scholarly journals The study of the relationship between life limiting factor and stress level for FGH96

2018 ◽  
Vol 165 ◽  
pp. 22031 ◽  
Author(s):  
Didi. Yang ◽  
Yi. Shi ◽  
Guolei. Miao ◽  
Xiaoguang. Yang ◽  
Duoqi. Shi
Keyword(s):  
Fatigue Life ◽  
Stress Level ◽  
Fatigue Tests ◽  
Limiting Factors ◽  
Limiting Factor ◽  
Lower Stress ◽  
Surface Residual Stress ◽  
Nickel Based Superalloy ◽  
Loading Ratio ◽  
Lower Stress Level

FGH96 is a Chinese made powder metallurgy nickel based superalloy. This reserach aims to investigate the effect of stress on the microstructure of the worst fatigue life at 600°C. The specimens were first polished by abrasive paper and then electropolished to elimate the effect of surface residual stress. The fatigue tests were conducted at 600°C, and the loading ratio was 0.05 at the frequency of 5Hz. Tests were conducted at 900, 1000, 1100, 1200MPa respectively. The fatigue life under the same condition were compared and the fractography of specimens were examined under SEM to further identify the life-limiting factors of the material. The initiation mode transferred from facet initiated to inclusion initiated from lower stress level to higher stress level. Meanwhile, the initiation position transferred from internal to surface with the increase of stress level. This means at higher stress level, fatigue life is mainly limited by inclusion at surface while at lower stress level the limit is controlled by internal facet.

Fatigue behavior of precipitation strengthened Cu–Ni–Si alloy modified by Cr and Zr addition

2020 ◽  
Vol 11 (6) ◽  
pp. 861-873
Author(s):  
Ş. Hakan Atapek ◽  
Spiros Pantelakis ◽  
Şeyda Polat ◽  
Apostolos Chamos ◽  
Gülşah Aktaş Çelik
Keyword(s):  
Design Methodology ◽  
Fatigue Behavior ◽  
Fatigue Tests ◽  
Lower Stress ◽  
Content Type ◽  
Hardened Alloy ◽  
Zr Addition ◽  
Nucleation Sites ◽  
The Matrix ◽  
Lower Stress Level

Purpose The purpose of this paper is to investigate the fatigue behavior of precipitation-strengthened Cu‒2.55Ni‒0.55Si alloy, modified by the addition of 0.25 Cr and 0.25 Zr (wt%), using mechanical and fractographical studies to reveal the effect of microstructural features on the fracture. Design/methodology/approach For strengthening, cast and hot forged alloy was subjected to solution annealing at 900°C for 60 min, followed by quenching in water and then aging at 490°C for 180 min. Precipitation-hardened alloy was exposed to fatigue tests at R=−1 and different stress levels. All fracture surfaces were examined within the frame of fractographical analysis. Findings Fine Ni-rich silicides responsible for the precipitation strengthening were observed within the matrix and their interactions with the dislocations at lower stress level resulted in localized shearing and fine striations. Although, by the addition of Cr and Zr, the matrix consisted of hard Ni, Zr-rich and Cr-rich silicides, these precipitates adversely affected the fatigue behavior acting as nucleation sites for cracks. Originality/value These findings contribute to the present knowledge by revealing the effect of microstructural features on the mechanical behavior of precipitation-hardened Cu‒Ni‒Si alloy modified by Cr and Zr addition.

The effect of the lower stress level on the cyclic creep behavior of an ods superalloy

1991 ◽  
Vol 18 (6) ◽  
pp. 1029-1033
Author(s):  
William L. Kimmerle ◽  
Vincent C. Nardone ◽  
John K. Tien
Keyword(s):  
Stress Level ◽  
Creep Behavior ◽  
Cyclic Creep ◽  
Lower Stress ◽  
Lower Stress Level

Damage Rate is a Predictor of Fatigue Life and Creep Strain Rate in Tensile Fatigue of Human Cortical Bone Samples

