Dynamic Fragmentation Research Articles

On the Dynamic Fragmentation and Lubrication of Coseismic Landslides

AbstractThe three‐dimensional discrete element method has been employed to analyze the dynamic fragmentation and lubrication mechanisms of coseismic Tangjiashan landslide induced by the 2008 Ms 8.0 Wenchuan earthquake. The numerical results show that the internal rock damage occurs and propagates gradually along the basal failure plane due to seismic shaking. At the peak seismic shaking, a sudden increase of tensile and shear stresses can lead to the complete breakage of basal bonds. This is associated with a sudden relief of overburden stress and rapid decrease of basal stress ratio. Thus, the slope fails as a whole and moves quickly downslope. In this process, several large transversal cracks develop at the middle and upper rear regions, disintegrating the slope mass into several large blocks. During landslide propagation, the thickness of basal fragmented layer increases progressively due to intense shearing, and the basal stress ratio reduces accordingly from 0.68 to 0.28. The reduction of landslide basal stress ratio occurs when the strong basal resistance is overcome by seismic‐ and gravity‐induced shear forces together with intense particle rearrangements. It can be quantified by vibrational and rotational granular temperatures of the basal shear layer, with the peak values of 35.2 and 11.6 m2/s2, respectively. The widespread internal slope fragmentation and subsequent lubrication have been identified as the key mechanisms governing landslide motion, which appear to be the intrinsic features of landslide irrespective of its triggering mechanism. The seismic shaking is more relevant to the detachment than to the spreading of landslide mass.

Unsupported shock wave induced dynamic fragmentation of matrix in lead with surface grooves

The material damage and fragments features under certain shock waveform are of great significance in the shock compression phenomena. Herein, molecular dynamics simulations were performed to investigate the dynamic fragmentation process under unsupported shock of bulk Pb with sinusoidal surface grooves and the corresponding clusters distribution during the disintegration. Significant subsurface damage was observed when compared with the typical spike-bubble structure under supported shocks. Due to periodic surface grooves, the superposition of the intrinsic decaying shock wave and the reflected waves resulted in the generation of strong tension stress beneath free surface. Consequently, accompanying the evolution of micro-jets, the subsurface area Pb experienced multiple fracture processes, characterized by the lateral stretching damage and the formation of slugs. In the following process, the slugs fragmented in a similar way as the jets, with the volume distribution of clusters changing from power law to exponential function. Thus, the relationship of characteristic volume from steady-state clusters between jets and slugs could be predicted by their strain rate difference based on the Grady’s energy principle.

Fragmentation-based dynamic size effect of layered roller compacted concrete (RCC) under impact loadings

For further investigating the dynamic size effect of roller compacted concrete (RCC), this paper focuses on the concrete fragmentation under impact loadings, which compensates the one-sidedness of pure strength and deformation analysis. 101 RCC specimens with different size have been prepared and tested under impact loadings. Then, more comprehensive understandings on size-dependence and strain-rate sensitivity of dynamic behaviors for RCC can be obtained in terms of failure process, fragment size distribution, and fractal characteristics. The experimental results indicate that the dynamic fragmentation process is highly related to the multiaxial stress state in the specimens. The fragment size distribution can be used to depicture the dynamic behaviors of RCC, indicating the tight correlation among crack propagation, energy dissipation and failure strength. The suggested exponential growth models, interpreting dynamic compressive strength and toughness with fractal dimension, provide an effective way to evaluate the dynamic behaviors of RCC based on the fragment size distribution.

