The coefficient of transverse strain and strain hysteresis under cyclic loading

Fomichev, P. A.; Trubchanin, I. Yu.

doi:10.1007/bf02767817

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“…Transversal strain measured by the extensometer was employed during all investigations, with the relationship between transversal and longitudinal strain during cyclic loading previously investigated and reported in paper. 21 Although it is possible to calculate axial strain at the smallest cross-section of the specimen gauge, in the authors' opinion, transversal strain can also be used for the investigation of the damage progress, significantly simplifying the processing of data without any loss of credibility. Fatigue damage develops locally around imperfections, voids, inclusions and microcracks accumulated in the region of minimum cross-section where axial stress reaches maximum values; this should also be reflected by changes in the macroscopic strain of the specimen in the area of minimum cross-section.…”

Section: Experimental Techniquementioning

confidence: 99%

“…This ability is essential because of the fact that the two most important phenomena exhibit different tendencies, whereas the generation of new defects derived from local plastic deformation in stress concentration regions around inclusions and other structural imperfections initially tends to homogenise for the selected cross‐section, debonding, crack initiation and propagation are local phenomena strongly related to the initial distribution of material defects. Transversal strain measured by the extensometer was employed during all investigations, with the relationship between transversal and longitudinal strain during cyclic loading previously investigated and reported in paper . Although it is possible to calculate axial strain at the smallest cross‐section of the specimen gauge, in the authors' opinion, transversal strain can also be used for the investigation of the damage progress, significantly simplifying the processing of data without any loss of credibility.…”

Section: Introductionmentioning

confidence: 99%

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A fatigue damage indicator parameter for P91 chromium‐molybdenum alloy steel and fatigue pre‐damaged P54T carbon steel

Socha

Dietrich

2013

Fatigue Fract Eng Mat Struct

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A B S T R A C T Two grades of structural steel were subjected to fully reversible, constant stress amplitude cyclic loading. The local strain response of the material was measured and recorded during the test, with the applied testing technique enabling the monitoring of hysteresis loop variation for the narrowest cross-section of the hourglass specimen. Changes in hysteresis loop width, representing the local inelastic response of the material, were recorded in order to monitor the density of structural imperfections. Material ratcheting behaviour was observed as changes in the mean strain for selected load cycles. Ratcheting was attributed to local deformation of the material in the vicinity of imperfections such as voids or inclusions, as well as deformation induced by the propagation of microcracks. Definitions of a damage indicator parameter and damage parameter were proposed. The fatigue behaviour of the two investigated grades of steel was finally illustrated in the form of damage curves for different stress amplitudes and for undamaged and fatigue pre-damaged material.Keywords fatigue damage; inelastic strain; ratchetting; damage accumulation; damage parameter. N O M E N C L A T U R Ea = crack length D = damage parameter N, n = number of load cycle N f = number of cycles to failure R = cycle asymmetry ratio ε i = inelastic strain range for load cycle ε m = mean strain for load cycle φ = damage indicator parameter σ a = stress amplitude I N T R O D U C T I O NIn the two hundred years since fatigue in metal alloys was first investigated, 1 numerous studies have been carried out with the aim of identifying the physical phenomena underlying the accumulation of fatigue damage and leading to final failure of construction components. Although significant progress has been achieved, with the results of investigations published in many papers, the basic procedure for the estimation of fatigue life in construction components is still based on Wöhler's proposition. 1 This is because of the fact that observations of changes in internal structure have revealed the huge complexity of physical phenomena underlying fatigue damage accumulation. Many attempts have been made to relate identified phenomena to changes in the macroscopically observed mechanical properties of the investigated alloys. A summary regarding the elaborated damage models can be found in a number of review books 2 and papers. [3][4][5] Because finding relationships between changes in material mechanical characteristics and the physical phenomena underlying fatigue damage accumulation is very difficult, none of the mathematical models developed in this way have as yet been accepted by the engineering community for the estimation of component fatigue life.One obvious result of fatigue damage accumulation is the formation of dominant crack. The rapid development of fracture mechanics theory and testing methods have Correspondence: G. Socha.

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Section: Experimental Techniquementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%