Search

Laminated ceramics containing layers of pottery materials with high and low Young's moduli were developed to mimic the nacre structure of abalone shells with high resistances against dynamic fractures. The layers with the low Young's modulus moderated crack deflection and impact, thereby exhibiting a high fracture resistance. The ceramic pores were formed by the CO2 gas generated through the oxidation of SiC during firing. The dynamic fracture resistance was enhanced by elastic wave scattering owing to the difference between the Young's moduli of the dense and porous layers. The effect of lamination on the dynamic fracture resistance was observed because the elastic waves were scattered owing to the difference in the elastic modulus between the porous and dense layers, and their propagation to the back sample surface was suppressed. The fracture energy of the 5‐layer laminate was determined to be about four times larger than that of the dense monolayer, which indicates that the introduction of intentional defects is effective in improving the dynamic fracture resistance of the pottery ceramics. [ABSTRACT FROM AUTHOR]

The tensile failure of complex branching cracks will cause irreversible damage to the structures. In this paper, the effects of the crack orientations, the local branch lengths, and the different load forms on the crack propagation pattern and the bearing capacity of structures are investigated based on the phase field method and experimental research method. The results show that the bearing capacity and propagation patterns of the specimens change significantly with the change of the orientation of the Y-shaped crack under tensile load. The local branch length of the crack only affects the sequence in which the regional crack reaches the final failure and the bearing capacity of the specimen. Under the dynamic impact load, the bifurcation phenomenon occurs, and with the increase of the dynamic impact load, the number of bifurcations increases. The crack propagation pattern in the numerical simulation is completely consistent with the experiment, and the difference in the maximum reaction force is 2.5%. [ABSTRACT FROM AUTHOR]

In this paper, we consider a dynamic model of fracture for viscoelastic materials, in which the constitutive relation, involving the Cauchy stress and the strain tensors, is given in an implicit nonlinear form. We prove the existence of a solution to the associated viscoelastic dynamic system on a prescribed time-dependent cracked domain via a discretization-in-time argument. Moreover, we show that such a solution satisfies an energy-dissipation balance in which the energy used to increase the crack does not appear. As a consequence, in analogy to the linear case this nonlinear model exhibits the so-called viscoelastic paradox. [ABSTRACT FROM AUTHOR]

The influence of confining pressure on the dynamic fracture mechanical behavior of deep rock masses is crucial in the exploitation of deep resources and the development of underground spaces. In this study, dynamic caustics experiments were conducted using transparent epoxy resin materials to investigate the crack propagation behavior and interaction mechanisms of double cracks under confinement. The experimental results indicate that biaxial confining pressure suppresses crack propagation, interaction between double cracks, and penetration. Without confining pressure, cracks do not penetrate until the relative vertical distance ΔH between crack tips is 20 mm, whereas with confining pressure, cracks cease to penetrate when the relative vertical distance between crack tips is 10 mm; however, interaction between crack tips still exists at this point. During the crack interaction stage, both fracture toughness and propagation velocity of crack tips exhibit significant fluctuations under no confining pressure conditions, whereas under confining pressure, both decrease rapidly. Additionally, under confining pressure conditions, the fluctuation range of crack propagation direction during crack interaction is relatively small. Confining pressure rapidly reduces the degree of stress concentration at crack tips, increases the rate of energy release at crack tips, and enhances the ability of dynamic cracks to resist the influence of other crack tips or crack surfaces. Under confining pressure, continuous Rayleigh waves are typically observed at crack tips due to an imbalance between stored strain energy and the energy release rate. These waves dissipate part of the strain energy, promoting crack deflection and branching.

Dynamic fracture propagation significantly affects water flooding efficiency in tight oil reservoirs. This phenomenon, where moderate fracture openings can enhance water flooding volume and alleviate injection challenges, has been underexplored in current literature. Understanding dynamic fracture behavior poses a challenge due to the difficulty in characterizing them within traditional reservoir numerical simulators. In this study, we propose a numerical simulation method that integrates the KGD dynamic fracture model with a two-phase flow model. This approach enables detailed exploration of dynamic fracture evolution in reservoir scenarios featuring one injector and one production well. Our findings reveal that fractures extend from the water injection well to the oil production well, exhibiting rapid initial growth followed by a slower rate. Fluctuations in fracture tip pressure correspond to cycles of opening and closure. We observe that cumulative oil production increases more rapidly when injection pressure exceeds the fracture opening pressure. However, this growth rate diminishes beyond a certain threshold, highlighting the critical role of injection parameters in dynamic fracture efficacy. Optimal water flooding performance is achieved when injecting water slightly above the fracture opening pressure. Furthermore, we compare water cut curves generated by conventional commercial simulators with our fracture propagation model. Our model's water cut curve aligns better with on-site data, indicating improved historical fitting accuracy. In conclusion, our study underscores the importance of dynamic fractures in enhancing water flooding efficiency in tight oil reservoirs and presents a robust numerical simulation framework for better understanding and management of reservoir dynamics. [ABSTRACT FROM AUTHOR]

