Outline of the method for determination of the fatigue life on the basis of density function distribution for a number of fatigue cycles

A mixture of C60D36 with 24.5 \pm 4.5% C60 by weight has been analysed by neutron diffraction techniques. The diffraction data was converted to a reduced density function G(r) by Fourier transformation. The C60 component of the G(r) was subtracted out. This enabled a comparison for five molecular models of C60D36, with symmetries T, Th , S 6 and two D 3 d isomers, with the experimental G(r). This specimen of C60D36 was found to be best described by a T symmetry isomer, in agreement with 13C NMR and IR data for C60H36 [Attalla et al. (1993). J. Phys. Chem. pp. 6329–6331].

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Energy for crack growth in model rubber components

Journal of Strain Analysis ◽

10.1243/03093247v072132 ◽

1972 ◽

Vol 7 (2) ◽

pp. 132-140 ◽

Cited By ~ 60

Author(s):

P B Lindley

Keyword(s):

Fatigue Life ◽

Crack Growth ◽

Crack Surface ◽

Uniform Stress ◽

Numerical Techniques ◽

Surface Displacements ◽

Tearing Energy ◽

Crack Growth Rates ◽

Essential Prerequisite

The determination of tearing energy, i.e. the energy available for crack growth, is an essential prerequisite for the estimation of the fatigue life of rubber components. Three methods of determining tearing energy are considered: from changes in total energy, from crack surface displacements, and by comparison with known values for the same crack growth rates. It is shown by applying experimental and numerical techniques to plane-stress testpieces, not necessarily of uniform stress or thickness, that the methods are satisfactory.

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Fatigue life determination of plasma nitrided medical grade CoCrMo alloy

Fatigue & Fracture of Engineering Materials & Structures ◽

10.1111/j.1460-2695.2010.01442.x ◽

2010 ◽

Author(s):

Ö. BAYRAK ◽

A. F. YETİM ◽

A. ALSARAN ◽

A. ÇELİK

Keyword(s):

Fatigue Life ◽

Cocrmo Alloy ◽

Medical Grade

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Design Formulas of Blind End Closures for High Pressure Vessels

Journal of Pressure Vessel Technology ◽

10.1115/1.2967886 ◽

2009 ◽

Vol 131 (3) ◽

Author(s):

R. D. Dixon ◽

E. H. Perez

Keyword(s):

High Pressure ◽

Fatigue Life ◽

Maximum Stress ◽

Accurate Determination ◽

Pressure Vessels ◽

Stress Distributions ◽

Fatigue And Fracture ◽

Asme Code ◽

Section Viii

The available design formulas for flat heads and blind end closures in the ASME Code, Section VIII, Divisions 1 and 2 are based on bending theory and do not apply to the design of thick flat heads used in the design of high pressure vessels. This paper presents new design formulas for thickness requirements and determination of peak stresses and stress distributions for fatigue and fracture mechanics analyses in thick blind ends. The use of these proposed design formulas provide a more accurate determination of the required thickness and fatigue life of blind ends. The proposed design formulas are given in terms of the yield strength of the material and address the fatigue strength at the location of the maximum stress concentration factor. Introduction of these new formulas in a nonmandatory appendix of Section VIII, Division 3 is recommended after committee approval.

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Fatigue Life Assessment of Self-Expandable NiTi Stent

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.627.45 ◽

2014 ◽

Vol 627 ◽

pp. 45-48

Author(s):

Cristian Sorin Nes ◽

Angelica Enkelhardt ◽

Lucian Bogdan ◽

Nicolae Faur

Keyword(s):

