Study of the ratcheting by the indentation fatigue method with a flat cylindrical indenter: Part I. Experimental study

2006 ◽  
Vol 21 (7) ◽  
pp. 1793-1797 ◽  
Author(s):  
B.X. Xu ◽  
Z.F. Yue
Keyword(s):  
Steady State ◽  
Fatigue Test ◽  
Indentation Depth ◽  
Fatigue Testing ◽  
Indentation Load ◽  
Compression Tests ◽  
Constant Rate ◽  
Secondary Stage ◽  
Indentation Fatigue ◽  
Analogous Equation

Generally, ratcheting is studied on round specimens under tension–compression tests with a nonzero mean load. This work explored the possibility of studying ratcheting by indentation fatigue with a flat cylindrical indenter. In the experiment, emphasis was concentrated on the influence of maximum indentation load (Pmax.), indentation load variance (ΔP = Pmax − Pmin) and frequency of cycling (f) on the indentation depth–cycle curves. The experimental results showed that the indentation depth–cycle curves are analogous to the conventional strain–cycle curve of uniaxial fatigue testing, which has a primary stage of decaying indentation depth per cycle followed by a secondary stage of nearly constant rate of indentation depth per cycle. It was found that the steady-state indentation depth per cycle is an approximate linear function of maximum indentation load (Pmax) and indentation load variance (ΔP = Pmax − Pmin) in the log–log grid. This relationship can be given with a power-law expression as an analogous equation of steady-state ratcheting rate. Further study showed that the influence of frequency of cycling on the steady state indentation depth per cycle can be ignored when the frequency of cycling exceeds a certain value. Finally, comparison was made between the conventional uniaxial fatigue test and indentation fatigue test for the steady-state stage. It was shown that the conventional uniaxial fatigue parameters can be obtained by the indentation fatigue method.

Numerical investigation of indentation fatigue on polycrystalline copper

2009 ◽  
Vol 24 (3) ◽  
pp. 1007-1015 ◽  
Author(s):  
B.X. Xu ◽  
Z.F. Yue ◽  
X. Chen
Keyword(s):  
Fatigue Test ◽  
Indentation Depth ◽  
Elastic Solid ◽  
Fatigue Loading ◽  
Cyclic Fatigue ◽  
Polycrystalline Copper ◽  
Fatigue Load ◽  
The Mean ◽  
Indentation Fatigue ◽  
Number Of Cycles

The dynamic indentation response of polycrystalline copper under cyclic fatigue loading is studied with a flat cylindrical indenter. First, a simple analytical model shows that in a purely elastic solid, the indentation depth responds with the same wavelength and frequency as the applied sinusoidal fatigue load. Next, a numerical simulation of an indentation fatigue test on an elastic-plastic solid (polycrystalline copper) is performed. Finite element analyses reveal that the mean indentation depth is controlled by both the mean of the indentation fatigue load and the load amplitude, while the amplitude of the indentation depth is independent of the mean load. Further investigations indicate that with an increased number of cycles, the increment of indentation depth reaches a constant rate. The steady state indentation depth rate is dependent not only on the amplitude of indentation fatigue load but also on the fatigue mean load, which is similar to strain accumulation during a conventional fatigue test. A parallel indentation experiment on annealed polycrystalline copper also confirms the effect of the fatigue mean load, indicating consistency with numerical results.

Study of ratcheting by the indentation fatigue method with a flat cylindrical indenter. Part II. Finite element simulation

2007 ◽  
Vol 22 (1) ◽  
pp. 186-192 ◽  
Author(s):  
B.X. Xu ◽  
Z.F. Yue
Keyword(s):  
Residual Stress ◽  
Finite Element ◽  
Indentation Depth ◽  
Fatigue Testing ◽  
Kinematic Hardening ◽  
Fatigue Behavior ◽  
Preceding Paper ◽  
Fem Analysis ◽  
Von Mises Stress ◽  
Indentation Fatigue

The finite element method (FEM) was used to study the flat cylindrical indentation fatigue behavior using a kinematic hardening model (A-F model). This study was motivated by the experimental work of the preceding paper [B.X. Xu and Z.F. Yue, J. Mater. Res.21, 1793 (2006)], in which there were obvious similarities in the behavior of conventional fatigue specimens and indentation fatigue specimens. It is proposed that the A-F model can predict the indentation fatigue behavior. Generally, the experimental behavior of the indentation fatigue testing can be explained by the FEM analysis. In addition, the effect of residual stress on the indentation depth per cycle was studied. The effect of friction between the indenter and the specimen and evolution of von Mises stress beneath the indenter was also investigated. Numerical results showed that the effect of friction on the indentation depth propagation can be neglected. Further analysis showed that the steady-state indentation depth per cycle increases with increasing compressive residual stress and decreasing tensile residual stress.

