Rate Of Damage Accumulation Research Articles

A friction energy-based damage model for discrete element simulation of fatigue damage evolution in concrete

The discrete results of concrete fatigue tests limit the research of concrete fatigue theory. Numerical simulation methods can model the damage of materials from multiple scales, which helps to reveal the fatigue damage mechanism and compensate for the inadequacy of physical tests. This study presents a novel damage model for simulating the fatigue damage evolution of cementitious materials within the framework of discrete element methods. The proposed friction energy-based fatigue damage model is underpinned by a clear fatigue damage mechanism and has only two independent parameters. The model underwent validation through a comparison between its predictions and the results of compression cycle tests performed on concrete specimens. The model reproduces the evolution characteristics of various fatigue damage indicators, including deformation, modulus, hysteretic energy, and number of cracks, and the fatigue damage accumulation rate presents sensitivity to the stress level. Furthermore, the model predicts a clear regularity in the fatigue damage thresholds, which is an important reference value for establishing fatigue failure criteria. The model can be used to predict fatigue life of fatigue tests with various maximum and minimum stress levels and the S-N curves obtained from the simulations fall within the range of test results.

Experiment and prediction of the strain-range dependent ultra-low-cycle fatigue based on micromechanical cyclic void growth model

Under severe seismic action, the local stress concentration region in steel structures is prone to the ultra-low-cycle fatigue (ULCF) under high triaxiality and irregular cyclic deformation with intensively varying strain amplitudes. It emphasizes the necessity of the jointed effects of the stress triaxiality and strain range incorporated in the ULCF life prediction. Given the limited relevant studies in terms of the underlying micro-mechanisms, this paper focuses on experimental and modeling studies of the combined effects of stress triaxiality and strain range on the ULCF failure, based on Gurson-Tvergaard-Needleman (GTN) microvoid evolution theories. Monotonic tensile tests on three types of notched round bars suggest that fracture strain decreases with increasing triaxiality. Cyclic tests on two types of notched bars under various strain ranges confirm the combined effects of stress triaxiality and strain range. Given a specific triaxiality, the ULCF damage accumulation rate increases linearly as the tensile plastic strain range ramps up. For the same tensile plastic strain range, higher triaxiality results in a greater damage accumulation rate. In the modeling studies, the consistency of the GTN and uncoupled damage models has been proven in terms of ULCF failure of structural steel. Based on GTN theories, a new micromechanical cyclic void growth model (GCVGM) is proposed, considering the detailed processes of void nucleation, growth, and coalescence under monotonic and cyclic loadings. Moreover, the joint effects of stress triaxiality and strain range can be explicitly described within a unified framework, without additional empirical assumptions. Based on experimental and simulation results, the proposed GCVGM shows significant advantages over conventional models in accurately predicting ULCF failure under various loading protocols, with low average errors of 2.73 % and −0.91 % for two types of notched bar specimens, respectively.

Evaluating the risk of data loss due to particle radiation damage in a DNA data storage system

DNA data storage is a potential alternative to magnetic tape for archival storage purposes, promising substantial gains in information density. Critical to the success of DNA as a storage media is an understanding of the role of environmental factors on the longevity of the stored information. In this paper, we evaluate the effect of exposure to ionizing particle radiation, a cause of data loss in traditional magnetic media, on the longevity of data in DNA data storage pools. We develop a mass action kinetics model to estimate the rate of damage accumulation in DNA strands due to neutron interactions with both nucleotides and residual water molecules, then utilize the model to evaluate the effect several design parameters of a typical DNA data storage scheme have on expected data longevity. Finally, we experimentally validate our model by exposing dried DNA samples to different levels of neutron irradiation and analyzing the resulting error profile. Our results show that particle radiation is not a significant contributor to data loss in DNA data storage pools under typical storage conditions.

