simulation results show that the irregular structure of the flange bearing frog crossing causes significant wheel-rail dynamic interaction, with the maximum wheel-rail force occurring in the bearing flangeway. The ratio of the tangential contact force to the normal contact force can be exacerbated by the geometric discontinuity of the crossings during impact. The main failure mechanism for different sections in the flange bearing frog crossing is different.

The effect of cross-section shape on deformation, damage and failure of rock-like materials under uniaxial compression from both a macro and micro viewpoint

The mechanical properties of rock-like materials always attract the interest of many researchers. In this paper, we study the influence of specimen cross-section shape on uniaxial compressive strength as well as their deformation, damage and failure characteristics by uniaxial compression tests. The diameter and height of circular cross-section specimens are 50 and 100 mm, respectively, and the height and cross-sectional area of other specimens are equal to that of circular cross-sectional ones. Simulation and experimental results show that the cross-sectional shape has little effect on uniaxial compressive strength. Moreover, the effect on other mechanical properties is also very limited before the peak strength, such as stress–strain curve, rotation and motion of particles, contact damage and energy evolution of particles; however, it gradually becomes obvious after the peak strength. This is a very important feature, which affects the macroscopic form of failure of specimens and reflects the difference between failure surfaces. The shapes of failure surfaces obtained from numerical simulations are quite similar to the experimental results, which verify the reliability of numerical simulation results. Finally, the achievements can serve as a reference for related engineering issues.

The structural characteristics and contact loading behavior of gas powder laser clad CoNiCrW coating

The microstructure, phase composition, microhardness and micromechanical properties of the laser clad Co-31.8Ni-22.6Cr-4.1W coating, as well as its contact endurance under contact-fatigue loading according to the scheme of the pulsing non-impact “sphere-to-surface” contact, have been studied. It has been found that the phase composition of the coating is γ + CoB + Cr23C6 + Cr(B,C), with the size of the strengthening phases (chromium carbides and carboborides) ranging between 1 and 10 µm. The average microhardness of the coating surface is 810 HV0.1. The process of fatigue degradation of the coating is characterized by a pronounced periodicity, with alternating periods of increasing size of contact damages and periods when it remains unchanged. Using the microindentation data, the ability of the Co-31.8Ni-22.6Cr-4.1W coating to resist mechanical contact action has been estimated and compared with two laser clad NiCrBSi coatings. It has been shown that the microindentation method (single loading) can be used for estimating and comparing the ability of laser clad coatings from alloys of different systems to withstand repeated contact loads if the coatings have identical size of the strengthening phases.

Double-layer gradient MoSi2-borosilicate glass coating prepared by in-situ reaction method with high contact damage resistance and interface bonding strength

High emissivity coating is an important part of spacecraft thermal protection system. MoSi2-borosilicate glass coatings prepared by the in-situ reaction method showed excellent thermal endurance and oxidation resistance. However, radial cracks were prone to appear under external forces due to high cohesive of in-situ reaction dense coatings, and few studies focused on the mechanical properties of gradient coatings. In this study, a double-layer gradient MoSi2-borosilicate glass coating with a porous interface layer and a dense surface layer was prepared on mullite fibrous insulation tiles by in-situ reaction method. The double-layer gradient coating was compared with a mono-layer dense coating and a high-density gradient coating (another gradient coating with higher interface layer density) with reference to microstructure, contact damage resistance, interface bonding strength and thermal shock resistance. Compared with mono-layer dense coating and high-density gradient coating, double-layer gradient coating showed higher bearing capacity and avoided radial crack initiation and propagation in Hertzian indentation test. Besides, the double-layer gradient coating endured the most thermal shock cycles between 1500 °C and 20 °C and presented substrate fracture instead of interface fracture. In addition, double-layer gradient coating and high-density gradient coating possessed much higher interface bonding strengths than mono-layer dense coating. The total emissivities of three coatings were all greater than 0.87. The porous interface in double-layer gradient coating presented the advantages in enhanced mechanical and thermal compatibility between the in-situ reaction dense coating and substrate through reducing elastic modulus and thermal expansion coefficient differences.

