Prediction of strain localization during sheet metal forming using bifurcation analysis and Gurson-type damage

The strain localization phenomenon that may occur during sheet metal forming represents a major cause of defective parts produced in the industry. Several instability criteria have been developed in the literature to predict the occurrence of these instabilities. The proposed work aims to couple a Gurson-type model to the Rice’s localization criterion. The implementation of the modeling is achieved via a user subroutine (Umat) in Abaqus/std using a Runge-Kutta explicit integration scheme. Finally, we show the effectiveness of the proposed coupling for the prediction of the formability of stretched metal sheets.Projet ANR Formef & Région Lorrain

Plastic Instability Based on Bifurcation Analysis: Effect of Hardening and Gurson Damage Parameters on Strain Localization

In this work, we propose to couple the Gurson-Tvergaard-Needleman (GTN) model, known for its widespread use to describe damage evolution in metallic materials, to the Rice localization criterion. The implementation of the constitutive modeling is achieved via a user material (UMAT) subroutine in the commercial finiteelement code ABAQUS. Large deformations are taken into account within a three dimensional co-rotational framework. The effectiveness of the proposed coupling for the prediction of the formability of stretched metal sheets is shown and Forming Limit Diagrams (FLDs) are plotted for an Aluminum alloy. A sensitivity analysis with respect to hardening parameters is carried out, andit is shown that these effects are much smaller for the case of the Rice criterion when compared toclassical criteria commonly utilized in metal forming

Prediction of strain localization during sheet metal forming using bifurcation analysis and Gurson-type damage

The strain localization phenomenon that may occur during sheet metal forming represents a major cause of defective parts produced in the industry. Several instability criteria have been developed in the literature to predict the occurrence of these instabilities. The proposed work aims to couple a Gurson-type model to the Rice’s localization criterion. The implementation of the modeling is achieved via a user subroutine (Umat) in Abaqus/std using a Runge-Kutta explicit integration scheme. Finally, we show the effectiveness of the proposed coupling for the prediction of the formability of stretched metal sheets.Projet ANR Formef & Région Lorrain

Ductility limit prediction using a GTN damage model coupled with localization bifurcation analysis

Because the localization of deformation into narrow planar bands is often precursor to material failure, several approaches have been proposed to predict this phenomenon. In this paper, the Gurson–Tvergaard– Needleman (GTN) elastic–plastic–damage model for ductile materials is considered. A large-strain version of this constitutive model is coupled with the Rice localization criterion, which is based on bifurcation theory, to investigate strain localization. The resulting loss of ellipticity condition is then used to determine ellipticiy loss diagrams (ELDs) associated with strain paths that are those typically applied to metals under biaxial stretching. A sensitivity analysis is conducted with respect to the model parameters on a representative selection of ductile materials. The analysis shows that the damage parameters have a significant impact on the predicted ELDs, which confirms the predominant role of damage-induced softening in triggering plastic flow localization with the adopted constitutive description combined with the bifurcation approach. As a consequence of this high sensitivity, it appears that the proper identification of damage parameters is a key issue for accurate plastic flow localization predictions using the GTN model coupled with bifurcation theory. The effect of the dense matrix hardening parameters on the strain localization predictions of the voided aggregate, although found much smaller in the whole, is more noticeable for the plane strain tension loading path or, more generally, when the critical hardening modulus required for localization is not strongly negative

The suitability of an uncemented hydroxyapatite coated (HAC) hip hemiarthroplasty stem for intra-capsular femoral neck fractures in osteoporotic elderly patients: the Metaphyseal-Diaphyseal index, a solution to preventing intra-operative periprosthetic fracture

This study will seek to identify a measurable radiographic index, the Metaphyseal-Diaphyseal Index (MDI) score to determine whether intra-operative fracture in osteoporotic bone can be predicted

Prédiction de la localisation par une approche d’endommagement micromécanique couplée à une analyse de bifurcation : application à la mise en forme des tôles

