Preparation and Properties of Friction Materials by Using Two Kinds of Fibrous Industrial Minerals

The basic technology and properties of the brake blocks made of modified needle-like wollastonite and fibrous sepiolite were intensively researched.The impact strengthes and fixed velocity friction of the brake blocks prepared by different recipes were tested. The testing results show that it is feasible for needle-like wollastonite and fibrous sepiolite to take the place of asbestos as the reinforced materials of friction materials.The braking effect of the brake blocks is the best when the ratio of the needle-like wollastonite to the fibrous sepiolite was 1∶6.

Friction and Wear Behavior of Ti-6Al-7Nb Biomaterial Alloy

Titanium has been increasingly applied to biomedical application because of its improved mechanical characteristics, corrosion resistance and biocompatibility. However their application remains limited, due to the low strength and poor wear resistance of unalloyed titanium. The purpose of this study is to evaluate the friction and wear behavior of high-strength titanium alloys: Ti-6Al-7Nb used in femoral stem (total hip prosthesis). The oscillating friction and wear tests have been carried out in ambient air with oscillating tribotester in accord with standards ISO 7148, ASTM G99-95a, ASTM G 133-95 under different conditions of normal applied load (3, 6 and 10 N) and sliding speed (1, 15 and 25 mm.s-1), and as a counter pair we used the ball of 100C 6, 10 mm of diameter. The surface morphology of the titanium alloys has been characterized by SEM, EDAX, micro hardness, roughness analysis measurements. The behavior observed for both samples suggests that the wear and friction mechanism during the test is the same for Ti alloys, and to increase resistance to wear and friction of biomedical titanium alloys used in total hip prosthesis (femoral stems) the surface coating and treatment are required.

EFFECT OF FRICTIONAL FORCE ON GEARING CONTACT FATIGUE STRENGTH

The model for computing frictional coefficient between two teeth faces at the state of mixed elastohydrodynamic lubrication is established. And then more than 80 sets of numerical calculations and six sets of disc fatigue tests are completed. The results show that when the film thickness ratio λ 〈1.6, frictional coefficient μ is drastically decreased as λ. rises; Thereafter it decreases smoothly until λ=4.5. When λ〉4.5, however, it goes up again with λ, which indicates that the excessive film thickness ratio will deteriorate gearing contact fatigue strength. At the end, the formulae for determining the frictional coefficients are formed.

Unloading damage patterns of rock slopes in open pit mines and analyses of their mechanisms

The stability of slopes is essential for ensuring safe production in open-pit mines.Analyzing and managing the deformation and failure of the slope rock mass becomes more challenging as the slope height increases.To investigate the damage patterns of slopes with varying heights,three slope models were developed based on a rock slope in Dagushan,China.The deformation failure processes of slopes under the influence of excavation and unloading were analyzed using the base friction test method in combination with digital image technology contrasting.The results supported the following findings:(1)Unloading tensile stress caused lateral partitioning in the slope.Both the foot and top of the slope underwent initial tensile cracks.(2)The destabilization mechanism of unloading deformation in slopes of different heights involved a combination of traction at the foot of the slope or pushing at the top of the slope,followed by accelerated deformation,deceleration creep,and overall destabilization.(3)The unloading damage patterns of slopes at different heights were summarized as follows:compression tension cracking,traction,and slip damage for medium and low slopes;compression tension cracking,traction,and slip failure for the upper part of high slopes;and relaxation tension cracking,pushing,traction,and slip failure for the lower part.Moreover,the upper part of ultra-high slopes exhibited compression tension cracking,traction,and slip failure,while the middle and lower parts displayed relaxation tension cracking,pushing,traction,and slip patterns.Finally,numerical simulations were conducted to verify the results of the test analyses,which demonstrated good consistency.These research results were of great engineering value for proposing effective safety management measures for high slopes.

Experimental study on mechanical properties of methane-hydrate-bearing sediments

Mechanical properties of methane hydrate- bearing-sediments （MHBS） are basic parameters for safety analysis of hydrate exploration and exploitation. Young＇s modulus, cohesion, and internal friction angle of hydrate- bearing sediments synthesized in laboratory, are investigated using tri-axial tests. Stress-strain curves and strength parameters are obtained and discussed for different compositions and different hydrate saturation, followed by empirical expressions related to the cohesion, internal friction angle, and modulus of MHBS. Almost all tested MHBS samples exhibit plastic failure. With the increase of total saturation of ice and methane hydrate （MH）, the specimens＇ internal friction angle decreases while the cohesion increases.

Study of base friction simulation tests based on a complicated engineered bridge slope

In this paper,a physical base friction test model of a slope is established.The model is based on similarity principles and the geological conditions of a complicated bridge slope during construction,deformation and failure.The behavior of the slope in both its natural state and during excavation loading is qualitatively analyzed through base friction tests.The base friction test results are then subjected to comparison and analysis using finite element numerical simulation.The findings show that the whole engineered slope tends to stabilize in its natural state,whereas instabilities will arise at faulted rock masses located near bridge piers during excavation loading.Therefore,to ensure normal construction operation of bridge works,it is suggested that pre-reinforcement of faulted rock masses be performed.

A review on food oral tribology

Food entering the oral cavity undergoes a series of complex processing behaviors.It is subjected to compression and shearing by the teeth,tongue,and palate to reduce its size and mix with saliva until it is swallowed.The oral processing behaviors are thought to be closely related to both food and oral frictional properties.Much effort has been made in recent decades about food oral tribology to explore this complicated lubrication behavior.Understanding the lubrication mechanism of food in the mouth is important for improving the consumption experience and developing the novel food.This paper provides a new perspective on the effects of composition,texture,structure,and saliva-food component interactions on lubrication properties of different foods,the relationship between sensory perception and oral frictional behavior,and the mechanism and pattern of lubrication categorized by common food types.The roles of tribology in the improvement of food taste,the search for healthier ingredient substitutes,functional foods,and the development of green foods are analyzed.Conceptual and numerical prediction models among physical properties,sensory perception,and frictional behavior of food are discussed.Studies of simulating oral processing,such as the selection of friction pair materials,physical modification of contact surfaces,addition of saliva,different modes of motion,and contact forms are concluded and classified.The progress of commercial friction apparatus as well as customized friction devices applied to the food sector in recent years are described.The characteristics,performances,and applications of these tribological instruments are analyzed and compared.In addition,the results achieved by oral tribology in identifying adulterated foods and ensuring food safety are presented.Finally,some suggestions are put forward for the current challenges and future development of food oral tribology.