Structural Orientation and Anisotropy in Biological Materials: Functional Designs and Mechanics

AbstractBiological materials exhibit anisotropic characteristics because of the anisometric nature of their constituents and their preferred alignment within interfacial matrices. The regulation of structural orientations is the basis for material designs in nature and may offer inspiration for man‐made materials. Here, how structural orientation and anisotropy are designed into biological materials to achieve diverse functionalities is revisited. The orientation dependencies of differing mechanical properties are introduced based on a 2D composite model with wood and bone as examples; as such, anisotropic architectures and their roles in property optimization in biological systems are elucidated. Biological structural orientations are designed to achieve extrinsic toughening via complicated cracking paths, robust and releasable adhesion from anisotropic contact, programmable dynamic response by controlled expansion, enhanced contact damage resistance from varying orientations, and simultaneous optimization of multiple properties by adaptive structural reorientation. The underlying mechanics and material‐design principles that could be reproduced in man‐made systems are highlighted. Finally, the potential and challenges in developing a better understanding to implement such natural designs of structural orientation and anisotropy are discussed in light of current advances. The translation of these biological design principles can promote the creation of new synthetic materials with unprecedented properties and functionalities.

Effect of Inhomogeneity of FGM Coating on Contact with Adhesion under the Axisymmetric Indenter

The contact with adhesion between the FGM coating and axisymmetric indenter is probed into in the present paper. Coating is made of FGM with linear varying modulus. Poisson’s ratios of coating and substrate are chosen to 1/3. The Maugis-type adhesive model is used to describe the adhesive interaction in the adhesion zone. According to the basic equations for axisymmetric problem, the controlling singular integral equations of the contact problem with adhesion are gained by making use of Hankel integral transformation. These integral equations are solved by applying a numerical collocation technique. The results show that the contact damage and deformation on the coating surface can be reduced by adjusting the inhomogeneity of the coating.

Contact pressure in misaligned spline couplings

Spline couplings are increasingly being studied because of their growing use, particularly in the field of electric cars. Due to clearances, geometrical obligations and elastic deformation, spline couplings operate mainly in slightly misaligned situations. From these kinds of situations, problems could appear such as vibrations or contact damages. The purpose of this article is to analyse the misalignment of splined couplings and the effects it induces. In order to identify behavioural trends, this work offers analytical approaches for estimating contact pressures in spline connections. In the chosen approach, the simplifying hypotheses necessary for equations are detailed as well as the various analytical modelling. Despites these assumptions, comparisons with pure numerical approaches illustrates the quality of analytical approach adopted in this paper. This method of modelling contact pressure allows the identification of the main mechanical factors to be identified including stiffness, thus deceasing problems due to misalignments.

Microstructures and intrinsic lubricity of in situ Ti3SiC2–TiSi2–TiC MAX phase composite fabricated by reactive spark plasma sintering (SPS)

MAX phase composite Ti3SiC2–TiSi2–TiC based on the Tin+1SiCn system was synthesized by spark plasma sintering (SPS) under vacuum sintering conditions. The microstructural evolution upon synthesis and Vickers indentation contact damage were characterized using scanning electron microscopy (SEM) and optical microscopy (OM). Tribological behaviour of the SPSed MAX phase composite was investigated under dry sliding ambient conditions for evidence of intrinsic lubricity as well as to understand the influence of second phase TiC particles on the wear behaviour of this composite system. Further, the underlying wear mechanisms was elucidated via detailed analyses of the worn surfaces using Raman spectroscopy, SEM-EDS and transmission electron microscopy (TEM). Exhaustive analyses of the worn surface revealed evidence of solid lubrication. Transition in friction and wear is attributed to change in wear mechanism from tribo-oxidative to deformation-induced wear due to the disruption of the tribofilm architecture.

ВІБРАЦІЙНА НАВАНТАЖЕНІСТЬ ТА РУЙНУВАННЯ ЗУБЧАСТИХ ПЕРЕДАЧ ВЕРТОЛІТНИХ РЕДУКТОРІВ

Роглянута вібраційна навантаженість високошвидкісних зубчастих передач вертолітних редукторів на злітному і крейсерському режимах експлуатації, розподіл навантаження між зубцями в зоні багатопарного зачеплення, динамічні навантаження в зачепленні зубчастих коліс та їх пошкоджуваність і руйнування.

