Effect of Thermal Fatigue Loading on Tensile Behavior of H13 Die Steel with Biomimetic Surface

<正> Biomimetic surface is an effective ways to promote the performance grade and applied range of materials without alteringtheir substrate.Many improved properties such as resisting fatigue,enduring wear,etc,have been achieved by applyingbiomimetic morphology or structure to some engineering material surfaces.In this paper,aiming to reveal the relationshipbetween thermal cracking behavior and mechanical properties of engineering materials with biomimetic surface,biomimeticspecimens were fabricated using laser technique by imitating the heterogeneous structure on the surface of plant leaves.Theeffect of thermal fatigue cycling on the tensile properties of H13 die steel specimens with different surfaces (several types ofbiomimetic surfaces and a smooth surface) was compared and investigated.As a result,due to the coupling effects of themorphological features on the surface and the microstructure characteristics within unit zone,these specimens with biomimeticsurface exhibit remarkably enhanced Ultimate Tensile Strength (UTS) and 0.2% Yield Strength (YS) compared with referencespecimens while corresponding ductility remains largely unaffected even heightened,whether the thermal fatigue loads or not.The relative mechanisms leading to these improvements have been discussed.     

Thermal Cycling Effect on the Wear Resistance of Bionic Laser Processed Gray Iron

Thermal fatigue and wear both seriously affect the service life of some working parts. Environmental temperature will modify the surface conditions and influences the result of wear. In this research, to come close to working conditions, specimens were tested by a combination of thermal cycles and wear. Different cycles of thermal fatigue was carried out first on the gray iron specimens and subsequently wear test was performed to evaluate the effect of these thermal fatigue cycles. In this case, bionic laser processing was used to enhance the wear performance. The results indicated that bionic laser processing reduces the negative effects from thermal fatigue, such as grain fragmentation and oxidation. Because the initiation and growth of cracks as well as oxidation are suppressed in bionic processed areas. Bionic specimens exhibit high wear resistance compared with the common one. The process described can be considered as an effective method to improve the performance of gray iron in combined thermal fatigue and wear service conditions.     

Wear Resistance of 3Cr2W8V Rough Surfaces

Three types of rough surface were processed by laser irradiation on the 3Cr2W8V material hot-work die steel surface.The wear experiments with smooth surface and rough surface samples were repeated on the pin-tray wear machine. According to the wear results, we studied the regularity of wear resistance of different rough surface samples. The results indicated that bionic rough surface can improve the wear resistance of the material and the wear resistance can be increased 1 - 2 times, compared with the smooth surface. Also, the wear resistance of the rough surface was affected by laser current and duration of impulse. The bigger the laser current or the impulse duration, the better is the wear resistance. When the distance between the same kind of units which are distributed on the surfaces is changed, the wear resistance changes. The wear resistance of a bionic rough surface on which the grid units were distributed at spacing of 1 mm was the best. And we designed the wear models.     

Effects of Plasma Nitriding on Microstructure and Tribological Properties of CoCrMo Alloy Implant Materials

##正## Medical forged CoCrMo alloy was treated by plasma nitriding process.The microstructures were characterized by 3Dprofiler,SEM and XRD.The tribological properties were investigated under lubrication of 25% bovine serum solution.Resultsshow that plasma nitriding is a promising process to produce thick,hard,and more wear resistant layers on the surface of CoCrMoalloy.All nitrided samples showed an important increase in the surface hardness due to the formation of harder CrN andCr_2N phases with compact nano-crystalline structures.The typical hardness values of HV_(0.05) increased almost two times thanuntreated one.Under bovine serum lubrication,at low nitriding temperature the Coefficient of Friction (COF) of nitrided samplewas lower than that of untreated sample,but at high nitriding temperature the COF was almost the same as the untreated one.Compared with the untreated sample,the nitrided samples showed lower wear rates and higher wear resistance under differentnitriding temperatures.The adhesive wear is the main mechanism for untreated CoCrMo alloy and the wear mechanisms ofnitrided ones are the fatigue wear and slight adhesive wear.It is concluded that the improvement of wear resistance is ascribed tothe hard nitride formation of CrN and Cr_2N phases at the nitrided surfaces.     

