Crystal plasticity model of residual stress in additive manufacturing using the element elimination and reactivation method

Selective laser melting is receiving increasing interest as an additive manufacturing technique. Residual stresses induced by the large temperature gradients and inhomogeneous cooling process can favour the generation of cracks. In this work, a crystal plasticity finite element model is developed to simulate the formation of residual stresses and to understand the correlation between plastic deformation, grain orientation and residual stresses in the additive manufacturing process. The temperature profile and grain structure from thermal-fluid flow and grain growth simulations are implemented into the crystal plasticity model. An element elimination and reactivation method is proposed to model the melting and solidification and to reinitialize state variables, such as the plastic deformation, in the reactivated elements. The accuracy of this method is judged against previous method based on the stiffness degradation of liquid regions by comparing the plastic deformation as a function of time induced by thermal stresses. The method is used to investigate residual stresses parallel and perpendicular to the laser scan direction, and the correlation with the maximum Schmid factor of the grains along those directions. The magnitude of the residual stress can be predicted as a function of the depth, grain orientation and position with respect to the molten pool. The simulation results are directly comparable to X-ray diffraction experiments and stress–strain curves.

BleTIES: Annotation of natural genome editing in ciliates using long read sequencing

Ciliates are single-celled eukaryotes that eliminate specific, interspersed DNA sequences (internally eliminated sequences, IESs) from their genomes during development. These are challenging to annotate and assemble because IES-containing sequences are much less abundant in the cell than those without, and IES sequences themselves often contain repetitive and low-complexity sequences. Long read sequencing technologies from Pacific Biosciences and Oxford Nanopore have the potential to reconstruct longer IESs than has been possible with short reads, and also the ability to detect correlations of neighboring element elimination. Here we present BleTIES, a software toolkit for detecting, assembling, and analyzing IESs using mapped long reads. Availability and implementation: BleTIES is implemented in Python 3. Source code is available at https://github.com/Swart-lab/bleties (MIT license), and also distributed via Bioconda. Contact: [email protected] Supplementary information: Benchmarking of BleTIES with published sequence data.

A Numerical Approach for Simulation of Rock Fracturing in Engineering Blasting

An approach for simulation of rock fracturing as a result of engineering blasting is presented in this paper. The approach uses element elimination technique within the framework of finite element method to capture the physics of engineering blasting. The approach does not require pre-placement of fracture paths which is the severe drawback of the other existing methodologies and approaches. Results of plane stress modelling for isotropic brittle rock behaviour are presented in this paper and these results are in good agreement with the existing knowledge base. The authors also review the existing approaches of numerical modelling to compare the efficacy of the element elimination technique. It is anticipated that the further developments with this approach can prove to be good experimental tool to improve engineering blasting operations.

Two FEM Thermal Models for Shallow and Deep Grinding

Grinding is a stochastic process applied in the last stages of the manufacturing cycle. In last decades, grinding research has focused on prediction of thermal damage on ground workpiece since it is of considerable importance from both research and industrial perspectives. A number of numerical and analytical thermal models have been carried out so far. However, new grinding processes such as peel grinding, creep feed grinding and others such as plongee grinding need new models which consider the effect of higher depth of cuts, but there is no information about the minimum depth of cut to consider the elimination of grounded material in FEM models. This article establishes the frontier from which the removed ground material should be physically eliminated to obtain an accurate FEM thermal model. Results show valuable information to decide which kind of model (with or without element elimination) is enough accurate for their purpose and application.

A Numerical Approach for Simulation of Rock Fracturing in Engineering Blasting

An approach for simulation of rock fracturing as a result of engineering blasting is presented in this paper. The approach uses element elimination technique within the framework of finite element method to capture the physics of engineering blasting. The approach does not require pre-placement of fracture paths which is the severe drawback of the other existing methodologies and approaches. Results of plane stress modelling for isotropic brittle rock behaviour are presented in this paper and these results are in good agreement with the existing knowledge base. The authors also review the existing approaches of numerical modelling to compare the efficacy of the element elimination technique. It is anticipated that the further developments with this approach can prove to be good experimental tool to improve engineering blasting operations.

Méthodes numériques de propagation de fissures appliquées au découpage des métaux

The purpose of this paper is to propose an efficient numerical tool to simulate the blanking process and predict the geometric and mechanical characteristics of the blanked component. Two different strategies are proposed to simulate the crack propagation: a finite element elimination method and a discrete cracking approach. First, these methods are evaluated on the set-up test of an asymmetrical plate submitted to traction. Second, the ability of these methods to predict a realistic cut edge profile is analyzed within the framework of blanking. The load - penetration punch curves obtained by both fracture propagation methods are compared to the experimental one.