Science China Technological Sciences

A novel linear microprobe array (LMPA) has been developed by a conventional microfabrication method from silicon. The LMPA leverages the properties of conventional microwire with additional features of naturally formed regular spacing. With the help of periodic microprobe arrays and double-side V-grooves fabricated in advance between each pair of the two microprobes’ rear ends, the number of microprobe units for assembly in one array can be flexibly chosen by cleavage fracture from the LMPA. The fabrication method was demonstrated and the prototype device was assessed by electrochemical impedance spectroscopy (EIS) and in vivo test. The SNR of the spikes recorded was 6.

To obtain a conceptual design for a hybrid rocket motor (HRM) to be used as the Ascent Propulsion System in the Apollo lunar module, the deterministic design optimization (DDO) method is applied to the HRM design. Based on the results of an uncertainty analysis of HRMs, an uncertainty-based design optimization (UDO) method is also adopted to improve the design reliability. The HRM design process, which is a multidisciplinary system, is analyzed, and a mathematical model for the system design is established to compute the motor performance from the input parameters, including the input variables and model parameters. The input parameter uncertainties are quantified, and a sensitivity analysis of the model parameter uncertainties is conducted to identify the most important model parameter uncertainties for HRMs. The DDO and probabilistic UDO methods are applied to conceptual designs for an HRM to be used as a substitute for the liquid rocket motor (LRM) of the Ascent Propulsion System. The conceptual design results show that HRMs have several advantages as an alternative to the LRM of the Ascent Propulsion System, including nontoxic propellant combination, small motor volume, and comparable functions, such as restarting and throating. Comparisons of the DDO and UDO results indicate that the UDO method achieves more robust and reliable optimal designs than the DDO method. The probabilistic UDO method can be used to develop better conceptual designs for HRMs.

Indentation hardness is found to be related to indentation depth when indentation test is applied on homogeneous materials under small indentation depth, which shows strong size effect in the indentation. While in contrast, indentation hardness has a very limited relationship with indentation depth when it is large, showing distinct scaling relationships between hardness and material properties. Previous studies on scaling relationships under deep indentation condition of elastic-perfectly plastic homogeneous materials have been carried out systematically by finite element analysis. In this paper, a heterogeneous material, particle-reinforced matrix composite is detailed studied to investigate its scaling relationships under deep indentation with different particle positions and material properties by finite element analysis.

A novel heat treatment process, stepping quenching and partitioning (S-Q-P), has been developed to manipulate microstructure and mechanical properties of steels. Based on incomplete partitioning of carbon from martensite to austenite, volume fraction and distribution of the retained austenite resulting from the following quenching of the steels could be effectively controlled, and then the synthesized mechanical properties of the steels would be improved. In this paper, 20SiMn2MoVA steel was treated with conventional quenching-tempering (Q-T), currently prevailing quenching-partitioning (Q-P) and S-Q-P processes, respectively. The results indicated that the volume fraction of the retained austenite of the steel treated by Q-P and S-Q-P processes increased significantly that resulted in the increase of ductility and decrease of strength. The product of strength and ductility of the steel treated by S-Q-P process reached 23.7GPa%, that was increased by about 13% and 7% compared with that after Q-T and Q-P processes, respectively. Compared with the great improvement of the synthesized mechanical property obtained by S-Q-P process with another steel 35SiMn, there would be some factors that deteriorated the effect of S-Q-P process on 20SiMn2MoVA steel. It was found by microstructural testing that the carbide forming elements V and Mo in the steel led to precipitation of carbides during partitioning period and lack of carbon in austenite. As a result, less austenite would remain after final quenching and mechanical properties of the steel would be influenced. The results would be beneficial for understanding the principle of S-Q-P process and improving the design of the S-Q-P steel compositions.

The purpose of the vibration test of spacecrafts is to assess their adaptability to low-frequency vibration environment during lift-off. This paper gives the simulation of the satellite ground vibration test (GVT) and the state of the satellite along with rocket during lift-off. The simulation results of these two states are compared on condition that the lateral vibration of satellite/launching vehicle (S/LV) interface is the same. It is shown that the dynamic responses of satellite vertex are totally different. This is because there is angular motion of S/LV interface during lift-off, but in the GVT, the angular motion is restrained. By means of numerical simulation of the lift-off state, the angular motion related to the translation motion of S/LV interface can be determined. Then, using this angular motion as supplementary condition to simulate the vibration test, the calculated dynamic responses of satellite vertex are identical with the lift-off state. It demonstrates that supplementing angular motion condition is an effective method to improve spacecraft ground vibration test more identically with the real lift-off environment. Furthermore, it is useful for the application of the multi-degree-of-freedom shaking table, and provides the basis for test condition requirement.

In this study, we mainly focus on the structural morphology and inter-atomic bonding state of tribofilms resulting from a highly-hydrogenated amorphous carbon (a-C:H) film in order to ascertain the underlying mechanisms for its superlubric behavior (i.e., less than 0.01 friction coefficient). Specifically, we achieved superlubricity (i.e., friction coefficients of down to 0.003) with this film in dry nitrogen and argon atmospheres especially when the tribo-pair is made of an a-C:H coated Si disk sliding against an a-C:H coated steel ball, while the a-C:H coated disk against uncoated ball does not provide superlubricity. We also found that the state of superlubricity is more stable in argon than in nitrogen and the formation of a smooth and uniformly-thick carbonaceous tribofilm appears to be one of the key factors for the realization of such superlubricity. Besides, the interfacial morphology of sliding test pairs and the atomic-scale bond structure of the carbon-based tribofilms also play an important role in the observed superlubric behavior of a-C:H films. Using Raman spectroscopy and high resolution transmission electron microscopy, we have compared the structural differences of the tribofilms produced on bare and a-C:H coated steel balls. For the a-C:H coated ball as mating material which provided superlow friction in argon, structural morphology of the tribofilm was similar or comparable to that of the original a-C:H coating; while for the bare steel ball, the sp2-bonded C fraction in the tribofilm increased and a fingerprint-like nanocrystalline structure was detected by high resolution transmission electron microscopy (HRTEM). We also calculated the shear stresses for different tribofilms, and established a relationship between the magnitude of the shear stresses and the extent of sp3-sp2 phase transformation.

Polymer insulating through-silicon-vias (TSVs) is an attractive approach for high-performance 3D integration systems. To further demonstrate the polymer insulating TSVs, this paper investigates the thermal stability by measuring the leakage current under bias-temperature condition, studies the thermal stress characteristics with Finite Element Analysis (FEA), and tries to improve the thermal mechanical reliability of high-density TSVs array by optimizing the geometry parameters of pitch, liner and redistribution layer (RDL). The electrical measurements show the polymer insulating TSVs can maintain good insulation capability (less than 2×10−11 A) under challenging bias-temperature conditions of 20 V and 200°C, despite the leakage degradation observation. The FEA results show that the thermal stress is significantly reduced at the sidewall, but highly concentrates at the surface, which is the potential location of mechanical failure. And, the analysis results indicate that the polymer insulating TSVs (diameter of 10 μm, depth of 50 μm) array with a pitch of 20 μm, liner thickness of 1 μm and RDL radius of 9 μm has an optimized thermal-mechanical reliability for application.