Damage Evolution Model Research Articles

Fatigue behavior of selective laser melted 316L stainless steel: Experiments and modeling

Selective laser melting (SLM) is extensively applied in fabricating 316L stainless steel structures. In this study, a series of mechanical tests were conducted on SLM 316L stainless steel, including tensile testing, high cycle fatigue (HCF) testing at various stress ratios and mean stresses, and low cycle fatigue (LCF) testing at different strain amplitudes. A efficient method of processing CT images was employed to analyze the porosity and fatigue failure behavior of material. Additionally, we proposed an elasto-plastic fatigue damage evolution model takes porosity into account, with relevant parameters determined through experiments. The predicted life under experimental conditions was calculated using the UMAT and DISP subroutines in ABAQUS software. Results indicate that mean stress significantly reduces fatigue strength, and irregularly shaped pores are the primary cause of material failure and reduction in strength. The predicted life of the elasto-plastic fatigue damage model is in good agreement with the experimental results. These results have important implications for the design and maintenance of SLM 316L stainless steel structures.

Investigation of damage mechanisms in thermomechanical fatigue of nickel-based single-crystal alloys

Thermomechanical fatigue (TMF) is essential for ensuring the safety and efficiency of various thermal engineering systems, however, the underlying damage mechanisms remain unclear. In the present work, a damage evolution model is used to quantify damage mechanisms in nickel-based single-crystal superalloy DD6. The isothermal creep-fatigue model combining the fatigue and creep damages is developed to elucidate their interactions and validated by the tension-dwelling experiments. Finally, the experimentally measured TMF damage is quantitatively decomposed into fatigue, creep and extra TMF components. Significant TMF damage in the in-phase TMF is identified, especially in the [001] specimens, potentially attributed to the non-isothermal creep or oxidation, while damage in out-of-phase TMF aligns with the spiking oxidation mechanism.

Effects of steel fibers on the flexural fatigue performance of recycled aggregate concrete

To explore the flexural fatigue performance of steel fibers reinforced recycled aggregate concrete (SF-RAC), the flexural fatigue test and residual strength test with different stress levels were conducted. Besides, the fatigue cracks propagation under cyclic loading were observed and analyzed by digital image correlation (DIC) technology. The results show that the flexural fatigue life of SF-RAC increases when the content of steel fibers increases, and it is proved to be well in accordance with the three-parameter Weibull distribution. The flexural fatigue life equation with different stress level and reliability (S-N-P equation) is obtained based on it, which shows that when the fiber volume content is 1.5%, the fatigue strength of SF-RAC is about 37.2% higher than that of RAC without fibers. Then, a fatigue strain-based damage evolution model is established, and the derived residual strength model can well predict the damage degree and residual life of SF-RAC. Moreover, the steel fibers can improve the critical crack propagation length and loading cycles of RAC. The crack propagation rate can be decreased by 97.63% when the fiber volume content is 1.5%, and it is increased with the development of stress level. Finally, the influence mechanism of steel fibers on flexural fatigue performance of RAC were explained through microstructure tests.

A progressive damage model for 3D woven composites integrating kinking-buckling competition

In this work, a progressive damage model (Kinking-Buckling PDM) considering fiber micro-buckling failure, fiber kinking failure, transverse inter-fiber failure of yarns, matrix failure and interface debonding, is proposed to predict the compressive mechanical behavior of 3D woven composites (3DWC). Fiber kinking and fiber micro-buckling failure are adopted in the form of competition to characterize the longitudinal failure of fiber yarns. A bilinear damage evolution model is established to control the damage accumulation of each constituent. Meanwhile, a material tangent constitutive tensor characterizing the constitutive behavior of 3DWC is derived. The complex failure process of 3DWC under compression is displayed through Kinking-Buckling PDM. As the fiber initial misalignment angle increases, the compressive strength of 3DWC declines significantly, meanwhile, the main failure mode of 3DWC will be transformed from fiber micro-buckling to fiber kinking in warp yarns. The relevant experimental results are used to confirm the accuracy of the PDM.

