Crack Closure Behavior Research Articles

Unveiling the self-healing behavior of marine exposed concrete: Nondestructive ultrasonic detection and Vickers hardness characterization

Cracking is a widespread phenomenon throughout the service of concrete structures for marine and offshore engineering. In this paper, the effect of sulfate ions and related cations on the crack closure behavior of cracked mortar in chloride-containing environments was studied. To this end, the mortars are cracked before transferring to the pure chloride solution as well as composite chloride and sulfate solutions (CNS and CMS series). The self-healing behavior is assessed by the evolution of crack width, water absorption, and nondestructive ultrasonic detection. The Vickers hardness test is applied to evaluate the micro-hardness of self-healing products generated in the crack gaps. Thermodynamic modeling of the phase volume expansion from the mortar matrix to the crack surface is conducted using Gibb’s free energy theory to explore the self-healing mechanisms. Experiment results suggest that the existence of sulfate ions in chloride-containing solutions is beneficial for crack closure, and self-healing could be more obvious if the cations that bind to sulfate are magnesium ions. The distributions of Vickers hardness on the mortar surface across the crack reveal that the brucite layer diminishes the overall Vickers hardness of the mortar matrix, whereas it is favorable for the micro-hardness enhancement of self-healing products in the CMS series. Thermodynamic modeling interprets the expansion rates relative to the original unhydrated cement under the action of different soaking solutions.

Equations for efficient cycle-by-cycle computation of fatigue crack retardation and acceleration due to amplitude changes

The paper presents an efficient methodology for computation of the evolution of the fatigue crack retardation and acceleration effects due to crack closure during variable amplitude loading. The presented approach can lead to a very effective tool for estimation of residual fatigue life of engineering structures. Conventionally, consideration of variable-amplitude loading is either computationally too demanding, such as in finite element modelling, or challenging to unify the strip-yield model with another computational code. The simple analytical formulae available in literature are based on residual stress, which does not describe correctly the delayed retardation effect and in some cases it can be non-conservative. This work presents simple analytical equations describing the development of the crack closure based on the results of the strip-yield model for amplitude changes at the load ratio R = 0.1. The parabolic function enables simple computation of the maximum crack closure occurring after an overload without running any simulation. The equations also enable computation of crack closure behaviour following amplitude changes with the consideration of various cyclic material properties reflected in the tuneable ratio between the monotonic and cyclic plastic zone sizes.

Multi-scale characterization of fatigue crack tip deformation and propagation in QP steel

A novel measurement method for multi-scale characterization of fatigue crack tip deformation and propagation behaviors in high strength and plasticity, multi-phase, fine-grain Quenching and Partitioning (QP) steel was proposed. The fatigue crack propagation (FCP) test system with the macro/micro images acquisition devices was built to measure the FCP rate and crack tip deformation simultaneously. First, at the mesoscale, the evolution characteristics of the crack tip deformation fields, plasticity induced crack closure (PICC) behaviors and plastic zone during the FCP process were analyzed using the sub-image stitching and matching digital image correlation (DIC) method. Then, the FCP models were established with special emphasis on the model considering the PICC effect based on the obtained crack opening load at the mesoscale. Moreover, the corresponding microscale surface crack and fracture morphologies, microstructure phase transformation and deformations were observed and analyzed by electron backscatter diffraction (EBSD) and scanning electron microscope (SEM) techniques.

Improvement on Strength, Durability, and Crack Closure Behavior of Bacteria Concrete under Marine Soil Exposures

