High speed synchrotron X-ray imaging studies of the ultrasound shockwave and enhanced flow during metal solidification processes

The highly dynamic behaviour of ultrasonic bubble implosion in liquid metal, the multiphase liquid metal flow containing bubbles and particles, and the interaction between ultrasonic waves and semisolid phases during solidification of metal were studied in situ using the complementary ultrafast and high speed synchrotron X-ray imaging facilities housed respectively at the Advanced Photon Source, Argonne National Laboratory, US, and Diamond Light Source, UK. Real-time ultrafast X-ray imaging of 135,780 frames per second (fps) revealed that ultrasonic bubble implosion in a liquid Bi-8 wt. %Zn alloy can occur in a single wave period (30 kHz), and the effective region affected by the shockwave at implosion was 3.5 times the original bubble diameter. Furthermore, ultrasound bubbles in liquid metal move faster than the primary particles, and the velocity of bubbles is 70 ~ 100% higher than that of the primary particles present in the same locations close to the sonotrode. Ultrasound waves can very effectively create a strong swirling flow in a semisolid melt in less than one second. The energetic flow can detach solid particles from the liquid-solid interface and redistribute them back into the bulk liquid very effectively

Quantification of Biventricular Strains in Heart Failure With Preserved Ejection Fraction Patient Using Hyperelastic Warping Method

Heart failure (HF) imposes a major global health care burden on society and suffering on the individual. About 50% of HF patients have preserved ejection fraction (HFpEF). More intricate and comprehensive measurement-focused imaging of multiple strain components may aid in the diagnosis and elucidation of this disease. Here, we describe the development of a semi-automated hyperelastic warping method for rapid comprehensive assessment of biventricular circumferential, longitudinal, and radial strains that is physiological meaningful and reproducible. We recruited and performed cardiac magnetic resonance (CMR) imaging on 30 subjects [10 HFpEF, 10 HF with reduced ejection fraction patients (HFrEF) and 10 healthy controls]. In each subject, a three-dimensional heart model including left ventricle (LV), right ventricle (RV), and septum was reconstructed from CMR images. The hyperelastic warping method was used to reference the segmented model with the target images and biventricular circumferential, longitudinal, and radial strain–time curves were obtained. The peak systolic strains are then measured and analyzed in this study. Intra- and inter-observer reproducibility of the biventricular peak systolic strains was excellent with all ICCs > 0.92. LV peak systolic circumferential, longitudinal, and radial strain, respectively, exhibited a progressive decrease in magnitude from healthy control→HFpEF→HFrEF: control (-15.5 ± 1.90, -15.6 ± 2.06, 41.4 ± 12.2%); HFpEF (-9.37 ± 3.23, -11.3 ± 1.76, 22.8 ± 13.1%); HFrEF (-4.75 ± 2.74, -7.55 ± 1.75, 10.8 ± 4.61%). A similar progressive decrease in magnitude was observed for RV peak systolic circumferential, longitudinal and radial strain: control (-9.91 ± 2.25, -14.5 ± 2.63, 26.8 ± 7.16%); HFpEF (-7.38 ± 3.17, -12.0 ± 2.45, 21.5 ± 10.0%); HFrEF (-5.92 ± 3.13, -8.63 ± 2.79, 15.2 ± 6.33%). Furthermore, septum peak systolic circumferential, longitudinal, and radial strain magnitude decreased gradually from healthy control to HFrEF: control (-7.11 ± 1.81, 16.3 ± 3.23, 18.5 ± 8.64%); HFpEF (-6.11 ± 3.98, -13.4 ± 3.02, 12.5 ± 6.38%); HFrEF (-1.42 ± 1.36, -8.99 ± 2.96, 3.35 ± 2.95%). The ROC analysis indicated LV peak systolic circumferential strain to be the most sensitive marker for differentiating HFpEF from healthy controls. Our results suggest that the hyperelastic warping method with the CMR-derived strains may reveal subtle impairment in HF biventricular mechanics, in particular despite a “normal” ventricular ejection fraction in HFpEF

Ultrafast synchrotron X-ray imaging studies of microstructure fragmentation in solidification under ultrasound

