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Skin can be damaged by the environment easily. Skin cream is an effective and rapid way to moisten the skin by changing the skin surface properties. Rat skin and pig skin are common animal models for studies and were used as skin samples in this study. The nano- and macroscale friction and durability of damaged skin were measured and compared with those of virgin (intact/undamaged) skin. The effect of skin cream on friction and durability of damaged and virgin skin samples is discussed. The effects of velocity, normal load, relative humidity and number of cycles were studied. The nanoscale studies were performed by using atomic force microscope (AFM), and macroscale studies were performed by using a pin-on-disk (POD) reciprocating tribometer. It was found that damaged skin has different mechanical properties, surface roughness, contact angle, friction and durability compared to that of virgin skin. But similar changes occur after skin cream treatment. Rat and pig skin show similar trends in friction and durability.

Tactile perception is essential for humans to perceive the world, and it usually results in mechanical responses from the finger. In this study, a nonlinear, viscoelastic, and multilayered finite element model of the finger was developed. The relationship between the mechanical responses within the finger and tactile perception while the finger scanned different surface textures was studied. The results showed that the sensitivity of tactile perception is affected by the peak value of von Mises stress, which is itself determined by the shape and density of a given texture. The von Mises stress varies periodically with time, and this variation depends on the periodicity of the texture. Displacement signals around Pacinian corpuscles have periodic variation. The period of displacement decreases as the density of the texture increases. The spectral centroid increases as the spacing of the texture decreases. The related mechanisms are discussed in this article.

The effect of displacement amplitude on fretting fatigue behavior of steel wires in low cycle fatigue at two cyclic strain levels was investigated. Evolutions of normalized tangential force and morphologies of contact scars were investigated to examine the wear mechanisms. Fretting regime and fretting fatigue life were explored. Acoustic emission technique was utilized to reveal wire failure mechanisms. The results show that an increase of displacement amplitude increases normalized tangential force but decreases the fretting fatigue life. Fretting contact conditions are all mixed fretting regimes. Fretting damage and crack nucleation and propagation accelerate with increasing displacement amplitude.

The stratum corneum is the outermost layer of mammalian skin, serves as a penetration, dehydration, and protection barrier against various environmental hazards. In this article, the microtribological and dynamic micromechanical properties of stratum corneum are studied. The rat stratum corneum is chosen as the animal model. In the microtribological tests, it is found that the coefficient of friction of stratum corneum decreases with the increasing of normal load and a linear viscoelastic contact model of stratum corneum is developed. In the dynamic micromechanical tests, the results show that there are initial maxima in storage ( E′) and loss ( E″) moduli with both increasing of frequency and penetration depth. After the maxima, there are marked decreases in storage and loss moduli with increasing of frequency and penetration depth. It is suggested that this decrease is due to a water gradient across the stratum corneum. In addition, although the loss modulus is less than the storage modulus, there is a gradual increase in their ratio with increasing of displacement into stratum corneum. This indicates a shift toward more viscous behavior. This study provides key stratum corneum tribological and mechanical properties when moving on and penetrating into stratum corneum for the exploitation of drug delivery systems, artificial skin, textile, skin care production, and other studies related to stratum corneum.

PVA-HA-Silk composite hydrogel was synthesized with polyvinyl alcohol (PVA), nano-hydroxyapatite (HA) and natural silk by using the method of repeated freezing and thawing. A series of tests were performed to study water content, stress relaxation behavior, elastic modulus, and creep characteristics of PVA-HA-Silk composite hydrogel. Orthogonal experimental design method was used to analyze the influence degree of PVA, HA and silk (three kinds of raw materials) on mechanical properties and water content of the PVA-HA-Silk composite hydrogel to select the best material ratio according to their overall performance. The results demonstrate that the mass percentage of PVA has the greatest impact on the water content, followed by HA and silk. Compression stress-strain variation of PVA-HA-Silk composite hydrogel presents a nonlinear relationship, which proves that it is a typical viscoelastic material. Comparing the mechanical properties of 16 formulas, the formula of PVA-HA-silk composite hydrogel with mass percentage of PVA 15%, HA 2.0% and silk 1.0% is the best.

The effect of various kinematic parameters of mine hoist on fretting parameters of the hoisting rope was investigated and a new fretting fatigue test apparatus was designed. A simulation model of the rope tension was presented to examine the role of various kinematic parameters on the rope tension and tension amplitude during lifting. Ranges of fretting parameters of the rope during lifting with different kinematic parameters were determined. The results show that different kinematic parameters induce different modal shapes of the vibrating systems during lifting, which results in distinct ranges of fretting parameters of the rope.

Fretting corrosion tests of steel wires inside a rope were performed on a self-made fretting wear test rig to understand the fretting corrosion behaviors of steel wires under the environment of alkaline mine water trickling using a simulated alkaline corrosion medium. The results indicate that the corrosion rate of steel wire decreases rapidly and then increases with the increase in the duration of immersion. For late immersion, the corrosion rate tends to be smooth because of the large accumulation of corrosion products. It is also found that the evolution of friction coefficient vs fretting cycles can be divided into five stages. With the increase in the fretting cycles, there is an increase in the weight loss of materials and the evolution processes of damage rate can also be divided into four stages. All the results conclude that interaction of corrosion and wear dominates the fretting corrosion and leads to material loss.

