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Bond deterioration between steel bars and concrete in reinforced-concrete beams mostly occurs close to the primary (i.e., bending induced) cracks. To investigate bond-cracking interaction, a novel bond-slip relationship is introduced in this study, where bond parameters are a function of crack-opening displacement. Such a displacement is in turn evaluated based on the highly variable strain profiles in the concrete, through an iterative procedure. The effectiveness of the proposed approach is validated against a set of tests on RC beams well-documented in the literature, which show a clear trend for the local bond stresses to decrease close to the primary cracks. The bond-slip relationships along the bar and the maximum bond stress depend on the applied loads and on the crack pattern, with a mutual interaction that affects both the crack-opening displacement and the bond stresses, causing a nonlinear increase in the steel strains. Nevertheless, the bond-slip relationships display descending branches characterized by remarkably similar slopes within a given region, irrespective of the loads. Consequently, if the descending branch for this region is known under a particular load, the branches under other loads can be obtained by horizontally translating the known branch. The proposed approach may provide a useful tool to describe bond behavior in RC members and to understand the complex interaction among the displacements due to crack opening, bond stresses and their structural effect. [ABSTRACT FROM AUTHOR]

We employed a novel combination of digital image correlation (DIC) and grain-based hybrid finite–discrete element method (GB-FDEM) to improve the comprehension of the relationships between microstructural features and the mechanical properties of granitic rocks. DIC and numerical results showed that macrocracks initiated and propagated along grain boundaries among different minerals driven by the high stiffness contrast between the compliant biotite and the stiffer feldspar/quartz grains. Surface deformation analyses revealed that tensile-dominated macrocracks open at monotonically increased rates before the crack damage threshold, and the opening accelerated afterwards with the increased shear component. The onset of the acceleration of the opening rate of macrocracks can be used to infer the crack damage threshold. Both strain and acoustic emission were used to infer damage stress thresholds in the synthetic numerical samples. Numerical results showed that the damage stress thresholds and uniaxial compressive strength decrease with increasing grain size following log-linear relations. Coarse-grained samples tend to fail by axial splitting, while fine-grained samples fail by shear zone formation. Biotite and quartz contents significantly affect mechanical properties, while quartz to feldspar ratio is positively related to the mechanical properties. Our study demonstrates the capacities of DIC and GB-FDEM in inferring damage conditions in granitic rocks and clarifies the microstructural control of the macroscopic mechanical behaviors. Our results also provide a comprehensive understanding of the systematics of strain localization, crack development, and acoustic emission during the rock progressive failure process. Highlights: Digital image correlation analysis and numerical modeling using grain-based hybrid finite–discrete element method can be used to evaluate damage stress thresholds. The onset of the acceleration of the crack opening can be used to infer the crack damage threshold. Strain field from digital image correlation revealed that stiffness contrast between mineral grains act as nuclei for crack initiation. Damage stress thresholds and uniaxial compressive strength decrease with increasing grain size following log-linear relations. [ABSTRACT FROM AUTHOR]

The use of high-strength and highly flexible wire ropes as internal shear reinforcement may be a solution to reduce the congestion of steel reinforcements and facilitate their installation in reinforced concrete (RC) elements. This paper aims to study the effectiveness of continuous wire ropes in substituting traditional shear reinforcement and its effect on the RC beam's shear behavior. Four-point bending tests were performed on 32 beam specimens. Fourteen different configurations of shear reinforcement were tested, of which four were reinforced in a conventional manner and ten with wire ropes. Deflection and crack opening were measured using Digital Image Correlation (DIC) technique. Test results show that the experimental shear capacities of beams with wire ropes are in good agreement with the estimated theoretical values. The difference in behavior of the two types of beams—transversely reinforced with wire ropes or traditional steel rebars—occurs at the appearance of the first diagonal crack. A progressive evolution of the crack opening occurs when using traditional rebars, while a sudden crack opening accompanied by loss of shear strength occurs in beams reinforced with wire ropes. This sudden loss is repeated several times during the test before reaching the final failure drop. The conjunction of two phenomena may be at the origin of this difference in the beam behavior: the smooth stiffness of the wire rope under tensile stresses associated with a weak wire rope-concrete bond. [ABSTRACT FROM AUTHOR]