This article presents high‐fidelity observations of the time evolution of unstable delamination growth in tapered composite beams under tensile loading via ultra‐high‐speed camera in conjunction with digital image correlation. Asymmetrically tapered GFRP laminates, with a thickness drop from 18 plies to 12 plies, are manufactured in three different layup configurations with grouped drop‐offs: [06/(02)3/06], [06/06/06], and [06/(±45)3/06]. Beam specimens are subjected to quasi‐static tensile loading in a servo‐hydraulic axial testing machine, and the damage evolution on one edge of the tapered beam is monitored in situ at 124,000 fps with a high‐speed camera (HSC). In selected tests, digital image correlation (DIC) analyses are conducted either on the edge or on the tapered surface to obtain the full‐field strain and elucidate failure mechanisms. Real‐time HSC observations of the damage sequence consistently affirm that the initial failure mechanism is a transverse crack at the nearest drop‐off to the thin section, which is followed by delaminations at interfaces of sublaminates. Unstable delamination growth is characterized by measurements of lower bounds of crack tip speeds. The unique crack speed data provide evidence for the existing effect of through‐the‐thickness stresses on delamination growth. The detailed sequence and patterns of dynamic failure presented in this paper can serve as a benchmark to validate damage models used in simulations of tapered laminates. Highlights: The sequence of unstable delamination growth in tapered GFRP beams is investigated experimentally.Characterized unstable delamination growth based on crack tip speed measurements.Strain fields are evaluated along beam edges using DIC in real‐time.In‐situ observations of dynamic failure can serve as a benchmark to validate damage models. [ABSTRACT FROM AUTHOR]

Using the Split Hopkinson Pressure Bar technique, strain-limited dynamic compressive loading experiments were performed on TA1/TA15 heterostructure (HS) materials. The plastic deformation mechanisms, fracture forms, and energy absorption properties of an HS material with a metallurgical bonding interface (MB) and an HS material without a metallurgical bonding interface (NMB) are compared and analyzed. The results show that there is no significant difference between the two deformation mechanisms. The fracture forms are all "V-shaped" fractures within the TA1 part. The NMB was carried for 57 μs before failure and absorbed 441 J/cm3 of energy. The MB was carried for 72 μs before failure and absorbed 495 J/cm3 of energy. Microstructure observations show that there is a coordinated deformation effect near the MB interface compared to the NMB, with both TA1 and TA15 near the interface carrying stresses. This causes an enhancement of the MB load-bearing time and a 12% increase in energy absorption. [ABSTRACT FROM AUTHOR]

The phase field approach to fracture becomes popular for complicated fracture problems in recent years. However, its widespread application is hindered by its high computational cost. In this article, we propose an efficient parallel explicit‐implicit solution scheme for the phase field approach to dynamic fracture based on a domain decomposition method, specifically, the dual‐primal finite element tearing and interconnecting (FETI‐DP) method. In this scheme, the displacement field is updated by an explicit algorithm in parallel, and the phase field is implicitly solved by the FETI‐DP method. In particular, Lagrange multipliers are introduced to ensure the interface continuity of the phase field. In the computational process, the information exchange among subdomains merely exists in a few substeps, which renders the cost for communication very small. Moreover, the size of equations to be solved is proportional to the total area of subdomain interfaces, which is significantly reduced compared with a typical single‐domain solution procedure. The solution scheme is able to perform phase field simulations with a million of degrees of freedom using only 0.034 core hours per load step, and has flexible extensibility for existing phase field codes. Several numerical examples demonstrate the accuracy and efficiency of the proposed scheme. [ABSTRACT FROM AUTHOR]

