Influência da temperatura de embutimento no retorno elástico em aços de alta resistência

Orientador : Paulo Victor Prestes MarcondesCoorientador : Sérgio Fernando LajarinTese (doutorado) - Universidade Federal do Paraná, Setor de Tecnologia, Programa de Pós-Graduação em Engenharia Mecânica. Defesa: Curitiba, 15/02/2017Inclui referências : f. 111-118Resumo: A substituição dos aços convencionais por aços de alta resistência é uma aposta da indústria automotiva para fabricação de peças embutidas. Isto possibilita o uso de chapas mais finas com a manutenção das propriedades mecânicas e pode ser associada à redução do peso de componentes e redução de custos. Porém, o uso dos aços de alta resistência implica no agravamento de alguns problemas de fabricação, dos quais se destaca o aumento do retorno elástico quando comparado aos aços convencionais. O retorno elástico é uma deformação geométrica da peça embutida e que, para processos realizados na temperatura ambiente, pode ser controlado por ajustes na geometria da ferramenta e pelo ajuste da tensão na chapa. O controle da temperatura de embutimento também é apontado como outra alternativa para controle do retorno elástico. Ele pode medido em peças obtidas de experimentos práticos de embutimento, e também pode ser previsto computacionalmente através da análise numérica pelo método de elementos finitos. A compreensão dos relacionamentos entre a temperatura de embutimento, as características dos materiais, os parâmetros práticos e os parâmetros computacionais, pode melhorar a previsão do retorno elástico para peças embutidas em aços de alta resistência. Por isto, o objetivo deste trabalho foi estudar a influência de temperatura de embutimento no retorno elástico em aços de alta resistência. Para isto, foram realizados ensaios de tração para várias temperaturas para os aços HSLA350/440 e DP350/600. Também foram realizados experimentos práticos de embutimento com várias temperaturas, baseados no benchmark problem, proposto originalmente na conferência Numisheet (1993). Foi medido o retorno elástico nas peças embutidas, e foram realizados ensaios de metalografia e microdureza. Foram realizados experimentos computacionais com base no modelo de Hensel-Spittel que considera fatores mecânicos e metalúrgicos para previsão do comportamento dos materiais em função da temperatura. Como principal resultado, foi comprovado que o aumento da temperatura de embutimento resulta na redução do retorno elástico. Foi observado um comportamento peculiar nas peças embutidas na temperatura de 600°C, que sugere trabalhos futuros. Palavras-chave: Aços de alta resistência. Embutimento. Retorno elástico. Temperatura. Simulação numérica.Abstract: The replacement of conventional steels with high strength steels is a commitment of the automotive industry to manufacture of deep drawing parts. As a result, the use of thinner sheets with maintenance of mechanical properties can be associated with reduced component weight and reduced costs. However, the use of high strength steels implies the aggravation of some manufacturing problems, especially the springback increase, when compared to conventional steels. Springback in deep drawing parts processed at room temperature is the geometric deviation that can be set by adjustments in tool geometry and by adjusting the tension in the sheet. The deep drawing temperature control is another alternative for springback control. Springback can be measured in deep drawing experiments parts and can be predicted computationally by numerical analysis using the finite element method. Understanding the relationships between the deep drawing temperature, material characteristics, practical parameters and computational parameters, can improve prediction of elastic return for deep drawing parts in high strength steels. The objective of this work was to study the influence of deep drawing temperature on the springback in high strength steels. It were performed tensile tests at various temperatures for the HSLA350/440 and DP350/600 steels. It were also performed practical deep drawing experiments with various temperatures, based on the benchmark problem originally proposed at the Numisheet (1993) conference. It was measured springback on the deep drawing parts, and it were performed metallography and micro hardness tests. Computational experiments based on the Hensel-Spittel model that considers mechanical and metallurgical factors to predict the behavior of materials as a function of temperature. As the main result, the increase in temperature results in the reduction of the springback in deep drawing parts. One special behavior in the deep drawing parts at the temperature of 600°C suggests future works. Keywords: High Strength Steels. Deep drawing. Springback. Temperature. Numerical simulation

