Damage Evolution Behavior Research Articles

Numerical analysis of off-axial tensile behavior of 3D five-directional braided composites containing interface

ABSTRACT The microstructure of 3D five-directional braided composites (5DBCs) comprises the following three constituents: yarn, matrix and interface. The interface is the bridge between yarn and the matrix, and it controls the mechanical properties of composites. In this paper, a meso-scale finite element (FE) model containing an interface is proposed to analyze the off-axial tensile behavior of 5DBCs. Hashin criteria and maximum stress criteria with a gradual degradation scheme are employed to capture the damage evolution behavior of yarn and the matrix; zero-thickness cohesive elements ruled by a bilinear traction–separation constitutive relation are applied to simulate the interface debonding. These constitutive models are coded into a user-defined material subroutine VUMAT and implemented to attain a numerical solution based on ABAQUS/Explicit solver. The meso-scale FE model is verified with available experimental data in the on-axial loading condition and then utilized to predict the mechanical response in diverse off-axial tensile cases. The damage evolution process of a 5DBC specimen under typical off-axial loading is provided, and the corresponding failure mechanism is analyzed in detail. This work provides a transferable approach for numerical study on the interface and off-axis load problems in other textile composites.

Damage evaluation of rock salt under multilevel cyclic loading with constant stress intervals using AE monitoring and CT scanning

When salt caverns are used for the medium of underground energy storage, the surrounding rock experiences cyclic loading due to periodical injection-production. The cyclic load contains constant stress intervals and varied stress amplitudes, which threatens the stability of the salt caverns. In this study, multilevel cyclic loading with constant stress intervals on rock salt were conducted under uniaxial compression conditions. Acoustic emission (AE) monitoring and post-test computed tomography (CT) scanning were used to evaluate the damage evolution during the loading process. Results show that the density of the hysteresis loops in overall stress-strain curves present two-stage alternating sparse and dense loops during the loading. The cumulative AE count/energy increases with increasing the number of cycles and loading stage, and the growth rate for a single stage gradually becomes constant. The AE signals were divided into six kinds according to frequency-amplitude distribution. The presence of stress intervals increases the number of cracks and the median scale cracks account for about 90% of the total number of cracks. By analyzing the CT images, the crack morphology of the salt sample without hold time shows several inclined main cracks with numerous branch microcracks while that with the hold time of 20 s shows multiple branch cracks and numerous microcracks. To quantitatively evaluate damage evolution during the loading process, a damage variable is defined based on the relative variation of AE parameters. The damage accumulation for a single loading stage presents a two-phase pattern, and the damage degree during the accelerated deformation accounts for approximately half of the total damage. This study can provide guidance for designing the operation parameters when salt caverns are used for the storage of natural gas, air and CO 2 . • Multilevel cyclic loading tests with constant stress intervals are conducted on rock salt. • The AE parameters characteristics are analyzed. • The crack distribution and fracture behavior are visualized by CT images. • Damage evolution behavior is quantitatively evaluated.

Predicting interlaminar damage behaviour of fibre-metal laminates containing adhesive joints under bending loads

This study includes experimental and numerical investigations on fibre-metal laminate structures containing adhesive joints under static bending loads. Experimental tests were carried out on Glare® 4B specimens manufactured in-house and containing doubler joint features. Numerical analyses were performed using Abaqus software including damage in the glass fibre reinforced polymer layers, ductile damage in the resin pockets (FM94 epoxy) and plasticity in the metal layers. A new cohesive zone model coupling friction and interfacial shear under through-thickness compressive stress has been developed to simulate delamination initiation and growth at the metal/fibre interfaces with the adhesive joint under flexural loading. This model is implemented through a user-defined VUMAT subroutine in the Abaqus/Explicit software and includes two main approaches, firstly, combining friction and interfacial shear stresses created in the interlaminar layers of the fibre-metal laminate as a result of through-thickness stresses and secondly, considering elastic-plastic damage behaviour using a new cohesive zone model based on the trapezoidal law (which provides more accurate results for the simulation of toughened epoxy matrices than the commonly used bilinear cohesive zone model). Numerical results have been validated against experimental data from 4-point bending tests and a good correlation observed with respect to both crack initiation and evolution. Delamination and shear failure were noted to be the predominant failure modes under bending stresses as expected. This is due to the higher mode-II stresses introduced during bending which cause different damage evolution behaviour to that seen for axial stresses. Finite element results revealed that both friction and shear strength parameters generated from through-thickness compression stresses have a significant effect in predicting damage in fibre-metal laminate structures under this type of loading.