Macro- and fractographic studies of fractures of CTOD specimens after fatigue testing of essential steel rolled products with a thickness of 82 mm for fixed offshore structures of the S420MLO quality category, produced using the technology of thermomechanical processing with accelerated cooling, are presented. Fracture nature and the mechanisms of fatigue crack propagation at test temperatures of minus 10 and minus 30°C were studied. The potential reasons for the formation of a "secondary" fatigue crack propagation front and its potentially negative impact on the final test results are described. Research results and testing were used in passing, with a positive result of certification tests of rolled products of quality categories S355MLO and S420MLO with a thickness of up to 82 mm in accordance with the requirements of EN10225-1:2019 and NORSOK M-120. [ABSTRACT FROM AUTHOR]

Using the energy approach formulated earlier by the authors, a mathematical model was constructed, which in turn is the basis of the calculation method for predicting the residual life time of the rectification column for production of ethylene under the wind load and atmospheric corrosion. It should be noted that wind load is shunting in nature with constant pressure on the column and frequent gusts. There is an external surface corrosion-mechanical crack in the circular weld, by which the column is attached to the base. The corrosive environment penetrates into this crack. Such a corrosive environment together with the shunting wind load intensifies crack propagation to the size, which causes failure of the column. Using the energy approach, this problem is reduced to special differential equations with special delta functions, which are solved approximately for a large number of wind gusts. Using the energy approach the dependence of the 09G2C steel column residual life time on the number of wind gusts, was investigated. [ABSTRACT FROM AUTHOR]

The assessment of the transfer properties evolution along the steel-concrete interface (SCI) subjected to various shear loadings is vital for ensuring the durability of reinforced concrete (RC) structures. This program explores the mechanical behaviours of RC specimens under push-in tests and analyses gas transfer properties of the SCI at various shear loadings. Concrete specimens, reinforced with ribbed and round smooth steel rebars were prone to mechanical and transfer properties tests. Real time and residual gas transfer properties tests were performed during the push-in tests and after unloading, respectively. The apparent transfer properties are calculated using Darcy's law for compressive fluids and the applicability of the Klinkenberg approach was limited to a specific set of inlet gas pressures. Analysis of the apparent transfer properties to determine a purely viscous transfer property is performed using Klinkenberg approach for different loading states. The initial transfer properties were found alike for RC specimens with ribbed or round smooth steel rebar, equal on average to 4.95 × 10 − 17 m 2 . Results for ribbed steel concrete specimens show a significant increase in transfer properties up to a factor of 11 in the pre-peak phase. The transfer property evolution is then described by a plateau in the post-peak phase. On contrary, for the round smooth steel concrete specimens, only a slight increase in the viscous transfer property, compared to RC specimens with ribbed steel, namely in the pre-peak phase, is observed. Generally, transfer properties of the SCI were not affected when subjected to shear stresses up to 2.85 MPa. Average crack openings were evaluated by applying an inverse analysis based on modified Poiseuille's law. Results indicate that crack openings reached at maximum 45 µm for concrete with ribbed steel due to shear whereas it was around 30 µm for concrete with smooth round rebar. Finally, for all flow measurements, the transfer properties under loading and after unloading were found of the same order of magnitude. • Transfer properties at the steel rebar – concrete interface under shear loadings and after unloading are assessed. • This paper has led to original permeability measurements for various shear loadings at the steel-concrete interfaces. • Two types of steel reinforcement are studied, ribbed and smooth steel rebars. • Flow values and apparent transfer properties are analyzed to determine viscous ones. • Local crack openings are estimated by applying an inverse analysis. [ABSTRACT FROM AUTHOR]

To improve the flexural behavior of thin bonded cement-based overlays, this study was carried out on the use of repair material incorporating amorphous metallic fibers (AMFs) in combination with the rubber aggregates obtained from grinding of worn-out tires. For this study, sixteen mortar mix compositions were prepared to contain AMFs and/or rubber aggregates to be used as overlay material while the substrate used was plain cement mortar. Rubber aggregates were incorporated at three different replacement ratios (i.e., 10%, 20% and 30%) by an equivalent volume of sand, and AMFs were added in three different dosages (i.e., 10 kg/m3, 20 kg/m3 and 30 kg/m3). In this study, composite beams (500 × 100 × 140 mm) comprising substrate (500 × 100 × 100 mm) and repair layer (500 × 100 × 40 mm) were prepared and investigated under flexural loading. Experimental results showed that the increase in rubber content resulted in a decrease compressive strength, flexural strength and modulus of elasticity. Rubberized fiber-reinforced cementitious composites (30R30F) exhibited higher flexural toughness and the flexural toughness improved up to 400%. Toughness and maximum deflection of composite beams enhanced significantly due to synergetic effect of AMF and rubber aggregates. It was observed that before peak load, rubber plays its role by delaying the micro-crack propagation. Results also revealed that the steel fibers reinforcement plays an important role in restraining the crack openings under flexure loading. In the post-peak region, steel fibers control the cracks from propagating further by bridging action and provide higher post-peak residual strength. [ABSTRACT FROM AUTHOR]

