The ongoing studies of the influence of internal defects on fatigue strength of additively manufactured metals adopted an internal crack or notch-like model at which the threshold stress intensity ...factor is the driving mechanism of fatigue failure. The current article highlights a shortcoming of this approach and offers an alternative based on X-ray microcomputed tomography and cyclic plasticity with a hybrid formulation of Chaboche and Armstrong-Frederick material laws. The presented tessellation and geometrical transformation scheme enabled a significantly more realistic morphological representation of internal defects that yielded a cyclic strain within 2% of the experimental values. This means that cyclic plasticity models have an accurate prediction of mechanical properties without repeating a full set of experiments for additively manufactured arbitrary microstructures. The coupling with a material law that is oriented towards the treatment of cyclic hardening and softening enabled more accurate computation of internal stresses under cyclic loading than ever before owing to the maturity of tessellation and numerical tools since then. The resulting stress-strain distributions were used as input to the Fatemi-Socie damage model, based on which a successful calculation of fatigue lifetime became possible. Furthermore, acting stresses on the internal pores were shown to be more than 450% concerning the applied remote stress amplitude. The results are a pretext to a scale bridging numerical solution that accounts for the short crack formation stage based on microstructural damage.
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•If SPY ≤ 0.24 the heat dissipations by convection and radiation are negligible.•Entropy generation during fatigue mechanism is path independent.•Normalized entropy generation ...generally is not equal to normalized cycle.•Normalized entropy generation is similar to normalized total plastic work.•FFE has higher variability during low-cycle fatigue for Al 2024-T4.
In this study, thermodynamic entropy generation is employed as a degradation model for analysis of metal fatigue failure. An analytical solution is carried out to evaluate the temperature of the specimen during the test. Based on the analytical solution, two new models are developed for entropy generation. The first one is applicable to the case that plastic work density is measurable. The second one is useful for temperature monitoring techniques. A set of experiments are conducted on specimens Al 2024-T4 as a case study. The results show that cumulative entropy generation increases with respect to the number of cycles.
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•A correlation is developed to predict damage evolution during fatigue of metals.•The correlation is applied to both constant and variable amplitude cyclic loading.•A remaining ...fatigue life prediction method is presented.•Experimental results are presented to validate the proposed method.
An experimental procedure to estimate damage evolution and remaining fatigue life of metals associated with fatigue loading is presented. Experimental phase involves uniaxial tension–compression fatigue tests performed with solid API 5L X52 and tubular carbon steel 1018 specimens subjected to both constant and variable amplitude loading. A correlation between the so-called damage parameter and the thermal response of a material at different damage levels is proposed. Results demonstrate that the correlation can estimate damage evolution with reasonable accuracy in both constant and variable amplitude fatigue processes. It is shown that under the conditions tested the evolution of damage parameter with respect to the normalized fatigue life is independent of the load amplitude, load ratio, loading sequence, material properties, and specimen geometry. The proposed correlation and the relationship between the damage parameter and the normalized fatigue life are employed to develop a non-destructive method to predict the remaining fatigue life of metallic specimens with prior fatigue damage. The method is applied to both constant and variable amplitude loading and the predicted results are found to be in good agreement with those obtained from the experiments.
The energy industry, transportation and even the smallest consumer electronics benefit from the practical applications of rechargeable batteries. Expectations of battery performance are greatly ...related to capacity, power output and available lifetime. However, the lifetime is affected by gradual chemical and mechanical degradation of the internal battery structure that cannot easily be predicted prior to installation. The reduction in performance is closely related to a particular usage pattern which is unique to the user and application, and is thus difficult to predict. Reliable real-time prediction of the remaining battery life therefore remains an important research topic. In this paper we show that fading battery performance under cyclic loading can be effectively and continuously followed by introducing the concept of the damage parameter derived from mechanical durability modelling approaches. The damage parameter is calculated continuously by the novel macro-scale hysteresis damage operator model. The hysteresis model is formed by a system of constitutive spring-slider modelling elements, here bridging the complex relation between the battery load and the durability data. The spring and the slider properties are individually calibrated for lithium nickel manganese cobalt oxide (NMC) batteries, however other battery structures can also be used. The durability data is obtained experimentally under controlled steady thermal and cyclic loading (constant charge/discharge current) conditions. The approach is validated on a standardised driving pattern with a complex current history. The predicted battery life is in good agreement with observed repetitions of a simulated load block until 90% of the initial battery capacity; with 589, 590 and 698 repetitions for the combined test and simulation prediction, full simulation prediction and experiment, respectively. When compared to established equivalent circuit or analytical approaches, the proposed approach requires only a small number of cyclic durability tests with constant current and temperature. In addition, the approach supports the battery design process by allowing simulations for different usage patterns, material and durability data.
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•A novel macro-scale approach for continuous battery life prediction is developed.•A new battery related damage parameter is introduced.•Lifetime prediction is made in real-time for complex current and temperature histories.•The model can be calibrated for NMC and other rechargeable battery structures.•The approach is successfully verified on a standardised (WLTC) EV driving profile.