Alternative fatigue–creep performance of rock‐backfill composite structure material in mine stopes under high static stress: Disturbed amplitude effect

AbstractThis work aims to investigate the dynamic stress amplitude on the mechanical responses of rock‐backfill composite structure material under alternative low‐cycle fatigue loading and creep loading tests. Results show that deformation, damage propagation, and failure pattern are all impacted by the stress amplitude, and volumetric deformation is the largest for a sample subjected to strong stress disturbance. The equivalent lifetime decreases with the increase of disturbed amplitude. A notable positive interaction between the fatigue damage and time‐dependent damage is found, and they promote each other. Additionally, a novel damage evolution model is proposed by the irreversible radial strain, and the model matches well with the testing data. Moreover, post‐test computed tomography imaging reveals that cracks at rock‐backfill interfaces are relatively easy to be stimulated under low stress disturbance, and it is suggested that tension‐splitting failure is more likely to occur within the surrounding rock, and shear failure seems to occur within the cemented tailings backfill for all the tested samples.

Experimental and numerical investigation on mechanical and fatigue performance of corroded Q690D high-strength steel

As a prevalent environmental factor in the service process of steel structures, corrosion have a significant impact on the mechanical and fatigue properties of steel, thus deteriorating service safety. In this article, focused on corroded Q690D high-strength steel, experimental and numerical investigations have been performed. Electrolytic accelerated corrosion experiments were conducted, and 3D surface morphology measurements were employed to analyse the surface properties of specimens with various corrosion degrees. Mechanical and high-cycle fatigue tests were carried out on the corroded specimens, then degradation models between the mechanical behaviours and corrosion characteristics were established. Furthermore, the fatigue damage evolution model of Q690D high-strength steel was calibrated based on continuum damage mechanisms (CDM), and numerical simulations of the corroded specimen corresponding to the monotonic tensile tests and high cycle fatigue tests were conducted. The results show that with the increase of corrosion degree, the elastic modulus, yield stress, and tensile stress would decrease, and the fatigue performance would deteriorate. Corrosion has a greater effect on the fatigue life of long-life range and the slopes of the S-N curves after corrosion are more uniform. With the CDM parameters of non-corroded Q690D and the numerical model with consideration of surface roughness, the fatigue life of corroded Q690D could be well simulated.

Performance enhancement of damaged RC structures with viscoelastic dampers: Damage assessment and optimal placement

Evaluating the performance degradation of the earthquake-damaged structure and optimizing the placement of dampers is important for retrofitting post-earthquake structures. In this study, a damage evolution model is developed to evaluate the degradation of strength, stiffness, and energy dissipation capacity for earthquake-damaged structures. The proposed damage model is validated using previous experimental results based on the nonlinear finite element analysis. Then, research on the optimal design of damper parameters and quantity is carried out. Considering the optimization range of earthquake-damaged structures, a genetic algorithm with multi-objective functions is developed to determine the optimal placement of viscoelastic dampers in damaged structures. The results demonstrate that the proposed damage model can effectively describe the performance degradation of damaged structures. The control effects of the acceleration response increase exhibited a maximum enhancement of 3.38 times after accounting for the optimization range of earthquake-damaged structures. The optimization results of the multi-objective function with the optimization range are better aligned with the objectives of designers.

White etching area damage induced by shear localization in rolling contact fatigue of bearing steel

AbstractWhite etching area (WEA) is a primary damage in rolling contact fatigue (RCF) of bearing steels. In spite of extensive investigations, there is a large discrepancy in the existing mechanisms of WEA formation. We attempt to unify the mechanisms from the perspective of shear localization and plastic damage accumulation based on ductile damage. RCF tests were conducted to generate WEAs with various microstructures and compositions. A thermodynamically consistent model of the ductile damage evolution from an inclusion was established by developing the phase field damage coupled with the crystal elastic‐viscoplastic constitutive relationship under RCF. The model was implemented into the FE framework through a user materials subroutine. The results indicated that the WEA is the shear band resulting from shear localization. The large inhomogeneity and scatter in WEA's microstructure are due to the influence of the crystal orientation. The development and orientation of SBs predicted by the model and the experimental observation of the WEA are in good agreement. The large micro‐shear strain in the WEA provides the driving force for mechanically controlled austenite phase transformation. The shear band center, which has the largest strain and the least stress, is where cracks initiate. This demonstrates that contrary to earlier reports that WEA is induced by previously formed crack faces friction, cracks actually initiate from the interior of the WEA.