Axial distribution of fragments from the dynamic explosion fragmentation of metal shells

The investigation of the fragmentation properties along the axis of a metal shell under explosive loading is valuable for understanding the fragment formation principles of a warhead. To investigate the axial fragmentation distribution of a metal shell, herein the fragmentation from different axial positions of a metal shell under single-end detonation conditions was analyzed based on the microelement method. Moreover, a corresponding simplified model for the average fragment mass was established. The fragment distribution characteristics at different axial positions and the internal features from the metal shell fragmentation was analyzed by designing an experiment for fragment segmented recovery and fragment perforation occurring in the fragmentation of a 1045 metal steel cylinder shell filled internally with 8701 high explosives. The similarity between the fragment perforation contour and the projected contour of fragments was applied to verify the accuracy of the simplified model of the fragmentation along the axial direction, which can provide an important reference for the design of warheads and the performance of protective architecture.

Physical Origin of the Fine-Particle Problem in Blasting Fragmentation

Reducing the amount of fine particles (fines) in dynamic brittle fragmentation is important within the mining industry, to save energy and reduce environmental hazard. Blasting-round design to achieve this has been held back by a lack of understanding of the fundamental physics, and by the technical complexity of blasting-process measurements. The authors use numerical simulations and experimental data to study the physical origin of fines generated in civil-engineering blasts. Surprisingly, the fragments can be classified according to universal mechanisms. This insight has the potential to generate innovative engineering solutions that may save resources and protect the environment.

Workflow scheduling applying adaptable and dynamic fragmentation (WSADF) based on runtime conditions in cloud computing

Workflows are a set of tasks and the dependency among them, which are divided into scientific and business categories. To avoid problems of centralized execution of workflows, they are broken into segments that is known as fragmentation. To fragment the workflow, it is highly important to consider the dependency among tasks and runtime conditions. The cooperation between the scheduler and fragmentor must be such that the latter generates appropriate tasks with optimized communication cost, delay time, response time, and throughput. To this end, in the present study, a framework is proposed for scheduling and fragmentation of tasks in scientific workflows that are conducted in fragmentation and scheduling phases. In the fragmentation phase, the fragments are generated with regard to the number of virtual machines available during runtime. In the scheduling phase, the virtual machines are selected with the aim of reducing bandwidth usage. The experiments are performed with three Configurations during both phases of fragmentation and scheduling. Response time, throughput, and cost (BW and RAM) were improved compared to the baseline studies on Sipht, Inspiral, Epigenomics, Montage, and CyberShake workflows as datasets.

Dynamic fragmentation and spheroidization of α phase grains during hot deformation of Ti-6Al-4V alloy

AbstractDevelopment of mechanical properties of titanium alloys is usually achieved by the control of their microstructure (globular, lamellar, bimodal). Dynamic fragmentation and spheroidization of elongated α phase grains, formed from martensite laths, in the microstructure of Ti-6Al-4V alloy are considered in the paper. The effects of α phase grain spheroidization was evaluated in tensile tests over a temperature range of 800–900°C and strain rate range of 10−3–10−2s−1. Completed spheroidization of elongated α phase grains and subsequent growth of equiaxed grains for all deformation modes were found. A low value of apparent activation energy for deformation was calculated – suggesting grain boundary sliding was the main deformation mechanism. The results showed good correlation with the kinetic rate equation based on the Zener–Hollomon parameter.

Inelastic deformation micromechanism and modified fragmentation model for silicon carbide under dynamic compression

The underlying micromechanism remains to be clarified for the bulk inelastic behaviour of specific ceramics under impact loads. In this study, the silicon carbide materials were subjected to the split-Hopkinson pressure bar compression in which the strain rate was not constant but increased to the dynamic level at high stresses. The inelastic deformation occurs in the high strain rate stage in compression, followed by the final transgranular fracture. The post-test fragments were examined in both the SEM and high resolution TEM. It was found that macroscopic inelastic behaviour is dominated by the dislocation motion and the localised amorphisation that arise at high strain rates. The damage and thus the degraded modulus in the dynamic inelastic deformation were incorporated to modify a dynamic fragmentation model to evaluate the fragment size as a function of strain rates. The modified model more accurately predicts the size of fragments produced at high strain rates.