Abstract To explore the progressive damage and fracture mechanics characteristics of brittle rock materials under combined dynamic-static loading. Taking account of the coupling effect of the constraint states of uniaxial stress (σ 1 ≥ σ 2 = σ 3 = 0), biaxial stress (σ 1 ≥ σ 2 > σ 3 = 0) and true triaxial stress (σ 1 ≥ σ 2 ≥ σ 3 ≠ 0) and impact load, the strain rate effect and prestress constraint effect of dynamic mechanical characteristics of sandstone are studied. The progressive damage evolution law of sandstone under the coupling of true triaxial stress constraint and cyclic impact load is discussed. The results show that with the increase of axial stress σ 1, the dynamic compressive strength and peak strain gradually decrease, and the strain rate gradually increases, resulting in crushing failure under high strain rate. When the axial stress is fixed, the lateral stress constraint reduces the damage degree of sandstone and improves the dynamic compressive strength. With the increase of strain rate, the sample changes from slight splitting failure to inclined shear failure mode. Under the true triaxial stress constraint, the intermediate principal stress σ 2 obviously enhances the dynamic compressive strength of sandstone. Under the constraints of triaxial stress, biaxial stress and uniaxial stress, the enhancement effect of dynamic compressive strength and the deformation resistance of sandstone are weakened in turn. Under the coupling of true triaxial stress constraint and high strain rate, sandstone samples show obvious progressive damage evolution effect under repeated impacts, and eventually inclined shear failure occurs, resulting in complete loss of bearing capacity.

The paper considers application of artificial neural networks (ANNs) for fast numerical evaluation of a residual impactor velocity for a family of perforated PMMA (Polymethylmethacrylate) targets. The ANN models were trained using sets of numerical results on impact of PMMA plates obtained via dynamic FEM coupled with incubation time fracture criterion. The developed approach makes it possible to evaluate the impact strength of a particular target configuration without complicated FEM calculations which require considerable computational resources. Moreover, it is shown that the ANN models are able to predict results for the configurations which cannot be processed using the developed FEM routine due to numerical instabilities and errors: the trained neural network uses information from successful computations to obtain results for the problematic cases. A simple static problem of a perforated plate deformation is discussed prior to the impact problem and preferable ANN architectures are presented for both problems. Some insight into the perforation pattern optimization using a genetic algorithm coupled with the ANN is also made and optimized perforation patterns which theoretically enhance the target impact strength are constructed.

Crack propagation velocity is a crucial discussion for understanding dynamic fracture. Classical dynamic fracture theory predicts a “forbidden velocity zone” for mode Ⅱ cracks, i.e., the velocity between the Rayleigh and shear wave speeds. However， supershear transition has been demonstrated theoretically and experimentally for mode-Ⅱ crack constrained to weak interfaces. Such transition is commonly accepted to be governed by the Burridge-Andrews mechanism (also known as “mother-daughter” crack), which predicts direct nucleation of a secondary intersonic daughter crack induced at the Rayleigh wave speed. Nevertheless, to our knowledge, “mother-daughter” crack pairs are rarely reported with visual observations, and the supershear rupture without the daughter crack forming has also been found in some previous reports. Recently, Prof. Liangbin Li ’s group at University of Science and Technology of China and the coworkers reported the Sub-Rayleigh to supershear transition of dynamic mode-Ⅱ cracks based on numerical simulations. Their numerical experiments successfully reproduced the “mother-daughter ” cracks for the first time in phase-field fracture modeling, as well as the supershear transition without the daughter crack. Given that, a crack tip blunting-tearing hypothesis was presented to explain that cracks comply with different mechanisms from Sub-Rayleigh to supershear regimes, and a critical prestress level was revealed below which no supershear transition can be accomplished from the Sub-Rayleigh propagation. Furthermore, the criteria were also proposed for predicting the occurrence of the daughter crack through systematic simulations. This paper briefly presents their progress in the studying of the Sub-Rayleigh to supershear transition for dynamic mode-Ⅱ interfacial fracture. [ABSTRACT FROM AUTHOR]

The paper considers application of artificial neural networks (ANNs) for fast numerical evaluation of a residual impactor velocity for a family of perforated PMMA (Polymethylmethacrylate) targets. The ANN models were trained using sets of numerical results on impact of PMMA plates obtained via dynamic FEM coupled with incubation time fracture criterion. The developed approach makes it possible to evaluate the impact strength of a particular target configuration without complicated FEM calculations which require considerable computational resources. Moreover, it is shown that the ANN models are able to predict results for the configurations which cannot be processed using the developed FEM routine due to numerical instabilities and errors: the trained neural network uses information from successful computations to obtain results for the problematic cases. A simple static problem of a perforated plate deformation is discussed prior to the impact problem and preferable ANN architectures are presented for both problems. Some insight into the perforation pattern optimization using a genetic algorithm coupled with the ANN is also made and optimized perforation patterns which theoretically enhance the target impact strength are constructed. [ABSTRACT FROM AUTHOR]