Numerical Investigation of Failure in Epoxy-Based Adhesive Joints

Currently, adhesive bonding has been increasingly used in various industrial applications such as in automobile lightweight structures for multi-material assembly. However, adhesive joints show a complex failure behavior. Their failure modes can be either adhesive failure, cohesive failure, or mixed mode failure depending on their interfacial strength and also the strength of adhesive layer which also varies with hydrostatic pressure. In this study, the failure of the adhesive joints with an epoxy-based adhesive bonded to metallic substrates are investigated numerically using FEA. The damage evolution model is implemented in the finite element model to predict the failure of adhesive joints. The adhesive strengths under different states of stress for a damage evolution model are characterized using the modified Arcan fixture which is specifically designed to study of hydrostatic pressure effect on an adhesive behavior. The validation of the failure model is carried out with the results of single lap shear test. A good agreement is finally found between FEA and experiments.

On the fracture and energy characteristics of rock–backfill composite structure specimens exposed to fatigue–creep interaction loading

AbstractA series of stress‐controlled fatigue–creep interaction loading tests were performed on rock–backfill composite structure (RBCS) samples. The testing results reveal the influence of cement/tailing (c/t) on deformation, energy dissipation, damage evolution, and macro–meso failure patterns. The equivalent lifetime of RBCS is the largest for a sample with smaller stiffness filling, a smaller stiffness filling leads to weaker volumetric expansion. Additionally, strain energy is relatively large for larger stiffness filling, indicating a larger proportion of energy release at failure. A dissipated energy‐based damage evolution model is proposed to describe damage propagation at the entire fatigue–creep process which fits well with the experimental data. Moreover, the macro–meso failure pattern reveals the interactions between surrounding rock and filling material, failure seems to change from tension splitting to shear with increasing c/t. Good agreement was found among the volumetric deformation, energy dissipation, and failure pattern. It is suggested that flexible backfilling is benefit to prevent rock spalling and collapse.

Analysis on dynamic shear fracture based on a novel damage evolution model

Dynamic shear experiments and relevant numerical simulations are crucial for comprehensively understanding shear fracture mechanisms under diverse strain rates. In numerical simulations, damage evolution models are important for accurately capturing fractures and for guiding engineering applications under impact loading. To better predict dynamic fractures, a novel dynamic fracture model based on statistic damage mechanics is proposed. Based on the two-dimensional phase-field theory, the acceleration of void deformation is introduced into the void number continuity equation from the mesoscale. As fracture surfaces are formed by void evolution, a novel damage level is defined as the ratio of the statistical cross-sectional area of voids to the cross-sectional area of representative elements. Combining the void number continuity equation and the abovementioned damage level, a novel damage model is established based on void nucleation and ellipsoidal void growth. Based on percolation theory, a damage-softening function suitable for such a model is derived to characterize the effect of void coalescence on damage. Subsequently, dynamic shear tests are conducted at different strain rates using Split Hopkinson Pressure Bar (SHPB) and double-shear specimens with different shear zone widths. Two groups are defined to perform the dynamic shear experiments. One group is used to obtain the numerical model parameters and the other is used to investigate the fracture and void evolution. Scanning electron microscopy (SEM) tests are performed to analyze the effect of strain rate on void evolution. Moreover, the damage evolution model is used in the numerical simulation and its reliability is verified. The numerical results are consistent with the experimental results in terms of the strain signals and void number distributions. The effects of strain rate on fracture and void evolution are investigated via numerical simulations. All the results indicate that the proposed model can accurately predict dynamic shear fractures under different strain rates, thus serving as a useful reference for engineering design.

