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Normal Load (normal + load)
Selected AbstractsAbout 200 years after Mohs , Nanoscratching LiB3O5CRYSTAL RESEARCH AND TECHNOLOGY, Issue 11 2008P. Paufler Abstract Though simple scratch hardness tests after Mohs are still used today, the development of diamond nanoscratching equipment offers new possibilities to meet demands of modern nanotechnology. Preceding approaches to assign hardness values to materials are briefly reviewed, and scratch hardness is related to indentation hardness. Taking single-crystalline LiB3O5 as an example, the dependence of scratch morphology on the direction of scratching is demonstrated quantitatively. The coefficient of friction depends on normal load and varies between 0.25 and 0.37. Moreover, it is oscillating during scratching thus reflecting processes at nanoscale. Dislocation etch pits were observed due to scratching. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Similarities of stress concentrations in contact at round punches and fatigue at notches: implications to fretting fatigue crack initiationFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 7 2000Giannakopoulos A linear elastic model of the stress concentration due to contact between a rounded flat punch and a homogeneous substrate is presented, with the aim of investigating fretting fatigue crack initiation in contacting parts of vibrating structures including turbine engines. The asymptotic forms for the stress fields in the vicinity of a rounded punch-on-flat substrate are derived for both normal and tangential loading, using both analytical and finite element methods. Under the action of the normal load, P, the ensuing contact is of width 2b which includes an initial flat part of width 2a. The asymptotic stress fields for the sharply rounded flat punch contact have certain similarities with the asymptotic stress fields around the tip of a blunt crack. The analysis showed that the maximum tensile stress, which occurs at the contact boundary due to tangential load Q, is proportional to a mode II stress intensity factor of a sharp punch divided by the square root of the additional contact length due to the roundness of the punch, Q/(,(b,,,a),,b). The fretting fatigue crack initiation can then be investigated by relating the maximum tensile stress with the fatigue endurance stress. The result is analogous to that of Barsom and McNicol where the notched fatigue endurance stress was correlated with the stress intensity factor and the square root of the notch-tip radius. The proposed methodology establishes a ,notch analogue' by making a connection between fretting fatigue at a rounded punch/flat contact and crack initiation at a notch tip and uses fracture mechanics concepts. Conditions of validity of the present model are established both to avoid yielding and to account for the finite thickness of the substrate. The predictions of the model are compared with fretting fatigue experiments on Ti,6Al,4V and shown to be in good agreement. [source] A 2-D constitutive model for cyclic interface behaviourINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 11 2002Giuseppe Mortara Abstract The paper concerns a 2-D constitutive model for interface behaviour between sand and solid inclusions under cyclic loading. The model is based on the experimental results obtained from laboratory direct shear interface tests conducted under both constant normal load (CNL) and constant normal stiffness (CNS) conditions. The model is formulated in terms of interface stresses and relative velocities and has been derived by extending an elastoplastic isotropic model previously formulated for monotonic loading to stress reversal paths. Such extension consists in adding to the isotropic hardening mechanism a kinematic rotational one defined by an inner conical surface rotating around the origin of the stress space. This allows one to store the memory of the previous stress and relative displacement history giving to the model the capability to analyse the interface behaviour under cyclic loading. After a brief description of the criteria governing the monotonic model, the paper describes in detail the features of the kinematic hardening. Finally, the predictions of the model are compared with the experimental results obtained from CNL and CNS interface tests. Copyright © 2002 John Wiley & Sons, Ltd. [source] Source signature and elastic waves in a half-space under a sustainable line-concentrated impulsive normal forceINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 4 2002Moche Ziv Abstract First, the response of an ideal elastic half-space to a line-concentrated impulsive normal load applied to its surface is obtained by a computational method based on the theory of characteristics in conjunction with kinematical relations derived across surfaces of strong discontinuities. Then, the geometry is determined of the obtained waves and the source signature,the latter is the imprint of the spatiotemporal configuration of the excitation source in the resultant response. Behind the dilatational precursor wave, there exists a pencil of three plane waves extending from the vertex at the impingement point of the precursor wave on the stress-free surface of the half-space to three points located on the other two boundaries of the solution domain. These four wave-arresting points (end points) of the three plane waves constitute the source signature. One wave is an inhibitor front in the behaviour of the normal