Crack Distribution Research Articles

Research on crack distribution characteristics and control technology of surrounding rock in soft rock roadway under different lateral pressure coefficients

AbstractTo solve the problem of controlling large deformation of surrounding rock in deep soft rock roadway, the distribution characteristics and deformation mechanism of surrounding rock cracks in soft rock roadway under different lateral pressure coefficients are studied using numerical simulation, theoretical analysis, and field measurement. The results show that under different lateral pressure coefficients, the range of surrounding rock cracks shows three forms: round, oval, and butterfly. No matter what lateral pressure coefficient the roadway is in, the surrounding rock cracks always appear in the plastic zone, and there is a high correlation between the surrounding rock crack range and the plastic zone. The stress characteristics of the surrounding rock in the plastic zone include two main aspects. One is that the direction of the principal stress of the surrounding rock is deflected, which is manifested as an annular distribution of the direction of the maximum principal stress around the roadway. The direction of the minimum principal stress in the upper part of the roadway points to the center of the roadway, and the direction of the minimum principal stress in the lower part of the roadway deviates from the center of the roadway. Second, the ratio of the maximum to minimum principal stress in the surrounding rock is large. Under this stress characteristic, the surrounding rock in the plastic zone has strong shear dilation. The shear dilation makes the crack of the surrounding rock open so that the surrounding rock is squeezed into the roadway space, and then the roadway produces large deformation. Due to the large range of cracks in the butterfly‐shaped plastic zone, the shear dilation deformation produced by the butterfly‐shaped plastic zone is far more than that of the round/oval plastic zone. According to the crack range of roadway surrounding rock under different lateral pressure coefficients, the corresponding support scheme is put forward. Field experiments show that the support scheme can effectively control the deformation of surrounding rock and meet the requirements of roadway use.

Damage and fracture characteristics of thermal-treated granite subjected to ultra-high pressure jet

The water jet rock breaking technology has broad application prospects in geoenergy development engineering. However, the influence of reservoir temperature on the rock breaking effect is still unclear during the jet rock breaking process. To explore the mechanism of temperature on rock breaking by high-pressure water jets, experiments on the erosion of high-temperature granite by ultra-high pressure pure water jets (UHP-PWJ) and ultra-high pressure abrasive water jet (UHP-AWJ) were conducted at five rock temperatures: 25 °C, 100 °C, 200 °C, 300 °C, and 400 °C. Through three-dimensional reconstruction and microscopic observation techniques, the macroscopic and microscopic characteristics of rock fragmentation were analyzed, ultimately revealing the dynamic damage and rock breaking mechanisms of ultra-high pressure water jet. The results indicated that rock temperature influences result in different fragmentation characteristics under the action of two types of jets, with UHP-PWJ demonstrating significantly superior rock-breaking effects on high-temperature granite compared to UHP-AWJ. As granite temperature increases from 25 °C to 400 °C, the damage depth range for the UHP-PWJ is 30–75 times the nozzle diameter, while for the UHP-AWJ, it is only 30–40 times the nozzle diameter. For UHP-PWJ, the rock breaking mechanism is mainly driven by thermal stress, supplemented by high-speed jet impact. The significant increase in rock temperature significantly enhances its rock breaking effect, with erosion pits appearing in a spindle shape and more complex crack distribution around the pores. Compared with 25 °C granite, the damage caused by 400 °C granite jet impact increased by 6.8 times and the surface area of cracks increased by 6.5 times. For UHP-AWJ, high temperature hard rock fragmentation still relies mainly on jet impact and abrasive grinding. The thermal stress caused by rock temperature has a relatively small impact on its rock breaking effect, and the D value of the internal damage degree of granite at different temperatures is less than 0.005. The erosion pits are conical in shape, and no macroscopic cracks caused by jet impact and thermal cracking can be clearly observed around the pit. The research results can provide a theoretical basis for optimizing the parameters of high-pressure jet development technology for deep geoenergy.