A stiffened cylindrical shell is normally used in refuge chambers of a coal mine. Based on the method of application and shape characteristics of a refuge chamber, we simplified its shell as an orthotropic cylinder. The basic buckling equation of the stiffened cylindrical shell under uniform axial compression was deduced by using a Donnell function. The factors affecting its buckling capacity were studied by theoretical analysis and numerical calculations. The results reveal that the torsional rigidity of the longitudinal stiffener had little effect on the buckling capacity of the shell and that the critical load of an externally stiffened cylindrical shell is higher than that of an internally stiffened cylindrical shell. Keywords: Refuge chamber, Buckling, Axial compression, Stiffened cylindrical shell

The study of topography of wear surface is an effective method to determine the mechanism of material's wear. So, in this article, the process of materials' sliding wear at room temperature was simulated based on the pin-on-disk wear test. The change of three-dimensional surface topography of a specific spot on the sliding wear surface was studied. Then the wear mechanism was analyzed. The results indicated that friction coefficient can reflect the interfacial properties of the wear of materials in real-time. The change of three-dimensional surface topography of a specific spot can directly reflect the change of material's surface structure during the wear process, providing an important experimental evidence for the analysis of material's wear mechanism.

The effect of strain amplitude on fretting–fatigue behavior of steel wires in low cycle fatigue was investigated using a fretting–fatigue test rig which was capable of applying a constant normal contact load. The fretting regime was identified based on the shape of the hysteresis loop of tangential force versus displacement amplitude. The variations of the normalized tangential force with increasing cycle numbers and fretting–fatigue lives at different strain amplitudes were explored. The morphologies of fretting contact scars after fretting–fatigue tests were observed by scanning electron microscopy and optical microscopy to examine the failure mechanisms of steel wires. The acoustic emission technique was used to characterize the fretting–fatigue damage in the fretting–fatigue test. The results show that the fretting regimes are all located in mixed fretting regimes at different strain amplitudes. The increase in strain amplitude increases the normalized tangential force and decreases the fretting fatigue life. The abrasive wear, adhesive wear and fatigue wear are main wear mechanisms for all fretting–fatigue tests at different strain amplitudes. The accumulative total acoustic emission events during fretting–fatigue until fracture of the tensile steel wire decrease with increasing strain amplitude. An increase of the strain amplitude results in the accelerated crack nucleation and propagation and thereby the decreased life.

Severe production conditions in coal mines cause damage and failure problems with the oriented sliding boots of the mechanical shearer. Wear has been an especially vexing problem. Plasma cladding methods were used to study optimized sliding boot design. By cladding the substrate steel the surface may be made of a material more resistant to wear. The iron based alloy Cr 4 MnTi was coated onto a modified 45 steel matrix material in these tests. The results show that the alloy cladding layer is high strength, has high hardness, and is highly resistant to wear. After hardening and tempering, 45 steel substrate has great tenacity so the combined structure meets the performance requirements for the construction of shearer sliding boots.

Fretting wear of carburized titanium alloys was investigated on the universal multifunctional tester (UMT) with the ball-on-flat fretting style under bovine serum lubrication. The tangential load and friction coefficient during the fretting process were analyzed, and the evolution of fretting log during the fretting process was investigated to understand the wear mechanism of the titanium alloy and carburized titanium alloy. Furthermore, the wear scar was examined using a SEM and three-dimension surface profiler. It was found that the friction coefficient of the titanium alloy increased faster than that of carburized titanium alloy in the first stage under serum lubrication, and then remained steady with a similar value in the second stage. The Ft–D curve indicated that there was wear mechanism transition from gross slip to mixed stick and slip. Finally, it was observed that there was a slight damage of the titanium alloy and carburized titanium alloy showed excellent performance during the fretting wear process under serum lubrication. All of the results suggested that carburized titanium alloy was a potential candidate for the stem material in artificial joints.

A highly ordered porous alumina template with pores of 45 nm in diameter was synthesized by a two-step electrochemical anodizing process. The influence of pore-enlargement treatment on the porous structure and tribological properties of the film was investigated, and ultrasonic impregnation technology was applied on it to form self-lubricating surface. The structure of the self-lubricating film and its tribological properties were investigated in detail. It can be concluded that the optimum time of pore-enlargement treatment is 20 min. The diameter of the pores and the surface porosity of the film are about 70 nm and 30%, respectively, while the film maintains the property of its high hardness. Under the same friction condition, the frictional coefficient of the self-lubricating film is 0.18, much lower than that of the anodic aluminum oxide template, which is 0.52. In comparison with the lubricating surface of non-porous dense anodic aluminum oxide template, the lubricating surface fabricated by the ultrasonic impregnation method on the porous anodic aluminum oxide template keeps longer period with low friction coefficient. SEM examination shows that some C60 particles have been embedded in the nanoholes of the anodic aluminum oxide template by the ultrasonic impregnation technology.

