Local Damage Evolution Research Articles

Damage evolution analysis of C/SiC screwed/bonded hybrid joints based on in-situ micro-CT technique

Due to own good high temperature mechanical properties, the C/SiC screwed/bonded hybrid joints are considered as an important development direction of vehicle connection structures. However, the difficulty of directly monitoring the interior of the hybrid joints during the bearing presents a potential challenge to the structural damage assessment. In this study, the damage process of the hybrid joints subjected to tensile loading was monitored and characterized based on the in-situ micro-CT technique. The intrinsic relationship between the mechanical responses of the hybrid joints and the local damage evolution was elucidated by observing the variation of the deposited SiC void volume at the overlap interface. The dual inhomogeneity of SiC bonding layer was quantitatively characterized utilizing the average failure rate and determination coefficient. The coupling influence mechanism of prefabricated bottom hole size and online connection process on the final assembly clearance was revealed.

An efficient multi-scale method for failure mechanism analysis of SiCf/Ti composites with experimental validation

This study focuses on developing and validating a high-precision concurrent multi-scale finite element model considering the progressive damage model (PDM) and the cohesive zone model (CZM) for predicting the damage evolution of SiCf/Ti composites. At the macro-scale, a constitutive model describing the anisotropic damage criterion of SiCf/Ti composites was implemented by means of a user-defined subroutine (VUMAT). Meanwhile, based on the submodelling, a representative volume element (RVE) model was developed to systematically analyze the failure modes of the SiC fibers, the matrix, and the interface, respectively. Specifically, the crack initiation and propagation in the stress concentration zones were further discussed. Simultaneously, experimental methods were employed to verify the feasibility of the current model. During the uniaxial compression, the brittle fracture of the SiC fibers and ductile fracture of the matrix are the predominant failure modes of SiCf/Ti composites, with fiber fracture being the dominant factor. The crack initiates at the fibers, propagates rapidly to the fiber-matrix interface, and then extends into the matrix. Moreover, the fracture locations are suscepticle to stress concentrations, leading to the crack initiation and propagation. The predicted results show that the local damage has a significant effect on the failure mechanism of SiCf/Ti composites and this multi-scale model provides a scientific reference for the design and optimization of composites.

Multi-phase shear thickening fluid based on ionic liquid dispersion medium for impact resistance and wear protection

Shear thickening fluids (STFs) have attracted increasing attention as smart materials with unique rheological properties. However, the preparation of STFs usually relies on a composite system of spherical nanoparticles with polyethylene glycol. In this work, novel multi-phase STFs (ILSTFs) were prepared in an ionic liquid by incorporating nanosized SiO2 and rod-shaped calcium metasilicate (CaSiO3) particles as a dispersed phase. Compared to traditional STFs, ILSTFs demonstrate excellent thermal stability. Rheological tests indicate that ILSTFs exhibit continuous shear thickening behavior, resulting in excellent energy absorption and impact wear resistance. In addition, ILSTFs can serve as a new type of lubricant. The tribological properties and impact resistance of ILSTFs were highly correlated with the shear thickening effect, with the multi-phase ILSTF system with CaSiO3 demonstrating superior impact wear resistance compared to the single-phase system. In this study, finite element analysis (FEA) is further utilized to investigate the local damage evolution and energy absorption rate of STF under impact loading, providing insights into the underlying mechanism. This ionic liquid-based STF holds promise for applications as a flexible filling component in the fields of lubrication technology and impact protection structures.

Fatigue life prediction of notched components under size effect based on strain energy density gradient

AbstractIn practical mechanical components, the characteristic of geometric discontinuous generates non‐uniform energy field near the notch, which affects the local damage evolution process of the notched specimens. Therefore, it is particularly crucial to formulate a parameter that can characterize such inhomogeneous state distribution. First, a strain energy density gradient factor is introduced to describe the complexity of strain energy density distribution near the notch. Meanwhile, a size effect factor is given considering the strain energy gradient factor and notch geometry parameter. Then, taking into account the impact of phase difference, a direct damage parameter considering non‐proportionality of different multiaxial load levels is developed. Furtherly, the modified strain energy density parameter is determined. Finally, the comparison between the proposed model and the other three models emphasizes the advantages of the model.

