Correlating R-ratio Effects on FCG Behavior Using ΔKd Function

Fatigue crack propagation was modeled by using the cyclic plasticity material properties and fatigue constants for crack initiation. The cyclic elastic-plastic stress-strain field near the crack tip was analyzed using the finite element method with the implementation of a robust cyclic plasticity theory. An incremental multiaxial fatigue criterion was employed to determine the fatigue damage. A straightforward method was developed to determine the fatigue crack growth rate. Crack propagation behavior of a material was obtained without any additional assumptions or fitting. Benchmark Mode I fatigue crack growth experiments were conducted using 1070 steel at room temperature. The approach developed was able to quantitatively capture all the important fatigue crack propagation behaviors including the overload and the R-ratio effects on crack propagation and threshold. The models provide a new perspective for the R-ratio effects. The results support the notion that the fatigue crack initiation and propagation behaviors are governed by the same fatigue damage mechanisms. Crack growth can be treated as a process of continuous crack nucleation.

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Comparison of High Temperature Mechanical Behaviour and Microstructure of the New Gamma–TiAl8Ta with Gamma-TiAl8Nb Alloy

Advances in Science and Technology ◽

10.4028/www.scientific.net/ast.72.40 ◽

2010 ◽

Vol 72 ◽

pp. 40-45

Author(s):

Giuliano Angella ◽

Valentino Lupinc ◽

Maurizio Maldini ◽

Giovanni Onofrio

Keyword(s):

High Temperature ◽

Mechanical Behaviour ◽

Low Cycle Fatigue ◽

Fatigue Properties ◽

Stress Intensity Factor Range ◽

Fatigue Crack Propagation Rate ◽

Difference Threshold ◽

Temperature Range ◽

R Ratio ◽

Significant Difference

The high temperature creep and fatigue properties of two  -TiAl base intermetallic alloys, for gas turbine components, have been investigated within the Integrated European project IMPRESS. The alloys contain 8% at. of Ta or Nb, respectively. The microstructure of both alloys was cross convoluted lamellar rather than the well known conventional lamellar, typical of the usual -TiAl. The microstructure of the Ta containing alloy was homogeneous in all the analyzed batches whilst that of the Nb alloy appeared significantly spread out from specimen to specimen. The creep properties of the alloys were investigated in the temperature range 700-850°C with applied stresses in order to have times to rupture up to about 3,000 h. The creep behaviour presented no steady state regimes, but only minima of the creep rates between significant decelerating and accelerating regimes. The minimum creep rates of the Ta alloy resulted to be significantly slower than the Niobium alloy at the same creep conditions. In low cycle fatigue at 650 and 700°C the Ta  -TiAl showed longer lives than the Nb alloy, whilst the fatigue crack propagation rate in the same temperature range did not show any significant difference. Threshold values of stress intensity factor range were accurately measured at different R ratio. The microstructures of the two alloys were analysed by scanning microscopy in order to rationalise the different mechanical behaviour.

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High and Low Cycle Fatigue of Orthorhombic Ti-22Al-27Nb Alloy

Materials Science Forum ◽

10.4028/www.scientific.net/msf.475-479.589 ◽

2005 ◽

Vol 475-479 ◽

pp. 589-594

Author(s):

Masuo Hagiwara ◽

A. Araoka ◽

Satoshi Emura

Keyword(s):

High Cycle Fatigue ◽

Low Cycle Fatigue ◽

Lamellar Microstructure ◽

Control Mode ◽

Load Control ◽

Cycle Fatigue ◽

Lamellar Morphology ◽

R Ratio ◽

Fatigue Mechanism

The effect of the lamellar morphology on the high cycle fatigue (HCF) and low cycle fatigue (LCF) behavior of the Ti-22Al-27Nb alloy was investigated. The HCF tests were performed in air at an R ratio of 0.1 in the load-control mode, whereas the LCF tests were performed in vacuum at 923 K in the strain-controlled mode. The specimens with fine lamellar microstructure exhibited a better resistance to HCF than those with coarse lamellar microstructure. The microstructure-insensitive behavior was, however, observed in the LCF tests at 923 K. The fatigue mechanism was discussed based on the concurrent observation of the initiation facet and the underlying microstructure, and the TEM observations.