Evaluation method of tunnel cracking disease under biased pressure based on enhanced image fractal features

This paper focuses on the tunnel cracking disease under biased pressure. Through model tests on three lining conditions, the study investigates the expansion process of surface cracks on the lining under biased pressure. Proposing an improved method for calculating fractal characteristics of lining crack disease based on box counting dimension. Quantifying crack disease through digital image processing to obtain two parameters: total width and fractal dimension. Discussed the relationship between quantification parameters of surface crack disease in linings and the service performance of the lining. 29 groups of crack disease quantization parameters obtained by model test were selected to establish the disease sample space, and the spatial data were automatically learned and grouped based on clustering method. Finally, a new diagnostic Index of Tunnel Lining Defect Index-Crack & Dimension (TLDI-C&D) and its disease classification criteria for the whole lining ring are proposed. The results indicate that under the biased pressure, regardless of the presence of pre-existing defects, the biased pressure region is the most severely diseased area in terms of cracking. Compared to the intact lining, the initial cracking loads for arch crown defects and arch waist defects are advanced by 33.1 % and 73.0 %, respectively. After the apparent cracks in the lining are fully formed, pre-existing defects no longer affect the speed and distribution of crack propagation.The larger the fractal dimension, the more complex the morphology of the corresponding crack disease. Under the same image area, the ratio of crack quantity to width has a greater impact on the fractal dimension. There is a corresponding relationship between quantification parameters of crack disease and the bearing performance of the lining structure, making them indicators for measuring the load-bearing capacity of the lining. The most reasonable grading level for lining crack disease under the biased pressure is four levels. The diagnostic index for tunnel lining cracks, TLDI-C&D is 1.0～2.2 (level I), 2.2～3.2 (level II), 3.2～4.3 (level III), and 4.3～5.5 (level IV). On-site measurements have proven the accuracy of this crack disease diagnostic evaluation method.

Analysis of Water Seepage Mechanism and Study on Mechanical Properties of Highway Tunnel Based on Fluid-Structure Coupling

Shaoguan was hit by a extremely heavy rainstorm, and the mountain water catchment of Dabaoshan Tunnel in the southern section of Beijing Hong Kong Macao Expressway in Guangdong increased sharply. Due to the rapid rise of groundwater level, water and mud gushed at ZK141+227 of Dabaoshan, and serious water seepage occurred in other areas, bringing soil into the tunnel, which seriously hindered the safe passage of the tunnel. According to the on-site investigation of water and mud gushing, it was found that there were branches sandwiched in the mud gushing out, and at the same time, it was found that there was water leakage at the foot of some walls where drainage holes were added. Based on the fluid structure coupling mechanism, the seepage mechanism of highway tunnels was deeply explored, and the mechanical properties of tunnels under seepage were analyzed through experimental data and numerical simulation. The experimental results show that under the action of seepage, the stress distribution of the tunnel lining changes, and the phenomenon of local stress concentration is obvious. When the seepage pressure reaches 3.5 MPa, cracks appear in the tunnel lining, with a total of 5 cracks. The distribution of cracks is closely related to the seepage field. The numerical simulation further reveals the interaction mechanism between the seepage field and the tunnel structure, confirming the influence of the seepage field on the stability of the tunnel lining. When the seepage pressure increases to 4.0 MPa, the displacement change rate of the tunnel lining reaches 0.3 mm/m, and the maximum lining stress is 15.7 MPa. The purpose of this study is to propose a maintenance plan for highway tunnels to improve their safety. Consider the impact of seepage on tunnel structure and adopt effective waterproofing and drainage design. Further research on the seepage mechanism and tunnel mechanical properties is recommended to provide more reliable theoretical support for engineering applications.

Study on the mechanical properties of recycled brick coarse aggregate concrete based on finite element modeling

In recent years, the use of recycled materials in concrete production has garnered significant attention due to their environmental and economic benefits. To promote the application of recycled aggregates, this study focuses on investigating the utilization of Recycled Brick Coarse Aggregate (RBCA) as a substitute for natural aggregate. This paper presents the development of stochastic convex polygonal RBCA through the utilization of a custom-programmed algorithm and proposes a finite element model designed to simulate the behavior of RBCA concrete under compression and splitting tensile. Numerical simulations were conducted to investigate the effects of brick aggregate Replacement Rate (RR) and porosity on the compressive and splitting tensile properties of RBCA concrete. A strong correlation was found between the Concrete Damage Plasticity (CDP) model developed in this study and experimental results, indicating high reliability. The results indicate that the replacement rate of brick aggregates has a more significant impact on the compressive strength than on the splitting tensile strength of concrete. Furthermore, the distribution of coarse aggregates and pores has a minor influence on the mechanical properties and ultimate failure mode of RBCA concrete but significantly affects the crack distribution pattern. The sequence of damage initiation in RBCA concrete was found to be: pores, old Interfacial Transition Zone (ITZ), old mortar, new ITZ, new mortar, RBCA, and Natural Coarse Aggregate (NCA). These findings contribute to a comprehensive understanding of RBCA's performance and offer valuable insights for optimizing its behavior.

