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Materials ◽  
2022 ◽  
Vol 15 (1) ◽  
pp. 363
Author(s):  
Abdulnaser M. Alshoaibi ◽  
Yahya Ali Fageehi

The aim of this paper was to present a numerical simulation of a crack growth path and associated stress intensity factors (SIFs) for linear elastic material. The influence of the holes’ position and pre-crack locations in the crack growth direction were investigated. For this purpose, ANSYS Mechanical R19.2 was introduced with the use of a new feature known as Separating Morphing and Adaptive Remeshing Technology (SMART) dependent on the Unstructured Mesh Method (UMM), which can reduce the meshing time from up to several days to a few minutes, eliminating long preprocessing sessions. The presence of a hole near a propagating crack causes a deviation in the crack path. If the hole is close enough to the crack path, the crack may stop at the edge of the hole, resulting in crack arrest. The present study was carried out for two geometries, namely a cracked plate with four holes and a plate with a circular hole, and an edge crack with different pre-crack locations. Under linear elastic fracture mechanics (LEFM), the maximum circumferential stress criterion is applied as a direction criterion. Depending on the position of the hole, the results reveal that the crack propagates in the direction of the hole due to the uneven stresses at the crack tip, which are consequences of the hole’s influence. The results of this modeling are validated in terms of crack growth trajectories and SIFs by several crack growth studies reported in the literature that show trustworthy results.


Author(s):  
Mohammad Salahi Nezhad ◽  
Dimosthenis Floros ◽  
Fredrik Larsson ◽  
Elena Kabo ◽  
Anders Ekberg

2022 ◽  
Author(s):  
Hui Jiang ◽  
Jun Ye ◽  
Peng Hu ◽  
Shengli Zhu ◽  
Yanqin Liang ◽  
...  

Co-crystallization is an efficient way of molecular crystal engineering to tune the electronic properties of organic semiconductors. In this work, we synthesized anthracene-4,8-bis(dicyanomethylene)4,8-dihydrobenzo[1,2-b:4,5-b’]-dithiophene (DTTCNQ) single crystals as a template to...


Metals ◽  
2021 ◽  
Vol 12 (1) ◽  
pp. 55
Author(s):  
Kirill Kalashnikov ◽  
Andrey Chumaevskii ◽  
Tatiana Kalashnikova ◽  
Andrey Cheremnov ◽  
Evgeny Moskvichev ◽  
...  

This work explores the possibility of using friction stir processing to harden the Ti-6Al-4V titanium alloy material produced by wire-feed electron beam additive manufacturing. For this purpose, thin-walled workpieces of titanium alloy with a height of 30 cm were printed and, after preparation, processed with an FSW-tool made of heat-resistant nickel-based superalloy ZhS6U according to four modes. Studies have shown that the material structure and properties are sensitive to changes in the tool loading force. In contrast, the additive material’s processing direction, relative to the columnar grain growth direction, has no effect. It is shown that increasing the axial load leads to forming a 𝛽-transformed structure and deteriorates the material strength. At the same time, compared to the additive material, the ultimate tensile strength increase during friction stir processing can achieve 34–69%.


2021 ◽  
Author(s):  
Shrok Allami

ZnO nanowires (or nanorods) have been widely studied due to their unique material properties and remarkable performance in electronics, optics, and photonics. This chapter presents a review of the current research of ZnO nanowires (or nanorods) synthesized by hydrothermal method. We discussed the mechanism of its nucleation and growth taking the effect of different parameters on its growth direction and their final morphology into account. A mixture of zinc nitrate and hexamine as precursor is the most popular. We reported the effect of precursor type and concentration, pH of the growth solution, bath temperature, substrate type and seeded layer, and duration time.


2021 ◽  
Vol 11 (1) ◽  
pp. 105-119
Author(s):  
Guangyu Qin ◽  
Xiaoxiao Huang ◽  
Xu Yan ◽  
Yunfei He ◽  
Yuhao Liu ◽  
...  

AbstractWood-derived carbon has a 3D porous framework composed of through channels along the growth direction, which is a suitable matrix for preparing electromagnetic wave (EMW) absorbing materials with low cost, light weight, and environmental friendliness. Herein, the carbonized wood decorated by short cone-like NiCo2O4 (NiCo2O4@CW) with highly ordered straight-channel architecture was successfully manufactured through a facile calcination procedure. The horizontal arrangement of the through channels of NiCo2O4@CW (H-NiCo2O4@CW) exhibits a strong reflection loss value of -64.0 dB at 10.72 GHz with a thickness of 3.62 mm and a low filling ratio of 26 wt% (with the density of 0.98 g·cm-3), and the effective absorption bandwidth (EAB) is 8.08 GHz (9.92–18.0 GHz) at the thickness of 3.2 mm. The excellent microwave absorption (MA) property was ascribed to the ordered-channel structure with abundant interfaces and defects from NiCo2O4@CW, which could promote the interfacial polarization and dipole polarization. What is more, this advantageous structure increased the multiple reflections and scattering. Finite element analysis (FEA) simulation is carried out to detect the interaction between the prepared material and EMW when the ordered channels are arranged in different directions. This research provides a low-cost, sustainable, and environmentally friendly strategy for using carbonized wood to fabricate microwave absorbers with strong attenuation capabilities and light weight.