Summary: This study presents an enhancement of the diffusive‐discrete crack transition scheme (10.1002/nme.7169) to describe dynamic fracture at finite strain. In the enhanced scheme, the crack initiation, propagation, and bifurcation processes are determined from an energy minimization problem based on crack phase‐field theory, and the predicted diffusive crack is replaced by the discrete representation using the finite cover method. In the meantime, numerical damping is introduced to maintain computational stability and avoid distortion of the physical mesh in the finite cover context. By taking advantage of the features of the diffusive‐discrete crack transition scheme, the proposed approach enables us to stably simulate a series of dynamic fracture events involving crack initiation at an arbitrary location, propagation, and bifurcation in arbitrary directions, arbitrary divisions of an original object into multiple portions, and independent motions of divided portions. After spatial and temporal discretizations by the finite cover method and the Newmark method are described, as well as the simulation algorithm of the enhanced finite cover‐based staggered iterative procedure for dynamic fracture, several representative numerical examples are presented to demonstrate the performance and capabilities of the developed approach. [ABSTRACT FROM AUTHOR]

AbstractTo study the interaction of moving cracks and pre-cracks of plexiglass (PMMA) under impact loading, a three-point bending experiment was carried out using dynamic caustics experimental system. Research showed that when the offset distance between the pre-crack and the defect is 9 mm, the failure mode of the crack is the most complicated. When the offset distance is 0 mm, the crack experiences the attraction force of the defect, the stress intensity factor and the crack growth speed increase gradually, and the peak value is reached when the defect and the crack intersect. When the offset distance is greater than 6 mm, the attraction effect of the defect on the crack is no longer significant, and the crack propagates toward the drop hammer location until it penetrates the specimen. As the crack propagates, the caustic speckle rotates counterclockwise and is subjected to compression and shear. [ABSTRACT FROM AUTHOR]

This paper presents a 3D spectral numerical scheme that can accurately model planarcracks of any shape residing on an interfacial plane between two elastic solids. The cracks propagate dynamically under the action of interfacial loads and interfacial constitutive laws. The scheme is a spectral form of the boundary integral equations (BIE) that relate the displacement discontinuity fields along the interfacial plane to the stress fields at the plane. In the BIE, the displacement discontinuities are expressed as a spatio‐temporal convolution of the traction components at the interface. This is in contrast with most previous studies which use a spatio‐temporal convolution of the displacement discontinuities or of the displacements at the interface. Due to the continuity of tractions across the interface, the present formulation is simpler, resulting in convolution kernels that can be written in closed‐form. Previous studies have relied on numerically obtained convolution kernels. The accuracy of the proposed scheme is validated with the known analytical solution of the 3D Lamb problem. Furthermore, new algorithms are developed for coupling the BIE with a slip‐weakening friction law, both for homogeneous materials as well as for bi‐material interfaces. This results in a widely applicable formulation for studying spontaneous rupture propagation. The algorithms are validated by comparing rupture simulation exercises to benchmark problems from Southern California Earthquake Center (SCEC). Finally, the methodology is used to simulate 3D frictional rupture propagation along a bi‐material interface. [ABSTRACT FROM AUTHOR]

In this work, the hybrid peridynamic and classical continuum mechanical model based on the element‐type numerical discretization is used to study the dynamic fracture problem of brittle materials. The weak form of the motion equation for the hybrid model is derived by applying Hamilton's principle. An element‐based spatial discretization scheme is set up using the peridynamics‐based finite element method (PeriFEM) (Han and Li). The δ$$ \delta $$‐convergence and m‐convergence of the hybrid model are analyzed to verify the numerical convergence and the mesh dependency. The influence of the area of the peridynamic model subdomain and the hybrid model subdomain on the calculation efficiency and accuracy is discussed. And the relationship between the crack propagation speed and the crack branching phenomenon is also investigated. Good agreements are obtained by comparing the crack path and the crack speed profile predicted by the hybrid model with those in the literature. Numerical results verify the ability and efficiency of the hybrid model for dynamic fracture problem. [ABSTRACT FROM AUTHOR]