Dynamic fragmentation of rock material: Characteristic size, fragment distribution and pulverization law

In this study, the dynamic fragmentation of granites at strain rates of 40–150/s is explored by using SHPB apparatus. Two mechanical classes (i.e. class I and class II) are observed from the stress vs. strain curves in high strain rate loading and the transition strain rate separated the two regimes is about 80/s. The samples are pervasively shattered when the strain rate exceeds the transition threshold and the dissipated energy density is as high as 2.0 J/cm3. Fragment size/mass distributions are quantified using image processing technique and Weibull distribution, which provide better agreements with experimental results. Then a novel energy-based fragmentation model for describing the cylindrical samples compacted by single direction impact is proposed to reasonably predict the characteristic fragment size. The compression kinetic energy item explains the catastrophic fracturing, which is a result of multi-dimensional breakage at high strain rate. The class I loading, described as 'strain energy controlled regime', produces larger-size, less-number debris and behaved as strain rate independent. The class II loading is kinetic energy controlled which results in pulverized debris and rate dependent failure strength.

Selective binding of facial features reveals dynamic expression fragments

The temporal correspondence between two arbitrarily chosen pairs of alternating features can generally be reported for rates up to 3–4 Hz. This limit is however surpassed for specialised visual mechanisms that encode conjunctions of features. Here we show that this 3–4 Hz limit is exceeded for eye gaze and eyebrow pairing, but not for eye gaze and mouth pairing, suggesting combined eye and eyebrow motion constitutes a dynamic expression fragment; a building block of superordinate facial actions.

Two combination stages of clustered One-Class Classifiers for writer identification from text fragments

Writer identification based on handwritten fragments has been reported to give interesting performance. However, while the fragmentation process, inconsistent fragments are generated and affect badly the identification accuracy. Hence, in this paper, a clustered-based One-Class Classifier (OCC) is proposed in order to generate more robust classification model than the distance-based classifier for handwritten fragments. Besides, the problem of inconsistent fragments expands its effect to the test step. Thus, a Dynamic Fragment Weighting Combination (DFWC) rule is proposed to reduce the effect of inconsistent test fragments. Furthermore, due to the difficulty of performing a generic descriptor, three different descriptors related systems are designed and combined through an effective combination scheme based on Choquet fuzzy integral operator. Experimental results conducted on the well-known IFN/ENIT and IAM datasets show good adaptation of the OCC with DFWC. Moreover, the Choquet combination scheme offers more improvements to achieve 97.56% and 94.51% for the used datasets, respectively. The obtained results highlight the reliability of the proposed system in comparison with recent studies for writer identification issue.

Dynamic Fragmentation of Jointed Rock Blocks During Rockslide‐Avalanches: Insights From Discrete Element Analyses

AbstractThe dynamic fragmentation of jointed rock blocks during rockslide avalanches has been investigated by discrete element method simulations for a multiple arrangement of a rock block sliding over a simple slope geometry. The rock blocks are released along an inclined sliding plane and subsequently collide onto a flat horizontal plane at a sharp kink point. The contact force chains generated by the impact appear initially at the bottom frontal corner of the rock block and then propagate radially upward to the top rear part of the block. The jointed rock blocks exhibit evident contact force concentration and discontinuity of force wave propagation near the joint, associating with high energy dissipation of granular dynamics. The corresponding force wave propagation velocity can be less than 200 m/s, which is much smaller than that of an intact rock (1,316 m/s). The concentration of contact forces at the bottom leads to high rock fragmentation intensity and momentum boosts, facilitating the spreading of many fine fragments to the distal ends. However, the upper rock block exhibits very low rock fragmentation intensity but high energy dissipation due to intensive friction and damping, resulting in the deposition of large fragments near the slope toe. The size and shape of large fragments are closely related to the orientation and distribution of the block joints. The cumulative fragment size distribution can be well fitted by the Weibull's distribution function, with very gentle and steep curvatures at the fine and coarse size ranges, respectively. The numerical results of fragment size distribution can match well some experimental and field observations.