Balance between asymmetric allocation and repair of somatic damage in unicellular life forms as an ancient form of r/K selection

Over the course of multiple divisions, cells accumulate diverse nongenetic, somatic damage including misfolded and aggregated proteins and cell wall defects. If the rate of damage accumulation exceeds the rate of dilution through cell growth, a dedicated mitigation strategy is required to prevent eventual population collapse. Strategies for somatic damage control can be divided into two categories, asymmetric allocation and repair, which are not, in principle, mutually exclusive. We explore a mathematical model to identify the optimal strategy, maximizing the total cell number, over a wide range of environmental and physiological conditions. The optimal strategy is primarily determined by extrinsic, damage-independent mortality and the physiological model for damage accumulation that can be either independent (linear) or increasing (exponential) with respect to the prior accumulated damage. Under the linear regime, the optimal strategy is either exclusively repair or asymmetric allocation, whereas under the exponential regime, the optimal strategy is a combination of asymmetry and repair. Repair is preferred when extrinsic mortality is low, whereas at high extrinsic mortality, asymmetric damage allocation becomes the strategy of choice. We hypothesize that at an early stage of life evolution, optimization over repair and asymmetric allocation of somatic damage gave rise to r and K selection strategists.

Phase field modeling of fatigue crack growth retardation under single cycle overloads

A zone-based crack retardation model that responds to single cycle overloads is applied to a phase field fatigue framework. Fatigue crack growth is incorporated through the degradation of fracture toughness in the phase field fracture model where a representative loading strategy is followed instead of explicit cyclic loading. The model is demonstrated to capture Paris-Erdogan law type behavior. Crack growth retardation following an overload cycle is simulated through a zone ahead of the crack tip taking inspiration from existing plastic zone-based retardation models. The retardation zone is described through a strain energy density limit, with the overload ratio controlling the extent to which the fatigue damage accumulation rate is slowed inside the retardation zone. The model is implemented utilizing user subroutines in Abaqus with coupled-temperature displacement elements where temperature acts as a stand in for the phase field parameter. The model is found capable of reproducing experimental levels of fatigue life gains and reduction in crack growth rate for compact tension and center-cracked tension panel specimens when various overload levels are applied. Furthermore, the model is demonstrated to be able to capture complex crack paths with great accuracy.

A prediction method for fatigue crack growth under high stress levels using accumulative plastic damage properties

The objective of this research is to elucidate the characteristics of low-cycle fatigue crack propagation from the perspective of accumulative plastic damage, proposing a reliable prediction model for assessing the crack growth in EH-36 steel subjected to high stress levels. The plastic damage of the crack-tip is measured by the plastic energy at the critical distance point from the crack-tip. And, a prediction program is developed to calculate the fatigue damage accumulation and fatigue crack growth rates. In order to verify the validity of the prediction method, a sequence of quantitative loading experiments is conducted on specimens consisting of cracked plates and stiffened plates (made of EH-36 steel). The findings show that the prediction model effectively represents the fatigue crack growth behavior in high stress conditions. Increasing the mean stress and stress amplitude is beneficial to increase plastic energy increments, thereby accelerating the progression of fatigue damage towards the critical threshold.

An integrated computational and experimental study of the failure mode in Mg/Al laminated composite under three-point bending

The deformation behavior of hot-roll-bonded Mg/Al laminated metal composites (LMCs) is investigated, focusing on the crack formation around the interface. The material demonstrates a positive strain rate sensitivity mainly arising from the Mg matrix. A diffusion layer was formed at the Mg/Al interface with a serrated morphology during the two-pass rolling process, which consists of the Al3Mg2 and Mg17Al12 phases. The mechanical responses of the LMCs are evaluated using uniaxial tension, interfacial debonding tests (in normal and shear modes), and microstructure characterization techniques, which clarify the interfacial heterogeneity. The fracture constants of the interface were calibrated and incorporated in the finite element models to predict the failure modes of heterogeneous Mg/Al interface under three-point bending. With the increased thickness ratio of the Mg layer, the damage accumulation rate decreases at the interface and increases in the Mg matrix. As a result, the failure mode transferred from interface failure to matrix fracture. The findings of the present work provide new insight into the failure mechanism in laminated metal composites under bending conditions and can provide theoretical guidance for the plastic forming of such materials.