Short-term effect of monocuspid valves on pulmonary insufficiency and clinical outcome after surgical repair of tetralogy of fallot

AbstractIn the surgical repair of tetralogy of Fallot, monocuspid valves are sometimes inserted within a transannular patch to prevent pulmonary insufficiency. To determine whether this monocuspid valve prevents short-term postoperative pulmonary insufficiency and improves clinical outcome, we reviewed clinical data and preoperative and postoperative echocardiographic variables from 61 patients who underwent one of three different procedures for repair of tetralogy of Fallot between August 1992 and March 1994. We compared features from 24 patients who had undergone transannular patch repair with a monocuspid valve (patch-valve) with those from 17 patients who had undergone patch repair without a monocuspid valve (patch) and 20 patients who had undergone repair without a transannular patch (no patch). We used the ratio of pulmonary valve insufficiency jet width to pulmonary artery diameter, as measured by color-flow Doppler flowmetry, as an index of severity of pulmonary insufficiency. Moderate to severe pulmonary insufficiency was arbitrarily defined as a ratio of at least 0.50. We found no significant differences in ratios among the patch-valve group (0.73 ± 0.25, mean ± standard deviation), the patch group (0.79 ± 0.20), and the no patch group (0.59 ± 0.23). The percentages of patients with moderate to severe pulmonary insufficiency did not differ among the three groups (patch-valve 80%, patch 90%, no patch 64%). Clinical data (including mortality, number of reoperations, intensive care unit and hospital lengths of stay, and postoperative hemodynamics) were similar in the three groups. We conclude that insertion of a monocuspid valve in repair of tetralogy of Fallot does not prevent short-term postoperative pulmonary insufficiency and does not improve immediate postoperative outcome for these patients. (J Thorac Cardiovasc Surg 1996;112:33-7

A screen for downstream effectors of Neurogenin2 in the embryonic neocortex

Neurogenin (Ngn) 1 and Ngn2 encode basic-helix-loop-helix transcription factors expressed in the developing neocortex. Like other proneural genes, Ngns participate in the specification of neural fates and neuronal identities, but downstream effectors remain poorly defined. We set out to identify Ngn2 effectors in the cortex using a subtractive hybridization screen and identified several regionally expressed genes that were misregulated in Ngn2 and Ngn1; Ngn2 mutants. Included were genes down-regulated in germinal zone progenitors (e.g., Nlgn1, Unc5H4, and Dcc) and in postmitotic neurons in the cortical plate (e.g., Bhlhb5 and NFIB) and subplate (e.g., Mef2c, srGAP3, and protocadherin 9). Further analysis revealed that Ngn2 mutant subplate neurons were misspecified and that thalamocortical afferents (TCAs) that normally target this layer instead inappropriately projected towards the germinal zone. Strikingly, EphA5 and Sema3c, which encode repulsive guidance cues, were down-regulated in the Ngn2 and Ngn1; Ngn2 mutant germinal zones, providing a possible molecular basis for axonal targeting defects. Thus, we identified several new components of the differentiation cascade(s) activated downstream of Ngn1 and Ngn2 and provided novel insights into a new developmental process controlled by these proneural genes. Further analysis of the genes isolated in our screen should provide a fertile basis for understanding the molecular mechanisms underlying corticogenesis

Right ventricular dysfunction in children supported with pulsatile ventricular assist devices

