Display omitted
This work aims at quantitative analysing the effect of different microstructures on the velocity at stress-free and stress coefficient (K) of longitudinal critical refraction (LCR) ...wave in measuring welding residual stress process, ameliorating the traditional LCR wave method for improving its’ effectiveness and accuracy. The longitudinal critically refracted wave attenuation velocity (LCR-AV) method was proposed in the evaluation of residual stresses in A7N01 welded joints. The same initial status base materials samples are used to produce different levels of grain size and precipitation by heat treatment technology, obtained the velocity at stress-free and attenuation of LCR wave. As expected, the voltage amplitude changes linearly with velocity and stress coefficient, and the precipitation effect can be ignored. The LCR-AV method based on the liner relationship between velocity, attenuation and grain size are efficient to decrease the errors resulting from the different microstructure (base metals, heat-affected zones, and welded zones). Differ with the traditional LCR waves method, the LCR-AV method also measures the voltage amplitude, and the measured results of LCR-AV method compared with those obtained by the hole-drilling reference method shows more sufficient measurement reliability and precision. It shows that LCR-AV method is a valuable quantitative technology to estimate the residual stress of welded joints.
This paper experimentally investigates the application of an X-ray stress measurement called “cos α method” to analyze the electrical pitting generated on rolling bearings. First, a small size ball ...bearing rotation test was conducted in which an electric current passed continuously through the test bearings under various rotating conditions such as current density and electrical conductivities of lubricating greases. Then, the residual stress and full width at half maximum (FWHM) on the electrically damaged bearing raceway were measured. From the correlation between the residual stress and FWHM and the shape of the damage on the raceway surface, it was found that when the bearing was lubricated by the non-conductive grease, the surface was softened by the electric current and the characteristic shape of surface damage occurred. It was also found that lubrication by the conductive grease could reduce the thermal energy during discharge and suppress the surface softening. These findings demonstrate the validity of applying the X-ray stress measurement for electrical pitting analysis.
The distortion in machining aeronautical aluminum alloy parts (AAAPs) is one of the serious challenges in the aviation industry, and the residual stresses produced in multimanufacturing steps are the ...main cause. In order to get a comprehensive understanding of the problems about residual stresses and distortion in machining AAAPs, the state-of-the-art in several aspects including the generation reasons of residual stresses, the factors influencing distortion during machining, the measurement methods of residual stresses, the prediction and controlling methods of distortion are summarized in this paper. The generation mechanism of the bulk residual stress inner materials and the machining-induced residual stresses, as well as the factors affecting two kinds of residual stresses are stated. Also, the influences of residual stresses and machining process conditions on distortion are analyzed. Furthermore, the common residual stress measurement methods and its application scope are summarized. Significantly, the differences, advantages, and disadvantages of various prediction methods are analyzed. The methods of controlling distortion before and after machining are summarized. Finally, the paper gives out further research on the distortion in machining AAAPs in aeronautical manufacturing.
This study presents a novel stress measurement method utilizing the Rayleigh waves virtual superimposed interference spectrum (RW-VSIS). This method achieves stress measurements by exploiting the ...effect of stress on the superimposed interference spectrum of two beams of Rayleigh waves. Firstly, the effect of stress on Rayleigh wave velocity is theoretically investigated by partial wave theory and matrix solving algorithm. The theoretical results show that the Rayleigh wave propagation direction versus the stress direction will affect the wave velocity and the time of flight (TOF). Then, a theoretical model of RW-VSIS under pre-stress is derived. It's found that the stress will dominate the first characteristic frequency (FCF). The regulation effects of propagation distance and angle on FCF are discussed. Finally, the feasibility of stress measurement based on the FCF is validated through experiments. The impact of stress on TOF and FCF is comparatively analyzed. The results show a significant improvement of stress measurement by FCF in the superimposed interference spectrum, compared to the TOF in time domain waveform. With a calibration and verification test for the unknow coefficient of an aluminum specimen, the experimental examination of the stress shows a maximum error of less than 4 MPa indicating good measurement accuracy.
•A novel stress measurement method utilizing the RW-VSIS is presented.•A theoretical model of RW-VSIS under pre-stress is derived.•The first critical frequency (FCF) is strongly related to the stress state of the medium.•A relative change in FCF, which is more obvious than the TOF indicators.
Neurotransmitters play essential roles in regulating neural circuit dynamics both in the central nervous system as well as at the peripheral, including the gastrointestinal tract
. Their real-time ...monitoring will offer critical information for understanding neural function and diagnosing disease
. However, bioelectronic tools to monitor the dynamics of neurotransmitters in vivo, especially in the enteric nervous systems, are underdeveloped. This is mainly owing to the limited availability of biosensing tools that are capable of examining soft, complex and actively moving organs. Here we introduce a tissue-mimicking, stretchable, neurochemical biological interface termed NeuroString, which is prepared by laser patterning of a metal-complexed polyimide into an interconnected graphene/nanoparticle network embedded in an elastomer. NeuroString sensors allow chronic in vivo real-time, multichannel and multiplexed monoamine sensing in the brain of behaving mouse, as well as measuring serotonin dynamics in the gut without undesired stimulations and perturbing peristaltic movements. The described elastic and conformable biosensing interface has broad potential for studying the impact of neurotransmitters on gut microbes, brain-gut communication and may ultimately be extended to biomolecular sensing in other soft organs across the body.
Display omitted
•Improve the precision of non-contact stress measurement for mistuned blisk.•The novel method depends on the data gotten by Blade Tip Timing.•The precision can be increased at least ...4% compared with the direct method.•The maximum relative error is 0.5% in numerical simulation and 12% in experiment.
It is crucially important to monitor the dynamic stress of turbomachinery rotating blades for residual fatigue life prediction and health management, especially for the aircraft engine mistuned blisk. This paper presents an improved non-contact dynamic stress measurement method based on fundamental mistuning model (FMM). The precision of the dynamic stress measurement can be improved at least 4% by the novel method compared with the direct calculation method, and the total stress measurement error is less than 12%. In this paper, only the tuned finite element model, mistuned natural frequency and vibration displacements at each blade tip are needed. The mistuned dynamic stress is expressed in the mistuned modal coordinate system with the stress coordinate base and coordinate values. The numerical and experimental investigations were carried out. This study provides a roadmap to measure the dynamic stress of rotating mistuned blisk, with a strong application potential in the stress online monitoring for the industrial turbomachinery with a blade tip timing (BTT) monitoring system.
PDF
