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The bonding performance of CFRP-steel joints between carbon fiber reinforced polymer （CFRP） plate and steel is seriously affected by marine environment. In order to evaluate the bonding strength of CFRP-steel joints exposed to marine environment， a double-lap shear joint on five specinmens with different bonding lengths were corroded for 7 to 21 days in the NaCl solution. The technique of digital image correlation （DIC） was applied to measure the normal strain distribution on the surface of CFRP. Scanning electron microscope （SEM） and energy dispersive spectrometer （EDS） were used to observe microscopic information and monitor element content changes of CFRP surface. The results show that the contents of Na+ and Cl- on the CFRP surface are increased with the increase of corrosion period， which induces charge compensation. Electrolyte penetration into the interface leads to free volume expansion， resulting in a decrease in the interfacial binding strength. The adhesion failure at the interface of adhesive and CFRP is observed in the experiment. The corrosion is aggravated with the increase of time， leading to the decrease of the ultimate load and the ductility. The interface ductility decreases after corroding for 7 to 14 days and the strain softening disappears and exhibits characteristics of the brittle failure after corroding for 21 days. The finite element model was established based on the Fickian theory and bonding-slip constitutive parameters.The diffusion characteristics of seawater between bonding interfaces and the interface typeⅡ delamination process were simulated，and the numenical results are in good agreement with the expermental results.

Background: Digital Image Correlation (DIC) is an advanced measurement technique capable of capturing full-field surface displacements in a non-invasive manner. However, the application of such measurements in the identification of bimodular materials remains insufficiently exploited. Objective: Recalibration with Analytic Solution Updating (RAU) has been proposed for the identification of mechanical elastic parameters of asymmetric constitutive law behavior using the Brazilian test. This method accomplishes identification by minimizing the gap between the measurements and the semi-closed form solution. Methods: Two types of data are employed: the first derived from the semi-closed form solution and the second measured on a 42-day aged mortar specimen using DIC. In the RAU method, three distinct cases are implemented to identify mechanical elastic parameters. These cases are determined by the nature of the data utilized, which can be categorized into axial displacement field, strains at the center, and full-field surface displacement measured on a given specimen area. Results: The RAU method successfully identified the compressive, tensile Young's modulus, and the compressive Poisson's ratio from the surface data provided. The identification with full-field surface displacement presented the highest level of accuracy in the RAU method using the identified results of synthetic data. Conclusion: The RAU method demonstrates significant accuracy and practicality in identifying the mechanical elastic parameters of bimodular materials. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Materials Engineering / Cailiao Gongcheng is the property of Journal of Materials Engineering Editorial Office 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.)

The uniaxial tensile mechanical properties of PVC foam considering the effects of strain rate ( ε ˙ = 0.0007 − 523 s − 1 ) and anisotropy (R = 1 − 1.57) have been investigated by quasi-static and dynamic (Split Hopkinson Tensile Bar, SHTB) tests. Combined high-speed camera system and Digital Image Correlation (DIC) technique, the real-time surface strain field of the specimen during the whole tensile process was obtained. On this basis, the macroscopic response and failure mode of PVC foam were investigated. The failure mechanism of PVC foam under tensile loading was revealed through Scanning Electron Microscope (SEM) images on fracture cross-section of loaded specimen. Finally, based on experimental data, a prediction equation on tensile strength of PVC foam considering the effects of strain rate and loading angle (anisotropy) is proposed. Furthermore, a nonlinear constitutive model is developed to describe the uniaxial tensile mechanical properties of PVC foam. [ABSTRACT FROM AUTHOR]

In order to study the Brazilian splitting characteristics of the frozen stone mixture under the coupling effect of freezing temperature and size effect, Brazilian splitting experiments were conducted on 5-10, 10-15, 15-20, and 5-20 mm particle size frozen soil-rock mixture samples after freezing at −10, −15, −20, −25, −30, −35, and −40 ℃ to investigate the effects of freezing temperature and different particle sizes on the splitting tensile strength of the samples. The effects of freezing temperature and different particle sizes on the splitting tensile strength of the samples were investigated, and the strain field evolution of the frozen soil-rock mixture during the Brazilian splitting experiments was further reproduced by digital imagine correlation (DIC). The experimental results show that the tensile strain is concentrated in the sample center with initial crack produced and the splitting damage pattern of the samples is curved and folded, and the larger the particle size is, the more curved the crack is; frozen soil-rock mixture goes through the linear elastic deformation stage when it breaks, and goes through the plastic-brittle damage stage with the increase of tensile stress and the decrease of freezing temperature; the splitting tensile strength has strong temperature sensitivity and increases approximately linearly with the decrease of freezing temperature; the size effect leads to the variability of sample strength, and the splitting tensile strengths are in the order of 5-10, 5-20, 10-15, and 15-20 mm particle size samples.

