Analysis of the resistance to crack propagation in SENT test specimens printed in ABS using parallel or crossed filaments between layers

Additive manufacturing techniques continue to develop and cover all industrial fields. However, the performances of aspect and mechanical behavior of the parts obtained by this process remain to be mastered and are still the subject of current research works. Among these performances, the one corresponding to the resistance to the propagation of cracks. In order to improve this very interesting property in various industrial fields, it is desirable to master the understanding of crack propagation in this type of structure obtained by 3D printing. The objective of this paper is to analyze and understand the effect of the adopted raster angle on the crack propagation in SENT specimens obtained by FDM in ABS (Acrylonitrile-Butadiene-Styrene). Two approaches were developed: one is experimental to determine the critical stress intensity factor KIC and the other is numerical to predict the possible paths of crack propagation

Expression of Nestin by Neural Cells in the Adult Rat and Human Brain

Neurons and glial cells in the developing brain arise from neural progenitor cells (NPCs). Nestin, an intermediate filament protein, is thought to be expressed exclusively by NPCs in the normal brain, and is replaced by the expression of proteins specific for neurons or glia in differentiated cells. Nestin expressing NPCs are found in the adult brain in the subventricular zone (SVZ) of the lateral ventricle and the subgranular zone (SGZ) of the dentate gyrus. While significant attention has been paid to studying NPCs in the SVZ and SGZ in the adult brain, relatively little attention has been paid to determining whether nestin-expressing neural cells (NECs) exist outside of the SVZ and SGZ. We therefore stained sections immunocytochemically from the adult rat and human brain for NECs, observed four distinct classes of these cells, and present here the first comprehensive report on these cells. Class I cells are among the smallest neural cells in the brain and are widely distributed. Class II cells are located in the walls of the aqueduct and third ventricle. Class IV cells are found throughout the forebrain and typically reside immediately adjacent to a neuron. Class III cells are observed only in the basal forebrain and closely related areas such as the hippocampus and corpus striatum. Class III cells resemble neurons structurally and co-express markers associated exclusively with neurons. Cell proliferation experiments demonstrate that Class III cells are not recently born. Instead, these cells appear to be mature neurons in the adult brain that express nestin. Neurons that express nestin are not supposed to exist in the brain at any stage of development. That these unique neurons are found only in brain regions involved in higher order cognitive function suggests that they may be remodeling their cytoskeleton in supporting the neural plasticity required for these functions

Effect of infill and density pattern on the mechanical behaviour of ABS parts manufactured by FDM using Taguchi and ANOVA approach

Purpose: The present work aims to investigate the effect of many infill patterns (rectilinear, line, grid, triangles, cubic, concentric, honeycomb, 3D honeycomb) and the infill density on the mechanical tensile strength of an Acrylonitrile Butadiene Styrene (ABS) test specimen manufactured numerically by FDM. Design/methodology/approach: Computer-Aided Design (CAD) software has been used to model the geometry and the mesostructure of the test specimens in a fully automatic manner from a G-code file by using a script. Then, a Numerical Design of Experiments (NDoE) has been carried out by using Taguchi method and the Analysis of Variance (ANOVA). The tensile behaviour of these numerical test specimens has been studied by the Finite Element Analysis (FEA). Findings: The FEA results showed that a maximal Ultimate Tensile Strength (UTS) was reached by using the ‘concentric’ infill pattern combined with an infill density of 30%. The results also show that the infill pattern and the infill density are significant factors. Research limitations/implications: The low infill densities of 20% and 30% that have already been used in many previous studies, we have also applied it in order to reduce the time of the simulations. Indeed, with high infill density, the simulations take a very excessive time. In an ongoing study, we predicted higher percentages. Practical implications: This study provided an important modelling tool for the design and manufacture of functional parts and helps the FDM practitioners and engineers to manufacture strong and lightweight FDM parts by choosing the optimal process parameters. Originality/value: This study elucidated the effect of various infill patterns on the tensile properties of the test specimens and applied for the first time a NDoE using numerical test specimens created by the mesostructured approach, which considerably minimized the cost of the experiments while obtaining an error of 6.8% between the numerical and the experimental values of the UTS

Concentrated stress location areas for welded tubular T-joints under deflected bending load