Creep-fatigue life prediction of notched structure after an advanced surface strengthening treatment in a nickel-based superalloy at 650°C

The elucidation of creep-fatigue damage mechanisms is still controversial for high-temperature structures after surface strengthening treatments, which serves as a critical foundation for the development of an accurate life prediction method. In this work, a numerical procedure is constructed for the prediction of creep-fatigue life improvement, where a dual-scale modeling approach is proposed to integrate important strengthening factors and microstructure features. The macro-scale finite element (FE) simulation aims to investigate the cyclic deformation behavior in a notched structure by using a viscoplastic constitutive model. The initial stress field is predetermined based on the experimental residual stress. The micro-scale FE analysis is employed to investigate the local damage evolution occurring at the notched root by combining size-dependent crystal plasticity with grain boundary cavity model. The cycle-by-cycle deformation histories are extracted from the macro-scale FE model and subsequently are utilized as boundary conditions in the micro-scale FE one. From the experimental perspective, the submerged micro-abrasive waterjet peening (SMA-WJP) process is carried out for creep-fatigue life improvement of the notched structure. Results shows that the notched structure treated by the SMA-WJP process forms an obvious plastic layer with the depth of 20 μm and residual stress with the maximum value of -926 MPa. The predicted numbers of cycles to crack initiation agree with the creep-fatigue experimental ones before and after SMA-WJP. In detail, the surface residual stress and plastic layer are unable to suppress the cavity nucleation on the grain boundaries of internal material. As a consequence, the creep-fatigue life improvement is diminished as the hold time increases, which can be accurately predicted by the developed numerical procedure.

Modelling of Creep Rupture in Grade 92 Steel Using a Microstructure-Type Finite Element Mesh

Conventional finite element (FE) modelling, which employed structured mesh, is unable to simulate local damage evolution at microstructure level. This paper aims to investigate the creep rupture and damage behaviour of Grade 92 steel under a creep environment using microstructural-type FE mesh. The idealised microstructures of the material were generated based on the Voronoi tessellation technique. Three notched bar specimens with different notch acuities were modelled in Abaqus v6.13 software and a ductility exhaustion based damage model was employed to estimate the damage state. The influence of the notch constraint on the ductility is accounted for in the simulation. It is found that the results obtained from the proposed technique are in good agreement with the experimental data. All the prediction points fall within the scatter band of +/- factor of 2. The damage was predicted to initiate at a distance offset from the notch tip. As the acuity increases, the damage initiation site shifts further away from the notch.

Study on Stress Intensity Factor of the Pit-Crack Model for Portal Crane Girders

In shipbuilding gantry cranes in long-term service in the coastal humid salt-spray environment, the main beam is affected in many places by corrosion fatigue-formed corrosion pits, affecting the structural strength of the main beam. This paper focuses on the impact of corrosion-generated pits under the conditions of crack nucleation. Corrosion fatigue crack nucleation is a local damage evolution process and the stress intensity factor criterion is one of the critical conditions to discern whether a crack sprouts at the corrosion pit. This paper establishes a corrosion pit-crack model based on the overall finite element model of the portal crane, and uses ANSYS software to simulate the stress intensity factor under complex boundary conditions. The results show that the different sizes and depth-to-diameter ratio of the pits greatly affect the value of the stress intensity factor and the stress concentration phenomenon may be the main factor causing the emergence of cracks; the change in the size of the pits on the stress intensity factor is not obvious, but with the increase in the depth-to-diameter ratio of the pits, the stress intensity factor of the pit-crack model is significantly increased. According to the hypothesis of semi-ellipsoidal pitting, the relationship between the stress intensity factor and the stress concentration factor at the pit is proposed, and its calculation results are within 5% error compared with the finite element method, and it is found that the effect of the etch pit on the stress intensity factor is positively correlated with the stress concentration factor; with the increase in the etch pit depth–diameter ratio, the crack budding location changes with the change in the stress concentration location, and the crack is more likely to be generated from the shoulder of the etch pit when the depth–diameter ratio of etch pit exceeds 1.