With the excavation of underground opening, the roof rock block may fall under external dynamic disturbance. In this paper, the roof rock mass was simplified as a rock block system composed of trapezoidal rock blocks. A series of experiments and numerical simulations were performed to study the sliding process of the key block under the horizontal static clamping load and vertical impact disturbance. The propagation of stress wave in the block system were captured and analyzed by using high-speed camera and digital image correlation technique. The results reveal that a pendulum-type wave was generated due to the propagation and superposition of stress waves in the block system. Therefore, the governing mechanism of the sliding displacement of the key block was clarified based on the propagation of incident stress waves or pendulum-type waves. Meanwhile, it is found that the sliding distance of the key block decreases in a power function with the increasing friction coefficient, or decreases in a parabolic function with the increasing trapezoid internal angle. Finally, a case study on the roof block sliding of the roadway at a gold mine was conducted, and it is concluded that the sliding of the key block resulted from the coupled effects of “shear driving” and “low friction” driven by stress wave propagation, regardless of a single or multi-layer rock block system. These results may provide technical guideline for preventing rock-falling accidents caused by blasting disturbances in underground mining.

This article presents an effective test method for evaluating the shear performance of repaired honeycomb sandwich panels consisting of glass fiber/epoxy matrix skin and Nomex honeycomb core. Addressing the insufficient research on the shear performance of honeycomb sandwich panels after repair in existing literature, this study conducted mechanical performance tests on the honeycomb sandwich panels before and after repair using the picture frame test method. Surface strain measurements are obtained using digital image correlation (DIC) techniques, and load–displacement and shear stress–strain curves are generated from the experimental results. The study concludes that the repair method utilized in this investigation is effective in restoring the mechanical properties of the sandwich panels. In addition, finite element models of the honeycomb sandwich panels before and after repair are established, and a comparative analysis is conducted between the experimental and simulation results. The study examines the shear modulus, ultimate load, and failure mode of the repaired and unrepaired specimens. The findings verify the feasibility of the picture frame test method for evaluating the shear performance of honeycomb sandwich panels. This study provides valuable insights into the design of shear performance repair for honeycomb sandwich panels and offers theoretical support for material recycling. [ABSTRACT FROM AUTHOR]

Copyright of Fly Ash Comprehensive Utilization is the property of Hebei Fly Ash Comprehensive Utilization Magazine Co., Ltd. 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.)

In order to study the influence of tunnel volume loss on adjacent framed buildings with different shallow foundations, this paper carried out physical model experiments with two common types of footings (isolated and strip footings) under different working conditions based on the digital image correlation (DIC) technique. The main finding of the present paper is that the increase in formation loss rate will aggravate the deformation and damage of the structure, and the strip foundation shows stronger integrity and stability compared with the isolated foundation in this process. With the increase in the eccentricity of the frames with respect to the tunnel, the overall tilt and damage degree of structural elements increases first and then decreases for both foundations, reaching the maximum value with the eccentric distance of one multiple of the tunnel diameter. Interestingly, when the isolated footings are located directly above the tunnel, the damage in the inner panels is the most severe and gradually decreases with eccentricity, changing from a sagging mode to a hogging mode for the frame form. While the strip footings always maintain slight hogging, and the trend of the damage degree of panels is similar to that of elements, with the eccentric distance reaching two times the tunnel diameter, the strip foundation structure tends to be stable, while the isolated one still needs attention for its potential possibility of damage in panels. The research results have reference value for the impact assessment of adjacent shallow-foundation framed buildings in subway tunnel construction. [ABSTRACT FROM AUTHOR]

Understanding the mechanical properties and failure process of cemented paste backfill with recycled rubber (RCPB) is the foundation of backfill design in underground mining. In this study, physical and mechanical tests were conducted on RCPB to obtain its mechanical property parameters, such as its uniaxial compressive strength (UCS), toughness, and peak strain. The influence of the rubber dosage on the mechanical properties of RCPB was also analyzed. In addition, the deformation behavior, fracture development, and failure process of RCPB with different rubber contents were observed using the digital image correlation (DIC) technique. The experimental results suggested that, although the UCS of RCPB is reduced as more rubber is added, its toughness and ability to absorb energy is increased. Moreover, the impact resistance of RCPB is improved by this increased toughness. With the increase in the rubber content, the deformation corresponding to the plastic yield stage of RCPB increased, which resulted in better ductility and improved impact resistance. The failure of the RCPB specimens mainly showed an "X" shape. The results of this study help us to better understand the mechanical behavior of RCPB after backfilling underground. [ABSTRACT FROM AUTHOR]

Copyright of Acta Materiae Compositae Sinica is the property of Acta Materiea Compositae Sinica 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.)

