Domain discretizations for numerical solution of fracture problems

В работе для численного моделирования хрупкого разрушения с целью повышения эффективности громоздких расчетов предлагается использовать двухуровневую процедуру построения сетки дискретизации. На верхнем уровне генерируется сетка фрагментов - локусов задаваемых размеров и произвольной случайной формы, по границам которых может происходить разрушение. На нижнем уровне каждый локус разбивается на сетку конечных элементов. Разрыв связей между конечными элементами по траектории разрушение между локусами реализуется с помощью процедуры сцепляющей среды. Для построения сетки дискретизации верхнего уровня использована диаграмма Воронова. Разработан алгоритм процедуры создания локусов на телах произвольной формы в двумерной и трехмерной постановках. Процедура реализована на языке APDL, для использования в программном комплексе ANSYS. Алгоритм протестирован при различных значениях задаваемых параметров и на объектах разнообразной формы. Численное решение задачи о разрушении цилиндрического образца из хрупкого материала по бразильскому тесту определения прочностных характеристик материала на растяжение продемонстрировало хорошее согласование полученной картины разрушения с реальной. In this paper, for numerical modeling of brittle fracture in order to increase the efficiency of complex calculations, it is proposed to use a two-level procedure for generating a discretization network. At the upper level, a network of fragments – locus’s, of specified sizes and arbitrary random shape, is generated. At the lower level, each locus is meshed by FE. The breaking of connections between finite elements along the trajectory of destruction between locus is realized using the cohesive zone procedure. The properties of the Voronov diagram are used to generate the upper-level discretization network. The algorithm of the procedure for creating locus on bodies of arbitrary shape in two-dimensional and three-dimensional formulations is developed. The procedure is implemented in the APDL, for use in the ANSYS. The algorithm is tested at various values of the specified parameters and on objects of various shapes. The numerical solution of the problem of the destruction of a cylindrical sample made of brittle material according to the Brazilian test for determining the tensile strength characteristics of the material demonstrated a good agreement of the obtained fracture pattern with the real one.

Movement and Protection for Random Shape Rockfalls in Steeply Dipping Coal Seams

In view of the randomness of rockfalls shape and irregularity of the bottom floor of working face in steeply dipping coal seams (SDCS), it is difficult to accurately simulate rockfall movement, and it is consequently unable to effectively protect against multirockfalls. Therefore, a method for generating random shape rockfalls based on ellipsoid equation is proposed, and a 3D grid model of real bottom floor of working face is established based on the geographic information system data. In order to verify the accuracy and feasibility of the method and 3D model, the trajectory simulated by Rockyfor3D software is compared, and the proposed method and 3D model prove to be effective in simulating rockfall movement more accurately. Then the proposed method and 3D grid model are applied to solve the problem of multirockfalls protection in numerical simulation, and the main factors affecting the structural stress response of protective netting are analyzed by taking three incident modes of parallel heights, ladder parallel, and the same trajectory. In the simulation, it is found out that the trajectory of irregular rockfalls is greatly affected by the shape of rockfall and working face floor; during the process of multiple rockfalls colliding with the protective netting, the peak stress on the protective netting is inversely proportional to both the time interval between each rockfall and the distance between each rockfall. The findings presented in this research contribute to rockfall prediction and protection against rockfall hazards.

Image Analysis and Functional Data Clustering for Random Shape Aggregate Models

This study presents a random shape aggregate model by establishing a functional mixture model for images of aggregate shapes. The mesoscale simulation to consider heterogeneous properties concrete is the highly cost- and time-effective method to predict the mechanical behavior of the concrete. Due to the significance of the design of the mesoscale concrete model, the shape of the aggregate is the most important parameter to obtain a reliable simulation result. We propose image analysis and functional data clustering for random shape aggregate models (IFAM). This novel technique learns the morphological characteristics of aggregates using images of real aggregates as inputs. IFAM provides random aggregates across a broad range of heterogeneous shapes using samples drawn from the estimated functional mixture model as outputs. Our learning algorithm is fully automated and allows flexible learning of the complex characteristics. Therefore, unlike similar studies, IFAM does not require users to perform time-consuming tuning on their model to provide realistic aggregate morphology. Using comparative studies, we demonstrate the random aggregate structures constructed by IFAM achieve close similarities to real aggregates in an inhomogeneous concrete medium. Thanks to our fully data-driven method, users can choose their own libraries of real aggregates for the training of the model and generate random aggregates with high similarities to the target libraries.