Process-performance-prediction integration for fatigue life improvement technologies: An implementation in cold expansion of hole structures

In this work, the process-performance-prediction integration (3P integration) is developed to improve the fatigue life and reveal the strengthening mechanisms of holed structures after a novel cold expansion process (CEP), where a specific dual-scale modelling approach is proposed to refine the close-loop system. In macro-scale simulation, the cyclic deformation behavior is addressed by an isotropic constitutive model, where the residual stress distribution extracted from CEP simulation is set as initial stress field. The local deformation histories in weak region calculated from the macro-scale simulation are supplied to micro-scale simulation as boundary conditions. The micro-scale simulation solves the local damage evolution of holed structures after CEP by using a modified crystal plasticity theory that grain size effect is considered. Excellent agreements between experimental data and predicted results in terms of fatigue life and damage mechanisms prove the robustness and accuracy of the proposed dual-scale modelling approach. Finally, a feedback link in 3P integration is established by the proposed approach combined with different residual stresses and plastic layers. The significant fatigue life improvement is mainly ascribed to residual stress, while plastic layer plays a synergistic role in life performance.

Determination of concrete fracture parameters using inverse analysis: Influence of the tensile softening model

The paper is focused on the identification of selected mechanical fracture parameters of concrete. An inverse analysis based on an artificial neural network is used for this purpose. In this approach the laboratory measurements are matched with the results gained by reproducing the same test numerically. The identification of mechanical fracture parameters is carried out from the records of three-point bending and wedge-splitting tests performed using three specimen sizes. The ATENA software is employed for the numerical simulation of the fracture tests. The material model with the exponential and bilinear tensile softening law is selected to govern the gradual evolution of localized damage. The obtained parameters are finally analyzed and discussed in terms of their dependence on the size of the initial uncracked ligament. The results show that both tensile softening models are able to capture the behavior of the specimens in the softening phase reasonably well. The tensile softening model does not affect the modulus of elasticity values but has a slight effect on the tensile strength and fracture energy. For the latter two parameters, both models detected the influence of specimen size on their values.

The Effect of the Energy Release Rate on the Local Damage Evolution in TRIP Steel Composite Reinforced with Zirconia Particles

In this study, the effect of the energy release rate on the transformation-induced plasticity (TRIP) steel composite reinforced with 5 vol% ceramic particles is determined using the crystal plasticity simulation of the coupled brittle-ductile damage model and validated by experimental results. A miniature dog bone tensile sample is subjected to an interrupted in situ quasi-static tensile test up to a true strain of 20.3%. Using the commercial digital image correlation program VEDDAC and the image processing method in MATLAB, the test data are utilized to monitor the progress of local microstrain and damage. The impact of the energy release rate of ceramic particles is investigated by simulation using a coupled crystal plasticity-dislocation density model with ductile-brittle criteria for the corresponding phases. It can be shown that the local deformations predicted by the numerical simulation and the experimental data are qualitatively comparable. The damage pixel of the experiment, smaller Ecr (1.0 × 108), and larger Ecr (1.2 × 108) cases of energy release rates are 4.9%, 4.3%, and 5.1%, respectively. Furthermore, on a global strain of 20.3%, the relative error between simulation and experimental validation of smaller Ecr (1.0 × 108) and larger Ecr (1.2 × 108) cases is 12.2% and 4%, respectively.

Influence of Failure Criteria and Intralaminar Damage Progression Numerical Models on the Prediction of the Mechanical Behavior of Composite Laminates

This work evaluates the effectiveness of commonly adopted local damage evolution methods and failure criteria in finite element analysis for the simulation of intralaminar damage propagation in composites under static loading conditions. The proposed numerical model is based on a User Defined Material subroutine (USERMAT) implemented in Ansys. This model is used to predict the evolution of damage within each specific lamina of a composite laminate by introducing both sudden and gradual degradation rules. The main purpose of the simulations is to quantitatively assess the influence of the adopted failure criteria in conjunction with degradation laws on the accuracy of the numerical predictions in terms of damage evolution and failure load. The mechanical behavior of an open hole tension specimen and of a notched stiffened composite panel under shear loading conditions have been numerically simulated by Progressive Damage Models (PDM). Different failure criteria have been implemented in the developed Ansys USERMAT, together with sudden and gradual degradation rules based on the Continuum Damage Mechanics (CDM) approach. Numerical results have been validated against experimental data to assess the effects of the different failure criteria and damage evolution law on the global mechanical response and local damage predictions in composite laminates.