Recent Studies of Tire Braking Performance

1973 ◽  
Vol 1 (2) ◽  
pp. 121-137 ◽  
Author(s):  
J. L. McCarty ◽  
T. J. W. Leland
Keyword(s):  
Steady State ◽  
Rapid Cycling ◽  
Single Cycle ◽  
Steering Angle ◽  
Slip Ratio ◽  
Factors Affecting ◽  
Braking Performance ◽  
Constant Rate

Abstract The results from recent studies of some factors affecting tire braking and cornering performance are presented together with a discussion of the possible application of these results to the design of aircraft braking systems. The first part of the paper is concerned with steady-state braking, that is, results from tests conducted at a constant slip ratio or steering angle or both. The second part deals with cyclic braking tests, both single cycle, where brakes are applied at a constant rate until wheel lockup is achieved, and rapid cycling of the brakes under control of a currently operational antiskid system.

Control of an adiabatic continuous reactor by feeding catalyst

1980 ◽  
Vol 45 (11) ◽  
pp. 2903-2918 ◽  
Author(s):  
Josef Horák ◽  
Zina Valášková ◽  
František Jiráček
Keyword(s):  
Steady State ◽  
Reaction Temperature ◽  
Continuous Reactor ◽  
Control Element ◽  
Inlet Temperature ◽  
Switching Cycle ◽  
Point Temperature ◽  
Set Point ◽  
Constant Rate ◽  
Laboratory Reactor

Algorithms have been presented, analyzed and experimentally tested to stabilize the reaction temperature at constant inlet temperature and composition of the feed by controlled dispensing of the catalyst. The information for the control element is the course of the reaction temperature. If the temperature of the reaction mixture is below the set point, the catalyst is being fed into the reactor at a constant rate. If the reaction temperature is higher the catalyst dispenser is blocked; dispensing of the catalyst is not resumed until the set point temperature has been reached again. The amount of catalyst added is a function of the duration of the switching cycle. The effect has been discussed of the form of this function on the course of the switching cycle. The results have been tested experimentally on a laboratory reactor controlled in an unstable steady state.

Resistance to Outflow of Cerebrospinal Fluid Determined by Bolus Injection Technique and Constant Rate Steady State Infusion in Humans

Neurosurgery ◽  
1985 ◽  
Vol 16 (3) ◽  
pp. 336-340 ◽  
Author(s):  
Michael Kosteljanetz
Keyword(s):  
Cerebrospinal Fluid ◽  
Steady State ◽  
Bolus Injection ◽  
Point Of View ◽  
Injection Technique ◽  
Communicating Hydrocephalus ◽  
Constant Rate ◽  
High Degree ◽  
Infusion Technique

Abstract Two methods for the determination of resistance to the outflow of cerebrospinal fluid, the bolus injection technique and the constant rate steady state infusion technique, were compared. Thirty-two patients with a variety of intracranial diseases (usually communicating hydrocephalus) were studied. There was a high degree of correlation between the resistance values obtained with the two methods, but values based on the bolus injection technique were systematically and statistically significantly lower than those obtained with the constant rate infusion test. From a practical point of view. both methods were found to be applicable in a clinical setting.

Salivary Flow Induction by Buccal Permucosal Pilocarpine in Anesthetized Beagle Dogs

1992 ◽  
Vol 71 (11) ◽  
pp. 1762-1767 ◽  
Author(s):  
M.L. Weaver ◽  
J.M. Tanzer ◽  
P.A. Kramer
Keyword(s):  
Steady State ◽  
Salivary Flow ◽  
Salivary Secretion ◽  
Reversed Phase ◽  
Use Of Data ◽  
Constant Rate ◽  
First Pass ◽  
Steady State Plasma Concentration ◽  
Anesthetized Dogs ◽  
Drug Solution

