A study of techniques in the evaluation of springback and residual stress in hydroforming

The increasing need for high strength complex hollow bodies for automotive application is pushing towards the use of sheet hydroforming techniques in conjunction with high strength steels. Unfortunately high strength steels are characterised by high springback levels. In this paper the springback and residual stresses have been analysed by means of laboratory trials carried out using the double sheet hydroforming technique. The attention has been focused on the upper blank of TRIP800 steel. The analysis has been performed using different approaches: i) characterisation of sample accuracy by means of a 3D coordinate measuring machine using a new proposed method based on the standard deviation calculation; ii) FE-analysis of both hydroforming and springback stages using an implicit FEM code; iii) residual stress evaluation by means of X-ray diffraction and laser cutting techniques. The effect of pressure, die insert geometry and friction at the blank holder on springback and residual stresses have been analysed and discussed in detail.     

Prediction of flow curves and forming limit curves of Mg alloy thin sheets using ANN-based models

Multivariable empirical models based on artificial neural networks were developed in order to predict the flow curves and forming limit curves of AZ31 magnesium alloy thin sheets, in warm forming conditions, vs. process parameters and fibre orientation. Experimental tensile and hemispherical punch tests were carried out in order to obtain the experimental data set, in terms of flow curves and forming limit curves, to be used to train the artificial neural networks. A preliminary study, based on the leave one-out-cross validation methodology, has proven the very good predictive capability of the ANN-based models in modelling both flow curves (flow stress level, curve shape and strain at the onset of necking) and forming limit curves (curve shape, major strain values and minor strain limit) under different process conditions and fibre orientations. Then, the generalisation capability of the neural models in capturing the effect of process parameters and fibre orientation on flow curves and formability has been proven by the excellent agreement, in terms of the high correlation coefficients, low relative errors and average absolute relative errors, between predicted and experimental results not investigated in the training set.     

Ultrasonography in the detection of aneuploidy in the first trimester

Ultrasonography has been used increasingly in the first trimester to identify fetal anomalies as early as possible in gestation. First trimester sonographic screening may detect a greater proportion of aneuploid fetuses than sonography performed later in pregnancy, and it may allow determination of potential markers for prediction of chromosomal anomalies.     

Time-sequential changes of differentially expressed miRNAs during the process of anterior lumbar interbody fusion using equine bone protein extract,rhBMP-2 and autograft

The precise mechanism of bone regeneration in different bone graft substitutes has been well studied in recent researches. However, miRNAs regulation of the bone formation has been always mysterious. We developed the anterior lumbar interbody fusion （ALIF） model in pigs using equine bone protein extract （BPE）, recombinant human bone morphogenetic protein-2 （rhBMP-2） on an absorbable collagen sponge （ACS）, and autograft as bone graft substitute, respectively. The miRNA and gene expression profiles of different bone graft materials were examined using microarray technology and data analysis, including self-organizing maps, KEGG pathway and Biological process GO analyses. We then jointly analyzed miRNA and mRNA profiles of the bone fusion tissue at different time points respectively. Results showed that miRNAs, including let-7, miR-129, m iR-21, miR-133, miR-140, miR-146, miR-184, and miR-224, were involved in the regulation of the immune and inflammation response, which provided suitable inflammatory microenvironment for bone formation. At late stage, several miRNAs directly regulate SMAD4, Estrogen receptor 1 and 5-hydroxytryptamine （serotonin） receptor 2C for bone formation. It can be concluded that miRNAs play important roles in balancing the inflammation and bone formation.     

