Mechanism of Gradient Strengthening Layer Formation Based on Microstructure and Microhardness of Inconel 718 Grinding Surface

Gradient strengthening layer will emerge on the grinding surface of Inconel 718 due to the difference of microstructure. The surface microstructure and microhardness are not independent of each other, and the microhardness is the embodiment of the microstructure evolution in the strength aspect. In this paper, the microstructure observation, microhardness experiments and strengthening theory were combined to analyze. The experimental results show that the grinding surface consists of grain refinement layer and high-density dislocation layer. The grain refinement layer is constituted of equiaxed nano-grains and elongated grains, in which grain boundary strengthening occurred leading to an increase in microhardness. Dislocation strengthening occurred in the high-density dislocation layer, in which the increment of dislocation density is approximately 3.54 × 109 mm− 2 compared with inner matrix. Microhardness of high-density dislocation region reaches the maximum (438.6 ± 11.1 HV0.01) because of the dislocation strengthening. The variation of microhardness is discussed from two strengthening mechanisms of grain boundary strengthening and dislocation strengthening, and the strengthening mechanism in the different regions of grinding surface is revealed. The calculated microhardness increments through these mechanisms in the refined-grain region and the high-density dislocation region are basically consistent with the measured values.

Test on Rigid-flexible Composite Anti-breaking Measure for Tunnels across Stick-slip Fault

In this paper, based on the F8 stick-slip fault section of Longxi Tunnel in China, the effect of the anti-breaking measure of rigid-flexible composite (reinforcement of the secondary lining & construction of the reducing dislocation layer between the primary support and the secondary lining) is studied by using the method of indoor model test in order to improve the anti-breaking performance of the tunnel across stick-slip fault in the actual tunnel engineering. The test results show that the anti-breaking effect is limited by adopting structural strengthening measures to resist the influence of stick-slip dislocation on the tunnel structure and the anti-breaking effect is obvious by adopting the measures of reducing dislocation layer only. However, the structural safety of the tunnel with stick-slip fault in the strong seismic intensity area can be greatly improved by adopting the anti-breaking measure of rigid-flexible composite, and the structural safety factor can be significantly improved. The research results of this paper can provide a reference for the anti-breaking design of the tunnel across stick-slip fault in the high seismic intensity area.

Model Tests on the Antibreaking Countermeasures for Tunnel Lining Across Stick-Slip Faults

In order to improve the structural safety and stability of the tunnels crossing stick-slip fault, an indoor model test on the effect of tunnel antibreaking measures under the influence of fault stick-slip movements was conducted. Using contact pressure, longitudinal strain, and safety factor, the antibreaking effect of tunnels was compared and analyzed under 5 kinds of operating conditions, mainly including no measures, structural strengthening, structural strengthening and reducing dislocation layer, structural strengthening and reducing dislocation joint, structural strengthening and reducing dislocation layer, and reducing dislocation joint. The results showed that the longitudinal strain and contact pressure of the tunnel changed markedly (from severe change to more uniform change) when the reducing dislocation measures were adopted in the test, reducing dislocation layer/joint or reducing dislocation layer and reducing dislocation joint. The effect of reducing the fault stick-slip dislocation on the tunnel structure is very limited by only taking structure strengthening measures. The effect of reducing the fault stick-slip dislocation on the tunnel structure is obvious by using the reducing dislocation method, and the minimum safety factor is increased by more than 8 times. The effect of resisting and reducing the fault stick-slip dislocation on the tunnel structure is remarkable by adopting the measures of the structural strengthening and reducing dislocation layer and reducing dislocation joint, and the minimum safety factor is increased by more than 25.45 times. The results can provide reference for the design of antibreaking for the stick-slip fault tunnel in high earthquake intensity and dangerous mountainous areas.

Non-uniformly loaded row of moving shear cracks in magnetoelectroelastic media

Derivations and discussions are obtained in detail of the closed-form representations of the components of the deformation fields at a general point created by a moving row of smart magnetoelectroelastic shear cracks that are subjected to non-uniform mechanical, electric, and magnetic loadings. The creative analysis exploits a generalization of the basic dislocation layer method. Near a crack tip, their angular variations and the corresponding stress, electric displacement and magnetic induction intensity factors are deduced. Graphical displays of some illustrative numerical data are presented. As a particular case, the results for an analogous stationary row of non-constantly loaded magnetoelectroelastic cracks are derived. The correctness and validity of the results of this novel analysis are examined by the verification of their agreement with those previously presented for various limiting particular cases.

Model Test Study on the Antibreaking Technology of Reducing Dislocation Layer for Subway Interval Tunnel of the Stick-Slip Fracture

Based on the background of the Line F2-3 interval tunnel section of Jiujiawan in Urumqi Subway Line 1, this paper carries out the model test research on the antibreaking technology of the reducing dislocation layer in the tunnel section of the stick-slip fracture. The antibreaking effect of different locations and number of reducing dislocation layers in tunnel engineering is analyzed in this paper. The results show that when the double reducing dislocation layer, respectively, set between the surrounding rock and the primary support, and the primary support and the secondary lining, the antibreaking effect is the best. It is recommended to use this scheme for antibreaking design. The research results can provide reference for antibreaking design of traffic tunnels in active fault zones.

Study of electronic transport parameters on the heterojunction of AlGaN/GaN, grown on Sapphire: two layer model

In spatially confined system such as heterojunction of high and low band gap material, carriers are transferred from higher band gap to the lower band gap. It causes the band bending and the formation of a triangular quantum well at the junction. Such system behaves as quantum-two dimension (Q2D) system because the carriers are free to move on a plane, perpendicular to the junction. Mobility of such quantized system is very high as compare to the bulk system due to the reduction of various scattering mechanisms. GaN is a very useful material. However, a non availability of single crystalline form of GaN and perfectly matched substrates are always problems for GaN. Hence GaN, grown on a substrate such as sapphire is having a very large dislocations at the interface. Such interfacial layer significantly affects the transport parameters of the material, where the transport properties are highly dominated by scattering due to dislocations. The authors have calculated the mobilities of AlGaN/GaN, a heterojunction considering the GaN, grown on Sapphire with reference to the two layer model of Look, in which the 2nd layer is the dislocation layer of GaN and the 1st layer is the junction of AlGaN/GaN where carriers are in the form of two dimensional electron gas (2D EG). The obtained calculated results are also compared with the experimental results as obtained by Sibel Gokden et al. It is observed that the nature of the curve is found to be in agreement with the experimental curve when the ratio of the thicknesses is taken to be 1:1.BIBECHANA 16 (2019) 137-144