Digital Image Correlation Technique Research Articles

Mechanical characteristics and damage model for rock-like specimen with two parallel grout-filled cracks

To investigate the mechanical properties of rock-like specimens with two parallel cracks filled with grout, uniaxial compression tests in combination with digital image correlation (DIC) and acoustic emission (AE) techniques have been performed on grout-filled cracked specimens with different rock bridge dip angles β. Results indicated that with the increase of β, the uniaxial compression strength, cumulated AE count, AE energy, as well as shear crack proportion initially decreases and subsequently increases. The overall AE b-value and the DIC-based maximum principal strain initially increases and subsequently decreases as β increases. The failure mode also varies from tensile to mixed tensile-shear mode. Furthermore, a particle flow code (PFC) model, which considers the grout filling, grout-rock interface, and rock, has been proposed. Numerical results showed that the range of microcracks inclination angle first decrease from 70°−100° to 70°–90° and then increases to 70°–110°. Besides, existence of grout filling and changes of bridge angle leads to significant difference in PFC particle displacement, which can cause the changed of crack initiation positions and failure modes. Finally, a damage model considering stress intensity factor for the grout-filled specimen was established. Both of pre-crack damage and loading damage were considered in this model, and a damage repair factor was proposed to describe effect of grout filling. The results showed that grouting could can effectively suppress stress concentration caused by pre-existing crack, thereby changes the strength of cracked specimen.

Experimental evaluation of geotextile in-filled sand cushioning system against rock fall impact using 2D digital image correlation technique

Rockfall on slopes always poses potential threat to the safety of people and infrastructures. Though, constructions of rockfall protection shelters were considered an appropriate solution, still there is a lack of understanding on rock mass-structure-sand cushion interaction which was mainly due to the impact and rebound characteristics of the detached falling rock mass. Considering rockfall induced impact response, geotextile in-filled sand bags have been developed in this study as a confined energy dissipation member against rock fall conditions. Using scaled down model structure, the performance of geotextile in-filled sand cushioning system against impact forces were evaluated and compared. Additionally, the study specially used 2D Digital Image Correlation technique for displacement, strain estimation and force calculation measurement on the structure and geotextile in-filled sandbags due to rock fall impact. The observations proved that, provision of geotextile in-filled sand bags over the structure showed 99% energy dissipation against impact load and can be an alternative to conventional sand cushioning layer with minimum additional load on the rock fall protection system. Also, 2D DIC monitoring found reliable in impact application studies for estimating force and displacement measurement.

Effect of Adhesive Layer Thickness on Strength of Carbon-Fiber-Reinforced Plastic/Aluminum Bond-Riveted Joints

This paper investigated the mechanical performance, progressive failure process, and failure modes of riveted joints, bonded joints, and hybrid joints with different adhesive layer thicknesses connecting carbon-fiber-reinforced plastic (CFRP) and aluminum alloy subjected to quasi-static tensile loading. The 2D digital image correlation technique was used to record the deformation and strain of the overlap area. The results show that the thickness of the adhesive layer had a negative effect on the mechanical properties of the hybrid joints, and when the thickness of the adhesive layer was increased from 0.2 to 0.8 mm, the peak load and the energy absorption (EA) values of the hybrid joints were reduced by 14.38 and 23.22%, respectively. Compared with the bonded and riveted joints, hybrid joints showed better performances in peak load and EA values, and rivets were able to continue carrying loads when the adhesive layer failed. The typical failure modes of the hybrid joints included CFRP compressive failure, adhesive failure, fiber-tear failure, and light-fiber-tear failure. It was further found that the adhesive could disperse the stress around the rivet holes and effectively reduce the stress concentration around the rivet holes.

