ABSTRACT
Tribological conditions can change drastically during heavy loaded regimes as experienced in metal forming; this is especially critical when lubrication can only be applied at the early stage of the process because the homogeneous lubricant layer can break along the die-workpiece interface. In these cases, adopting a constant friction factor for the lubricant-surface pair may not be a valid assumption. This paper presents a procedure based on the use of dual friction factor maps to determine friction factors employed in heavy loaded regimes. A finite element (FE) simulation is used to obtain the friction factor map for the alloy UNS A96082. Experiments were conducted using four lubricants (aluminum anti-size, MoS2 grease, silicone oil, and copper paste) to determine the actual friction curves. The experimental procedure is based on the application of lubricant only at the beginning of the first stage of ring compression, and not at intermediate stages as is usual in typical ring compression tests (RCTs). The results show that for small reductions (rh < 20%), the conventional RCT can be applied because the tribological conditions remain similar. For large reductions (rh > 20%), it is recommended to obtain an average value of the friction factor for every lubricant-surface pair in the range of deformation considered.
ABSTRACT
OBJETIVO: Analizar la relación del control glucémico materno con el peso final del recién nacido (RN) en pacientes con diabetes gestacional (DG). MÉTODOS: Estudio retrospectivo de 214 gestaciones únicas con DG. Se analizaron las características maternas, los resultados del RN y el control glucémico durante el embarazo. Este se evaluó por las hemoglobinas glucosiladas (HbA1c) medidas en diferentes momentos del tercer trimestre (3T), glucemias basales, glucemias capilares preprandiales, posprandiales a la hora (PP1h) y a las 2 h (PP2h). RESULTADOS: El porcentaje de RN grandes para la edad gestacional (GEG) fue del 9,9% (macrosomía 5,4%), sin diferencias entre sexos. Las madres con RN GEG tenían mayor peso y porcentaje de grasa corporal antes de la gestación (p < 0,05), mayor ganancia de peso durante el embarazo (p < 0,01) y mayor tasa de insulinización. En los embarazos con RN GEG la HbA1c media en el 3T y la HbA1c media (p < 0,01) fueron más elevadas, así como las glucemias PP1h (p < 0,05), PP2h (p < 0,01) y la glucemia media capilar (p < 0,05). La HbA1c del 3T y la glucemia PP2h se correlacionaron con el índice ponderal fetal (r = 0,22, p < 0,01, y r = 0,17, p < 0,05, respectivamente). CONCLUSIONES: Las madres con RN GEG tienen peor control glucémico, a pesar de recibir un tratamiento más intensivo, por lo que las estrategias de tratamiento deben implementarse de forma precoz, sin olvidarse del tratamiento del sobrepeso materno. La HbA1c y la glucemia PP2h son los únicos parámetros de control glucémico que se correlacionan con el peso del RN en nuestro grupo
OBJECTIVE: To assess the relationship between maternal glycaemic control and final newborn (NB) birth weight in patients with gestational diabetes (GD). METHODS: A retrospective study was conducted on 214 singleton pregnancies with GD. Maternal characteristics, newborn outcomes and glycaemic control during pregnancy were analysed. GD was assessed by measurements of glycated haemoglobin (HbA1c) at different times during the third trimester (3T), fasting, pre-prandial, and 1 and 2 hour post-prandial capillary blood glucose (1hPP-2hPP). RESULTS: The percentage of NB large for gestational age (LGA) was 9.9% (macrosomia 5.4%), with no differences between genders. Mothers with LGA NB had a higher weight and percentage of body fat before pregnancy (P < 0.05), more weight gain during pregnancy (P < 0.01), and required more insulin. In pregnancies with LGA NB, the mean third trimester HbA1c and mean HbA1c (P < 0.01), were higher, as well as 1hPP (P < 0.05), 2hPP (P < 0.01) blood glucose and mean capillary blood glucose (P < 0.05). The mean third trimester HbA1c and 2hPP blood glucoses were correlated with the fetal weight index (r = 0.22, P < 0.01, and r = 0.17, P < 0.05, respectively). CONCLUSIONS: Mothers with LGA NB have worse glycaemic control, despite having received a more intensive treatment. Treatment strategies should be implemented early during pregnancy, not forgetting maternal overweight treatment. HbA1c and 2hPP blood glucose are the only control parameters that correlated with NB weight in our group
