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1.
    
The transition from a mild wear situation to a severe (adhesive) wear situation is of great interest to be able to design highly loaded concentrated contacts operating in the boundary lubricated regime. In this article a method is described to estimate this transition, based on a thermal criterion. It is stated that if a certain percentage of the contacting asperities transcends a critical temperature which is determined experimentally the transition from mild to severe wear takes place. The theory presented is validated with a model system and the results from experiments are is good agreement with the simulations.  相似文献   

2.
    
Tribological contacts in sheet metal forming are accompanied by several wear phenomena. One of which is the transfer of material from the softer sheet material to the harder tool surface, namely adhesive wear. Forming of aluminum alloys makes high demands on forming processes. Aluminum alloys show a strong tendency of adhesion on common tool materials. Adhesions on tools reduce the surface quality, the dimensional accuracy of the parts and the process stability. In order to avoid adhesive wear during forming, nowadays a high amount of lubricant is applied to the aluminum sheets. Though economically and ecologically attractive, dry forming processes with aluminum sheets seem not to be possible. In order to develop advantageous tribological systems a comprehensive understanding of the acting mechanisms is necessary. This paper discusses the influence of the alloy composition and the influence of oxide layers on the adhesive wear in aluminum forming.  相似文献   

3.
    
In this research two grades of polysulfide resin with low and high molecular weight (respectively G4 and G112) as reactive modifier was used to toughen epoxy resin. The effect of modifier molecular weight on impact resistance, thermal expansion coefficient, storage and loss modulus, decomposition temperature and adhesion properties of toughened epoxy was investigated. The impact strength and the thermal expansion coefficient (CTE) of epoxy resin was increased with increasing polysulfide but the G112 modified epoxy samples showed higher CTE values and impact resistance than those of modified with G4. Comparing of the same weight percent inclusion of G4 and G112 effect on decomposition temperature show that G4 modified epoxy resin has lower decomposition temperature than the G112 modified epoxy resin. Also addition of G112 up to 10 weight percent leads to higher bond strength with aluminum sheets. According to the DMTA graphs, glass transition temperature (Tg) of the modified epoxy was decreased with increasing polysulfide weight percent in composition. At the same time G4 modified epoxies have lower Tg and storage modulus than that of modified with G112.  相似文献   

4.
The adhesion and failure mechanism at well‐designed titanium‐PEEK interfaces within Ti‐CF/PEEK laminates are investigated by superposed mode I‐ and mode II‐loading before and after hydrothermal aging. The laser‐induced columnar structured oxide layer enhances the adhesion at the Titanium‐PEEK interface. PEEK‐Polymer that is locked mechanically in the capillary gaps of the columnar oxide structure are stretched and stiffed in the case of loading resulting in good adhesion. The adhesion at the oxide structure reduces by the influence of hydrothermal aging. Basically, the failure mechanism is not changed. Thus, the columnar oxide structure leads to enhanced humidity resistance of the adhesion between titanium and PEEK. The PEEK‐Polymer is also locked in the undercuts between the depressions and rims of the laser‐induced dot‐like surface structure resulting in adhesion. The adhesion at the dot‐like structured surface is nearly completely reduced by the influence of hydrothermal aging. The failure mechanism is changed from ductile failure within the PEEK‐Polymer to party disrupted rims and melt spatter.  相似文献   

5.
    
Surface Modification of Titanium for Improvement of the Interfacial Biocompatibility We report the CVD‐polymerisation of amino‐functionalized [2,2]‐paracyclophane for polymer coating and functionalization of titanium surfaces. Additionally, the functionalization was carried out by silanization with 3‐aminopropyl‐triethoxysilane. The generated amino‐groups were used for covalent immobilization of bioactive substances to stimulate the adhesion and growth of osteoblasts. As bioactive substances the pentapeptide GRGDS and the growth factor BMP‐2 were chosen. The covalent bonding was achieved by activation with hexamethylene diisocyanate. Each modification step was characterized by X‐ray‐photoelectron‐spectroscopy (XPS), atomic force microscopy (AFM) and contact angle measurements. The covalent bonding of the bioactive substances was proven by radiolabelling and surface‐MALDI‐ToF‐MS. In vitro‐biocompatibility tests with primary, human osteoblasts demonstrated the improved cell adhesion and spreading on the bioactive modified titanium surfaces.  相似文献   

6.
    