Digital Image Correlation (DIC) technique is used to collect the whole‐field strain of concrete subjected to bending loads under different temperature change cycles, cooling rates, and water‐binder ratio. The bending damage behavior of concrete under large‐difference temperature circulation is analyzed with the whole‐field strain cloud map and data. In addition, with the whole‐field strain obtained by 3D‐DIC technology, the strain‐based damage variable is defined. Furthermore, the damage degree of concrete specimen in the bending process is quantified, and the bending damage evolution process of concrete under the action of temperature circulation is discussed. The results show that the damage of concrete in areas with large temperature differences is related to the number of temperature change cycles as well as the cooling rate. Moreover, the increase in the number of temperature change cycles and the cooling rate will aggravate the bending damage of the concrete. Additionally, the higher the water‐binder ratio, the more serious the adverse effect of temperature circulation on the concrete. This paper provide certain reference for the evaluation of concrete bending deformation damage in areas with a large temperature difference. [ABSTRACT FROM AUTHOR]

To study the effect of freeze-thaw (FT) cycles on the fatigue performance of composite crumb rubber modified asphalt mixtures (CCRMA), a semicircular bending fatigue test based on the digital image correlation technique (DIC) was used to measure the fatigue life (N f) of CCRMA and SBS modified asphalt mixtures (SBSMA) and the horizontal strain (Exx) of the DIC deformation field under repeated loading. The variation laws of N f , Exx and the damage factor (D) defined based on Exx were analyzed under FT cycle conditions. In addition, considering the important influence of FT cycles on the N f and damage evolution characteristics of asphalt mixtures, based on the classical Chaboche damage evolution model, the influence of FT cycle was considered, a fatigue-freeze-thaw damage evolution model that reflects the effects of FT cycling variables and stress levels on asphalt mixtures was constructed. The results indicate that the Exx peak of asphalt mixture shifts forward with increasing FT cycle number. After 20 FT cycles, the N f of CCRMA decreased by 73.4 %, 62.1 %, and 75.1 %, while that of SBSMA decreased by 76.5 %, 58.6 %, and 74.6 % at stress ratios of 0.2, 0.3, and 0.4, respectively. The fatigue-freeze-thaw damage evolution model predictions were in agreement with experimental results, with the goodness of fit (R2) of all N f prediction models being greater than 0.9. With the exception of a few outliers, the relative error between the measured and predicted N f for the two asphalt mixtures was within 15 %. This indicates that the model can effectively predict the N f and damage evolution laws of asphalt mixtures at different stress levels after an arbitrary number of FT cycles. The related research results provide a theoretical basis for predicting the N f of new roads in cold regions under FT cycles. • The fatigue performances of CCRMA and SBSMA were compared. • The influence of freeze-thaw cycles on fatigue properties was quantitatively analyzed. • A fatigue-freeze-thaw damage evolution model was established. • Predicted data is in good agreement with experimental results. [ABSTRACT FROM AUTHOR]

• TPB beams with small span-depth ratios were tested to study the fracture behaviors of concrete. • The evaluations of the K R -curve, FPZ length and CTOD were studied. • The evaluations of horizontal strain fields along the FPZ were revealed by the DIC technique. • The effects of strain rates on the crack propagation were discussed. Three-point bending (TPB) beams with small span-depth ratios, i.e. TPB beams with the same span of 400 mm but various depths (100 mm, 150 mm and 200 mm), were tested to study the crack propagation behaviors of concrete. The evaluations of crack extension resistance curve (K R -curve), fracture process zone (FPZ) length, l FPZ , and crack tip opening displacement (CTOD) were studied. The digital image correlation (DIC) technique was utilized to monitor the entire loading process. Moreover, the effects of strain rates (10−5/s, 10−4/s, 10−3/s and 10−2/s) on the fracture process of TPB beams with small span-depth ratios (2, 2.5 and 3) were discussed based on findings in literature. The results shown that (1) with the increase of specimen depth from 100 mm to 200 mm, the obtained K R -curves and initial fracture toughness were not influenced by the small span-depth ratios, while different increase trends were observed for the unstable fracture toughness, the average maximum value of l FPZ and the value of CTOD. (2) With the loading rate increasing from 10−5/s to 10−2/s, the obtained K R -curve and the maximum length of FPZ increased slightly, while the evolution of CTOD was not affected by the loading rate. [ABSTRACT FROM AUTHOR]

In order to study the influence of tunnel volume loss on adjacent framed buildings with different shallow foundations, this paper carried out physical model experiments with two common types of footings (isolated and strip footings) under different working conditions based on the digital image correlation (DIC) technique. The main finding of the present paper is that the increase in formation loss rate will aggravate the deformation and damage of the structure, and the strip foundation shows stronger integrity and stability compared with the isolated foundation in this process. With the increase in the eccentricity of the frames with respect to the tunnel, the overall tilt and damage degree of structural elements increases first and then decreases for both foundations, reaching the maximum value with the eccentric distance of one multiple of the tunnel diameter. Interestingly, when the isolated footings are located directly above the tunnel, the damage in the inner panels is the most severe and gradually decreases with eccentricity, changing from a sagging mode to a hogging mode for the frame form. While the strip footings always maintain slight hogging, and the trend of the damage degree of panels is similar to that of elements, with the eccentric distance reaching two times the tunnel diameter, the strip foundation structure tends to be stable, while the isolated one still needs attention for its potential possibility of damage in panels. The research results have reference value for the impact assessment of adjacent shallow-foundation framed buildings in subway tunnel construction.

