Energy-Derived, Damage-Based Failure Criterion for Fatigue Testing

Abstract

Determination of the failure limit in a repeated-load fatigue test in the laboratory has relied entirely on the arbitrary selection of a fixed criterion. The constant strain and constant stress modes of fatigue loading have been described by a consistent definition of failure in flexural fatigue testing because of the distinctly different application of energy during the loading history. The most widely accepted definition is a decrease in initial stiffness by 50 percent. Procedures examining energy input and dissipated energy have required different schemes for each mode in an attempt to describe similar states of damage in the mixture. A proposed method is presented for examining dissipated energy to select a consistent level of material behavior that is indicative of the damage accumulation in the mixture. This procedure shows the similarity between the constant stress and constant strain modes of testing and is shown to provide the potential for unifying the now phenomenological description of fatigue with a more rational energy-based description.

New simplified approach for obtaining a reliable plateau value in fatigue analysis of bituminous materials

“…The subtraction in the numerator of Eq.4 and Eq.5 between the consecutive cycles is believed to eliminate energies like viscoelastic damping, plastic deformation energy and thermal energies that are not causing damage while keeping the relative amount of incremental damage coming from each additional load cycle [13,22,23]. As previously depicted by Ghuzlan and Carpenter [16] and Shen, Chiu and Huang [23], three distinct phases can be identified when the RDEC is plotted…”

“…This approach enables an independent fatigue law to be derived regardless of loading mode, frequency, rest periods and temperature [13,15,16,18]. When viscoelastic materials are subjected to cyclic loading, they generate different paths for the loading and unloading cycles leading to hysteresis loops.…”

“…The Ratio of Dissipated Energy Change (RDEC) approach, from which the Plateau Value (PV) is derived, was first introduced by Ghuzlan and Carpenter [16]. The uniqueness associated with the RDEC approach compared to other energy approaches, such as the total accumulated dissipated energy, is its ability to minimise the effect of energies that are involved in nonlinearity, heating and thixotropy which may not be directly related to fatigue damage.…”

“…Therefore, Ghuzlan and Carpenter [16] proposed the use of the Dissipated Energy Ratio (DER) to study the fatigue behaviour. The DER or the Ratio of Dissipated Energy Change (RDEC) approach was then developed by Carpenter and Shen [21] who emphasised the fact that damage will only be generated when there is a difference in dissipated energy between consecutive cycles.…”

“…2 fundamental material properties and an intrinsic fatigue law [13][14][15][16]. The Ratio of Dissipated Energy Change (RDEC) approach, from which the Plateau Value (PV) is derived, was first introduced by Ghuzlan and Carpenter [16].…”