Crack Propagation Research Articles

The hydromechanical coupled numerical method in pseudo-3D axisymmetric domain with cracks extension and coalescence applies to the decompression failure problem

The stress-strain state of the saturated porous media determines the behavior of fracturing, which defines the efficiency of developing tight oil, shale, coalbed, and thermal energy fields. Therefore, reliable hydromechanical coupled simulations with destruction reconstruction are critical.The proposed innovative simulator has a strong interrelation between fluid flow and rock deformation of porous media and realizes a fully coupled pseudo-transient numerical method by high-performance computing (HPC) tools. To increase the detail of the results in the problem, a finite difference numerical algorithm was implemented in the axisymmetric cylindrical domain, which reduces from three to two dimensions without loss of precision. Highly efficient parallelization using CUDA on the GPU computes meshes of up to one billion cells, allowing the simulation of a total core sample to sub-micrometer resolution in an appropriate time. The algorithm has been validated to find the exact solution to the cylinder problem. The proposed model accounts for cracks propagation with their coalescence within a single computational static grid, which keeps timing close to the continuous model.This comprehensive implementation enables solving industrial problems, such as modeling core sample damage during rapid decompression. High-resolution simulations help reconstruct fracture propagation, analyze the initial stress state, and identify critical damage factors. The comparison with the exact solution to the cylinder problem confirmed the reliability of the algorithm. The calculation results show a strong dependence of decompression failure on the coalescence and elongation of cracks, influenced significantly by the rock's cohesion. Microcracks length and distribution play a decisive role in the decompressive destruction behavior of the rock sample. For the first time, the simulations demonstrated the decompressive destruction of a core sample during an uncontrolled, rapid core retrieval operation.

Research on the wheel wear and rolling contact fatigue of metro vehicle induced by the rail corrugation

The rail corrugation is a common disease on the track, which exacerbates the wheel-rail interaction and accelerates wheel wear and crack propagation. This study focuses on the wheel wear and rolling contact fatigue of metro vehicle under the rail corrugation. Firstly, the characteristics of the rail corrugation under service conditions are determined by the statistical analysis of the field data, and the rail corrugation is applied to the established vehicle-track coupled dynamics model. Then, the wear index and the work of friction force as indicators of wheel wear are studied. Finally, based on the Shakedown Map and the criterion of maximum amplitude of shear stress, the simulation analysis of wheel-rolling contact fatigue under the rail corrugation is carried out. The results show that the increases in superficial fatigue index and accumulated fatigue are 1.52 and 6.16 times in the wavelength range of 30-90 mm larger than those in the range of 90-210 mm, respectively. Furthermore, the cracks more easily occur 2-4 mm from the outer surface of wheel, and expand along the wheel tread.

Seismic Performance of Precast Drift-Hardening Concrete Walls Connected by Grout–Sheath Duct

In order to find a suitable size of sheath duct and a reliable construction method for precast walls, a cast-in-place and five 1/2 scale precast drift-hardening concrete walls reinforced with weakly bonded ultra-high strength SBPDN rebars were fabricated and tested under reserved lateral load and constant compression. The experimental variables were the diameter of sheath ducts (45 mm, 100 mm, and 120 mm), embedded length (20d and 35d; d is the nominal diameter of SBPDN rebars), axial load ratio (0.075 and 0.15), and the construction method. The experimental observations, hysteresis behaviors, envelope curves, residual deformation, crack propagation, and energy dissipation were compared in the study. Moreover, a formula was applied to calculate the bond strength of the sheath duct. The experimental and calculated results revealed that increasing the axial load ratio and embedment length could not enhance the bond strength of the sheath ducts, and increasing the diameter decreased the bond strength significantly. Anchored the SBPDN rebars in smaller sheath ducts separately was a more stable connection method for precast concrete shear walls and provided sufficient drift-hardening capability, even at a large drift level (over 3%).