We tested whether permucosal delivery of pilocarpine nitrate could be used to elicit significant salivary secretion. Pilocarpine (pKa 6.6 at 37°C) was applied as solutions (pHs 5.6, 6.6, 7.6; 15 mg/mL) to the buccal mucosa (2.8 cm2) of 6 anesthetized dogs. Saliva was collected continuously from cannulated submandibular and parotid ducts and blood sampled during and after drug administration. Plasma pilocarpine levels were determined by reversed-phase HPLC. Absorption rates were determined by use of data from separate zero-order intravenous infusions to the same dogs. Pilocarpine was buccally absorbed at a constant rate of 72.9 ± 38.5 μg/kg/h following its application at pH 7.6. At this pH of the drug solution, the time to appearance of pilocarpine in blood plasma was 0.31 ± 0.08 h, and the time to appearance of salivary flow was 0.86 ± 0.32 h. A threshold dose of 32.9 ± 7.5 ug/kg was required to induce secretion with the pH 7.6 drug, the steady-state plasma concentration was 28.9 ± 19.3 ng/mL, and the steady-state submandibular flow rate was 0.14 ± 0.11 mL/ min/gland pair. Salivary flow induction was symmetrical and reached levels as high as 0.35 mL/min/submandibular gland pair without apparent tachyphylaxis. Results at pHs 5.6, 6.6, and 7.6 were consistent with the hypothesis that pilocarpine is primarily absorbed as un-ionized drug. The data indicate that transmucosal delivery of pilocarpine, avoiding "first pass" hepatic loss, may hold promise for the treatment of xerostomia.

A Study of the Mechanical Role of Enamel and Dentin in Human Teeth

2012 ◽  
Author(s):  
Keyoung Jin Chun ◽  
Hyun Ho Choi ◽  
Jong Yeop Lee
Keyword(s):  
Surface Hardness ◽  
Mechanical Tests ◽  
Indentation Load ◽  
Bite Force ◽  
Compression Tests ◽  
Healthy Human ◽  
Human Teeth ◽  
Diamond Indenter ◽  
Dental Hard Tissues ◽  
Measured Hardness

The dental hard tissues of a tooth are combined of enamel and dentin together. The enamel protects the dentin and comes in direct contact with food during mastication. Bite force is expressed as compression force. The purpose of this study is to identify the primary roles of enamel and dentin during mastication by analyzing their mechanical properties and hardness. Healthy human teeth (age: 19.3 ± 4.1) were used as specimens for mechanical tests. The teeth, which underwent epoxy resin molding, were machine cut to make 10 enamel specimens, 10 dentin specimens and 10 enamel–dentin composite (ED) specimens of 1.2 mm × 1.2 mm × 3.0 mm (Width × Height × Length) in size. Compression tests were conducted using a micro-load system at 0.1 mm/min test speed. Teeth surface hardness (HV) was measured by a Vickers diamond indenter with a 300g indentation load. Data were obtained from 4 points on each enamel specimen and 4 points on each dentin specimen. The strain (%), stress (MPa) and modulus of elasticity (E, MPa) of the specimens were obtained from compression tests. The MAX. strain of the enamel, dentin and ED specimens were 4.5 ± 0.8 %, 11.9 ± 0.1 % and 8.7 ± 2.7 %, respectively. The MAX. stress of the enamel, dentin and ED specimens were 62.2 ± 23.8 MPa, 193.7 ± 30.6 MPa and 126.1 ± 54.6 MPa, respectively. The E values of the enamel, dentin and ED specimens were 1338.2 ± 307.9 MPa, 1653.7 ± 277.9 MPa and 1628.6 ± 482.7 MPa, respectively. The E of the dentin specimens was the highest and the E of the enamel specimens was the lowest, but the E values of all specimens was not significantly different in the T-test (P > 0.1). The measured hardness value of the enamel specimens (HV = 274.8 ± 18.1) was about 4.2 times higher than that of the dentin specimens (HV = 65.6 ± 3.9). Because of the values of MAX. stress and MAX. strain of the enamel specimens, the enamel specimens tended to fracture earlier than the dentin and ED specimens; therefore, enamel was considered to be more brittle than dentin and ED. Enamel is a harder tissue than dentin based on their measured hardness values. Therefore, enamel has a higher wear resistance, making it suitable for grinding and crushing, whereas dentin has a higher force function, making it suitable for abutment against bite force.

Indentation load relaxation experiments with indentation depth in the submicron range

1990 ◽  
Vol 5 (10) ◽  
pp. 2100-2106 ◽  
Author(s):  
W. R. LaFontaine ◽  
B. Yost ◽  
R. D. Black ◽  
C-Y. Li
Keyword(s):  
Indentation Depth ◽  
Metal Films ◽  
Indentation Load ◽  
Hard Substrate ◽  
Flow Properties ◽  
Load Relaxation ◽  
Relaxation Data ◽  
Flow Curves ◽  
Relaxation Experiments

Indentation load relaxation (ILR) experiments with indentation depths in the submicron range are described. Under appropriate conditions, the ILR data are found to yield flow curves of the same shape as those based on conventional load relaxation data. Variations in flow properties as a function of depth in submicron metal films deposited on a hard substrate are detected by the experiments described.

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