Experimental study on dynamic deformation and breaking mechanism of high-temperature hard rock cutting by abrasive water jet

The development of deep geothermal resources encounters challenges related to high temperatures and hard reservoir rocks. Abrasive water jets (AWJ) offer a potential solution to enhance the efficiency of breaking high-temperature hard rocks in deep ground. This mainly originated from their combined characteristics of jet cooling impact and high-speed abrasive grinding. In order to investigate the dynamic deformation process and rock-breaking mechanism of high-temperature hard rocks cut by AWJ, laboratory tests were conducted on high-pressure abrasive water jets cutting granite, sandstone, and marble. Rock strains were monitored using dynamic strain gauges and the digital image correlation (DIC) technique. The results indicate that in the process of abrasive jet cutting high-temperature hard rock, the rock strain is divided into three stages: compression deformation, deformation release, and stable deformation. The strain response zone can be divided into strain concentration zone, strain transition zone, and strain weak response zone. The high strain region and heat exchange region of high-temperature hard rock during AWJ cutting process are almost consistent. Jet vaporization weakens the water cushion effect during the water hammer stage, leading to high strain concentration at the stagnation point of the jet. During the stagnation stage, the fluid weakens the binding of particles, the abrasive becomes more divergent, and the range of high strain response region expands. Unlike the dynamic strain generated by jet erosion of hard rock, when jet cutting rocks, the strain in the vertical jet direction is generally greater than that along the jet direction. The cutting effect increases with the increase of rock temperature. When the rock temperature is 300 °C, the cutting depth of sandstone, granite, and marble increases by 50 %, 120 %, and 180 %, respectively. Under the combined effects of high-frequency jet impact, high-speed abrasive grinding, and thermal stress, hard rock undergoes varying degrees of damage and failure.

Bonding characteristics between existing concrete substrate and high ductility geopolymer overlays under direct shear loading

High ductility geopolymer (HDG) looks promising as an exceptional repair material due to the faultless mechanical properties and environmental benefits. The interfacial bonding characteristics between existing normal concrete (NC) substrate and HDG overlay are the vital impact on the overall performance of repaired structures. This study presented the NC-HDG bonding behavior under the direct shear tests, and totally 45 specimens were designed with various concrete strength grades, interface roughness and elongations of HDG. To capture the fracture characteristics, the digital image correlation (DIC) technique was employed. Test results showed that the direct shear bonding strength (τu) had an increasing trend as the NC strength dropped or the interface roughness and elongations of HDG were increased, among the interface roughness affected the τu mostly, with the improvement amount of 185.07 %∼343.28 %. The direct shear strength ratio (defined as the ratio of τu to the inherent shear strength of NC) was ranged as 0.110∼0.489, i.e., at least half of shear strength of NC was lost during repairing. Based on the DIC measured results, the improvement of NC strength, interface roughness and elongations of HDG all delayed the interfacial crack initiation under direct shear loading. Moreover, the upper-bound limit analysis was adopted, a simplified method for predicting the direct shear bonding strength of NC-HDG interface was proposed and showed a sufficient precision.

Harvesting deformation modes for micromorphic homogenization from experiments on mechanical metamaterials

A micromorphic computational homogenization framework has recently been developed to deal with materials showing long-range correlated interactions, i.e. displaying patterning modes. Typical examples of such materials are elastomeric mechanical metamaterials, in which patterning emerges from local buckling of the underlying microstructure. Because pattern transformations significantly influence the resulting effective behaviour, it is vital to distinguish them from the overall deformation. To this end, the following kinematic decomposition into three parts was introduced in the micromorphic scheme: (i) a smooth mean displacement field, corresponding to the slowly varying deformation at the macro-scale, (ii) a long-range correlated fluctuation field, related to the buckling pattern at the meso-scale, and (iii) the remaining uncorrelated local microfluctuation field at the micro-scale. The micromorphic framework has proven to be capable of predicting relevant mechanical behaviour, including size effects and spatial as well as temporal mixing of patterns in elastomeric metamaterials, making it a powerful tool to design metamaterials for engineering applications. The long-range correlated fluctuation fields need to be, however, provided a priori as input parameters. The main goal of this study is experimental identification of the decomposed kinematics in cellular metamaterials based on the three-part ansatz. To this end, a full-field micromorphic Integrated Digital Image Correlation (IDIC) technique has been developed. The methodology is formulated for finite-size cellular elastomeric metamaterial specimens deformed in (i) virtually generated images and (ii) experimental images attained during in-situ compression of specimens with millimetre sized microstructure using optical microscopy. The proposed IDIC method identifies the different kinematic fields, both before and after the microstructural buckling, and without any prior knowledge determines correctly the relevant patterning modes required by the homogenization scheme. It is further argued that patterning modes are independent of the unit cell size, the hole diameter to cell size ratio, as well as local material properties, allowing for modelling and design of (finite- and infinite-size) metamaterials and specimens with graded microstructures in terms of geometry and/or material properties. It is shown that the proposed methodology is also applicable to cellular metamaterials and structures with different microstructural designs.