Research on the Damage Model of Cold Recycled Mixtures with Asphalt Emulsion under Freeze-Thaw Cycles

Cold recycled mixtures with asphalt emulsion (CRME) suffer the majority of damage from freezing and thawing cycles in seasonal freezing regions. However, an effective model for describing the internal damage evolution behavior of the CRME is still lacking. The objective of this study is to explore the performance of the destroy and damage model of the CRME subjected to freezing and thawing cycles with various water contents. The damage degree of performance at 60 °C and −10 °C, as well as the mechanical properties, were first analyzed in the laboratory. Then, the damage evolution models were established based on macroscopic properties, reliability, and damage theory. The results showed that the performance of the CRME decreased obviously as the number of freezing and thawing cycles increased; after 20 freezing and thawing cycles, the damage degree of 60 °C shear strength and 15 °C and −10 °C indirect tensile strength were 21.5%, 20.6%, and 19.8% at dry condition, but they were 34.9%, 31.8%, and 44.8% at half water saturation condition and 51.5%, 49.1%, and 56.1% at complete water saturation condition; the existence of water and the phase transition of water changed the failure characteristics of the CRME; the correlation coefficient of the damage model parameters was more than 0.98, so the damage evolution model could reveal the internal damage evolution law. Clearly, the freezing and thawing cycles accelerated the damage caused by CRME.

Damage Model of Steel Fiber-Reinforced Coal Gangue Concrete under Freeze-Thaw Cycles Based on Weibull Distribution.

In order to improve the utilization rate of coal gangue and expand the application range of coal gangue concrete (CGC), a certain proportion of steel fiber was added to the concrete, and the freeze-thaw cycles (FTCs) and flexural tests were used to explore the effects of different mass replacement rates of coal gangue (0%, 25%, 50%, 75%, and 100%) and different proportions of the volumetric blending of the steel fiber (0%, 0.8%, 1.0%, and 1.2%) on the frost resistance of steel fiber-reinforced CGC (SCGC). The governing laws of mass loss rate, relative dynamic elastic modulus and load-midspan deflection curve were obtained on the base of the analysis of testing results. The damage mechanisms of the SCGC under the FTCs were analyzed using the results of scanning electron microscopy (SEM). Based on the Lemaitre's strain equivalence principle and Krajcinovic's vector damage theory, a damage evolution model of the SCGC under the FTCs was established by introducing the damage variable of the SCGC satisfying Weibull distribution. The results show an increasing mass loss rate of the SCGC and a decreasing relative dynamic elastic modulus with an increasing mass replacement rate of coal gangue. The proper content of the steel fiber can reduce the mass loss rate of concrete by 10~40% and the relative loss rate of dynamic elastic modulus of concrete by 2~8%, thus significantly improving the ductility and toughness of the concrete. The established damage evolution model is well validated by the experimental results, which further help to improve the modelling accuracy. This study provides key experimental data and a theoretical basis for a wider range of proper utilization of coal gangue in cold regions.

Experimental and numerical study on fatigue damage evolution of Q690D welding details

Steel structures are widely used in various types of structures, and welding details, which are fatigue-prone constructions, are typically utilized in steel constructions. In this study, regarding the high cycle fatigue performance and fatigue damage evolution behaviors of high strength steel welding details, experimental and numerical studies have been carried out on two typical types of Q690D high strength steel welding details, including butt-weld connections and cruciform load-carrying fillet weld (CLFW) connections. High cycle fatigue tests have been conducted, SN curves based on effective notch stress have been established and compared with the suggested curves in IIW specification, showing that FAT200 is more suitable for fatigue evaluation of high strength steel welding details. Fatigue damage evolution model and numerical simulation methods for Q690D welding details based on effective notch stress and continuum damage mechanic have been established and validated. Damage evolution analysis of welding details has been conducted based on the proposed numerical simulation method. The simulation method enables accurate characterization of fatigue damage locations.