2004 ◽  
Vol 127 (2) ◽  
pp. 213-219 ◽  
Author(s):  
John R. Cotton ◽  
Keith Winwood ◽  
Peter Zioupos ◽  
Mark Taylor
Keyword(s):  
Fatigue Life ◽  
Cortical Bone ◽  
Creep Strain ◽  
Stress Level ◽  
Fatigue Tests ◽  
Human Cortical Bone ◽  
Damage Rate ◽  
Tensile Fatigue ◽  
Stress Cycles ◽  
Cycles To Failure

We present results on the growth of damage in 29 fatigue tests of human femoral cortical bone from four individuals, aged 53–79. In these tests we examine the interdependency of stress, cycles to failure, rate of creep strain, and rate of modulus loss. The behavior of creep rates has been reported recently for the same donors as an effect of stress and cycles (Cotton, J. R., Zioupos, P., Winwood, K., and Taylor, M., 2003, “Analysis of Creep Strain During Tensile Fatigue of Cortical Bone,” J. Biomech. 36, pp. 943–949). In the present paper we first examine how the evolution of damage (drop in modulus per cycle) is associated with the stress level or the “normalized stress” level (stress divided by specimen modulus), and results show the rate of modulus loss fits better as a function of normalized stress. However, we find here that even better correlations can be established between either the cycles to failure or creep rates versus rates of damage than any of these three measures versus normalized stress. The data indicate that damage rates can be excellent predictors of fatigue life and creep strain rates in tensile fatigue of human cortical bone for use in practical problems and computer simulations.

Analysis on Fatigue of Natural Corrosion Steel Bars

2010 ◽  
Vol 163-167 ◽  
pp. 3237-3241 ◽  
Author(s):  
Shi Bin Li ◽  
Wei Ping Zhang ◽  
Xiang Lin Gu ◽  
Ci Mian Zhu
Keyword(s):  
Fatigue Life ◽  
Stress Level ◽  
Fatigue Tests ◽  
Power Exponent ◽  
Accelerated Corrosion ◽  
Negative Power ◽  
Axial Tensile ◽  
Attenuation Rate ◽  
Steel Bars ◽  
Natural Corrosion

To reasonablely assess the residual fatigue life of aged existing reinforced concrete(RC) bridges, axial tensile fatigue tests were conducted on fifteen naturally carbonation-induced corrosion steel bars. The fatigue test results indicate that the existence of corrosion pits reduces the fatigue life of steel bars significantly under the same fagitue stress; with the development of corrosion, the fatigue life of steel bars decays according to negative power exponent law approximately and the attenuation rate increases with stress level augment. The fatigue deterioration law of natural corrosion steel bars is similar to that of accelerated corrosion steel bars, but the attenuation rate is different from that of accelerated corrosion steel bars, and also the influence of stress level on the attenuation rate is just cross to that of accelerated corrosion steel bars. For the complexity of fatigue and corrosion, further pertinent conclusions remain to be confirmed.

scholarly journals A STUDY ON EFFECTS OF YOGA AND ACADEMIC ACHIEVEMENT OF HIGH SCHOOL STUDENTS

2018 ◽  
Vol 6 (7) ◽  
pp. 23-27
Author(s):  
Christal Jeba N
Keyword(s):  
High School ◽  
Academic Achievement ◽  
Academic Performance ◽  
High School Students ◽  
Stress Level ◽  
The Other ◽  
Competitive Performance ◽  
Lower Stress ◽  
School Students ◽  
Lower Stress Level

The article focuses on assessing facts of a study on effects of yoga and academic achievement of high school students’. Transcendental meditation reduces stress and improves academic performance mentally causes increased alertness, and the practice of yoga brings improvement in competitive performance. It is inferred from the present investigation that all the high school students have average level of effect of yoga with respect to all the background variables under study. It was proved that students under consideration scored higher grades and had lower stress level as compared to the other students who do not practice yoga.

scholarly journals Characterization of fatigue failed aged Cu-Ni-Si alloys

2018 ◽  
Vol 188 ◽  
pp. 02011
Author(s):  
Ş. Hakan Atapek ◽  
Spiros G. Pantelakis ◽  
Apostolos N. Chamos ◽  
Gülşah Aktaş Çelik
Keyword(s):  
Applied Stress ◽  
Stress Ratio ◽  
Crack Nucleation ◽  
High Strength ◽  
Fatigue Tests ◽  
Constant Amplitude ◽  
Lower Stress ◽  
Stress Levels ◽  
Lower Stress Level