Failure Analysis and Piezo-resistance Response of Intralaminar Glass/Carbon Hybrid Composites Under Blast Loading Conditions

Abstract In this study, damage mechanisms and the piezo-resistance response of glass/carbon intralaminar hybrid composites are examined under blast loading conditions. Two-ply orientations are considered, namely a repeating ((G45C45)R) and an alternating ((G45C45)A) +/− 45° glass/carbon layers, along with three boundary condition configurations: simply supported, partially fixed, and fully fixed are applied. A shock tube apparatus and the three-dimensional digital image correlation technique are utilized to investigate the interaction of shock waves with the composites and gather a comprehensive deformation field during the loading. A modified four-probe resistivity measurement method is implemented to comprehend the piezo-resistance response associated with damage evolution. The results underscore the substantial influence of boundary conditions on the blast mitigation capacity of the composites. Analysis following the experiments reveals that the damage to the specimens primarily involves the fracture of fibers accompanied by internal delamination. Thermal imaging of the tested composite specimens provides enhanced insight into the precise occurrences of internal fiber breakage and delamination. Composites of (G45C45)A type demonstrate an increased energy dissipation ranging from 18% to 33% compared to (G45C45)R composites, depending on the specific boundary conditions among the three types considered. Furthermore, the findings indicated a strong correlation between changes in piezo-resistance and the fracture of carbon fibers, coupled with the sustained deformation of the composites. Notably, (G45C45)A composites exhibited 100% ∼ 300% higher change in piezo-resistance compared to (G45C45)R composites, indicative of the superior damage-sensing capabilities of the former.

Flexural properties and evaluation of Al‐CFRP self‐pierce riveted laminates under three‐point bending loads

AbstractThis study aims to investigate the bending performance and evaluation of aluminum‐carbon fiber reinforced plastic (Al‐CFRP) riveted laminates under varying parameters via self‐pierce riveting and three‐point bending tests. Through the self‐pierce riveting process test, a riveted joint meeting standard requirement was obtained. Based on this joint combination form, Al‐CFRP self‐pierce riveted laminates were prepared. The bending performance test showed the riveted laminate with a span of 80 mm had the greatest bending resistance at a thickness of 2 mm, and the overall strain of the Al‐CFRP self‐pierce riveted laminates was observed by digital image correlation (DIC) technology. Subsequently, validated numerical simulation modeling was conducted by correlating with the test results. On this numerical simulation model basis, further parametric studies and bending performance evaluations (including number of rivets, CFRP lay‐up angle, and laminates width) of the Al‐CFRP self‐pierce riveted laminates were systematically carried out. It was found that the peak load F and bending strength R improved by 1.32% and 26.66%, respectively, while the mass M reduced by 8.99%, for the design variables of var1 of 20 mm, var2 of 6, and var3 of [0/90°]2s.Highlight An Al‐CFRP riveted laminate structure is proposed to improve the bending properties of riveted laminates by changing the rivet parameters and laminate parameters. The bending properties of riveted laminates with different spans were investigated under three‐point bending loading conditions. The DIC technique observed the changes in the strain field of riveted laminates during bending. The effects of different structural parameters on the bending performance of Al‐CFRP riveted laminates were investigated by numerical simulation. An evaluation method combining the gray correlation degree and the combination assignment method is proposed to obtain the optimum riveted laminate structure under bending load conditions.