Multiscale study on the properties and crack propagation of 2D woven SiCf/SiC with pores using elastoplastic phase field

AbstractTo understand the effect of processing and prefabricated pores on 2D woven SiCf/SiC composites (2DW‐SiCf/SiC), their crack propagation and mechanical response under tension load at meso‐ and macro‐ scale are investigated by a promising elastoplastic phase field method (EPPFM). Of much interest, the computational results are well consistent with the available experimental results, verifying the reliability of EPPFM. A significant dependence on pores is observed in the relationship between the strength, Young's modulus, work of fracture of 2DW‐SiCf/SiC and porosity when pores exist solely in the matrix out of yarns, and both in the matrix and yarns, respectively. Moreover, the more dangerous processing pores at mesoscale near yarn are attributed to the inconsistent deformation of the yarn and matrix. Finally, the EPPFM is used for the effect of geometry size on the joint failure mode of 2DW‐SiCf/SiC plate with prefabricated open holes under pin‐loading. Of importance, the more safe bearing failure mode occurs in 2DW‐SiCf/SiC plate when edge distance‐to‐hole diameter ratio and width‐to‐hole diameter ratio are greater than 1.5 and 3, respectively.

Analysis of initiation and growth of new transverse cracks in high crack density regions in cross-ply laminates

In cross-ply laminates under loading, multiple intralaminar (transverse) cracking in the 90-layers causes laminate stiffness reduction which can be predicted by analytical models studying average of the stress perturbation between transverse cracks. The commonly used analytical models such as shear-lag type or variational-type models assume that stress in damaged 90-layers does not depend on the laminate thickness coordinate. But with increase in crack density, the stress perturbations created by transverse cracks start to interact, generating high stress gradients in through-the-thickness direction in the 90-layers. Location of a new crack and features of its propagation in a high stress gradient region between two cracks in a cross-ply laminate are analyzed in this paper. FEM is used to calculate stress distribution between two cracks. The location of the next crack and its initial orientation is found using principal stresses and orientation of principal axes. Most often these cracks are initiated at ply interface in the middle between already existing cracks. Their propagation across the layer thickness is analyzed using energy release rate based criterion. It is shown that at very high crack density the crack propagation across the layer thickness is unstable in the beginning, but it is stopped when approaching the middle of the layer where the crack opening becomes zero. Presence of local delaminations at the tips of existing cracks changes the energy release rate for propagation of new transverse cracks.

Analysing Flexural Response in RC Beams: A Closed-Form Solution Designer Perspective from Detailed to Simplified Modelling

This paper presents a detailed analytical approach for the bending analysis of reinforced concrete beams, integrating both structural mechanics principles and Eurocode 2 provisions. The general analytical expressions derived for the curvature were applied for the transverse displacement analysis of a simply supported reinforced concrete beam under four-point loading, focusing on key limit states: the initiation of cracking, the yielding of tensile reinforcement and the compressive failure of concrete. The displacement’s results were validated through experimental testing, showing a high degree of accuracy in the elastic and crack propagation phases. Deviations in the yielding phase were attributed to the conservative material assumptions within the Eurocode 2 framework, though the analytical model remained reliable overall. To streamline the computational process for more complex structures, a simplified model utilising a non-linear rotational spring was further developed. This model effectively captures the influence of cracking with significantly reduced computational effort, making it suitable for serviceability limit state analyses in complex loading scenarios, such as seismic impacts. The results demonstrate that combining detailed analytical methods with this simplified model provides an efficient and practical solution for the analysis of reinforced concrete beams, balancing precision with computational efficiency.

In-depth molecular dynamics analysis of crack evolution in polycrystalline chromium under uniaxial tensile deformation

Because of its excellent wear resistance and high hardness, chromium is widely used in coating materials. Under external load, micro-cracks on the surface of electroplated chromium coating will cause crack propagation and reduce the performance of the material. Therefore, in this study, the crack evolution process of polycrystalline chromium under uniaxial tension was studied using molecular dynamics. The effects of average grain size, strain rate, and crack location on crack propagation behavior were analyzed, which provided a scientific basis for optimizing the performance of chromium materials. The results show that cracks in polycrystalline chromium tend to fracture along grain boundaries and that stacking faults and holes are the main factors for crack propagation. As the grain size decreases, the crack passivation becomes more pronounced and the rate of crack expansion slows down. As the strain rate increases, the crystal structure of polycrystalline chromium changes more sharply, and the ultimate stress increases. At high strain rates, the direction of crack propagation changes. The degree of crack tip passivation is affected by the initial crack location, and the crack tip can be effectively passivated when it is located at the grain boundary, thus hindering crack propagation. The results of these studies reveal the influence of multiple factors on the crack propagation mechanism of polycrystalline chromium and provide theoretical guidance for the reduction of chromium coating damage.