Experimental study on the flexural behaviors of ECC-reinforced masonry beams with GFRP mesh

This study aims to investigate the flexural behaviors of ECC-reinforced masonry beams with GFRP mesh under various interface treatment methods. Eleven sets of ECC-reinforced masonry beams with GFRP mesh were fabricated and subjected to a four-point bending test. The effects of the fibre volume fraction and thickness of ECC, interface treatment methods, GFRP mesh strength and layers on the flexural behavior of masonry beams were investigated and analyzed, including the failure mode, crack distribution, flexural strength, and load-deflection curves. The test results revealed that a transition in the failure mode of masonry beams from brittle failure to interfacial stripping failure or ductile failure after reinforcement. Increasing the number of GFRP mesh layers, the fibre volume fraction and thickness of ECC improved the flexural performance of the masonry beams, while increasing the GFRP mesh strength had the opposite effect. Among the variables, the interface treatment method exerted the greatest influence on the flexural performance of the masonry beams. The masonry beams treated with a bolt interface exhibited the best flexural performance, with flexural toughness and ultimate deflection increasing by 1.69 times and 0.32 times, respectively. Furthermore, the flexural performance of the masonry beams reinforced with a 15 mm thick ECC and single-layer GFRP mesh demonstrated similar reinforcement effects to the masonry beams reinforced with a 20 mm thick ECC, while reducing costs by 23 %. Based on the existing codes governing the calculation method of flexural strength and considering the influence of various factors, a calculation model for the flexural strength of ECC-reinforced masonry beams with GFRP mesh was established.

Forensic Analysis on Damage of a Cable-Stayed Bridge without Backstays Using BIM Information

Serious cracks were found in the pylon of a cable-stayed bridge without backstays. Based on forensic damage investigation, this paper uses the finite element (FE) method incorporating Building Information Modeling (BIM) to analyze the causes of cracking. The BIM model is established based on the survey of design, construction, and service information of the bridge. Then, FE analysis is conducted using BIM information. Finally, the causes of cracking in different regions of the pylon are explained in detail. The results show that the FE simulation agrees well with the inspected distribution of cracks, and the causes of cracks are closely related to the pylon construction process. The main cause of the cracks is the shrinkage difference between concrete segments of different ages. The anchorage effect of stayed cables also causes inclined cracks perpendicular to the cable direction. The combination of temperature load and concrete shrinkage results in cracks at the root of the pylon, and the reduction in cable forces exacerbates the cracking.

Damage Evolution and Fractal Characteristics of Granite under the Influence of Temperature and Loading

To study the damage characteristics and evolution law of granite under the influence of temperature and loading rate, uniaxial compression tests at different loading rates were performed for granite samples at 30 °C, 40 °C, 60 °C, and 80 °C. The damage characteristics and evolution law of granite were studied in conjunction with acoustic emission ringing, acoustic emission b values, acoustic emission signaling constellations, and fractal dimensions. The results showed the following: (1) At a low loading rate (0.005 mm/s), the peak stress of the granite increases gradually as the temperature increases. At high loading rates (0.01 mm/s and 0.02 mm/s), the peak stress of the granite first decreases, then increases as the temperature increases. The elastic modulus at different loading rates decreases first, then increases as the temperature increases. The elastic modulus of the granite is the lowest at 40 °C; (2) At the same temperature, specimens subjected to higher loading rates exhibit accelerated internal damage progression, with a precipitous decrease in the b-value occurring earlier. At a loading rate of 0.005 mm/s, the total number of acoustic emission ring-down events is at least 1.7 times greater than that at other loading rates, indicating a more complex development of internal cracks in the granite specimens. Moreover, as the temperature increases under a constant loading rate, the concentration of acoustic emission ring-downs intensifies during the unstable crack development and failure phases, accompanied by progressively larger fluctuations in the b-value; (3) Under the same temperature conditions, the acoustic emission signals in the specimens loaded at 0.005 mm/s and 0.01 mm/s propagate from one end to the other. At 0.02 mm/s, emissions appear simultaneously at both ends of the specimen and converge toward the center. The proportion of damage and energy associated with compression differs with temperature; at 30 °C and 40 °C, damage and energy are concentrated in the early phase of compression, whereas at 60 °C and 80 °C, they are more significant during the later stages; and (4) The fractal dimension of the granite specimens generally decreases, then undergoes a phase of fluctuating growth, followed by a decline. With increasing loading rates at a constant temperature, the compaction of the granite specimens decreases; the orderliness of the crack patterns gradually increases. As the temperature increases, the distribution of cracks during the compaction and failure phases becomes more orderly. During the crack initiation and development phases, the dispersion of cracks and the formation of crack networks are more pronounced. These findings provide a theoretical reference for understanding the microscale damage and failure mechanisms of granite under varying loading rates and temperatures.