Optimization of Laser Processing Parameters and Their Effect on Penetration Depth and Surface Roughness of Biomimetic Units on the Surface of 3Cr2W8V Steel

Biomimetic coupling surface is a recent development in surface science of materials. One of the important methods to achieve this surface is to manufacture large numbers of structural units by certain techniques, arranging them regularly on the surface layer of materials to form the biomimetic structure. The penetration depth and the surface roughness of units are two crucial factors that affect strongly the properties of materials. In this paper, a YAG pulsed laser with varied parameters (electrical current 200 A to 300 A, pulse duration 5 ms to 15 ms, frequency 4 Hz to 10 Hz and scanning speed 0.24 mm·s^?1 to 0.72 mm·s^?1) was used to fabricate these units on the surface of 3Cr2W8V die steel. The penetration depth and surface roughness of the units were investigated based on orthogonal experimental design. To maximize the penetration depth and minimize the surface roughness, the range analysis and subsequently overall balance method were adopted to identify the most significant factor and level. Meanwhile the most preferable combination of the laser processing parameters was selected. The effect of laser processing parameters on the penetration depth and surface morphology of units was analyzed. The interrelationship among the processing parameters, the penetration depth and the surface roughness was discussed.     

Study on Tribological Properties of Irradiated Crosslinking UHMWPE Nano-Composite

Ultra High Molecular Weight Polyethylene(UHMWPE)has been widely used as a bearing material for artificial joint replacementover forty years.It is usually crosslinked by gamma rays irradiation before its implantation into human body.In thisstudy,UHMWPE and UHMWPE/nano-hydroxyapatite(n-HA)composite were prepared by vacuum hot-pressing method.Theprepared materials were irradiated by gamma rays in vacuum and molten heat treated in vacuum just after irradiation.The effectof filling n-HA with gamma irradiation on tribological properties of UHMWPE was investigated by using friction and wearexperimental machine(model MM-200)under deionized water lubrication.Micro-morphology of worn surface was observedby metallographic microscope.Contact angle and hardness of the materials were also measured.The results show that contactangle and hardness are changed by filling n-HA and gamma irradiation.Friction coefficient and wear rate under deionized waterlubrication are reduced by filling n-HA.While friction coefficient is increased and wear rate is reduced significantly by gammairradiation.The worn surface of unfilled material is mainly characterized as adhesive wear and abrasive wear,and that of n-HAfilled material is mainly characterized as abrasive wear.After gamma irradiation,the degrees of adhesive and abrasive wear forunfilled material and abrasive wear of n-HA filled material are significantly reduced.Unfilled and filled materials after irradiationare mainly shown as slight fatigue wear.The results indicate that UHMWPE and UHMWPE/n-HA irradiated at the doseof 150 kGy can be used as bearing materials in artificial joints for its excellent wear resistance compared to original UHMWPE.     

Fatigue Performance of Medical Ti6Al4V Alloy after Mechanical Surface Treatments

Mechanical surface treatments have a long history in traditional engineering disciplines, such as the automotive or aerospace industries. Today, they are widely applied to metal components to increase the mechanical performance of these. However, their application in the medical field is rather rare. The present study aims to compare the potential of relevant mechanical surface treatments on the high cycle fatigue (R = 0.1 for a maximum of 10 million cycles) performance of a Ti6Al4V standard alloy for orthopedic, spinal, dental and trauma surgical implants: shot peening, deep rolling, ultrasonic shot peening and laser shock peening. Hour-glass shaped Ti6Al4V specimens were treated and analyzed with regard to the material’s microstructure, microhardness, residual stress depth profiles and the mechanical behavior during fatigue testing. All treatments introduced substantial compressive residual stresses and exhibited considerable potential for increasing fatigue performance from 10% to 17.2% after laser shock peening compared to non-treated samples. It is assumed that final mechanical surface treatments may also increase fretting wear resistance in the modular connection of total hip and knee replacements.     