Abstract In the concrete industry, bacteria-precipitated calcium carbonate (CaCO3) can be used to repair cracks. If cracks in concrete are not repaired in a timely manner, other durability problems arise, necessitating expensive crack repair methods. Bacteria can be isolated from an appropriate physical environment so that they continue to function effectively in concrete. In this study, suitable self-healing bacteria are isolated from a concrete dump yard and incorporated into concrete specimens. After 3 days of normal curing, the specimens were pre-cracked and kept in marine exposure conditions for a period of 56 days. Strength and durability properties such as compressive strength regain, ultrasonic pulse velocity (UPV), and dynamic Young’s modulus were studied, and a water absorption test was carried out for cubes exposed in marine soil conditions. Marine soil treated with a bacteria and nutrient solution (1:9) exhibited improved crack-healing behavior as well as increased strength and durability. Compressive strength regain of 45.98 %, an increased modulus of 54.04 %, and crack healing of 83.05 % were reached with a 60 % reduction in water absorption and 32.49 % increment in UPV values. A microstructure study demonstrates the presence of CaCO3 compounds in healed crack surfaces and treated marine soil, which is primarily due to bacterial action under marine exposures conditions.

Fatigue Crack Growth on Several Materials under Single-Spike Overloads and Aircraft Spectra during Constraint-Loss Behavior

Abstract The phenomenon of flat-to-slant crack growth has been studied by many in the fracture mechanics community. At low stress-intensity factors, a fatigue-crack surface is flat (tensile mode) and the crack-front region is under plane-strain conditions (high constraint). As the crack grows with higher stress-intensity factors, a 45° shear lip occurs through the thickness of the sheet or plate. This behavior is the shear mode, which is under low constraint or plane-stress conditions. In 1966, Schijve found that the transition from flat-to-slant crack growth on a 2024-T3 Alclad aluminum alloy over a wide range in stress ratios (R) occurred at a “constant” crack-growth rate. Also, Newman and Hudson showed the same behavior on 7075-Temper-6 and Ti–8Al–1Mo–1V alloys, validating Schijve’s observation that crack-growth rate was the key parameter for flat-to-slant crack-growth behavior. The materials considered herein are 2024-T3, 7075-T6, and 9310 steel. Crack-growth behavior during single-spike overloads and simulated aircraft spectrum loading are presented. The fatigue structural analysis (FASTRAN) crack-closure based life-prediction code was used to correlate the constant-amplitude (CA) crack-growth-rate data over a wide range in stress ratios (R = Smin/Smax) and rates from threshold to near fracture, and to calculate or predict the crack-growth behavior on single-spike overload tests. Crack-closure behavior is strongly dependent upon the level of constraint. The main objective was to see if the constraint-loss region is the primary reason for crack-growth delays after single-spike overloads. Also, crack-growth analyses are presented on tests that were conducted by Wanhill on 2024-T3 Alclad aluminum alloy under the transport wing standard (TWIST) spectrum. Crack-growth analyses using crack-closure theory without constraint loss was “unable” to predict crack growth under spike overloads or simulated aircraft spectra. However, predicted crack length against cycles with constraint-loss behavior compared reasonably well with all tests.

Polyaniline Microspheres with Corrosion Inhibition, Corrosion Sensing, and Photothermal Self-Healing Properties toward Intelligent Coating.

A smart coating integrating functions of corrosion inhibition, self-healing, and corrosion-sensing was developed based on a polyaniline (PANI) microsphere-loading corrosion sensing probe (8-hydroxyquinone, 8-HQ). The PANI microsphere was prepared in a facile one-pot process via the combination of photopolymerization and an emulsion template. The 8-HQ-loaded PANI microsphere achieved three synergetic effects simultaneously: corrosion inhibition, corrosion sensing, and photothermal self-healing abilities. Benefiting from the corrosion inhibition effect of PANI, the coating with the PANI microsphere exhibited significantly enhanced anticorrosion behavior. After soaking in NaCl solution for 35 days, its impedance was maintained at 1.26 × 109 Ω·cm2, nearly 3 orders of magnitude higher than that of pure resin coating. Meanwhile, the encapsulated 8-HQ exhibited pH-responsive release behavior thanks to the pH-responsive characteristics of PANI, which could chelate with Al3+ ions to form 8-HQ-Al3+ coordinates with a conspicuous fluorescence, achieving a real-time corrosion diagnosing function. Moreover, benefiting from the photothermal property of PANI, the coating with the PANI microsphere displayed rapid crack closure behavior under NIR light irradiation, and the healing efficiency could reach 83.56% under near-infrared irradiation. This work presents an innovative strategy for fabricating an intelligent self-healing, self-reporting, and anticorrosion coating, which provides a new vision to prolong the lifetime of metals.

