In continuous casting of steel, prevention of surface cracks on the slab is an important issue. For quantitative evaluation of cracks that occur in the continuous casting machine, the critical strain for crack generation was analyzed by a high-temperature tensile test and FEM simulation. Based on obtained material property values, a model for crack generation by tensile strain was constructed. The local strain at the notch relative to the strain in the whole specimen was determined by a simulation of the tensile test, and the critical strain for crack generation ϵc was calculated. The results of a crack simulation by FEM using ϵc showed that the average strain until crack initiation was small under deep notch conditions. The average strain at crack generation calculated by the simulation model was in good agreement with the value measured in the tensile test. As a result of the simulation applying temperature distribution to the slab, the depth change of the oscillation mark was more in-fluential to crack formation than the change of the width. The effect of the shape of the oscillation mark on the crack cannot be organized only by the stress concentration factor. Simulation analysis that includes the shape of the oscillation mark is considered to be effective. Using this simulation model, it is possible to predict the generation of cracking when the temperature distribution or the oscillation mark shape in actual operation changes.
Machining Simulation Crack
Download File: https://tweeat.com/2vH6Mh
N2 - In continuous casting of steel, prevention of surface cracks on the slab is an important issue. For quantitative evaluation of cracks that occur in the continuous casting machine, the critical strain for crack generation was analyzed by a high-temperature tensile test and FEM simulation. Based on obtained material property values, a model for crack generation by tensile strain was constructed. The local strain at the notch relative to the strain in the whole specimen was determined by a simulation of the tensile test, and the critical strain for crack generation ϵc was calculated. The results of a crack simulation by FEM using ϵc showed that the average strain until crack initiation was small under deep notch conditions. The average strain at crack generation calculated by the simulation model was in good agreement with the value measured in the tensile test. As a result of the simulation applying temperature distribution to the slab, the depth change of the oscillation mark was more in-fluential to crack formation than the change of the width. The effect of the shape of the oscillation mark on the crack cannot be organized only by the stress concentration factor. Simulation analysis that includes the shape of the oscillation mark is considered to be effective. Using this simulation model, it is possible to predict the generation of cracking when the temperature distribution or the oscillation mark shape in actual operation changes.
AB - In continuous casting of steel, prevention of surface cracks on the slab is an important issue. For quantitative evaluation of cracks that occur in the continuous casting machine, the critical strain for crack generation was analyzed by a high-temperature tensile test and FEM simulation. Based on obtained material property values, a model for crack generation by tensile strain was constructed. The local strain at the notch relative to the strain in the whole specimen was determined by a simulation of the tensile test, and the critical strain for crack generation ϵc was calculated. The results of a crack simulation by FEM using ϵc showed that the average strain until crack initiation was small under deep notch conditions. The average strain at crack generation calculated by the simulation model was in good agreement with the value measured in the tensile test. As a result of the simulation applying temperature distribution to the slab, the depth change of the oscillation mark was more in-fluential to crack formation than the change of the width. The effect of the shape of the oscillation mark on the crack cannot be organized only by the stress concentration factor. Simulation analysis that includes the shape of the oscillation mark is considered to be effective. Using this simulation model, it is possible to predict the generation of cracking when the temperature distribution or the oscillation mark shape in actual operation changes.
The presence, evolution, and coalescence of cracks affect the strength and damage of materials. However, simulating cracks in a finite or discrete element framework (high-fidelity) is very expensive and most continuum models (low-fidelity) do not account for the presence of cracks. Since modeling damage in a material is of interest to several applications, it is desirable to track individual cracks and reduced-order models that can provide information on the presence of cracks are desired. The physical phenomenon of interest is a flyer plate impact test. This work shows preliminary results on the prediction of the evolution of crack length distributions using recurrent neural networks (RNN) trained using synthetic data. Synthetic data was created artificially to test the RNN and that does not come from a physical model. Using synthetic data, we successfully predicted the evolution of the crack length probability density function and cumulative distribution function at nine-time steps given the initial distribution with a confidence of 0.95 using the Kolmogorov-Smirnov statistic test. Once the high-fidelity simulation results were available physics informed machine learning told us that informing the continuum model with all individual cracks was not necessary and evolving only the longest crack was all we needed to achieve the desired accuracy.
