Fragmentation in oblique impaction for nanoparticle-agglomerates with different structures

Impact fragmentation can be used to disperse nanoparticle-agglomerates. While the fragmentation of openly structured (fractal dimension D_f?<?2) agglomerates during perpendicular impaction was the subject of several investigations, the fragmentation during oblique impaction is not experimentally investigated so far. During oblique impaction a tangential velocity component acts on the agglomerates leading to an increased fragmentation for the investigated agglomerate structures (with D_f?=?1.6, 1.8, 2.3, 2.6 and 3.0). For the agglomerates with D_f?=?1.6. 1.8, 2.3 and 2.6 the degree of fragmentation can be described with the Weibull-statistics using the tangential impact velocity. This shows that the fragmentation during oblique impaction is determined by the tangential velocity component. The reason for the differing behavior of spherical agglomerates could not be elucidated but it is hypothesized, that a transition from sliding to rolling during the impact occurs affecting the fragmentation behavior.The breakage pattern is obtained by analyzing the fragment size distribution as a function of the impact energy. For agglomerates with fractal dimensions of D_f?=?1.6, 1.8, 2.3 and 2.6 a broad size distribution is observed containing small clusters/primary particles, bigger fragments and intact agglomerates at low impact energies. Increasing the impact energy shifts the whole fragment size distribution to smaller sizes. A nearly total disintegration at high impact energies is reached. The spherical agglomerates fracture into nearly equal sized fragments resulting in a narrower size distribution, which is shifted to smaller sizes at higher impact energies.     

Correlating common breakage modes with impact breakage and ball milling of cement clinker and chromite

Understanding the mechanisms of the breakage of ore particles is important to predict the particle size distribution in size reduction operations. This paper aims to show the presence of common breakage modes in impact breakage and ball milling of the cement clinker and chromite samples. For that purpose, narrow size fractions of the two samples were broken in a drop-weight tester or ball mill by changing the degree of applied energy. Then the resultant size distributions were evaluated to seek evidence for the common breakage modes. The results showed that increasing the breakage energy will produce a systematic change in the shapes of the size distributions, suggesting a sequential set of breakage modes. The breakage is initially due to tensile stresses at low breakage energies and compressive stresses at high breakage energies. Further studies should be done to assess if these breakage modes occur at size-reduction of different ores.     

Breakage Probability of Granules by Repeated Stressing

The breakage behavior of γ‐Al₂O₃ granules was investigated by repeated stressing with double impact and compression test. Regarding to the stressing point of particle surface, the experiment was established in two treatment conditions – fixed and rotated treatment. In the case of double impact test a hardening factor was introduced into the breakage probability model. The result described the breakage probability for both fixed and rotated granules during repeated stressing.     

Predicting breakage behavior and particle size of bronze and cast iron machining chips pulverized by jet milling

It has been proposed that the breakage behavior of particulate materials can be described by two material parameters f_mat and W_min. f_mat describes the resistance of the material to fracture in impact pulverization and W_min characterizes the specific energy which a particle can absorb without fracture. It is shown in this study that this concept can be used to quantify breakage behavior of bronze and cast iron chips in jet milling process and also to predict particle size of the jet milled product. Different tin bronze and cast iron chips with varying initial size were pulverized in a target plate jet mill with different velocity. f_mat was found to be in the range of 0.06–0.09 and 0.18–0.25 for bronze and cast iron alloys, respectively. For the cast iron alloys f_mat increased with increasing content of carbon and silicon. Similarly, for the bronze alloys, f_mat increased with increasing tin content. An equation was developed to predict mean particle size of the jet milled chips as a function of the kinetic energy, initial chip size and material parameters. The experimental results of various alloys confirmed that the mean particle size after single and multiple impacts were accurately predicted.     

Estimating energy in grinding using DEM modelling

The latest state of the art on Discrete Element Method (DEM) and the increased computational power are capable of incorporating and resolving complex physics in comminution devices such as tumbling mills. A full 3D simulation providing a comprehensive prediction of bulk particle dynamics in a grinding mill is now possible using the latest DEM software tools.This paper explores the breakage environment in mills using DEM techniques, and how these techniques may be expanded to provide more useful data for mill and comminution device modelling. A campaign of DEM simulations were performed by varying the mill size and charge particle size distribution to explore and understand the breakage environment in mills using DEM techniques. Analysis of each mill was conducted through consideration of the total energy dissipation and the nature of the collision environment that leads to comminution.The DEM simulations show that the mill charge particle size distribution has a strong influence on the mill input power and on the way the energy is distributed across the charge. The smaller particles experience higher energies while the larger experience less, but this variation is strongly dependent on the mill size. The results also showed that the average particle collision energy increases with increasing mill size, whereas its distribution over particle size is strongly influenced by the mill content particle size distribution. The simulations also captured the energy distribution within different regions of the tumbling charge, with the toe impact region having higher impact energies and the bulk shear region having higher tangential energies. Regardless of the mill size most of the energy is consumed by the particles in the mid-size range, which has the highest percentage mass of the total charge distribution.     