Phase-field modelling of cracks has gained popularity in the fracturing analysis recently. Originally developed for brittle fracture, the method has now been extended to cohesive fracture. In the latter case, the crack opening displacement is an essential variable, due to the dependence on it of the interface tractions. But also in brittle fracture, the crack opening displacement is crucial in certain applications, for instance for transport of fluids in the cracks. Herein, we derive the complete formulation for mixed-mode crack opening within the framework of the phase-field model, given for brittle as well as for cohesive fracture. The crack opening displacement is associated with a line integral that is perpendicular to the crack. Different factors and matrices apply in the integration for both fracture models and crack directions. These derivations have been validated analytically through an edge-cracked problem and numerically through curved crack scenarios. • A phase-field method is developed for mixed-mode fracture. • Both brittle fracture and cohesive fracture are considered. • Expressions to derive the crack opening and the crack sliding from the phase field are given. • Analytical validation through an edge-cracked problem. • Numerical validation through an example with a curved interface. [ABSTRACT FROM AUTHOR]

With the increased use of toughened epoxy adhesives in current transportation lightweighting efforts, it is critical that damage mechanisms, such as strain whitening, are understood and quantified. Damage quantification is needed for the constitutive models used in structural design; however, thin bond lines in adhesive joints limit direct observation. In this study, microscope observations of bulk toughened epoxy adhesive specimens subjected to tensile loading were linked to damage. Cracks on the surface opened during loading, leading to strain whitening at the crack tips and the initiation and propagation of shear bands. The stresses approximated at the crack tips suggested that particle cavitation could be occurring in these regions. Changes in specimen stiffness were linked to crack growth and the formation of shear bands. Material damage calculated using traditional load-unload stiffness (D ~ 35%) was higher than other methods such as change in material strength (D ~ 18%) and damage from changes in stiffness during load-reload (D ~ 19%). The differences were attributed to short-term viscoelastic effects. A new approach calculated damage from the strain whitening on the free surface (D ~ 21%). Values were in agreement with damage figures from other methods. The technique can quantify damage over the loading history and identify areas of damage localization. [ABSTRACT FROM AUTHOR]

Abstract Improvement in fracture behaviour of fibre-reinforced concrete (FRC) due to the inclusion of various types and combinations of fibres is widely reported. The fracture behaviour of FRC needs to be fully understood for the optimum use of these fibres in structural elements. Fracture behaviours of synthetic fibre-reinforced concrete (SynFRC), hybrid fibre-reinforced concrete (HFRC) and steel fibre-reinforced concrete (SFRC) are investigated in this study using digital image correlation (DIC) technique. This work focuses on improvement in the structural performance of FRC through a comprehensive study of the change in the crack length, crack opening and fracture process zone (FPZ) due to different fibres addition and their combinations. Three distinct fibre dosages of 0.50%, 0.75%, and 1.00%, of macro-polyolefin fibres, hooked end steel fibres and their hybrid combination are regarded as research parameters. Test outcomes indicate that HFRC offers higher post-cracking resistance when compared to SynFRC. SFRC showcases superior fracture performance than that of HFRC and SynFRC. Full-field strain measurements from DIC are used to measure the crack openings at different load levels during the fracture tests. Results of DIC analysis show good agreement with experimental measurements. Continuous monitoring of strain contours using DIC reveals the effective engagement of fibres along the depth at higher dosages for HFRC when compared to that of SynFRC. Also, HFRC had longer cracks than SFRC at a particular load.

In this paper, the real fracture structure of coal is obtained by SEM technology to solve the problem of non-uniformity characterization of coal. Based on the characteristics of fracture structure, the dynamic characteristics of gas flow are calculated by solving the Stokes equation by COMSOL. The calculation model of gas permeability is established, and the influence of fracture opening on permeability is studied quantitatively. The results show that the fracture opening has great influence on the permeability of CBM. When the Klinkenberg effect is considered, the gas crack flow model is modified.