A large-scale demonstration and sustainability evaluation of ductile-porous vascular networks for self-healing concrete

Self-healing cementitious materials show potential to reduce material consumption, maintenance costs, and environmental impacts within the construction sector. This study explores the feasibility of installing a ductile-porous vascular network in a series of retaining walls under realistic construction conditions, with the objective of both assessing the efficacy of the self-healing system and addressing any constructability issues that may arise. Numerical modelling was performed first to determine a suitable mix design and wall configuration that would promote cracking, so cracks would appear without mechanical intervention. The predicted crack distribution informed the optimal network configuration. Healing and sustainability considerations are discussed, and the benefits of implementing this technology are evaluated. When comparing a single maintenance activity using a vascular network versus manual repair, there is no significant benefit of using a vascular network. However, environmental impacts are substantially reduced when using a vascular network once multiple repair actions are considered.

Experimental and analytical investigations into flexural behavior of composite beams with UHPC T-section and HRS H-section

This study investigated the flexural behavior of composite beams with ultra-high performance concrete (UHPC) T-section and hot rolled steel (HRS) H-section. First, a four-point bending test on six specimens was conducted. The effects of stud spacing and tensile reinforcement ratio on flexural performance were investigated in terms of crack patterns, failure modes, ultimate load, load-strain response, relative interfacial slip, and ductility. The experimental results indicated that the stud spacing and the presence of tensile reinforcement had a visible effect on the crack patterns of UHPC web. The distribution of group cracks was observed at UHPC web of specimens with unreinforced UHPC bulb. During the failure stage, the whole HRS H-section in the constant moment region yielded. In particular, the partial cross section of HRS entered the strain hardening stage. In addition, an analytical approach verified by six tested specimens was developed to study the moment-curvature response of HRS-UHPC composite beams (HUCBs). The comparison results indicated the good accuracy of the analytical approach. Then, the proposed sectional analysis model was utilized to investigate the effects of the strength of HRS and UHPC, the total depth of cross section, and the depth of HRS H-section on yielding moment, including ultimate moment and ductility. The analytical results revealed that the strength of HRS and the total depth of cross section had a significant impact on the moment-curvature response of HUCBs. The sectional analysis also illustrated that the yielding point was mainly determined by the yielding of HRS H-beam. Compared with UC120, the ultimate moment and ductility coefficient of the composite beam using UC200 increased by 20.6 % and 87.7 %, respectively. However, the tensile strength of UHPC had a slight influence on the yielding and ultimate moment as well as ductility.

Concept and flexural performance of non-prestressed steel plate-UHPC-NC composite girder bridge

A novel non-prestressed composite girder bridge, incorporating steel plates, ultra-high performance concrete (UHPC), and normal concrete (NC), is proposed for small and medium-span bridges. For the proposed steel plate-UHPC-NC composite bridge, UHPC girders are reinforced with steel plates on the bottom in lieu of part of closely-spaced rebars in the beam. Cast-in-situ NC deck slab is adopted to ensure its transverse integrity and to reduce costs in comparison with UHPC bridge deck. To verify the performance of the proposed novel composite bridge, three types of UHPC-NC composite beams with same reinforcement ratio (reinforced with only rebars, only steel plates, both rebars and steel plates) were first conducted with bending test. The impact of various reinforcement types on the flexural behaviors of UHPC-NC composite specimens was identified, including failure mode, crack distribution pattern, and crack width development. The findings demonstrated that the UHPC girder reinforced with both steel plates and rebars would significantly enhance the crack resistance of UHPC girders during bending in comparison with the other two. In addition, the composite girder reinforced with steel plates and rebars can achieve a nominal stress of 31.41 MPa at the serviceability limit state (with a UHPC crack width of 0.05 mm). The commercial software DIANA is then utilized to numerically simulate the mechanical properties of the proposed composite beam. The deviation between the finite element (FE) results and the experimental load-bearing capacity is within 1.9 %. Parameter analysis demonstrates that the bridge deck's strength has negligible influence on the load-carrying capacity of the proposed composite beam. Finally, a design scenario for a 30 m-span simple-supported bridge is conducted, and the initial cost analysis indicates that the proposed steel plate-UHPC-NC composite girder is 2 % lower than the conventional prestressed concrete T-girder. The proposed non-prestressed steel plate-UHPC-NC bridge presents notable benefits, including cost-effectiveness, strong crack resistance, and the prospect of complete prefabrication, offering a feasible alternative for small and medium-span bridges.

