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A series of processable and high-temperature resistant polyimide resins terminated with 4-phenylethynyl phthalic anhydride were synthesized by PMR (for in situ polymerization of monomer reactants) using isopropyl alcohol as esterifying agent. The resin solution stored at room temperature for sixteen weeks has no solid precipitation, and the viscosity of the solution does not change significantly, which shows good storage stability at room temperature. The minimum melt viscosity of the imide oligomers is less than 300 Pa·s, which is suitable for compression moulding or autoclaved process. The cured polyimides exhibit extremely high glass transition temperatures (Tg) up to 462℃. The flexural strength and modulus of T300/PMR-PE-2 carbon fiber composite are 963 MPa and 53 GPa, respectively. The inter-laminar shear strength of the composite is 56 MPa. Moreover, the composite can maintain no lower than 66% of their room temperature mechanical properties at 300℃. After isothermal aging in air atmosphere for 500 h at 300℃, the mass loss of the composite is only 0.96%, meanwhile, the composite retention rate maintains 72% of its room temperature flexural strength and 98% of its room temperature inter-laminar shear strength, which demonstrates its excellent thermal-oxidative aging resistance.

In a tiered configuration, a geogrid-reinforced soil (GRS) wall is an acceptable alternative to a traditionally high gravity retaining wall. However, limited studies have been conducted so far to study the long-term performance of tiered GRS walls under working load conditions. In this study, four well-instrumented model tests were carried out to investigate the long-term performance of the two-tiered GRS walls subjected to the sustained loading of 30 kPa. The test results demonstrated that the additional vertical stress at the wall base for the single GRS wall increased over time but generally decreased for the two-tiered GRS walls. Overall, the reinforcement strains increased with the sustained time increasing at the initial loading stage, then decreased to some extent due to wall deformation and stress redistribution, and finally tended to be a slight increase due to the rate-dependent properties of the reinforcement. Moreover, the offset distance has a remarkable effect on the reinforcement layers adjacent to the location of the presence of offset distance. Besides, the lateral wall facing deformations and the settlement at the top surface increased at the initial loading stage and then tended to be relatively stable. A larger offset distance of the adjacent tiers caused a significant reduction in the lateral wall facing deformations and settlements. Finally, a modified analytical method for predicting the lateral wall facing deformation, accounting for the variation of the reinforcement secant stiffness with time, was presented in this study. The predicted lateral wall facing deformations agreed well with the experimentally measured ones in the lower portion of the single-tiered GRS wall and the lower wall of the two-tiered GRS walls. [ABSTRACT FROM AUTHOR]

Aiming at the increasingly complicated high-speed PCB power supply voltage fluctuation problem, a method based on PDN(Power Distribution Network) and target impedance co-simulation design is proposed for the 1.15 V power network. PI(Power Integrity) was studied. Mainly involved in two aspects：(1)DC analysis, by widening the copper area, reducing the return path and other measures to reduce the 1.15 V voltage drop from 9 mV to 2.5 mV, the temperature from 1.3 ℃ to 0.1 ℃, DC current density from 91.340 3 A/mm2 drops to 82.393 5 A/mm2；(2)AC analysis, from the resonance distribution and PDN input impedance analysis, add 22 μF decoupling capacitor at the 987.34 MHz resonance point to build a decoupling network to remove the risk point. The simulation results show that the method effectively reduces the risk of potential voltage fluctuation and target impedance mismatch in high-speed PCB circuits, thus improving the stability and reliability of the power system.