Numerical analyses of the influences of rock properties and joints on rock fragmentation in shaft sinking by drilling method

The mechanical rock-crushing efficiency is directly influenced by rock properties and joint structure. Tipped-hob is widely used in the construction of shafts. By analyzing the motion of tipped-hob and the mechanical properties of granite and sandstone, numerical rock samples with different mechanical properties were built to investigate the influences of rock properties and joint structure on rock-crushing efficiency using a single ring of tipped cutter. The results revealed correlations between compressive strength, tensile strength, hardness, brittleness, specific energy consumption, and the vibration of thrusting forces. It was suggested that the spacing, dip angle, and continuity of joints have a significant impact on the failure patterns and crack propagation in the process of rock fragmentation, as well as on the vibration frequency and amplitude of breaking-force of cutter and the specific energy consumption. This research is crucial for controlling the stability of drilling machine during shaft sinking by drilling method.

Damage behavior and toughening mechanism of SiCf/SiC-Ti3SiC2 composites: A combination of digital image correlation and acoustic emission

Matrix modification is an effective method to improve the mechanical properties of ceramic matrix composites, while the elucidation of corresponding damage mechanism is essential for the design and engineering application of composites. In this work, Ti3SiC2 particles were introduced into SiC matrix to fabricate Ti3SiC2 modified SiCf/SiC (SiCf/SiC-Ti3SiC2) composites by a hybrid technique of slurry suspension impregnation combined with polymer infiltration and pyrolysis. Compared with SiCf/SiC composites, the flexural strength and modulus of SiCf/SiC-Ti3SiC2 composites were increased by 17.8 % and 61.0 %, respectively. The three-point flexural damage behavior and failure mechanism of composites were systematically investigated and compared by the combination of digital image correlation and acoustic emission techniques. Based on the collaborative analysis of in-situ damage process, matrix micro-zone toughness and fracture morphology, the modification effect and toughening mechanism of Ti3SiC2 were revealed. The improved mechanical properties of SiCf/SiC-Ti3SiC2 composite could be ascribed to the more sufficient matrix cracking before composite failure and the increased matrix fracture energy by microcrack deflection. After matrix modification, the failure mechanism was dominated by the gradual propagation and growth of microcracks until the critical crack size, instead of the fast and unstable propagation of main crack.

High‐temperature behavior and self‐enhancing mechanisms of oxide‐bonded SiC porous ceramics

AbstractOxide‐bonded SiC porous ceramics (SCPCs), synthesized via reaction bonding, exhibit significant potential for high‐temperature applications. However, incorporating sintering aids inevitably results in a considerable quantity of amorphous glass phase within SCPCs, thereby introducing risks to their high‐temperature mechanical performance. In this study, we employ in‐situ characterization techniques to investigate the high‐temperature behavior of SCPCs. Our findings reveal that SCPCs demonstrate remarkable high‐temperature self‐enhancing properties, with a critical bending strength at 800°C. Beyond this temperature, the strength declines sharply. Intriguingly, the critical bending strength is 36.6% greater than at ambient temperature. Moreover, elevated temperatures enhance the elastic modulus and promote the transition of SCPCs from multilinear to nonelastic fracture. The neck phase, which imparts strength to the SCPCs, is composed of four distinct layers along the depth direction: silicate glass, oxygen‐containing, silicon‐rich, and SiC region, as revealed by FIB‐TEM. The transformation from α to β‐cristobalite in the oxygen‐containing region improves the thermal expansion match with SiC, thereby mitigating local stress concentration. Furthermore, the compressive stress within the neck region intensifies with increasing temperatures, thereby inhibiting crack propagation. This work provides a basis for the high‐temperature applications of SCPCs.