stress components and the particle velocity, while in the behaviour of the shear stress component, it is a surface-axis wave. The second is a surface wave in the behaviour of the horizontal components of the dependent variables, while the third is an inhibitor wave in the behaviour of the shear stress component. An inhibitor wave is so named, since beyond it, the material motion is dying or becomes uniform. A surface-axis wave is so named, since upon its arrival, like a surface wave, the dependent variable in question features an extreme value, but unlike a surface wave, it exists in the entire depth of the solution domain. It is evident from this work that Saint-Venant's principle for wave propagation problems cannot be formulated; therefore, the above results are a consequence of the particular model proposed here for the line-concentrated normal load. Copyright © 2002 John Wiley & Sons, Ltd. [source] Scaling of geological discontinuity normal load,deformation response using fractal geometryINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 8 2001Michael E. Plesha Abstract The mechanical behaviour of discontinuities in rock, such as joints, is known to be size-dependent. It is also suspected that the behaviour of larger size features, such as faults, is also size-dependent. This size dependence has serious implications for performing numerical response simulations of geological media. In this paper, we develop a new mathematical theory for scaling of one particular discontinuity property, namely the interface normal stiffness. To accomplish this, we idealize an interface to have fractal geometry, and we develop analytical relations which show that the interface normal stiffness, which is commonly thought to be a size-independent property, is in fact a size-dependent property and has fractal characteristics that may be exploited to develop a fundamental theory for scaling. Copyright © 2001 John Wiley & Sons, Ltd. [source] Characteristic modeling of the wear particle formation process from a tribological testing of polyethylene with controlled surface asperitiesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2007Hsu-Wei Fang Abstract To study the ultra-high molecular weight polyethylene (UHMWPE) wear particles-induced osteolysis which leads to the failure of artificial joints, microfabricated surfaces with controlled asperities have been applied to generate narrowly distributed UHMWPE wear particles with various sizes and shapes. Our previous study further facilitated single wedge sliding tests to investigate the mechanism of the UHMWPE particle generation. In this study, the attempt was made to characterize the particle generation process into a mathematical model to predict particle volume with a given surface-texture dimensions and mechanical loading conditions. The particle-generation process is decomposed into two steps: (1) penetration of the cutting edge, and (2) lateral sliding of the cutting edge. By combining the indentation experimental data, the viscoelastic responses of UHMWPE was incorporated in the model. The effects of normal load, feature height, and cutting edge angle on the wear particle volume were illustrated from model predictions. Both experimental results and model predictions indicate the same trend of effects of surface-texture geometry and mechanical conditions on the volume of particles. The results of the model predictions are close to the experimental results of the particle generation. However, the particle volume predicted by the model is larger than the experimental results. It is believed that the reprocessing of the generated particles and viscoelastic recovery of UHMWPE in the experiments account for this difference. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 587,594, 2007 [source] Laboratory fretting tests with thin wire specimensLUBRICATION SCIENCE, Issue 2 2007M.A. Urchegui Abstract Wire ropes, due to their construction and application, are prone to fretting damages. In order to know the wear behaviour of individual wires under fretting conditions, laboratory tests are required. The present work describes the preliminary fretting tests accomplished with thin steel wires to optimise the testing procedure. The tests were carried out with ,crossed-cylinders' configuration varying the stroke and normal load. Afterwards, the fretted surfaces were characterised by means of an optical and scanning electron microscope, and a diamond stylus. No significant influence of selected parameters was detected and a good correlation was proved for on-line measured parameters and off-line obtained values. Copyright © 2007 John Wiley & Sons, Ltd. [source] Investigation into the traction coefficient in elastohydrodynamic lubricationLUBRICATION SCIENCE, Issue 2 2004Y. S. Wang Abstract The elastohydrodynamic traction coefficients of two Chinese aviation lubricating oils were investigated for various loads, rolling velocities, and lubricant inlet temperatures using a self-made test rig. Traction coefficient versus slide-to-roll ratio curves were generated. The concept of critical load varying with the lubricant temperature is proposed. This paper presents a new empirical formula for the dynamic performance design of high-speed rolling bearings, that relates traction coefficient with normal load, rolling velocity, and lubricant inlet temperature. The coefficients of the formula may be computed by regression analysis of the experimental data. Two example calculations are presented. The predicted results