The aim of this work is to solve the methodological issues of the experimental study of the nucleation and propagation of deformation bands due to the Portevin-Le Chatelier effect under conditions of complex loading. It is of interest to determine the boundaries of unstable plastic deformation of the AMg6 alloy under complex loading conditions. A technique for controlling the loading process with a given rate of deformation intensity of materials has been worked out. Short stops of the loading process and unloading have an impact on the manifestation of the jerky flow. Stops and unloading reduce the strain level at which the diagram starts to manifest the effect Portevin-Le Chatelier. The experimental results show the evolution of inhomogeneous strain fields and local strain rates under conditions of manifestation of jerky flow during tension with torsion tests of Al-Mg alloy samples.

Understanding the mechanical properties and failure process of cemented paste backfill with recycled rubber (RCPB) is the foundation of backfill design in underground mining. In this study, physical and mechanical tests were conducted on RCPB to obtain its mechanical property parameters, such as its uniaxial compressive strength (UCS), toughness, and peak strain. The influence of the rubber dosage on the mechanical properties of RCPB was also analyzed. In addition, the deformation behavior, fracture development, and failure process of RCPB with different rubber contents were observed using the digital image correlation (DIC) technique. The experimental results suggested that, although the UCS of RCPB is reduced as more rubber is added, its toughness and ability to absorb energy is increased. Moreover, the impact resistance of RCPB is improved by this increased toughness. With the increase in the rubber content, the deformation corresponding to the plastic yield stage of RCPB increased, which resulted in better ductility and improved impact resistance. The failure of the RCPB specimens mainly showed an “X” shape. The results of this study help us to better understand the mechanical behavior of RCPB after backfilling underground.

According to the evidence of numerous advantages of earthen buildings, there is an increasing interest to study adobe elements for sustainable development. This paper presents experimental investigation alongside numerical simulation of several adobe elements under compression, direct tension, three-point bending and indirect shear tests to have a better understanding of their basic mechanical properties. Two different mix-design of clay adobes including plain and short tire fibers reinforced adobes with unique soil type, water content and compacting level are provided. The tire fibers are the waste production of tire factories which are hazardous to the green environment. Numerical simulations are conducted in ABAQUS software for further analysis. In this direction, the material constitutive model and the damage indices are defined based on the experimental stress-strain relations which are achieved during this study and the model of concrete damage plasticity was considered in the software. Furthermore, the experimental observations for direct tensile and indirect shear tests were documented by means of a Digital Image Correlation (DIC) technique from a 2-D DIC system. The effectiveness of the added short fibers on the mechanical properties of the reinforced adobe were thoroughly discussed. [ABSTRACT FROM AUTHOR]

The reinforced concrete structures with masonry infill walls are widely used to construct buildings in Algeria, as in many parts of the world. According to earthquake analysis, this type of construction can undergo serious damage under seismic load. The interaction between the infill wall and the surrounding reinforced concrete structure is considered a key parameter, which could trigger damage and even collapse in self-stable frame buildings. To study the behavior of this type of structures and the wall–frame interaction, four half-scale single-storey, single-bay reinforced concrete unfilled and unfilled frames were constructed and tested under in-plane lateral load. Furthermore, the experimental results were analyzed using the Digital Image Correlation (DIC) technique giving a detailed analysis of displacement and strain fields. The wall–frame interaction was evaluated in terms of displacement field evolution and interface slip in the contact contour. The masonry infill wall demonstrated a significant influence on the in-plane lateral response of this type of structure. The analysis of the results of the experiment are discussed in this paper.

The aim of this work is to solve the methodological issues of the experimental study of the nucleation and propagation of deformation bands due to the Portevin-Le Chatelier effect under conditions of complex loading. It is of interest to determine the boundaries of unstable plastic deformation of the AMg6 alloy under complex loading conditions. A technique for controlling the loading process with a given rate of deformation intensity of materials has been worked out. Short stops of the loading process and unloading have an impact on the manifestation of the jerky flow. Stops and unloading reduce the strain level at which the diagram starts to manifest the effect Portevin-Le Chatelier. The experimental results show the evolution of inhomogeneous strain fields and local strain rates under conditions of manifestation of jerky flow during tension with torsion tests of Al-Mg alloy samples. [ABSTRACT FROM AUTHOR]

The soil displacement field around a drill-expanded concrete pile is noticeably different from that of an equivalent section pile placed under axial load due to the mutual embedment between the expanded body and the soil. It is important to study the soil displacement field around drill-expanded concrete piles in order to understand the mechanisms of interaction between the pile and the soil. First, the model test of the half-face pile installed in undisturbed soil and the model test of the half-face pile installed in sand were used to study the soil displacement field around the pile. Then, the entire process of the soil displacement field's formation and development under the load was observed by using digital image correlation (DIC) techniques. Finally, numerical simulation was used to verify the results of the model tests. The results show that the displacement characteristics of the soil around the pile in the undisturbed soil and sand are basically the same. There is a clear soil compression zone under the expanded body, and the magnitude and density of the displaced soil in the compression zone are much higher than in other areas. Both the vertical displacement and the horizontal displacement gradually decrease as the distance from the expanded body and the burial depth increase. The horizontal displacement of the soil under the expanded body follows a trend of first moving toward the pile body and then moving away from it. The results of the numerical simulation are basically consistent with the results of the model test, indicating that the results of the model test are relatively reliable. [ABSTRACT FROM AUTHOR]