Statistical Curvature Change Analysis of Random-Shape Polyethylene Microplastics and their Toxicity from a Physical Perspective

BackgroundMicroplastics,plastics thathave gradually and randomly decomposed into small fragmentsafter exposure to physical and biological external stress,are emerging as a significant environmental threat. They are normally categorized into the following three types: particles, fibers, and random-shape fragments brokendown from bulk plastics. Here, we have demonstrated the in vitro toxicity of microplastics of two different shapes. To minimize the chemical effect, polyethylene (PE),which has abasic chemical polymer structure,was used. PE microplastics withtwo different shapes were prepared,high-density PE (HDPE) microbeads and randomly ground low-density PE (LDPE) from bulk pellets.ResultsTo quantify the randomness of the microplastic shape, the edge patterns of the generated PE microplasticswere converted into numerical values and analyzed using a statistical method. A10-fold difference in curvature value was observed between PE particles and ground PE microfragments. We found that the higher concentration and rough structure were associated with the toxicity of plastics toward immune- or non-immune cells, pro-inflammatory cytokinerelease, and hemolysis, even though PE is buoyant onto medium. The smooth PE particles did not exhibit severe cytotoxicity at any of the tested concentrations, but induced immune and hemolysis responses at high concentrations. ConclusionWhen comparing the toxicity of two different shapes of PE microplastics, we confirmed by statistical analysis that random-shape plastics with sharp edges and higher curvature differences may adversely affect human cells.

in vitro Chemical and physical toxicity of polystyrene microplastics in human-derived cells

Background With the increase of plastics production, a variety of toxicological studies regarding the microplastics have been reported since the microplastics could be ingested by the human body and cause serious diseases. However, the previous studies have been mainly focused on the toxicity of sphere type microbeads, which may be different from that of the randomly-shaped microplastics in real environment. Here, we have conducted the in vitro toxicology for randomly-shaped microplastics following the hypothesis that (1) physical cytotoxicity is affected from nano-/micro-size roughness in polystyrene (PS) microplastics and (2) chemical toxicity is caused by chemical reagents from microplastics.Results To prepare random shape of PS microplastics, we produced microfragments by ball mill grinding, then analyzed them via various toxicity tests in chemical and physical aspects with various kinds of human-derived cells. Ground PS microplastics were sorted in 3 ranges: 5-25 μm, 25-75 μm and 75-200 μm, and treated up to 1 mg/mL to cells based on weekly human intake of microplastics. We have confirmed that the PS microfragments induced 20 times increased acute inflammation for immune cells, production of reactive oxygen species and cell-death for fibroblasts and cancer cells by release of chemical reagents from microplastics. In addition, when the PS microfragments were in direct contact with the fibroblast and red blood cells, they lead to the lactose dehydrogenase release caused by a cell membrane damage and hemolysis by physical stress of microfragments. This phenomenon was amplified as microfragments concentration and roughness increases, we quantitatively analyzed roughness differences between microplastics, demonstrating that there are strong relationship physical damage of cells and roughness of microplastics.Conclusion We found that the PS microfragments have chemical toxicity. Furthermore, the physical toxicity by PS resulted in cellular membrane damage and correlated with statistically quantified-shape roughness. Therefore, we newly suggested the additional physical toxicity of random shape of microplastics. This provides the evidence of environmental and biological risks on random shape of microplastics.