Experimental Energy Balance During the First Cycles of Cyclically Loaded Specimens Under the Conventional Yield Stress

Abstract

This paper, as an extension of Maquin and Pierron (Mech Mater 41 (8): [928][929][930][931][932][933][934][935][936][937][938][939][940][941][942] 2009), presents an experimental procedure developed to macroscopically estimate the energy balance during the very first cycles of a uniaxially loaded metallic specimen at low stress levels. This energy balance is performed by simultaneously measuring the plastic input energy using a load cell and a strain gauge, and the dissipative energy using the temperature field provided by an infrared camera. Some experimental limitations led to restrain the present procedure to positive stress ratios, and to complement this energy balance by a second measurement while the material plastic work per cycle is negligible compared to the dissipative energy. Some results obtained on a cold rolled low carbon steel specimen are presented. First, a sensitivity study is undertaken to precisely determine the detection threshold on both thermal and plastic energies. Then, after having verified the homogeneity of the dissipative source fields, energy balances have been performed at different stress levels. It was thus confirmed that the slow variations of the dissipative sources occurring during the first cycles are due to micro-plastic adaptation, and that the dissipative N. Connesson (B) · F. Maquin · F. Pierron (SEM Member) sources remaining after some hundreds of cycles are due to viscoelastic (internal friction) phenomena. This procedure provides a better understanding of dissipation based approaches to fatigue found in the literature and an advanced tool to study viscoelastic phenomena in uniaxial loading.

A specific device for enhanced measurement of mechanical dissipation in specimens subjected to long‐term tensile tests in fatigue

“…This result confirms the link between the calorific quantity obtained from the proposed approach (s R ) and the irreversible mechanical phenomena occurring in the material. Interestingly, the results obtained here on a SMA are in agreement with those reported in Connesson et al [31] The latter concerns the cycling loading of another type of material, namely, a low carbon steel. The common feature is a mechanically dissipated energy, which varies due to the material adaptation and which converges toward a constant value while the material plastic work decreases.…”

“…Some precautions can be taken to reduce these effects: The specimen can be placed in a box with apertures for the grips and the IR camera in order to minimize air motion and radiation sources from the outside; [31,32] testing machine running several hours before the beginning of the mechanical test in order to minimize the temperature change of the grips; air conditioning in the testing room. However, long-term cyclic tests with a hydraulic fatigue machine are always accompanied by a significant temperature increase in the grips during the test itself.…”

An energy method for rapid evaluation of high-cycle fatigue parameters based on intrinsic dissipation

“…The symbol s 1D th stands for a time constant characterizing the lateral heat exchanges (i.e., thermal convection and radiation) between the specimen surface and the surroundings. Before the onset of damage localization, the thermoelastic source and the intrinsic dissipation source, just like stress and strain fields, are uniform within the specimen gauge part with constant cross-section at a macroscopic scale of observation [12,13].…”

“…An infrared image processing procedure was proposed to implement this estimation. Maquin et al [12][13][14] developed an experimental method and a data processing procedure to obtain the small heat source generated during the very first cycles and to reveal the physical basis of the rapid determination of fatigue limit. Yang et al [15,16] established the one-dimensional distribution of specimen surface temperature and determined the fatigue life using local plastic work.…”

Experimental investigations of elastic-plastic strain states on various stages of material plastifying

“…The experimental methods most commonly used to research work on elastic-plastic problems are: photoelasticity, especially the method of photoelastic coating (Pacey et (Lin, 2000;Balalov et al, 2007), electronic speckle pattern interferometry method (ESPI) (Diaz et al, 2001;Schajer et al, 2005), digital image correlation method (DIC) (Vural et al, 2011;Diaz et al, 2004;Tarigopula et al, 2008), strain gauge technique (Rasty et al, 2007;Olmi, 2010), thermography (Pieczyska et al, 2006;Connesson et al, 2011).…”