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The prediction of dynamic crushing behavior of aerospace-grade composites is a hard challenge for researchers. At coupons scale, such behavior implies the understanding of the initiation and propagation of the elementary damage mechanisms. Many results of the research confirm that the modulus and strength of composites increases with strain-rate. This paper presents the improvement of the constitutive model UL-Crush by adding dynamic stiffness modulus and strengths. The improved tool uses new approach by updating the stiffness and the strength values depending on strain-rates. In addition, parameter sensitivity investigations were conducted to assess the specific energy absorption capabilities of different material configurations. A new on-axis compression fixture was designed and manufactured to carry out tests of plain weave fabric composites, under quasi-static (QS) and low-velocity compression using MTS Insight 100 loading frame and drop tower CEAST Instron9340 facility. Two types of cross-section geometries were used: flat-plate and Hat-Shape coupons. Four types of triggering mechanism were adopted, including saw teeth, chamfer45°, steeple and corrugated, to ensure a continuous and stable crushing mode of failure. Detailed parameter sensitivity investigations were performed, including dimension scale, stacking sequences, trigger types and strain-rates. It was shown that the crush response is strain-rate dependent, and dynamic load decreases absorbed energy, which is indicative of microstructure disintegrating. Globally, big dimension scale, corrugated trigger, [0/45/45/0]s layup and decreasing strain-rate are the parameters to enhance the energy absorption capability of composite coupons. It has been observed that the improved numerical tool UL-Crush was able to significantly capture most crush mechanisms, reasonably correlate with experiments, and give an accurate dynamic response for crashworthy structures.

ABSTRACTRATIONALE: Obstructive sleep apnea (OSA) is associated with a variety of adverse health outcomes. Upper airway muscle training (UAMT) may represent a novel, effective treatment approach for OSA.OBJECTIVE: This study aimed to quantify the proportion of OSA patients who would consider UAMT and to investigate the influential physiological and sociodemographic factors.METHODS: A total of 158 consecutive newly diagnosed OSA patients were recruited to complete a self-administered survey, including assessment of their interest towards upper airway muscle training, anticipated ability to complete it and factors that could influence these attitudes. Sociodemographic information and sleep recording data were also obtained.RESULTS: The majority of patients were interested in such program (82.9%) and mentioned their ability to complete it 1 hour/day for 1 month (72.1%), especially if applied later only 2–3 times/week (82.9%). A total of 55.0% of them indicated that requirements of training schedule and duration might influence their choice. Patients with low socioeconomic status (SES) were more prone to complete such program 2–3 times/week when compared with high SES group (p < 0.05). Multivariate analysis revealed that age (OR: 1.04, 95% CI: 1.01–1.07; P = 0.02) was an independent determinant for interest to complete UAMT therapy. ODI (OR: 0.95, 95% CI: 0.94–1.00; P = 0.04) predicted preference for UAMT over the overnight-used conventional devices.CONCLUSIONS: This study demonstrates that the majority of OSA patients are interested in such therapy, suggests their ability to complete it, along with a preference over conventional therapies. The aforementioned attitudes are sensitive to gender, age, severity of disease and socioeconomic status.RÉSUMÉJUSTIFICATION: L'apnée obstructive du sommeil (AOS) est associée à divers effets néfastes sur la santé. La rééducation des muscles des voies respiratoires supérieures pourrait être un traitement novateur et efficace pour l'AOS.OBJECTIF: Cette étude visait à quantifier la proportion de patients atteints d'AOS qui envisageraient la rééducation des muscles des voies aériennes supérieures et à examiner les facteurs physiologiques et sociodémographiques influents.MÉTHODES: 158 patients consécutifs ayant récemment obtenu un diagnostic d'apnée obstructive du sommeil ont été recrutés afin de répondre à un questionnaire auto-administré évaluant leur intérêt pour la rééducation des muscles des voies respiratoires supérieures, leur capacité à suivre ce traitement jusqu'au bout, ainsi que les facteurs qui pourraient influencer ces attitudes. Les données sociodémographiques et les données d'enregistrement du sommeil ont aussi été obtenues.RÉSULTATS: La majorité des patients étaient intéressés à ce programme (82,9 %) et ont dit être capables de le suivre une heure par jour pendant un mois (72,1 %), en particulier s'il devait être appliqué seulement deux à trois par semaine par la suite (82,9 %). 55 % d'entre eux ont indiqué que les exigences de l'horaire et la durée de la rééducation pourraient influencer leur choix. Les patients de statut socioéconomique faible étaient plus enclins à suivre ce programme deux à trois fois par semaine comparativement au groupe de statut socioéconomique plus élevé (p < 0,05). Une analyse multivariée a démontré que l'âge (RC: 1,04, 95 % IC: 1,01 – 10,07; P = 0,02) était un déterminant indépendant de l'intérêt à suivre le traitement de rééducation des muscles des voies aériennes supérieures. L'IDO (RC: 0,95, 95 % IC: 0,94 – 1,00; P = 0,04) était prédicteur d'une préférence pour la rééducation des muscles des voies aériennes supérieures par rapport aux appareils conventionnels utilisés toute la nuit.CONCLUSIONS: Cette étude démontre que la majorité des patients atteints d'apnée obstructive du sommeil sont intéressés à ce traitement. Elle suggère aussi qu'ils sont aptes à le suivre jusqu'au bout et qu'ils le préfèrent aux traitements conventionnels. Les attitudes ci-dessus sont sensibles au genre, à la gravité de la maladie et au statut socioéconomique.