Research on the application of DIC technology in model tests of hydraulic structures

Digital image correlation (DIC) is a noncontact measurement technique that can visualize and measure a model body in an entire field without interference. This study performed the structural model test of a cemented sand and gravel (CSG) dam. The scale-free DIC technology was applied to the model test to monitor the CSG model dam during overload damage. The study results demonstrated the following results:1) The CSG dam experienced sliding shear failure along the dam foundation with an overload coefficient of 5.2 during failure. 2) The use of DIC technology for measurement could reflect the generation and development of the damage process of the model dam. 3) The DIC technique used in this test achieved an observation accuracy of 2 mm for displacement and 530 με for strain. 4) The conclusions of the measurement results of the DIC technique and the traditional method are identical. The DIC technique has considerable application potential in the model tests of hydro-structures. This study provides a new measurement method for hydraulic structure model tests and supports the development of an intelligent monitoring platform for subsequent hydraulic structure model tests.

A New Method for Determining Necking of Sheet Metal Based on Main Strain Topography

There are various methods to evaluate the forming limit of a sheet, and these criteria can be classified as position-dependent, time-dependent, and position-time dependent according to the basis of judgment. However, these criteria have a single function and can only find the forming limit of the sheet and cannot determine the strain distribution, strain change, or fracture location during the sheet forming process. This paper introduces a time–location-dependent method, i.e., the spatial strain rate method, which is used to detect the onset of necking of a sheet. The spatial strain rate is directly based on the strain and can not only find the forming limit of the sheet but also depict the strain distribution and strain variation during the two phases of the experimental process—distributed instability and concentrated instability—as well as predict the location of sheet fracture. The spatial strain rate of AA5083 aluminum alloy of different widths was analyzed and verified in detail via Nakazima experiments using digital image correlation techniques and compared with the guidelines published in the literature in recent years.

High-Temperature DIC Deformation Measurement under High-Intensity Blackbody Radiation

During the high-speed flight of a vehicle in the atmosphere, surface friction with the air generates aerodynamic heating. The aerodynamic heating phenomenon can create extremely high temperatures near the surface. These high temperatures impact material properties and the structure of the aircraft, so thermal deformation measurement is essential in aerospace engineering. This paper revisits high-temperature deformation measurement using the digital image correlation (DIC) technique under high-intensity blackbody radiation with a precise speckle pattern fabrication and a heat haze reduction method. The effects of the speckle pattern on the DIC measurement have been thoroughly studied at room temperature, but high-temperature measurement studies have not reported such effects so far. We found that the commonly used methods to reduce the heat haze effect could produce incorrect results. Hence, we propose a new method to mitigate heat haze effects. An infrared radiation heater was employed to make an experimental setup that could heat a specimen up to 950 °C. First, we mitigated image saturation using a short-wavelength bandpass filter with blue light illumination, a standard procedure for high-temperature DIC deformation measurement. Second, we studied how to determine the proper size of the speckle pattern in a high-temperature environment. Third, we devised a reduction method for the heat haze effect. As proof of the effectiveness of our developed experimental method, we successfully measured the deformation of stainless steel 304 specimens from 25 °C to 800 °C. The results confirmed that this method can be applied to the research and development of thermal protection systems in the aerospace field.

