Dynamic Breakage Research Articles

Simulation of rice grain breakage process based on Tavares UFRJ model

Understanding the breakage characteristics of rice grains is an important means to reduce rice breakage rate. However, the dynamic breakage mechanism of rice grain is unclear due to the lack of a reasonable breakage model. In this study, the uniaxial compression test and drop weight test of single rice were carried out, the breakage model of rice grain was constructed, the reliability of rice model was verified by the experiment and simulation results. The results showed that the fracture energy distribution of rice can be obtained by uniaxial compression test, the specific fracture energy of rice accords with a lognormal distribution, and the median specific fracture energy of rice is 479.75 J/kg. The damage accumulation coefficient and fragment size distribution of rice can be acquired by drop test, the result of damage accumulation coefficient of rice was 4.3. Rice grain breakage mainly occurs in the milling section of the vertical circulation rice mill.

Modelling dynamic breakage in rock blocks with different elongation and flatness ratios upon impact

AbstractThe two crucial shape factors (elongation ratio and flatness ratio) of brittle particles may influence the dynamic breakage of brittle particles upon impact. Hence, three‐dimensional discrete element method simulations of brittle rock blocks with different shapes upon normal impact were performed. The simulated results indicate that the elongation ratio, that is, ratio of width to length and flatness ratio, that is, ratio of thickness to width can significantly affect the breakage of brittle rock blocks. Three fracture mechanisms, that is, fragmentation, horizontal tensile fracture and vertical tensile fracture, were revealed, which determine the dynamic breakage of rock blocks. The fragmentation results in numerous single‐sphered fragments with velocities even larger than 2 times of the initial velocities. Fragmentation can provide a buffering effect at high impact velocities of larger than 4 m/s. With an increasing elongation ratio or flatness ratio, the phenomenon of fragmentation gradually disappears. The reflection of a compression stress wave results in horizontal tensile fracture. The expansion in the plane perpendicular to the impact velocity results in vertical tensile fracture.

Investigation of breakage behavior and its effects on spray-dried agglomerated whey protein-lactose powders: Effect of protein and lactose contents.

Particle breakage of dairy powders occurs easily during many processes, reducing the powder functionality. The characteristics of particles and the applied stress from processing conditions on the particles are 2 main factors that can be manipulated to reduce breakage. In this study, we explored the effect of whey protein and lactose contents on dynamic breakage in agglomerated whey protein-lactose powders to provide useful information, in terms of particle characteristics, for controlling unwanted dairy powder breakage. A series of model agglomerates with different whey protein:lactose ratios were produced under the same spray-drying conditions, through a pilot plant trial. We evaluated physical characteristics, composition, and structure of samples; analyzed dynamic breakage under different mechanical stresses; and investigated the rehydration and water adsorption properties of model powders before and after breakage. The particle size and irregularity of agglomerates with more lactose was significantly higher than of samples that contained more protein. This resulted in higher particle breakage during dynamic breakage for samples with more lactose. The breakage of agglomerates was affected by the moisture content of powders and fatigue, where particle breakage happens when mechanical loads, lower than the strength of particles, occur multiple times. Breakage changed the morphology and surface composition of particles and decreased particle size. It also decreased the dispersibility of powders and increased the wetting time of wettable samples but decreased the wetting time of powders with poor wettability. Breakage accelerated time-dependent crystallization and decreased the crystallization temperature but did not affect the glass transition temperature of samples. Thus, under the same drying conditions, composition of powders significantly affected breakage, mainly by altering the physical properties of their particles, which resulted in deteriorated functionality.