Independent research studies have shown notable dissimilarity in the machining behaviour of aluminum alloys AA6061−T6 and AA7075−T651 commonly used in automotive and aeronautical applications. The present work attempts to investigate this dissimilarity based on experimental and numerical data with a focus on chip formation and generated residual stresses under similar high−speed machining (HSM) conditions. The numerical data were calculated by a finite element modeling (FEM) developed using DeformTM 2D software. The results showed that both studied alloys exhibit different chip formation mechanisms and residual stress states at the machined surfaces. On one hand, the AA6061−T6 alloy generates continuous chips and tensile residual stresses whereas the AA7075−T651 alloy produces segmented chips and compressive residual stresses. FEM results showed that the AA6061−T6 alloy generates lower cutting temperature at the tool−chip interface along with higher equivalent total strains at the machined surface as compared to the AA7075−T651 alloy. Based on the experimental and numerical results, it was pointed out that the differences in terms of thermal conductivity and initial yield stress are the main reasons explaining the dissimilarity observed.

•Developing a finite element model for high speed machining of aluminum alloy 7075–T651.•Implementing the Johnson–Cook constitutive equation with damage criterion to simulate adiabatic shearing during serrated chip formation.•Analyzing the serrated chip morphology and serration intensity versus cutting speed.•Highlighting the physical mechanisms governing the serrated chip formation in machining of 7075–T651 alloy.•Comparing the numerical prediction with the analytical solution of the shear band spacing parameter.

Increasing acceptance and use of hydroforming technology within the aerospace industry requires a comprehensive understanding of critical issues such as the material characteristics, friction condition and hydroformability of the material. Moreover, the cost of experiments that can be reduced by accurate finite element modeling (FEM), which entails the application of adapted constitutive laws for reproducing with confidence the material behavior. In this paper, the effect of different constitutive laws on FEM of tubular shapes is presented. The free expansion process was considered for developing the FEM. Bulge height, thickness reduction and strains were determined at the maximum bulge height using different constitutive models, including Hollomon, Ludwik, Swift, Voce, Ludwigson. In order to minimize the effect of friction, the free expansion experiments were performed with no end feeding. The simulation results were compared with the experimental data to find the appropriate constitutive law for the free expansion process.