Experimental and numerical study on multiaxial creep behavior of 16MND5 steel at 700℃

In-vessel retention (IVR) is an effective strategy of ensuring the structural integrity of RPV under severe accidents. In the IVR condition, due to the geometric discontinuity of pressure vessel, multiaxial creep is the main form of failure of RPV. Moreover, 16MND5 steel undergoes a phase transition from bainite to austenite. In order to study the multiaxial creep failure mechanism, creep tests on different notched bar are carried out at 700℃. The influence of grain boundary precipitation on creep behaviors was studied by micro-structural observation. Furthermore, based on the Kachanov-Robotnov continuous damage model (CDM), the term of activation energy Q is adopted in the newly-developed model as the correction parameter that is used to study the damage evolution and multiaxial creep behaviors of 16NND5 steel. Finally, the good agreement is achieved between theoretical prediction and experimental results.

Viscoelastic–plastic constitutive model with damage of frozen soil under impact loading and freeze–thaw loading

This study aims to provide an understanding of the damage evolution and dynamic mechanical behavior of frozen soil under freezethaw (F-T) loading and impact loading.We used the split Hopkinson pressure bar (SHPB) device to evaluate the dynamic mechanical properties of frozen soil at different numbers and temperatures of F-T cycles. Our results indicate that the F-T process has a strong influence on the dynamic mechanical behavior of frozen soil. The peak stress of the frozen soil gradually weakens with an increase in the number of F-T cycles until the cycle number reaches the critical value for the steady state of the soil specimen (approximately 37 cycles). We observed a decrease in the peak stress of the frozen soil with a decrease in freezing temperature. We defined the F-T damage using wave impedance, which characterizes the microstructural properties of frozen soil, coupled it with the impact damage that satisfies the twoparameter Weibull distribution, and obtained the total damage of the frozen soil under F-T loading and impact loading. By combining the discretized ZhuWangTang (ZWT) model with the plastic theory that satisfies the DruckerPrager (D-P) yield criterion, which is based on the improved hardening criterion with strain rate terms, we constructed a viscoelasticplastic constitutive model with damage in frozen soil under F-T loading and impact loading. The results predicted by this model agree with the experimental data, validating its feasibility.

Effect of Confining Pressure on the Damage Evolution and Failure Behaviors of Intact Sandstone Samples During Cyclic Disturbance

Effect of Confining Pressure on the Damage Evolution and Failure Behaviors of Intact Sandstone Samples During Cyclic Disturbance

Damage evolution behavior of TiN/Ti multilayer coatings under high-speed impact conditions

The erosion of compressor blades by solid particles brings huge safety hazards to aero engines. The application of erosion-resistant hard coating has become a good solution to protect titanium alloy blades. In this work, TiN monolayer and TiN/Ti multilayer coatings were prepared on Ti-6Al-4V alloy using a magnetic filtered cathode vacuum arc system (FCVA) and a metal vapor vacuum arc (MEVVA) ion implantation device. The mechanical properties of the coatings were evaluated by nanoindentation and scratch tests. The damage evolution behavior and mechanism of TiN monolayer and TiN/Ti multilayer coatings are studied by single-particle impact test and finite element simulation. The results show that the fracture toughness of TiN monolayer coating is lower than that of TiN/Ti multilayer coating; TiN/Ti multilayer coatings exhibit good erosion resistance. The main reason lies in that the Ti layer dissipates part of impact energy by plastic deformation and reduces the tensile stress. The interfaces in the multilayer coating inhibited the propagation of cracks.

Damage constitutive model of pure copper at different annealing temperatures

Aiming at the problem of damage evolution of pure copper during the plastic deformation, the normalized shape factor is introduced based on the RO model (Ramberg-Osgood model). The mesoscopic damage constitutive model of pure copper at different annealing temperatures is established and the tensile deformation of industrial pure copper at different annealing temperatures is analyzed. The results show that the error between the calculated value and the experimental value of the damage constitutive model, based on normalized shape factor, at different annealing temperatures, is less than 10%. The model can effectively reveal the tensile damage evolution behavior of industrial pure copper and accurately predict the plastic tensile flow stress of industrial pure copper at different annealing temperatures. The hardening coefficient and hardening exponent in the model are closely related to the annealing temperature of the material. The annealing temperature has little effect on the hardening exponent and has a significant effect on the hardening coefficient and the hardening coefficient decreases with the increase in annealing temperature.

