Al2O3/Mo复合材料的磨料磨损性能

对Al2O3/Mo复合材料的微观形貌进行了分析,同时测试了Al2O3/Mo复合材料的磨损行为。结果表明,随Al2O3体积分数的增加,基体的密度先增大后减小,显微硬度逐渐增加,磨损过程中产生的切削、犁沟在数量、深度上都有一定程度的减少。当Al2O3的体积分数为3%时,随着磨粒粒度的减小,复合材料的比磨损率逐渐增加,Al2...     

Application of multifunctional base monomer to dental composite resins

Experimental composite resin systems were prepared with visible-light-cured multifunctional matrices to which various amounts of organic composite filler were added. In comparison with the unfilled resins, the filled resin systems were tested for Knoop hardness, compressive and diametral tensile tests, thermal properties, and water sorption. Analyses of the results obtained for the unfilled resins indicate that the increased hardness and mechanical strength were dependent on the multifunctional base monomer. The effective composite resin system was the one that was filled with organic composite filler in the multifunctional comonomer having triethylene glycol dimethacrylate as a diluent monomer.     

Structure property relationship among novel dental composite matrix resins

Several novel dimethacrylate monomers of propoxylated diphenols have been synthesized to establish a correlation between their structure and the important properties of viscosity, curing shrinkage and wetting behaviour. These dimethacrylates were designed to possess linear and flexed structures. These new monomers exhibited very much lower viscosities compared to the conventionally used Bis-GMA. Good correlations were obtained for variations of the monomer structures with bulk viscosities and curing shrinkages. However, the wetting behaviour of these resins did not show any trend.     

Abrasive wear of particle-filled polymers

The abrasive wear rates of quartz and glass particle-reinforced PMMA have been measured as a function of filler volume fraction for silicon carbide, quartz and calcite abrasives. The wear rates were found to exceed those predicted by a simple series model. Abraded surfaces were studied by surface profile measurement and SEM. The excess wear is attributed to rapid wear of the filler at the matrix interface and to particle pulls-outs.     

Abrasive wear in filled elastomers

The abrasive wear of rubbers is strongly affected by the filler particles dispersed in the elastomer matrix. The fillers are incorporated usually for the purposes of mechanical reinforcement and improving the conductivity of the neat resins. It is found that the wear rates of the filled silicone rubbers increase slowly with filler concentration until a critical volume fraction,v _c, is reached, at which point they increase very rapidly with increasing filler concentration. This behaviour appeared to be universal in all the filled silicones we studied, regardless of the type of filler and silicone rubber used. However the magnitude of the critical filler fraction,v _c, can be changed significantly with the filler shape, resin cross-linking density and filler surface treatments. No reasonable relationship could be found between this wear behaviour and the mechanical properties measured in a macroscopic manner. Experimental evidence suggests that the incipient cracks that lead to wear losses may start within the thin layers of highly stressed material, the damage zones, surrounding the rigid particles. A simple model taking into account the stress concentration induced by the rigid fillers shows excellent correlation between the wear rate and the damage zones volume. With this new model, the observed wear behaviours can be explained satisfactorily.     

Water sorption and water-induced molecular mobility in dental composite resins

Water sorption in two resin composites, Kulzer's Solitaire (S) and SDI's Wave (W), and in a polyacid-modified composite resin, 3M's F2000 (compomer F), was investigated by means of equilibrium sorption isotherms (ESI) and of dynamic sorption (DS) measurements. Molecular mobility in these materials was studied by means of dielectric relaxation spectroscopy (DRS) and of thermally stimulated depolarization currents (TSDC) measurements. The results of ESI measurements show that at equilibrium, water is molecularly distributed in the materials and the effects of hydrophilic sites and clustering are negligible. Hysteresis effects in sorption–desorption cycles are larger in the resin composites than in the compomer. Equilibrium water uptakes in both ESI and DS conditions are rather low, in the range 1–2%. Diffusion coefficients of water are about 1×10^–8 cm²/s in the resin composites and by a factor of about 2 smaller in the compomer. Molecular mobility increases with hydration, as suggested by preliminary DRS and TSDC measurements. Detailed dielectric measurements may give important information for understanding, at the molecular level, water-induced degradation in dental materials.     

