Elastic, Mechanical and Thermophysical properties of Single-Phase Quaternary ScTiZrHf High-Entropy Alloy

Consequent to the interaction potential model, the high-order elastic constants at high entropy alloys in single-phase quaternary ScTiZrHf have been calculated at different temperatures. Elastic constants of second order (SOECs) helps to determine other ultrasonic parameters. With the help of SOECs other elastic moduli, bulk modulus, shear modulus, Young’s modulus, Pugh’s ratio, elastic stiffness constants and Poisson’s ratio are estimated at room temperature for elastic and mechanical characterization. The other ultrasonic parameters are calculated at room temperature for elastic and mechanical characterization. The temperature variation of ultrasonic velocities along the crystal's z-axis is evaluated using SOECs. The temperature variation of the average debye velocity and the thermal relaxation time (τ) are also estimated along this orientation axis. The ultrasonic properties correlated with elastic, thermal and mechanical properties which is temperature dependent is also discussed. The ultrasonic attenuation due to phonon – phonon (p-p) interactions is also calculated at different temperatures. In the study of ultrasonic attenuation such as a function of temperature, thermal conductivity appears to be main contributor and p- p interactions are the responsible reason of attenuation and found that the mechanical properties of the high entropy alloy ScTiZrHf are superior at room temperature.

Are Children Suffering From Congenital Pseudarthrosis of the Tibia Associated With Bone Quality Decreased?

Background: Congenital pseudarthrosis of the tibia (CPT) is a rare and difficult to treat congenital disease in neonates. Our team's previous study found that exosomes derived from serum of children with CPT can reduce the effect of bone formation. In this study, we used ultrasound bone densitometry to detect the bone quality between children with CPT and those non-metabolic disease children, to determine the bone strength of children with CPT. Methods: A total of 37 CPT children and 40 children without the bone metabolic disease (control group) were recruited in our hospital. The ultrasonic bone densitometer was used to examine the bilateral calcaneus of the subjects. According to the measurement results, we collected the broadband ultrasonic attenuation (BUA), sound transmission velocity (SOS), quantitative ultrasound index (QUI), bone strength index(STI) and bone mineral density estimation(BMDe) values. For the intergroup analysis, t test was used to determine the differences of various quantitative measurements. Multivariable regression was used to examine the associations between quantitive ultrasound measurements differences and age, body mass index (BMI), neurofibromatosis type 1 (NF1) and CPT Crawford type. Intra-class correlation coefficient (ICC) was calculated to estimate intra- and inter-rater agreements. Results: Seventy-four calcaneus scans from CPT patients (23 boys and 14 girls) and 80 calcaneus scans (24 boys and 16 girls) from the control. The CPT patients exhibited significantly lower SOS (1368.75±136.78 m/s), STI (7.2319±38.6525), QUI (8.2532±56.1720) and BMDe (-0.0241±0.3552 g/cm3) than the control (SOS: 1416.02±66.15 m/s, STI: 7.96±16.884, QUI: 28.8299±25.461, BMDe: 0.0180±0.1610 g/cm3). Multiple linear regression revealed that SOS, STI, QUI was statistically significant and negatively correlated with CPT Crawford classification.Conclusions: We found the incidence of decreased bone quality in CPT group was higher than that in the non-bone metabolic disease group. This phenomenon was not related to NF1 while related to CPT Crawford classification, which suggested that the higher grade of the CPT Crawford classification, the lower the bone strength and the higher the risk of fracture.

Universality of ultrasonic attenuation coefficient of amorphous systems at low temperatures

The competition between unretarded dispersion interactions between molecules prevailing at medium range order length scales and their phonon induced coupling at larger scales leads to appearance of nano-scale sub structures in amorphous systems. The complexity of intermolecular interactions gives rise to randomization of their operators. Based on a random matrix modelling of the Hamiltonian and its linear response to an external strain field, we show that the ultrasonic attenuation coefficient can be expressed as a ratio of two crucial length-scales related to molecular dynamics. A nearly constant value of the ratio for a wide range of materials then provides a theoretical explanation of the experimentally observed qualitative universality of the ultrasonic attenuation coefficient at low temperatures.

Edge Illumination X-Ray Phase Contrast Imaging and Ultrasonic Attenuation for Porosity Quantification in Composite Structures

Carbon fiber reinforced composites are widely used in the aerospace industry, due to their low weight and high strength. Porosity often occurs during the manufacturing of composite structures, which can compromise the structural integrity of the part and affect its mechanical properties. In the aerospace industry a typical requirement for structural components is for the porosity content to be kept below 2%. Non-destructive evaluation (NDE) techniques are used to estimate the porosity content in composite components, the most common being ultrasonic attenuation and X-ray computed tomography (CT). Planar Edge Illumination X-ray Phase Contrast Imaging (EI XPCI) was used to quantify the porosity content in woven carbon fiber reinforced composite plates with porosity ranging between 0.7% and 10.7%. A new metric was introduced, the standard deviation of the differential phase (STDVDP) signal, which represents the variation of inhomogeneity in the plates for features of a scale equal to or above the system resolution (here 12μm). The SDTVDP was found to have a very high correlation with porosity content estimated from matrix digestion and ultrasonic attenuation, hence providing a promising new methodology to quantify porosity in composite plates.