Modified joint element constitutive model for FDEM to simulate the nonlinear mechanical behavior of rocks

The closure behavior of fractured rock, which is a crucial characteristic, is challenging to simulate accurately using commonly employed numerical models. To address this issue and accurately replicate the nonlinear mechanical behavior of rock, we propose a modified joint element constitutive model for the finite-discrete element method (FDEM). The modified model resolves the stress on both sides of the crack by considering the aperture of the broken joint element instead of contact. Additionally, Joint elements with virtual opening, which are referred to as preprocessed joint elements (Pre-JEs), are implemented in this model. We extensively discuss two parameters associated with Pre-JEs to elucidate their impact on the nonlinear mechanical behavior of rock. Our findings demonstrate that the incorporation of Pre-JEs leads to a reduction in the compressive strength of rock. Furthermore, increasing the thickness of Pre-JEs results in the softening of the elastic modulus. Moreover, we have made improvements to the conventional calibration procedure for input parameters in FDEM. By employing our enhanced methodology, we successfully reproduce the crack closure behavior and peak strength of Lac du Bonnet granite using the proposed model.

Improved plastic-damage cap model for shear behavior predictions of plain and reinforced concrete members

In this article, an improved continuous surface cap model (ICSC) with isotropic plastic-damage algorithms is proposed, namely to predict more accurately the shear behavior of both plain and reinforced concrete members. For this, a suitable yield surface is implemented and the critical shear-to-compression transition parameter in the ductile damage law is scrutinized and determined. Firstly, the mathematical framework of the plastic-damage cap model is summarized, namely the formulations in plasticity, the returning mapping algorithms of cutting plane and the isotropic damage law. Then, the proposed constitutive parameters in ICSC model are presented. The plastic-damage algorithms flowchart is presented and described, and the new proposed ICSC model is implemented in the software LS-DYNA. Next, the proposed ICSC model is validated against the original CSC model (MAT159 in LS-DYNA) and also against the previously improved CSC model with crack closure behavior developed by the authors. For this, several simulations using the three CSC models are performed and the results are compared with experimental results, which involve single concrete element under various loading conditions, plain concrete structure under direct shear load and simply supported reinforced concrete (RC) beams with or without stirrups under a center-point load. The results are presented and discussed. They show the superiority of the proposed ICSC model for the prediction of the ultimate concrete behavior at the material level, and a better prediction of the shear behavior for plain concrete and reinforced concrete beams.

Phase‐field Fracture Based on Representative Crack Elements (RCE): Inelastic Materials, Friction, Finite Deformations, Multi‐physics

AbstractThe concept of representative crack elements has been successfully introduced to phase‐field fracture in previous publications, where anisotropic elasticity [1], visco‐elasticity [2], elasto‐plasticity and crack surface friction [3] are considered at small deformations. This framework allows to overcome unrealistic predictions for the crack kinematics, reported e.g. in Strobl and Seelig [4], and Steinke and Kaliske [5], known from phase‐field models with approximations for the crack closure behaviour based on volumetric‐deviatoric, spectral or similar splits of stress or strain tensors.In the current contribution to the method of phase‐field fracture, the framework for representative crack elements is shown for finite deformations and fully coupled thermo‐mechanics. The iterative solution scheme for the representative crack element and the variational homogenisation method are sketched. Applications to elasto‐plasticity, crack surface friction, finite deformations and thermo‐mechanics with heat radiation through the crack demonstrate the flexibility of the framework.