Damage evolution behavior of bi-adhesive repaired composites under bending load by acoustic emission and micro-CT

In the field of composites patch repair, it is necessary to improve the repair performance of adhesive due to its important role in repair efficiency and durability. A bi-adhesive repair construction with two adhesives was designed and the carbon nanotubes were firstly applied in this bi-adhesive to carry out composites patch repair in this paper. Mechanical behaviors and deformation damages of different repair configurations under three-point bending loads were investigated using acoustic emission and X-ray micro-computed tomography. Failure mechanisms were deeply discussed through the analyses of characteristic signals and three-dimensional visualization of interior damage. The damage evolution behaviors were divided into three stages patch damage and edge debonding, further damage accumulation in adhesive layer and matrix, completely patch debonding and delamination by the clustering analysis and characteristic response of acoustic emission signals. Failure characteristics of scanning images on the adhesive interface and delamination interface revealed the changes of damage modes within different repaired specimens. The damage visualization analyses of X-ray micro-computed tomography was corresponding to the acoustic emission response of interior damage within repaired composites. A combination of these two technologies successfully realized the damage evolution in repaired composites, helping understand the evolvement rule of damage on the adhesive interface.

Prediction of damage evolution behavior in ductile metals by Lemaitre criterion and comparison with GTN and EGTN damage models

Prediction of damage evolution in ductile metals is among the most important challenges ahead of researchers. Most of damage models are divided into micromechanical and continuum damage mechanics models. In this paper, a fully coupled elastic-plastic-damage subroutine of Lemaitre’s ductile damage model is implemented. Employing the model, damage initiation, propagation, and fracture of steel samples under shear loadings are predicted and compared with the GTN and extended GTN (EGTN) models. The comparison reveals that although the EGTN model shows more realistic results rather than the GTN, but the Lemaitre’s model has a more accurate prediction for shear dominant damage evolution.

Creep damage and interaction behavior of neighboring notches in components at elevated temperature

Previous studies have focused on creep damage evolution behavior of components with one isolated notch, but two or more notches may be placed at the components due to the function requirements, the limitation of the structural size, or may be induced by chemical/physical damage processes. In this work, numerical analyses and creep tests on creep damage and interaction behaviors of neighboring notches in components under creep conditions are investigated. Effects of structural configurations on creep damage and interaction behavior are discussed. Results indicate that the notch still indicates a strengthening effect on rupture life of components despite the interaction behavior of the two adjacent notches. A negative interaction effect on rupture life of components with two notches is found. Creep damage and interaction behaviors of the components with two neighboring notches of various distance values are related to structural configurations of the components, including notch acuity ratio, notch open angle and notch depth.

Effect of intra-yarn hybridisation and fibre architecture on the impact response of composite laminates: Experimental and numerical analysis

Advanced composite laminates (i.e. glass composite laminates) are highly susceptible to low velocity impact, and the induced damage failures substantially reduced their residual mechanical properties and safe-service life during their application. Therefore, experiments and simulation efforts to predict their low-velocity impact damages and energy absorbing have significant importance in composite structures design. In this regards, experimental and finite element analysis (FEA) with aiding Abaqus software were respectively performed to investigate the influence of yarn hybridisation on the response of composite laminates under low velocity impact. The hybrid yarns, which consisted of S-glass and polypropylene yarns have been used to manufacture two types of composites; non-crimp cross-ply hybrid yarns and twill hybrid fabric composites. Additionally, for comparison, the non-crimp cross-ply and twill fabric composite laminates have been made from glass fibres only. The vacuum infusion resin process has been adopted to manufacture these composite laminates. The impact performance of composite laminates has been investigated using low-velocity impact at 15 J, 35, and 50 impact energy levels. The numerical analysis was executed using Abaqus/Explicit and Hashin failure criteria and continuum damage mechanics by using homogenous shell were adopted to simulate the intra-laminar damage in layers. Meanwhile, standard cohesive inter-laminar interfaces that inserted between composite layers with quadratic stress failure criteria have been used to model delamination failures. The numerical results regarding impact force-time, displacement–time and energy-time histories plots, as well as the damage evolution behaviour of matrix crack and fibre fracture, presented an agreement with experimental results.