Investigation on Wheel-Rail Contact and Damage Behavior in a Flange Bearing Frog with Explicit Finite Element Method

Flange bearing frogs are designed to provide continuous rolling surfaces for trains traveling on the through line, but the interaction between wheel and rail in a diverging line is more complex than that for a common crossing, especially including flange bearing mode and multipoint contact during the transition. The wheel load will be transited from tread to flange and back to tread, which will intensify the wheel-rail interaction. In this paper, a numerical procedure is presented for the analysis of wheel-rail rolling contact behavior and damage prediction for the flange bearing frog. The three-dimensional explicit finite element (FE) model of a wheel passing the flange bearing frog is established to obtain the dynamic wheel-rail interaction in both the facing and the trailing move. The evolution of contact forces, the distribution of adhesion-slip regions, and shear surface stress and microslip at the contact patch are revealed. Then, the competition relationship between RCF (rolling contact fatigue) and wear of a flange bearing frog is analyzed. The results of numerical simulations can contribute to an understanding of the mechanism of the transient rolling contact behavior and provide guidance in design optimization for flange bearing frogs.

Preparation and structure control of a scalelike MoSi2-borosilicate glass coating with improved contact damage and thermal shock resistance

The scalelike coatings with MoSi2 as emittance agent, flake fused quartz as coarse fillers, silica sol as dispersive medium of coating slurry, were prepared on rigid mullite fibrous ceramics to avoid fatal radial cracks and improve thermal shock resistance via combining slurry method with sol-gel method. And the particle size distribution of fused silica was changed to get different crack structure in scalelike coatings. Microstructure and phase composition of the coatings with different crack structure were investigated comprehensively. Contact damage resistance, thermal shock resistance and infrared radiating property were also studied. The results showed that only the coatings with mixing large and small particles of fused silica as coarse fillers could form crack network. The scalelike coatings with crack network went through 25 thermal cycles between 1500 °C and room temperature without peeling and spalling, and the bonding strength did not decrease after test. The scalelike structure with crack network also avoided radial cracks and exhibited some softness and less stiffness in Hertzian indentation test. The emissivity of coatings with different crack structure were all higher than 0.85; and the coatings with lower proportion of crack areas had higher emissivity.

Stretchable Parylene-C electrodes enabled by serpentine structures on arbitrary elastomers by silicone rubber adhesive

The delicate serpentine structures are widely used in high-performance stretchable electronics over the past decade. The metal interconnects encapsulated in biocompatible polymer Parylene-C film is a superior choice for long-term implantation in vivo, especially as neural interface to acquire electrophysiological signals or apply electrical stimulation. To avoid the physical contact damages from the neural tissues such as the brain or peripheral nerves, serpentine interconnects are utilized as stretchable electrodes and usually bonded to the soft elastomer substrate. The adhesion strength between the serpentine interconnects and the elastomer substrate becomes a considerable issue to ensure reliability and structural integrity. In this paper, the stretchable Parylene-C electrodes can be transfer printed onto arbitrary elastomer substrates by a thin layer of silicone rubber adhesive with low modulus for electrocorticogram (ECoG) recording. Mechanical simulation of serpentine structures consisting of same periodic arcs and different straight segments is investigated by uniaxial stretching. Then, the elastic stretchability of serpentine electrodes is further studied by simulation and experiments. After 5000 repetitive stretching cycles, the electrochemical impedance of microelectrodes remains in steady states. These results prove that the silicone rubber adhesive facilitates the interfacial bonding in the structure of stretchable electrodes as the compliant and reliable neural interface.

Enhancement of methanogenic activity in anaerobic digestion of high solids sludge by nano zero-valent iron

This study evaluated the effects of nano zero-valent iron (NZVI, 50 nm) on anaerobic digestion of high solids sludge (10 ± 0.5%). Compared to the blank group without NZVI, the group with NZVI at all levels (10, 20 and 30 mM) played a driving role in methane production. The maximal methane production was increased by 37.5% in the group of 30 mM NZVI. The dynamic changes of hydrogen content and VFAs showed that rapid hydrogen evolutional corrosion of NZVI made lower hydrogen partial pressure in the later stage, which was more conducive to conversion of propionic acid. The microscopic analysis indicated that NZVI could flocculate and adsorb on the extracellular polymeric substances (EPS) around the anaerobic microorganisms, protecting most active microbial cell membrane from contact damage. On the other hand, some decaying microbial cells membrane could be destroyed by NZVI and intracellular substances would be released due to the reduction of EPS.