Acoustic emission, damage and fracture mechanisms of structural steel under mixed-mode loading

Mechanical and acoustic properties, damage kinetics and fracture mechanisms of 30CrMnSiA structural steel under mixed loading modes (I + II) have been investigated. It is shown that the change in loading mode leads to changes in strength and acoustic parameters, microcrack accumulation kinetics and fracture mechanism. The greatest changes in average frequency (AF) and rise angle (RA) of acoustic emission signal with increase in load are observed when the sample is oriented at an angle of 15°, at which the AF decreases linearly depending on the average values of the signal RA. However, the acoustic emission characteristics are not only determined by the loading mode but also by the fracture mechanism: brittle fracture at an angle of 45° is accompanied by increase in many acoustic characteristics including RA and AF parameters and a change in the type of time dependence of the total number of acoustic signals (ΣNAE), bAE – value and cumulative energy of acoustic emission signals (∑EAE). The frequency analysis showed that the average values of the peak frequency and the frequency centroid at rupture exceed the values of these parameters under mixed loading modes. A change in the failure mechanism under mixed loading modes does not affect these acoustic characteristics.Analysis of the kinetics of microcrack accumulation showed that the rate of damage accumulation decreases as the shear component of the load increases.

Ductile fracture of LYP225 steel: Effects of stress states and loading histories

This paper presents the experimental and modeling studies of the ductile fracture initiation of LYP225 steel, considering the stress state and loading history dependency. The monotonic material tests, including the notched round bars (NRBs), flat grooved plates (FGPs), and the shear plates (SPs), confirm the prominent stress state dependency of the ductile fracture. The increased stress triaxiality will significantly reduce the fracture strain, and the shear effect quantified by the Lode angle parameter will degrade the deformability under similar triaxiality. The Hosford-Coulomb fracture criterion can well characterize the relationship between fracture strain and stress state variables. Regarding the cyclic loading, a generalized expression of the cut-off region is proposed to consider the temporarily frozen damage accumulation under compression applied. In addition, the premature cyclic fracture initiation predicted by the monotonic fracture criterion highlights the necessity of considering the loading history effect. Based on the plastic strain memory surface, a reduced factor is introduced for the lower damage accumulation rate under cyclic loading. By comparing the testing and predicted plastic deformation corresponding to fracture initiation, the proposed fracture model is validated under different stress states and loading protocols, as indicated by the low average percentage errors of 4.02% for monotonic loading and 16.7% for cyclic loading.

Study of the Influence of the Irradiation Flux Density on the Formation of a Defect Structure in AlN in the Case of the Effect of Overlapping of the Heavy Ion Motion Trajectories in the Near-Surface Layer.

The aim of this paper is to test the previously stated hypothesis and several experimental facts about the effect of the ion flux or ion beam current under irradiation with heavy ions on the radiation damage formation in the ceramic near-surface layer and their concentration. The hypothesis is that, when considering the possibilities of using ion irradiation (usually with heavy ions) for radiation damage simulation at a given depth, comparable to neutron irradiation, it is necessary to consider the rate factor for the set of atomic displacements and their accumulation. Using the methods of X-ray diffraction analysis, Raman and UV-Vis spectroscopy, alongside photoluminescence, the mechanisms of defect formation in the damaged layer were studied by varying the current of the Xe23+ ion beam with an energy of 230 MeV. As a result of the experimental data obtained, it was found that, with the ion beam current elevation upon the irradiation of nitride ceramics (AlN) with heavy Xe23+ ions, structural changes have a pronounced dependence on the damage accumulation rate. At the same time, the variation of the ion beam current affects the main mechanisms of defect formation in the near-surface layer. It has been found that at high values of flux ions, the dominant mechanism in damage to the surface layer is the mechanism of the formation of vacancy defects associated with the replacement of nitrogen atoms by oxygen atoms, as well as the formation of ON-VAl complexes.