Ultra-high molecular weight polyethylene (UHMWPE) has been the most commonly used bearing materials in the total joint replacement. The biodegradation of implanted UHMWPE components has notable influence on wear and fatigue resistance. Although accelerated aging protocols in vitro have been developed to evaluate the oxidation behavior of the UHMWPE materials, the mechanism still remains not accurately understood. Thus, the biodegradation of UHMWPE in simulated body fluid (SBF) was performed for up to 12 months and the chemical structure (i.e. oxidation and crystallinity) and scratch resistance, punch shearing strength, friction and wear behavior of biodegraded UHMWPE samples were investigated in this work. The results provided strong evidence that oxidation degradation significantly reduced the crystallinity and in consequent decreased the wear and scratch resistance of UHMWPE. It was found that the oxygen content on UHMWPE surface increased by almost two times and the crystallinity degree decreased by 16%, resulting in the reduction of scratch coefficient and peak breaking load by 30% and 15%, respectively, after one-year biodegradation. Also, significant wear rate increase up to 6 times for the one-year degraded UHMWPE sample was noticed in this study, and an exponential decay relation for the wear rate of UHMWPE to the crystallinity was identified. A bi-linear behavior of the crystallinity and oxidation index on UHMWPE sample was discovered, which corresponded to the two-stage wearing volume growth of degraded UHMWPE. The preliminary study suggested the necessity of a full-scale biodegradation test for UHMWPE materials including oxidative, hydrolysis and biodeterioration and even dynamic rubbing process. Moreover, it was indicated scratch test as an effective method to evaluate the superficial properties of UHMWPE samples which may be used as an important tool on comparing friction and wear behavior of this material.

Surface texturing has been recognized as a feasible method of surface engineering to improve the lubrication properties of mechanical components. This work focuses on the hydrodynamic lubrication properties of the textured surface with asymmetric microdimples. The validity of the Reynolds equation in asymmetric microdimples is discussed based on theoretical analysis and numerical simulation. The effects of modified Reynolds number, motion directions, and parameters of the microdimple profile are investigated. The following results were obtained: Firstly, the Reynolds equation is invalid under almost all of the general conditions used in experiments and industries. Secondly, the ultimate load-carrying capacity can be taken as a new characteristic parameter to assess the lubrication property of a textured surface. Thirdly, the motion directions have a great effect on the lubrication properties. The positive motion can generate more stable load capacity under all of the modified Reynolds numbers employed, ev...

The failure of steel wire rope mainly resulted from rust, wear or broken of steel wires. Effects of various corrosive mediums (dry friction, three kinds of corrosive solutions) on fretting wear behaviors of steel wires were investigated on the self-made fretting wear rig under varied normal forces (from 10 N to 30 N) and displacement amplitudes (from 5 μm to 200 μm). The fretting running behaviors, wear mechanisms and the effects of different corrosive mediums were analyzed by using scanning electron microscope and X-ray energy spectrum analysis. The results reveal that the fretting running regimes of fretting wear can be determined according to the curves of friction force versus displacement amplitude and damage morphologies. And finally the running condition fretting map (RCFM) was established. It was found that corrosive mediums could affect the friction behaviors, wear mechanisms and RCFM. Compared with the dry friction condition, three corrosive mediums not only transform the boundaries of partial slip regime (PSR)/mixed fretting regime (MFR) and MFR/slip regime (SR) obviously to the smaller displacement amplitudes, but also reduce friction coefficient and increase the materials loss. The fretting wear mechanisms are mainly delamination, abrasive wear and oxidative wear in the three fretting regimes under dry friction, whereas abrasive wear and electrochemical corrosion dominates the wear in three kinds of corrosive solution. It is observed that slight damage appears at the contact edges in PSR, strong plastic deformation accompanied with the damage occurs in MFR, and severer degradation on the wear scars appears in SR.

The article studied the friction and wear properties of UHMWPE when the surface was probed with micro-defect. The results indicated that the friction coefficient decreased when the micro-defect holes were gradually distributed on the friction surface uniformly. That was mainly because the uniform micro-defect holes formed regular texture, increasing the balance of friction and wear. The wear loss of UHMWPE decreased gradually with the increase of the amount of micro-defect holes, and there was a good linear relationship between them. When the friction surface was filled with uniformly distributed micro-defect holes, not only the wear loss decreased, but also wear debris with ideal size distribution was obtained. So, the theoretical and experimental basis was provided for the idea of the surface texturization of artificial arthrosis.

In this article, the basalt fibers were used to fill the UHMWPE because of their outstanding mechanical and tribological performances. The UHMWPE composites with the filler content of 5—20 wt.% were prepared. Then, the mechanical and tribological performances of the composites were tested. Also, the wear mechanism was analyzed. The results indicated that the UHMWPE composites’ impact toughness was decreased when filled with the basalt fibers, but the strength, hardness, and anti-indentation creep of the UHMWPE composites were improved. Under the same experimental conditions, the friction coefficient of the UHMWPE composites filled with basalt fibers was decreased to some extent, and the wear loss of the composites was significantly reduced. The analysis showed that the wear type of the UHMWPE composites was changed when filled with the basalt fibers. So, the wear-resistant performance of the UHMWPE composites was effectively enhanced.