Investigation on damage evolution and acoustic emission behavior of aluminum alloy sheet during blanking process

Investigation on damage evolution and acoustic emission behavior of aluminum alloy sheet during blanking process

Analysis of Damages in Layered Surrounding Rocks Induced by Blasting During Tunnel Construction

A layered rock mass is a special type of geological body. The existence of a bedding surface may lead to a poor cutting effect (over/under-excavation of the surrounding rock), falling of blocks, or collapse, thereby affecting most constructions in areas with such rocks. Given the lack of a proper quantitative analysis method for surrounding rock damages, the construction process of layered surrounding rock tunnels becomes difficult. To address these problems, three types of cut blasting models with single, double, and four holes are studied in this paper. With this, the LS-DYNA program is used to analyze the behaviors of stress wave propagation, crack propagation, and fracture modes, as well as fracture mechanisms of mudstone, sandstone, and layered rock. Using the image processing technology and fractal theory, the fractal dimension change trend and progressive damage evolution behavior of the three types of rocks under different cut blasting conditions are determined. Also determined is the corresponding relationship between the fractal dimension and the rock damage degree. The results indicate that crack initiation, propagation, bifurcation, and fractal dimension evolution are more closely related to the phenomenon where the compression wave is ahead of the tension wave, and the[Formula: see text]incompatible deformation of the bedding under single-hole blasting. Under double-hole and four-hole blasting, the phenomena, such as spalling, bedding crack penetration, and fracture connection between the explosive holes are caused mainly by the effects of stress concentration, reflected tension waves, and stress wave superposition. Moreover, under different blasting conditions, the rocks exhibit a similar progressive damage process, i.e. a rapid increase at first, then a slow rise, and finally a stabilization phase. The dynamic damage degree of the rock exhibits a linear increasing trend under different blasting holes. The study results provide a useful reference for blasting scheme design and optimization of underground engineering projects.

Interface Strength, Damage and Fracture between Ceramic Films and Metallic Substrates.

Interface strength, damage and fracture properties between ceramic films and metallic substrates affect the service reliability of related parts. The films’ thickness, grain size and residual stress affect the interface properties and fracture behavior, thus related studies attract great attention. In this paper, the interface damage evolution and fracture behavior between ceramic films and metallic substrates were simulated by developing a three dimensional finite element model of alumina films on Ni substrates with cohesive elements in the interfaces. The interface fracture energy as a key parameter in the simulation was firstly determined based on its thermodynamic definition. The simulation results show the Mises stress distribution and damage evolution of the film/substrate structures during uniaxial tensile loading. Specially, when grain size of the films is in nanoscale, the interface strength increases obviously, agreeing with the previous experimental results. The effects of residual stress on interface properties was further simulated. The interface strength was found to decrease with increasing radial residual force and the axial residual pressure increases the interface strength. When the thickness of the films increases, the interface strength keeps a constant but the speed of interface damage becomes faster, that is, the thicker films show catastrophic fracture. The underlying mechanism of damage speed was analyzed. Understanding these size effects and the effects of residual stress is helpful to guide the design of related parts.

Stress field and damage evolution in C/SiC woven composites: Image-based finite element analysis and in situ X-ray computed tomography tests

The construction and examination of meso-structural finite element models of a Chemical-Vapor-Infiltrated (CVI) C/SiC composite is carried out based on X-ray microtomography digital images (IB-FEM). The accurate meso-structural features of the C/SiC composites, which are consisted of carbon fiber tows and CVI-SiC matrix, in particular the cavity defects, are reconstructed. With the IB-FEM, the damage evolution and fracture behaviors of the C/SiC composite are investigated. At the same time, an in situ tensile test is applied to the C/SiC composite under a CT real-time quantitative imaging system, aiming to investigate the damage and failure features of the material as well as to verify the IB-FEM. The IB-FEM results indicate that material damage initially occur at the defects, followed by propagating toward the fiber-tow/SiC-matrix interfaces, ultimately, combined into macro-cracks, which is in good agreement with the in situ CT experiment results.

Numerical modelling of the crack-pore interaction and damage evolution behaviour of rocklike materials with pre-existing cracks and pores

The combined effect of pre-existing cracks and pores on the damage evolution behaviour and mechanical properties of rocklike materials under uniaxial compression was numerically studied. Simulations of cracks and pores alone showed that increasing crack length and pore diameter decrease uniaxial compressive strength (UCS) and elastic modulus. Subsequent simulations considered two types of combinations of pre-existing cracks and pores – two cracks either side of a centric pore, and two pores either side of a centric crack – and the distance between cracks and pores was changed. In the case of two cracks at either side of the pore, UCS increased only slightly when the distance between the cracks and pore was increased. This was attributed to the more profound effect of the presence of the pore on UCS, and was confirmed by the progressive crack development characteristics and the major principal stress distribution patterns, which showed that the cracks initiated from the tips of the two pre-existing cracks made little or no contribution to the ultimate macroscopic failure. In contrast, models with two pores at either side of a centric crack showed a marked dependency of UCS on the distance between the pores and the crack. Cracks propagating from pre-existing pores made a greater contribution to the ultimate macroscopic failure when the pores were close to the centric crack and the effect gradually diminished with increasing space between pre-existing pores and the centric crack. Major principal stress distributions showed an asymmetric mobilisation of compressive stresses at the right and left sides of the two pores, favouring macroscopic shear failure when they were close to the centric crack which had led to a lower UCS. Overall, this study presents some critical insights into crack-pore interaction behaviour and the resulting mechanical response of rocklike materials to assist with the design of rock structures.