Recent experiments in bonded PMMA layers have shown dramatic changes in dynamic crack growth characteristics depending on the interface location and its toughness. We present a peridynamic (PD) analysis of the problem and identify three necessary elements in a model aimed at reproducing the observed dynamic fracture behavior at an interface in PMMA: (1) softening near the crack tip to account for changes in PMMA properties due to heat-generation induced by the high strain rates reached around the crack tip in dynamic fracture, (2) independence of extension (mode I) and shear (mode II) modes of fracture, and (3) a two-parameter bond-failure model, that can match both strength and fracture toughness for any horizon size. The PD model with these elements captures the experimentally observed dynamic fracture characteristics in bi-layer PMMA: the presence/absence of crack branching at the interface, depending on the interface location; cracks running along the interface for a while before punching through the second PMMA layer; slight crack path oscillations as the cracks approach the free surface. The computed crack speed profiles are close to those measured experimentally. The simulations help explain the observed behavior of dynamic crack growth through an interface. The model shows an enlargement of the fracture process zone when the cracks running along the interface penetrate into the second PMMA layer, as observed experimentally. This is where nonlocality of the PD model becomes relevant and critical. [ABSTRACT FROM AUTHOR]

In this work, two non-local approaches to dynamic fracture are investigated: a novel peridynamic formulation and a variational phase-field approach. The chosen continuum-kinematics-based peridynamic model extends the current peridynamic models by introducing surface and volume-based interactions. The phase-field fracture approach optimizes the body's potential energy and provides a reliable method for predicting fracture in finite element computations. Both methods are able to efficiently compute crack propagation even when the cracks have arbitrary or complex patterns. We discuss the relations of critical fracture parameters in the two methods and show that our novel damage model for the continuum-kinematics-based peridynamics effectively manages fracture under dynamic loading conditions. Numerical examples demonstrate a good agreement between both methods in terms of crack propagation, fracture pattern, and in part, critical loading. We also show the limitations of the methods and discuss possible reasons for deviations. [ABSTRACT FROM AUTHOR]

Dynamic brittle facture in materials with many pores/perforations has been shown experimentally to feature complex evolution of crack morphologies that include crack branching, micro-branches that arrest, cracks restarting from pores and branching soon after. Computational models of these problems need to accurately account for the dynamic interactions between strain waves and stress concentration zones induced by the perforated geometry. In this paper, we aim to improve the predictive capabilities of computational simulations of dynamic brittle/quasi-brittle fracture in samples with complex geometries, like perforated plates, by introducing a discretization method using non-uniform grids near a boundary (NB-NUG) for 2D peridynamic fracture modeling. The NB-NUG avoids the steps and the corresponding artificial stress concentrations created in PD models when using uniform grids over domains with curved boundaries. The new method also reduces numerical errors compared with general non-uniform grids used for PD models. We apply the model for dynamic fracture of thin PMMA plates with different arrangements of periodic pores/perforations. The results match the experimental observations for all of the cases considered. Fine features observed in the experiments (multiple cracks branching and cracks that arrest soon after splitting, number of branching events, etc.) are captured by the new approach and not by the other PD models with different types of grids. The results show that the high strain energy density regions created around perforations attract a nearby crack tip, deflecting the crack path, altering its propagation velocity, and promoting crack branching in its wake, thus dissipating more energy. Nonlocality of damage helps here in allowing its unrestricted evolution in problems in which complex crack morphology is sensitive to small changes in the geometrical arrangement of pores in the structure. [ABSTRACT FROM AUTHOR]

The collision of detonation waves is widely used in weapon design due to its ability to efficiently achieve an ultra‐high pressure region. This work discusses the dynamic fracture of metal rods under the collision of cylindrical detonations. In the experiments, the detonation wave collision is generated by detonating an explosive charge at its end position along two parallel initiation lines, which are detonated by a plane wave generator. The recovered metal rods were broken around their centers due to the superposition of detonation waves. A blue oxidation zone appeared at the fracture surfaces of steel rods in the contact zone under the charge, indicating the local existence of high temperatures. A finite element model was used to simulate and describe the dynamic fracture of metal rods caused by detonation wave collision. The three‐shock theory was used to examine the detonation wave collision. When the incidence angle was between 0° and 40°, the reflected shock wave pressure was approximately 2.1 times the CJ pressure. At an incidence angle of 44.84°, the ratio of Mach and CJ pressure reached a maximum of 3.1. The concentration degree of detonation pressure was developed to evaluate the superposition influence on the dynamic fracture of metal rods. The microstructure of fracture surfaces revealed that metal rods preferred shear fracture under high pressure concentration. With a low degree of pressure concentration, a brittle fracture may emerge. This research serves as a guide for designing and evaluating multimode warheads. [ABSTRACT FROM AUTHOR]