Direct observation of three-dimensional short fatigue crack closure behavior in Ti-6Al-4V alloy using ultra-high-resolution X-ray microtomography

Local 3D short fatigue crack closure behavior was investigated in Ti-6Al-4V alloy using ultra-high-resolution X-ray microtomography (XMT). The results show that the inhomogeneous distribution of plasticity-induced and roughness-induced crack closure is caused by the variation of crack path morphologies. These crack path morphologies exhibited heterogeneous plastic deformation at the crack-tips due to the anisotropic nature of α grains and varying extents of crack tilting and twisting caused by the interaction of the crack front with α/α boundary or α/α + β interface. It was revealed via surrogate-based statistical analysis that the Schmid factor has the strongest effect on crack growth rate.

Plastic-Damage Cap Model with Crack Closure Behavior for Concrete Modeling

Plastic-Damage Cap Model with Crack Closure Behavior for Concrete Modeling

Modeling impact fracture in a quasi-brittle solids using a 3D nonlocal graph-based finite element analysis: Theory, finite element simulations, and experimental verification

In this work, the authors have developed and implemented a novel nonlocal three-dimensional graph-based finite element approach for simulating fracture in quasi-brittle solids as an extension of their previous work in two dimensions. In order to validate the nonlocal aspects of the model, the authors have also fabricated a gypsum-based particulate composite with silica particles of specific dimensions and mass fractions, thus the length scale of the material is fixed by the particulate media. The GraFEA fracture model is implemented in a graphics processing unit (GPU) parallel computing environment that allows substantial speed-up of the simulations in both cases of impact and quasi-static loading conditions. The improvement in computational performance is especially essential for carrying out the simulation of parametric study. Comparison of the physical response of this specially designed composite with the three-dimensional nonlocal GraFEA shows that the model is capable of simulating fracture in such materials. Finally, the efficacy of simulating impact response of concrete including crack closure behavior is tested by simulating hammer drop test for the concrete beam sample and cyclic shear loading on the circumferentially-notched concrete cylinder sample.

Research on the Evolution Law Physical Short Fatigue Crack and Tip Deformation Fields during Crack Closure Process of the Q&P Steel.

In this paper, a novel dual microscopic fatigue-crack and tip-deformation-fields measurement method based on a hybrid image-processing technique is proposed that was used to research the physical short fatigue crack (SFC) closure effect and the evolution law of the tip deformation fields of Quenching–Partitioning (Q&P) steel during the crack-closure process. The measurement problems are solved, such as the small SFC tip region, large deformation gradient, and strong material anisotropy. Microscopic crack and speckle images are acquired simultaneously on both sides of a compact tensile (CT) specimen of Q&P steel by dual microscopic cameras. A digital image processing (DIP) method is used to identify crack-growth morphology and measure crack length in Q&P steel, and the SFC growth rates are analyzed under different stress ratios. Microscopic digital image correlation (Micro-DIC) is used to analyze displacement fields at the crack tip of SFC and, combined with virtual extensometer technology, analyze the evolution law of crack closure and the evolution of crack-growing morphologies during the closure process under different lengths and stress ratios. Accordingly, the evolution of strain fields at the crack tip in one load cycle for different crack lengths and stress ratios during the SFC closure process is analyzed. The results show that the stress ratio affects the crack-closure behavior and crack growth rate of Q&P steel in the physical SFC crack-growing stage. The crack-closure effect has an obvious influence on the evolution process of displacement and strain fields at the crack tip. The evolution of short-fatigue-crack-tip morphology and strain field of Q&P steel conforms to the crack-closure law. The research results provide experimental and theoretical support for the further study of the SFC growth mechanism and fatigue life prediction of Q&P steel.

A quantitative model considering crack closure effect of rock materials

The crack closure effect of rock materials plays a key role in the evaluation of its compressive mechanical behavior. Based on the effective medium theory, an exponential model is proposed to describe the influence of the crack closure effect on the constitutive relation. The crack deformation is characterized by natural strain, and the crack propagation in the compaction phase and elastic phase can be captured by this quantitative model. Three model parameters can be determined from experimental data. The model was verified by our uniaxial compression tests on marble and other types of rocks from the published literature. The results show that the model can simulate the nonlinear phase of stress–strain curves of rocks under uniaxial and triaxial compression conditions. The crack closure behavior in the compression tests can be well reflected by this model. In addition, the microcrack volume ratio is positively correlated with the crack density parameters, and the material damage caused by microcracks can be identified and quantified by the microcrack volume ratio.

