Wear Studies of Hydroxyapatite Composite Coating Reinforced by Carbon Nanotubes

Multi-walled carbon nanotubes (CNTs) have been successfully introduced into hydroxyapatite (HA) coatings using laser surface alloying. It is evident from transmission electron microscopy (TEM) observations that the CNTs present in the matrix still keep their multi-walled cylinder graphic structure, although they undergo the laser irradiation. Scratching test results indicated that the as-alloyed HA composite coatings exhibit improved wear resistance and lower friction coefficient with increasing the amount of CNTs in the precursor material powders. These composites have potential applications in the field of coating materials for metal implants under high-load-bearing conditions. (c) 2006 Elsevier Ltd. All rights reserved.

Characteristics of the interface of a laser-quenched steel substrate and chromium electroplate

The interface of a laser-discrete-quenched steel substrate and as-deposited chromium electroplate was investigated by ion beam etching, dissolving-substrate-away and using a Vickers microhardness tester, in an attempt to reveal the mechanism that the service life of the chromium-coated parts is increased by the duplex technique of laser pre-quenching plus chromium post-depositing. The laser quenching of the steel substrate can reduce the steep hardness gradient at the substrate/chromium interface and improve the load-bearing capacity of chromium electroplate. Moreover, the laser quenching prior to plating has an extremely great effect on the morphologies and microstructure of the substrate/chromium interface: there is a transient interlayer at the original substrate/chromium interface while there is not at the laser-quenchedzone/chromium interface; the near-substrate surface microstructure and morphologies of the free-standing chromium electrodeposits, whose substrate was dissolved away with nital 30% in volume, inherit the periodically gradient characteristics of the laser-discrete-quenched substrate surface. (c) 2006 Elsevier B.V. All rights reserved.

PEO陶瓷层对铝基体上DLC薄膜承载特性的影响

重载作用下,类金刚石(DLC)薄膜直接应用于铝合金等软金属基体上易发生脆性破裂和剥离而导致过早失效.针对这一问题,以PEO陶瓷层作为承载层,采用有限元数值计算方法,对复合涂层在均布接触载荷作用下的应力场进行研究.结果表明:陶瓷层可明显降低DLC膜的表面拉应力和界面剪应力,起到了良好的载荷支撑作用;陶瓷层厚度对涂层表面拉应力,界面及基体内剪应力的分布有显著影响,其中陶瓷层厚度与接触半宽比为0.150.30时,涂层可以获得较为合理的表面和界面应力场,从而改善DLC膜在铝合金基体上的摩擦磨损性能

Effect of Cl- on the corrosive wear of AISI 321 stainless steel in H2SO4 solution

The effect of Cl- on the corrosive wear behaviour of AISI 321 stainless steel in H2SO4 solution was studied via the corrosive wear rate, the load bearing capacity of passive film and the relationship between pitting and corrosive wear. There is a critical load at natural potential, below which the corrosive wear rate is slightly lowered by Cl-, while above which is increased. At natural potential there are more pits at low load than that at a higher one in the wear tracks and the pits are also deeper. The load bearing capacity is lowered by Cl- at passive region and then the corrosive wear rate increased.