Increased conformational rigidity of humic substances by oxidative biomimetic catalysis

A synthetic water-soluble meso-tetra(2,6-dichloro-3-sulfonatophenyl)porphyrinate of iron(III) chloride, Fe(TDCPPS)Cl, was employed as a biomimetic catalyst in the oxidative coupling of terrestrial humic materials. High-performance size-exclusion chromatography (HPSEC), solid-state nuclear magnetic resonance (CPMAS-(13)C NMR), electron paramagnetic resonance (EPR), and diffuse reflectance infrared spectroscopy (DRIFT) were used to follow conformational and structural changes brought about in different humic materials by the oxidative coupling. Increase in apparent weight-average molecular weight (Mw(a)) occurred invariably for all humic substances with the oxidative polymerization catalyzed by Fe(TDCPPS)Cl. HPSEC further showed that the polymerization reaction turned the loosely bound humic supramolecular structures into more stable conformations which could no longer be disrupted by the disaggregating effect of acetic acid. DRIFT spectroscopy suggested the formation of new alkyl and aromatic ethers following the oxidative coupling with the biomimetic catalyst. CPMAS-(13)C NMR and EPR spectra suggested a reduced molecular mobility of humic components and enhanced stabilization of free radicals in larger oxidized fragments. All findings concur in indicating that the biomimetic catalysis by Fe(TDCPPS)Cl increased the molecular mass and chemical rigidity of humic materials by formation of intermolecular covalent bonds via a free-radical mechanism. The development of a technology based on oxidative polymerization by biomimetic catalysis may be of importance in controlling the properties and reactivity of humic matter for industrial and environmental applications.     

Biomimetic Anti-Abrasion Surfaces of a Cone Form Component Against Soil

The geometrical surfaces of soil-burrowing animals were imitated and modeled on a cone component, the measuring tip part of a soil cone penetrometer. These biomimetic surfaces are concave dimples, convex domes and two wavy forms. The conventional cone surface and the biomimetic cone surfaces were analyzed in ANSYS 11.0 program to estimate cone equivalent stress and soil equivalent stress. Results show that biomimetic surfaces with the geometrical structures have lower cone equivalent stresses and soil equivalent stresses than that with conventional (smooth) surface. The least maximum cone equivalent stress and least maximum soil equivalent stress were recorded for biomimetic surfaces with concave dimples and wavy form-2 respectively. The two-body abrasive wear of biomimetic cone surfaces and conventional (smooth) cone surface were run on a rotary disk type of abrasive wear testing machine. The biomimetic cone surfaces were found to have lower abrasive wear than the conventional surface. It was found that and biomimetic cone surface with concave dimples has the lowest abrasive wear among the all tested surfaces.     

Computational hip joint simulator for wear and heat generation

This paper presents a computational simulator for the hip to compute the wear and heat generation on artificial joints. The friction produced on artificial hip joints originates wear rates that can lead to failure of the implant. Furthermore, the frictional heating can increase the wear. The developed computational model calculates the wear in the joint and the temperature in the surrounding zone, allowing the use of different combinations of joint materials, daily activities and different individuals. The pressure distribution on the joint bearing surfaces is obtained with the solution of a contact model. The heat generation by friction and the volumetric wear is computed from the pressure distribution and the sliding distance. The temperature is obtained from the solution of a transient heat conduction problem that includes the time-dependent heat generated by friction. The contact and heat conduction problems are solved numerically with the Finite Element Method. The developed computational model performs a full simulation of the acetabular bearing surface behaviour, which is useful for acetabular cup design and material selection. The results obtained by the present model agree with experimental and clinical data, as well as other numerical studies.     

Chondroitin sulfate and epidermal growth factor immobilization after plasma polymerization: a versatile anti-apoptotic coating to promote healing around stent grafts

Bioactive coatings constitute an interesting approach to enhance healing around implants, such as stent-grafts used in endovascular aneurysm repair. Three different plasma techniques, namely NH? plasma functionalization and atmospheric- or low-pressure plasma polymerization, are compared to create amino groups and covalently bind CS and EGF bioactive molecules on PET. The latter presents the greatest potential. CS?+?EGF coating is shown to strongly decrease cell apoptosis and cell depletion in serum-free medium, while increasing cell growth compared to unmodified PET. This versatile biomimetic coating holds promise in promoting vascular repair around stent-grafts, where resistance to apoptosis is a key issue.     