The stress state of a piecewise-homogeneous elastic strip is considered, composed of two strips from different materials, one of which contains a crack of finite length, perpendicular terminating at the interface of materials. It is assumed that the composite strip on the side of the strip, in which there is a crack, is rigidly restrained, and the other side is free from stress. The strip is deformed under the influence of a normal load symmetrically applied to the crack edges. The stress intensity factors at the crack tips, contact stresses at the material interface, as well as the shape of the crack opening were determined. The study of the dependence of the indicated values on the elastic constants of the strip materials and the relative widths of the strips has been carried out. [ABSTRACT FROM AUTHOR]

This article presents a lattice-type numerical modelling method for analysing the thermo-mechanical behaviour of concrete subjected to compressive stresses at high temperature. The concrete is considered as a two-dimensional mesoscale structure consisting of three material phases: aggregates, cement paste and interfacial transition zones (ITZ). Subjected to a high temperature, concrete might be damaged due to the differences in thermal expansion between these components. The damage results in the initiation and propagation of cracks that affect the thermal conductivity of the material and thus the heat transfer within the structure. A modified damage-elasticity model, coupled with a nonlinear heat transfer equation taking into account the damage induced thermal conductivity change, is implemented in the lattice framework to describe the thermo-mechanical behaviour of concrete. Comparison of the current study to experimental and numerical results reported in the literature indicates the significance of the proposed model. [ABSTRACT FROM AUTHOR]

Increasing the bending capacity of reinforced concrete (RC) elements is one of important topics in structure engineering. The goal of this study is to develop a transferred stress system (TSS) on longitudinal reinforcement bars for increasing the bending capacity of RC frames. The study is divided into two parts, i.e., experimental tests and nonlinear FE analysis. The experiments were carried out to determine the load-deflection curves and crack patterns of the ordinary and TSS fixed frame. The FE models were developed for simulating the fixed frames. The obtained load-deflection results and the observed cracks from the FE analysis and experimental tests are compared to evaluate the validation of the FE nonlinear models. Based on the validated FE models, the stress distribution on the ordinary and TSS bars were evaluated. We found the load carrying capacity and ductility of TSS fixed beam are 29.39% and 23.69% higher compared to those of the ordinary fixed beams. The crack expansion occurs on the ordinary fixed beam, although there are several crack openings at mid-span of the TSS fixed beam. The crack distribution was changed in the TSS fixed frame. The TSS fixed beam is proposed to employ in RC frame instead of ordinary RC beam for improving the performance of RC frame. [ABSTRACT FROM AUTHOR]

Field observations of the foundations of high-head dams established the high sensitivity of the fluid to the crack opening and changes in the stress field, which is used for prediction purposes. [ABSTRACT FROM AUTHOR]

Copyright of Chinese Journal of Geological Hazard & Control is the property of China Institute of Geological Environmental Monitoring (CIGEM) Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

• Interaction between microcracking and the macrocrack opening in concrete is studied using DIC and AE techniques. • The study reveals a transient behaviour of macrocrack opening as microcracks are formed in the surrounding. • A fracture mechanics based approach is presented to consider the effects of micro-macro crack interaction. • An improved softening model is presented and local fracture energy is determined. During the fracture of concrete the formation of microcracks is a continuous process where new microcracks are formed in the vicinity of the macrocrack. As the fracture grows, these microcracks interact with the macrocrack and disrupt its smooth opening. In fracture mechanics based approaches; a smooth stress-crack opening softening behaviour is generally used to describe the local fracture process, where the effect of micro-macro crack interactions is lacking. This paper presents firstly an experimental study on the interaction between microcracking and the macrocrack opening (COD) in concrete using digital image correlation and acoustic emission techniques. The study reveals a transient behaviour of macrocrack opening as microcracks are formed in the surrounding. Based on the experimental results, the paper presents a new approach based on fracture mechanics to consider the effects of micro-macro crack interaction on the stress-crack opening softening behaviour. Local fracture energy is determined using the new softening model with micro-macro crack interaction for different geometrically similar sizes of the beams and at different locations on the crack profile. [ABSTRACT FROM AUTHOR]