This paper investigates the performance of Digital Image Correction (DIC) technique in determining the initial fracture toughness of mild steel with different strain hardening effects. To achieve this goal, the results of DIC technique-based method are compared with those of the commonly used unloading compliance (UC) method. The comparison results reveal that the DIC technique-based method exhibit a good agreement with the UC method in determining initial fracture toughness, with a deviation of less than 3.0 %. Additionally, the DIC technique-based method demonstrates the consistency in determining the initial fracture toughness, independent of the ratio of initial pre-crack length to width. Furthermore, the importance of strain hardening effects on initial fracture toughness follows the order of strain hardening capacity, effective yield stress, and yield offset. The significance of this paper is that it provides a deep understanding of the performance of the DIC technique in determining the initial fracture toughness of mild steel. [ABSTRACT FROM AUTHOR]

A series of geometrically similar concrete beams of small, medium and large beam sizes has been tested under the action of monotonic and fatigue loading. Digital image correlation technique has been utilized to understand the fracture processes and crack growth behavior in concrete. The tip of effective crack in concrete beams under static and fatigue loading has been calculated through DIC analysis. Further, existence of size effect has been observed when the results of geometrically similar concrete beams were compared.

A need to timely reveal operational damages and technological defects requires a prompt control of states of structures made from composite materials and their consequent repairs aimed at service life extension. This work is devoted to the experimental study of inelastic deformation and fracture of specimens made from layer composite materials with prior introduced technological defects related to a possible inappropriate compacting and inappropriate bonding of material layers at a given restricted domain. The analysis is carried on the evolution of inhomogeneous deformation fields on the surface of carbon plastic specimens with an internal delamination-type defect under complex stress state. The method of active infrared thermography was used to identify the location and parameters of defects configurations. The obtained experimental data will be used for further tests related to sufficiency evaluation of signals received from the built-in sensors under complex loadings.

It is now more popular to use basalt fibers in the engineering programs to reinforce the crack resistance of asphalt mixtures. However, research concerning the impact of the basalt fiber diameter on the macro performance of AC-13 mixtures is very limited. Therefore, in this paper, basalt fibers with three diameters, including 7, 13 and 25 μm, were selected to research the influences of fiber diameter on the crack resistance of asphalt mixtures. Different types of crack tests, such as the low temperature trabecular bending test (LTTB), the indirect tensile asphalt cracking test (IDEAL-CT), and the semi-circular bend test (SCB), were conducted to reveal the crack resistance of AC-13 mixtures. The entire cracking process was recorded through the digital image correlation (DIC) technique, and the displacement cloud pictures, strain, average crack propagation rate (V) and fracture toughness (FT) indicators were used to evaluate the crack inhibition action of the fiber diameter on the mixture. The results showed that the incorporation of basalt fiber substantially improved the crack resistance, slowed down the increase of the displacement, and delayed the fracture time. Basalt fiber with a diameter of 7 μm presented the best enhancement capability on the crack resistance of the AC-13 mixture. The flexibility index (FI) of the SCB test showed a good correlation with V and FT values of DIC test results, respectively. These findings provide theoretical advice for the popularization and engineering application of basalt fibers in asphalt pavement.

This work mainly investigates the effects of the hole number and layer direction on the tensile mechanical behavior and failure mechanisms of multihole fiber metal laminates by experimental and numerical methods. With the aid of digital image correlation technique, tensile tests are implemented to obtain mechanical responses of different multihole fiber metal laminates. Subsequently, numerical simulation considering thermal residual stress is conducted to elucidate the failure modes and progressive damage evolution of multihole fiber metal laminates, which integrates the progressive damage model of composite laminates and a cohesive zone model between aluminum sheet/composite laminates. Finally, numerical predictions are found in a good agreement with experimental measurements, in terms of mechanical responses and fracture morphologies. Results demonstrate that the number of holes has negligible influence on the ultimate tensile strength, whereas affects the final failure strain of multihole fiber metal laminates evidently. With the increase of layer direction, the fracture morphology changes from evident brittle fracture to fiber pull-out and matrix damage, which indicates that the critical failure mechanism of multihole fiber metal laminates changes from tension dominated to tension–shear dominated. Additionally, the longer loading history from initial damage to final failure of composite laminates demonstrates the significance of considering progressive damage behavior in numerical simulation. [ABSTRACT FROM AUTHOR]

Copyright of Engineering Mechanics / Gongcheng Lixue is the property of Engineering Mechanics 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.)