Particle breakage evolution of coral sand using triaxial compression tests

Particle breakage continuously changes the grading of granular materials and has a significant effect on their mechanical behaviors.Revealing the evolution pattern of particle breakage is valuable for development and validation of constitutive models for crushable materials.A series of parallel triaxial compression tests along the same loading paths but stopped at different axial strains were conducted on two coral sands with different particle sizes under drained and undrained conditions.The tested specimens were carefully sieved to investigate the intermediate accumulation of particle breakage during the loading process.The test results showed that under both drained and undrained conditions,particle breakage increases continuously with increasing axial strain but exhibits different accumulating patterns,and higher confining pressures lead to greater particle breakage.Based on the test results,the correlations between particle breakage and the stress state as well as the input energy were examined.The results demonstrated that either the stress state or input energy alone is inadequate for describing the intermediate process of particle breakage evolution.Then,based on experimental observation,a path-dependent model was proposed for particle breakage evolution,which was formulated in an incremental form and reasonably considers the effects of the past breakage history and current stress state on the breakage rate.The path-dependent model successfully reproduced the development of particle breakage during undrained triaxial compression using the parameters calibrated from the drained tests,preliminarily demonstrating its effectiveness for different stress paths.     

Analysis of stresses and breakage of crystalline silicon wafers during handling and transport

A significant challenge in using thinner and larger crystalline silicon wafers for solar cell manufacture is the reduced yield due to higher wafer breakage rates. At a given process step, wafer/cell breakage depends on the stresses produced in the wafer/cell due to prior processing, handling and/or transport and on the presence of structural defects such as cracks. Specifically, analysis of wafer breakage requires knowledge of the total in-plane stress state produced in the wafer due to handling and residual stresses from prior processing. This paper presents a systematic approach to breakage analysis of crystalline silicon wafers during handling via analysis of the total stress state produced in the wafer. The total stress state is determined using a combination of wafer deformation measurements and non-linear finite element analysis. Knowledge of the total stress state in conjunction with the crack size and location enables the determination of wafer breakage and the associated fracture stress. This approach is experimentally validated through breakage tests performed on edge-defined film-fed growth (EFG) wafers with cracks introduced via indentation. The results show that the wafer breakage stress during handling is proportional to the inverse of the square root of the crack length, which is consistent with the linear elastic fracture mechanics theory. The work also confirms the capability of the proposed approach to determine the handling conditions under which wafer/cell breakage will occur.     

刀具破损状态的特征提取及自动识别

文章采用机床功率法和声发射法对车削过程中的刀具破损进行监控。在试验中发现了刀具破损时机床功率信号的四种表现形式,说明了刀具破损形式的随机性。针对这种情况,首次提出了功率信号处理的延时方差法;对切削过程中发出的各种声发射（AE）信号采用时频分析进行处理并提取出反映刀具破损的特征量,最后利用神经网络ART2实现了刀具破损状态的自动识别。     

High-shear granulation: An investigation into granule breakage rates

Granule breakage is an important rate process in wet granulation that promotes product uniformity and controls product size and strength. In this work, a model to predict granule breakage is proposed and experimentally validated. The model assumes exponential of the surviving granules, dependent on a probability of breakage; a function of powder and binder properties, as well as operating parameters. Validation experiments were performed with a breakage-only granulator, filled with cohesive, non-granulating sand. Premade pellets made from lactose monohydrate and silicone oils were granulated at several impeller speeds, and the number of survivors was observed over time. The results revealed that the number of granules did indeed decay exponentially. It was found that the overall probability of breakage was inversely proportional to the capillary number. Moreover, the pore saturation played an important role in determining the probability of breakage, with higher pore saturations reducing breakage overall. A comparison with experimental data from literature revealed that the developed models agrees qualitatively with the experimental data, but is unable to fully capture the effect of powder properties and powder-binder interaction.