Damage evolution and strength prediction model of soda residue modified cemented tailings backfill under uniaxial compression

Recycling of solid waste materials reduces filling costs and reduces environmental pollution. This paper analyzed the availability of soda residue modified cemented tailings backfill (SRMCTB), and carried out uniaxial compression experiments to investigate the mechanical properties, energy evolution and damage characteristics of SRMCTB. The results show that the addition of soda residue effectively improves the compressive properties of SRMCTB. The uniaxial compressive strength and elastic modulus of SRMCTB increase and then decrease, and the elastic energy storage limit and total energy storage limit of SRMCTB increase and then decrease with increasing soda residue content. The damage constitutive models considering the compaction stage of SRMCTB were established and the damage evolution curves were plotted. Combined with the damage curves, the damage of SRMCTB can be divided into damage-free stage, damage stable development stage and damage rapid growth stage. The addition of soda residue has an effect on the stable development stage of the damage. When the soda residue content increased, the rate of variation of damage development stages first increases and then decreases. The proportioning parameters of SRMCTB were optimized in combination with the response surface methodology. It shows that when the soda residue content is at 5.45 wt%, the mass concentration is 76 wt% and the tailings gradation is 2:5, SRMCTB has the highest uniaxial compressive strength. A prediction model for the uniaxial compressive strength of SRMCTB was proposed and validated. The average error between the experimental and theoretical values is 8.30%, indicating that the model has a strong applicability and degree of extension.

Damage evolution model and failure mechanism of continuous carbon fiber-reinforced thermoplastic resin matrix composite materials

As a new composite material with high strength, toughness, and heat resistance, the continuous fiber-reinforced polyaryl ether sulfone ketone (PPESK) thermoplastic resin matrix composite (CFRP) has a wide temperature range, which is attributed to the complex temperature sensitivity of the matrix. The failure evolution characteristics under different conditions are not clear yet, which significantly limits its development and application to high-precision equipment. In this work, in order to deeply explore the full three-dimensional (3D) multi-scale multi-physics damage evolution mechanism of the CFRP over a wide temperature range, macroscale cross-temperature stretching/bending experiments, computer tomography (CT) scanning, and microscale scanning electron microscopy (SEM) are performed to effectively capture the overall damage morphology and local fiber/matrix damage failure characteristics of the material. The results show that the reinforcement with continuous fibers increases the tensile strength of the CFRP by 14–45 times and its bending strength by 2–6 times compared to those of the PPESK matrix in the cross-temperature domain. Moreover, the main failure mechanism of the CFRP in the cross-temperature domain is matrix crushing and fiber fracture at room temperature and fiber fretting slip and matrix viscous flow at high temperatures. This further explains the deformation mechanism of the CFRP, which can maintain its stability at high temperatures (low elongation at break: 1%–1.2%). The unique trans-temperature regional energy evolution and continuous fiber reinforcement of the material matrix resin PPESK lay the synergic stability of the high temperature performance and damage morphology of the CFRP. In particular, a cell model is constructed to further reveal the damage evolution characteristics of the matrix, fiber, and interface of the CFRP at the micro-scale. Combined with the failure mode theory and the performance degradation mechanism of composite materials, the temperature influence factor is introduced to formulate a multi-scale full 3D temperature-dependent damage evolution constitutive model of the CFRP over a wide temperature range. The constitutive model of the CFRP is incorporated in finite element software, and the simulation results are compared with the experimental ones for validation. The results show that the model developed in this work can effectively characterize the complex mechanical damage morphology and progressive failure characteristics of the CFRP over a wide temperature range.

Mechanical properties and damage characteristics of solidified body-coal combination in continuous driving and gangue backfilling