• The biaxial mechanics property of laminated sandstone specimens with pre-cracked U-shaped grooves was studied. • The effects of lateral stresses and the inverted structure on the deformation and failure behavior of the floor were investigated. • The displacement, strain evolution and failure extent of the floor were analyzed based on the DIC technique. • The deformation and failure mechanism of tunnel floor were analyzed, and the key points of treatment are put forward. Floor heave at the bottom of a tunnel is a common defect during tunnel service. To study the deformation behavior and failure characteristics of the floor, laminated sandstone specimens with precracked U-shaped grooves were prepared, and a series of biaxial compression tests were carried out in the laboratory. Two typical floor structures of a tunnel (with and without inverts) and four lateral stress levels (σ 2 = 0, 5, 10 and 15 MPa) were considered. The effects of lateral stress and inverted structure on the deformation and failure characteristics of the floor were investigated. The displacement, strain evolution and failure extent of the floor were analyzed based on the digital image correlation (DIC) technique. The testing results show that the stress concentration at the U-shaped grooves of the specimens can be effectively reduced by the inverted structure. The specimen with an invert can bear more axial deformation and axial stress than that without an invert. The V-shaped notch failure behavior occurred near the tunnel sidewalls for the specimen without an invert, and it occurred in the middle of the tunnel floor for the specimen with an invert. The failure intensity of the V-shaped notch was positively related to the lateral stresses. With the increasing of axial stress, the heave displacement at the tunnel floor gradually increased, while the settlement displacement of the sidewall showed a trend of first increasing and then decreasing. The tensile strain concentration area of the floor undergoes a process of increasing and then decreasing and finally transforms to compressive strain. The failure characteristics of the sandstone specimen observed in the laboratory tests are consistent with the phenomena in real tunnel engineering. In addition, the deformation and failure mechanism of the tunnel floor was analyzed. The key points for the treatment of tunnel floor heave are put forward based on the testing results. [ABSTRACT FROM AUTHOR]

The soil displacement field around a drill-expanded concrete pile is noticeably different from that of an equivalent section pile placed under axial load due to the mutual embedment between the expanded body and the soil. It is important to study the soil displacement field around drill-expanded concrete piles in order to understand the mechanisms of interaction between the pile and the soil. First, the model test of the half-face pile installed in undisturbed soil and the model test of the half-face pile installed in sand were used to study the soil displacement field around the pile. Then, the entire process of the soil displacement field’s formation and development under the load was observed by using digital image correlation (DIC) techniques. Finally, numerical simulation was used to verify the results of the model tests. The results show that the displacement characteristics of the soil around the pile in the undisturbed soil and sand are basically the same. There is a clear soil compression zone under the expanded body, and the magnitude and density of the displaced soil in the compression zone are much higher than in other areas. Both the vertical displacement and the horizontal displacement gradually decrease as the distance from the expanded body and the burial depth increase. The horizontal displacement of the soil under the expanded body follows a trend of first moving toward the pile body and then moving away from it. The results of the numerical simulation are basically consistent with the results of the model test, indicating that the results of the model test are relatively reliable.

Highlights • The global tensile and creep properties of TA2 and its welded joint determined by use of extensometer and DIC technique separately are consistent with each other very well. • The local tensile and creep behaviours of TA2 welded joint including BM, HAZ and WM based on DIC technique can be measured with high precision. • The full-field creep strain of welded joint described by a partition method is proposed in present paper. Then, by the constitutive parameters related with creep stress and distance from the welding centerline, the creep strain at a certain time and position of welded joint can be obtained by modified power law constitutive model. Abstract The tensile properties and creep behaviours of a pure titanium (TA2) welded joint are discussed based on the digital image correlation technique. The mechanical properties of welded, heat-affected, and base metals were evaluated separately and demonstrated significant differences. The global creep constitutive models for a TA2 welded joint were determined considering the influence of stress and the threshold stress of local regions. Subsequently, the full-field creep strain of the welded joint is described using a partition method. A modified power law constitutive model for full-field creep, related to creep stress and distance from the welding centreline, is proposed to predict the creep strain with high precision at any local position. The tensile and creep tests prove that the global deformation and mechanical properties of the TA2 welded joint are significantly different from those of TA2 and the local region. To design welded components, the effects of the difference between local properties and global properties, as well as the global response of the welded joint, must be considered. [ABSTRACT FROM AUTHOR]

A series of geometrically similar concrete beams of small, medium and large beam sizes has been tested under the action of monotonic and fatigue loading. Digital image correlation technique has been utilized to understand the fracture processes and crack growth behavior in concrete. The tip of effective crack in concrete beams under static and fatigue loading has been calculated through DIC analysis. Further, existence of size effect has been observed when the results of geometrically similar concrete beams were compared. [ABSTRACT FROM AUTHOR]

The present work focuses on investigating the characteristics of the fracture process zone (FPZ) in concrete. The Single-edge notched (SEN) concrete beams under three-points bending are employed for conducting mode I fracture propagation. The displacement fields on the specimen surface and the internal AE signal of specimen are obtained simultaneously in real time by digital image correlation (DIC) and acoustic emission (AE) techniques. The experimental and analytical results indicated that the crack tip position, the crack extension length and the stress intensity factors (SIF) are obtained dynamically and quantitatively by DIC technique, and the length of FPZ is identified, respectively, by DIC and AE techniques in the crack extension process. The distribution of internal AE events is consistent with that of FPZ identified from surface deformation of specimens. [ABSTRACT FROM AUTHOR]