Author(s):  
Klaus Köhler ◽  
Wilfried Pletschen ◽  
Lutz Kirste ◽  
Stefano Leone ◽  
Stefan Müller ◽  
...  

Abstract Leakage of AlxGa1-xN/GaN heterostructures was investigated by admittance–voltage profiling. Nominally undoped structures were grown by low-pressure metal-organic vapor-phase epitaxy (MOVPE). The investigated structures had an Al-content of 30 %. They are compared to structures with an additional 1 nm thick AlN interlayer placed before the Al0.3Ga0.7N layer growth, originally to improve device performance. Conductance of FET devices with AlN interlayer, measured from depletion of the two-dimensional electron gas (2DEG) to zero volt bias at frequencies ranging from 50 Hz to 10 kHz, could be described by free charge carriers using a Drude model. The voltage dependent conductance shows a behavior described by either Poole-Frenkel emission or Schottky emission. From the size of the conductance, as well as simulation of the tunneling current injected from the gate under off-state conditions by universal Schottky tunnelling, Schottky Emission is obvious. Evaluating the data by Schottky emission, we can locate the leakage path, of tens of nm in the range between gate and drain/source with contact to the 2DEG, originating from the AlN interlayer. The static dielectric constant in growth direction, necessary for the evaluation, is determined from various AlxGa1 xN/GaN heterostructures to ε||(0) = 10.7 +/- 0.1.


2021 ◽  
Author(s):  
Chang-sheng Zhu ◽  
Zi-hao Gao ◽  
Peng Lei ◽  
Li Feng ◽  
Bo-rui Zhao

Abstract The multi-phase field model of grain competitive growth during directional solidification of alloy was established, solving multi-phase field models for thin interface layer thickness conditions, grain boundary evolution and grain elimination during the competitive growth of SCN-0.24wt% camphor model alloy bi-crystals were investigated, the effects of different crystal orientations and pulling velocities on grain boundary microstructure evolution were quantitatively analyzed. The results show that in the competitive growth of convergent bi-crystals, when favorably oriented dendrites are in the same direction as the heat flow and the pulling speed is too large, the orientation angle of the bi-crystal from small to large is the normal elimination phenomenon of the favorably oriented dendrite blocking the unfavorably oriented dendrite, and the grain boundary is along the growth direction of the favorably oriented dendrite, and when the pulling speed becomes small, the grain boundary shows the anomalous elimination phenomenon of the unfavorably oriented dendrite eliminating the favorably oriented dendrite. In the process of competitive growth of divergent bi-crystal, when the growth direction of favorably oriented dendrites is the same as the heat flow direction and the orientation angle of unfavorably oriented grains is small, the frequency of new spindles of favorably oriented grains is significantly higher than that of unfavorably oriented grains, and as the orientation angle of unfavorably oriented dendrites becomes larger, the unfavorably oriented grains are more likely to have stable secondary dendritic arms, which in turn develop new primary dendritic arms to occupy the liquid phase grain boundary space, but the grain boundary direction is still parallel to favorably oriented dendrites. In addition, the tertiary dendritic arms on the developed secondary dendritic arms may also be blocked by the surrounding lateral branches from further developing into nascent main axes, this blocking of the tertiary dendritic arms has a random nature, which can have an impact on the generation of nascent primary main axes in the grain boundaries.


Author(s):  
Ryuga Yajima ◽  
Kei Kamada ◽  
Yui Takizawa ◽  
Masao Yoshino ◽  
Kyoung Jin Kim ◽  
...  

Abstract The 6LiBr/CeBr3 eutectic scintillator for thermal neutron detection has been developed due to achieving high 6Li concentration. The eutectics were grown by vertical Bridgman method. Molar ratio of 6Li in 6LiBr/CeBr3 eutectic is 35 %, which is higher than that of commercial neutron scintillators such Ce:LiCaAlF6 and Ce:Cs2LiYCl6. The grown eutectic had lamellar-type eutectic structure extending along the growth direction and optical transparency. The grown eutectics showed an emission peak at 360 and 380 nm ascribed to Ce3+ 4f-5d transition from CeBr3 scintillation phase. The measurements of scintillation performance of the 6LiBr/CeBr3 were performed using x-ray, gamma-ray and neutron irradiation to evaluate its potential as a neutron scintillator.


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