The tensile behaviour of textile reinforced mortar (TRM) is sensitive to the adopted matrix, textile, and their interfacial bonding. The matrix–textile bond varies with the nature of the adopted textile. In this study, the influence of textile crimp and orientation on the tensile and cracking responses of cement matrix-based TRM was studied for coated and noncoated (uncoated) carbon textiles using digital image correlation. This study also examined the behaviour of a hybrid TRM incorporating layers of coated and noncoated carbon. The results showed that the presence of load-aligned crimped yarns influenced the deformation, damage mode, cracking evolution, and crack opening of the TRMs. Finally, based on the observed deformations of the load-oriented crimped-yarn TRMs, a simple modification term for the second phase strains of the ACK model was proposed based on the textile geometry. The modified term produced strain values within 9.7–15% of the experimental strain. • Load oriented crimp yarn leads to larger deformations. • Crimp straightening needs to be considered for simulating tensile response of TRM with ACK. • Textile geometry and orientation influences the mechanical properties and failure modes in TRMs. [ABSTRACT FROM AUTHOR]

Abstract An experimental evaluation of crack propagation and post-cracking behavior in steel fiber reinforced concrete (SFRC) beams, using full-field displacements obtained from the digital image correlation technique is presented. Surface displacements and strains during the fracture test of notched SFRC beams with volume fractions (Vf) of steel fibers equal to 0.5 and 0.75% are analyzed. An analysis procedure for determining the crack opening width over the depth of the beam during crack propagation in the flexure test is presented. The crack opening width is established as a function of the crack tip opening displacement and the residual flexural strength of SFRC beams. The softening in the post-peak load response is associated with the rapid surface crack propagation for small increases in crack tip opening displacement. The load recovery in the flexural response of SFRC is associated with a hinge-type behavior in the beam. For the stress gradient produced by flexure, the hinge is established before load recovery is initiated. The resistance provided by the fibers to the opening of the hinge produces the load recovery in the flexural response.

Fiber-Reinforced Concrete (FRC) toughness parameters, crucial for structural design, can be obtained either by using load–deflection or load–crack opening displacement(COD) relationships. Therefore, determination of midspan-deflection under a given crack width is important in terms of flexural toughness characterization. This research is aimed at determining the relationship between midspan deflection and COD, depending on beam-thickness/fiber length(t/fL) ratio and fiber aspect ratio(d/fL). In this study, load–deflection and load–COD curves from 4-point flexural tests were evaluated in detail to figure out a relationship between the midspan deflections and crack openings. Proposed relationships were verified with the findings from literature and good results were obtained. [ABSTRACT FROM AUTHOR]

• DIC technique is used to understand crack width and crack slip behavior under shear loads. • Effect of steel fibers (0.5%, 1.0%) on the shear behavior of prestressed beams is studied. • Full-scale tests at a/d ratio of 2.4 are conducted to understand the effect of fibers on shear. • Dilatant behavior is similar for beams with and without fibers up to peak load. • Steel fibers reduced the crack opening and crack slip in the post-peak region. • Failure mode changed from brittle shear to less brittle flexure-shear with fiber addition. The effect of steel fiber reinforcement on the shear behavior of prestressed concrete beam is studied using digital image correlation (DIC) technique. Steel fiber reinforced prestressed concrete (SFRPC) beams with fiber dosages of 0.5% and 1.0% by volume were cast and tested under shear. SFRPC beams were tested under a three-point bending configuration at a shear span (a) to depth (d) ratio of 2.4 to simulate shear dominant behavior. Other parameters such as compressive strength of concrete, prestressing reinforcement ratio and level of prestressing were kept constant. The kinematics of diagonal shear cracks including crack opening and crack slip were monitored using DIC based full-field strain measurement technique. The improvement in aggregate interlock and residual tensile strength at the crack tip due to the addition of steel fiber was reflected in the post-peak response of SFRPC beams. DIC analysis revealed that the full depth crack was formed in all the SFRPC beams before reaching their peak loads. The dilatant behavior was found to be consistent for all the test specimens (control and fiber reinforced concrete beams) up to peak load. The test results portray that the addition of steel fibers stiffens the post-peak response and reduces the crack opening and crack slip. Moreover, the failure mode changed from shear (brittle) to flexure-shear (less brittle) mode. [ABSTRACT FROM AUTHOR]