Abstract:Demands for producing high quality glass components have been increasing due to their superior mechanical and optical properties. However, due to their high hardness and brittleness, they present great challenges to researchers when developing new machining processes. In this work, the discrete element method (DEM) is used to simulate orthogonal machining of synthetic soda-lime glass workpieces that are created using a bonded particle model and installed with four different types of seed cracks. The effects of these seed cracks on machining performance are studied and predicted through the DEM simulation. It is found that cutting force, random cracks, and surface roughness are reduced by up to 90%, 74%, and 47%, respectively, for the workpieces with seed cracks compared to the regular ones. The results show that high performance machining through DEM simulation can be achieved with optimal seed cracks.Keywords: discrete element method; orthogonal cutting; seed cracks; surface roughness
Abstract: This paper applies distinct element method (DEM) to simulate the material removal in conventional and Laser Assisted Machining (LAM) of silicon nitride ceramics. Simulation results demonstrate that DEM can reproduce the initiation and propagation of cracks, chip formation process and material removal mechanisms. Material removal is mainly realised by propagation of lateral cracks in both conventional and LAM. Crushing-type material removal is an important mechanism in conventional machining but not in LAM. The lateral cracks in LAM are easier to propagate to form larger chips. LAM creates less and smaller median cracks, therefore has less surface/subsurface damage than conventional machining. [Received 14 February 2008; Revised 30 June 2008; Accepted 4 August 2008]
Keywords: DEM; distinct element method; PFC; particle flow code; material removal process; LAM; laser assisted machining; conventional machining; silicon nitride ceramics; simulation; crack initiation; crack propagation; chip formation.
The propagation of small cracks contributes to the majority of the fatigue lifetime for structural components. Despite significant interest, criteria for the growth of small cracks, in terms of the direction and speed of crack advancement, have not yet been determined. In this work, a new approach to identify the microstructurally small fatigue crack driving force is presented. Bayesian network and machine learning techniques are utilized to identify relevant micromechanical and microstructural variables that influence the direction and rate of the fatigue crack propagation. A multimodal dataset, combining results from a high-resolution 4D experiment of a small crack propagating in situ within a polycrystalline aggregate and crystal plasticity simulations, is used to provide training data. The relevant variables form the basis for analytical expressions thus representing the small crack driving force in terms of a direction and a rate equation. The ability of the proposed expressions to capture the observed experimental behavior is quantified and compared to the results directly from the Bayesian network and from fatigue metrics that are common in the literature. Results indicate that the direction of small crack propagation can be reliably predicted using the proposed analytical model and compares more favorably than other fatigue metrics.
Modeling the propagation of small fatigue cracks, especially cracks that are intragranular in nature, requires information about how the underlying microstructure affects the crack behavior. While, crack initiation has been modeled as both stochastic1,2 and deterministic,3,4,5,6 there is still an open question if the small fatigue crack behavior can be predicted. Small crack propagation follows crystallographic directions and planes, and thus is said to be a slip-mediated process.7,8,9 The behavior of long cracks is well described by linear elastic fracture mechanics through the Paris law.10 While for small cracks, the propagation rate strongly deviates from linear elastic fracture mechanics behavior and exhibits large scatter,11,12,13 based on the complex interactions between the small crack and the local microstructure. Several relationships have been proposed to capture the small crack behavior, albeit these theories have not been validated at the appropriate length-scale due to prior limitations in the experimental measurements. With the advent of synchrotron-based x-ray tomography and diffraction techniques combined with in situ loading, the necessary data are available for the crack direction and propagation rate with respect to the microstructure. In this work, experimental data for the evolution of a fatigue crack relative to the local microstructure during in situ loading14,15 are used as the foundation to build a model for the driving force of small fatigue cracks. 2ff7e9595c
Comments