Microstructure influence on the fragmentation properties of dense silicon carbides under impact

The impact response of silicon carbide ceramics is a key issue due to the fact that they are increasingly used in lightweight armor solutions. In the present work, four silicon carbides with different microstructural properties are obtained by varying the sintering process (pressureless or spark plasma sintering in liquid or solid state). The dynamic fragmentation activated due to impact is investigated through three specific experiments: Edge-on Impact experiments are conducted in open, and sarcophagus configurations. Additionally, normal impact tests are performed with a sandwich configuration. The damage growth is observed with an ultra-high speed camera (open configuration), and the failure pattern and crack density are analysed by means of post-mortem observations of the recovered specimens after impact, or through an analysis of the fragment-size distribution (sarcophagus and sandwich configurations). The tests highlight the major role of the microstructure on the fragmentation process. The influence of microstructure is examined based on a closed-form analytical solution resting on the Denoual–Forquin–Hild (DFH) damage model. This micromechanical model predicts the fragmentation characteristics of ceramics based on a statistical description of the flaw population. A good correlation between the model predictions and experimental data confirms that the impact response of a ceramic is primarily determined by the flaw population disseminated in its microstructure.

Some issues for blast from a structural reactive material solid

Structural reactive material (SRM) is consolidated from a mixture of micro- or nanometric reactive metals and metal compounds to the mixture theoretical maximum density. An SRM can thus possess a higher energy density, relying on various exothermic reactions, and higher mechanical strength and heat resistance than that of conventional CHNO explosives. Progress in SRM solid studies is reviewed specifically as an energy source for air blast through the reaction of fine SRM fragments under explosive loading. This includes a baseline SRM solid explosion characterization, material properties of an SRM solid, and its dynamic fine fragmentation mechanisms and fragment reaction mechanisms. The overview is portrayed mainly from the author’s own experimental studies combined with theoretical and numerical explanation. These advances have laid down some fundamentals for the next stage of developments.

Dynamic Scaling of Exosome Sizes.

A model is proposed for characterizing exosome size distributions based on dynamic scaling of domain growth on the limiting membrane of multivesicular bodies in the established exosome biogenesis pathway. The scaling exponent in this model captures the asymmetry of exosome size distributions, which are notably right-skewed to larger vesicles, independent of the minimum detectable vesicle size. Analyses of exosome size distributions obtained by cryogenic transmission electron microscopy imaging and nanoparticle tracking show, respectively, that the scaling exponent is sensitive to the state of the cell source for exosomes in cell culture supernatants and can distinguish exosome size distributions in serum samples taken from cancer patients relative to those from healthy donors. Finally, we comment on mechanistic differences between our dynamic scaling model and random fragmentation models used to describe size distributions of synthetic vesicles.

PDV-based estimation of ejecta particles' mass-velocity function from shock-loaded tin experiment.

A metallic tin plate with a given surface finish of wavelength λ ≃ 60 μm and amplitude h ≃ 8 μm is explosively driven by an electro-detonator with a shock-induced breakout pressure PSB = 28 GPa (unsupported). The resulting dynamic fragmentation process, the so-called "micro-jetting," is the creation of high-speed jets of matter moving faster than the bulk metallic surface. Hydrodynamic instabilities result in the fragmentation of these jets into micron-sized metallic particles constituting a self-expanding cloud of droplets, whose areal mass, velocity, and particle size distributions are unknown. Lithium-niobate-piezoelectric sensor measured areal mass and Photonic Doppler Velocimetry (PDV) was used to get a time-velocity spectrogram of the cloud. In this article, we present both experimental mass and velocity results and we relate the integrated areal mass of the cloud to the PDV power spectral density with the assumption of a power law particle size distribution. Two models of PDV spectrograms are described. The first one accounts for the speckle statistics of the spectrum and the second one describes an average spectrum for which speckle fluctuations are removed. Finally, the second model is used for a maximum likelihood estimation of the cloud's parameters from PDV data. The estimated integrated areal mass from PDV data is found to agree well with piezoelectric results. We highlight the relevance of analyzing PDV data and correlating different diagnostics to retrieve the physical properties of ejecta particles.