Six combinations of layered composite rocks were prepared using sandstone, dali rock, and granite. The composite rock specimens underwent a dynamic impact test using the separated Hopkinson pressure rod test system, and the failure patterns of the specimens were recorded using high-speed cameras. The dynamic fracture mode, wave impedance effect, and energy dissipation nature of these composite rock specimens were analyzed, and the relationship between their kinetic energy and fracture energy was explored. The discrete lattice spring model was used to simulate the dynamic fracture process of the composite rock specimens, and the stress wave propagation characteristics and stress and damage evolution nature of the composite specimens were analyzed. The results show that the dynamic fracture characteristics of composite rock materials are strongly influenced by the uppermost and lowermost layer materials. When the dynamic cracking toughness of the material in the lower layer is low, the crack can maintain a high propagation speed and requires a short time from initiation to expansion to the rock cemented surface. The upper layer material has a greater influence on the stress conduction of the composite rock specimen. The overall transmission capacity depends on the upper layer material such that the greater its density, the more conducive it is to wave transmission and the better the stress conduction. The greater the difference in the densities of the lower and upper layer materials, the greater the difference between the stresses at the upper and lower ends of the rock cemented surface. Wave impedance has a significant effect on the propagation behavior of the stress wave. The propagation speed of the stress wave in the composite specimen is influenced by the porosity and density of the material. The larger the wave impedance, the faster the propagation speed of the stress wave, the larger the transmission coefficient, and the higher the energy transmitted. When energy is dissipated, the density, kinetic energy, and fracture energy of the composite rock specimen are influenced by the densities of the materials in the upper and lower layers. If the lower layer material is unchanged, a higher density of the upper layer material results in a smaller density and fracture energy when the energy is dissipated, yielding more kinetic energy when the specimen is completely fractured. When the upper layer material remains unchanged and the density of the lower material is increased, the cutting tip is more likely to crack, and the density and fracture energy are smaller when the energy is dissipated.

The finite-depth concrete panels have been widely applied in the protective structures, and its impact resistance and dynamic fracture failures, especially the scabbing/perforation limits, under high velocity projectile impact, are mainly concerned by protective engineers, which are numerically studied based on an improved dynamic concrete model in this study. Firstly, based on the framework of the KCC (Karagozian & Case concrete) model, a dynamic concrete model is proposed which considers an independent tensile damage model and a continued transition between dynamic tensile and compressive properties. Secondly, the strength surface, equation of state and damage parameters of the proposed model are comprehensively calibrated by a triaxial compressive test with high confinement pressure, the rationality of which is further verified based on the single element tests, e.g., uniaxial and triaxial compression as well as uniaxial, biaxial and triaxial tension. Thirdly, a series of projectile high velocity impact tests on thin and thick concrete panels are simulated, which indicates that the projectile residual velocity and dynamic fracture failures are reproduced satisfactorily, while the KCC model underestimates both the spalling and scabbing dimensions severely. Finally, based on the validated concrete model and finite element analyses approach, the validations of the existing five empirical formulae are evaluated, in terms of the depth of penetration (DOP) and scabbing/perforation limits of concrete panel. Both the Army corps of engineers (ACE) and modified National Defense Research Committee (NDRC) formulae are recommended in the design of the protective structure to avoid scabbing failure.

In this study, the Johnson–Cook constitutive and failure model parameters of A508-III steel are determined through quasi-static and dynamic tensile and fracture tests. The reliability of model parameters is then verified by dynamic fracture tests at different loading rates. Using the Johnson–Cook model, the dynamic fracture behavior of the SEB specimen of A508-III steel under various loading rates and geometric configurations has been simulated. The effect of loading rate and specimen geometric configuration on the dynamic fracture toughness of A508-III steel is investigated. The results reveal that the critical fracture force and impact absorbed energy increase with the increase of loading rate. The dynamic fracture behavior of deep-cracked specimens is more sensitive to the loading rate than that of shallow-cracked specimens. Moreover, the critical fracture force and impact absorbed energy increase linearly with increasing specimen thickness while the initial crack size remains constant. [ABSTRACT FROM AUTHOR]

Using the Split Hopkinson Pressure Bar technique, strain-limited dynamic compressive loading experiments were performed on TA1/TA15 heterostructure (HS) materials. The plastic deformation mechanisms, fracture forms, and energy absorption properties of an HS material with a metallurgical bonding interface (MB) and an HS material without a metallurgical bonding interface (NMB) are compared and analyzed. The results show that there is no significant difference between the two deformation mechanisms. The fracture forms are all “V-shaped” fractures within the TA1 part. The NMB was carried for 57 μs before failure and absorbed 441 J/cm3 of energy. The MB was carried for 72 μs before failure and absorbed 495 J/cm3 of energy. Microstructure observations show that there is a coordinated deformation effect near the MB interface compared to the NMB, with both TA1 and TA15 near the interface carrying stresses. This causes an enhancement of the MB load-bearing time and a 12% increase in energy absorption.