Abstract In this study, strain hardened cementitious composite is developed by systematically incorporating fibers of two different length scales, viz., PVA fibers (micro-fibers) and CNTs (nano-fibers) to improve the load transfer and crack formation mechanism at their corresponding scales. At first, the influence of individual fibers on the tension associated (axial tension-, fracture- and flexure-) properties is investigated. Then, the composite is developed using hybrid fibers with appropriate dosage to cater the desired performance. The tensile strength, stiffness, strain carrying capacity and fracture energy of the developed composite is found to be improved by almost 2 times, 3 times, 220 times and 130 times respectively to that of the original cement composite. The outstanding performance of the developed composite is resulted from the effective crack bridging and preferred load transfer in micro-scale due to incorporation of (a meagre amount of) hetero fibers of distinctly different length scales. In order to investigate the fracture and crack propagation phenomenon of the developed cementitious composite, Digital Image Correlation (DIC) technique is also employed. The findings of this study will lead towards development of multi-performance cementitious composite (MPCC) by tailoring the material to attain the desired level of strength, stiffness and ductility. [ABSTRACT FROM AUTHOR]

In this research, high strain rate response and energy absorption characteristics under dynamic compression loading of five different bio-composites were studied using a compression split Hopkinson pressure bar (SHPB) and DIC (digital image correlation) technique. This study is to map suitability of plant-based materials instead of petroleum-based plastic as a constituent raw material in composites. Bio-composites panels were made from Southern yellow pine (SYP), Corn starch (CS), and Methylene diphenyl diisocyanate (MDI) using a Dieffenbacher hot press. The ability of non-contact DIC analysis served as a valuable tool to measure the strains over a large range of deformation in wood-based bio-composites subjected to high strain rate compressive loading. Among all, Material 2 bio-composite with high manufacturing pressure had highest peak strength, shows that material behaviour at high strain rates is strongly dependent on the manufacturing pressure during fabrication. Presence of corn starch marginally increased the energy absorption capacity. [ABSTRACT FROM AUTHOR]

Abstract The demand for designing lightweight structures without any loss of strength or stiffness has conducted many engineers and researchers to seek for alternative joining methods. In this context, adhesive bonding may appear as an attractive joining method. However the interest of adhesive bonding remains while the structural integrity of the joint is ensured. According to recent literature the cohesive zone model (CZM) appears as a suitable approach able to predict both static and fatigue strength of adhesively bonded joints. This approach of the fracture process of adhesive layers is based on the modeling of the adhesive mechanical behavior through a set of adhesive cohesive properties in either mode I, mode II or mixed-mode I/II. The strength prediction of adhesively bonded joints is then highly dependent on the CZM parameters. The methods used to experimentally characterize them are thus essential. A new methodology, termed direct method, is presented and tested. It is based on the measurement of displacement field of bonded adherends at the crack tip of classical specimens allowing for the loading of the adhesive layer in pure mode I, pure mode II and mixed-mode I/II. The tested adhesive is a methacrylate–based two-component adhesive paste found under the reference SAF30 MIB manufactured by AEC Polymers (ARKEMA group). The adherends are in aluminium 6060. It is shown that it is possible to characterize the cohesive properties of the adhesive layer using the direct method. The numerical tests involve both adherends and adhesive nonlinearities. Nevertheless, the presented experimental implementation passes by the development of a dedicated data pre-processing to interpret the experimental measurements, highlighting the significance of the choice of the measurement means linked to the design of specimen. [ABSTRACT FROM AUTHOR]

A failure envelope that ignores the intermediate principal stress is typically adequate for the design of rock structures. To obtain the complete envelope, the rock cylinders should be tested using confined compression as well as confined extension tests. While confined compression tests are common, confined extension tests are rarely carried out. Current techniques available to test rocks under confined extension conditions require shaping the cylindrical specimens to a dog-bone geometry. The limited data available in the literature indicates that the results from these dog-boned shaped tests produces strengths that are considerably greater than the confined triaxial tests carried out on traditional cylindrical specimens. Whether this increased strength is real or simply an artifact of the stress path for triaxial confined extension tests (intermediate principal stress equal to the maximum principal stress) versus confined compression tests (intermediate principal stress equal to the minimum principal stress) is unknown. We propose here a new methodology to test rocks under confined extension condition with zero intermediate principal stress. We used the flattened Brazilian test and calculated the major and minor principal stresses from the strain on the surface of the specimens. To test the rock under increased confined conditions, we tested specimens with increasing depth of flattening. We derived equations to calculate the major and minor principal stresses in a flattened Brazilian specimen considering the bi-modularity in the stress-strain equations. We tested Lac du Bonnet granite specimens for major principal stress range 15-37% of its UCS and observed that the minor principal stresses remains in the range of Brazilian strength of the material (11.6 MPa). The results suggest that the nonlinear Hoek-Brown failure criterion based on only compressive triaxial results provides a reasonable estimate of the tensile strength. [ABSTRACT FROM AUTHOR]