The precipitation hardenable and non-toxic Cu-Ni-Si alloys are good alternatives to Cu-Be and Cu-Co-Ni-Be alloys due to their high strength and high conductivity that can be attained by not only alloying but also thermo-mechanical routes. In this study, the fractographic analysis was carried out to understand the fatigue failure of aged 2.55Ni-0.55Si-0.25Zr-0.25Cr (wt-%) alloy which is a member of Corson family. In fatigue tests, a constant amplitude loading was applied at a stress ratio (R = σmin/σmax) of -1 and different stress levels (400, 350, 200 and 175 MPa) were used. The fracture response of the alloy was discussed depending on the applied stress levels and microstructural features. It was concluded that (i) Ni,Zr-rich precipitates and Cr-rich precipitates at the grain boundaries caused crack nucleation at all stress levels and (ii) the interaction between Ni-rich silicides and dislocations at lower stress level resulted in localized shearing and fine striations.

The effect of the lower stress level on the cyclic creep behavior of an ods superalloy

1987 ◽  
Vol 18 (6) ◽  
pp. 1029-1033 ◽  
Author(s):  
William L. Kimmerle ◽  
Vincent C. Nardone ◽  
John K. Tien
Keyword(s):  
Stress Level ◽  
Creep Behavior ◽  
Cyclic Creep ◽  
Lower Stress ◽  
Lower Stress Level

scholarly journals Optimasi Bentuk Struktur Elemen Cangkang Pada Pondasi Terapung Menggunakan Metode Algoritma Genetik

2018 ◽  
Vol 18 (2) ◽  
pp. 1-11
Author(s):  
Augusta Adha ◽  
Mahadi Kurniawan
Keyword(s):  
Finite Element ◽  
Stress Level ◽  
Contact Area ◽  
Shell Structure ◽  
External Load ◽  
Plate Theory ◽  
Mindlin Plate ◽  
Lower Stress ◽  
Floating Foundation ◽  
Lower Stress Level

[ID] Prinsip dasar pondasi terapung adalah keseimbangan antara berat struktur atas dan total berat tanah (termasuk didalamnya air tanah) yang dipindahkan oleh konstruksi pondasi tersebut sehingga tidak menghasilkan penurunan struktur. Pondasi terapung sangat baik digunakan pada daerah dengan daya dukung tanah yang rendah atau pada daerah yang memiliki tanah dengan derajat pemadatan yang bervariasi. Hal ini dikarenakan karakteristik pondasi terapung yang membagi gaya ke area kontak yang sangat besar sehingga seluruh area kontak tersebut hanya mengalami tegangan yang relatif kecil. Namun demikian, karena kapasitas dukung pondasi terapung sangat tergantung pada luasan area, maka pondasi terapung menjadi tidak efektif untuk diterapkan pada daerah yang kecil. Salah satu solusi yang dapat digunakan untuk mengatasi permasalahan ini adalah dengan penerapan struktur pelat cangkang (shell structure) pada pondasi terapung untuk meningkatkan luas area bidang kontak pondasi terapung dan tanah. Paper ini membahas optimasi bentuk pelat cangkang yang digunakan pada pondasi terapung agar memiliki daya dukung yang cukup untuk menahan gaya yang ditransferkan oleh struktur atas. Metode algoritma genetik digunakan dalam proses optimasi dimana koordinat dari titik yang menyusun bentuk (shape) struktur cangkang (cn) dipakai sebagai desain variabel. Pada penelitian ini, proses optimasi menggunakan pemodelan dengan 11, 13 dan 15 variabel desain untuk melihat sensitivitas desain variable tersebut terhadap hasil optimasi. Tegangan yang terjadi pada struktur cangkang tersebut di evaluasi dengan Analisa Elemen Hingga dengan perilaku element cangkang seperti model teory pelat Reissner-Midlin. Fungsi tujuan pada penelitian ini adalah meminimalkan penggunaan material untuk membentuk sebuah pondasi terapung dengan fungsi penalti tegangan pada elemen cangkang. [EN] The basic principle of floating foundation is counterforce balancing between the weight of the structure and thetotal weight of the soil (including groundwater) which is displaced by the structure. Floating foundation is effective in areas with low soil bearing capacity because the external load is widely spread that resulting lower stress level in contact area; Hence, it is necessary to design the shape of floating structure that provide adequate uplift whilst also create lower stress level by spreading the external load to wider contact area. This paper discusses the shape optimization of the floating foundations to have sufficient capacity to resist the force transferred by the upper structure whilst also minimize the use of material without resulting element overstress. Genetic algorithm method is used in the optimization process where the coordinates of the points that shape the shell structure (cn) are used as variable designs. In this study, the multivariable optimization using finite element model is investigated . The stress that occurs in the shell structure is evaluated by Finite Element Analysis with the behavior of shell elements based on Reissner-Mindlin plate theory.