Flexural behaviour of damaged concrete T-beams reinforced with ultra-high performance concrete filling

To improve the flexural performance of damaged reinforced concrete T-beams, a method of filling ultra-high performance concrete (UHPC) in the damaged area was adopted. Experimental studies were conducted on two UHPC-reinforced concrete T-beams with different lengths of damaged areas and one undamaged concrete T-beam as a reference. Crack distribution, failure modes, cracking loads, flexural capacities, and strain variation of the specimens were analyzed. Subsequently, a nonlinear finite element (FE) model of the UHPC-reinforced T-beam was developed using ABAQUS, and the FE model results were compared with the experimental results to validate the accuracy of the FE simulation method. The results indicated that the two UHPC-reinforced T-beams exhibited a similar flexural failure process to the undamaged T-beam. The longitudinal tensile strain distribution at the mid-span section showed that the composite section formed by the filling of UHPC in the damaged region still adhered the assumption of the planar section. Owing to the excellent bond performance between UHPC and the existing concrete, the main cracks of the UHPC-reinforced T-beams appeared in the chiseled area, and the crack widths of the UHPC-reinforced T-beams under the same load were smaller than those of the reference T-beam. Overall, the reinforcing method of filling UHPC in the damaged region can restore or even enhance the flexural performance of the damaged reinforced concrete T-beams.

Identifying the dominant influencing factors of secondary lining cracking risk in an operating mountain tunnel

PurposeA risk-based method is proposed to identify the dominant influencing factors of secondary lining cracking in an operating mountain tunnel with weak surrounding rock.Design/methodology/approachBased on the inspection data from a mountain tunnel in Southwest China, a lognormal proportional hazard model is established to describe the statistical distribution of secondary lining cracks. Then, the model parameters are obtained by using the Bayesian regression method, and the importance of influencing factors can be sorted based on the absolute values of the parameters.FindingsThe results show that the order of importance of the influencing factors of secondary lining cracks is as follows: location of the crack on the tunnel profile, rock mass grade of the surrounding rock, time to completion of the secondary lining, and void behind the secondary lining. Accordingly, the location of the crack on the tunnel profile and rock mass grade of the surrounding rock are the two most important influencing factors of secondary lining cracks in the investigated mountain tunnel, and appropriate maintenance measures should be focused on these two aspects.Originality/valueThis study provides a general and effective reference for identifying the dominant influencing factors of secondary lining cracks to guide the targeted maintenance in mountain tunnels.

Experimental study on the effect of flexible joints of a deep-buried tunnel across an active fault under high in-situ stress conditions

