Physicomechanical aspects of fretting and fretting fatigue of metallic stiff joints

The models of fretting corrosion and fretting fatigue mechanisms and the processes in the contact zone of parts subjected to fretting fatigue are discussed. Experimental data on the fretting and fretting fatigue mechanisms and on the effect of fretting on the fatigue resistance of structural materials are presented.     

A new suction device for microsurgery

A new suction device for microsurgical procedures is presented. This device is made of soft, compliant PVC, which enables all fluids to be evacuated from the surgical field without damaging the surrounding soft tissue. The device is designed with front and radial ports that allow placement onto the blood vessel or nerve while the anastomosis is being performed. There is a tapered end providing the surgeon with fine control of the suction. Unlike other bulky suction devices, this one readily fits into the operative field without inhibiting operative procedures. It also readily fits varying sizes of conventional Frazier-type tips. The device has been used in over 100 microsurgical procedures and it has served well.     

A high-frequency shear device for testing soft biological tissues

Accurate mechanical property data obtained at large shear deformations and high frequencies are a fundamental component of realistic numerical simulations of soft tissue injury. Although many commercial systems exist for testing shear properties of viscoelastic materials with properties similar to soft biological tissue, none are capable of determining properties at high loading rates necessary for modeling soft tissue injury. Previous custom shear testing systems, though capable of high-frequency loading, indirectly measure tissue properties by using analytical corrections for inertial effects. To address these limitations, a new custom designed oscillatory shear testing apparatus (STA) capable of testing soft biological tissues in simple shear has been constructed and validated. Through a proper selection of sample thickness, direct measurement of material properties at high frequencies is achieved mechanically without analytical inertial adjustments. The complex shear modulus of three mixtures of silicone gel with viscoelastic properties in a range similar to soft biological tissue was characterized in the STA over a dynamic frequency range of 20-200 Hz and validated with a commercially available solids rheometer. The frequency-dependent complex shear modulus measurements of the STA were within 10% of the rheometer measurements for all mixtures over the entire frequency range tested. The STA represents substantive improvement over current shear testing methods by providing direct measurement of the shear behavior of soft viscoelastic material at high frequencies. Mechanical property data gained from this device will provide a more realistic basis for numerical simulations of biological structures.     

Effect of contact pad rigidity and fretting fatigue design curve

In fretting fatigue the nucleation and early propagation of fatigue crack depends on the state of stress near the contact edge. Contact pad rigidity is one of the factors that influence the stress state near the contact edge, there by influencing fretting fatigue strength. In the present study the effect of contact pad rigidity on fretting fatigue strength of turbine steels (Ni-Cr-Mo-V steel specimen with 12 Cr steel contact pads) were investigated. To study the effect of contact pad rigidity, contact pads with different pad foot height were used. FEA was performed to evaluate the stress distribution near the contact edge. The results showed that with increase in contact pad rigidity the fretting fatigue strength decreased. The results obtained were explained based on the stress distribution near the contact edge evaluated by using FEA. By combining the experimental results and FEA, fretting fatigue design curves were proposed.     

A novel inclusion inspection method employing 20 kHz fatigue testing

In this report, we propose a novel inclusion inspection method based on the use of 20 kHz fatigue tests. In these fatigue tests, which take a little time, the most harmful inclusions or internal facets appear automatically at the origin of fish-eye fractures. The novel inclusion inspection employing fatigue tests was demonstrated, in two high-strength steels, to be superior to a conventional inspection by scanning of polished surfaces. Our novel inspection method was first demonstrated with a JIS-SUP12 spring steel that contained relatively large Al₂O₃ inclusions. The novel inspection method appeared to detect larger Al₂O₃ inclusions than the conventional inspection, since the inspection volume was 22 times more extensive than that of conventional inspections. On the other hand, there was little difference in the maximum Al₂O₃ inclusion sizes estimated for several volumes of steel between the novel and conventional inspections. Second an inclusion inspection was conducted on JIS-SCM440 low-alloy steel. For this steel, the discussion focuses on TiN inclusions. Fatigue tests appeared to be the only way of conducting inspections for TiN inclusions, since the inclusions could not be detected in the conventional inspection. In measuring the TiN inclusion sizes, however, etching of the fracture surfaces was found to be absolutely necessary, since the inclusion sizes on the fracture surfaces were significantly different from the true sizes. The difference seriously influenced the estimation of the maximum inclusion sizes. Even in the case of internal-facet-originated type fish-eye fractures etching was found to be necessary, since TiN inclusions occasionally appeared after etching.     