Fatigue Life ◽

Arterial Wall ◽

Cylindrical Tube ◽

Life Assessment ◽

Cyclic Loads ◽

Fatigue Life Assessment ◽

A Value ◽

Vessel Stenosis ◽

Fatigue Characteristics

Objectives: This paper presents a numerical fatigue life assessment of a self-expandable Nitinol stent. The analysis was performed using the ANSYS 11 software. Methods: Stent durability is an issue which must be addressed during the design of implants. Given the corrosive properties of blood and the cyclic loads that are applied on the stent (the cyclic variation of blood pressure), the determination of fracture parameters and fatigue characteristics of the implant is highly recommended. Breaking of the stent’s wire is particularly dangerous because it can cause the dislocation of a piece of stenotic plaque, which in turn can block a smaller artery, causing a heart attack. On the other hand, any discontinuity in stent structure acts as an accumulating place for stenosis particles, significantly shortening the life of the implant. The stent consists of a cylindrical tube 22.42 mm long, with a diameter of 8.3 millimeters. The wire section is square, 0.2x0.2 millimeters. The stent is only subjected to the pressure generated by the stenoted arterial wall. This evenly distributed pressure is defined at the outer surface of the stent and has a value of 2.5 MPa, corresponding to a 56% blood vessel stenosis. This way, the most severe loading conditions for the stent could be simulated. The stress distribution was then used to asses the fatigue life of the stent. Results and conclusions: The results showed that, in normal conditions (with the maximal internal pressure of 139 mm Hg = 18533 Pa), no damage appears on the stent after 107 cycles.

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Determination of the Anand Viscoplasticity Model Constants for SnAgCu

Advances in Electronic Packaging, Parts A, B, and C ◽

10.1115/ipack2005-73352 ◽

2005 ◽

Cited By ~ 22

Author(s):

Bryan Rodgers ◽

Ben Flood ◽

Jeff Punch ◽

Finbarr Waldron

Keyword(s):

Fatigue Life ◽

Plastic Strain ◽

Test Specimen ◽

Strain Curve ◽

Temperature Cycling ◽

Displacement Rate ◽

Experimental Measurements ◽

Strain Rates ◽

Constant Displacement

The major focus of this work was the determination of the nine constants required for Anand’s viscoplastic constitutive model for a lead-free solder alloy, 95.5Sn3.8Ag0.7Cu and to compare them with those for SnPb. The test specimen was a cast dog bone shape based on ASTM E 8M-01, with a diameter of 4mm and a gauge length of 20mm. A series of tensile experiments were carried out: constant displacement tests ranging from 6.5 × 10−5/s to 1.0 × 10−3/s at temperatures of 20°C, 75°C, and 125°C; constant load tests at a range of loads from 10MPa to 65MPa, also at temperatures of 20°C, 75°C, and 125°C. A series of non-linear fitting processes was used to determine the model constants. Comparisons were then made with experimental measurements of the stress-plastic strain curves from constant displacement rate tests: it was found that the model matched the experimental data at low strain rates but did not capture the strain hardening effect, especially at high strain rates. A finite element model of the test was also constructed using ANSYS software. This software includes the Anand model as an option for its range of viscoplastic elements, requiring that the nine constants be input. In this case, an 8-noded axisymmetric element (VISCO108) was used to model the test specimen under constant displacement rate loading. The model was then used to predict the stress-plastic strain curve and this was compared to both the experimental measurements and the fitted Anand model. Reasonable agreement was found between the Anand model and the FE predictions at small strain rates. Finally, a BGA device was simulated under accelerated temperature cycling conditions using ANSYS with the fitted Anand for the SnAgCu solder joints. A Morrow-type fatigue life model was applied using empirical constants from two published sources and good agreement was found between experiment and predicted fatigue life.

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The Fictitious Radius as a Tool for Fatigue Life Estimation of Notched Elements

Materials Science Forum ◽

10.4028/www.scientific.net/msf.726.27 ◽

2012 ◽

Vol 726 ◽

pp. 27-32 ◽

Cited By ~ 4

Author(s):

Grzegorz Robak ◽

Marcel Szymaniec ◽

Tadeusz Łagoda

Keyword(s):

Fatigue Life ◽

Notch Root ◽

Experimental Tests ◽

Life Estimation ◽

Fatigue Life Estimation

In this paper, the fictitious radius - according to Neuber’s method for determination of stresses at the notch root was used. Next, the fatigue lives of elements of the ring notches were calculated, and then compared with results of experimental tests of S235JR steel samples. However, the obtained fatigue lives did not bring satisfactory results. It has been demonstrated that the fictitious radius strongly depends on the expected fatigue life

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