The welded tubular joints can be used in several industrial fields including, metallic bridges, telecommunication tripods, oil platforms and pipelines. These structures can be damaged by concentrated stresses located in the toe weld vicinity. Semi-parametric formulas, currently available in the literature, can be used to predict the value of the stress concentration factor without given the hot spot location. In this work, a Finite Elements modeling was carried out for a T-joint, in order to have the concentrated stress value around the weld toe. This work was investigated for a series of combined loads

Fracture toughness of ABS additively manufactured by FDM process

Purpose: The purpose on this article is to study the failure of FDM printed ABS by exhibiting an exhaustive crack growth analysis mainly based on raster angle parameter. Design/methodology/approach: Two approaches have been developed in this study; On one hand, mechanical experiments were carried out to determine the critical stress intensity factor KIC. On the other hand, numerical analysis was used to predict the paths within the part as well as the crack propagation. Findings: This work has clearly shown the effect of raster angle on the damage mechanism of the ABS printed by FDM. Indeed, for the combination 1 (0°/90°), the structure presents an important stiffness and a high degree of stress distribution symmetry with respect to the notch. Moreover, the crack propagation is regular and straight, and the damage surfaces are on the same plane. However, for the combination 2 (-45°/45°), the structure is less resistant with an asymmetrical stress distribution according to two different planes. Research limitations/implications: In order to present an exhaustive study, we focused on the effect of two raster angles (including 0°/90°, -45°/45°) on the ABS crack propagation, additively manufactured. This study is still in progress for other raster angles, and will be developed from a design of experiments (DoE) design that incorporates all relevant factors. To highlight more the cracking mechanisms, microscopic observations will be developed in more depth. Practical implications: Our analysis can be used as a decision aid in the design of FDM parts. Indeed, we can choose the raster angle that would ensure the desired crack propagation resistance for a functional part. Originality/value: In this article, we have analyzed the mechanism of damage and crack propagation. This topic represents a new orientation for many research papers. For our study, we accompanied our experimental approach with an original numerical approach. In this numerical approach, we were able to mesh distinctly raster by raster for all layers

Stress analysis at singular points of micromachined silicon membranes

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Prion early kinetics revisited using a streptomycin-based PrP(res) extraction method.

International audienceThe use of streptomycin in the PrP(sc) detection procedures represents a new and attractive way to detect more PrP(sc), the best marker for the transmissible spongiform encephalopathies (TSEs). Actually, the streptomycin PrP(sc) aggregating property reported recently was established as beneficial in PrP(sc) detection using immunohistochemistry in diagnostic as well as in experimental conditions. The present study reports in details how to use advantageously this original streptomycin property in PrP(res) biochemical extraction and detection. Using TSE diagnostic brain material, specificity and increased sensitivity using streptomycin-treated samples were substantiated. Then an early sequential brain and spleen sampling (from 7 to 49 days post-inoculation) from C57Bl/6 mice inoculated intra-cerebrally or intra-peritoneally with C506M3 scrapie strain was analysed using streptomycin versus ultracentrifugation PrP(res) extraction. Whatever the inoculation route, streptomycin allowed earlier PrP(res) detection in spleen (7 d.p.i.), then in brain suggesting a stronger affinity of the infectious agent for the lymphoid compartment.The use of streptomycin in the PrP(sc) detection procedures represents a new and attractive way to detect more PrP(sc), the best marker for the transmissible spongiform encephalopathies (TSEs). Actually, the streptomycin PrP(sc) aggregating property reported recently was established as beneficial in PrP(sc) detection using immunohistochemistry in diagnostic as well as in experimental conditions. The present study reports in details how to use advantageously this original streptomycin property in PrP(res) biochemical extraction and detection. Using TSE diagnostic brain material, specificity and increased sensitivity using streptomycin-treated samples were substantiated. Then an early sequential brain and spleen sampling (from 7 to 49 days post-inoculation) from C57Bl/6 mice inoculated intra-cerebrally or intra-peritoneally with C506M3 scrapie strain was analysed using streptomycin versus ultracentrifugation PrP(res) extraction. Whatever the inoculation route, streptomycin allowed earlier PrP(res) detection in spleen (7 d.p.i.), then in brain suggesting a stronger affinity of the infectious agent for the lymphoid compartment