[Purpose] The purpose of this study was to study the correlation of knee range of motion between walking and squatting for young and elderly populations. [Subjects] Sixteen young and eight elderly healthy subjects were recruited for this study. [Methods] Three-dimensional joint motions of each subject were captured while they performed walking and squatting exercises. [Results] Significant differences in the non-sagittal plane knee motions (peak adduction, and peak external and internal rotation) were revealed between the young and the elderly during squatting. Correlations of three-dimensional knee range of motion between walking and squatting were positive and high in all three planes for the young subjects (R(2)=0.70, 0.52, and 0.45, respectively), but not for the elderly subjects (R(2)=0.23, 0.0004, and 0.05, respectively). [Conclusion] We suggest that changes in secondary knee kinematics and poor correlations between walking and squatting for the elderly may result from degeneration of the sensory and neuromuscular systems. It could be injurious for the elderly to perform high flexion activities.

Given that fretting wear causes failure in steel wires, we carried out tangential fretting wear tests of steel wires on a self-made fretting wear test rig under contact loads of 9 and 29 N and fretting amplitudes ranging from 5 to 180 μm. We observed morphologies of fretted steel wire surfaces on an S-3000N scanning electron microscope in order to analyze fretting wear mechanisms. The results show that the fretting regime of steel wires transforms from partial slip regime into mixed fretting regime and gross slip regime with an increase in fretting amplitudes under a given contact load. In partial slip regime, the friction coefficient has a relatively low value. Four stages can be defined in mixed fretting and gross slip regimes. The fretting wear of steel wires increases obviously with increases in fretting amplitudes. Fretting scars present a typical morphology of annularity, showing slight damage in partial slip regime. However, wear clearly increases in mixed fretting regime where wear mechanism is a combination of plastic deformation, abrasive wear and oxidative wear. In gross slip regime, more severe degradation is present than in the other regimes. The main fretting wear mechanisms of steel wires are abrasive wear, surface fatigue and friction oxidation.

Surface texturing has been recognized to be very efficient in modifying the tribological performances of sliding surfaces. In the present article, a three-dimensional hydrodynamic lubrication model of the incompressible Newtonian fluid is proposed on the textured surface with a single spherical cap microdimple based on the full Navier-Stokes equation. The three-dimensional pressure field and velocity field of lubrication film are obtained by employing the finite volume method (FVM). The effects of geometric parameters and Reynolds number on pressure field, load-carrying capacity, friction force, and friction coefficient are investigated. Numerical simulation led the authors to conclude that the load-carrying capacity of the lubrication film is monotonously enhanced with increasing microdimple width and Reynolds number, and a reverse tendency is obtained for friction force and friction coefficient. The dimensionless optimum microdimple depth increases with the increase of the width and decreases with the i...

Poly(vinyl alcohol) (PVA) / hydroxyapatite (HA) composite hydrogel specimens were prepared with 15% PVA and 1%, 2%, 3%, 4% and 5% HA by repeated freezing-thawing. The tests of static and dynamic mechanical properties were carried out to discuss the influence of different contents of HA and freezing-thawing cycles on the mechanical properties of PVA/HA composite hydrogel. The results of static mechanical tests showed that the PVA/HA composite hydrogel with 3% HA and nine freezing-thawing cycles had excellent stress relaxation properties, higher relaxation ratio, lower stress equilibrium value and presented better properties of creep and recovery. The results of dynamic mechanical test showed that the PVA/HA composite hydrogel with nine freezing-thawing cycles had higher storage modulus and loss modulus, so was the PVA/HA composite hydrogel with 3% HA.

Static charge of skin surface has a significant effect on skin feel, look, and health. For this reason, controlling the charge buildup is an important issue in the commercial skin care industry. In this study, a systematic triboelectrification study of skin and skin cream was carried out. The surface potential of virgin skin and cream treated skin was measured using the Kelvin probe microscopy with an atomic force microscope. Since skin surface is not microscopically smooth, many interactions take place at microasperities, and there are also many microspherical particles in the environment interacting with skin surface. Triboelectrification of skin was studied by charging skin surface using a polystyrene plate on the macroscale and a polystyrene microsphere on the microscale. Since triboelectric charge is expected to be a function of normal load, velocity, and rubbing time, the influence of velocity, normal load, and rubbing time on the surface potential of virgin skin and cream treated skin were studied. Finally, charging mechanisms are discussed.

After a coal mine disaster, especially a gas and coal dust explosion, the space-restricted and unstructured underground terrain and explosive gas require coal mine rescue robots with good obstacle-surmounting performance and explosion-proof capability. For this type of environment, we designed a mobile platform for a rocker-type coal mine rescue robot with four independent drive wheels. The composition and operational principles of the mobile platform are introduced, we discuss the flameproof design of the rocker assembly, as well as the operational principles and mechanical structure of the bevel gear differential and the main parameters are provided. Motion simulation of the differential function and condition of the robot running on virtual, uneven terrain is carried out with ADAMS. The simulation results show that the differential device can maintain the main body of the robot at an average angle between two rockers. The robot model has good operating performance. Experiments on terrain adaptability and surmounting obstacle performance of the robot prototype have been carried out. The results indicate that the prototype has good terrain adaptability and strong obstacle-surmounting performance.

