Fatigue Damage of Materials with Small Crack Calculated by the Ratio-Method under Cyclic Loading

2005 ◽  
pp. 79-86
Author(s):  
Yan Gui Yu
Keyword(s):  
Cyclic Loading ◽  
Fatigue Damage ◽  
Small Crack ◽  
Ratio Method

Fatigue Damage of Materials with Small Crack Calculated by the Ratio-Method under Cyclic Loading

2005 ◽  
Vol 9 ◽  
pp. 79-86
Author(s):  
Yan Gui Yu
Keyword(s):  
Cyclic Loading ◽  
Functional Relation ◽  
Strain Range ◽  
Material Constant ◽  
Small Crack ◽  
Practical Significance ◽  
Ratio Method ◽  
Plastic Behavior ◽  
Plastic Strain Range ◽  
Material Constants

This paper offers some new calculating equations on the small crack growth rate for describing the elastic-plastic behavior of materials under symmetric or un-symmetric cyclic loading. And it yet suggests the estimating formulas of the life relative to varied small crack size aoi at each loading history. The method is to adopt the ratio e p e e D D / by plastic strain range to elastic strain range as a stress-strain parameter, using some staple material parameters as the material constants in damage calculating expression. And it gives out a new concept of the composite material constant, that it is functional relation with each staple material constants, average stress，average strain and critical loading time. The calculated results are accordant with the Landgraf’s equation, so could avoid unnecessary fatigue tests and will be of practical significance to stint times, manpower and capitals, the convenience for engineering applications.

scholarly journals Analysis of Damage Evolution in Concrete under Fatigue Loading by Acoustic Emission and Ultrasonic Testing

Materials ◽  
2022 ◽  
Vol 15 (1) ◽  
pp. 341
Author(s):  
Marc Thiele ◽  
Stephan Pirskawetz
Keyword(s):  
Acoustic Emission ◽  
Elastic Modulus ◽  
Cyclic Loading ◽  
Fatigue Damage ◽  
Fatigue Loading ◽  
Measurement Methods ◽  
Material Structure ◽  
Fatigue Process ◽  
Acoustic Methods ◽  
Normal Strength

The fatigue process of concrete under compressive cyclic loading is still not completely explored. The corresponding damage processes within the material structure are especially not entirely investigated. The application of acoustic measurement methods enables a better insight into the processes of the fatigue in concrete. Normal strength concrete was investigated under compressive cyclic loading with regard to the fatigue process by using acoustic methods in combination with other nondestructive measurement methods. Acoustic emission and ultrasonic signal measurements were applied together with measurements of strains, elastic modulus, and static strength. It was possible to determine the anisotropic character of the fatigue damage caused by uniaxial loading based on the ultrasonic measurements. Furthermore, it was observed that the fatigue damage seems to consist not exclusively of load parallel oriented crack structures. Rather, crack structures perpendicular to the load as well as local compacting are likely components of the fatigue damage. Additionally, the ultrasonic velocity appears to be a good indicator for fatigue damage beside the elastic modulus. It can be concluded that acoustic methods allow an observation of the fatigue process in concrete and a better understanding, especially in combination with further measurement methods.

Beyond Shakedown-Ratcheting Boundary

2018 ◽  
Author(s):  
R. Adibi-Asl ◽  
W. Reinhardt
Keyword(s):  
Cyclic Loading ◽  
Plastic Strain ◽  
Fatigue Damage ◽  
Thermal Load ◽  
Pressure Vessels ◽  
Growth Strain ◽  
Strain Condition ◽  
Element Analysis ◽  
Permanent Strain ◽  
Section Viii

The ASME Boiler and Pressure Vessel Code (Section III and Section VIII) provides requirements to avoid a ratcheting (accumulating permanent strain) condition under cyclic thermal load application. The ratchet check in this code is based on the solutions presented by Miller in 1959. One important focus in Miller’s work was to estimate the accumulated plastic strain under cyclic loading. The existing pressure vessels and piping codes have been adopting Miller’s ratchet boundary solution where there is no cyclic plastic accumulation of strain. However, some of these codes also provide limit on accumulated plastic strain under ratcheting conditions. Since the cyclic loading also causes fatigue damage in thee component, the question how to account for the interaction of ratchet deformation, which may contribute to damage in the material, and fatigue damage arises, since the fatigue curves are obtained from tests in the absence of ratcheting. This paper investigates the solutions to calculate growth strain (incremental plastic strain) and their application in design including taking into account the interaction with fatigue. Finite element analysis is presented to validate the analytical solutions.

Metal Coercivity as a Measure of Microdamages for Evaluation of Fatigue and Recovery of Mechanical Properties

NDT World ◽  
2016 ◽  
Vol 19 (3) ◽  
pp. 59-61
Author(s):  
Сорочинский ◽  
Sergey Sorochinskiy ◽  
Казак ◽  
Irina Kazak ◽  
Вакуленко ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Plastic Deformation ◽  
Cyclic Loading ◽  
Coercive Force ◽  
Fatigue Damage ◽  
Surface Plastic Deformation ◽  
Surface Plastic ◽  
Partial Recovery ◽  
Fatigue Damage Accumulation ◽  
Intermediate Surface

Introduction. The problem of determining the current state of metal parts mechanical properties is always relevant. For its solution a simple, cheap and sufficiently informative NDT method is needed. Today the method of magnetic coercive force seems to be the most suitable. The purpose of this work was to determine patterns of change in a coercive force after cyclic loading of steel samples in the initial state and after surface plastic deformation (work hardening). Method. Two batches of 40X steel cylindrical samples in the delivery condition were put to cyclic tests. The both batches were tested in the same range of tension amplitudes but for the second batch the tests were carried out in two steps with intermediate surface plastic deformation. The change in the level of accumulated fatigue damage was determined by the coercive force method. Results. The most significant coercive force increase (up to 1.5%) was observed in the initial stages of the specimens’ elongation. For samples subjected to preliminary cyclic loading, surface plastic deformation leads to lower coercive force values (by 9%–17%) and to 2.8–3.4 times longer operating life. This effect can be explained by “healing” the accumulated defects by the surface treatment. Discussion. The results indicate high sensitivity of the coercive force to changes in structural state of the metal as a result of both fatigue damage accumulation and partial recovery of the metal structure due to defect “healing”.

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