Mechanical properties and energy response of like rock-sprayed high ductility concrete combined body under smooth and wavy interfaces

• A new method for preparing like rock-SHDC combined body with interface roughness (JRC) of 28. • The static and dynamic mechanical properties and energy response characteristics of like rock-SHDC combined body under different roughness interfaces are studied to improve the research of SHDC in the engineering field and provide a basis for supporting structure design. • In the impact compression test, when the incident wave energy passes through the interface, reflection and transmission will occur. Therefore, the combined body of double-layer media has more reflected energy than SHDC monomer. • When SHDC is applied in engineering, the surrounding rock roughness should not be too large. Under the condition of high ground stress and large deformation surrounding rock (argillaceous siltstone), the green and low-cost sprayed high ductility concrete (SHDC) used in the initial support structure of tunnels and coal mines can effectively solve the problem of insufficient ductility, toughness and crack resistance of ordinary sprayed concrete. The layered double medium composed of SHDC and surrounding rock near the interface as the research object, replacing surrounding rock with similar materials for rapid machining of high roughness interface. Aiming at the four common problems during construction, static compression, notched three-point bending and impact compression tests were carried out. The static and dynamic mechanical properties and energy response of the like rock-SHDC combined body under smooth and wavy interfaces (different roughness) were deeply explored, the crack propagation law of the combined body were analyzed by using DIC technology and failure modes. The results show that like-rock is feasible as the similar material of surrounding rock. Under static test, with the increase of interface roughness, most of the performance parameters will be significantly reduced, and only a few performance parameters increased. In the compression process, the cracks of the combined body under the waviness interface are dispersed and converged. However, only crack convergence occurs under the smooth interface. In the three-point bending process, the crack development direction of different specimens is consistent, but the crack growth position of the combined body under the waviness interface is shifted. Under impact test, with the increase of interface roughness, the peak stress, elastic modulus and absorbed energy decreased significantly, while the peak strain and reflected energy increased. In addition, deflection cracks appeared in the combined body, and cracks dispersed under the smooth interface, while cracks converged under the waviness interface. The combined body’s static and dynamic breakage degree under the waviness interface is more serious than that under the smooth interface. Therefore, the combined body has relatively better working performance (compression and bending) under the smooth interface, when SHDC is applied in engineering, the surrounding rock roughness should not be too large.

Dynamic breakage of double glass spheres chain subjected to impacting loading

Strain energy releasing due to local failure plays an important role in the dynamic breakage of the brittle medium. A series of experiments are conducted based on the Split Hopkinson pressure bar (SHPB) device. Two contact modes, i.e. the rigid contact between two spheres and the elastic contact between the sphere and the impact/support bar, are introduced by using the double sphere chain sample. Two methods, e.g. the Infrared temperature measurement (ITMS) method and the Digital image correlation (DIC) method, are utilized to trace the fracture sequence of the chain samples under impact velocity 5.0–13.0 m/s. The effects of strain energy releasing to the force-displacement curves, the temperature rising process, and the broken products of the chain samples are demonstrated in detail. Releasing of strain energy causes a delayed recompression process, and the delayed time decreases with increasing of impact velocity, which was caused by the formation and releasing of local strain in elastic contact mode. The approaches to evaluate the effects of strain energy releasing are then proposed to analyze the force-displacement curves and the temperature rising process. The elevated temperature is estimated to be a linear relationship to ε˙2/3. It is of great significance for the profound understanding of the failure mechanism of sphere aggregates.

Self-Adaptive Dirhodium Complexes in a Metal-Organic Framework for Synthesis of N-H Aziridines.

Conformational dynamics of active sites in enzymes enable great control over the catalytic process. Herein, we constructed a metal-organic framework with conformationally dynamic active sites (Rh2-ZIF-8). The active sites in Rh2-ZIF-8 were composed of the imidazolate-bridged bimetallic center with a catalytic dirhodium moiety and structural zinc site. Even though the coordination sphere of the dirhodium species was saturated with two circularly arranged esp groups and two axial 2-MeIm ligands, it could still effectively catalyze the direct synthesis of N-H aziridines from olefins with high activity. We found that such a self-adaptive catalytic process was based on the dynamic breakage and reformation of the rhodium-zinc imidazolate bridges. Interestingly, the in situ generated dirhodium site with a unique Rh2(esp)2(2-MeIm)1 configuration was able to exhibit obviously enhanced selectivity compared to homogeneous catalyst Rh2(esp)2. Furthermore, the surrounding zinc imidazolate groups could effectively protect the dirhodium moieties from harsh environments, and this ultimately endowed it with high stability.