Misorientations across interfaces in spark plasma–sintered WC–Co cemented carbides

AbstractThis interdisciplinary work concerns misorientations across various interfaces in spark plasma–sintered (SPSed) WC–Co cemented carbides, as well as how these misorientations affect the intergranular fracture. The whole boundaries in cemented carbides were divided according to the phases on the two sides of the boundary plane, and carbide/carbide grain boundaries were further divided according to the misorientation across the boundary plane. Stereological statistics and five‐parameter analysis were comprehensively performed on the concerned boundary types. For Σ2 carbide/carbide boundaries, multiple boundary structures are observed. How Σ2 twist inhibits intergranular fracture and how such boundary structure is formed are analyzed. For random carbide/carbide boundaries, the habit planes that they are terminated by are calibrated, and their responses to intergranular fracture are examined according to their energy anisotropy. For WC/α‐cobalt and WC/β‐cobalt phase boundaries, misorientations across these boundary planes and the corresponding crack propagation routines are illustrated. On these bases, approaches to improve the fracture strength of SPSed cemented carbides are suggested.

Study on Multi-Crack Damage Evolution and Fatigue Life of Corroded Steel Wires Inside In-Service Bridge Suspenders

The parallel steel wires used in arch bridge suspenders experience random corrosion damage on their surfaces during service. Corrosion damage, including micro-cracks, pitting, and a combination of both, leads to significant stress concentration under axial loading, which affects the performance of the steel wires. The change in the stress field caused by surface damage alters the stress intensity factor at the crack tip, and the presence of adjacent crack tips significantly amplifies the stress intensity factor, thereby accelerating crack propagation. The development of small surface damages in the steel wires is difficult to control and observe through experiments. By utilizing finite element methods for simulation, it is possible to intuitively analyze the crack propagation process, the trend of stress changes at the crack tip, and the interaction between damages. Numerical simulation results based on Paris’ law indicate that corrosion pits have a certain impact on the stress intensity factor at the crack tip. The propagation process of coplanar double cracks is highly sensitive to the initial crack size and the distance between adjacent crack tips. When the crack spacing is less than the crack depth, the stress intensity factor at the adjacent crack tips exhibits significant amplification. Based on this phenomenon, the coplanar double-crack system can be simplified to a complete single crack for analysis. By comparing the fatigue life of the double-crack system with that of the equivalent single crack, the effectiveness of the simplification rule has been validated.

Experimental Study on the Flexural Performance of the Corrosion-Affected Simply Supported Prestressed Concrete Box Girder in a High-Speed Railway

Prestressed concrete box girders are commonly employed in the development of high-speed railway bridge constructions. The prestressed strands in the girder may corrode due to long-term chloride erosion, leading to the degradation of its flexural performance. To examine the flexural performance of corrosion-affected simply supported prestressed concrete box girders, eight T-shaped mock-up beams related to the girders used in the construction of high-speed railway bridges were manufactured utilizing similarity theory. Seven of the beams underwent electrochemical accelerated corrosion, and then each beam was subjected to failure under the four-point load test method. Measurements recorded and analyzed in detail during the loading process included the following: crack propagation, crack width at various loads, crack load, ultimate load, deflection, and concrete strain of the mid-span section. The results demonstrate that a corrosion rate of just 8.31% has a considerable impact on the structural integrity of the beams, as evidenced by a pronounced reduction in flexural cracks and a tendency towards reduced reinforcement failure. Furthermore, the corrosive process has a detrimental effect on mid-span deflection, ductility, and ultimate flexural bearing capacity, which could have significant implications for bridge safety. This study provides valuable insights for the assessment of flexural performance and the development of appropriate maintenance strategies for corroded simply supported box girders in high-speed railways.

Investigating the Anisotropic Mechanical Behaviour of Steel Fibre-Reinforced Aluminium-Base Composites