Low-Cycle Fatigue of Nickel-Based Superalloy Hastelloy X at Elevated Temperatures

2001 ◽  
Author(s):  
Lijia Chen ◽  
Peter K. Liaw ◽  
Robert L. McDaniels ◽  
James W. Blust ◽  
Paul F. Browning ◽  
...  
Keyword(s):  
Fatigue Life ◽  
Stress Relaxation ◽  
Test Temperature ◽  
Low Cycle Fatigue ◽  
Hold Time ◽  
Cyclic Hardening ◽  
Fatigue Tests ◽  
Cycle Fatigue ◽  
Hastelloy X ◽  
Nickel Based Superalloy

The fully-reversed total strain-controlled low-cycle fatigue tests with and without hold times, as well as stress-relaxation tests, were conducted at 816°C and 927°C in laboratory air on a nickel-based superalloy, HASTELLOY X. The influence of temperatures and hold times on low-cycle fatigue behavior of the alloy was investigated. At both temperatures of 816°C and 927°C, the alloy exhibited initial cyclic hardening, followed by a saturated cyclic stress response or cyclic softening under low-cycle fatigue without hold times. For low-cycle fatigue tests with hold times, however, the alloy showed either cyclic hardening or cyclic stability, which is closely related to the test temperature and the duration of the hold time. It was also observed that the low-cycle fatigue life of the alloy considerably decreased due to the introduction of strain hold times. Generally, a longer hold time would result in a greater reduction in the fatigue life. However, for the tests without hold times, the test temperature seems to have little influence on the fatigue life of the alloy at the test temperatures used in this investigation. The stress relaxation tests show that at the beginning of strain hold, the stress drops very quickly and then decreases very slowly with prolonging time. In addition, the fracture surfaces of the fatigued specimens were observed using scanning electron microscopy to determine the crack initiation and propagation modes. The fatigue life was predicted by the frequency modified tensile hysteresis energy method. The predicted lives were found to be in good agreement with the experiment results.

scholarly journals Experimental Observation on the Pure Torsional Ratchetting of Polycarbonate Polymer at Room Temperature

2020 ◽  
Vol 2020 ◽  
pp. 1-11
Author(s):  
Fucong Lu ◽  
Bencheng Zhang ◽  
Bo Wu ◽  
Zhiwen Wu ◽  
Xiao Suo
Keyword(s):  
Cyclic Loading ◽  
Stress Level ◽  
Room Temperature ◽  
Stress Amplitude ◽  
Peak Stress ◽  
Stress Rate ◽  
Mean Stress ◽  
Loading History ◽  
Lower Stress ◽  
Lower Stress Level

The stress-controlled pure torsional cyclic tests are carried out to investigate the torsional ratchetting of polycarbonate (PC) polymer at room temperature. The effects of applied shear mean stress, stress amplitude, stress rate, peak stress hold, and stress history on the torsional ratchetting are discussed. The shear strain of tubular specimen is measured by a noncontact digital image correlation (DIC) apparatus. The results show that the torsional ratchetting of the polymer obviously depends on the applied shear stress level, stress rate, and peak stress hold; the shear ratchetting strain and its rate increase with the increasing mean stress, stress amplitude, and peak stress hold time and with the decreasing stress rate. Moreover, the torsional ratchetting depends on the stress history. A higher stress level cyclic loading history restrains the evolution of torsional ratchetting in the subsequent lower stress level cyclic loading, while the lower stress level cyclic loading history promotes the torsional ratchetting of the subsequent higher level cyclic loading.

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