The main aim of the present work is to experimentally evaluate the deep drawing behaviour of adhesive bonded sheets at different adhesive properties and predict the same using finite element simulations. The deep drawing quality steel and SS316L stainless steel are used as base materials for experiments and simulations. The deep drawing behaviour is also predicted using available analytical equations and proposed semi‐empirical equations. Such predictions are validated with experimental results. It is observed that due to increased plasticity of adhesive layer, the hardener rich formulation of adhesive improves the deep drawability of adhesive bonded blanks. The presence of carbon black in the adhesive has improved the drawability of bonded sheets up to a certain limit, say 2% by weight in the present work. The deep drawing behaviour predicted either by approach 1 (by giving experimentally evaluated adhesive properties as input) and by approach 2 (adhesive properties evaluated from rule of mixtures) are almost same, which indicates that both the methods can be used for forming behaviour prediction. The deep drawability predictions are moderately accurate with respect to experimental observation. The accuracy of analytical models for maximum load predictions is encouraging while comparing it with experimental results and numerical predictions. The proposed semi‐empirical equations show promising results to obtain initial estimate about the load‐progression behaviour of bonded sheets.  相似文献   

7.
    
Hastelloy‐C276 is a nickel based superalloy that is widely used in chemical, petro‐chemical, environmental and nuclear industries due to its outstanding performance in a wide range of corrosive mediums. The superior properties of nickel based superalloys impair their machinability which increases the difficulty in obtaining a good surface finish. Because most of the components' failures are initiated from surface defects, several researchers have been concerned about surface integrity in machining aerospace superalloys particularly Inconel‐718. Due to the lack of studies done on machining corrosion‐resistant superalloys, this study aims to investigate surface damages and tool wear modes in milling Hastelloy‐C276 under dry and wet conditions. The absence of cooling and lubricating actions in dry machining resulted in the formation of craters, severe plastic deformation, voids, debris re‐deposition and materials drag. The breakage of the nucleated carbide phases resulted in the formation of nucleated cavities on the machined surface in both wet and dry machining. Adhesive tool wear was less in dry machining due to the formation of oxide layers on tool faces which suppressed the formation of built‐up edges due to the weak adhesion properties of oxide compounds which resulted in less surface roughness at vc = 50 m/min. On the other hand, the higher temperature and friction in dry machining resulted in severer tool coating delamination.  相似文献   

8.
    
The adhesion behaviour of osteoblastic cells on implant surfaces is a main focus during the development of osteoconductive implant surfaces. Therefore, besides cell spreading and proliferation on surfaces the adhesion strength of cells to the substrate is of high interest. There are different approaches to determine cell adhesion but only few quantitative methods. For this purpose, we have developed an adhesion device based on the spinning disc principle in conjunction with an inverse confocal laser scanning microscope (LSM). Mirror polished disc‐shaped test samples made of titanium‐ (Ti6Al4V) and cobalt‐alloys (Co28Cr6Mo), as well as stainless steel (316L), were seeded with osteoblasts, stained with a fluorescent dye, at defined radial positions and were incubated for 18 h in cell culture medium (DMEM). After incubation the test samples were placed into the adhesion chamber filled with DMEM. By means of a computer controlled motor the test samples were rotated for 3 min. Using the LSM the detachment of the cells at defined radial positions was determined and the cell count was recorded before and after rotation with the help of imaging software. An average shear stress of 47.1 N/m2, 53.2 N/m2 and 49.4 N/m2 was assessed for the mirror polished Ti6Al4V, Co28Cr6Mo and 316L surfaces respectively. The technique is suitable for studying bone cell adhesion strength on orthopaedic implant materials. Future investigations will focus on different bioactive and anti‐infectious implant surfaces, as well as soluble bioactive factors.  相似文献   

9.
    
Metal plastic hybrids combines the properties of the components: the high strength and rigidity of the metal, as well as the excellent possibilities of the lightweight thermoplastic in moulding processes. This allows the production of new parts with integration of different functions. Assembly injection moulding is a very effective and low‐cost technology for the metal plastic hybrid manufacture. We investigate three layer hybrids of steel plate, low module polyurethane and an adhesion layer. A new developed low temperature uretdione polyurethane powder coating material in two different curing grades is used as the adhesion layer. This curing grades are the allophanate‐ and the urethane group grades. The aim of our work consist in the investigation of the influence of the two curing grades on the three layer hybrid bond strength. The results of the model tests as well as of the analytical investigations are in good correlation to the bond strength level. This allowed us to make two thesis: on the one hand the fusing thesis and on the other hand the reaction thesis.  相似文献   

10.
    
A Fe‐based composite coating reinforced by in situ synthesized TiC particles was fabricated on Cr12MoV steel by using 6 KW fiber laser cladding. A serial of experiment has been carried out with different laser power, scanning speed, and powder feed rate, from which TiC could be in situ synthesized only in certain realms laser cladding parameters. X‐ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, transmission electron microscope and a hardness tester are used to test the microstructure, micro‐hardness and component distribution. The coating is mainly composed of alpha ;‐Fe, TiC and Fe3C. TiC particles were commonly precipitated in three kinds of morphologies, such as quadrangle, cluster, and flower‐like shape. The grains were refined, and there were no cracks and few stomas. Defect‐free coating with metallurgical joint to the substrate was obtained. TiC distributed more concentratively in the upper layers than the middle and bottom layers. From the surface of cladding layer 0.8 mm the highest micro‐hardness was up to HV930, obviously higher than that of the substrate.  相似文献   

11.
    