ObjectivesTo describe the incidence and severity of right ventricular dysfunction (RVD) in pediatric ventricular assist device (VAD) recipients and to identify the preoperative characteristics associated with RVD and their effect on outcomes.MethodsChildren bridged to transplantation from 2004 to 2011 were included. RVD was defined as the use of a left VAD (LVAD) with an elevated central venous pressure of >16 mm Hg with inotropic therapy and/or inhaled nitric oxide for >96 hours or biventricular assist (BiVAD).ResultsA total of 57 children (median age, 2.97 years; range 35 days to 15.8 years) were supported. Of the 57, 43 (75%) had an LVAD, and of those, 10 developed RVD. The remaining 14 (25%) required BiVAD. Thus, RVD occurred in 24 of 57 patients (42%). Preoperative variables such as younger age (P = .01), use of extracorporeal mechanical support (P = .006), and elevated urea (P = .03), creatinine (P = .02), and bilirubin (P = .001) were associated with RVD. Multiple logistic regression analysis indicated that elevated urea and extracorporeal mechanical support (odds ratio, 26.4; 95% confidence interval, 2.3-307.3; and odds ratio, 27.8; 95% confidence interval, 2.5-312.3, respectively) were risk factors for BiVAD. The patients who developed RVD on LVAD had a complicated postoperative course but excellent survival (100%), comparable to those with preserved right ventricular function (91%). The survival for those requiring BiVAD was reduced (71%).ConclusionsRVD occurred in approximately 40% of pediatric VAD recipients and affects their peri-implantation morbidity and bridging outcomes. Preoperative extracorporeal membrane oxygenation and elevated urea were risk factors for BiVAD. Additional studies of the management of RVD in children after VAD implantation are warranted

Subaortic stenosis in the spectrum of atrioventricular septal defects Solutions may be complex and palliative

AbstractFrom July 1982 through September 1994, 19 children had operative treatment of subaortic stenosis associated with an atrioventricular septal defect. Specific diagnosis were septum primum defects in 7, Rastelli type A defects in 6, transitional defects in 4, inlet ventricular septal defect with malattached chordae in 1, and tetralogy of Fallot with Rastelli type C defect in 1. Twenty-seven operations for subaortic stenosis were performed. Surgical treatment of the outlet lesion was performed at initial atrioventricular septal defect repair in 3 children and in the remaining 16 from 1.2 to 13.1 years (mean 4.9 years, median 3.9 years) after repair. Eighteen of the 19 children had fibrous resection and myectomy for relief of obstruction. Seven children had an associated left atrioventricular valve procedure. One child received an apicoaortic conduit. Seven children (36.8%) required 8 reoperations for previously treated subaortic stenosis. Time to the second procedure was 2.8 to 7.4 years (mean 4.9 years). Follow-up is 0.4 to 14.0 years (median 5.6 years). Six-year actuarial freedom from reoperation is 66% ±15%. The angle between the plane of the outlet septum and the plane of the septal crest was measured in 10 normal hearts (86.4 ±13.7) and 10 hearts with atrioventricular septal defects (22.2 ±26.0; p <0.01). The outflow tract can be effectively shortened, widened, and the angle increased toward normal by augmenting the left side of the superior bridging leaflet and performing a fibromyectomy. Conclusion: Standard fibromyectomy for subaortic stenosis in children with atrioventricular septal defects leads to a high rate of reoperation. Leaflet augmentation and fibromyectomy may decrease the likelihood of reoperation. (J THORAC CARDIOVASC SURG 1995;110:1534-42

β3-Adrenoceptor Antagonist SR59230A Attenuates the Imbalance of Systemic and Myocardial Oxygen Transport Induced by Dopamine in Newborn Lambs