Path-dependent institutional change to collective land rights: The collective entrenched in urbanizing Guangzhou

ABSTRACTEconomic reform brings about socioeconomic and organizational changes, which give rise to institutional change as a result. Collective land rights are undergoing continuing institutional change in the context of dynamic, bottom-up, rural change and consequent problematic spatial fragmentation, ecological deterioration, exclusiveness of migrants, and land underutilization in the Pearl River Delta region. The implementation of the Renewal and Refurbishment Program in Panyu, a district in Guangzhou, reveals that the collective land use right, owned by the villages, has constituted an effective holding power to bargain for institutional change to the collective land rights in favor of the rural collective. As a result, path-dependent institutional change to the collective land rights leads to the collective entrenched in the urbanizing metropolis.

A closed form, energy-based theory of dynamic fragmentation

A statistical fragmentation model is presented, which predicts the average size and distribution in sizes of fragments emanating from an explosively driven, naturally fragmenting cylinder. The model builds on the energy-based fracture model of [Kipp and Grady, J. Mechanical Phys. Solids 33, 399 (1985)] by closing the calculation of average fragment size with the introduction of a crack velocity, which determines the time required for a newly initiated fracture to proceed to completion. Fracture energy is accounted for in the solution, resulting in a bimodal distribution function. Calculations are presented in comparison to experimental data for explosively driven metal sleeves and impact fragmentation. From comparison to existing fragmentation models and test data, we demonstrate the feasibility of the proposed approach.

Research on the volume and line fractal dimension of fragments from the dynamic explosion fragmentation of metal shells

The shape features and size distribution of fragments produced by metal shells under explosion loading have great significance for studies on weapons, industrial structures, and aircraft technology. However, it is unclear how best to describe the morphological characteristics and mass distribution of fragments, or whether a similar quantitative relationship exists between each fragment. Therefore, this paper reports the fragment characteristics and internal features of the fragmentation of metal shells under instantaneous explosion loading. An experiment was designed to measure the fragmentation and perforation of a steel cylinder shell filled with high explosives. Using fractal mathematical models, expressions for the volume and line fractal dimensions of the fragments are obtained. The volume fractal dimension, which is used to describe the mass or size distribution of the fragments, and the line fractal dimension, which is used to describe the projected contour of fragments or fragment perforations, were measured using a MATLAB mathematical model. The results reveal that the characteristic mass distribution and morphology of the fragments are statistically self-similar and can be characterized by the fractal dimension. The Gauss–Newton iterative method for the Rosin–Rammler distribution is superior to the existing fitting method, and the resulting volume and line fractal dimensions satisfy the relationship D3 + 2D1 = 5.

Energy dissipation from two-glass-bead chains under impact

The mechanisms of energy dissipation during the dynamic fracture and fragmentation of granular materials play a significant role in controlling the evolution of geological structures, enhancing the efficiency of industrial comminution and blasting, and reducing the geoenvironmental hazards. In this research, impact tests on two-glass-bead chains accompanied by micro-CT of crushed fragments are performed. The results reveal that only a small portion of the input stress wave energy is dissipated through the fragmentation of the two-bead-chain system and that the energy dissipation efficiency increases with increasing input energy. It is found that generally the glass bead at the back of the chain always experiences more damage regardless of the input stress wave energy level. The micro-CT results show that the fracture energy only accounts for a small portion (0.3%–1.4%) of the chain system absorbed energy. Such a low conversion rate is attributed to the underestimated surface area of the micro-cracks, caused by the finite resolution of the micro-CT. By pursuing a fractal dimension analysis, designed to account for the undetected micro-crack surface area, it is estimated that the energy conversion rate could be increased to 0.7%–5.1%. It appears that friction dissipation appears to always be predominant, in particular during severe fragmentation.