Influence of stress state on dynamic breakage of quartz glass spheres subjected to lower velocity impacting

The breakage process of glass spheres under impact loading is very complex due to the transition of two failure mechanisms, i.e. tensile failure and shear failure, with the increase of loading rate. In order to investigate the influences of stress state adjustment on sphere breakage, three kinds of transmission bars, i.e. steel bar, aluminum bar, PMMA bar, and double-sphere specimens are employed by the modified conventional Split Hopkinson Pressure Bar (SHPB) device. These experiments are conducted under lower impact velocity, which evaluated by the critical state of single sphere failure. Larger critical strain and lower critical strain rate for sphere breakage are obtained when replacing the steel transmission bar with the PMMA bar. The failure properties of inner geometric structures by adjusting failure sequences of the double-sphere specimens. Based on the evolution of particle size distributions and local deformation distribution by the Digital Image Correlation (DIC) method, two-stage failure model is obtained. The first stage of sphere breakage results from the diffusion of local Hertz cracks at the contact areas, which mainly caused by local shear failures, and the second stage results mainly from the penetrated oblique cracks along impact direction, which mainly caused by transversal tensile failures. Adjustment of stress and strain fields by these two schemes reveals these intrinsic influences on sphere breakage, and failure law, involving the effects of local strain, local strain gradients, and local strain rates, is preliminarily discussed. Further theoretical analyses are conducted to investigate the movement of the diffusion fronts. It is of significant reference for understanding the dynamic failure mechanism of brittle granular matter.

Investigation of the influence of powder characteristics on the breakage of dairy powders

Dairy powder breakage occurs in many processes and deteriorates powder properties and functionalities. This study investigated the influence of powder and particle characteristics on the dynamic breakage of dairy powders during the dispersion and conveying in a powder venturi feeder to provide information on assessing and reducing powder breakage during production and transportation. Four kinds of dairy powders (fifteen samples) were analysed: lactose crystals, agglomerates, commercial and lab-scale non-agglomerates. During the dispersion and conveying, breakage degree increased with increasing particle size and decreasing particle structural strength. Considering particle structure, the strength of crystals was the highest, followed by the continuum solids, followed by particles with numerous small holes throughout the particle, followed by particles with a small number of randomly distributed internal holes, followed by the hollow sphere particle with a very thin shell. The breakage behaviour of crystals during conveying was different from the other powders due to the difference in particle structures. Besides, the fat in particles might decrease the breakage of powders.

Dynamic Breakage Characteristics of Shale with Different Bedding Angles under the Different Ambient Temperatures

The dynamic mechanical experiments were carried out on shales with the different bedding angles (θ = 0°, 30°, 45°, 60°, 90°) using the 50 mm split Hopkinson pressure bar (SHPB) test system with the thermo-mechanical coupling equipment. Firstly, the dynamic parameter of shales, such as the stress–strain curve, peak stress, peak strain, dynamic elastic modulus, and energy partition were acquired. The failure modes of shale samples were obtained by sorting out the fragments after impact tests. Secondly, the fracture roughness of shale was obtained using the 3D profile scanner. The experimental results revealed that the shale with different bedding angle has different critical temperature, which is based on the relative transition temperature of dynamic mechanical parameters. The dynamic mechanical properties of shale vary greatly before and after the critical temperature. The absorption energy is positively correlated with the crushing degree, the dynamic compressive strength is positively correlated with the fracture roughness, and the failure degree of shale samples is closely related to the temperature. Additionally, the dynamic mechanical properties of the shales with 0° and 90° bedding angles are obviously different from the shales with 30°, 45° and 60° bedding angles. The related findings could provide significant theoretical support for exploitation of shale gas.