The optimal design of double-edge wedge-splitting tensile test for ultra high performance concrete

The double-edge wedge-splitting (DEWS) test is a new indirectly tensile test, those of stress distribution similar with the uniaxial tension state. However, there are no standard rules regarding the splitting specimen and groove dimensions suitable for the UHPC tensile properties. In this paper, DEWS test, conventional splitting test, and direct tensile test were performed to measure the tensile strength and tensile stress vs. crack opening response of UHPC. The digital image correlation (DIC) technique was utilized to detect the crack propagation paths and fracture modes. Two specimen shapes, three groove angles and three fiber types are utilized to this investigation. The experimental results of 18 DEWSs under tensile loading, including peak strength, tensile stress-COD curves, fracture modes and properties, and the crack paths, are presented. The results show that the UHPC tensile performance used with cubic specimen is less sensitive to groove angle than in the cylinder. An important finding is that DEWS test used with 45° grooved cube specimen presents the lowest variation in peak strength and stress-COD curve for UHPC tensile behaviors. After comparison, the tensile strengths using DEWS test and direct tension test are essential equal in first-cracking and peak strength. The crack paths and fracture mode are basically the same inside the DEWS and direct tension specimens. Accordingly, the DEWS test used with 45° grooved cubic specimen is suggested for measuring the UHPC tensile property.

Analysis of Fault Influence on Geostress Perturbation Based on Fault Model Test

The distribution of the geostress field in reservoirs holds significant implications for the precise exploration and efficient development and utilization of oil and gas resources, especially in deep strata regions where faults are prevalent. Geological structural movements in these deep strata regions exacerbate the complexity of geostress field distributions. To elucidate the perturbation of the geostress field in deep reservoirs caused by faults, this study initially conducted a series of physical model tests on single fault dislocation, employing digital image correlation techniques to capture the displacement fields of various types of fault dislocations. Subsequently, a numerical model of the fault interface element was established, and fault element parameters were determined through sensitivity analysis and trial calculation. This study further analyzed the perturbation of the geostress field using this numerical model. Finally, a multi-fault numerical simulation model was constructed to clarify the perturbations in the regional geostress field under the influence of multiple faults. The results indicate that the geostress perturbation range under the action of multiple faults spans from 183.06 to 310.06 m.

Investigation on uncoordinated deformation and failure mechanism and damage modeling of rock mass with weak interlayer zone

The weak interlayer zone (WIZ) is a high-risk geotechnical system with poor mechanical properties, strong ductility, loose structure, and wide distribution. To comprehensively investigate the uncoordinated deformation characteristics and failure mechanism of rock mass with WIZ, a series of uniaxial loading tests using digital image correlation (DIC) technique, and numerical simulation tests were carried out. Besides, the damage constitutive model of rock mass with WIZ was established, then the damage evolution law was also analyzed. Results show that a high strain localized zone appears in the WIZ from the beginning of loading, which then develops towards the contact surface between the WIZ and the rock mass. As loading proceeds, the WIZ exhibits layered spalling and ultimately forms through-cracks after the initiation of micro-cracks, and vertical tensile cracks to appear in the rock. causing vertical tensile cracks to appear in the rock. With the increase of the WIZ thickness and dip angle, the uniaxial compressive strength and deformation modulus of specimen show a negative exponential decay. When rock mass with WIZ collapse, the bonding of WIZ particles fails and the number of tensile-shear cracks gradually increases, eventually resulting in the plastic squeezing-out of WIZ. Moreover, the particles of the rock masses with smaller WIZ dip angles are mainly displaced vertically, and the failure is mainly caused by tensile splitting. The significant lateral displacement of particles in the rock mass with larger WIZ dip angles leads to the destruction of the rock mass mainly through shear slip, in particular a pronounced sliding down along the WIZ. Furthermore, the damage constitutive model of the rock mass with WIZ was established by distinguishing the total damage of the rock mass with WIZ into the damage of the WIZ and the damage of the rock mass. The model prediction results show that the total damage D increases with the increase of WIZ thickness and dip angle, and develops faster in the early stage and slower in the later stage. The research can provide effective basis and feasible ideas for the uncoordinated deformation and failure evolution, macro–micro failure mechanism, as well as the constitutive model of rock mass with WIZ in underground cavern under high geostress.