Copyright of Scientific Bulletin of National Mining University is the property of National Mining University, State Higher Educational Institution and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Highlights • A damage model based on standard and non-standard plasticity is described. • The permeability tensor of cracked brittle materials is computed anisotropically. • A reversed Rankine criterion is used to manage the crack reclosure processing. • The permeability can decrease as the crack reclose. • The flow rate is computed through a concrete sample loaded and then unloaded. • Permeability can be modelled accurately thanks to the crack reclosure processing. Abstract A macroscopic model intended to predict the change of permeability with respect to cracking is described. This development allows both diffuse and localized damage to be considered when computing the permeability. In compression, diffuse microcracking is initiated with respect to the material dilatancy. In this stage, the model adopts Poiseuille's law and uses the transverse expansions obtained with a non-associated Drucker-Prager yield function to compute the anisotropic permeability components. In tension, Poiseuille's law is also used to compute the flow rate through the localized crack. The permeability model uses the orthotropic crack opening information obtained by the mechanical model to compute the anisotropic permeability tensor. In addition, a reversed Rankine criterion is used to manage the localized crack reclosure processing and allows the principal crack opening and its associated permeability components to decrease. Finally, the model is used to simulate the flow rate through a real concrete specimen that has been subjected to tensile loading and then unloaded. With this application, the contribution of the crack reclosure processing to the permeability variations can be highlighted and utility of modelling crack reclosure accurately is demonstrated. [ABSTRACT FROM AUTHOR]

Earlier, we proposed a technique to estimate the fracture toughness of a metallic material. It differs from standard techniques in the determination of the operating stresses in an improved compact specimen with an edge crack. Using this technique, we determine the corrosion damage resistance of martensitic 30KhGSA (σu ≈ 1080 MPa) and VKS-9n (σu ≈ 2010 MPa) steels under full-scale and laboratory conditions and analyze their corrosion fracture kinetics. The corrosion fractures of the steels with different strength levels are found to have different characters: the 30KhGSA steel is likely to undergo anodic dissolution at the crack tip, and the high-strength VKS-9 steel undergoes hydrogen embrittlement. [ABSTRACT FROM AUTHOR]

The fracturing of six granite cubes (400 × 400 × 400 mm3) in response to blast loading was investigated using a combination of data collected from strain gauges and generated by digital image correlation (DIC) of pictures captured using a high-speed camera. This instrumentation permits the observation of the crack initiation, crack opening velocity, fracture pattern, full-field strain variation, and fragment movement at the cube's surface. In each experiment, an explosive charge was positioned at the center of the block in a vertical drill hole. Two charge weights, 6 g and 12 g, of pentaerythritol tetranitrate (PETN) were used. Using the high-speed camera, dominant vertical cracks were found to initiate on the surface of the cubes within 250 µs of the charge detonation. Two or three dominant vertical cracks appeared in specimens with a 12 g charge, while a single dominant vertical crack came into view in specimens with a 6 g charge. In addition, a single dominant horizontal crack was observed in all specimens, irrespective of charge weight. The maximum concentration of strain obtained from a DIC analysis agreed well with the dominant cracks and fracture patterns observed in the specimens. By combining the results from the strain gauges and the results from the DIC analysis for the specimen with a 12 g charge, the first crack initiation was found to occur at 67 µs after detonation. The crack opening velocities were determined using a boundary identification method and ranged from 5.0 to 7.6 m s−1, whereas the observed in-plane fragment velocities were slightly less. These experiments may contribute to a better understanding of the fundamental mechanisms of the rock fracture by blasting. [ABSTRACT FROM AUTHOR]

Different approximate crack opening models in a porous stratum are derived, based on a priori representations of the crack size, accurate solutions of motion equations of viscous fluid, approximate expressions of the filtering model in the stratum, and approximate expressions of the theory of elasticity of the stratum. The law of conservation of mass of the fluid in the crack is used to obtain quasilinear parabolic equations, describing the crack opening. [ABSTRACT FROM AUTHOR]

Highlights • Creep behavior of cracked fiber reinforced concrete is analyzed in service conditions. • Different stress levels and pre-cracking damages are considered. • Creep does not generate negative effects on the residual post-creep behavior. • Crack Opening Rate depends on both pre-cracking damage and applied stress level. • An expression to predict Crack Opening Rate values is proposed. Abstract This paper presents an experimental study on creep behavior of cracked Fiber Reinforced Concrete (FRC). To this end, a conventional strength concrete incorporating hooked-end steel fibers was used. In order to represent service conditions, specimens under low sustained loads with small pre-cracking damage (lower than 0.5 mm) were tested and analyzed. Taking as a reference the residual stress f R,1 determined according to EN 14651:2007, different stress levels for the creep tests were applied: 25%, 35% and 45% of f R,1. For the pre-cracking damage, several initial crack openings were considered: 0.05, 0.1, 0.2, 0.3 and 0.5 mm. The specimens were tested under a four-point bending scheme for 180 days in controlled environmental conditions. The Crack Opening Rate (COR) was used as parameter to characterize the creep behavior of cracked FRC. After the creep tests, conventional flexural tests were carried out to evaluate the residual capacity and to survey the fiber density of each specimen. Both the stress level and the initial crack opening factors affected significantly the creep behavior. In all cases, the measured increases in crack openings resulted compatible with service conditions, and no negative effects on the residual post-creep behavior were observed. An expression to predict Crack Opening Rate values is proposed. [ABSTRACT FROM AUTHOR]