UHMWPE composites reinforced with Bovine Bone Hydroxyapatite (BHA) in different contents were prepared by heat pressing formation method. A hip joint wear simulator was used to investigate the biotribological behavior of UHMWPE/BHA composite acetabular cups against CoCrMo alloy femoral heads in bovine synovia lubrication at 37 ±1 °C. It was found that the addition of BHA powder to UHMWPE can improve the hardness and creep modulus of UHMWPE/BHA composites, and decrease their wear rates under bovine synovia lubrication. When the content of BHA filler particles was up to 30 wt%, UHMWPE/BHA composites demonstrated the well design performances of the surface and biotribological properties. Fatigue, ploughing and slight adhesive wear were the main wear mechanisms for UHMWPE and its composites. In addition, the sizes of wear particles became larger with an increase in BHA powder addition. These results suggest that BHA filler is a desirable component to increase the wear resistance of UHMWPE/BHA composites for biomedical applications.

Micro-porous titanium carbide coating was successfully synthesized in a vacuum gas carburizing furnace by using a sequential diffusion technology. The composition and structure of the as-synthesized TiC were examined by X-ray diffraction, X-ray photoelectron spectroscopy (XPS) and glow discharge mass spectrometry (GDMS), and scanning electron microscopy (SEM). All of the XRD, XPS and GDMS analysis results indicate that carbon atoms effectively diffused into the titanium alloys and formed a uniform acicular TiC coating with micro-porous structure.

Microporous titanium carbide coating was successfully synthesized on medical grade titanium alloy by using sequential carburization. Changes in the surface morphology of titanium alloy occasioned by sequential carburization were characterized and the wettability characteristics were quantified. Furthermore, the dispersion forces were calculated and discussed. The results indicate that sequential carburization is an effective way to modify the wettability of titanium alloy. After the carburization the surface dispersion force of titanium alloy increased from 76.5 × 10−3 J·m−2 to 105.5 × 10−3 J·m−2, with an enhancement of 37.9 %. Meanwhile the contact angle of titanium alloy decreased from 83° to 71.5°, indicating a significant improvement of wettability, which is much closer to the optimal water contact angle for cell adhesion of 70°.

Nitrogen ion implantation was performed on biomedical titanium alloys by using of the PBII technology to improve the surface mechanical properties for the application of artificial joints. The titanium nitride phase was characterized with X-ray photoelectron spectroscopy (XPS). The nanohardness of the titanium alloys and implanted samples were measured by using of in-situ nano-mechanical testing system (TriboIndenter). Then, the fretting wear of nitrogen ion implanted titanium alloys was done on the universal multifunctional tester (UMT) with ball-on-flat fretting style in bovine serum lubrication. The fretting wear mechanism was investigated with scanning electron microscopy (SEM) and 3D surface profiler. The XPS analysis results indicate that nitrogen diffuses into the titanium alloy and forms a hard TiN layer on the Ti6Al4V alloys. The nanohardness increases from 6.40 to 7.7 GPa at the normal load of 2 mN, which reveals that nitrogen ion implantation is an effective way to enhance the surface hardness of Ti6Al4V. The coefficients of friction for Ti6Al4V alloy in bovine serum are obviously lower than that in dry friction, but the coefficients of friction for nitrogen ion implanted Ti6Al4V alloy in bovine serum are higher than that in dry friction. Fatigue wear controls the fretting failure mechanism of nitrogen ion implanted Ti6Al4V alloy fretting in bovine serum. The testing results in this paper prove that nitrogen ion implantation can effectively increase the fretting wear resistance for Ti6Al4V alloy in dry friction, and has a considerable improvement for Ti6Al4V alloy in bovine serum lubrication.

In this work, investigations were conducted to analyze the properties of diamond-like carbon (DLC) film deposited on ultra-high molecular weight polyethylene (UHMWPE) by radio frequency plasma enhanced chemical vapor deposition (RF-PECVD) at a low temperature of 50 °C. Composition and structure of the films were characterized by scanning electron microscopy (SEM) and Raman spectroscopy. Hardness and wettability of the film were tested. Tribological characterizations were carried out on a universal micro-tribometer, and reciprocating friction against ZrO 2 ball was adopted with 25% bovine serum as lubrication. Results show that DLC film was successfully deposited on UHMWPE surface by RF-PECVD and the sp 3 content was about 20% in the film. The film increased the macrohardness of the substrate by about 42% and the wettability was improved too. Tribology test showed a higher friction coefficient but a much smaller wear volume after the deposition due to the surface roughening and strengthening.

Ultra-high molecular weight polyethylene (UHMWPE) is a kind of biomaterial applied as the acetabular cup in artificial hip joints. However, wear debris generation of UHMWPE materials after their replacements in human body has been proved to induce aseptic loosening and osteolysis, which is the main cause of long-term failure of total hip joints composed of UHMWPE and hard femoral balls. In this paper, natural coral (NC) particles in the size within 50 μm were applied as reinforcement fillers into UHMWPE to increase the wear resistance of UHMWPE composites as artificial acetabular cups. The micro-hardness and scratch resistance of UHMWPE/NC composites were studied. A hip joint wear simulator was operated to investigate the wear behavior of UHMWPE/NC composites against CoCrMo balls, the wear tests were lubricated by 25% bovine serum solutions. The wear mass loss and wear debris distribution through one million test cycles were examined in the paper. It is shown that the adding of NC particles in UHMWPE resulted in the enhancement of micro-hardness and scratching resistance of the UHMWPE/NC composites. The micro-hardness of UHMWPE/NC composites increased with natural coral contents in the linear relationship. The scratch coefficients of UHMWPE/NC composites increased in contents range of 10 wt% NC particles, the scratch depth decreased with the increasing NC contents. The wear resistance of UHMWPE/NC composites increased with the increasing contents of natural coral particles. It was found that the relation of wear mass loss of UHMWPE acetabular cup to the micro-hardness followed a negative power law. The wear mechanism of UHMWPE/NC composites was mainly controlled by adhesive wear. The NC contents in UHMWPE changed the severity of adhesive wear. The investigation of UHMWPE wear debris revealed that adding of NC particles in UHMWPE resulted in variations of size distribution of UHMWPE wear debris. Because micro-hardness of natural coral materials was much lower compared to CoCrMo alloy, few metal debris from CoCrMo ball were captured in the filter paper.