Plastic-deformation-history effects on the cyclic ductile fracture of steel sheet under high triaxiality

This paper presents the experimental and modeling studies of the plastic deformation history effects on the cyclic ductile fracture of thin steel sheet under high triaxiality. The center-holed plate specimens with three cutting radiuses are tested respectively under three cyclic loading protocols, i.e., the ascending-descending (AD), the descending-ascending (DA), and the random deformation amplitude. The prestrain-induced enhanced ductility effect is identified through comparisons between AD and DA testing, as the earlier applied large deformation might reduce the damage accumulation rate when the subsequent lower deformation amplitude is applied. A new cyclic void-induced damage model (CVOID model) is proposed to characterize the damage accumulation and succeeding softening evolution. The damage accumulation is attributed to the void growth and shrinkage subjected to cyclic deformation, which will trigger the softening initiation and development due to the internal micro-crack propagation. Furthermore, a new plasticity state variable is introduced to quantify the current plastic deformation state to consider the reduced damage rate dependent on the prestrain effect. Using the proposed CVOID model, the full-range cyclic hardening–softening behaviors can be accurately predicted under all concerned triaxialities and loading protocols, especially under random cyclic loading. It achieves better prediction of the cyclic softening behaviors than three conventional models (i.e., the CVGM, SWDFM, and the JIA cyclic fracture model), as indicated by the profound percentage errors of the accumulated critical deformation (AcD) lower than 2.1% compared with the errors from 20% to 60% via the existing models.

Uncovering Dislocation- and Precipitate-Induced Viscoplastic Damage in Al-Zn-Mg Alloy.

The existing phenomenological theories of plastic forming of sheet metal lack the predictability of the influences of dislocations and precipitates on viscoplastic damage in Al-Zn-Mg alloys. This study examines the evolution of grain size that occurs when the Al-Zn-Mg alloy undergoes a hot deformation process, specifically concentrating on dynamic recrystallization (DRX). The uniaxial tensile tests are conducted at deformation temperatures ranging from 350 to 450 °C and strain rates of 0.01-1 s-1. The intragranular and intergranular dislocation configurations and their interactions with dynamic precipitates are revealed by transmission electron microscopy (TEM). In addition, the MgZn2 phase induces microvoid formation. Subsequently, an improved multiscale viscoplastic constitutive model is established that emphasizes the effect of precipitates and dislocations on the evolution of microvoid-based damage. Using a calibrated and validated micromechanical model, the simulation of hot-formed U-shaped parts is conducted through finite element (FE) analysis. During the hot U-forming process, the formation of defects is expected to have an impact on both the distribution of thickness and the level of damage. In particular, the damage accumulation rate is influenced by temperature and strain rate, and local thinning is caused by the damage evolution of U-shaped parts.

Radial impact fracture characteristics and crack initiation criterion of concentric perforated granite after high temperature-water cycle

In this study, the radial impact fracture characteristics and crack initiation criterion of concentric perforated granite after high temperature-water cycle were evaluated based on the engineering environment such as high temperature, water encounter and dynamic disturbance experienced by the wellbore surrounding rock in the energy storage area during deep geothermal energy mining. And the combination of mechanical test, numerical simulation and theoretical analysis was used. The results revealed that the concentric perforated granite treated with high temperature and water soaking under radial impact load successively underwent three stages: transient elastic deformation, stable and unstable expansion of internal cracks. Finally, the tensile failure was produced and the granite was split into four pieces of approximately symmetrical. The main fracture direction of the rock sample was the impact direction revealed by the strain, fracture history and lateral strain clouds of the inner bore wall of the sample. Meanwhile, the tensile cracks firstly sprouted from the inner bore wall of the sample in the impact direction and expanded to the outer wall, and then from the outer wall in the vertical direction to the inner bore wall. Then, based on the test results, the damage variables were defined according to the proportion of damage degree caused by single factor and the law of crack germination inside the rock sample. It was calculated that the damage accumulation rate of concentric perforated granite under radial impact load after high temperature and water immersion experienced three typical stages: “slow-fast-slow”. Finally, the energy structure relationship of the micro-element of concentric perforated granite was constructed. The crack initiation criterion of the rock sample with concentric perforated structure under radial impact load was established by considering the initial damage caused by heating and water immersion and using the parameters such as the energy storage limit of the rock sample and the energy required for crack initiation. In addition, the rationality was also verified. The research can provide a theoretical reference for the formation of heat transfer channel caused by fracture of stored rock mass and the stability control of surrounding rock of geothermal wellbore, which have great engineering practice and scientific significance.