纳米技术在牙科复合树脂改良中的应用

以牙科复合树脂现存缺点为背景,对纳米技术对复合树脂的改良情况进行了研究,着重讨论了纳米材料对复合树脂的聚合收缩、抗菌性能和机械性能改良的一系列问题。研究结果表明,使用纳米技术和材料可以很好地改进复合树脂多方面的性能,同时对复合树脂的发展方向和研究前景进行了展望。     

Abrasive wear behaviour of polymeric materials

In this study the abrasive wear behaviour of aliphatic polyketone (APK), polyoxymethylene (POM), ultrahigh molecular weight polyethylene (UHMWPE), polyamide 66 (PA66), and 30% glass fibre reinforced polyphenylenesulfide (PPS + 30%GFR) engineering polymers at room temperature were studied. Pin-on disc arrangement wear tests were carried out at 1 m/s test speed and load value of 10 N. Tests were carried out for 50, 100, 150 and 200 m sliding distances. Emery paper grid varying from 150 to 1200 grade were used as an abrasive disc surface. After each test the mass loss of the pin was recorded. Finally the specific wear rates were deduced from wear volume of the pin for test duration distances of 50, 100, 150 and 200 m. The results showed that the highest wear rate is for POM with a value of 8.5 × 10⁻⁴ mm³/N m and the lowest wear rate is for UHMWPE with a value of 3.36 × 10⁻⁵ mm³/N m. Furthermore, for all materials the wear rate increases linearly with increasing wear duration distance.     

Contact wear mechanisms of a dental composite with high filler content

The contact wear behavior of a dental ceramic composite containing 92 wt% silica glass and alumina filler particles in a polymeric resin matrix was examined. Because this composite is used for dental restorations, the tests were conducted under contact conditions that were relevant to those that exist in the mouth. Wear tests were conducted on a pin-on-disk tribometer with water as a lubricant. Results on wear volume as a function of load indicated two distinct regimes of wear. The wear volume increased slightly as the load was increased from 1 to 5 N. As the load was further increased to 10 N, the wear volume increased by one order of magnitude. At loads above 10 N (up to a maximum of 20 N), the wear volume was found to be independent of load. Examination of the wear tracks by SEM revealed that a surface film had formed on the wear tracks at all loads. Examination of these films by TEM showed that the films contained a mixture of small gamma-Al₂O₃ crystallites and glass particles. FTIR analysis of the adhered films indicated the presence of hydrated forms of silica and alumina, suggesting reaction of filler particles with water. Chemical analysis by ICP-MS of water samples collected after the wear tests confirmed the presence of Al and other elemental constituents of the filler particles. It is proposed that three simultaneous processes occur at the sliding contact: tribochemical reactions and film formation, dissolution of the reacted products, and mechanical removal of the film by microfracture. At low loads, wear occurs primarily by a tribochemical mechanism, i.e., formation and dissolution of the reaction products. At higher loads, wear occurs by a combination of tribochemical processes and mechanical detachment of the surface film.     

Abrasive wear of diamond-coated dental burs and its impact on the parameters of the finished surface

The aim of this study was to evaluate the character and the abrasive wear rate of the dental diamond tools as well as their influence on the parameters of enamel surface of the tooth.     

Factors influencing mechanical and wear performance of dental composite: A review

With environmental concerns, the development of a posterior restorative as a true alternative to dental amalgam is needed. Hence in this regard, the development of dental composites have gained more and more research interest, as they have the advantages of better aesthetic look, better physical, mechanical and tribological properties over the other available dental materials. In this study, the physical, mechanical and wear behavior of dental composite materials have been reviewed. Numerous experimental results, analytical studies and their significance were also discussed for various dental composite materials. The wear performances of dental composite materials depend up on various factors including oral environment, resin chemistry, filler technology and interfacial bonding strength etc. In oral environment, the presence of medium such as water, air, heptane, ethanol, artificial saliva etc. and durations up to which composite is kept such as seven days, one month or three months etc. affect the performance of dental composite. Abrasion and erosion are two major causes for the wear behavior of dental composite / human teeth. The major issue, most significant challenges and effect of each of those factors affecting the performance of dental composite materials were also presented along with some recommendation.     

Abrasive wear and craze breakdown in polystyrene

The role of craze breakdown during the fracture process of abrasive wear in glassy polystyrene was investigated. At first, the wear resistance, _w, was compared with the craze breakdown strain as a function of molecular weight and diluent concentration. It was found that _w increases with molecular weight and decreases with the diluent concentration. Although craze breakdown strain also increases with molecular weight and decreases with the diluent concentration, the wear data do not converge into a single curve in a plot against the craze breakdown strain. Selected specimens were then studied by micro-indentation and micro-scratching experiments. An analysis of the scratch patterns and contact load at the polymer surface indicated that a critical stress criterion, rather than a critical strain criterion, may be suitable for the onset of the failure process in brittle polymer wear. With this criterion, the critical load for crack opening, _c, can be related to the craze breakdown strain and Young's modulus, and the observed deviation between the craze breakdown strain and _w can be explained.     

