Quality control of the induction hardened layer and the grinding process in aerospace ball screws via magnetic Barkhausen noise analysis
Reducing the weight of aircraft and helicopters is a common way to reduce fuel consumption and achieve greener operations. Nowadays, hydraulic actuators are used to move the control surfaces that are responsible for commanding the flight. Hydraulic systems have a considerable weight and therefore one of the major challenges in the aeronautic sector is to substitute these actuators with lighter electrical actuators. However, electrical actuators must be highly reliable and able to work under severe conditions. In this respect, electro-mechanical actuators (EMA) represent the next generation of actuation systems for commercial aircraft and aero engines. EMAs are equipped with a motor, a ball/roller screw and the control electronics. Actuators are safety-critical components of an aerospace system and an undetected failure can lead to serious consequences. Therefore, the quality of these ball screws has to be controlled and certified with the most advanced non-destructive techniques. In this context, the present work presents magnetic Barkhausen noise analysis (BNA) as a non-destructive technique for controlling the quality of ball screws, thereby ensuring the induction hardened layer has formed properly and detecting the local overheating regions, known as grinding burns, which may have occurred during the grinding process. With the aim of analysing the sensitivity of the BNA, several induction hardening treatments were applied to produce samples with different profiles and hardened layer depths. Moreover, grinding conditions were varied to obtain grinding burns of different intensities. Magnetic Barkhausen noise measurements were taken with a system designed and implemented by the authors, and the derived parameters were compared with microhardness measurements made at various depths after the different induction hardening and grinding processes. The results show that various parameters derived from the magnetic Barkhausen noise envelope can be used to identify both the different layer depths after induction hardening and the decrease in hardness produced by the grinding burns in such a way that a set of thresholds can be used to determine and assure the quality of the hardened layer and the grinding process of the ball screws. More info about this article: http://ndt.net/?id=19690
Barkhausen noise characterisation during elastic bending and tensile-compression loading of case-hardened and tempered samples
This study examined the Barkhausen noise (BN) response of carburising case-hardened steel with varying tempering stages. The test material was loaded in bending and in alternating loading. The aim of the study was to obtain relevant multiparameter BN data from different loading conditions and to investigate the effect of applied stress on the BN response. The test bar series was made from case-hardened steel. Different tempering parameters were used to vary the surface hardness and the surface residual stresses of the studied series of test bars. In the bending tests, the samples were subjected to incrementally applied loading in the purely elastic deformation region. In addition, uniaxial stepwise loading with tensile and compressive stress was applied to selected samples simultaneously with the BN measurements. The BN measurements were performed under different loading conditions along with X-ray diffraction strain measurements in bending. The results revealed linear behaviour between the reciprocal root mean square value and the stress values obtained with strain gages and X-ray diffraction for the tempered samples.
Papacy and Law in the Gregorian Revolution: The Canonistic Work of Anselm of Lucca
PART I: PAPACY AND LAW ON THE EVE OF THE GREGORIAN REVOLUTION PART II: A CANONIST IN THE AGE OF REFORM