Optimizing toughness and cost-effectiveness in one-part geopolymers via fiber reinforcement: A comprehensive investigation of PVA, PE, and glass fibers

This study explores developing and characterizing a one-part geopolymer, an innovative and sustainable construction material. The effects of incorporating polyvinyl alcohol (PVA), polyethylene (PE), and glass fibers (GF) on the toughness of slag and fly ash-based one-part geopolymer mortars were investigated through compressive, three-point flexural, and four-point bending tests. The findings demonstrate that fiber incorporation reduces fluidity and compressive strength due to increased porosity, lower elastic modulus of fibers, and weak interfacial bonding. However, fibers significantly enhance damage resistance and toughness via crack bridging and load transfer mechanisms. Formulations with 2 % PVA fibers and combinations of 1 % PVA with 1 % PE fibers and 1 % PVA mixed with 0.5 % PE and 0.5 % GF demonstrate excellent toughness. Notably, the latter two fiber blends achieve 14 % and 10 % cost reductions, respectively, compared to using only PVA fibers, making them economically viable for large-scale applications. Scanning electron microscopy and X-ray diffraction provided insights into the toughening mechanisms, including crack bridging, fiber pull-out, and enhanced stress distribution within the geopolymer matrix. Digital image correlation techniques further elucidated the fibers' role in improving the post-cracking behavior and structural resilience under load.

Optimal interply angle of bio-inspired composite curved panels with helicoidal fiber architecture

The exoskeleton structure of mantis shrimp’s dactyl clubs presents an extraordinary helicoidal reinforcement pattern, holding immense potential for revolutionizing fiber-reinforced composite materials. While extensive investigations have shed light on its unique advantages, the inherent nature of curved Bouligand structures remains incompletely comprehended. To elucidate these unexplored characteristics, the present study introduces a novel analytical model to efficiently calculate the interlaminar shear and normal stresses in helicoidal laminated curved beams under transverse loading. The analytical model systematically determines the optimal uniform fiber interply (pitch) angle for these bio-inspired structures with an arbitrary number of layers. The computational analysis revealed that achieving minimum interlaminar stresses always requires the precise orientation of π or 2π helicoids along the laminate thickness when the number of layers exceeds two. This theoretical discovery is remarkably identical to the study of stacked chitin fibrils in arthropod clubs reported in the literature. For a 37-ply composite, the flat and shallow-curved beam configurations primarily resulted in a 5° optimal pitch angle, while the deep-curved configuration yielded a 10° optimal angle. To validate the model, three-point bending testing were performed. Four fiber pitch angles were thoroughly examined, including the optimal and quad angles. The digital image correlation (DIC) technique was employed to analyze the structural responses and detect the onset of delamination. The numerical and experimental results demonstrated good consistency, exhibiting significant enhancement in the delamination resistance of up to 30 percent with the optimal angle.

Local strain heterogeneity and damage mechanisms in zirconia particle-reinforced TRIP steel MMCs: in situ tensile testing with digital image processing

In this work, the microstructural deformation and damage mechanisms of TRIP steel metal matrix composites (MMCs) reinforced with Magnesia Partially Stabilized Zirconia (Mg-PSZ) particles are investigated by employing in situ tensile testing within a scanning electron microscope chamber, complemented by digital image correlation and advanced image processing techniques. The study is carried out on samples with varied volume fractions (0%, 10%, and 20%) of zirconia particles and damage mechanisms in different samples under specified loading conditions. Through both qualitative and quantitative assessments of deformation, damage, and clustering, the investigation provides a comprehensive understanding of the distribution and damage initiation. The study findings reveal that, generally, the steel matrix exhibits high toughness, with minimal occurrences of microcracking at high strains that cause significant damage. In samples with increasing particle content, delamination at the matrix–particle interface and cracking of Mg-PSZ particles were found to be critical contributors to material failure and were quantitatively analyzed using computational analyses conducted with MATLAB. The work highlights the initiation and evolution of each damage mechanism in zirconia particle-reinforced TRIP steel MMCs to facilitate scientists and engineers in improving manufacturing and application decisions in industries such as automotive, aerospace, and heavy machinery, which demand materials with exceptional toughness and durability.Graphical