Base metals are often reinforced with fibres to improve their mechanical behaviour; however, it is imperative to decide the range of fibres orientation that would yield favourable strength. In this work, using sand casting method, aluminium is reinforced with galvanized steel fibres at different orientations with the aim of investigating the anisotropic mechanical behaviour of the composites. The fibre orientations considered are 0°, 30°, 60° and 90°; while the mechanical properties evaluated are impact energy, tensile, compressive and fatigue properties. Unreinforced aluminium exhibits impact energy, elongation-at-fracture, ultimate tensile strength, and maximum compressive strength of 5.15 J, 15.88%, 72.56 MN/m2, and 231.13 MN/m2, respectively. With deviation of composite fibre orientation from 0° to 30°, 60° and 90°, impact energy decreases from 8.68 to 5.56, 4.75 and 4.61 J; elongation-at-fracture decreases from 24.58 to 17.91, 12.20 and 11.87%; ultimate tensile strength decreases from 132.70 to 89.17, 63.67 and 60.34 MN/m2; and maximum compressive strength decreases from 310.66 to 251.06, 226.91 and 209.93 MN/m2. At fatigue stress amplitude of 850 MN/m2, the fatigue life of unreinforced specimen is 26 numbers of cycles-to-failure; while the deviation of composite fibre orientation from 0° to 30°, 60° and 90° yielded reduction in fatigue life from 64 to 36, 20 and 14 numbers of cycles-to-failure. Also, reduction in fatigue stress amplitude was found to increase the fatigue life of the specimens. The fatigue limit (or endurance limit) of unreinforeced specimen, and composite specimen having 0°, 30°, 60° and 90° fibre orientations are found to be 40, 70, 45, 35 and 25 MN/m2, respectively; and the corresponding fatigue life are observed to be 35480, 199518, 112195, 10021 and 5297 numbers of cycles-to-failure, respectively. The findings in this work show that specimens with 0° fibre orientation have the highest endurance of deformation before fracture, followed by specimens with 30° fibre orientation, unreinforced specimens, specimens with 60° fibre orientation and specimens with 90° fibre orientation. This could be attributed to the fact that 0° fibre orientation offers continuous reinforcement spanning the longitudinal axis of the specimens, while fibre orientation from 30° to 90° offer areas of different degrees of shear stress concentration at fibre-matrix contacts aiding fibre-matrix debonding and crack propagation. In conclusion, this work shows that orientation of steel fibre reinforcement in aluminium matrix could be varied to achieve ranges of mechanical properties and performance needed for different practical applications.

Torsional Fatigue Performance of a Spot-Welded Structure: An XFEM Analysis

This study delves into the exploration of the fatigue performance of a structure that has been spot-welded and is being loaded with torsional fatigue. The extended finite element method (XFEM) was applied to simulate the intricate interaction of spot welds in response to cyclic loading. The developed model was validated through experiments. The influences of different parameters, such as the number of spot welds used to join the adherends, the diameters of the spot welds, and the load ratio applied, on the fatigue performance of the box were investigated. The first two parameters studied had a significant influence on the extent of the fatigue failure-affected spot welds, where the crack propagation rate can be decreased by more than 700%.

The effect of deep-sea pressure during long-term aging on the tribological performance of fabric-reinforced phenolic composites

The influence of hydrostatic pressures up to 30 MPa on the friction and wear behavior of fiber reinforced polymer composites (FRPCs) was investigated together with seawater absorption, interfacial structure and mechanical properties. The results revealed that after aging in the deep-sea environment, the wear rate of the FRPC increased from 1.53 × 10−6 mm3/N∙m to 3.61 × 10−6 mm3/N∙m, and the mechanical strength decreased reversibly. The damage mechanism was assumed to be dominated by the combined effect of crack propagation in the polymer matrix and interfacial debonding at high seawater pressures, characterized by a decreased resin modulus and increased interfacial thickness.

Small fatigue crack behavior of CP-Ti in thin-walled cruciform specimens under biaxial loading

This study investigates the small fatigue crack propagation behavior of commercially pure titanium (CP-Ti) using thin-walled cruciform specimens under in-plane biaxial loading, considering the effects of biaxial ratio and phase angle. Increasing phase angle results in more secondary cracks merging with main cracks perpendicular to the rolling direction (RD) and transverse direction (TD), a phenomenon attributed to the rise in shear stress that accelerates main crack growth. Higher loading biaxiality or a lower phase angle leads to decreased crack propagation rates and increased biaxial fatigue life. Electron backscatter diffraction (EBSD) analysis reveals that when the maximum normal stress aligns with the RD, prismatic slip primarily governs crack propagation, thereby accelerating crack propagation rates. Conversely, alignment with the TD reduces prismatic slip activity and crack propagation rates. Under equi-biaxial loading, prismatic slip activity decreases further, and crack propagation is dominated by multiple slip and twinning, consequently resulting in the slowest propagation rates. Additionally, a higher proportion of prismatic slip under high phase angle also accelerates crack propagation. Finally, incorporating Findley equivalent stress into the Chapetti model, which considers the crack length-dependent threshold effect, a highly accurate biaxial small fatigue crack propagation rate model is proposed.