预应力结构抗滑桩设计计算方法及其在滑坡治理中的应用研究

Landslide is a kind of serious geological hazards and its damage is very great. In recent years, landslides become more and more frequent along with increase of scale of engineering constructions and cause greater loss. Consequently, how to protect landslides has become important research subject in the engineering field. This paper improves the method how to compute landslide thrust and solves the irrational problem in the design of piles because of the irrational landslide thrust according to the theory and technology of existed anti-slide piles and pre-stressed cable anti-slide piles. Modern pre-stressing technology has been introduced and load balancing method has been used to improve the stressing behavior of anti-slide piles. Anchor cables, anti-slide piles and modern pre-stressing technology have been used to prevention complicated landslide. It is an important base to select values for the landslide thrust. An improved method to calculate design thrust of anti-slide piles has been presented in this paper on the base of residual thrust method by comparing existing methods to select values of landslide thrust in the design of anti-slide piles. In the method, residual landslide thrust behind the anti-slide piles and residual skid resistance before the piles has been analyzed, equitable distribution of residual landslide thrust behind the piles has been realized, and the method to select value of design thrust becomes more reasonable. The pre-stressed cable anti-slide piles are developed from the common anti-slide piles and are common method to prevent landslide. Their principle is that internal force of anti-slide piles is adjusted and size of section is diminished by changing constraint conditions of anti-slide piles. For landslides with deep slip surface and large scale of slopes, limitation of the method appears. Such landslides are in need of long piles and anchor cables which are not only non-economic but also can generate larger deformation and leave potential danger after prevention. For solving the problem, a new kind of anti-slide piles, inner pre-stressing force anti-slide piles, is presented in this paper, and its principle is that an additional force, which is generated in the inner anti-slide piles by arranging pre-stressed reinforcement or tight wire in a certain form in interior of anti-slide piles and stretching the steel reinforcement or tight wire, may balance out the internal force induced by landslide thrust whole or partly (load balancing method). The method will change bending moment which anti-slide piles are not good at bearing into compressive stress which piles are good at bearing, improve stressing performance of anti-slide piles greatly, diminish size of section, and make anti-slide piles not fissured in the natural service or postpone appearance of the fissures, and improve viability of anti-slide piles. Pre-stressed cable anti-slide piles and inner pre-stressing force anti-slide piles go by the general name of pre-stressed structure anti-slide piles in the paper, and their design and calculation method is also analyzed. A new calculation method is provided in the paper for design of anti-slide piles. For pre-stressed structure anti-slide piles, a new computation mode is firstly presented in the paper on the foundation of cantilever piles. In the mode, constraint form of load-bearing section of the anti-slide piles should be confirmed according to reservoir conditions in order to figure out amount of pre-stress of the anchor cables, and internal force should be analyzed for the load-bearing section of pre-stressed structure anti-slide piles so as to confirm anchorage section of anti-slide piles. Pre-stressed cables of the pre-stressed cable anti-slide piles can be arranged as required. This paper analyzes the load-bearing section of single-row and double-row pre-stressed cable anti-slide piles and provides a calculation method for design of the pre-stressed cable anti-slide piles. Inner pre-stressing force anti-slide piles are a new kind of structural style. Their load-bearing section is divided into four computation modes according to whether pre-stressed cables are applied for exterior of the anti-slide piles, and whether single-row or double-row exterior pre-stressed cables are applied. The load balancing method is used to analyze the computation modes for providing a method to design the inner pre-stressing force anti-slide piles rationally. Pre-stressed cable anti-slide piles and inner pre-stressing force anti-slide piles are applied to research on Mahe landfall in Yalong Lenggu hydropower station by the improved method to select value of design thrust of anti-slide piles. A good effect is obtained in the analysis.

Vertical Bearing Capacity of a Partially-Embedded Pipeline on Tresca Soils

Slip-line field solutions are presented for the ultimate load of submarine pipelines on a purely cohesive soil obeying Tresca yield criterion, taking into account of pipe embedment and pipe-soil contact friction. The derived bearing capacity factors for a smooth pipeline degenerate into those for the traditional strip-line footing when the embedment approaches zero. Parametric studies demonstrate that the bearing capacity factors for pipeline foundations are significantly influenced by the pipeline embedment and the pipe-soil frictional coefficient. With the increase of pipeline embedment, the bearing capacity factor Nc decreases gradually, and finally reaches the minimum value (4.0) when the embedment equals to pipeline radius. As such, if the pipeline is directly treated as a traditional strip footing, the bearing capacity factor Nc would be over evaluated. The ultimate bearing loads increase with increasing pipeline embedment and pipe-soil frictional coefficient.

On the Bearing Capacity of Suction Bucket Foundations in Saturated Sand

Abstract: The static bearing capacity of suction caisson with single-and four-caissons in saturated sand foundation is studied by experiments. The characteristics of bearing capacity under vertical and horizontal loadings are obtained ex- perimentally. The effects of loading direction on the bearing capacity of four-caissons are studied under horizontal load- ing. The comparison of the bearing capacity of single-caisson and four-caisson foundation, the sealed condition of cais- son’s top and loading rate are analyzed.

Response of the Bucket Foundation in Calcareous Sand under Horizontal Dynamic Load

Abstract: Experiments to determine the horizontal static bearing capacity are carried out first. The static bearing capacity is a reference for choosing the amplitudes of dynamic load. Then a series of experiments under dynamic horizontal load are carried out in laboratory to study the influences of factors, such as the scales of bucket, the amplitude and frequency of load, the density of soils etc.. The responses of bucket foundations in calcareous sand under horizontal dynamic load are analyzed according to the experimental results. The displacements of bucket and sand layer are analyzed.

Effects of 'sinking in' and 'piling up' on estimating the contact area under load in indentation

The phenomena of the 'piling up' and 'sinking-in' of surface profiles in conical indentation in elastic-plastic solids with work hardening are studied using dimensional and finite-element analysis. The degree of sinking in and piling up is shown to depend on the ratio of the initial yield strength Y to Young's modulus E and on the work-hardening exponent n. The widely used procedure proposed by Oliver and Pharr for estimating contact depth is then evaluated systematically. By comparing the contact depth obtained directly from finite-element calculations with that obtained from the initial unloading slope using the Oliver-Pharr procedure, the applicability of the procedure is discussed.