Prediction of fracture and dilatancy in granite using acoustic emission signal cloud

The invisibility of fracture network evolution in the rock under triaxial compression seriously restricts the correlation modeling between dilatancy behavior and fracture interconnectivity. The key to solving such a challenge is strongly dependent on the accurate modeling of the spatial correlation in fracture network, which could be indirectly re-constructed by the acoustic emission (AE) signal cloud. Considering the interaction of local fractures, a cube cluster approach is established to describe the spatial correlation. The evolutional cube clusters effectively present the geometric characteristics induced by the increasing dilatancy of fracture. Two descriptors (i.e. three-axis length sum and pore fraction) are introduced to correlate cluster model with dilatancy behavior. Most fitting results support the linear correlation between two descriptors and volumetric strain, which verifies the sensitiveness of the cube cluster model to dilatancy. More importantly, by the statistical analysis of cluster structure, the cluster model shows the potential of calculating fracture angle. Moreover, a comparison between dilatancy-based damage and porosity-based damage is made not to prove the best but provide an AE-based prediction of local damage evolution. Finally, four classical models for calculating fracture angle are compared. The deviations prove the huge difficulty of describing the development of the fracture network uniquely dependent on a fracture angle. The proximity of measured angle and cluster-based angle supports the effectiveness of predication by the cube cluster approach.

A continuum damage-based three-dimensional fracture simulation method for brittle-like materials

Current numerical methods cannot simulate well three-dimensional (3D) fracture process of solids. In order to study 3D fracture process of brittle-like materials and improve crack growth path prediction accuracy, a method is developed based on continuum damage mechanics and finite element method. In the developed method, damage is computed by homogenizing stress or strain in the preset characteristic field for reducing the spurious mesh sensitivity. Meanwhile, an additional procedure is used to consider the unstable and competing fracture process, which can be used to consider stress redistribution due to local damage evolution during the fracture process simulation. In addition, a damage model of concrete is also developed and used to describe material damage. Finally, 3D fracture process of two numerical examples, were simulated and compared with the experimental results by using the developed method. The 3D crack growth path and macroscopic mechanical behaviors can be predicted by the developed method coupled with a damage model. From the comparison, the effectiveness and modeling capability of the developed method are verified, which can be used to study 3D fracture mechanisms of concrete-like materials.

Damage evolution of biodegradable magnesium alloy stent based on configurational forces

Magnesium alloy has attracted most of the recent attention as a candidate for stent material due to their biocompatible and biodegradable nature. However, their corrosion behavior in the human body is still a major issue in research today. In this paper, a strategy to simulate damage evolution in biodegradable magnesium alloy stent is given by introducing a configurational damage model. In the framework of continuum thermodynamics, one can characterize the development and evolution of local damage of materials by establishing internal variables in phenomenological method. We believe that corrosion can damage alloy in two different ways: surface corrosion and stress corrosion. Surface corrosion is described using uniform damage, when the structure is exposed in a corrosion environment; Configurational force is used to describe stress corrosion when the structure is exposed in a stimulating environment. We then select global damage and radial resistance force to perform the changes of macroscopic mechanical properties during stent degradation. Finally, the well performance of the proposed model is demonstrated through several numerical examples. This model has the potential to assist stent design and development in the future.

Effect of film cooling holes on the mechanical properties of 3D braided SiCf/SiC composites at 1350 °C in air

3D braided SiCf/SiC composites are the preferred material for turbine blades of advanced aero engines, but film cooling holes (FCHs) severely destroy the structural integrity and affect the mechanical properties. There are few studies concerning the mechanical performance of composites with FCHs. This paper presents the effect of FCHs on the mechanical properties of 3D braided SiCf/SiC composites at 1350 °C in air. The number of drilled holes were 1, 5, 10 (rectangular) and 11 (triangular), and the average diameter was 0.5 mm. Monotonic tensile tests, microstructure characterization and finite element method were performed to investigate the initiation and evolution of local damage around the FCHs. The results indicated that the coating effectively prevents oxygen penetration in short-term tests and composites with FCHs still maintain excellent ultimate tensile strength (UTS). The UTS of the composites seriously decrease due to stress concentration and unbridged cracking propagation around the FCHs in long-term tests. A triangular arrangement should be avoided in FCHs design of 3D braided composites because specimens with 11-H present low UTS. The failure mechanism of the composites with FCHs was discussed in detail according to the FEM calculation results. The research results of this paper provide a reference for the design of SiC composite turbine blades.