We propose and assess a new experimental technique to measure the fracture toughness of engineering materials and its sensitivity to strain rate. The proposed method is based on a ring expansion technique and it overcomes the limitations of current dynamic fracture tests, as it is not affected by transient stress wave propagation during loading and it results in spatially uniform remote stress and strain fields prior to fracture; the method is also suitable to achieve remote strain rates well in excess of 1000 s−1. We demonstrate the technique by measuring the plane-stress Mode I fracture toughness of PMMA specimens at remote strain rates ranging from 10−3 s−1 to 102 s−1. The experiments show an increase of the toughness of the material with increasing strain rate.

As a typical failure behavior, the dynamic fracture is critical for material safety assessment and design, whose rapid evolution in the crack tip over a short time causes tremendous challenges in characterizing the evolution of the local temperature field. Although researchers have pointed out that temperature significantly affects fracture toughness, the temperature rise and the role of thermal softening in the crack tip region during the dynamic crack initiation need to be clarified. This work aims to evaluate the temperature rise effect at crack initiation in TC4 (Ti-6Al-4V) alloy under impact loading. We developed a thermal-mechanical coupled in-situ measurement system to obtain synchronized COD (crack-tip opening displacement) and temperature field evolution for the dynamic mode I fracture with high temporal and spatial resolution. The evolution of synchronous COD and temperature field during crack initiation under dynamic loading was investigated. The corresponding simulation was conducted to analyze the thermal softening effect at dynamic crack initiation. In TC4 alloy, the maximum temperature detected at crack initiation is about 130 °C, and the thermal effect on the material property is minor. The results of this work fulfill data support for investigating the coupled thermal-mechanical fracture behavior of metal. [ABSTRACT FROM AUTHOR]

• A DII-integral is established for dynamic fracture analysis of nonhomogeneous MEE media. • The DII-integral is domain-independent for multi-interface MEE composites. • The stiffness and density of MEE layer affect the dynamic IFs significantly for a crack in the PM phase. • The stiffness, density, PE and PM coefficients of MEE layer affect IFs significantly for a crack in PE phase. Magneto-electro-elastic (MEE) materials are composed of piezoelectric (PE) and piezomagnetic (PM) phases, leading to the existence of a large number of interfaces between phases. Complex interface distributions bring a challenge for the dynamic fracture analysis of MEE composites, as the available fracture mechanics approaches usually need to avoid material interfaces. This work establishes a dynamic domain-independent interaction integral (DII-integral) to extract the dynamic intensity factors (IFs) for MEE materials. The DII-integral exhibits apparent superiority over available I-integral methods in the dynamic fracture studies of MEE composites with complicated interfaces due to its domain-independence for interfaces and avoidance of material property derivatives. After verifying the accuracy, the DII-integral method is applied to investigate the dynamic fracture of PE-MEE-PM layered composites. It is found that as the crack tip approaches the MEE middle layer, the dynamic IFs decrease for a crack in PE phase (BaTiO 3) but increase for a crack in PM phase (CoFe 2 O 4). The elastic stiffness, PE coefficient, PM coefficient and dielectric permittivity of MEE middle layer have a significant effect on the dynamic IFs, and the other material parameters have slightly effect. [ABSTRACT FROM AUTHOR]

Behavior of the dynamic fracture of different nanocomposites filled with single- and hybrid-phase nanoparticles, including multilayered graphene nanoplates (GNPs) and functionalized multiwalled carbon nanotubes (CNT@X) treated by a nonionic surfactant was investigated based on 2D Digital Speckle Correlation (DSC) and highspeed camera technologies. In particular, synergistic toughening effects of hybrid CNT@X+GNPs particles with various filler ratios on the fracture toughness of the epoxy matrix, mainly referring to the mode-I stress intensity factors (SIFs), were revealed. An improved mode-I crack initiation toughness KIi, = 3.47 ± 0.14 MPa·m1/2 was found in the case of EP/T@X+G_7/3, which even doubled over the EP/GNPs_1.0 specimen. These results can be attributed to the synergistic toughening mechanism of hybrid CNT@X+GNPs fillers in the epoxy matrix, which generated highly rough fracture surfaces and an extensive shear failure. [ABSTRACT FROM AUTHOR]