Ultrasound processing of metal alloys is an environmental friendly and promising green technology for liquid metal degassing and microstructural refinement. However many fundamental issues in this field are still not fully understood, because of the difficulties in direct observation of the dynamic behaviours caused by ultrasound inside liquid metal and semisolid metals during the solidification processes. In this paper, we report a systematic study using the ultrafast synchrotron X-ray imaging (up to 271,554 frame per second) technique available at the Advanced Photon Source, USA and Diamond Light Source, UK to investigate the dynamic interactions between the ultrasonic bubbles/acoustic flow and the solidifying phases in a Bi-8%Zn alloy. The experimental results were complimented by numerical modelling. The chaotic bubble implosion and dynamic bubble oscillations were revealed in-situ for the first time in liquid metal and semisolid metal. The fragmentation of the solidifying Zn phases and breaking up of the liquid-solid interface by ultrasonic bubbles and enhanced acoustic flow were clearly demonstrated and agreed very well with the theoretical calculations. The research provides unambiguous experimental evidence and robust theoretical interpretation in elucidating the dominant mechanisms of microstructure fragmentation and refinement in solidification under ultrasound.The authors would like to acknowledge the financial support from the UK Engineering and Physical Sciences Research Council (Grant No. EP/L019965/1, EP/L019884/1, EP/L019825/1,), the Royal Society Industry Fellowship (for J. Mi), and the Hull University & Chinese Scholarship Council (Hull-CSC) PhD Studentship (for D. Tan). The awards of the synchrotron X-ray beam time (EE8542-1) by the Diamond Light Source, UK, and those (GUP 23649 and GUP 26170) by the Advanced Photon Source, Argonne National Laboratory, USA are also gratefully acknowledged. Use of the Advanced Photon Source, an Office of Science User Facility operated for the U.S. Department of Energy (DOE) Office of Science by Argonne National Laboratory, was supported by the U.S. DOE under Contract No. DE-AC02-06CH11357

DESIGN AND OPTIMIZATION OF A HARD DISK DRIVE SUSPENSION

Master'sMASTER OF SCIENCE IN HIGH PERFORMANCE COMPUTATION FOR ENGINEERED SYSTEM

Diffusionally-accommodated Grain Boundary Sliding: Effects on Seismic Wave Attenuation

According to existing experiments on fine-grained polycrystalline mantle materials, in the seismic frequency band, mechanical loss Q-1 decreases with increasing angular frequency &omega in an absorption background; roughly Q-1 &sim &omega&alpha with different investigators reporting values of &alpha ranging from &sim -0.35 to &sim -0.2. There is inconclusive evidence that, under some conditions, a weak local maximum may be superposed on that absorption background. To understand this behaviour, we use a combination of analytical and numerical methods to analyze the Raj-Ashby bicrystal model of diffusionally-accommodated grain boundary sliding on a finite slope interface. In that model, two perfectly elastic layers of finite thickness are separated by a given fixed spatially periodic interface; dissipation is confined to that interfacial (grain boundary) region having an effective viscosity. It occurs by two processes: time-periodic shearing of the interfacial region; and time-periodic diffusion of matter along the interface. Two timescales govern these processes; namely, a characteristic time t&eta taken for the interfacial shear stress to relax and a characteristic time tD taken for matter to move by grain-boundary diffusion over distances of order the grain size.Of particular interest is the case when the timescales are widely separated. Under that condition, we established two previously unrecognized features of the mechanical loss spectrum. First, the mechanical loss Q-1 in the seismic frequency band &omega tD >> 1 can be described by a strict power--law Q-1 &sim &omega&alpha if corners along the interface are geometrically identical. For the two orthogonal sliding modes found in a regular array of hexagonal grains, the values of &alpha is roughly -0.3. Second, our analysis reveals a mechanism allowing the magnitude of &alpha to decrease slowly as &omega is increased; when the corner angle varies from one corner to another along the interface , the rate of decrease in Q-1 gradually slows. Ultimately Q-1 is controlled by the corner having the most singular stress behaviour. Though these results are obtained from the idealized bicrystal model, we argue physically that similar behaviour will be found in numerical models of polycrystal. Overall, our analysis suggests that the range of &alpha -values found empirically may, in part, reflect the differing ranges of &omega tD covered in different experiments.Because in experiments conducted on certain materials, a weak and broad peak superposed onto the power--law absorption background is observed in the loss spectrum whereas in others, the peak is completely absent, we evaluate three proposed factors that may weaken and broaden the peak. We show that the peak can be weaken moderately by (i) sharpening of corners along the interface, (ii) spatial variation in grain size and (iii) spatial variation in interfacial (grain boundary) viscosity. Reduction of the peak by these factors, however, does not suggest it to be completely hidden in the absorption background. By contrast, we show that the loss peak can be markedly broadened if the interfacial viscosity differs by an order of magnitude across adjacent interfaces. The shape of the loss peak is insensitive to the other two factors