Microstructural and damage parameter effect analysis on the failure mechanism of fibrous soft tissues with a structure-based unit cell model

The presence of hierarchical microstructures in natural materials, such as connective tissues, makes them possess exceptional mechanical performance and undergo complex damage behaviors. Accordingly, in this study, a structure-based unit cell model (UCM) in which controllable irregular crimped fiber is embedded into soft matrix is constructed for the analysis of microstructural effects. An anisotropic hyperelastic constitutive model enhanced with different damage parameters is applied in finite element program, and the effects of damage parameters on the mechanical responses of fibrous soft tissues are investigated. The numerical results indicate that the fiber waviness plays a significant role in determining the stiffness of the tissues and that the microstructure controlled by the fiber crimp amplitude H, waviness χ and number of inflection points ω, mainly determines the fluctuation of the nominal stress–strain curves of these tissues with damaged fibers. In addition, a damage parameter analysis indicates that the attenuation of the strength and amplitude of the stress strongly depend on the strain energy limiter, and the parameter m mainly determines the rate of damage accumulation by the fibers with smaller strain energy limiters. The results of this study deepen the understanding of the mechanical behaviors of such fibrous soft tissues and provides a template for the optimization of structural and material designs for bioinspired composites.

Detection of ice using ship propulsion and navigation measurements

The presence of sea-ice influences the operation of ships in polar waters. Ice navigation leads to increased rates of damage accumulation in propulsion machinery. Methods and algorithms used to monitor the condition of the propulsion machinery can benefit from indicators that detect either operation in ice-infested waters or direct detection of propeller–ice interaction. This paper explores existing methods that inform the novel application of automatically detecting sea-ice based on high frequency shaft response measurements, low frequency propulsion control measurements, and navigation data. These methods include rule-based approaches, machine learning based classification, and statistical change detection. Methods are evaluated based on misclassification errors during cross-validation. It is shown that detection using the selected data is possible and able to give satisfactory prediction accuracy based on a case-study vessel. The results also show that machine learning approaches provide a solution that balances prediction accuracy and the rate of false negative predictions. The recommended method is to use support vector machine classifiers with a radial basis function kernel.

Global damage behavior and formability prediction of AA2219 FSW blanks at cryogenic temperature

The cryogenic deformation damage and formability of AA2219 FSW blanks were systematically studied with a novel hybrid damage model. The model combined the meso-GTN model and modified Mohr‒Coulomb ductile fracture model considering the complex stress states. The damage parameters of the weld and BM zone were obtained by the finite element reverse calibration method. The tensile properties, forming limits and deep drawability of the FSW blanks were analyzed with calibrated damage model. The damage differences and accumulation rate of the weld and BM zone both decreased, and the deformation uniformity of the FSW joints was improved at −196 °C. In addition, the proposed model can accurately predict the damage and cracking of FSW blanks under uniaxial tension, plane strain and biaxial tension. The maximum standard deviation of the major strain is only 11.7%. The global damage behavior of the weld zone was analyzed during cryogenic deep drawing of the hemispherical bottom cylindrical part. The predicted fracture position and direction of the simulations were in good agreement with those of the experiments, and the LDR increased to 1.9 at −196 °C. The improved formability of the deep drawn parts was mainly due to the increased damage resistance of the weld zone. The decreased voids coalescence rate and dense slip bands were all conducive to the improvement of damage resistance.