Applying bamboo in construction is expected to reduce carbon footprint and promote environmental protection. Very limited information is available in the literature about the shear behavior of glued laminated bamboo (glubam, i.e., a type of engineered bamboo) beams. To this end, this paper presents an experimental investigation of shear behavior for full-scale glubam beams using three-point loading test. Fourteen specimens were tested, considering the effect of shear span-depth ratio (a / d) and beam depth on the shear response of glubam beams. Digital Image Correlation (DIC) technique was conducted to measure the strain fields on two specimens with different shear span-depth ratios. The test results show that the glubam beams with a / d = 1.0 occurred local compressive damage at the loading region and the mixed local compression-flexure damage; and beams with a / d = 2.0 exhibited flexure-dominated damage together with a minor local compressive settlement at the loading region. Specifically, increasing the shear span-depth ratio reduces the load capacity but improves the ductility and minimizes the global damage in the glubam beam. Larger shear area of the beam has a smaller shear stress, which demonstates the scale effect on the shear behavior of the glubam beam. DIC technique is feasible for monitoring the shear behavior of glubam beams with a small shear span-depth ratio. Meanwhile, this technique can also be employed for the beams with a relatively large shear span-depth ratio to monitor the shear behavior at a relatively small deformation. • Full-scale glubam beams were tested to investigate their shear behavior. • Failure mechanism of glubam beams influenced by shear span-depth ratio was investigated. • The scale effect on the shear behavior of the glubam beam was presented. • The shear strain field of glubam beams was measured using Digital Image Correlation technique. [ABSTRACT FROM AUTHOR]

• The fracture characteristics of salt rock after treatment coupled thermo-hydro-mechanical environment are studied. • The fracture surface characteristics of salt rock after treatment coupled thermo-hydro-mechanical environment coupling conditions are studied. • The fracture process zone of salt rock after treatment coupled thermo-hydro-mechanical environment are studied. It is crucial to observe the fracture characteristics and roughness of rocks subjected to thermo-hydro-mechanical (THM) coupling experiments. Previous studies have predominantly focused on investigating fracture characteristics in mode I, with comparatively less attention given to mode II fractures of rocks, especially following combined THM treatment. Therefore, this study focuses on utilizing salt rock as the primary subject, and the specimens are pretreated using a self-designed THM coupling triaxial tester. Subsequently, the three-point bending (SCB) test is conducted under ambient pressure conditions. At the peak load stage, the length of the fracture process zone is determined using the digital image correlation (DIC) technique. Additionally, macroscopic and microscopic fracture information on the fracture surface is recorded using 3D laser scanning and electron microscopy. Fracture roughness is evaluated using the apparent tilt function. The findings indicate that: 1) When subjected to various THM coupling conditions, the fracture toughness of salt rock in mode II exhibits a similar evolutionary pattern to that of mode I. However, its value experiences a rapid decrease once the temperature exceeds 500 °C. 2) With increasing temperature, the number of microcracks in salt rock and the degree of microdamage both escalate, leading to a progressive extension of the fracture process zone at the crack tip during the peak stage. 3) Gradually increasing temperature causes a progressive rise in the fracture roughness of salt rock. This is evident in the fact that the roughness along the crack propagation direction is less than that perpendicular to the crack propagation direction. The anisotropy of fracture roughness diminishes gradually. [ABSTRACT FROM AUTHOR]

The in-plane biaxial specimen can well reflect the complex stress state of sheet metal. However, there is no standard for small-sized specimens used in the low-power biaxial fatigue testing machine. The main goal of this paper is to apply the finite element method and orthogonal experiment method to design the cruciform specimen, considering the influence of three main parameters including the diameter of the central semispherical thinning area, the minimum thickness of the center and the arm thickness of the specimen. According to the central strain dispersion coefficient and the strain concentration coefficient proposed in this paper, we ensured that the distribution of strain in the gauge area is uniform and the strain it at its maximum value at the same time. The optimized specimen is verified by a biaxial fatigue test with the digital image correlation (DIC) technique. It is found that the fatigue crack appears in the center region, which proves that the optimized specimen can be effectively used for biaxial fatigue test.

A need to timely reveal operational damages and technological defects requires a prompt control of states of structures made from composite materials and their consequent repairs aimed at service life extension. This work is devoted to the experimental study of inelastic deformation and fracture of specimens made from layer composite materials with prior introduced technological defects related to a possible inappropriate compacting and inappropriate bonding of material layers at a given restricted domain. The analysis is carried on the evolution of inhomogeneous deformation fields on the surface of carbon plastic specimens with an internal “delamination-type” defect under complex stress state. The method of active infrared thermography was used to identify the location and parameters of defects configurations. The obtained experimental data will be used for further tests related to sufficiency evaluation of signals received from the built-in sensors under complex loadings.