Long crack propagation and closure in DC(T) specimens of Ni-based superalloy Inconel 718 and stainless steel AISI 301 after shot peening

In this study, the effects of severe shot peening on ambient temperature long crack growth, threshold and closure behavior in Nickel-based superalloy Inconel 718 and stainless steel AISI 301 were investigated. To assess the relationship between shot peening, crack tip shielding and crack growth, pre-cracked disk-shaped compact tension (DC(T)) specimens were treated at distinct locations around and ahead of the crack front. A beneficial influence of shot peening on crack propagation and closure was only identified in Inconel 718, albeit limited to shot peening of the entire area around the crack front. In contrast, the applied shot peening treatments had detrimental effects on crack growth properties in AISI 301. While the effective threshold of Inconel 718 was not affected by shot peening, AISI 301 featured a decreased intrinsic resistance against the onset of crack propagation. Strain-induced near-surface α′-martensite formed due to shot peening of AISI 301 was found to promote martensite formation during crack growth, giving rise to embrittlement of the material.

Three‐dimensional DEM simulation of the nonlinear crack closure behaviour of rocks

AbstractCrack‐closure behaviour of rock materials is well‐known, while the three‐dimensional discrete element method (DEM) simulation of crack‐closure behaviour is still a challenge. Hence, a numerical method was proposed through the combination of notional surface method and flat‐joint model. The pre‐existing microcracks with finite width can be inserted into the three‐dimensional numerical sample through the present method. Since the two physical mechanisms, that is, closure of pre‐existing microcracks and fracture of flat‐joint bonds, are included in the simulations, various evolution trends of crack‐closure stage can be captured through the present method. Due to the high computational efficiency of flat‐joint model, the three‐dimensional DEM simulations of crack‐closure behaviour can be achieved. The results of parametric study show that the crack intensity determines the crack‐closure behaviour and the crack width significantly influences the evolution trend of crack‐closure stage. The simulated unconfined compressive strength (UCS) and tensile strength (TS) significantly decrease with the increase of crack intensity. The crack width significantly influences the deformation parameters, such as elastic modulus, Poisson's ratio and crack closure strain. A calibration procedure was proposed to ease the calibration of mechanical parameters and crack‐closure behaviour. Through the proposed numerical method and calibration procedure, the basic mechanical parameters and crack‐closure behaviour of sandstone were well matched.

Elasto-Plastic Fatigue Crack Growth Behavior of Extruded Mg Alloy with Deformation Anisotropy Due to Stress Ratio Fluctuation.

Fatigue crack growth (FCG) experiments were performed using a low-temperature extruded magnesium alloy AZ31 with texture. Under a constant maximum stress intensity factor (Kmax), the stress ratio R was changed from 0.1 to −1 during the fatigue crack growth process, and the FCG behavior before and after the R change was investigated. As a result, tensile twins were generated owing to the fatigue load on the compression side of R = −1, and the FCG velocity was accelerated. In addition, when the maximum compressive stress at R = −1 (|(σmin)R = −1|) exceeded the compressive yield strength of the material (σcy), the FCG velocity after R fluctuation greatly accelerated. On the other hand, under the condition |(σmin)R = −1| < σcy, the degree of acceleration of the FCG velocity due to R fluctuation was small. In either case, the degree of acceleration in the FCG increased as the Kmax value increased. The above FCG acceleration mechanism due to the R fluctuation was considered based on the observation of the deformation and twinning states of the fatigue crack tip, the fatigue crack closure behavior, and the cyclic stress–strain curve of the fatigue process. The FCG acceleration mechanism was as follows: First, the driving force of the FCG increased owing to the increase in crack opening displacement due to the generation of tensile twins. Second, the coalescence of the main crack and a plurality of microcracks were generated at the twin interface. The elasto-plastic FCG behavior after the stress ratio fluctuations is defined by the effective J-integral range ΔJeff.