Tube hydroforming (THF) is an advanced metal forming process that is used widely in automotive industry, but the application of the THF process in aerospace field is comparatively new with many challenges due to high strength and limited formability of aerospace materials. The success of THF process largely depends on many factors, such as mechanical properties of the material, loading path during the process, tool geometry and friction condition. Due to complexity of this process, finite element modeling (FEM) can largely reduce the production cost. One of the important input in FEM is the material behavior during hydroforming process. The true stress-strain curve before necking can be easily determined, using either tensile testing or bulge testing, but for an accurate failure prediction in a large deformation, such as hydroforming, the study of true stress-strain curve after necking is important because it improves the quality of the analysis due to utilizing a real extended stress-strain curve. Hence, the objective of this research was to establish a methodology to determine the true stress-strain curve after necking in order to predict burst pressure in the THF of aerospace materials. Uniaxial tensile tests were performed on standard tensile samples (ASME E8M-04) to determine the true stress-strain before and after necking, using an analytical method presented in this study. To validate the approach, burst pressure in the THF process was predicted using the extended stress-strain curve in conjunction with Brozzo's decoupled fracture model. The approach was evaluated using data obtained from the free expansion (tube bulging) tests performed on stainless steel 321 tubes with 2 inches diameter and two different thicknesses, 0.9 mm and 1.2 mm. The comparison of the predicted and measured burst pressures was promising, indicating that the approach has the potential to be extended to predict formability limits in THF of complex shapes.

This paper presents a new formulation of the non-linear discrete Kirchhoff quadrilateral shell element applicable for the analysis of geometrically nonlinear structures undergoing finite rotations. The shell director is directly interpolated and the exact linearization of the discreet form of the equilibrium equations is derived in closed form. The consistent tangent stiffness matrix is symmetric and is given explicitly in this paper. Two or three rotational variables are used at each node. To improve the in-plane deformation enhanced incompatible modes are introduced. The formulation is then illustrated by a comprehensive set of numerical experiments selected from the literature.

Dans cet article nous nous intéressons à la modélisation et à la simulation par la méthode dynamique des éléments finis du comportement viscoélastique d'une membrane thermoplastique mince, isotrope et incompressible. Le modèle de comportement intégral viscoélastique de Lodge est considéré. La formulation lagrangienne et l'hypothèse de la théorie des membranes sont utilisées pour la modélisation. Pour les validations des calculs numériques nous avons confronté nos résultats numériques à des mesures expérimentales pour le soufflage libre d'une membrane polymérique en ABS (Acrylonitrile butadiène styrène). Ensuite, nous avons étudié l'influence de la loi de comportement de Lodge sur la distribution des épaisseurs et des contraintes au sein de la feuille thermoplastique pour trois types de chargement. Finalement, un exemple simple de thermoformage d'une pièce en ABS est présentée.

Abstract: In this paper, superconvergent patch recovery techniques [see Refs Zienkiewicz and Zhu (1992); Blacker and Belytschko (1994)] which have been proposed for linear elliptic problems are generalized here to the elastoplastic axisymmetrical problems. Numerical examples for axisymmetrical problems (using 4-node quadrilateral elements) are presented to illustrate the reliability of this generalization. As an outcome of our study, the superior performance of the modified post-processing technique, Blacker and Belytschko (1994), in comparison with the standard one, Zienkiewicz and Zhu (1992), is found through the numerical results.

The aim of the present study was to assess the effects of one-week tongue-task training (TTT) on sleep apnea severity in sleep apnea subjects. Ten patients with sleep apnea (seven men, mean [± SD] age 52±8 years; mean apnea-hypopnea [AHI] index 20.9±5.3 events/h) underwent 1 h TTT in the authors’ laboratory on seven consecutive days. A complete or limited recording and tongue maximal protruding force were assessed before and after one-week TTT. One-week TTT was associated with a global AHI decrease (pre-TTT: 20.9±5.3 events/h; post-TTT: 16.1±5.1 events/h; P<0.001) and AHI decrease during rapid eye movement sleep (pre-TTT: 32.2±18.4 events/h; post-TTT: 16.7±6.6 events/h; P=0.03), while protruding force remained unchanged. The authors consider these results to be potentially clinically relevant and worthy of further investigation in a large randomized trial.