Abrasive wear study of bainitic nodular cast iron

The abrasive wear properties of the bainitic nodular cast iron under different austenitizing and isothermal transformation temperature and time were studied in the present paper. Using Optimol Schwingung reibung verschleiß wear tester, the point contact is adopted to compare the effect of those various heat-treatment conditions on wear properties. The weight loss, wear-scar diameter and friction coefficient were measured to evaluate the wear properties. Using scanning electron microscopy, the wear mechanisms can be understood by observing the worn surface. From the results of weight loss, wear-scar diameter and friction coefficient, it can be concluded that the wear resistance increased with increasing austenitizing temperature and the most suitable austempering temperature of the material used in the present study is from 270–300 °C for 4 h.     

Abrasive wear of Al‐SiC composites

The two‐ and three‐body abrasion of aluminium matrix composites, reinforced with silicon carbide particles, have been investigated. The metal matrix composites were fabricated by a powder metallurgy route involving a final hot extrusion step. Air atomised aluminium powder Al 1100 was used as matrix and α‐SiC_p as reinforcement with mean sizes of 10, 27 and 43 μm; in the proportions of 5, 10 and 20 vol.%. Using a pin‐on‐disc apparatus and a wet monolayer tester, two‐ and three‐body abrasion tests were carried out respectively against silicon carbide and alumina abrasives with four different grit sizes. The microstructural characterizations were performed using light microscopy. The dominant wear mechanisms were identified using scanning electron microscopy. The influence of type of the abrasive particles on wear resistance and dominating wear mechanisms was reported. Relationships between size and volume fraction of the SiC_p reinforcement and wear resistance were discussed. It was shown that SiC_p particles reinforcement increases the abrasion resistance against all the abrasives used. This increase was generally higher against alumina than against silicon carbide abrasives.     

Aging effect of pH on the mechanical and tribological properties of dental composite resins

This study evaluated the microhardness and wear behavior alterations of dental resins exposed to strong acid and alkaline degradation regimens. Fifty specimens of AP-X, Z350, P60, VITA ZETA and VITA LC resins were distributed into 10 groups. The control group was not subjected to aging treatment, while the other nine groups were assigned to the following pH solutions: 1, 7 or 13 for 1, 13 or 20 d, respectively. Vickers microhardness and wear behavior of materials without aging served as the reference. Repeated measurements were conducted for other specimens. Scanning electron microscopy was used to observe the morphology. Data were analyzed by repeated-measures one-way ANOVA, followed by the least significant difference (LSD) t-test (P?≤?0.05) for multiple comparisons. The aging process was aggravated over time. Alkaline medium significantly decreased the microhardness and wear resistance of resins, and led to serious surface damage. AP-X, P60 and Z350 immersed in different media showed a lower degradation than the nanoresin. The mechanical degradation of resin composites was aggravated with increased aging time. Strong alkaline media induced the largest reduction in mechanical and tribological properties. Hybrid resin composites with high filler loading exhibited better mechanical performance than nanoresins with low filler loading under different pH conditions.     

Effect of dilution on the kinetics of cross-linking thermal polymerization of dental composite matrix resins

The effect of dilution of 2,2-bis-(4-(2-hydroxy-3-methacryloxyprop-1oxy) phenyl) propane (bis-GMA) with trethyleae glycol demethacrylate (TEGDMA) on the extent of polymerization, Ep, has been studied using differential scanning calorimetry. The isothermal and dynamic measurements indicate that the Ep is affected dramatically by dilution. The residual polymerization was also found to be strongly influenced by dilution. However, the apparent activation energy, Eapp, was found to be independent of dilution.     

Abrasive wear behaviour of bio-active glass ceramics containing apatite

In this study, abrasive wear behaviour of bio-active glass ceramic materials produced with two different processes is studied. Hot pressing process and conventional casting and controlled crystallization process were used to produce bio-active ceramics. Fracture toughness of studied material was calculated by fracture toughness equations using experimental hardness results of the bio-active glass ceramic material. Two fracture toughness equations in the literature were used to identify the wear behaviour of studied ceramics. Wear resistance results that identified with both of the equations were similar. The results showed that the abrasive wear resistance of the bio-active glass ceramics produced with hot pressing process was found to be higher than that of the ceramics produced by conventional casting and controlled crystallization process.