During dislocation, a tunnel crossing the active fault will be damaged to varying degrees due to its permanent stratum displacement. Most previous studies did not consider the influence of the tunnel’s deep burial and the high in-situ stress, so the results were not entirely practical. In this paper, the necessity of solving the anti-dislocation problem of deep-buried tunnels is systemically discussed. Through the model test of tunnels across active faults, the differences in failures between deep-buried tunnels and shallow-buried tunnels were compared, and the dislocation test of deep-buried segmental tunnels was carried out to analyze the external stress change, lining strain, and failure mode of tunnels. The results are as follows: (1) The overall deformation of deep-buried and shallow-buried tunnels is both S-shaped. The failure mode of deep-buried tunnels is primarily characterized by shear and tensile failure, resulting in significant compressive deformation and a larger damaged area. In contrast, shallow-buried tunnels mainly experience shear failure, with the tunnel being sheared apart at the fault crossing, leading to more severe damage. (2) After the segmental structure design of the deep-buried tunnel, the “S” deformation pattern is transformed into a “ladder” pattern, and the strain of the tunnel and the peak stress of the external rock mass are reduced; therefore, damages are significantly mitigated. (3) Through the analysis of the distribution of cracks in the tunnel lining, it is found that the tunnel without a segmental structure design has suffered from penetrating failure and that cracks affect the entire lining. The cracks in a flexible segmental tunnel affect about 66.6% of the entire length of the tunnel, and cracks in a tunnel with a short segmental tunnel only affect about 33.3% of the entire length of the tunnel. Therefore, a deep-buried tunnel with a short segmental tunnel can yield a better anti-dislocation effect. (4) By comparing the shallow-buried segmental tunnel in previous studies, it is concluded that the shallow-buried segmental tunnel will also suffer from deformation outside the fault zone, while the damages to the deep-buried segmental tunnel are concentrated in the fault zone, so the anti-dislocation protection measures of the deep-buried tunnel shall be provided mainly in the fault zone. The results of the above study can provide theoretical reference and technical support for the design and reinforcement measures of the tunnel crossing active fault under high in-situ stress conditions.

Tensile analysis of loop joints with different overlap lengths

ABSTRACT In order to achieve rapid bridge construction, on-site wet joint joining techniques for prefabricated bridge decks are commonly used. The primary method involves mainly lap welding, but this form poses some drawbacks such as difficult lap jointing of two steel bars and a hefty welding workload. To address these issues, this study conducts model experiments on the unwelded structure of loop joints. We compare and analyze the displacement, crack distribution, crack development process, and strain variability of loop joints across three different overlap lengths, along with one type of straight bar lap-welded wet joints. It is observed that, despite the comparable ultimate tensile capacity of loop joints with the main rib to that of the welded wet joint with the main rib, the failure mode varies, and the crack direction changes with the overlap length. From a structural stress perspective, if the U-bar of the loop joint meets a specific overlap length, the wet joint adequately fulfills stress requirements and can be applied in practical engineering.

Enhancing shear strength of RC beams through externally bonded reinforcement with stainless-steel strips and FRCM jacket to mitigate the failure risk

This study aims to assess the efficacy of innovative and sustainable methods in improving the shear performance of Reinforced Concrete (RC) beams lacking shear stirrups. Eleven specimens, including two control specimens and nine strengthened ones, underwent monotonic loading through three-point testing. Various strengthening configurations were investigated, involving the application of Stainless-Steel Strips (SSSs) affixed to the beam surface in the defective zone, along with a Fiber-Reinforced Cementitious Matrix (FRCM) jacket. In the first set of beams, SSSs were vertically applied, while the second set featured beams with SSSs inclined at 60°, and the third set had SSSs inclined at 45°. Each set comprised three beams, allowing for the examination of the impact of SSS thicknesses, set at 1 mm, 1.25 mm, and 1.50 mm. After the installation of SSSs, all strengthened beams received an FRCM jacket, including a 5 mm Engineered Cementitious Composites (ECC) layer with embedded Glass Fiber Reinforced Polymer (GFRP) textile. The study concludes that incorporating SSS strips with an FRCM jacket delays the initiation of the first crack in defective beams. Increasing SSSs thickness contributes to a more favorable crack distribution. The 60° inclined SSSs proves to be the most effective, rectifying the deficiency from the absence of shear stirrups and surpassing the original beam's performance. Additionally, finite element analysis was conducted, and the results supported the accurateness of the developed model in simulating responses and crack patterns throughout all loading stages.

Nonlinear interfacial contact laws in multi-layer elastic-viscoelastic structural systems

Layered structures are widely used in construction, such as pavement structures consisting of multiple layers of different materials or interfaces between bricks and mortar in masonry structures, etc. In analyzing such structures, understanding the properties of the interface between two layers of materials is essential. If one layer of material contains cracks and layers exhibit viscoelastic behavior, determining the properties of the interface becomes challenging. This study proposes a constitutive mechanical law to model the behavior of the interface between a microcracked viscoelastic medium and an undamaged elastic body based on the homogenization method. The interface is modeled by a layer of zero thickness. The coupling between the homogenization technique and the Griffith’s theory is used to provide the effective behavior of the micro-cracked medium. The interface is modelled as an effective medium (EF) characterized by normal and tangential stiffnesses (CN, CT ). In this work, two viscoelastic models are considered, i.e., Burger and Modified Maxwell. The formulas of CN and CT for two cases of crack distributions (isotropic and transversely isotropic) are obtained by asymptotic techniques where the thickness of the joint tends to zero

Effects of crack-γ/γ' interface relative distributions on the deformation and crack growth behaviors of a nickel-based superalloy.