Meso equivalent calculation model for frost evaluation of concrete

The frost resistance of concrete is a significant indicator of the degradation of mechanical properties on reinforced concrete (RC) structures in cold areas. To accurately evaluate the damage evolution law of concrete with freeze–thaw cycles (FTCs), a meso calculation method was proposed based on the equivalent method and the cumulative damage model for concrete after FTCs. Subsequently, the evolution of the pore structure of concrete with FTCs was analyzed to obtain the damage evolution behavior of it. Based on this evolution law, the meso equivalent calculation model was established. The results show that the meso equivalent calculation model can better reflect the heterogeneous behavior of concrete. The calculation model can reflect the cumulative and random distribution characteristics of FT damage. The calculation results of macro mechanical performance on the concrete after FTCs are in good agreement with the test data. The maximum deviation between the calculation result and the test result of the dynamic elastic modulus is only 7.85% (100 FTCs), while the maximum deviation of the uniaxial compressive strength is only 2.91% (100 FTCs). The calculation model can be used to predict the degradation of mechanical performance on RC structures in cold environments.

Effect of void nucleation on microstructure and stress state in aluminum alloy tailor-welded blank

The microscopic damage initiation characteristic in welded joint greatly determines the subsequent damage evolution and fracture behavior of aluminum alloy tailor-welded blank (TWB) during plastic forming. In this study, the interactive dependence of void nucleation on microstructure and stress state in the welded joint of a 2219 aluminum alloy TWB was quantitatively explored by in-situ SEM testing. Moreover, a micromechanical model based on actual microstructure was adopted to reveal the underlying mechanisms from the perspective of microscopic heterogeneous deformation. The results showed that three void nucleation mechanisms, including particle-cracking, interface-debonding and matrix-cracking, coexisted in the deformation at different microstructure regions and stress states. The nucleation strain of each mechanism mainly depended on the particle volume fraction, grain size and stress triaxiality. Besides, the proportions of particle-cracking and interface-debonding greatly varied with the grain size and particle volume fraction, and the variation law changed with the stress state. The proportion of matrix-cracking had a weak dependence on the microstructure, while increased with the stress triaxiality decreasing. It made the damage initiation in aluminum alloy welded joint transit from particle-cracking dominance to matrix-cracking dominance with the stress triaxiality decreasing. The micromechanical modeling results suggested that the changes of evolutions and distributions of Mises stress in particle, hydrostatic stress at interface and plastic strain in matrix with microstructure and stress state were responsible for the above effects.

Modeling the damage evolution and recompression behavior during laser shock loading of aluminum microstructures at the mesoscales

Damage evolution in metals during laser-shock loading (spallation) is a complex phenomenon accompanied by extremely high temperatures, pressures, and strain rates that affect the void nucleation/growth mechanisms. The current modeling efforts at the atomic scales to investigate the evolution of microstructure undergoing the spall failure at the atomic scales are limited to a hybrid atomistic–continuum method that combines the two-temperature model (TTM) with the molecular dynamics (MD) simulations. This manuscript demonstrates this capability by investigating the mechanisms of nucleation/evolution of voids for a nanocrystalline Al system experiencing an ultrafast laser pulse. This capability, however, is unable to model the laser shock response of experimental systems (with grain sizes greater than 100 nm and thicknesses in the microns) as well as the post-spall behavior (damage growth or recompression behavior). This work combines the TTM with the quasi-coarse-grained dynamics (QCGD) method to extend MD-TTM simulations to the mesoscales. The hybrid QCGD-TTM approach retains the laser energy absorption, heat generation/transfer, and microstructure evolution (melting, defects, and damage) behavior predicted by MD-TTM simulations. The QCGD-TTM simulations allow the investigation of the wave propagation behavior, the evolution of microstructure (defects and damage), temperature, and pressure at the time and length scales of laser-shock experiments. The QCGD-TTM simulations reported here investigate the nucleation and post-spall damage evolution behavior during spall failure of sc-Al and 0.5 µm grain-sized pc-Al films with a thickness of up to 2 µm. The QCGD-TTM-predicted damage evolution behavior captures the post-spall behavior observed experimentally and retains the atomistic characteristics of void nucleation and void collapse.