Background In neonates, the increase in O 2 -delivery (DO 2 ) by dopamine is offset by a greater increase in O 2 -consumption (VO 2 ). This has been attributed to β 3 -adrenergic receptors in neonatal brown fat tissue. β 3 receptors in the heart have negative inotropic properties. We evaluated the effects of SR59230A, a β 3 -antagonist, on the balance of systemic and myocardial O 2 -transport in newborn lambs treated with dopamine. Methods Lambs (2-5 days old, n = 12) were anesthetized and mechanically ventilated. Heart rate (HR) and rectal temperature were monitored. VO 2 was measured by respiratory mass spectrometry and cardiac output (CO) by a pulmonary artery transonic flowmeter. Arterial, jugular bulb venous and coronary sinus blood gases and lactate were measured to calculate DO 2 , O 2 extraction ratio (ERO 2 ), myocardial O 2 and lactate extraction ratios (mERO 2 , mERlac). After baseline measurements, lambs were randomized to receive SR59230A at 5 mg/kg iv (SRG) or placebo. Both groups received incremental doses of a dopamine infusion (0-5-10-15-20 mcg/kg/min) every 15 min. Measurements were repeated at the end of each dose. Results After SR59230A infusion, CO and HR trended to decrease ( P = 0.06), but no significant changes occurred in other parameters. Over the incremental doses of dopamine, temperature increased in both groups ( P 0.1). DO 2 trended to a small increase ( P = 0.08). VO 2 increased in both groups ( P < 0.0001) but to a lesser degree in SRG ( P < 0.0001). As a result, ERO 2 increased in both groups ( P < 0.0001), but to a lesser degree in SRG ( P < 0.0001). mERO 2 was lower in SRG ( P = 0.01) with a faster increase ( P < 0.0001). mERlac was higher in SRG ( P = 0.06) with a faster decrease ( P = 0.04). Conclusion Although SR59230A tends to induce an initial drop in CO, it significantly attenuates the rise in VO 2 and hence the imbalance of systemic and myocardial O 2 transport induced by dopamine at higher doses. Studies are warranted to examine the effect of SR59230A in cases of cardiac dysfunction and increased VO 2 , observed after cardiac surgery

The Registry and Follow-Up of Complex Pediatric Therapies Program of Western Canada: A Mechanism for Service, Audit, and Research after Life-Saving Therapies for Young Children

Newly emerging health technologies are being developed to care for children with complex cardiac defects. Neurodevelopmental and childhood school-related outcomes are of great interest to parents of children receiving this care, care providers, and healthcare administrators. Since the 1970s, neonatal follow-up clinics have provided service, audit, and research for preterm infants as care for these at-risk children evolved. We have chosen to present for this issue the mechanism for longitudinal follow-up of survivors that we have developed for western Canada patterned after neonatal follow-up. Our program provides registration for young children receiving complex cardiac surgery, heart transplantation, ventricular assist device support, and extracorporeal life support among others. The program includes multidisciplinary assessments with appropriate neurodevelopmental intervention, active quality improvement evaluations, and outcomes research. Through this mechanism, consistently high (96%) follow-up over two years is maintained

Plasma matrix metalloproteinases in neonates having surgery for congenital heart disease

During cardiopulmonary-bypass matrix-metalloproteinases released may contribute to ventricular dysfunction. This study was to determine plasma matrix-metalloproteinases in neonates after cardiopulmonary-bypass and their relation to post-operative course. A prospective observational study included 18 neonates having cardiac surgery. Plasma matrix-metalloproteinases-2 and 9 activities were measured by gelatin-zymography pre-operatively, on starting cardiopulmonarybypass, 7–8 min after aortic cross-clamp release, and 1h, 4h, 24h, and 3d after cardiopulmonary-bypass. Plasma concentrations of their tissue inhibitors 1 and 2 were determined by enzyme-linked immunosorbent assay. Cardiac function was assessed by serial echocardiography. Paired t-tests and Wilcoxon tests were used to assess temporal changes, and linear correlation with simultaneous clinical and cardiac function parameters were assessed using Pearson's product-moment correlation coefficient. Plasma matrix-metalloproteinases activities and their tissue inhibitor concentrations decreased during cardiopulmonary-bypass. Matrix-metalloproteinase-2 plasma activity increased progressively starting 1h after cardiopulmonarybypass and returned to pre-operative levels at 24h. Matrix-metalloproteinase-9 plasma activity increased significantly after release of aortic cross-clamp, peaked 7–8min later, and returned to baseline at 24h. Plasma tissueinhibitor 1 and 2 concentrations increased 1h after cardiopulmonary-bypass. Cardiac function improved from 4h to 3d after surgery (p<0.05). There was no evidence of significant correlations between matrix-metalloproteinases or their inhibitors and cardiac function, inotrope scores, organ dysfunction scores, ventilation days, or hospital days. The temporal profile of plasma matrix-metalloproteinases and their inhibitors after cardiopulmonary-bypass in neonates are similar to adults. In neonates, further study should determine whether circulating matrix-metalloproteinases are useful biomarkers of disease activity locally within the myocardium, and hence of clinical outcomes