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Novel Approach for the Lifetime Prediction of Composite Materials under Static Loads

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.809.620 ◽

2019 ◽

Vol 809 ◽

pp. 620-624

Author(s):

Stefan Gloggnitzer ◽

Gerald Pilz ◽

Christian Schneider ◽

Gerald Pinter

Keyword(s):

Composite Materials ◽

Creep Rupture ◽

Stress Rate ◽

Testing Time ◽

Creep Tests ◽

Static Loads ◽

Rate Dependent ◽

R Ratio ◽

Structural Applications ◽

Load Rate

Composite materials in structural applications that are subjected to static loads for several decades tend to change material performance over their lifetime. Classical creep tests with constant static loading are quite simple tests with low demands on the test equipment. Unfortunately, these tests require uneconomically long test times, which is why a shortening of the test times with various accelerated approaches is being researched. Within this work two approaches for reduction of the testing time were investigated. On the one hand a fatigue test with the variation of R-ratio and following extrapolation to an R-ratio of 1 was done. On the other hand a Stress Rate Accelerated Creep Rupture Test (SRCR) was developed, where a defined initial stress σi is applied at the beginning of the loading process, followed by an increase load with a constant rate instead of the static stress segment of the classic creep rupture tests. Changing the load rate in several individual tests leads to stress rate-dependent fracture strengths with associated fracture times, which allows extrapolation to a fracture time at a load rate of zero. In particular, the approach of the SRCR offers great potential for greatly reducing test times with an acceptable prediction quality.

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FORMULATION AND EVALUATION OF FUROSEMIDE LIQUISOLID COMPACT

International Journal of Applied Pharmaceutics ◽

10.22159/ijap.2017v9i6.21458 ◽

2017 ◽

Vol 9 (6) ◽

pp. 39

Author(s):

Zainab E. Jassim

Keyword(s):

Dissolution Rate ◽

Content Uniformity ◽

Drug Release Profile ◽

Scanning Calorimetry ◽

Polyethylene Glycol 400 ◽

Coating Materials ◽

Disintegration Time ◽

Weight Variation ◽

R Ratio

Objective: The purpose of this study was to enhance the dissolution pattern of the practically water-insoluble diuretic drug, furosemide through its formulation into liquisolid tablets.Methods: A mathematical model was used to formulate four liquisolid powder systems using polyethylene glycol 400 as a non-volatile water miscible liquid vehicle. The liquid loading factors of the vehicle were used to calculate the optimum quantities of carrier (Avicel PH 102) and coating materials (Aerosil 200) needed to prepare acceptably flowing and compactible powder mixtures and (R) ratio used was 25. The liquisolid tablets were evaluated for weight variation, percent friability, hardness, content uniformity, disintegration time and in vitro drug release profile. Drug and the prepared systems were characterized by fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) and powder x-ray diffraction (PXRD) studies.Results: The enhanced dissolution rate due to the increased wetting properties and the large available surface areas for dissolution were obtained in case of the liquisolid tablets. The selected optimal formulation (F2) of 50% drug concentration released 90% of its content during the first 10 min compared to 65% of DCT. FTIR studies revealed that there was no interaction between drug and polymers. DSC and PXRD indicated conversion of crystalline to amorphous form of furosemide. Conclusion: The dissolution rate of furosemide can be enhanced to a great extent by liquisolid technique.

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Numerical Study of Viscoelastic Micropolar Heat Transfer from a Vertical Cone for Thermal Polymer Coating

Nonlinear Engineering ◽

10.1515/nleng-2018-0064 ◽

2019 ◽

Vol 8 (1) ◽

pp. 449-460 ◽

Cited By ~ 1

Author(s):

K. Madhavi ◽

V. Ramachandra Prasad ◽

A. Subba Rao ◽

O. Anwar Bég ◽

A. Kadir

Keyword(s):