The experimental results of an investigation of the steady‐state motion of individual grain boundaries (GBs) of natural deformation twin and individual twin GBs in bicrystals and tricrystals with triple junction (TJ) are obtained. For experimental observation of GB mobility from the dependence on GB inclination the Zn specimens with individual GBs and TJs were produced. The mobility of natural deformation twin GBs and twin GBs in bicrystals and tricrystals are compared in connection with the GB inclination.  相似文献   

12.
原位反应结合多孔Si3N4陶瓷的制备及其介电性能   总被引：2，自引：0，他引：2  
以氮化硅(Si3N4)和氧化铝(Al2O3)为起始原料, 利用原位反应结合技术制备Si3N4多孔陶瓷. 研究烧结温度和保温时间对Si3N4多孔陶瓷的微观结构、力学性能以及介电性能的影响. 结果表明: 烧结温度在1350℃以下, 保温时间<4h时, 随着烧结温度的升高, 保温时间的延长, 样品的强度和介电常数增大; 但条件超出这个范围, 结果刚好相反; 物相分析表明多孔陶瓷主要由Si3N4和Al2O3以及Si3N4氧化生成的SiO2(方石英)组成. 所制备的多孔Si3N4陶瓷的气孔率范围为25.34%～48.86%, 抗弯强度为34.77～127.85MPa, 介电常数为3.0～4.6, 介电损耗约为0.002.  相似文献   

13.
Surface pretreatment for adhesive bonding of aluminium with adhesive mediator SIP The present contribution describes the influence of different surface pretreatments including adhesive mediator SIP for adhesive bonding of aluminium alloy AlMg4,5Mn0,4. The investigations were performed using two cold hardening two‐components epoxy‐adhesives, one hot hardening one‐component epoxy‐adhesive and one cold hardening two‐components polyurethane‐adhesive. The adhesive bonds with epoxy‐adhesives show after three‐step pretreatment degreasing + corundblasting + SIP coating the highest adhesive strength values whereas adhesive bonds with polyurethane‐adhesive showed a decrease of bond strength as compared with the delivering surface condition.  相似文献   

14.
    
The microscopic surface films existing on the top of metallic layers play an important role in the process of joining by plastic deformation. The bond formation during cold welding processes is basically associated with the fracturing of surface films to produce intimate metallic contacts. The present paper aims at providing a numerical model to describe the cracking pattern of brittle surface films bonded to the ductile substrates. A microscale finite element model is developed which takes into account the fracturing mechanisms of thin surface films in roll bonding processes. The presented model is calibrated by using the existing experimental data for an aluminum alloy covered by a thin layer of oxide film. The model is also validated against a well‐known analytical model for periodic cracking. The distribution of stresses within the fractured surface film demonstrates that the generated cracks in the surface film have essentially a periodic pattern. Moreover, it is shown that the crack spacing is highly dependent on the properties of the surface film. Finally, the obtained results for the roll bonding show that a crack density saturation takes place at the entry of the roll bite where a small surface expansion is applied to the rolled samples.  相似文献   

15.
    
Metal plastic hybrids will become more important as components for lightweight constructions. It is reported about optimisation of making three layer hybrids consisted of a steel plate, an adhesion layer based of uretdione powder coating material and a flexible component polyurethane in model experiments. Hybrid formation is performed in a compression moulding process. The adhesion layer and the polyurethane are modified to increase the hybrid bond strength. Peel test are conducted to quantitatively characterize the bond strength and an apparent energy release rate is calculated based on the peel force. For hybrids with widths of 2 mm polyurethane stripes it is possible to increase the apparent energy release rate for about 30 % to 16 N/mm in comparison with a hybrid with unmodified components. These hybrids have the same high bond strength level as the strongest hybrids reported in literature. Concluding the optimisation results are discussed related to their relevancy for the interpretation of the adhesion mechanisms in the interface between adhesion layer and polyurethane.  相似文献   

16.
    