Shear force effects on fretting fatigue behavior of Ti-6Al-4V

The present study examined the role of shear force on fretting fatigue behavior as well as its interdependence on other test variables, such as bulk stress, normal load, relative slip, and coefficient of friction, by using a fretting test system where shear force was controlled independent of other applied loads. Two contact geometries were used: cylinder-on-flat and flat-on-flat. For a given applied bulk stress and normal load condition, there is a simple relationship between shear force and relative slip up to a maximum value of shear force where contact condition changes from partial slip to gross slip. The effects of shear force and relative slip therefore can be combined together to characterize fretting behavior such as in a fretting map. Under a prescribed loading condition, fretting fatigue life decreases as shear force increases in partial slip condition. Further, the inter-relationships between shear force and other variables appear to be independent of contact geometry. In the tests where shear force is not applied independently rather when generated indirectly through the compliance of fretting setup, it is affected by the applied bulk stress and normal load, which in turn affect the relative slip range. Therefore, there is a complex interaction among various variables, and it is difficult to isolate their effects on fretting behavior in such test conditions. An independent control of relative slip in the fretting test thus provides an alternate means to characterize the variables’ effects and their interdependence.     

铝电解质初晶温度测定装置及初晶点数模的研究

电解质初晶温度是铝电解生产过程中的一个重要参数,本文研究了直接测定铝电解质初晶温度的装置。整套装置由进样系统、高温炉、炉温控制系统、计算机测控系统组成。采用新装置可以在线实时读取数据并自动绘制温度曲线,获取结果方便准确,减少了人为误差。同时采用均匀设计法进行试验设计,考察了Na3AlF6-Al2O3-MgF2-CaF2-LiF五元体系的初晶温度,并由此建立了该体系初晶温度的数学模型。由此模型得出的预报值与实测值之间的绝对误差在±5℃以内。     

一种新型涡流检测法及其检测效果

涡流检测法是非常常用的金属材料缺陷检测的无损检测方法,为了改进传统涡流检测法难以微型化的不足,提出了一种新型涡流检测法,分别用小永磁体和高精度磁传感器代替了传统涡流检测法的激励线圈和接受线圈.通过试验和数值模拟相结合的研究方法,对新型涡流检测法的原理及检测效果进行了研究.结果表明,新型涡流检测法的检测原理可行,检测装置...     

A new osteoblast cell culture system for standardized testing of biomaterials

For in vitro testing of new biomaterials cultured fibroblasts are employed. In the case of the agar diffusion test survival of cells is involved in the presence of the material to be tested. Further statements on the biological effects of a biomaterial require the use of cell cultures adapted to the tissue concerned and the underlying problem being investigated. In the present study, an osteoblast cell culture system with which implant surfaces in contact with bone can be tested as required by the relevant standards is described. Test bodies made of titanium, polystyrene or copper were used in the conventional agar diffusion test, and were also overgrown with fibroblasts or a cell line of foetal human osteoblasts. For the agar diffusion test, the test criterion was the extent of the inhibition area on staining with neutral red, while for the overgrowth, the mean cell diameter and the number of cells was employed. The phenotype of the osteoblast cell line was determined immunohistochemically by means of alkaline phosphatase or immunohistologically by means of collagen I and osteocalcin. Calcification was demonstrated using the v. Kossa stain. In the case of the osteoblasts, a differentiation of a collagen I and alkaline phosphatase-positive phenotype over an osteocalcin-positive phenotype to an increase in calcium deposition was shown. As in the case of the agar diffusion test, direct overgrowth also revealed no cytotoxic effect for titanium and polystyrene. In contrast, a cytotoxic effect consisting in a decrease in the number of cells and also a left shift in the size distribution was observed for copper. The standard deviations of the individual tests were less for overgrowth than for the agar diffusion test. The culture system for osteoblast cells thus meets the criteria of the EN/DIN 30993-5 in terms of the quality and accuracy of the results obtained. In addition to excluding direct cytotoxicity, this test system offers a new possibility of examining the influence of the material on cell growth. Consequently, it permits a repeatable examination of proliferation and differentiation of the osteoblasts on each material surface.     