Heat Transfer ◽

Boundary Layer ◽

Angular Velocity ◽

Numerical Study ◽

Relaxation Times ◽

Viscoelastic Model ◽

Deborah Number ◽

Convection Boundary Layer ◽

Density Parameter ◽

R Ratio

Abstract A mathematical model is developed to study laminar, nonlinear, non-isothermal, steady-state free convection boundary layer flow and heat transfer of a micropolar viscoelastic fluid from a vertical isothermal cone. The Eringen model and Jeffery’s viscoelastic model are combined to simulate the non-Newtonian characteristics of polymers, which constitutes a novelty of the present work. The transformed conservation equations for linear momentum, angular momentum and energy are solved numerically under physically viable boundary conditions using a finite difference scheme (Keller Box method). The effects of Deborah number (De), Eringen vortex viscosity parameter (R), ratio of relaxation to retardation times (λ), micro-inertia density parameter (B), Prandtl number (Pr) and dimensionless stream wise coordinate (ξ) on velocity, surface temperature and angular velocity in the boundary layer regime are evaluated. The computations show that with greater ratio of retardation to relaxation times, the linear and angular velocity are enhanced whereas temperature (and also thermal boundary layer thickness) is reduced. Greater values of the Eringen parameter decelerate both the linear velocity and micro-rotation values and enhance temperatures. Increasing Deborah number decelerates the linear flow and Nusselt number whereas it increases temperatures and boosts micro-rotation magnitudes. The study is relevant to non-Newtonian polymeric thermal coating processes.

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276 THE EFFECT OF CUMULUS CELLS DURING MATURATION ON THE RISE IN THE CONCENTRATION OF INTRACELLULAR Ca2+ ([Ca2+]i) OF PORCINE OOCYTES INDUCEDBY INOSITOL 1,4,5-TRISPHOSPHATE

Reproduction Fertility and Development ◽

10.1071/rdv17n2ab276 ◽

2005 ◽

Vol 17 (2) ◽

pp. 288

Author(s):

T. Amano ◽

T. Mori ◽

K. Matsumoto ◽

T. Watanabe ◽

A. Iritani

Keyword(s):

Cumulus Cells ◽

Immature Oocytes ◽

R Ratio ◽

Transient Rise ◽

Activation Rate ◽

Sperm Penetration ◽

Cytoplasmic Maturation ◽

Student’S T ◽

Rate Of Activation

Increase of inositol 1,4,5-triphosphate (IP3) in the cytoplasm of mammalian oocytes is said to be responsible for [Ca2+]i oscillation observed in the oocytes immediately after sperm penetration, and the [Ca2+]i oscillation is known to be essential for the development of embryos. On the other hand, cumulus cells have been reported to play an important role in cytoplasmic maturation of oocytes and affecting the embryonic development. To obtain more information about the role of cumulus cells in cytoplasmic maturation, the effects of cumulus cells during maturation on the rise in [Ca2+]i and on the rate of activation of porcine mature oocytes induced by IP3 injection were investigated. The immature porcine oocytes were divided into three groups: COCs (intact cumulus-oocyte complexes), DOs (oocytes denuded of their cumulus cells), Co-culture (DOs attached to separated cumulus cells). These groups of immature oocytes were cultured in NCSU23 46 h for maturation. To examine the function of cumulus cells, two groups of immature oocytes were also prepared: DOs + pyruvate (DOs put into NCSU23 with pyruvate) and COCs-glucose free (COCs put into NCSU23 without glucose). The mature oocytes from each group were loaded with Ca2+ indicator fluorescent dye Fura2-AM, and then were irradiated by 340 nm and 360 nm of ultraviolet immediately after the injection of IP3. The intensities of emission light caused by the irradiation of 340 nm and 360 nm ultraviolet were recorded as E340 and E360. Since coupling of Ca2+ and the dye intensifies E340, but does not change E360, the level of [Ca2+]i was shown as R (ratio = E340/E360) in this study. Activation rate was calculated by counting the number of the oocytes that formed pronuclei by injection of IP3. ANOVA and Student's t-test were used in this study. Transient rise in [Ca2+]i was observed in the mature oocytes from every group. The peak R of the rise in [Ca2+]i of the mature oocytes derived from COCs, Dos, and Co-culture and induced by IP3 were 7.2, 4.0, and 6.9, respectively. The R of DOs was significantly lower than those of the others (P < 0.05). Also, the activation rate of the mature oocytes from DOs was significantly lower than those from COCs and Co-culture (31, 66, and 66%). The mature oocytes from DOs + pyruvate showed the same level of peak R compared with those from COCs (7.4 and 6.3), but COCs-glucose free showed a slight but significantly lower peak R compared with the mature oocytes from COCs (6.0 and 7.4, P < 0.05). In conclusion, cumulus cells appeared to support the rise in [Ca2+]i of porcine oocytes induced by IP3 during maturation and the following activation. Moreover, a function of cumulus cells supposedly produces pyruvate by metabolizing glucose and provides it to oocytes during maturation for promoting the cytoplasmic maturation. A part of this study was supported by a Grant-in-Aid for the 21st Century COE Program of the Japan MEXT, and by a grant from the Wakayama Prefecture Collaboration of Regional Entities for the Advancement of Technological Excellence of the JST.

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