Le phénomène de localisation des déformations plastiques, qui apparait lors d’opérations de mise en forme des tôles, représente l’une des principales causes de rebut des pièces produites dans l’industrie. Plusieurs critères d’instabilités ont été développés dans la littérature afin de prédire le moment d’apparition de ce phénomène. Le travail proposé ici consiste à coupler un modèle d’endommagement de type Gurson au critère de localisation de Rice. L’implantation est réalisée sous forme d’une routine utilisateur (UMAT) dans Abaqus/std via un schéma d’intégration explicite de type Runge-Kutta. Enfin, l’efficacité de la modélisation utilisée, pour la prédire les limites de formage des tôles est explorée.The strain localization phenomenon that may occur during sheet metal forming represents a major cause of defective parts produced in the industry. Several instability criteria have been developed in the literature to predict the occurrence of these instabilities. The proposed work aims to couple a Gurson-type model to the Rice localization criterion. The implementation of the modeling is achieved via a user subroutine (UMAT) in Abaqus/std using a Runge-Kutta explicit integration scheme. Finally, we show the effectiveness of the proposed coupling for the prediction of the formability of stretched metal sheets.Projet ANR FORMEF & Région Lorrain

Prédiction de la localisation par une approche d'endommagement micromécanique couplée à une analyse de bifurcation : application à la mise en forme des tôles

Le travail proposé ici consiste à coupler un modèle d'endommagement de type Gurson au critère de localisation de Rice. Ce couplage permet de décrire l'évolution de l'endommagement jusqu'à apparition des premières bandes de localisation. L'effet Bauschinger et l'anisotropie de la matrice sont est pris en compte dans l'étude. Enfin, nous étudions l'effet des différents paramètres du modèle (anisotropie, écrouissage, pré-déformation, etc.) et du critère de localisation (présence des termes convectifs) sur la limite de formabilité des tôles

Plastic Instability Based on Bifurcation Analysis: Effect of Hardening and Gurson Damage Parameters on Strain Localization

In this work, we propose to couple the Gurson-Tvergaard-Needleman (GTN) model, known for its widespread use to describe damage evolution in metallic materials, to the Rice localization criterion. The implementation of the constitutive modeling is achieved via a user material (UMAT) subroutine in the commercial finiteelement code ABAQUS. Large deformations are taken into account within a three dimensional co-rotational framework. The effectiveness of the proposed coupling for the prediction of the formability of stretched metal sheets is shown and Forming Limit Diagrams (FLDs) are plotted for an Aluminum alloy. A sensitivity analysis with respect to hardening parameters is carried out, andit is shown that these effects are much smaller for the case of the Rice criterion when compared toclassical criteria commonly utilized in metal forming

Relieving Pain in Oral Lesions of Pemphigus Vulgaris Using the Non-ablative, Non-thermal, CO2 Laser Therapy (NTCLT): Preliminary Results of a Novel Approach

Introduction: Pemphigus vulgaris (PV) is a chronic, serious autoimmune mucocutaneous bullous disease. Oral lesions in PV may be extremely painful. This pain may adversely affect the patients’ oral intake and quality of life. This before-after clinical trial was designed to assess the pain relieving effects of single session of non-ablative, non-thermal CO2 laser therapy (NTCLT) in oral lesions of PV.Methods: Fifty painful oral lesions of fourteen patients with PV were illuminated by CO2 laser (power: 1 W, scanning the lesions with rapid circular motion of the handpiece) passing through a thick layer of transparent gel with high water content. The pain severity of the oral lesions was reported by the patients up to the fourth postoperative day. They were also asked to continue their existing systemic treatment during the course of this study as a precondition for the participation.Results: The severity of contact and non-stimulate (non-contact) pain declined immediately and significantly after NTCLT (P < 0.001). The pain relieving effect was sustained during the four successive days of follow-up. The procedure was pain free and no kind of analgesics was required. Following NTCLT, there were no visible thermal complications such as destruction, ablation or irritation of the oral lesions.Conclusion: The results of the trial proposed that single session of NTCLT could immediately and significantly relieve pain in oral lesions of PV, without any visible thermal complications