Prediction of Fatigue Life With and Without Hold Times Using the Chaboche Viscoplastic Constitutive Theory

1990 ◽  
Vol 112 (2) ◽  
pp. 188-197 ◽  
Author(s):  
S. S. Chiu ◽  
J. Eftis ◽  
D. L. Jones
Keyword(s):  
Fatigue Life ◽  
Yield Stress ◽  
Stress Level ◽  
Life Prediction ◽  
Hold Time ◽  
Fatigue Life Prediction ◽  
Initial Yield Stress ◽  
Initial Yield ◽  
Rate Dependent ◽  
Rate Of Loading

The titanium alloy Ti-6Al-4V is known to exhibit creep behavior at temperatures as low as room temperature. Consequently, for cyclic loading with hold times it is possible that the rate dependent behavior of Ti-6Al-4V can have negative bearing upon the low cycle fatigue life. If this effect is shown to be present at room temperatures, then it will certainly be magnified and, therefore, very important at elevated temperatures. In order to account for the effects of strain rate dependent deformation in fatigue life prediction methodology, it was considered necessary to incorporate a viscoplastic constitutive equation into the fatigue life calculational algorithm. After critical evaluation of a score of recently proposed viscoplastic constitutive theories, the Chaboche theory, which employs a yield condition, was considered to offer the most promise for description of a wide range of inelastic material behavior characteristics. The six viscoplastic material parameters that are required for nonelevated temperature applications were determined from data of uniaxial tests, conducted elsewhere and made avialable to this study. The fatigue life testing of smooth round bar specimens included load cycles with load hold times. Fatigue life predictions were performed using the equivalent fully reversed symmetric cycle, and the Smith-Watson-Topper parameter, for load cycles having varying stress amplitudes and varying hold times. The predicted fatigue life results indicate that: (i) For a given stress level above the initial yield stress, shorter load hold time periods result in longer fatigue lives. (ii) The higher the stress level (above the initial yield stress) the more pronounced becomes the effect of the load hold time on the fatigue life prediction. (iii) The rate of loading also has an effect on fatigue life. Analysis indicates that the slower the rate of loading, the higher the rate dependent (primary creep) deformation, and consequently, the lower the resulting fatigue life.

A Modified Peric Model for Al-Mg Alloy Sheet with Rate-Independent Initial Yield Stress at Warm Temperatures

2019 ◽  
Vol 287 ◽  
pp. 3-7
Author(s):  
Yong Zhang ◽  
Qing Zhang ◽  
Yuan Tao Sun ◽  
Xian Rong Qin
Keyword(s):  
Flow Stress ◽  
Plastic Strain ◽  
Strain Rate ◽  
Yield Stress ◽  
Constitutive Models ◽  
Mg Alloy ◽  
Initial Yield Stress ◽  
Initial Yield ◽  
Rate Dependent ◽  
Dependent Flow

The constitutive modeling of aluminum alloy under warm forming conditions generally considers the influence of temperature and strain rate. It has been shown by published flow stress curves of Al-Mg alloy that there is nearly no effect of strain rate on initial yield stress at various temperatures. However, most constitutive models ignored this phenomenon and may lead to inaccurate description. In order to capture the rate-independent initial yield stress, Peric model is modified via introducing plastic strain to multiply the strain rate, for eliminating the effect of strain rate when the plastic strain is zero. Other constitutive models including the Wagoner, modified Hockett–Sherby and Peric are also considered and compared. The results show that the modified Peric model could not only describe the temperature-and rate-dependent flow stress, but also capture the rate-independent initial yield stress, while the Wagoner, modified Hockett–Sherby and Peric model can only describe the temperature-and rate-dependent flow stress. Moreover, the modified Peric model could obtain proper static yield stress more naturally, and this property may have potential applications in rate-dependent simulations.