Direct determination of rare earth elements at the subpicogram per gram level in antarctic ice by ICP-SFMS using a desolvation system

A method, based on inductively coupled plasma sector field mass spectrometry coupled with a microflow nebulizer and a desolvation system, has been developed for the direct determination of rare earth elements (REE) (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) down to the subpicogram per gram level (1 pg/g = 10(-12) g g(-1)) in approximately 1 mL of molten Antarctic ice. Contamination problems were carefully taken into account by adopting ultraclean procedures during the sample pretreatment phases. The use of a desolvation system for sample introduction during the analysis greatly reduced spectral interferences from oxide formation; the residual interfering contributions were calculated and subtracted whenever necessary. A matched calibration curve method was used for the quantification of the analytes. Instrumental detection limits ranged from 0.001 pg/g for Ho, Tm, and Lu to 0.03 pg/g for Gd. The precision, in terms of relative standard deviation on 10 replicates, ranged from 2% for La, Ce, Pr, and Lu, up to 10% for Er, Tm, and Yb. This methodology allowed the direct determination of REE in a 1-mL sample of ancient Antarctic ice with concentration ranges between 0.006 and 0.4 pg/g for Tm and 0.9-60 pg/g for Ce.     

Nailfold capillary microscopy in patients with antiphospholipid syndrome

In this paper we tried to define the capillaroscopic pattern of anti phospholipid syndrome able to differentiate between the primary (PAPS) and the systemic lupus erythematosus-associated form (SLE-APS) and to be a predictive marker of thrombotic manifestations. Eight PAPS and five SLE-APS patients were studied. In each patient the evaluation was based on anti cardiolipin antibody levels, nailfold capillaroscopy, retinal fluorangiography and transcranial doppler sonography. Statistical analysis has been performed using chi 2 analysis. Morphological alterations of capillary loops, venular visibility and sludging of blood were often observed in both groups. While we found in higher prevalence a variability of capillary loop length in PAPS patients, the SLE-APL group significantly differed for the presence of microhaemorrhages (p < 0.001). When we evaluated the clinical history, a marked microcirculatory damage was related with the occurrence of thrombotic manifestations in the PAPS patients. Anti cardiolipin antibody levels, retinal fluorangiography and transcranial doppler sonography did not correlate with clinical history in either group. In conclusion, nailfold capillaroscopy can be usefully employed in the differentiation between primary and SLE-associated anti phospholipid syndrome, and it can help to identify the patients at higher risk of thrombotic disease.     

Performances and limits of a parallel oscillator for electrochemical quartz crystal microbalances

This paper describes a driving circuit for an electrochemical quartz crystal microbalance (EQCM) adapted to a wide range of applications. The oscillator is a Miller-type parallel oscillator using an operational transconductance amplifier (OTA). A theoretical study of the oscillating circuit led to the analytical expression of the microbalance frequency as well as to an overestimation of the error on the mass measurement. The reliability of the EQCM was then experimentally verified through electrochemical copper deposition and dissolution. The limit of operation of the EQCM was also investigated, both analytically and experimentally. This work shows that parallel oscillators using few electronic components allow a very reliable EQCM to be obtained for mass measurements on metallic films, even if they are highly damped.     

Electrochemical investigation of locally depassivated iron. A comparison of various techniques

Electrochemical aspects of the damage caused in situ to the passive film on iron have been investigated by means of ac impedance and spectral analysis of the current fluctuations. These techniques can provide useful information on the individual depassivation-repassivation transient and its interaction with the surrounding passive surface. It has been shown that it is rather difficult to define an intrinsic rate of repassivation which could be independent of the depassivation technique. Firstly the repassivation has been studied by potential jump experiments. Secondly depassivation by abrasion due to the projection of a suspension of particles or focused laser pulse have been developed. The results are discussed in terms of the classical model involving a sequence of depassivation-repassivation events induced by local breakdown of the film.     

Application of a decision making method in the forging condition optimisation for manufacturing automotive components

In the present paper, a decision making method based on the Analytic Hierarchy Process is used for the selection of the best forging condition for manufacturing AI-MMC automotive components. Three candidate solutions, in terms of three different sets of initial die and billet temperatures, and die speed, were defined by means of FEM simulations; they were performed in proper strain rate and temperature windows determined by hot formability studies on 6061/Al₂O₃/10p composite. Five criteria for evaluating the different alternatives with respect to the overall goal were defined: i) product quality, ii) production rate, iii) die cost, iv) heating cost, and v) forging load. The AHP method allowed to establish that the alternative characterised by an initial die temperature of 350°C, an initial billet temperature of 400°C, and a die speed of 3 mm/s is the optimum solution since it has the highest global priority level.