Low-velocity impact response and breakage characteristics of hollow brittle particles

Low-velocity impact responses of typical hollow brittle particles (HBPs) were tested with a strain-limited loading technique to investigate the particle breakage characteristics at both macro and particle levels. The quasi-static compressions were also conducted for comparison. Effects of strain rate and particle size distribution on the stress-strain response, particle breakage and macro deformation behaviors were discussed. Results show that the strength, plateau stress and energy dissipation of hollow brittle particles all exhibited significant strain rate sensitivity. The particle size gradations after single-impact compression were obtained through the laser diffraction technique. Quantitative analysis on the fragmentations and the Hardin relative breakage shown that the dynamic breakage ratio and the breakage extent of the hollow particles at the same strain were larger than that under quasi-static compressions. Moreover, it was found that the Hardin relative breakage generated by specific energy dissipation decreased with the strain rate. The reduction of fracture energy dissipation efficiency and the rate-dependent breakage response of particle breakage are the intrinsic reasons for bulk-scale strain rate effects of HBPs. Finally, the macro deformation behaviors of hollow brittle particles were analyzed through digital image correlation (DIC) technique. It was observed that there exists a competition mechanism between the boundary effect and the inertial effect in dominating the compression patterns. The deformation mechanism was sensitive to the loading velocity.

A comprehensive geomechanical method for the assessment of rockburst hazards in underground mining

Rockburst hazard in mining industry all over the world is one of the most severe hazards. It is becoming increasingly common because of the ever-growing depths of mining operations accompanied by the increasing strength of rocks. One of the most difficult issues is to predict this hazard before the mining operations, whether geophysical investigations have been conducted or not. Polish experience in this field shows that in such cases an effective solution can be the geomechanical method. Therefore, extensive studies on rockburst hazard should focus on three main aspects: (1) rock mass and rock (and coal) predisposition to rockburst–laboratory tests and empirical analyses based on lithology, (2) identification of the potential places with stress and elastic energy concentration in the rock mass within the area planned for exploitation, and (3) the assessment of the impact of mining tremors on the surface. This preliminary geomechanical analysis assesses the propensity of the rock mass to dynamic breakage and provides quantitatively the level of rockburst hazard. The paper presents Polish experience in rockburst hazard assessment with the use of geomechanical method, as well as some solutions and examples of such analyses.

Numerical investigation of impact breakage mechanisms of two spherical particles

Recently developed peridynamic (PD) simulations, allowing spontaneous crack nucleation and propagation, have been conducted to investigate the dynamic breakage behavior of impact spherical particles as a function of impact speeds. With the increase of impact speed, the Hertzian cracks, primary meridian cracks, secondary meridian cracks, circumferential cracks, and crack bifurcations are observed. The crack propagation speeds can reach 62% Rayleigh wave speed at impact speed of 20 m/s. Then with the further increase of impact speed, crack bifurcation is observed due to dynamic path instability, leading to the catastrophic failure of impact spheres. The evolution of damage ratio, defined as the ratio of broken bonds to total initial bonds in PD model, agrees with previous results using discrete element method (DEM), validating the current model. Furthermore, the comparison between computed and theoretic contact force is performed along with experimental measurements. The research provides additional insights into breakage mechanisms of particles.

Testing Impact Load Cell Calculations of Material Fracture Toughness and Strength Using 3D-Printed Sandstone

Short impact load cell (SILC) tests provide insight on the dynamic breakage behaviour of rocks. The measured impact force to first fracture of a rock specimen is used to calculate properties such as fracture toughness, tensile strength, and stiffness. To explore the repeatability and performance of the SILC test and verify the underlying assumptions for interpreting the test measurements, a comprehensive SILC testing program was conducted using additively manufactured (3D-printed) sandstone. 3D-printed sandstone specimens with known mechanical properties were used to indirectly determine the mechanical properties of specimens from SILC test measurements with respect to different sizes (from 5 to 12 mm diameter), shapes (sphere, flattened sphere, ellipsoid, and cylinder) and fabric orientations (i.e. angle variation of microstructures relative to the impact or loading direction). Unconfined compressive strength tests were also conducted on twin sets of various sized cylinder-shaped specimens to verify the estimation of compressive strength from the SILC test. Confidence in interpretation of SILC testing results is obtained by excluding the intrinsic material variability. Ultrahigh-speed digital camera was used to observe the fracture mechanism and to verify the force–time profiles against specimen physical response. Well-defined shaped specimens instead of irregular single-particles showed clear peaks corresponding to the force to first fracture on the force–time profiles. The study found that the minimum energy required to fracture the specimen, therefore the specimen strength, was strongly influenced by the shape effect.