Identification of wear particles of joint prostheses in tissues using laser microprobe mass analysis (LAMMA)]

The definite identification of wear particles from joint prostheses is of great importance for the development of joint replacement, as the type and quantity of different wear particles gives information on the wear resistance of implant materials. From the types of prostheses nowadays in use polyethylene wear of the sockets, bone cement wear, metallic and ceramic wear can be generated. Whereas polyethylene wear can be easily identified by its bright luminescence in polarized light and its characteristic configuration, the distinction of the small granular wear particles of the bone cement, metal and ceramic by light microscope is difficult. The laser microprobe mass analysis (LAMMA) is a method, which allows the analysis of single light microscopically detectable wear particles in tissues. Not only contrast medium particles of the bone cements (zirconium oxide or barium sulfate) but also metallic and aluminum oxide particles could be definitely identified within the pseudocapsules as well as in regional lymph nodes by LAMMA-analysis, whereby the bone cement wear predominated. In addition, the distinction between organic substances (as blood degradation products), which may appear similar to wear particles in configuration and colour, and the foreign material is also possible with this method.     

Experiments on Ultrasonic Lubrication Using a Piezoelectrically-assisted Tribometer and Optical Profilometer

Friction and wear are detrimental to engineered systems. Ultrasonic lubrication is achieved when the interface between two sliding surfaces is vibrated at a frequency above the acoustic range (20 kHz). As a solid-state technology, ultrasonic lubrication can be used where conventional lubricants are unfeasible or undesirable. Further, ultrasonic lubrication allows for electrical modulation of the effective friction coefficient between two sliding surfaces. This property enables adaptive systems that modify their frictional state and associated dynamic response as the operating conditions change. Surface wear can also be reduced through ultrasonic lubrication. We developed a protocol to investigate the dependence of friction force reduction and wear reduction on the linear sliding velocity between ultrasonically lubricated surfaces. A pin-on-disc tribometer was built which differs from commercial units in that a piezoelectric stack is used to vibrate the pin at 22 kHz normal to the rotating disc surface. Friction and wear metrics including effective friction force, volume loss, and surface roughness are measured without and with ultrasonic vibrations at a constant pressure of 1 to 4 MPa and three different sliding velocities: 20.3, 40.6, and 87 mm/sec. An optical profilometer is utilized to characterize the wear surfaces. The effective friction force is reduced by 62% at 20.3 mm/sec. Consistently with existing theories for ultrasonic lubrication, the percent reduction in friction force diminishes with increasing speed, down to 29% friction force reduction at 87 mm/sec. Wear reduction remains essentially constant (49%) at the three speeds considered.     

Mechanisms underlying the regulation of motor unit contraction in the skeletal muscle.

The control of movements is made posible thanks to the activity of motor units in skeletal muscles. In the present paper the influence of frequency and pattern of motoneuronal firing on the tension of contraction and the tension-time area is presented and discussed. The most resistant to fatigue slow-twitch motor units are low susceptible to changes in a pattern of impulses and therefore they are well prepared to participate in long-lasting movements at low but rather stable levels of tension. Moreover, their contraction is very effective and it is performed at a low metabolic charge. Fast-twitch units have lower resistance to fatigue and they have higher tension but they have high susceptibility to a pattern of pulses and their tension can be effectively regulated by an increase or a decrease in the interpulse interval. Therefore, fast motor units are specialized to participate in the regulation of the movement force. The existence of different functional groups of motor units in skeletal muscles enables the performance of different motor tasks very effectively and at possibly low metabolic costs.     

贝壳珍珠层不同取向弹性模量的研究

研究天然生物材料的组织结构特征与其性能之间的关系对于材料的仿生有重要意义．在自制的激光测试设备上用三点弯曲法对贝壳珍珠层不同取向的弹性模量进行了研究,报道了不同取向和加载方式条件下弹性模量的变化规律。结果表明,在平行和倾斜于生长纹路方向上弹性模量的平均值分别为60．3GPa和56．7GPa,而垂直于纹路方向的为48GPa,呈现出各向异性。弹性模量的各向异性主要来自于珍珠层微观组织结构和贝壳生长纹结构的特点．     

A review: synthesis of alkaloids by oxidative phenol and nonphenol coupling reactions

Experiments concerned with biomimetic synthesis of alkaloids by intramolecular oxidative phenol and nonphenol coupling reactions are described. Preliminary investigations of intramolecular and intermolecular oxidative coupling reactions by iron-DMF and iron-DMSO complexes, and intramolecular oxidative coupling reactions by electrochemical methods followed by biomimetic syntheses of crinine, morphinandienone, and phenanthroquinolizidine alkaloids and a new synthesis of the alkaloid colchicine are presented.     