Poly (vinyl alcohol)/hydroxylapatite (PVA/HA) composite hydrogel was prepared by repeated freezing and thawing. The water loss properties of the resultant hydrogel were investigated by using optical microscope. Long time immersion tests of PVA/HA composite hydrogel were carried out in the diluted calf serum solution to study the change laws of swelling properties with the freezing-thawing cycles and HA content. The micro-morphologies of PVA/HA composite hydrogel after long time immersion were observed by means of the high-accuracy 3D profiler. The results show that the swelling process of PVA/HA composite hydrogel is the converse process of its water loss. Long time swelling ratio curves of PVA/HA composite hydrogel in the calf serum solution are manifested as four stages of quick increase, decrease, slow decrease and stable balance, and its equilibrium swelling ratio decreases with the increase of freezing-thawing cycles and HA content. It is revealed that the network structure of the composite hydrogel immersed for a long period is significantly improved with the increase of HA content. Perfect network structures of PVA/HA composite hydrogel as well as full and equilibrium tissues after swelling equilibrium are obtained when the HA content is 3% and the number of freezing-thawing cycles is 7.

To study the effect of electrolytic concentration, bioactive ceramic films containing Ca and P on the surface of the Ti6Al4V alloy were prepared by micro-arc oxidation (MAO) in aqueous solutions of different concentrations. Composition, micro-morphology, wettability of the films and their corrosion behavior in a Hank's SBF were studied. Our experimental results show that the film is mainly composed of anatase, rutile and amorphous phases. With an increase in electrolytic concentration, the ratio of rutile in films enlarge and small amounts of calcium phosphate (Ca3(PO4)2) and hydroxyapatite (HA) appear. The number of micropores in films increases but their dimensions decrease and their porosities increase slightly. As the surface roughness of MAO film increases with concentration, the wettablility of the oxide film improves continually, while micro-hardness increases at first and then decreases. MAO treatment clearly improves the corrosion resistance of substrates in a Hank's SBF.

Based on the irregular surface of natural cartilage configurations, the tribological characteristics of coupling motion between natural cartilage pairs were investigated by the variation of rotated offset and velocity. Contact displacement, contact load, friction force and coefficient of friction from natural cartilage pairs were measured by a UMT-2 testing machine. In order to obtain the steady part and wavy part, the contact load and contact displacement were decompounded by the five-point sliding average method. These results showed that the contact load was composed of steady load and wavy load. And the contact displacement was composed of cartilage deformation and surface outline. The steady load was similar to exterior load while natural cartilage deformation increased nonlinearly with the sliding time. Wavy load had the correlative coefficient 0.235 with surface outline due to the irregular surface of friction configurations. The coefficient of friction from cartilage friction configurations was less influenced by smaller magnitude in rotated parameters. A few strange summits were obtained in the area of coefficient of friction, and significantly related with local minimal values corresponding to the contact loads. The rotated offsets had clear impact on contact load and a slight impact on contact displacement. Larger offset produced higher wavy magnitude of the contact load. The rotated velocities played an evident role in cartilage deformation, but had a less influence on contact load. Lower velocity brought larger cartilage deformation.

Poly(vinyl alcohol)/Hydroxylapatite (PVA/HA) composite hydrogel was prepared with poly(vinyl alcohol) and hydroxylapatite as raw materials, using the method of repeated freezing and thawing. The morphologies of PVA/HA composite hydrogel were observed by means of high-accuracy 3D profiler and scanning electron microscope (SEM). The compressive elastic modulus and the stress relaxation characteristics of PVA/HA composite hydrogel were measured using the flat-head cylinder indenter. The friction and wear tests between PVA/HA composite hydrogel and bovine knee articular cartilage were performed on the micro-tribometer. The worn morphologies of PVA/HA composite hydrogel were observed with environmental scanning electron microscope (ESEM). The results showed that PVA/HA composite hydrogel has the cross-link network microstructure which is similar to that of the natural bovine knee articular cartilages. With the increase of freezing-thawing cycles and the HA content, the degree of cross-link and the crystallization of PVA/HA composite hydrogel both increase, the elastic modulus increases evidently, the rate of stress relaxation is improved and the value of balance stress decreases. The friction coefficient decreases with the increase of the freezing-thawing cycles and the HA content. The more the freezing-thawing cycles are, the earlier the friction coefficient reaches the stable balance value. The friction deformation depth between PVA/HA composite hydrogel and bovine knee articular cartilage is inversely proportional to freezing-thawing cycles and the HA content. The main wear mechanisms of PVA/HA composite hydrogel are plastic flowing and adhesive flaking. The wear severity degree decreases with the increase of freezing-thawing cycles and the HA content.