Detection of crack-closure during fatigue loading by means of Second Harmonic Thermoelastic Stress Analysis

The harmonic content of the temperature measured via a Thermoelastic Stress Analysis setup in a Single Edge Notched Tension stainless steel specimen is analyzed to obtain information about crack-closure during crack propagation. The first harmonic amplitude maps, combined with the Williams’ stress solution, are used to monitor the crack growth and evaluate the Stress Intensity Factor, enabling the extraction of a Paris’ law. Particular attention is devoted to the detection of crack-closure, via the second harmonic component of temperature. A study of the effects of the cyclical load that acts on the flanks of the crack is presented, and the experimental campaign allows to validate the theoretical assumptions made. It is shown that the load that acts on the wake of the crack has a significant component at twice the loading frequency, that is codified at a specific angular position. Furthermore, the analysis of a previously overloaded specimen allows to highlight the different crack closure behavior due to a residual stress state at the crack tip. The work proves that the proposed second harmonic thermoelastic analysis represents a powerful and robust tool for studying crack closure during crack propagation.

A novel 3D-FDEM method using finite-thickness cohesive elements to simulate the nonlinear mechanical behaviors of rocks

The crack closure stage and a high ratio of unconfined compressive strength (UCS) to tensile strength (TS) are frequently observed in laboratory tests of highly fractured rocks. However, few numerical methods can capture the crack closure behavior and high UCS/TS ratio in three dimensions. Hence, in this study, a novel three-dimensional finite-discrete element method (3D-FDEM) using finite-thickness cohesive elements was proposed, and random initial microcracks were introduced to the method. The crack closure stage and high UCS/TS ratio of highly fractured rock (Lac du Bonnet granite) are well matched through the present method. The simulated results show that the crack intensity determines the occurrence of the crack closure stage and the crack width significantly influences the evolution process of tangent modulus and crack closure strain. Due to the combination of stiffness degradation and failure of cohesive elements and initial microcrack closure, this method can capture the evolution trends of tangent modulus of various rock materials. The decreases in the simulated UCS, TS and elastic modulus with an increase in crack intensity are consistent with the experimental results of rocks after thermal treatment. A calibration procedure, which can ease the calibration of the parameters of this method, was proposed.

Effect of twins and plastic-deformation anisotropy of extruded magnesium alloy on fatigue crack growth and crack closure behavior

To study the effect of twins and plastic deformation anisotropy on the fatigue crack growth (FCG) behavior and crack closure behavior of extruded AZ31B magnesium alloys, two types of single-edge notched tensile specimens were prepared, with loading directions parallel (specimen E) and perpendicular (specimen T) to the extrusion direction (ED). FCG experiments using these specimens were performed at stress ratios R = 0.1 and −1, and cyclic speed of 10 Hz.In extruded magnesium alloy materials, the c-axis of the crystal is radially oriented on a plane perpendicular to the ED, indicating the generation of a strong texture.In the FCG experiment at R = −1 for specimen E, elongation in the c-axis direction occurred under compressive load, which generated {101‾2} <101‾1> tensile twins. The tensile twins increased the material deformation and fatigue crack opening distance. As a result, the effective stress intensity factor range ΔKeff increased, leading to the acceleration of the FCG velocity. At R = 0.1, tensile twins were not generated because the load waveform had no compressive load component; there was no change in ΔKeff and no acceleration of FCG.For specimen T at R = 0.1 and −1, tensile twin generation was expected because elongation in the c-axis direction occurred under tensile load. However, tensile twins did not occur, which is attributed to the effect of plastic deformation anisotropy. Therefore, for specimen T, the increase in ΔKeff and FCG acceleration did not occur, and no difference due to the R value was observed.