• Electronic speckle pattern interferometry (ESPI) was used to measure the full-field deformation of graphite beams. • The J-integral of graphite was evaluated using the full-field displacement measured by ESPI as a boundary condition. • The J-integral of graphite beams was evaluated using a single specimen method and the geometric factors η were determined. • For different a 0 / D , the behaviour of the R-curves was evaluated using experimental and numerical. • Fracture parameters of graphite beams under typical loading stages were evaluated. Three-point bending tests were performed on centrally notched graphite beams to study the fracture properties of nuclear graphite. Electronic speckle pattern interferometry (ESPI) was used to measure the full-field deformation of graphite beams. In order to understand crack growth in graphite, numerical simulations were performed using a combination of ABAQUS software and the extended finite element method (XFEM). The numerical results were compared with the experimental results and good agreement was observed, confirming the validity of the numerical models. For evaluation of the J-integral, single specimen method is recommended; however, its geometric factor is uncertain and not easily determined. Thus, the load–displacement curves of beams with similar geometry and different notch depths were computed using the numerical simulations and a formula was proposed to obtain the geometric factor. Based on the ESPI results, the J-integral for crack extension was obtained by numerical computations using the measured full-field displacements as boundary conditions. Furthermore, the fracture resistance (R-curves) of the graphite was evaluated experimentally and compared with that calculated by way of the empirical formulas. The results indicated that energy dissipation rose rapidly to approximately 137 N/m before the peak load, and then increased gradually until reaching a plateau of approximately 209 N/m, when the fracture process zone was fully developed. Finally, the fracture parameters, including the critical crack opening displacements and J–integral at the fracture initiation of the graphite beams, were evaluated. [ABSTRACT FROM AUTHOR]

• Limestone beams with different a 0 were tested under 3-point bending and measured by DIC. • Fracture parameters including CMOD c , CTOD c , K Ic un , G f and length of FPZ were obtained. • The effects of a 0 on σ N , CMOD c , CTOD c , δ c , K Ic un , G f , and l mFPZ were investigated. • Based on the boundary effect model, the a 0 / D versus K Ic un and G f curves were fitted. Due to limitations in equipment and testing methods, there is currently little literature studying the effect of initial crack length (a 0) on fracture parameters. Considering that limestone is often associated with the construction of cultural heritage buildings, monuments, tunnels, subways and power stations, so limestone beams were used as the experimental objects, and were used to conduct three-point bending (3-p-b) tests based on digital image correlation (DIC) technique to study the influence of a 0 on fracture parameters, including critical crack tip opening displacement (CTOD c), nominal strength without considering the crack (σ N), nominal strength considering the crack (σ n), critical mid-span deflection (δ c), critical crack mouth opening displacement (CMOD c), unstable fracture toughness (K Ic un), fracture energy (G f) and fully developed fracture process zone length (l mFPZ). In addition, based on the boundary effect model (BEM), the relationships between the crack-to-depth ratio (α 0 = a 0 / D) with K Ic un and G f were analyzed. The findings indicate that, as a 0 increases, σ N , K Ic un , G f , and l mFPZ decrease gradually, while CMOD c , CTOD c , and δ c increase gradually; as two important parameters of the BEM, the boundary influence length (A 1) and size-independent fracture energy (G F) are 27.08 mm and 74.67 N/m, respectively. [ABSTRACT FROM AUTHOR]

The phase-field model treats discrete cracks in a smeared sense by a regularisation technique. It holds attractive properties: there is no need to consider cracks as geometric discontinuities, and it avoids remeshing around crack tips. The method has been employed in the analysis of brittle and cohesive fracture problems. In the brittle fracture model, a Griffith-like energy functional is used in the simulation, while in the cohesive fracture model, the fracturing problem exploits a displacement jump governed energy functional. Obviously, the displacement jump is crucial in the cohesive fracture model and in certain other applications, e.g. for hydraulic fracturing. In the current study, the approximated form of the crack opening displacement is derived for the brittle and cohesive fracture models. In both models, the crack opening displacement is associated with a line integral normal to the crack, but different factors in front of the integral apply. The derived integrals are verified analytically in a one-dimensional setting and numerically in multi-dimensional set-ups, featuring straight and curved cracks. • A procedure is developed for recovering crack opening displacements from strains in phase-field models. • While the recovery is identical for brittle fracture and cohesive-zone models, the expressions are different. • The procedure is validated analytically in a one-dimensional setting. • Numerical validation has been carried out for a two-dimensional case. [ABSTRACT FROM AUTHOR]

