Creep-age forming of AA7475 aluminum panels for aircraft lower wing skin application

Creep-age forming (CAF) is an interesting process for the airframe industry, as it is able to form or shape panels into smooth, but complex, curvatures. In the CAF process, the ageing cycle of the alloy is used to relax external loads imposed to the part, through creep mechanisms. Those relaxed stresses impose a new curvature to the part. At the end of the process, significant spring back (sometimes about 70%) is observed and the success in achieving the desired form depends on how the spring back can be predicted in order to compensate it by tooling changes. Most of the applications relate to simple (non stiffened) panels. The present work deals with the CAF of aluminum panels for aircraft wing skin application. CAF was performed using vacuum-bagging autoclave technique in small scale complex shape stiffened panels, machined from an AA7475 alloy plate. An analytical reference model from the literature was employed estimate the spring back effect in such panel geometry. This model that deals with simple plates was adapted to stiffened panels using a geometric simplification, resulting in a semi-empirical model. The results demonstrate that CAF is a promising process to form stiffened panels, and the spring back can be roughly estimated through a simple model and few experiments.Empresa Brasileira de Aeronáutica S.A.Universidade Federal de São Paulo (UNIFESP) Departamento de Ciência e TecnologiaUNIFESP, Depto. de Ciência e TecnologiaSciEL

ELECTROMYOGRAPHY OF TRUNK MUSCLES IN TIME-FREQUENCY DOMAIN DURING CORE STABILITY EXERCISES

The aim of this work was to compare the electromyogram (EMG) of trunk muscles, in the time-frequency domain, among core exercises. The EMG of 17 men was recorded by electrodes placed on external oblique (EO), rectus abdominis (RA), lumbar erector spinae (LES) and multifidus (MT) muscles. Short-time Fourier transform was performed and instantaneous median frequency (MedFreq) was calculated and averaged. MedFreq of the EO and RA were significantly higher (p < 0.0001) during double leg back bridge exercise. Contrarily, LES and MT showed significant higher (p < 0.0001) MedFreq during frontal and left side bridge. Antagonist muscles showed greater MedFreq than agonist muscles. This may be explained by the low-pass filtering effect of the adipose tissue, which could attenuate the increase of high frequencies EMG energy of agonist muscles

Energy expenditure and cardiovascular response to traumatic lower limb amputees gait

Introduction: Amputations cause functional, musculoskeletal and cardiovascular alterations and, the more proximal the amputation, the larger the alterations. Objectives: To observe the effect of using lower limb prosthetics and that of gait speed on heart rate (HR), blood pressure (BP), oxygen consumption (VO2) and energy cost (EC) during gait in traumatic lower limbs amputees. Materials and methods: The sample was composed of 30 men with unilateral amputations, 10 transfemoral and 10 transtibial, compared to 10 people with no amputations. All of them selected a pleasant walking speed (PWS) on the treadmill, and two other speeds were calculated, 20% above and 20% below the original one. The subjects walked for 10 minutes at each of the speeds and, in the last three minutes, the VO2, HR, and BP were assessed. In order to compare variables between groups the variance was performed (ANOVA) followed by the Post Hoc Sheffé test (p elt; 0.05). Results: The amputees selected lower values of PWS and had higher HR, BP, and EC, VO2 during gait when compared to normal individuals. The transfemoral amputees had higher VO2 and EC compared to the transtibial ones. By analyzing the speed effect, it was observed that, although the VO2 did not increase with the increased speed, there was increased cardiovascular response and reduced EC. Conclusions: Traumatic lower limb amputees have higher energy expenditure and cardiovascular responses during gait and, at higher speeds, they become more economical, reducing the EC

Energy expenditure and cardiovascular response to traumatic lower limb amputees’ gait

Introduction Amputations cause functional, musculoskeletal and cardiovascular alterations and, the more proximal the amputation, the larger the alterations. Objectives To observe the effect of using lower limb prosthetics and that of gait speed on heart rate (HR), blood pressure (BP), oxygen consumption (VO2) and energy cost (EC) during gait in traumatic lower limbs amputees. Materials and methods The sample was composed of 30 men with unilateral amputations, 10 transfemoral and 10 transtibial, compared to 10 people with no amputations. All of them selected a pleasant walking speed (PWS) on the treadmill, and two other speeds were calculated, 20% above and 20% below the original one. The subjects walked for 10 minutes at each of the speeds and, in the last three minutes, the VO2, HR, and BP were assessed. In order to compare variables between groups the variance was performed (ANOVA) followed by the Post Hoc Sheffé test (p < 0.05). Results The amputees selected lower values of PWS and had higher HR, BP, and EC, VO2 during gait when compared to normal individuals. The transfemoral amputees had higher VO2 and EC compared to the transtibial ones. By analyzing the speed effect, it was observed that, although the VO2 did not increase with the increased speed, there was increased cardiovascular response and reduced EC. Conclusions Traumatic lower limb amputees have higher energy expenditure and cardiovascular responses during gait and, at higher speeds, they become more economical, reducing the EC

Características morfogênicas e estruturais do capim-braquiária em pastagem adubada com nitrogênio avaliadas nas quatro estações do ano Morphogenetical and structural characteristics of the signalgrass in a nitrogen fertilized pasture evaluated over the seasons of the year

Este experimento foi realizado com o objetivo de avaliar o efeito da adubação nitrogenada sobre as características morfogênicas e estruturais de Brachiaria decumbens sob pastejo. Os tratamentos consistiram da aplicação de quatro doses de nitrogênio (75, 150, 225 e 300 kg/ha.ano) antes do início das avaliações experimentais, realizadas em 2002 durante as estações de verão, outono, inverno e primavera. Utilizou-se o delineamento em blocos completos casualizados, com duas repetições. A taxa de alongamento de folha, o comprimento final da folha, o índice de área foliar e as porcentagens de colmo e de lâmina foliar aumentaram linearmente, enquanto a porcentagem de material morto decresceu com a adubação nitrogenada da Brachiaria decumbens sob pastejo. Não foi constatado efeito da adubação nitrogenada sobre o número de folhas vivas, de folhas emergentes e de folhas totais e as taxas de alongamento do colmo e de senescência foliar. A taxa de alongamento de folha e de colmo, o número de folhas vivas, o comprimento final da folha, o índice de área foliar e a porcentagem de lâmina foliar e de colmo de Brachiaria decumbens variaram entre estações do ano, apresentando valores menores no inverno.<br>This experiment was carried out to evaluate the effects of nitrogen fertilization upon the morphogenetical and structural characteristics of Brachiaria decumbens under grazing. Four nitrogen rates (75, 150, 225 and 300 kg/ha.yr) were applied before the beginning of the experimental evaluations, which were performed during the Summer, Fall, Winter and Spring seasons. The randomized complete block design was used with two replications. Linear increases were observed for the leaf elongation rate, final leaf length, leaf area index, stem and leaf blade percentage. The percentage of dead material decreased with the nitrogen fertilization. On the other hand, N fertilization had no effect on the number of alive leaf, number of emerging leaves, total numbers of leaves, stem elongation rate and senescence rate. Leaf and stem elongation rates, number of alive leaf, final leaf length, leaf area index, leaf blade and stem percentages in the Brachiaria decumbens varied among seasons, lower values occurring in the winter