Biology Coupling Characteristics of Mole Crickets' Soil-Engaging Components

Mole cricket (Gryllotalpa orientalis) is a typical animal living under ground. The soil-engaging components of mole cricket have the capacity of wear resistance against soil. In this paper, the foreleg, tergum and forewing of mole cricket were chosen as soil-engaging components and were observed by stereomicroscope (SM), Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM). The functions of the components were analyzed from the viewpoints of both entomology and bionics. The factors for function realization were found, and the single effect and coupling effect of these factors were investigated. Results show that the wear resistance characteristic of mole cricket is realized by biology coupling. The research of biology coupling provides a foundation to the technology of bionic coupling.     

Influence of Bio-Lubricants on the Tribological Properties of Ti6Al4V Alloy

Titanium alloy is one of the best materials for biomedical applications due to its superior biocompatibility, outstanding corrosion resistance, and low elastic modulus. However, the friction and wear behaviors of titanium alloys were sensitive to the environment including lubrication. In order to clarify the wear mechanism of titanium alloy under different lubrications including deionized water, physiological saline and bovine serum, the friction and wear tests were performed between Ti6Al4V plates and Si₃N₄ ball on a universal multi-functional tester. The friction and the wear rate of titanium alloy were measured under dry friction and three different lubrication conditions. The worn surfaces were examined by scanning electron microscopy. The results revealed that under the dry friction, the wear resistance of titanium alloy was the worst since the wear mechanism was mainly the combination of abrasive wear and oxidation wear. It was also found that Ti6Al4V alloy had low friction coefficient and wear rate under three lubrication conditions, and its wear mechanism was adhesive wear.     

Tribological Behavior of Gampsocleis Gratiosa Foot Pad Against Vertical Flat Surfaces

Some tribological behavior between mature Gampsocleis gratiosa foot pads and vertical flats of different materials were studied in this work. stereomicroscope （SMS） and scanning electron microscope （SEM） were used to measure the morphology of the Gampsocleis gratiosa foot pads. An atomic force microscope （AFM） was used to measure the morphologies of the surfaces of glass and a wall doped with calcium carbonate material. The attaching behavior of Gampsocleis gratiosa feet on the two vertical surfaces was observed. The attaching force （perpendicular to the vertical surface） and the static frictional force （along the direction of gravitation） of Gampsocleis gratiosa foot pads on a vertical glass were measured. It was shown that the average attaching force is 50.59 mN and the static frictional force is 259.10 mN. The physical models of the attaching interface between Gampsocleis gratiosa foot pads and the two vertical surfaces were proposed. It was observed that the foot pads are smooth in macroscale; however, the pad surface is composed by approximate hexagonal units with sizes of 3 μm to 7 μm in microscale; the adjacent units are separated by nanoscale grooves. The Observations showed that the Gampsocleis gratiosa can not climb the vertical calcium carbonate wall; in contrast, they can easily climb the vertical glass surface. Based on the features of the geometrical morphologies of the foot pads and the glass surface, we speculate that the attaching force and strong static frictional force are attributed to the interinlays between the deformable Gampsocleis gratiosa foot pads and the nanoscale sharp tips of the glass surface.     

Biomimetic Materials to Characterize Bacteria-host Interactions

Bacterial attachment to host cells is one of the earliest events during bacterial colonization of host tissues and thus a key step during infection. The biochemical and functional characterization of adhesins mediating these initial bacteria-host interactions is often compromised by the presence of other bacterial factors, such as cell wall components or secreted molecules, which interfere with the analysis. This protocol describes the production and use of biomimetic materials, consisting of pure recombinant adhesins chemically coupled to commercially available, functionalized polystyrene beads, which have been used successfully to dissect the biochemical and functional interactions between individual bacterial adhesins and host cell receptors. Protocols for different coupling chemistries, allowing directional immobilization of recombinant adhesins on polymer scaffolds, and for assessment of the coupling efficiency of the resulting “bacteriomimetic” materials are also discussed. We further describe how these materials can be used as a tool to inhibit pathogen mediated cytotoxicity and discuss scope, limitations and further applications of this approach in studying bacterial - host interactions.