Mechanical properties and tribological behavior of nylon composites filled with zinc oxides were investigated in this paper. Different effects of ZnO particles and ZnO whiskers filling on the friction and wear behavior of nylon 1010 (PA1010) composites under dry friction condition were observed. The hardness, tensile strength and scratch coefficients of two kinds of nylon composites filled with the ZnO particles and whiskers were measured. Experimental results show that ZnO particles and ZnO whiskers improve the mechanical and tribological properties of nylon composites without affecting the crystallinity of nylon matrix. Hardness, tensile strength and scratch coefficient of composites are increased by the addition of ZnO particles and ZnO whiskers. Filler shape has little effect on the friction coefficients of nylon-based composites. These composites filled with particles and whiskers have nearly the same friction coefficients which locate between 0.4 and 0.45. The wear rates of composites are strongly dependent on filler shape and filler content. Particle-filled composites exhibit the lower wear rates than whisker-filled composites when the content of filler is lower than 10 wt.%. After that, the case is reversed. Ploughing and adhesion are the main wear mechanisms of composites with the addition of both ZnO particles and ZnO whiskers.

The frictional performance of gaskets is greatly affected by frictional heat in operational mine hoists. Based on frictional mechanism and heat transfer theory, the mathematical model of the temperature field of the PVC gasket in an operational mine hoist was investigated, a numerical simulation using ANSYS is presented and the distribution of the temperature and heat flux were studied under basic assumptions. The results show that the temperature gradually decreases as the radius of the model increases and the isotherms are arcs of concentric semi-circle. The heat flux is of bilateral symmetry in the model and decreases radially. The theoretical values correspond with the measured values for a short time (τ ≤ 100 s) when the steel wire rope slides.

MiaoXAM2.5X-50X Ultrahigh Precision Surface 3D Profiler is introduced to research the relations between thickness of UHMWPE’s wear debris and positive pressure of tribological system. Research results show that thickness of wear debris owns evident classification, and the first grade thickness math model and the second grade thickness math model are built. By the second grade thickness math model, the true force condition in the tribological system can be gotten, and the model can be used as a tool to modify simulating parameters of the tribological system, and it is an important inspecting method to the airtight system which cannot be examined in real time. The first grade thickness math model can describe the true working load and surface condition of work piece in the tribological system, and is an effective description method for the running condition of frictional pairs. The research results at different lubricating conditions testify the relations between thicknesses of wear debris and positive pressure of the tribological system. The fractal relation between maximal thickness of wear debris and positive pressure is discussed. The conceptions of the immutability principle and characteristic granularity of wear debris thickness are brought forward and discussed. In conclusion, as a stable tribological parameter owning mechanical theory basis, wear debris thickness will play an important part in fault diagnosis, especially for the airtight system such as artificial joint.

The study of frictional properties of human skin is important for medical research, skin care products and textile exploitation. In order to investigate the influence of normal load and sliding speed on the frictional properties of skin and its possible mechanism, tests were carried out on a multi-specimen friction tester. When the normal load increases from 0.1 N to 0.9 N, normal displacement and the friction coefficient of skin increase. The friction coefficient is dependent on the load, indicating that both adhesion and deformation contribute to the friction behaviour. The deformation friction was interpreted using the plough model of friction. When sliding speed increases from 0.5 mm·s−1 to 4 mm·s−1, the friction coefficient increases and “stick-slip” phenomena increase, indicating that hysteretic friction contributes to the friction. The hysteretic friction was interpreted using schematic of energy translation during the rigid spherical probe sliding on the soft skin surface, which provides an explanation for the influence of the sliding speed on the frictional characteristics of the skin.

Pin-on-disk dry sliding wear tests at sliding speeds ranging from 0.6 to 1.25 m/s and under loads ranging from 3.98 to 6.37 MPa (50–80 N) were conducted for pin specimens of composites with Al-5083 matrices reinforced with 5 and 10 wt.% B 4 C particles. The wear rate of the composite with 10 wt.% B 4 C was approximately 40% lower than that of the composite with 5 wt.% B 4 C under the same test condition. Two stages were observed in the reduction of pin length/sliding distance curves in several specimens, with the length reduction rate in the first stage being one to two orders of magnitude lower than that in the second stage. The low length reduction rate in the first stage corresponded with a flat stage with a low coefficient of friction (COF) in the COF/sliding distance curve.

Four kinds of wear tracks possibly occurred in the wear of artificial hip joints, including uni-directional sliding, oval curvilinear sliding, double-elliptical sliding, triple-elliptical sliding, were simulated on the UMT wear tester by using of a Si3N4 ball sliding on the UHMWPE disc under bi-directional sliding motion. The wear behavior and wear particle distribution of UHMWPE in plasma solution lubrication were studied for these sliding motions. The experimental results indicate that the wear mass loss in uni-directional reciprocating sliding is much smaller than those in bi-directional sliding modes. The wear rates of UHMWPE in bi-directional sliding modes are linearly inverse proportional to the defined frequency factor, as agreed with the cross-shear theory. This result suggests that cross-shear movement with larger intersection angles is a significant factor influencing the wear rate of UHMWPE, and the bi-directional sliding path at direction reversals will play an important role on the increasing of UHMWPE wear compared to uni-directional sliding motion. In bi-directional sliding modes, the wear particle distribution range decreases when direction reversal path increases in the sliding motions. So, the complex wear tracks are harmful to the implant joint due to the higher wear and more active wear particles. The particles sizes follow a lognormal distribution. The central size and the peak accumulation of UHMWPE particles decreases and increases against the frequency ratio, respectively, besides the uni-directional reciprocating sliding. These suggest that the intersection angle increasing on sliding path will contribute to the size decreasing of UHMWPE wear particle. Also, cross-points on sliding track will produce wear particles in smaller size. The radius of curvature of the curvilinear paths may be dictating the size reducing of UHMWPE wear particles. The main wear mechanisms are ploughing in uni-directional reciprocation, while plastic deformation, adhesion and fatigue in the bi-directional sliding modes.