Influence of the CO2–brine–rock interaction on the plastic zone of sandstone

During the long-term CO2 storage process, the CO2–brine–rock interaction (CBRI) may change the elastic-plastic behaviors of sandstone reservoirs, potentially leading to rock damage and CO2 leakage. A good understanding of the influence of the CBRI on the plastic zone of sandstone is crucial for evaluating the rock fracturing processes. In this paper, three-point bending tests were conducted under both monotonic and cyclic loading conditions, and the digital image correlation technique was used to analyze the elastic and plastic characteristics of the samples. The experimental results showed that the CBRI decreases the yield strength and corresponding crack mouth opening displacement by 25 % and 65%, respectively, thus increasing the probability of fracturing. Additionally, it was found that the CBRI enlarges the plastic zone by about 20 %. The size of the theoretical plastic zone in the sandstone sample for different loads was determined, and the ratio of the plastic zone size in the samples with CO2–brine saturation to that without CO2–brine saturation was found to be about 1.18. Finally, the mesoscale factors affecting the plastic zone size after CO2–brine saturation were analyzed. This study helps to understand the effect of the elastic-plastic behavior of sandstone on reservoir stability during long-term CO2 storage.

Shear Performance and Damage Characterization of Prefabricated Basalt Fiber Reactive Powder Concrete Capping Beam Formwork Structure

Basalt Fiber Reactive Powder Concrete (BFRPC) semi-prefabricated composite capping beam structures can effectively improve the shortcomings of ordinary concrete capping beams' construction difficulties and insufficient bearing capacity. In this study, with the objective of analyzing the shear damage and damage characteristics of a prefabricated BFRPC capping beam formwork, structural damage tests under different levels of loading were carried out to obtain the mechanical parameters of key nodes. Acoustic emission (AE) and Digital Image Correlation (DIC) techniques were used to acoustically and visually characterize the formwork damage. The research results showed that the damage stage of the capping beam formwork was divided, and an early damage warning method was proposed based on the acoustic parameters. Using the DIC technique to identify the crack width evolution pattern during the shear process, it was found that the cracks expanded steadily as the load increased. Combining the experimental and simulation results as well as the Subdivision Superposition Theory, a half-open stirrup strength discount factor β was introduced and suggested to take a value of 0.79. The formula for calculating the shear capacity of BFRPC capping beam formwork is proposed to provide a theoretical basis for its application in prefabricated assembled structures.

A rate-dependent damage mechanics model for predicting plasticity and ductile fracture behavior of sheet metals at high strain rates

Uniaxial tensile tests were performed on H340 steel sheets at different strain rates (10-4 to 103s-1) and temperatures (–30 °C and 280 °C). Oscillation-free forces were measured during high-speed tests at strain rates of up to 1000 s-1 using specimens with different stress states. Material hardening curve, strain rate sensitivity, temperature effects, and Taylor-Quinney coefficient for adiabatic temperature calculations were determined in experiments. Digital image correlation (DIC) technique was employed to measure displacement, deformation, and local strain fields. Meanwhile, the temperature fields of specimen gauge section were measured with a high–speed thermal camera in the uniaxial tensile tests at various strain rates. Damage and fracture-related parameters were calibrated and validated using porosity measurements on SEM micrographs and in combination with finite element (FE) simulations. A rate– and temperature–dependent plasticity and damage mechanics model (e2MBW) was proposed and calibrated to predict the plasticity and fracture behavior of H340 under different loading speeds. The study demonstrated good agreement in the overall experimental and simulated force–displacement responses and local strain evolution across all fracture specimens at loading speeds from 0.005 mm/s to 10000 mm/s.