Dynamic breakage of porous hexagonal boron nitride ceramics subjected to impact loading

Based on the Split Hopkinson Pressure Bar (SHPB) device, a series of experiments have been conducted to reveal the intrinsic mechanism of dynamic breakage for hexagonal boron nitride ceramics (HBNC) under impact loading at strain rates ranging from 400 s−1 to 1000 s−1. Firstly, high speed camera and the digital image correlation (DIC) method are employed to trace the strain field on specimen surface. Evolution of number density of strain amplitude is found to obey the bimodal (two-peak) Weibull distribution. The first peak (peak 1) and the second peak (peak 2) owe respectively to deformations of the matrix part and the failure part of specimen. Secondly, by using the 4-units HgCdTe infrared detector, the in-situ instantaneous temperatures elevating at three positions on specimen surface are measured. Contributions of two main mechanisms, e.g. the plastic work and the macro fracture energy, to the elevated temperature are distinguished when taking the temperature profiles of strain rate 400 s−1 as reference. Relations of peak 2 to the elevated temperatures induced by the macro fractures (TIF) are then established and analyzed in details. The TIFs show linear relationship to 1/R, where R denotes the characteristic fragment size. The results should be helpful for temperature controlling in powder grinding and medical pill refining.

Numerical simulations of rock blasting damage based on laboratory-scale experiments

In order to study the damage induced by rock blasting, a numerical simulation method based on the Johnson–Holmquist II (JH-2) damage model combined with the arbitrary Lagrangian–Eulerian (ALE) method is proposed. The process of dynamic breakage and damage evolution of Barre granite is reproduced using explicit hydrocode, ANSYS/LS-DYNA, based on the prototype experiments in the laboratory. The results show that both the crack patterns and measured pressures are in agreement with the results from the lab-scale experiments. The attenuation curves of the pressure and particle peak velocity (PPV) along the radial direction are respectively determined, and the corresponding theoretical formulas are summarized together with the most suitable attenuation exponent α. In addition, comparisons of blasting tests separately carried out using the discrete element method-smoothed particle hydrodynamics hybrid method and the ALE/JH-2 method demonstrate similar crack patterns formed both in intact rock disks and jointed rock disks. In the jointed rock disk, the pressure sharply declines when crossing the joint surface, while the PPV close to the joint increases before going across the joint surface, representing the 'weak transmission—strong reflection' effect of the joint surface. Different yield stresses of joint properties are further studied, which indicate that joints with a lower magnitude of yield stress can prevent more transmissions of waves crossing the joint surface. In future studies, the ALE method combined with the JH-2 damage model can be applied to larger-scale rock engineering problems to optimize the blasting design.

Dynamic breakage of glass sphere subjected to impact loading

The dynamic compression responses of four glass spheres with diameters 7.71 mm, 11.90 mm, 17.88 mm, and 24.87 mm are investigated by the modified split Hopkinson pressure bar device (SHPB). Based on the high speed images, the dynamic compression of the spheres can be divided into three stages, e.g. the quasi-elastic deformation stage, the non-linear deformation stage, and the brittle failure stage. The formation and growth of the shadow areas observed at the impact end and the support end in the spheres are the main causes of the catastrophic failure. The movement of the plane-like fronts of the shadow areas is activated and driven by local velocity gradients. Dynamic breakage of the spheres is then analyzed by the particle size distribution, the fractal properties, etc. The results show that there are two main failure mechanisms in the process of sphere breakage, e.g. the tensile failure mechanism and the shear failure mechanism. In order to investigate the transition of these two failure modes, a bimodal Weibull distribution model is preliminarily established on the Weibull statistical strength. The model shows both good simulations to the experimental data and obvious the transition process of two failure mechanisms. The scaling laws and the strain rate effects of breakage strength are then discussed. The results are helpful for the controlling of pulverization for brittle particles.