Fatigue Life Prediction of Thick-Section S2-Glass/Vinyl-Ester Composites Under Flexural Loading1

2000 ◽  
Vol 122 (4) ◽  
pp. 402-408 ◽  
Author(s):  
Hassan Mahfuz ◽  
Kamruz Zaman ◽  
Anwarul Haque ◽  
Costee Foy ◽  
Hisham Mohamed ◽  
...  
Keyword(s):  
Fatigue Life ◽  
Stress Level ◽  
Vinyl Ester ◽  
Life Prediction ◽  
Mathematical Formulation ◽  
Prediction Equation ◽  
Fatigue Life Prediction ◽  
Loading Cycle ◽  
Material Parameters ◽  
Two Parameters

Fatigue life prediction of S2-Glass/Vinyl-ester composites has been studied analytically using the fatigue modulus concept. Traditionally it is assumed that the fatigue modulus degradation is a function of loading cycle only. In our present investigation, it is found that the fatigue modulus is not only a function of loading cycle but also a function of applied stress level and thickness of the specimen. Using this concept, a practical and applicable method for predicting fatigue life is established. The method requires two distinct parameters that arise from the mathematical formulation. These two parameters are determined in two ways. In one case, the parameters are determined using failure cycle numbers at two different stress levels. In the other case, the parameters are determined using fatigue modulus values at two different cycles at a particular stress level. These material parameters have been determined experimentally using both the procedures. Utilizing the experimental data two appropriate functions for these two material parameters were obtained and incorporated into the life prediction equation. Fatigue life predictions using this method have been found to be within 10 percent of the experimental values. [S0094-4289(00)02404-X]

Normalized creep–fatigue life prediction model based on the energy dissipation during hold time

2007 ◽  
Vol 460-461 ◽  
pp. 195-203 ◽  
Author(s):  
Chang Yeol Jeong ◽  
Jung-Chan Bae ◽  
Chang-Seog Kang ◽  
Jae-Ik Cho ◽  
Hyeon-Taek Son
Keyword(s):  
Fatigue Life ◽  
Energy Dissipation ◽  
Prediction Model ◽  
Life Prediction ◽  
Hold Time ◽  
Fatigue Life Prediction ◽  
Model Based ◽  
Creep Fatigue ◽  
Life Prediction Model

Creep and Creep-Fatigue Deformation and Life Assessment of Ni-Based Alloy 740H and Alloy 617

2018 ◽  
Author(s):  
Shengde Zhang ◽  
Yukio Takahashi
Keyword(s):  
Fatigue Life ◽  
Life Prediction ◽  
Hold Time ◽  
Fatigue Tests ◽  
Fatigue Life Prediction ◽  
Life Assessment ◽  
Prediction Methods ◽  
Creep Tests ◽  
Alloy 617 ◽  
Creep Fatigue

This paper presents creep and creep-fatigue deformations and lives of both Ni-based alloys, Alloy 740H and Alloy 617. Creep tests were performed using solid bar specimens at 650°C-800°C, and effect of cyclic loading on creep deformation and rupture was discussed. Strain controlled creep-fatigue tests were also performed under triangular and trapezoidal waveforms at 700°C. Alloy 740H showed stronger creep-fatigue resistance compared to Alloy 617. Creep-fatigue lives in trapezoidal waveform were smaller than those in the pure fatigue test and the creep-fatigue lives decreased as the hold time increased. Applicability of four representative creep-fatigue life prediction methods was discussed.

A Modified Peric Model for Al-Mg Alloy Sheet with Rate-Independent Initial Yield Stress at Warm Temperatures

2018 ◽  
Vol 30 ◽  
pp. 8-12
Author(s):  
Yong Zhang ◽  
Qing Zhang ◽  
Yuan Tao Sun ◽  
Xian Rong Qin
Keyword(s):  
Flow Stress ◽  
Plastic Strain ◽  
Strain Rate ◽  
Yield Stress ◽  
Constitutive Models ◽  
Mg Alloy ◽  
Initial Yield Stress ◽  
Initial Yield ◽  
Rate Dependent ◽  
Dependent Flow

The constitutive modeling of aluminum alloy under warm forming conditions generally considers the influence of temperature and strain rate. It has been shown by published flow stress curves of Al-Mg alloy that there is nearly no effect of strain rate on initial yield stress at various temperatures. However, most constitutive models ignored this phenomenon and may lead to inaccurate description. In order to capture the rate-independent initial yield stress, Peric model is modified via introducing plastic strain to multiply the strain rate, for eliminating the effect of strain rate when the plastic strain is zero. Other constitutive models including the Wagoner, modified Hockett–Sherby and Peric are also considered and compared. The results show that the modified Peric model could not only describe the temperature-and rate-dependent flow stress, but also capture the rate-independent initial yield stress, while the Wagoner, modified Hockett–Sherby and Peric model can only describe the temperature-and rate-dependent flow stress. Moreover, the modified Peric model could obtain proper static yield stress more naturally, and this property may have potential applications in rate-dependent simulations.

Sign in / Sign up

Export Citation Format

Share Document