Experimental and Numerical Research on Fracture Properties of Mass Concrete Under Quasi-Static and Dynamic Loading

The dynamic fracture behavior of mass concrete is crucial to the dynamic analysis and safety evaluation of concrete dams subjected to strong earthquake shocks in the framework of fracture mechanics. In the presented research, cylindrical specimens with a ring of preset cracks were cast by three-graded mass concrete, and direct tension tests were performed with two loading rates considered, i.e., 10−6/s for quasi-static loading and 10−3/s for dynamic loading. The load–crack mouth opening displacement (P-CMOD) curves were obtained, from which the fracture toughness, fracture energy, and characteristic length of the mass concrete were obtained. In this process, the influence of the eccentricity in the tests was compensated by the numerical modeling of the tests. Next, the crack propagation process of the mass concrete was modeled using the extended finite element method. From the test results, it is found that, under quasi-static loading, the crack generally propagates along the interface between the aggregates and the matrix, while, under dynamic loading, more aggregates are fractured. As compared to the case of quasi-static loading, the energy absorption capacity, fracture energy, and fracture toughness increase for dynamic loading, while the characteristic length decreases. Moreover, the numerically predicted P-CMOD curves agree reasonably well with the experimental measurements.

Phase Field Coupled Finite Deformation Plasticity Formulation of Ductile Fracture With Nonlinear Kinematic Hardening and Modified Energy Release Function

ABSTRACTA ductile damage theory is presented by coupling the covariant formulation of finite deformation plasticity with the phase field modeling of fracture, including kinematic hardening for the ductile response of the materials. A phase field coupled nonlinear kinematic hardening equation is proposed in the reference configuration having equivalent representation through the Lie derivative of the kinematic hardening tensor by push‐forward operation in the spatial configuration, thus ensuring the satisfaction of frame invariance. To capture the correct physical response of the material by the phase field evolution equation, the fracture driving function, that is, the difference between the sum of elastic and plastic energies and threshold energy, after the damage initiation is modified by an energy release controlling function, which is an empirical relation of equivalent plastic strain. In defining the energy release controlling function, well‐defined points with physical significance in the experimental load versus displacement curve are used. To simulate the response of the material in relatively large time steps, a modified staggered scheme is presented, evaluating the fracture driving and energy release controlling functions from the previous converged step and using the updated phase field variable in the weak form of the momentum balance equation. To quantify different material parameters from available experimental results in the literature, the developed phase field coupled elasto‐plastic model uses a neural network optimization procedure consisting of neural network training together with optimization in MATLAB and finite element model evaluation in Abaqus user element subroutine UEL. Model capabilities are demonstrated by simulating the crack propagation in complex 3D geometries such as the second and third Sandia Fracture Challenges.

Particle flow simulation of crack propagation and penetration in Brazilian disc under uniaxial compression

The presence of rock mass fractures has always been a subject of study for the prevention and control of related natural disasters. To understand the effects of different dip angles and horizontal distances on crack development, numerical simulation experiments on Brazilian disks under uniaxial compression were con-ducted using the PFC2D particle flow program. A function module was utilized to monitor the expansion and quantity of cracks. The numerical simulation results under 0° conditions were in good agreement with the experimental results, validating the rationality of the numerical simulation. The simulation results indicate that: under single fracture conditions with different dip angles, samples with angles between 30° and 60° produced typical wing-shaped cracks. At 0°, cracks propagat-ed through the center of the fracture, while at 90°, cracks initiated from the tip of the fracture and propagated through the sample. The peak stress and the number of cracks in the samples first decreased and then increased with the increase of the dip angle, reaching a maximum at 90°. For samples with double fractures and varying horizontal distances, all produced wing-shaped cracks. Their peak stress and the number of cracks increased monotonically with the increase in distance, reaching a maximum at a distance of 30mm. The experimental results confirmed that the PFC2D program can effectively simulate the process of crack initiation and development, and the research findings provide a reference for correctly understanding the fracture mechanics of fractured rock masses.