A novel explicit phase field material point method (ex‐PFMPM) is proposed for modeling dynamic fracture problems. The rate‐dependent phase field governing equation is discretized by a set of particles, and the phase field is updated by the explicit forward‐difference time integration. Furthermore, the stability of the ex‐PFMPM is studied. A novel explicit critical time step formula is obtained based on the system eigenvalues in one dimension and then extended to two and three dimensions. The critical time step formula takes the effect of particle position and neighboring cell interaction into consideration, and can also be used in an explicit phase field finite element method. Several numerical examples, including a dynamic crack branching, a plate with pre‐existing crack under velocity boundary conditions and a three point bending problem are studied to verify the proposed ex‐PFMPM. The use of the history field in the explicit method is studied, which shows that it will lead to fake phase field update and overestimation of the fracture energy in the unloading case. All of the numerical results show that the proposed ex‐PFMPM has the capacity of modeling the crack initiation and propagation problems with both accuracy and efficiency. [ABSTRACT FROM AUTHOR]

Investigation of fracture mechanics problems with computational tools has always been a great challenge due to singularities present at the crack tip. FRAC3D is an effective finite element tool that benefits from enriched element methodology. The dynamic version of this code enables the analysis of structures with stationary cracks subjected to impact loading. Response of the components in these problems are highly influenced by stress wave propagation phenomenon. In this study, bimaterial interface cracking in an electronic packaging structure is analyzed considering transient behavior. Besides the complications associated with the finite element solution of such a problem, long computational times may also be an issue considering model sizes. Multiprocessing of finite element codes could save significant times if corresponding algorithms are restructured with parallel processing tools in an efficient form. Up to 75 % reductions in time for the given example were obtained by using newly implemented multiprocessing code. [ABSTRACT FROM AUTHOR]

This contribution presents a concept to dynamic fracture with continuum-kinematics-based peridynamics. Continuum-kinematics-based peridynamics is a geometrically exact formulation of peridynamics, which adds surface- or volume-based interactions to the classical peridynamic bonds, thus capturing the finite deformation kinematics correctly. The surfaces and volumes considered for these non-local interactions are constructed using the point families derived from the material points' horizon. For fracture, the classical bond-stretch damage approach is not sufficient in continuum-kinematics-based peridynamics. Therefore it is here extended to the surface- and volume-based interactions by additional failure variables considering the loss of strength in the material points' internal force densities. By numerical examples, it is shown that the presented approach can correctly handle crack growth, impact damage, and spontaneous crack initiation under dynamic loading conditions with large deformations.

This work studied the ductile-brittle transition process of 15MnTi steel under different dynamic loading conditions. The strength of 15MnTi steel increased with strain rate because dislocation movement and element diffusion were inhibited. The fracture mode was different under different loading speeds. When the loading speed was lower than 0.025 m/s, the fracture mode was complete ductile fracture; when the loading speed was 0.1 –0.4 m/s, the fracture mode was ductile-brittle fracture; and when the loading speed was higher than 0.5 m/s, the fracture mode was a brittle fracture. In the three-point bending test, the dynamic brittle fracture rate of 15MnTi steel decreased with increasing crack tip constraint, and the brittle fracture resistance decreased with increasing loading rate. In the Charpy impact test, the fracture mode of the prefabricated crack specimens was a ductile fracture. In addition, when the loading rate was 0.1 m/s, the toughness characteristics were not obvious. The fracture had tear dimples at loading rates ranging from 1 to 3.5 m/s, showing certain ductile fracture characteristics. There were many dislocations in the matrix, and TiC was distributed in the matrix. Plenty of dislocations accumulated around the particles, which improved the strength by hindering the movement of the dislocations. [ABSTRACT FROM AUTHOR]

The paper is devoted to the study of dynamic growth of shear cracks in brittle materials with various degrees of inhomogeneity of the internal structure. The study was carried out by DEM modeling using an advanced model of fracture based on the principles of kinetic theory of strength and taking into account the finite time of local fracture. The complexity of the material internal structure was effectively taken into account by changing the key parameter of the model – the fracture incubation time. It is shown that an increase in the degree of inhomogeneity of the internal structure leads to a decrease in the crack propagation velocity according to a logarithmic law. The key result of the research is the assessment of the size of fracture process zone. It is shown that the size of fracture process zone is not constant, but changes during dynamic crack growth. The nature of its change, as well as the average value, depends on the degree of heterogeneity of the material structure. [ABSTRACT FROM AUTHOR]