The running-in wear experiments were preformed on the pin-on-disc tester. Time series signals of both frictional force and vibration were distilled by the computer data-collecting system, at the same time the fractal dimensions of the signals were obtained by the correlation-dimension method. It was found that the signals had an apparent fractal nature. Their fractal dimensions altered with the change of friction time, that is, increased gradually with the running-in procedure going on to reach its maximum ultimately. This indicated that the running-in process was ended from the initial friction of two surfaces to their fitted state (i.e. running-in state). In addition, the fractal dimension of friction signals was consistent with the fractal dimension of worn surfaces in the running-in process. So we can predict the progress of running-in wear process and identify the running-in state of a friction pair by the change of fractal dimension of frictional signals.

The ultra-high molecular weight polyethylene (UHMWPE) samples were prepared with three pressure of 10 MPa, 15 MPa and 20 MPa in this paper. Then these samples were applied to do bulk hardness measurement, scratch testing and punch testing. Meanwhile, the friction and wear behavior of UHMWPE samples were studied by using of Si 3 N 4 ball sliding on UHMWPE disc under plasma lubrication. The eight-figure sliding track was generated on the UMT tribotester. The experiment results indicate that the molding pressure has significantly influence on the mechanical property and tribological behavior of UHMWPE samples. Among three UHMWPE samples prepared with pressure of 10 MPa, 15 MPa and 20 MPa, the UHMWPE sample molded in pressure of 15 MPa obtains the highest values of bulk hardness up to 28.5 MPa, the scratch coefficients up to 3.41 and the punch breaking loads up to 201.6 N. The coefficients of friction of this UHMWPE sample result in the lowest value around 0.025, the lowest wear mass loss of 0.93 mg is obtained for 10,000 cycles testing. There is no apparent difference in the frequency distribution of worn particles with respect to particle size for the UHMWPE samples from three levels of molding pressure. The wear particle size concentrates at about 8 μm. The microstructures of UHMWPE are influenced by compression pressure. Low compression pressure of 10 MPa results in grain defects to reduce the bonding strength between grain boundaries. The compression pressure of 20 MPa results in stress-induced orientation microstructure in UHMWPE.

In this paper, radar graph fractal method is introduced to describe wear debris boundaries. Research results show that it is a nice way to describe wear debris boundaries. Since the longest axis is selected as the first coordinate axis, its center point selected as the center point of the radar graph, and the coordinate value of wear debris boundary selected as the measure parameter, the limitations existing in Yard fractal measure method can be avoided. For any wear debris, its radar graph fractal dimension value is one and only, and as the wear debris shape changes from round to strip, the radar graph fractal dimension value also changes from low to high, showing strong uniqueness and independence. Due to the fact that the researched wear debris is gotten in different wear states, the results also prove that radar graph fractal dimension value is correlated with frictional pairs work condition and wear state. Radar graph fractal method is compared with Yard fractal measure methods, and results show that radar graph fractal dimension values gotten from different wear debris have enough value grads to avoid effect of errors, and provide higher sensitivity for wear debris shape. This paper also discusses the influencing factors for radar graph fractal method. With the increase of the decomposing degree value, the radar graph fractal dimension tends to keep stable at one certain value, showing the typical characteristic of the fractal theory. All this proves that radar graph fractal method is an effective description method for wear debris boundaries.

The wear of ultra high-molecular weight polyethylene (UHMWPE) has been implicated as the major cause of osteolysis, implant loosening, and late aseptic failure in total hip arthroplasties in vivo, so increasing its wear resistance will be beneficial to obtain high-quality artificial joints. In this paper, the artificial joint acetabular materials of UHMWPE composites reinforced with titanium powders were prepared by the hot pressing formation method. A hip joint wear simulator was run to investigate the biotribological behaviours of these composites against 316L stainless steel in simulated body fluids (SBF-9) lubrication at 35 ± 1°C. The experimental results indicate that the addition of titanium particles in UHMWPE is beneficial for increasing wear resistance of UHMWPE. Under SBF-9 lubrication, the addition of titanium particles into UHMWPE has effect to decrease the wear rates of UHMWPE/Ti composites cups against 316L steel ball heads. The Maximum reduction in wear rates is 50 per cent for the UHMWPE/Ti composite cups with 20 (W) content of titanium particles. Abrasive wear and fatigue wear are found to be the main wear mechanisms of UHMWPE or UHMWPE/Ti composites in hip joint simulator wear under SBF-9 lubrication. The addition of titanium particles in UHMWPE will increase the wear debris size when the content of titanium particles is over 12 wt%.