A flexible various-scale approach for soil-structure interaction and its application in seismic damage analysis of the underground structure of nuclear power plants

In simulations of geotechnical engineering, interface elements are versatile tools and are widely used in the modeling of the relative displacements between soils and structures. To consider the case of a local failure adjacent to a soil-structure interaction region, a partial mesh refinement should be performed. In this study, a three-dimensional (3D) interface element with an arbitrary number of nodes is developed as a new technique to reduce the complexity and difficulty of managing the various scales between soil and structure. An asymmetric number of nodes is permissible on the two sliding surfaces. In this manner, soil and structure can be discretized independently, and the various-scale model is established conveniently and rapidly. The accuracy of the proposed method is demonstrated through numerical examples. The various-scale approach is employed in an elasto-plastic seismic damage analysis of a buried concrete drainage culvert of a nuclear power plant. The results indicate that by applying the proposed method, the number of elements decreased by 72.5%, and the computational efficiency improved by 59% with little influence on accuracy. The proposed method is powerful for local damage evolution analyses of both soil and structure and possesses great practical significance and the potential for further application, especially for nonlinear analysis of large-scale geotechnical engineering.

A simplified method for predicting burst pressure of type III filament-wound CFRP composite vessels considering the inhomogeneity of fiber packing

The present study proposes a method to predict the burst pressures (BPs) of type III filament winding carbon fiber-reinforced plastic (CFRP) composite pressure vessels considering the inhomogeneity of carbon fiber packing through experimental work and simplified mechanical models reflecting the evolution of local damage in the CFRP layers. Vessels that had different carbon fiber volume fractions (Vfs) were prepared and tested to measure their BPs. The inhomogeneity of carbon fiber packing was evaluated using Weibull probability based on the microscopic observation of CFRP cross-sections in the virgin vessels. Detailed stress analyses of pressurized composite vessels considering the carbon Vf were conducted. Unstable fracture of the hoop layer was demonstrated by a simplified mechanical model combined with the inhomogeneity of the carbon Vf and de-bonding between the fiber and matrix. About 20% difference in the BP was measured between tested vessels with and without glass fiber-reinforced plastic layers over CFRP layers. The proposed method for predicting the BP based on the constant stress model enables consideration of the development of local fiber breaking prior to catastrophic fracture and to quantitatively estimate the change in the BP due to the difference in Vf.

Contact Fatigue Life Investigations and Wear Mechanisms of Different Case Hardened and Nidrided Steels

The present work examines experimentally the local damage evolution and compares the differences in fatigue behaviour of case-hardened and plasma nitrided layers under rolling contact fatigue (RCF). The RCF experiments are accompanied by damage assessments. In order to assess experimentally the extreme conditions of point contact, the experiments are performed on a ball-on-rod (BoR) test rig. Results showed that nitrided surface get more important to RCF at lower contact pressure due to the comparable thin nitration depth, whereas at high contact stress the crack initiation starts on the surface of the compound layer and crack grow further in the diffusion layer. The carburised layer of case-hardened surfaces do not show any surface crack initiation.

Concurrent multi-scale modelling and updating of long-span bridges using a multi-objective optimisation technique

This paper aims at developing an innovative technique of concurrent multi-objective optimisation for updating the multi-scale model of long-span bridges. A multi-scale model is established for the purpose of concurrently analysing the global response of the structure and nonlinear local damages in order to assess structural state and local damage evolution or deteriorating, respectively. A multi-objective optimisation technique is proposed in this work for concurrent multi-scale model updating, in which several key issues including the determination of the objective functions and constraint conditions, the multi-objective optimisation algorithm and how to find the optimal solution from many non-inferior solutions are studied. The proposed concurrent multi-objective optimisation technique is applied to update the initial multi-scale model of Runyang Suspension Bridge (RYSB) near Shanghai, and the updated model is validated by the data from the field tests conducted for obtaining the response in global (dynamic properties) and local levels.

Interfacial damage in biopolymer composites reinforced using hemp fibres: Finite element simulation and experimental investigation

The present study aims at considering the effect of interfacial damage on the mechanical performance of a starchy composite reinforced using hemp fibres. Mechanical behaviour is approached experimentally using tensile testing coupled to digital image acquisition. Thermomoulded samples with single fibres are designed to allow sample testing perpendicularly to the direction of fibre alignment. Experimental evidence of localised damage is then highlighted in the elasticity stage. Finite element computation is attempted to explain the observed damage using an adequate mechanical model that considers weak adhesion between phases and dynamic evolution of damage. Predicted results show that the FE model is able to reproduce the observed behaviour suggesting that local damage evolution is a serious mechanism affecting the performance of the studied composite.