Fatigue damage development of grouted connection under varying cyclic loading

• Axial fatigue test of grouted connection under variable load range and sequencing. • Concrete damage plasticity-based model parameters used for numerical simulation. • Damage accumulation rate increased after sudden high load. • Load sequencing affects damage accumulation rate. • The damage accumulation of the real sized model was similar to the experimental model. The jacket structures of offshore wind turbines connect the foundation piles through a grout annulus. The grouted connections of the jacket structures are predominantly under the action of low-range fluctuating axial fatigue loads. However, they are sporadically subject to sudden large loads. The process of recurrent loading of the connection can lead to lose of capacity due to the gradual grout damage. Therefore, it is essential to study the damage accumulation process under variable fatigue loading. The cyclic compression tests of grouted connection scale model were performed and the influence of load-range, loading-sequence, and sudden large load on the fatigue damage accumulation was studied. The finite element models of experimental specimens and actual sized model were numerically simulated. An initial constant low load range yielded constant value of damage index and a sudden large load applied caused damage acceleration of the grout, which enhanced the development of damage under the subsequent low-range cyclic load. The larger load range prior to smaller load range created greater damage accumulation and reduced the residual vertical bearing capacity of the connection. The work offers a numerical basis for damage assessment of grouted connections of offshore wind turbines under variable axial fatigue load using the scalar damage degradation parameter in Abaqus finite element software.

Quantitative description of low-cycle fatigue damage accumulation in contact interaction zone by local strain evolution

The novel non-destructive method for quantitative description of low-cycle fatigue damage accumulation is expanded to a case of contact interaction in the stress concentration area. Investigated objects are plane aluminium specimens with the centred hole filled by cylindrical steel inclusion. The specimen is subjected to cyclic pull-push loading. The key point, that defines scientific novelty and powerfulness of the developed approach, consists of involving local deformation parameters as current damage indicators. Required strain values follow from distributions of all three displacement components along the filled hole edge measured by reflection hologram interferometry. The data, which are derived at different stages of low-cycle fatigue for the single specimen, provide normalized dependencies of local strain values from number of loading cycle, which are a source of damage accumulation functions. These functions are constructed for the specimen with the filled hole and geometrically analogous specimen with the open hole. Obtained data quantitatively describe a difference in damage accumulation rates for two cases.

Fatigue characterization analysis of a submerged fishing farm platform through spectral-based fracture mechanics

This study proposes a general direct calculation approach for fatigue crack growth evaluation and life predictions through a spectral-based fracture mechanics method. First, equivalent damage accumulation rates are introduced to describe the crack propagation characteristics under short-term sea states, integrating wave spectrum and fracture mechanics. Subsequently, a general fatigue crack growth program is integrated to realize automatic crack growth, accurate stress intensity factor (SIF) calculation and reliable fatigue life prediction through coupling analysis of meter-scale structures and millimeter-scale cracks. Finally, a parameter study is implemented to explore the influence of wave direction and initial crack size/shape on the fatigue performance of the fishing farm platform. Results indicate that the remaining fatigue life is evidently longer under 90° wave direction than that under 0 and 45°, which can be well characterized through SIF transfer functions. Critical fatigue life decreases with the increase of crack size and aspect ratio with the shortest duration of 12.8 years, demonstrating that residual fatigue life is closely associated with initial crack state. Fatigue failure is more predominant at lower tubular joints with the critical fatigue life ranging from 15 to 30 years, indicating the self-developed program possesses good universality and applicability in dealing with fatigue issues.

The Effect of APS-HVOF Bond Coating Thickness Ratio on TBC Furnace Cycle Lifetime

Combinations of NiCoCrAlY APS and high-velocity oxygen fuel (HVOF) bond coatings were deposited on alloy 247 disk substrates with APS yttria-stabilized zirconia (YSZ) top coatings to assess the benefit of air plasma sprayed (APS) ‘flash’ bond coatings. Using 1-h cycles at 1100 ℃ in air with 10% H2O and HVOF-only and APS-only bond coatings as a baseline, it was found that APS flash coatings extended the average coating lifetime by 16% to 35% with the thicker flash coating performing best. Principal component analysis and energy dispersive spectroscopy (EDS) compositional mapping on coatings characterized after 0, 100, 300 and 500 cycles and after failure showed that the Al in the bond coatings was depleted due to both oxidation and back diffusion into the substrate. The APS-only bond coating had significant oxidation throughout the bond coating and was so depleted in Al, that Al diffused from the substrate to the coating. Residual stress maps of the thermally-grown alumina scale were obtained every 100 cycles using photo-stimulated luminescence piezospectroscopy (PLPS) revealing that the Thick Flash coating had the slowest rate of damage accumulation in the oxide scale.