• Long tensile cracks parallel to a free plane are considered. • For 2D cracks linear links between the crack faces are introduced. • Cracks are loaded by uniform load or concentrated forces or moments applied at the centre. • Simple approximate formulas for Stress intensity factors and crack opening are derived. Straight 2D and disc-like cracks situated close to a parallel free plane are considered and asymptotic solutions for the stress intensity factors (SIFs) and crack opening are developed. Two asymptotic terms with respect to the small ratio of distance from the surface to the crack length/radius are derived. The derivation is based on considering the material between the crack and the free surface as an elastically supported beam or circular plate. The crack is considered to be opened either by uniform tensile stress or a pair of concentrated forces or moments representing the action of central defects (these represent for instance the crack growth from initial inclined crack or pore under compression acting parallel to the free surface). A crack with non-interacting surfaces (the conventional crack) and a crack with linear links between the surfaces are considered. Interaction with the free surface is shown to considerably increase the crack opening and SIFs, while the presence of the elastic links can reduce these crack parameters. In particular, the opening and SIFs of a crack with linear links under a pair of concentrated forces/moments exponentially vanish with the crack dimensions tending to infinity. The obtained asymptotic solutions provide a simple and accurate tool for investigating mechanisms of surface delamination and spallation (including thermal spallation and strain rockbursts). [ABSTRACT FROM AUTHOR]

The present study investigated the strain response of a distributed optical fiber sensor (DOFS) sealed in a groove at the surface of a concrete structure using a polymer adhesive and aimed to identify optimal conditions for crack monitoring. A finite element model (FEM) was first proposed to describe the strain transfer process between the host structure and the DOFS core, highlighting the influence of the adhesive stiffness. In a second part, mechanical tests were conducted on concrete specimens instrumented with DOFS bonded/sealed using several adhesives exhibiting a broad stiffness range. Distributed strain profiles were then collected with an interrogation unit based on Rayleigh backscattering. These experiments showed that strain measurements provided by DOFS were consistent with those from conventional sensors and confirmed that bonding DOFS to the concrete structure using soft adhesives allowed to mitigate the amplitude of local strain peaks induced by crack openings, which may prevent the sensor from early breakage. Finally, the FEM was generalized to describe the strain response of bonded DOFS in the presence of crack and an analytical expression relating DOFS peak strain to the crack opening was proposed, which is valid in the domain of elastic behavior of materials and interfaces.

Following the significant improvement in their properties during the last decade, Distributed Fiber Optics sensing (DFOs) techniques are nowadays implemented for industrial use in the context of Structural Health Monitoring (SHM). While these techniques have formed an undeniable asset for the health monitoring of concrete structures, their performance should be validated for novel structural materials including Ultra High Performance Fiber Reinforced Cementitious composites (UHPFRC). In this study, a full scale UHPFRC beam was instrumented with DFOs, Digital Image Correlation (DIC) and extensometers. The performances of these three measurement techniques in terms of strain measurement as well as crack detection and localization are compared. A method for the measurement of opening and closing of localized fictitious cracks in UHPFRC using the Optical Backscattering Reflectometry (OBR) technique is verified. Moreover, the use of correct combination of DFO sensors allows precise detection of microcracks as well as monitoring of fictitious cracks’ opening. The recommendations regarding use of various SHM methods for UHPFRC structures are given.

При помощи математического моделирования рассматривается ситуация, когда в кровле магматического очага, расположенного глубоко под конусом вулкана, мгновенно возникает трещина, давление в которой первоначально близко нулю. При падении давления в магматической камере вероятен «взрывной» рост пузырьков в магме за фронтом волны разгрузки и соответствующее увеличение объема магматического расплава. С помощью моделирования быстропротекающего процесса раскрытия возникшей трещины в кровле магматического очага под действием дегазирующегося магматического расплава показано, что раскрытие трещины останавливается на расстояниях гораздо меньших, чем глубина расположения кровли магматического очага.