Fatigue Life Prediction for Complex Load Versus Time Histories

1983 ◽  
Vol 105 (3) ◽  
pp. 206-214 ◽  
Author(s):  
N. E. Dowling
Keyword(s):  
Fatigue Life ◽  
Life Prediction ◽  
Fatigue Life Prediction ◽  
Constant Amplitude ◽  
Discrete Events ◽  
Complex Load ◽  
Stress Effects ◽  
Fatigue Data ◽  
Time Histories ◽  
Damage Type

Fatigue life prediction for complex load versus time histories is considered from the viewpoint of separating the history into discrete events, or cycles, which may then be used with constant amplitude fatigue data in a cumulative damage type of analysis. Highly irregular histories require special attention, with minor load excursions being considered in cycle counting as temporary interruptions of larger load cycles. Local notch plasticity and mean stress effects are interrelated, and such effects are most rationally accounted for in terms of local notch stresses and strains. The paper describes and discusses a life prediction procedure for notched members which is based on modeling of the stresses and strains occurring locally at the notch.

Application of a Multiaxial Fatigue Criterion for the Evaluation of Life of Gears of Complex Geometry

2003 ◽  
Author(s):  
Leonardo Borgianni ◽  
Paola Forte ◽  
Luigi Marchi
Keyword(s):  
Fatigue Life ◽  
Stress State ◽  
Life Prediction ◽  
Complex Geometry ◽  
Biaxial Stress ◽  
Fatigue Life Prediction ◽  
Random Loading ◽  
Complex Load ◽  
Biaxial Stress State ◽  
Principal Axes

Gears can show significant biaxial stress state at tooth root fillet, due to the way they are loaded and their particular geometry. This biaxial stress state can show a significant variability in principal axes during meshing. Moreover loads may have non predictable components that can be evaluated with the aid of recorded data from complex spectra. In these conditions, commonly adopted approaches for fatigue evaluation may be unsuitable for a reliable fatigue life prediction. This work is aimed at discussing a computer implementation of a fatigue life prediction method suitable for multiaxial stress states and constant amplitude or random loading. For random loading a counting procedure to extract cycles from complex load histories is discussed. This method, proposed by Vidal et al., is based on the r.m.s. value of a damage indicator over all the planes through the point where the fatigue life calculation is made. Miner’s rule is used for the evaluation of the overall damage. The whole fatigue life of the component is evaluated in terms of the numbers of repetitions of the loading block. FEM data are used to evaluate stresses under load. The implementation was validated using test data found in the technical literature. Examples of applications to gears are finally discussed.

Fatigue Modulus Concept and Life Prediction of Thick-Section S2-Glass/Vinylester Composites Under Flexural Loading

1999 ◽  
Author(s):  
Hassan Mahfuz ◽  
Kamruz Zaman ◽  
Anwarul Haque ◽  
Uday Vaidya ◽  
Hisham Mohamed ◽  
...  
Keyword(s):  
Fatigue Life ◽  
Applied Stress ◽  
Life Prediction ◽  
Fatigue Tests ◽  
Fatigue Life Prediction ◽  
Analytical Prediction ◽  
Thick Section ◽  
Cycle Number ◽  
Material Constants ◽  
Fatigue Data

Abstract Fatigue life prediction of thick-section S2-Glass fiber reinforced Vinylester composites has been studied analytically using fatigue modulus concept. Flexural fatigue tests were conducted under three point bend configuration. A stress ratio of R = 0.1 and a frequency of 3 Hz has been used for the fatigue tests. Fatigue data have been generated at five load levels; 85%, 80%, 70%, 60% and 55% of the ultimate flexural strength. Using these fatigue data, S-N diagram has been generated. Fatigue modulus has been determined by the slope of the line drawn on a plot of applied stress vs. resultant strain at specific loading cycle. Since fatigue modulus degrades with cycle number, it was assumed that the degradation rate follows a power function of fatigue cycle. Using this concept, a practical and applicable equation for predicting fatigue life is established. The Fatigue Life Prediction method used in this investigation requires two distinct parameters, namely applied stress level and two material constants. These material constants have been determined from the fatigue test data. A comparison has been made between the analytical prediction and the experimentally obtained S-N curve. The correlation between the two has been observed to be excellent. Flexural failure modes have also been identified as extensive delamination, fiber fracture and fiber kinking. Microscopic observation shows that all failures are predominantly on the tensile side with slight fiber kinking and matrix crushing on the compression side.

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