Increasing Critical Sensitivity of the Load/Unload Response Ratio before Large Earthquakes with Identified Stress Acclumulation Pattern

The Load/Unload Response Ratio (LURR) method is proposed for short-to-intermediate-term earthquake prediction [Yin, X.C., Chen, X.Z., Song, Z.P., Yin, C., 1995. A New Approach to Earthquake Prediction — The Load/Unload Response Ratio (LURR) Theory, Pure Appl. Geophys., 145, 701–715]. This method is based on measuring the ratio between Benioff strains released during the time periods of loading and unloading, corresponding to the Coulomb Failure Stress change induced by Earth tides on optimally oriented faults. According to the method, the LURR time series usually climb to an anomalously high peak prior to occurrence of a large earthquake. Previous studies have indicated that the size of critical seismogenic region selected for LURR measurements has great influence on the evaluation of LURR. In this study, we replace the circular region usually adopted in LURR practice with an area within which the tectonic stress change would mostly affect the Coulomb stress on a potential seismogenic fault of a future event. The Coulomb stress change before a hypothetical earthquake is calculated based on a simple back-slip dislocation model of the event. This new algorithm, by combining the LURR method with our choice of identified area with increased Coulomb stress, is devised to improve the sensitivity of LURR to measure criticality of stress accumulation before a large earthquake. Retrospective tests of this algorithm on four large earthquakes occurred in California over the last two decades show remarkable enhancement of the LURR precursory anomalies. For some strong events of lesser magnitudes occurred in the same neighborhoods and during the same time periods, significant anomalies are found if circular areas are used, and are not found if increased Coulomb stress areas are used for LURR data selection. The unique feature of this algorithm may provide stronger constraints on forecasts of the size and location of future large events.

Acoustic Emission Experiments of Rock Failure under Load Simulating the Hypocenter Condition

A series of acoustic emission (AE) experiments of rock failure have been conducted under cyclic load in tri-axial stress tests. To simulate the hypocenter condition the specimens are loaded by the combined action of a constant stress, intended to simulate

Load-Unload Response Ratio and Accelerating Moment/Energy Release Critical Region Scaling and Earthquake Prediction

The main idea of the Load-Unload Response Ratio (LURR) is that when a system is stable, its response to loading corresponds to its response to unloading, whereas when the system is approaching an unstable state, the response to loading and unloading becomes quite different. High LURR values and observations of Accelerating Moment/Energy Release (AMR/AER) prior to large earthquakes have led different research groups to suggest intermediate-term earthquake prediction is possible and imply that the LURR and AMR/AER observations may have a similar physical origin. To study this possibility, we conducted a retrospective examination of several Australian and Chinese earthquakes with magnitudes ranging from 5.0 to 7.9, including Australia's deadly Newcastle earthquake and the devastating Tangshan earthquake. Both LURR values and best-fit power-law time-to-failure functions were computed using data within a range of distances from the epicenter. Like the best-fit power-law fits in AMR/AER, the LURR value was optimal using data within a certain epicentral distance implying a critical region for LURR. Furthermore, LURR critical region size scales with mainshock magnitude and is similar to the AMR/AER critical region size. These results suggest a common physical origin for both the AMR/AER and LURR observations. Further research may provide clues that yield an understanding of this mechanism and help lead to a solid foundation for intermediate-term earthquake prediction.

Comparison of Various Adhesion Contact Theories and the Influence of Dimensionless Load Parameter

Three models, JKR (Johnson, Kendall and Roberts), DMT (Derjaguin, Muller, and Toporov) andMD (Maugis-Dugdale),are compared with the Hertz model in dealing with nano-contact problems. It has been shown that both the dimensionless load parameter, P D P=.1/4

Micro/Nanomechanical and Tribological Properties of thin Diamond-Like Carbon Coatings

The diamond-like carbon (DLC) films with different thicknesses on 9Crl8 bearing steels were prepared using vacuum magnetic-filtering arc plasma deposition. Vickers indentation. nanoin-dentation and nanoscratch tests were used to characterize the DLC films with a wide range of applied loads. Mechanical and tribological behaviors of these submicron films were investigated and interpreted. The hardnesses of 9Crl8 and DLC, determined by nanoindentation, are approximately 8GPa and 60GPa respectively; their elastic moduli are approximately 25OGPa and 600GPa respectively. The friction coefficients of 9Crl8, DLC. organic coating, determined by nanoscratch, are approximately 0. 35, 0. 20 and 0. 13 respectively. It is demonstrated that nanoindentation and nanoscratch tests can provide more information about the near-surface elastic-plastic deformation, friction and wear properties. The correlation of mechanical properties and scratch resistance of DLC films on 9Crl8 steels can provide an assessment for the load-carrying capacity and wear resistance