Using the molecular dynamics (MD) method, we investigated the effects of crack distributions on the deformation and crack growth of a nickel (Ni)-based superalloy. The results indicated that as the distance between two cracks increased, both tensile strength and plasticity decreased, while the crack growth rate significantly increased. In systems with short crack distances, strong interactions occurred between the dislocations that emitted from two cracks and the γ/γ' interface mismatched dislocation network. These interactions led to an overlap in the plastic zones ahead of the crack tips at the γ/γ' interface, which resulted in significant passivation at the front and middle regions of the cracks. Consequently, the two cracks merged in the X-direction to form a wide crack. The cracks coalescence consumed a lot of external deformation work, resulting in the highest tensile strength and plasticity. In this study, we proposed a potential approach to simultaneously enhance the strength and plasticity of multidefect systems, providing a theoretical basis for explaining deformation mechanisms and crack growth in these systems.

Experimental Study on the Strength and Damage Characteristics of Cement–Fly Ash–Slag–Gangue Cemented Backfill

In order to achieve the goal of effectively utilizing solid waste resources and improving mining stability, it is necessary to incorporate various types of solid wastes in the production of cemented backfill. For investigating the compressive strength and damage characteristics of Cement–Fly Ash–Slag–Gangue (CFSG) cemented backfill under loading, real-time X-ray Computed Tomography (CT) scanning was employed to capture two-dimensional (2D) grayscale slices and three-dimensional (3D) fracture models during uniaxial compression testing. The study quantitatively assessed the evolution of cracks and microstructural damage in CFSG cemented backfill. The results indicate that the specimens underwent four stages of transformation, including compaction, linear elasticity, yielding, and residual deformation, during the uniaxial compression process. The specimens exhibited a measured compressive strength of 3.44 MPa and a failure strain of 0.95%. As the axial strain increased, there was an increase in 2D porosity observed in the CT images and a greater dispersion of crack distribution. A 3D model constructed from CT slices illustrated the feature of cracking expansion, with the fracture volume gradually increasing during the elastic deformation phase and experiencing rapid growth during the yielding and residual deformation phases. The damage variable, obtained from the volume of 3D cracks, exhibited a slow-growth pattern, characterized by a rapid increase followed by a more gradual rise with the increase in axial strain. This study serves as a significant reference for comprehending the micro-mechanisms involved in the damage process and cracking characteristics of cemented backfill mixed with solid wastes under external loading conditions.

Numerical-experimental analysis of laser-welded small energy absorbers with direct impact Hopkinson method

This research paper presents a comprehensive numerical-experimental analysis of the phenomena observed during the compression of small energy absorbers (EAs) with dimensions 23 × 23 mm and a thickness of 0.6 mm. This study uses the direct impact Hopkinson (DIH) method. The locus is the detailed prediction of the strength of laser-welded joints in terms of energy absorption under both quasi-static and dynamic loading conditions. Furthermore, the paper explores the potential utility of the described methodology for modeling and predicting the failure mechanisms of small energy absorbers. This investigation delves into key factors that affect the distribution of cracks in deformed energy absorbers. These include: the detail of the reproduction of the absorber geometry, the impact of finite element formulations and modeling method (2D/3D elements) and the complexity of the material model for propagated cracks. Two material models are considered, the simplified Johnson–Cook model and the tabulated Johnson-Cook with Hockett–Shelby extrapolation model, which incorporate linear damage dependent on the stress triaxiality and Lode angle. The study also highlights the advantages and disadvantages of the DIH test method. Some features cannot be effectively observed through experimental testing alone. The experimental procedure involved initial testing and calibration of the material models for both the parent material and the welded joints at three different strain rates. Subsequently, the validated energy absorber models are subjected to static and dynamic crushing. The results are subsequently compared with the virtual results obtained using the gravity hammer method, which is a more readily accessible testing approach. Remarkably, a very high correlation between the numerical simulation and experimental data is observed, providing a comprehensive understanding of the research problem related to laser-welded absorbers.