In this paper, two different forms of an original multiaxial fatigue damage parameter related to the maximum fatigue damage plane are proposed for performing fatigue life prediction under various ...loading conditions loadings. The proposed fatigue damage parameters have been applied to uniaxial and multiaxial loading conditions for geometrically different bodies. Both the damage parameters are correlated to sets of experimental data published in the literature to verify the prediction accuracy of the damage parameters. The damage parameter in the form of the GSA, when applied to the uniaxial loading, provides very good correlations with four sets of experimental mean stress fatigue data for Incoloy 901 super alloy, ASTM A723 steel, 7075-T561 aluminum alloy and 1045 HRC 55 steel. In the case of multiaxial loadings, both the GSE and GSA parameters are found to correlate well with fatigue data of 1045 steel and Inconel 718 tubular specimens under proportional and non-proportional loadings. In addition, the damage parameters show reasonably acceptable correlations with experimental fatigue data of SAE 1045 steel notched shafts subjected to proportional and non-proportional loadings.
Damage is a progressive physical process that results in fracture. Recently, study of damage and failure in materials, particularly ductile metals has been of great importance for mechanical and ...structural engineers. So far, numerous criteria have been presented to predict damage behavior in ductile metals, each criterion is known by its advantages, disadvantages, and accuracy. One of the most famous models has been proposed by Lemaitre which is an accurate model and requires only one parameter to attain damage behavior of materials. In this article, employing the Lemaitre's ductile damage criterion, a new explicit, simple, and quick method is suggested to numerically determine the Lemaitre's damage parameter and damage behavior of ductile metals. This approach is much easier and cheaper than former conventional experimental methods because only needs a simple standard tensile test. Accuracy of the current numerical approach is validated through the experimental tests such as the standard, single and double notched tensile tests, and also the Nakazima fracture test. The numerical simulation results show suitable accuracy together with negligible percentage of error and perfect correlation in comparison with the experimental results.
•The decision of diffusion equation is based on the introduction of a diffusion front.•The time to fracture of the plate is determined using a fractional linear creep model.•The times to fracture ...while using scalar and vector damage parameters are compared.
Delayed fracture of bended rectangular plate is researched under creep condition in unsteady complex stress state considering the influence of the ambient medium. Using Rabotnov's kinetic theory, time to fracture of such plate is determined during sequential bending in different planes. Piecewise constant dependence of the bending moment direction and level on time is considered. The time to fracture of the plate is determined using a linear fractional creep model. The effect of the ambient medium on the creep and the creep rupture of the plate is attributed to diffusive penetration of the ambient medium elements into the material of the plate. An approximate method based on the introduction of a diffusion front is used to evaluate the diffusion process rate. The ambient medium effect is taken into consideration by introducing the function of cumulative average concentration into the constitutive and kinetic linear fractional equations. The times to fracture for the scalar and vector damage parameters are compared.
The study of rock damage evolution is of great significance in the field of underground engineering. In this paper, the damage development of deep formation rock was quantitatively evaluated by ...acoustic emission (AE) test. The Young’s modulus of the test rock specimens under ideal intact state was obtained by assuming a linear relationship between the AE rate parameter and the damage variation based on the rate process theory. Through the multi-stage cyclic loading test, the damage parameters corresponding to the peak stress of the previous stage were calculated by using the tangent modulus at the initial moment. The results showed that there was abrupt transition stage of damage development with the linear increase of stress. The damage parameter curves of rock specimens during loading process were obtained by using the method of cumulative AE energy, and the development trend of the curves was analyzed simply by combining the concepts of crack initiation stress and crack damage stress. Comparing the two methods of obtaining damage parameters by using cyclic loading test and cumulative AE energy, the results of them were highly consistent except for some deviation in the initial and final stages.
Strengthening breakwaters can reduce the damages that lead to hydraulic instability. Aiming to enhance the stability of reshaping breakwaters, this experimental study presents a method for ...controlling and reducing structural damages against waves by attaching a submerged obstacle to the structure toe and installing a floating wave barrier at a certain distance. In the tests, the breakwater was exposed to a total of 3000 random waves based on the JONSWAP spectrum. By generating an integrated 3D digital model of the structure using close-range photogrammetry, the displacement of armour units was recorded, and the damage parameter was calculated. Moreover, a comparison of the results between reinforced and simple breakwater indicated that the damage parameter was reduced by 37.19 and 34.14 percent by, respectively, attaching the submerged obstacle and installing the floating wave barrier, which confirms the good performance of the proposed models. Breakwater reinforcement with the submerged obstacle and the floating wave barrier simultaneously reduced the damage parameter by 51.79 percent, which was the highest efficiency among the different models. Also, the results show that with increasing the stability number, the damage parameter also increases, and the interaction between the wave steepness and the damage parameter indicates that the damage parameter decreases with increasing the wave sharpness values.
The purpose of this study is to identify the crack initiation and damage stress thresholds of granite from the Korea atomic energy research institute’s Underground Research Tunnel (KURT). From this, ...a quantitative damage evolution was inferred using various methods, including the crack volumetric strain,
b
value, the damage parameter from the moment tensor, and the acoustic emission (AE) energy. Uniaxial compression tests were conducted, during which both the stress–strain and AE activity were recorded simultaneously. The crack initiation threshold was found at a stress level of 0.42–0.53
σ
c
, and the crack damage threshold was identified at 0.62–0.84
σ
c
. The normalized integrity of KURT granite was inferred at each stress level from the damage parameter by assuming that the damage is accumulated beyond the crack initiation stress threshold. The maximum deviation between the crack volumetric strain and the AE method was 16.0 %, which was noted at a stress level of 0.84
σ
c
. The damage parameters of KURT granite derived from a mechanically measured stress–strain relationship (crack volumetric strain) were successfully related and compared to those derived from physically detected acoustic emission waves. From a comprehensive comparison of damage identification and quantification methods, it was finally suggested that damage estimations using the AE energy method are preferred from the perspectives of practical field applicability and the reliability of the obtained damage values.
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