Friction tube hydroforming process : friction characterization by pure expansion test in a square section die

L’objectif de cette thèse est d’étudier la possibilité de caractériser le coefficient de frottement par un modèle analytique. Tout d’abord, le modèle analytique (Orban-Hu,2007) a été programmé à l’aide du logiciel « Matlab » puis validé par simulation numérique à l’aide du logiciel « Ls-Dyna ». Ensuite, on a réalisé des essais expérimentaux afin de caractériser les propriétés mécaniques du cuivre d’une part et étudier la mise en forme de tubes par hydroformage de tubes. Par suite, le coefficient de frottement a été caractérisé aussi bien par le modèle analytique que par le test classique ‘pion sur disque’. Les simulations numériques avec les coefficients de frottement obtenus ont permis de valider les résultats issus des essais expérimentaux pour une matrice carrée. Les mêmes résultats ont été également obtenus pour d’autres configurations géométriques (section rectangulaire, trapézoïdale et trapèze.)The objective of this thesis is to study the possibility of characterizing the friction coefficient by an analytical model. First, the analytical model (Orban-Hu, 2007) has been programmed using "Matlab» software and has been validated by numerical simulation using "LS-Dyna" software. Then, experimental tests were carried out in order i) to characterize the mechanical properties of copper and ii) to study the tube hydroforming in a square section. As a result, the friction coefficient was characterized by the analytical model and the pin-on-disk test. Then, the numerical simulation with the friction coefficients obtained allowed to validate the experimental results for a square section. The same findings were obtained using other die geometries (rectangular, trapezoidal and trapezoid-sectional die)

Frottement en hydroformage de tube : caractérisation du frottement par le test d'expansion en matrice carrée

The objective of this thesis is to study the possibility of characterizing the friction coefficient by an analytical model. First, the analytical model (Orban-Hu, 2007) has been programmed using "Matlab» software and has been validated by numerical simulation using "LS-Dyna" software. Then, experimental tests were carried out in order i) to characterize the mechanical properties of copper and ii) to study the tube hydroforming in a square section. As a result, the friction coefficient was characterized by the analytical model and the pin-on-disk test. Then, the numerical simulation with the friction coefficients obtained allowed to validate the experimental results for a square section. The same findings were obtained using other die geometries (rectangular, trapezoidal and trapezoid-sectional die).L’objectif de cette thèse est d’étudier la possibilité de caractériser le coefficient de frottement par un modèle analytique. Tout d’abord, le modèle analytique (Orban-Hu,2007) a été programmé à l’aide du logiciel « Matlab » puis validé par simulation numérique à l’aide du logiciel « Ls-Dyna ». Ensuite, on a réalisé des essais expérimentaux afin de caractériser les propriétés mécaniques du cuivre d’une part et étudier la mise en forme de tubes par hydroformage de tubes. Par suite, le coefficient de frottement a été caractérisé aussi bien par le modèle analytique que par le test classique ‘pion sur disque’. Les simulations numériques avec les coefficients de frottement obtenus ont permis de valider les résultats issus des essais expérimentaux pour une matrice carrée. Les mêmes résultats ont été également obtenus pour d’autres configurations géométriques (section rectangulaire, trapézoïdale et trapèze.

On the friction effect on the characteristics of hydroformed tube in a square section die : analytical, numerical and experimental approaches

International audienceA focus on the effect of friction condition on tube hydroforming during corner filling in a square section die is proposed. Three approaches have been developed: an analytical model from the literature has been programmed, finite element simulations have been conducted and experiments have been carried out. Effect of friction coefficient on the thickness distribution in the square section of the hydroformed tube is studied. Critical thinning is found to take place in the transition zone between the straight wall and the corner radius and this minimal thickness seems to be the more appropriate parameter for the evaluation of the friction coefficient

Effect of the lubrication between the tube and the die on the corner filling when hydroforming of different cross-sectional shapes

International audienceThis paper presents an experimental study on corner filling in the tube hydroforming process. A single-step tube hydroforming process was retained based on pure expansion hydroforming with the conjunction of only internal pressure loading. Several hydroforming experiments were performed with differently shaped dies, such as a square, a rectangular, a trapezoidal, and a trapezoid-sectional die. The distribution of thickness was studied under both dry and lubricated conditions. The main results revealed that thinning occurred in the transition zone, between the corner radius and the straight wall, for both the square and rectangular dies. However, for the trapezoidal and trapezoid-sectional dies, the thinning took place in the sharp zone. The use of Teflon as a lubricant between the die and the tube led to significant changes in terms of thickness distribution and the reduction of thinning. For each of the various dies that were used, it was found that the lubrication of the contact tube/die offered a more uniform thickness for the final hydroformed product

On the tube hydroforming process using rectangular, trapezoidal, and trapezoid-sectional dies : modeling and experiments