from the formula agree well with experimental observations. [source] The role of the calcar femorale in stress distribution in the proximal femurORTHOPAEDIC SURGERY, Issue 4 2009Qi Zhang MD Objective:, To investigate the role of the calcar femorale in stress distribution in the proximal femur. Methods:, Twenty-five specimens of proximal femurs were fixed to simulate single-limb stance. Strain gauges were applied to record the strain under different loads. Strain values of 27 selected sites in the proximal femur were recorded and analyzed at the level of 100 N, 200 N, 300 N, 400 N, 500 N, 600 N and 700 N, respectively before and after disruption of the calcar femorale. Results:, When a normal load was being borne, strain values measured in the posterior and medial aspects of the proximal femur were greater than those measured in the anterior and lateral aspects, no matter whether the calcar femorale was disrupted or not. However after disruption of the calcar femorale, strain values in the posterior and medial aspects of the proximal femur increased significantly, whereas those of the anterior and lateral aspects decreased significantly. Conclusion:, The calcar femorale redistributes stress in the proximal femur by decreasing the load in the posterior and medial aspects and increasing the load in the anterior and lateral aspects. [source] How Well Are Bones Designed to Resist Fracture?,JOURNAL OF BONE AND MINERAL RESEARCH, Issue 4 2003John D Currey Abstract Because bone is obviously in some way adapted to the loads falling on it and because fracture is usually the failure of mechanical competence of main clinical importance, it is often thought that bones are adapted to resist fracture. In this perspective, I consider that this may not be the case. Bones may be designed to be very stiff, and therefore highly mineralized, and therefore brittle; they may be adapted to normal loads, but not to the characteristic loads occurring in falls, or may be very poorly designed to stop cracks traveling once they have started. Bones may also potentially fail in completely contrasting modes, and therefore their design has to be a compromise that does not resist either mode completely successfully. The greatly differing fracture incidences in different bones seen in pre-senile adults suggest that safety factors have been adapted, over evolutionary time, to produce the best compromise for a host of different design constraints. [source] Effect of contact configuration on the durability and friction coefficient of pressure-sprayed MoS2 coatings under fretting conditions,LUBRICATION SCIENCE, Issue 5 2009D. B. Luo Abstract Fretting wear is often found at the contact surfaces of a tight assembly where small-amplitude oscillatory movement occurs, which can be the concealed origin of some enormous accidents. Employment of solid lubrication coatings, as one of effective measurements to palliate the fretting damage, has been widely acknowledged. The present work studied the fretting behaviour of a molybdenum disulphide coating on SUS 316 stainless steel substrate by a relatively cheap and easy-to-use process: pressure spraying. Two contact configurations (cylinder-on-flat and ball-on-flat) were used in the tests with different displacement amplitudes (from 5 to 75,µm) and normal loads (from 100 to 400,N for ball-on-flat and from 400 to 1000,N for cylinder-on-flat). The results showed that large displacement amplitude is adverse to friction coefficient and coating lifetime and that under a critical contact pressure, coating endurance is improved contact pressure increases. Contact configuration influences friction coefficient by changing contact area and distribution of contact pressure. One master curve of average dissipated energy per cycle in initial stable stage was obtained for two contact configurations, which can be employed to approximately predict coating lifetime. Copyright © 2009 John Wiley & Sons, Ltd. [source] Tribological behavior of pure and graphite-filled polyimides under atmospheric conditionsPOLYMER ENGINEERING & SCIENCE, Issue 8 2003P. Samyn As the use of common engineering plastics in tribological systems is limited to low sliding velocities and low loads because of creep and insufficient temperature resistance, there is increasing interest in application of high-performance polymers such as polyimides, characterized by their ability to maintain favorable mechanical properties up to their melting point. However, for practical design, tribotesting remains necessary for determination of the material's performance under a given contact situation. In this article, two commercially available polyimides are tested at relatively high sliding velocities and contact pressures under atmospheric conditions of temperature and humidity. A consistent overview of tendencies in friction and wear for pure polyimides as a function of applied normal loads and sliding velocities is given. Addition of 15% by weight graphite powder as internal solid lubricant strongly influences friction and wear. Its behavior is compared with pure polyimide grades and differences are discussed in relation with experimental measured bulk-temperatures. A linear temperature law is derived as a function of pv-levels and a steady-state condition is found at different temperature levels, in accordance with thermal conductivity of the polymer bulks. In case of graphite additives, a steady state in temperature coincides with the regime condition of wear rate. [source] | ||||||||||||||||