Numerical Study of Fracture Process on Full-Scale Concrete Foundations by Means of Controlled Blast Method Utilizing Galvanized Steel Charge Holders

Mechanical breakage systems are generally employed to demolish a portion of a concrete building, however it is time consuming and costly. And the mechanical demolition work involves various risks such as those associated with occupational safety and presents a noise hazard to the general public living in the vicinity. Therefore, alternative methods for such work have been sought. For this purpose, a dynamic breakage system utilizing diamond-shaped charge holders was proposed to rapidly remove the desired portion of the concrete foundation. The charge holders which initiate crack growth were placed inside a concrete mass along the desired fracture plane. In this study, full-scale blast experiments utilizing the charge holders were introduced and the roughness of fracture planes was observed using a 3-dimensional photography system. In order to verify the effect of the charge holders on fracture controlling in full-scale blast experiments, the fracture processes of the concrete blocks were analyzed using the dynamic fracture process analysis (DFPA) code. The mechanism required to achieve controlled breakage was discussed after taking into account the influence of various loading conditions and crack tip velocity. It was found that the DFPA tool is a useful instrument in the analysis of full scale blast experiments.

Microstructure and deformation behavior of Ti-10V-2Fe-3Al alloy during hot forming process

The microstructure evolution and formability of Ti-10V-2Fe-3Al alloy related to the initial microstructures and processing variables were investigated during hot forming process. The experimental results show that the α-phase growth is controlled by solute diffusion during the heat treatment processes. Four different microstructures were established by combinations of several heat treatments, and Ti-10V-2Fe-3Al alloy shows excellent formability both above and below the β transus temperature. The alloy possesses low deformation resistance and active restoration mechanism during the deformation. A constitutive equation describing the hot deformation behavior of Ti-10V-2Fe-3Al alloy was obtained. Higher flow stress was observed for the acicular morphology of α phase in microstructures with large aspect ratios as compared with that of small aspect ratios. Due to the dynamic recovery in soft β phase, and the dynamic recrystallization and breakage of acicular α-phase, flow softening occurred significantly during deformation. Dynamic recrystallization also occurred especially in the severely deformed regions of forged parts.

The role of contact friction in the dynamic breakage behavior of granular materials

Based on the discrete element method, a multi-scale model is employed to investigate the role of contact friction in the dynamic compression responses of brittle granular materials. Four numerical granular samples with different particle friction coefficients ranging from 0.0 to 2.0 are tested and the particle breakage extent is quantified with the Einav breakage index. It is observed that the relationship of the breakage extent with the axial stress is apparently non-monotonic concerning the particle friction coefficient. At the same stress level, the breakage extent exhibits a minimum when the particle friction coefficient is around 0.1 but increases significantly with the particle friction coefficient to both sides. The micro physical origin of this non-monotonic behavior is a distinct transition in dominant particle-breakage modes from tension to shear. Moreover, energy analyses also show non-monotonic evolution of the frictional and damping dissipation with the particle friction coefficient. The joint effect of these two dissipation terms contributes to the non-monotonic behavior of particle breakage. In addition, the accuracy and competence of two frequently-used micro quantities, fraction of sliding contacts and average coordination number, are discussed.

Influence of particle breakage on the dynamic compression responses of brittle granular materials

The dynamic compression responses of dry quartz sand are tested with a modified spilt Hopkinson pressure bar (MSHPB), and the quasi-static compression responses are tested for comparison with a material testing system. In the experiments, the axial stress–strain responses and the confining pressure of the jacket are both measured. Comparison of the dynamic and the quasi-static axial stress–strain curves indicate that dry quartz sand exhibits obvious strain-rate effects. The grain size distributions of the samples after dynamic and quasi-static loading are obtained with the laser diffractometry technique to interpret the rate effects. Quantitative analyses of the grain size distributions show that at the same stress level, the particle breakage extent under quasi-static loading is larger than that under dynamic loading. Moreover, the experimental and the theoretical relationships of the particle breakage extent versus the plastic work show that the energy efficiency in particle breakage is higher under quasi-static loading, which is the intrinsic cause of the strain-rate effects of brittle granular materials. Using the discrete element method (DEM), the energy distributions in the brittle granular material under confined compression are discussed. It is observed that the input work is mainly transformed into the frictional dissipation, and the frictional dissipation under dynamic loading is higher than that under quasi-static loading corresponding to the same breakage extent. The reason is that more fragmentation debris is produced during dynamic breakage of single grains, which promotes particle rearrangement and the corresponding frictional dissipation significantly.