International audienceIt is generally known that the contact between tube and die, in the case of tube hydroforming process, leads to the appearance of friction effects. In this context, there are many different models for representing friction and many different tests to evaluate it. In the present paper, the pin-on-disk test has been used and the theoretical model of Orban-2007 has been chosen and developed to evaluate friction coefficient. The main goal is to prove the capacity of theoretical model to present the friction conditions in comparison with the pin-on-disk test. From the Orban model, values of 0.05 and 0.25 of friction coefficient have been found under lubricated and dry tests, respectively. On the other hand, by the classical pin-on-disk test, other values were experimentally obtained as friction coefficient at the copper/steel interface. In the case of pure expansion hydroforming, based on an internal pressure loading only, a “corner filling” test has been run for tube hydroforming. Both dry and lubricated contacts have been considered. Various configurations and shapes have been studied such as the rectangular, trapezoidal, and trapezoid-sectional dies. Finite element simulations with 3D shell and 3D solid models have been performed with different values of friction coefficients. From the main results, it was found that the critical thinning occurs in the transition zone for the square and rectangular section die and in the sharp angle for the trapezoidal and trapezoid-sectional die. The comparison between numerical data and experimental results shows a good agreement. Moreover, the thickness distribution along the cross section is relatively consistent with those measured for the 3D shell model; however, the 3D solid models do not provide a realistic representation of the thickness distribution in the shaped tube. Finally, the results obtained from the theoretical model were more efficient than the results obtained from the pin-on-disk test

Evaluation of the friction coefficient in tube hydroforming with the “corner filling test” in a square section die

International audienceFriction conditions are very critical in metal forming because they can lead to important thinning in the final manufactured product. The value of the friction coefficient is then of particular importance for performing predictive finite element (FE) simulation of forming operations. Classically, numerical simulations are run with values of the friction coefficient found in technical database where the Coulomb’s coefficient has been evaluated with the pin-on-disk test. Moreover, the friction coefficient is often used as a set up parameter for running FE simulations. The pin-on-disk test is not automatically suitable for characterizing the friction coefficient in tube hydroforming. The “corner filling” test has been developed for tube hydroforming and several authors have developed analytical models for representing this test. Among them, the authors have chosen to exploit the Orban-Hu model. This model permits to build graphs. On those graphs, experimental data are overlaid in order to evaluate the friction coefficient. Thus, a friction coefficient (μ) of 0.4 has been found by the proposed method against the value of about 0.1 found in technical database. FE simulations with 3D shell and 3D solid models have been performed with the two values of the friction coefficients. The conclusion is that FE simulations with 3D shell model permit definitely better predictions for thickness evaluation. Moreover, running the simulations with μ = 0.4 leads to a more critical representation of the minimal thickness in the final component. Finally, an experimental method is proposed for the evaluation of the friction coefficient without advanced numerical methods

Study of localized thinning of copper tube hydroforming in square section die : effect of friction conditions

International audienceThe friction conditions are responsible of the thickness distribution in a part realized by tube hydroforming. Then it is essential to have a good evaluation of the friction coefficient for running predictive finite element simulations. The tube expansion in a square die is one of tests proposed for the friction evaluation. In the literature, several analytical models have been developed for this specific test. The present paper concentrates on one of this model and results obtained from the analytical analysis, FE simulations and experiments are compared. The repartition of the thickness over the shaped tube and its evolution during the process are studied. The tendencies are in agreement but some complementary evaluations are proposed for using the proposed approach for the evaluation of the friction coefficient with the analytical model

Clinical features of otogenic cerebral sinovenous thrombosis: Our experience and review of literature

Abstract Otogenic cerebral sinovenous thrombosis is an intracranial complication secondary to otogenic disease; it is rare but could be a life‐threatening condition. Its management is always challenging. This study aimed to focus on clinical features, on diagnosis of this pathology and to review the most controversial aspect of management of otogenic cerebral sinovenous thrombosis. We reviewed retrospectively 10 inpatients treated with cerebral sinus thrombosis secondary to otitis between 1995 and 2020. Ten inpatients (eight males and two females) with ages ranging from 11 to 77 years were diagnosed with ontogenesis sinus thrombosis. The most commonly reported symptoms were headaches and otalgia. Five patients had mastoiditis, and 7 of the 10 patients had other concurrent complications: cerebellar abscess (three patients) and extradural empyema in two patients, retropharyngeal abscess in one patient, and meningitis in one patient. All patients were treated with broad‐spectrum antibiotherapy, anticoagulation was used to treat nine patients, and surgery was required in nine patients. Nine patients had satisfactory resolution of their symptoms, but one patient had sequel as permanent loss of visual acuity. Because of the inconspicuous clinical presentation, and the probability of a fatal evolution, suspicion is essential for a proper diagnosis and suitable treatment

Post-intubation laryngotracheal stenosis: clinical presentation and management approaches

Abstract Introduction Addressing acquired laryngotracheal stenosis presents a complex healthcare dilemma. Results We present a case series of 48 acquired post-intubation laryngotracheal stenosis cases managed within our Department of ENT Surgery at Farhat Hached Tunisia. Diagnosis relied on imaging and endoscopic findings. Among these cases, 28 exhibited tracheal stenosis, with 60% falling into grade 2–3 severity. Management approaches included sole endoscopic dilation for 17 patients, surgical intervention for 19 patients, and T-tube placement for 10 patients. Conclusions The management of laryngotracheal stenosis poses a challenge for ENT surgeons. Prevention is paramount, encompassing various measures such as employing high-volume, high tracheostomy, and extended intubation practices