An Energy Based Critical Fatigue Life Prediction Method

2011 ◽  
Author(s):  
Todd Letcher ◽  
M.-H. Herman Shen ◽  
Onome Scott-Emuakpor ◽  
Tommy George ◽  
Charles Cross
Keyword(s):  
Fatigue Life ◽  
Energy Density ◽  
Strain Energy Density ◽  
Strain Energy ◽  
Life Prediction ◽  
Failure Process ◽  
Prediction Method ◽  
Fatigue Life Prediction ◽  
Stress Strain ◽  
Energy Behavior

The capability of a critical life, energy-based fatigue prediction method is analyzed in this study. The theory behind the prediction method states that the strain energy accumulated during monotonic fracture and fatigue are equal. Therefore, a precise understanding of the strain energy density behavior in each failure process is necessary. The initial understanding of energy behavior shows that the accumulated strain energy density during monotonic fracture is the area underneath the experimental stress-strain curve, whereas the sum of the constant area within every stress-strain hysteresis loop of the cyclic loading process is the total strain energy density accumulated during fatigue; meaning, fatigue life is determined by dividing monotonic strain energy density by the strain energy density in one cycle. Further observation of the energy trend during fatigue shows that strain energy density per cycle is not constant throughout the process as initially assumed. This finding led to the incorporation of a critical life effect into the energy-based fatigue prediction method. The analysis of the method’s capability was conducted on Al 6061-T6 ASTM standard specimens. The results of the analysis provide further improvement to the characterization of strain energy density for both monotonic fracture and fatigue; thus improving the capability of the energy-based fatigue life prediction method.

Hysteresis Strain Energy Behavior of Al6061-T6 With Multi-Fatigue Load Levels as Applied to an Energy-Based Fatigue Life Prediction Method

2013 ◽  
Author(s):  
Todd Letcher ◽  
Sepehr Nesaei ◽  
Cody Auen ◽  
Matt Nielsen ◽  
Fereidoon Delfanian
Keyword(s):  
Fatigue Life ◽  
Strain Energy ◽  
Life Prediction ◽  
Prediction Method ◽  
Fatigue Life Prediction ◽  
Representative Specimen ◽  
Energy Behavior ◽  
Stress Levels ◽  
Single Stress ◽  
Life Predictions

Fatigue testing is a time and resource-consuming task. Historically, SN testing was conducted at many stress levels on simple representative specimen in order to determine an SN curve, which could then be used to design a component from the same type of material. Recently, an energy-based fatigue life prediction method has been in development. The goal of this method is to quickly determine a material’s fatigue characteristics using simple test procedures. The main theory behind the energy-based fatigue life prediction method is that the strain energy in a monotonic tensile test is equal to the cumulative hysteresis energy of a cyclic test. This theory has always been tested using a single stress level on each specimen. The hysteresis loop information was then used to make fatigue life predictions at other stress levels. Further testing has been done to learn more about the hysteresis energy behavior throughout the lifetime of a specimen, but only for a single stress value. In this study, several stress levels were tested on a single specimen. This new information will help make fatigue life predictions by completely removing the difficult and inconsistent process of determining experimental curve fit coefficients traditionally used in the energy-based fatigue life prediction method.

Fatigue Life Law Based on Inelastic Strain Energy Density of Solder Alloys and its Simple Prediction Method

2020 ◽  
Author(s):  
Tomoya Fumikura ◽  
Mitsuaki Kato ◽  
Takahiro Omori
Keyword(s):  
Fatigue Life ◽  
Energy Density ◽  
Fatigue Test ◽  
Strain Energy Density ◽  
Strain Energy ◽  
Prediction Method ◽  
Strain Range ◽  
Inelastic Strain ◽  
Stress Strain ◽  
Wide Range

Abstract In recent years, a fatigue life law based on inelastic strain energy density as proposed by Morrow has been applied to solder materials. In this study, the effectiveness of the fatigue life law based on inelastic strain energy density was compared with the conventional law based on inelastic strain range. First, the fatigue properties of Sn-Ag-Cu solder alloy were investigated by a torsional fatigue test with strain control. It was found that the stress–strain hysteresis loop arising from inelastic deformation occurred even under a low strain load with a fatigue life of about 1 million cycles. Therefore, as an extension of the low-cycle fatigue test, evaluation was performed using inelastic strain range and inelastic strain energy density. Experimental results show that when fatigue life was evaluated using inelastic strain energy density, a single power law was found over a wide range from the low-cycle region to the high-cycle region, and the validity of the fatigue life law based on inelastic strain energy density was confirmed. Next, a simple prediction method for the fatigue life law based on inelastic strain energy density was examined, taking the physical background into account. Two material constants of the fatigue life law based on the inelastic strain energy density were estimated from the stress–strain curve for a monotonic load and shown to be close to the actual fatigue test results.