Recovery of the coal buried under buildings, railways and water bodies and the residual coal in irregularly arranged fully mechanized mining faces is a common engineering problem facing underground coal mining. In this study, a mining technology of continuous driving and gangue backfilling (CDGB) was proposed. The technology, which can not only alleviate ground subsidence and gangue discharge, but also release the above-mentioned coals, contributes to green and efficient sustainable development of mining. The stability of the system of the solidified body-reserved coal pillar combination (S-C combination) is crucial to the CDGB technology. Therefore, it is of great significance to explore the mechanical and damage characteristics of S-C combination in the synergistic bearing process. First, four sets of different-shaped S-C combination specimens were fabricated and a S-C combination bearing structure in CDGB was constructed to explore the differences in mechanical characteristics and damage modes of different-shaped S-C combination specimens during CDGB. Subsequently, their surface strain field evolutions and acoustic emission (AE) response characteristics in the load-bearing process were obtained with the aid of the digital image correlation technique and the AE signal monitoring system. Furthermore, a damage evolution model based on AE parameters and mechanical parameters was established to clarify the damage evolution law. The following results were obtained: (1) The free area of S-C combination can serve as a quantitative index to evaluate the stability of the overburden control system; (2) The concept of critical value k of the free area was first proposed. When the free area exceeds the critical value k (free area ratio greater than 1.13), the deformation resistance and the free area changes becomes negatively correlated; (3) As the free area expands, the failure of the S-C combination specimen evolves from tensile failure to shear failure. The distribution characteristics of the axial strain field also verified such a change in the failure mode; (4) When the free area expands, the peak AE count gradually changes from “double peaks” to “a single peak”. In this process, the expansion of free area shortens the time for accumulating and releasing energy during loading. Micro cracks generated in the specimen change from a phased steep growth to a continuous increase, and the process in which micro cracks develop, converge, intersect and connect to form macro cracks accelerates. The damage evolution law concluded based on AE parameters and mechanical parameters can well characterize the damage evolution process of S-C combination, providing certain reference for the study on the synergistic bearing of S-C combination during CDGB.

Very High Cycle Fatigue Life Prediction of SLM AlSi10Mg Based on CDM and SVR Models

A novel fatigue evolution model considering the effect of defect size and additive manufacturing building direction based on the theories of continuum damage mechanics and its numerical implementation in ABAQUS is proposed in this paper. First, the constitutive model, fatigue damage evolution model and their parameter calibration methods are presented. Second, using the ABAQUS platform, the proposed model is implemented with user-defined subroutines. After that, based on the proposed model and its numerical implementation, the fatigue life of additively manufactured AlSi10Mg is predicted and its applicability is verified through experimental results. Finally, a support vector regression model is established to predict the fatigue life, and its results are compared to those of the numerical finite element method. The results show that the support vector regression model makes better predictions than the finite element method.

Damage evolution and constitutive model of the rock masses with non-penetrating cracks under repeated impact loading.

A large number of cracks exist in natural rock masses, which significantly affects the stability of surrounding rocks in engineering under impact loading. Repeated impact tests by Split Hopkinson Pressure Bar are performed on non-penetrating cracked granite specimens with different prefabricated-crack inclination angles (0, 30, 45, 60, and 90°). The damage evolution law of cracked rock under repeated impact loading is investigated. Macroscopic damage variables considering geometric and mechanical parameters of cracks are proposed. Further, a constitutive model for the impact loading test is developed based on the coupling damage. It has been found that, the impact resistance of fractured rock first decreases and then increases with the increased prefabricated-crack inclination angle. The impact resistance for specimens with an inclination angle of 45° is the minimum. Theoretical results from the developed model agree with the experimental data. The model could well describe the progressive damage characteristics of cracked rock masses.

Fatigue behaviors and damage mechanisms for Nb3Sn triple-helical structure at liquid nitrogen temperature

Nb3Sn triple-helical structure is the elementary structure in the superconducting cable of ITER magnets and undergoes prolonged fatigue loading in extreme environments leading to serious damage degradation. In this paper, the fatigue behaviors of the Nb3Sn triple-helical structure have been investigated by the strain cycling fatigue experiments at liquid nitrogen temperature. The results indicate that Nb3Sn triple-helical structures with short twist-pitches possess excellent fatigue damage resistance than that of long twist-pitches, such as longer fatigue life, slower damage degradation, and smaller energy dissipation. Meanwhile, a theoretical model of damage evolution has been established to reveal the effects of twist-pitches on fatigue properties for triple-helical structures, which is also validated by the present experimental data. Furthermore, one can see that the Nb3Sn superconducting wires in a triple-helical structure with the shorter twist-pitches have a larger elongation of helical structure and less cyclic deformation, which can be considered as the main mechanism of better fatigue damage properties for the triple-helical structures during the strain cycling processes. These findings provide a better understanding of the fatigue properties and damage mechanisms for Nb3Sn triple-helical structures in superconducting cables of ITER magnets.