The mechanisms that control the lifetime of thermal barrier coating (TBC) systems have been traced by two particular overlay bondcoats serving as model systems: superalloy pins (IN100, CMSX‐4) with two alternative NiCoCrAlRE (RE: Hf, Y) bond coat compositions (i) NiCoCrAlY without and (ii) with co‐dopants of silicon and hafnium. On top an electron‐beam physical‐vapor deposited (EB‐PVD) yttria partially stabilized zirconia (YPSZ) TBC commonly mixed with 2 wt.% hafnia, or, rarely with 10 wt.%, was applied. The test pins were thermo‐cycled at 1100 and 1150 °C until failure. Identical lifetimes in cyclic tests on YPSZ TBCs with 2 (relatively high sintering rate) and 10 wt.% hafnia (relatively low sintering rate) preclude an effect of diffusion mechanisms of the YPSZ TBC on lifetime. The fit of lifetimes and test temperatures to Arrhenius‐type relationships gives activation energies for failure. These energies agree with the activation energies for anion and cation diffusion in alumina for the respective bondcoat variant: (i) for the NiCoCrAlY/TBC system for O2‐ diffusion in alumina, (ii) for the NiCoCrAlYSiHf/TBC system for Al3+ diffusion in alumina. SEM and EDS investigations of the thermally grown oxides (TGOs) confirm the mechanisms responsible for TBC failure as indicated by activation energies. Two categories of failure can be distinguished: (i) NiCoCrAlY coatings fail by an “adhesive mode of failure” along smooth bond coat/TGO interfaces driven by a critical TGO thickness. (ii) NiCoCrAlYSiHf coatings fail later and more reluctantly by a “cohesive” crack mode via de‐cohesion at the TGO/TBC interface. In the latter case a quasi‐integrity of the crack‐affected TGO is lengthily maintained up to failure by a crack‐pinning mechanism which runs via Al3+ supply from the bondcoat.  相似文献   

17.
    
Deformable sandwich sheet materials have the advantage to be produced as raw materials and to be formed afterwards to even complex geometries. Moreover they are cost effective and predestinated for mass production. For such systems the necessity is given for a good bonding to guarantee a good shear transfer between the single layers. Because of deformation, failures by delamination often occur at the interface between the metal and the epoxy layer. Therefore investigations at this interface were performed using Atomic Force Microscopy (AFM) and X‐ray Photoelectron Spectroscopy (XPS), to understand the basic effect of the surfaces’ bonding behavior in selected preparation steps of the system. Basic information about the adhesion mechanisms between the stainless steel 316L and the epoxy is given. The chemical interaction between the epoxy and the steel results in a significant reduction of Fe3+ to Fe2+.  相似文献   

18.
The model uncertainty has significant role in determination of safety factor. Eurocode has been considered partial factor covering uncertainties in the resistance model. Moreover, the model uncertainty has important role in full probabilistic verification. A stochastic analysis may yield to realistic results, only if the uncertainties have been involved in the calculation, properly. The uncertainty in predicted load‐carrying model may be identified by comparing the observed (experimental records) load‐carrying behaviour with the predicted value. Some general recommendations for considering uncertainty in probabilistic verifications are available in literature. In this study, the deviation of predicted values according to DIN EN 1996‐1‐1/NA model of masonry shear wall from test results has been derived. The best‐fitted distribution with associated statistical parameters (type of distribution, mean and coefficient of variation) has been proposed for uncertainty model. The uncertainty models have been compared with recommendations in the literature.  相似文献   

19.
    
Structural adhesives are used increasingly in new applications replacing conventional joining methods. Epoxy adhesives have the widest range of application of the various classes of adhesives arising principally from their extremely wide set of performance properties. They are known for their high stiffness and strength, as well for their low ductility and toughness. Currently, there is an increasing interest in developing methods of improving toughness. A toughened adhesive in general contains elastic or thermoplastic domains dispersed in discrete form throughout the resin matrix, in order to increase the resistance to crack‐growth initiation. This paper provides an overview of the current developments in the use of reinforcement materials and introduces the reader to early findings on the use of micro particles for toughness enhancement of adhesives. The theme of the use of materials of natural origin as reinforcement materials, giving special emphasis to the use of cork particles as toughener material is also presented.  相似文献   

20.
    
Loading novel metal nanosheets onto nanosheet support can improve their catalytic performance, but the morphological incompatibility makes it difficult to construct a well‐contacted interface, which is of particular interest in supported catalysts. Herein, Pd nanosheets (Pd NSs) are supported onto graphitic carbon nitride nanosheets (CNNSs) with intimate face‐to‐face contact through an in situ growth method. This method overcomes the limitations of the morphological incompatibility and ensures the intimate interfacial contact between Pd NSs and CNNSs. The nitrogen‐rich nature of CNNSs endows Pd NSs with abundant anchoring sites, which optimizes the electronic structure and improves the chemical and morphological stability of Pd NSs. The supported Pd NSs demonstrate high dispersion and exhibit largely enhanced activity toward the reduction of 4‐nitrophenol. The concentration‐normalized rate constant is up to 3052 min?1 g?1 L, which is 5.4 times higher than that obtained by unsupported Pd NSs. No obvious deactivation is observed after six runs of the recycling experiments. It is believed that the supported novel metal nanosheets with the intimately contacted interface may show promising applications in catalysis.  相似文献   

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