Chronic fatigue syndrome: A new clinical application.

Chronic fatigue syndrome (CFS), a poorly understood illness of uncertain etiology, has received scant attention in the psychological literature. This article reviews the CFS research literature from a clinical perspective, presents explanatory models of the illness, and describes cognitive–behavioral interventions for CFS. Finally, case management issues that are based on the author's research and clinical observations are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The CO2 laser otoscope. A new application device for paracentesis

The CO2 laser myringotomy is a current low-pain procedure for middle-ear ventilation for secretory otitis media (SOM) that can be performed under topical anesthesia, even in children. The duration of middle-ear ventilation is essentially determined by the size of the perforation created. Perforations with a diameter greater than 2 mm ventilate the tympanic cavity for approximately 3 weeks, thus avoiding tympanic ventilation tubes. To date, the CO2 laser beam can only be reliably applied to the tymapanic membrane via a micromanipulator system coupled to an ear microscope. The CO2 laser otoscope is a new application system that markedly reduces the technical complexity of surgery and improves the mobility and availability of the system. The incorporation of a small inexpensive CO2 laser in the otoscope represents a significant development in SOM therapy.     

A novel implantable electromechanical ventricular assist device. First acute animal testing

A method for the simultaneous determination of eight kinds of conjunct bile acids in human bile was developed by HPLC. They were separated on a YWG-C18 (3 microns) column at 30 degrees C, with methanol/water (65/35, V/V, pH3.0) as mobile phase, and detection wavelength at UV 210 nm. The linear ranges were 50-1,000 microns.ml-1, the recoveries were 91.2%-108.6%. The biles of 30 cases with cholelithiasis cholecystolithiasis and 20 cases without gallstone were detected by HPLC. The results showed that the constitution of bile acids was different between patients with cholelithiasis cholecystolithiasis and patients without gallstone.     

The thermal fatigue testing of heat-resisting sheet materials

Summary A study was made of temperature distribution along the axis of a specimen from a heat-resisting sheet material during thermal fatigue testing. The use of special plates made from a sintered silicon carbide base material for equalizing the temperature distribution is proposed. Curves and formulas are given for the temperature distribution with and without such plates.     

Evolution of fretting fatigue damage and relaxation of residual stress in shot-peened Ti-6Al-4V

The evolution of fretting fatigue damage was investigated in shot-peened Ti-6Al-4V samples, by measuring the changes in the surface residual stress, using the X-ray diffraction technique. The surface residual stress was found to relax as the number of fretting fatigue cycles increased. The relaxation behavior of the residual stress with the increasing number of fretting fatigue cycles was observed to occur in three stages. In the first 20 pct of the fretting fatigue life, a drastic relaxation was observed. In the second part (between 20 and 70 pct), a gradually increasing behavior was observed. During the last 20 to 30 pct of the fretting fatigue life, a dramatic relaxation of the residual stress was found to occur. A complete relaxation of the residual stress occurred in the fracture region. A scanning electron microscope observation of the microstructure of the damaged region was used to examine the mechanisms leading to the relaxation of the residual stress. The development of delaminations at the early stages of the accumulation of the fretting fatigue damage was observed to be the main cause of the initial relaxation. The generation of microcracks from the voids left behind by the delaminations is responsible for the additional relaxation of the residual stress. The coalescence of the microcracks generated from different delaminated regions produced yet more relaxation of residual stress and, ultimately, the final fracture of the specimen.