Multiscale Investigation of Strain Energy Density for Fatigue Life Prediction

2017 ◽  
Author(s):  
Casey M. Holycross ◽  
Onome E. Scott-Emuakpor ◽  
Tommy J. George ◽  
M.-H. H. Shen
Keyword(s):  
Fatigue Life ◽  
Stress Intensity ◽  
Energy Density ◽  
Dynamic Loading ◽  
Strain Energy Density ◽  
Strain Energy ◽  
Life Prediction ◽  
Damage Parameter ◽  
Fatigue Life Prediction ◽  
Static And Dynamic Loading

A fatigue life prediction method using strain energy density as a prediction parameter has had success predicting the lifetimes greater than 105 cycles for room and elevated temperatures under axial, bending, and shear loading for different material systems. This method uses monotonic strain energy density determined at the macroscale as a damage parameter for fatigue, despite the differences in damage behavior of static and dynamic loading. Recent studies have brought this method into question, as cyclic energy for low cycle fatigue loading has been found to be significantly greater. Amendments of the fatigue life model have addressed this discrepancy for continuum level measurements, but have yet to examine the localized effects of machined notches. This study investigates strain energy density for static and dynamic loading at cycle counts from one (monotonic) to 105 for plain and notched specimens, exposing the differences between damaging strain energy density at continuum and local length scales. Continuum level strain energy density is simply determined by using the load and strain feedback from a standard mechanical test procedure using a common extensometer and a servohydraulic load frame. Local strain energy density is determined more elaborately by using three methods. Localized energy is determined from compliance and a closed form relationship between stress intensity factor and strain energy density. The influence of the notch is considered in the stress intensity calculation, but its influence on stress concentration is disregarded. All calculations are based on the net section stress and linear elasticity is assumed. The analyses revealed two distinct groups, but one data set indicated coincidence with total accumulated strain energy density. These data also corroborate the theory that average strain energy density at the continuum level changes mechanisms governing damage evolution. Monotonic strain energy density is refuted as an appropriate damage parameter to predict fatigue lifetimes, and a statically equivalent strain energy density is proposed. An amended continuum level model is proposed, increasing prediction accuracy over fatigue lifetimes less than 106. Additionally, a localized model is proposed, expanding prediction capability to geometries with notch like features.

scholarly journals Fatigue Life Prediction of Radial Tire Bead Using a Maximum Strain Energy Density Range Method

2021 ◽  
Vol 11 (12) ◽  
pp. 5477
Author(s):  
Guolin Wang ◽  
Weibin Wang ◽  
Chen Liang ◽  
Leitian Cao
Keyword(s):  
Fatigue Life ◽  
Energy Density ◽  
Strain Energy Density ◽  
Strain Energy ◽  
Life Prediction ◽  
Fatigue Testing ◽  
Fatigue Life Prediction ◽  
Density Range ◽  
Maximum Strain ◽  
Radial Tire

The damage that occurs around the tire bead region is one of the critical failure forms of a tire. Generally, the prediction of tire durability is carried out by the experimental method. However, it takes a lot of money and time to conduct experiments. Therefore, to determine the fatigue life of radial tire bead, a reasonable prediction method is proposed in this paper. Fatigue testing of bead rubber compounds to determine the ΔSED-number of the cycle (Nf) was applied. The maximum strain energy density range (ΔSEDmax) of several bead compounds was obtained by steady-state rolling analysis with a finite element method. This quantity is then inserted into a fatigue life equation to estimate the fatigue life. The experimental results of the 175/75R14 tire were compared with the estimated value, which showed a good correlation. It is concluded that the method can be effectively applied to the fatigue life prediction of the tire bead.

A modified strain energy density exhaustion model for creep–fatigue life prediction

2016 ◽  
Vol 90 ◽  
pp. 12-22 ◽  
Author(s):  
Run-Zi Wang ◽  
Xian-Cheng Zhang ◽  
Shan-Tung Tu ◽  
Shun-Peng Zhu ◽  
Cheng-Cheng Zhang
Keyword(s):  
Fatigue Life ◽  
Energy Density ◽  
Strain Energy Density ◽  
Strain Energy ◽  
Life Prediction ◽  
Fatigue Life Prediction ◽  
Creep Fatigue
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