RECENT PROGRESS OF NANO-MECHANICAL MAPPING

Nano-mechanical mapping by atomic force microscopy has been developed as an useful application to measure mechanical properties of soft materials at nanometer scale.To date,the Hertzian theory was used for analyzing force- distance curves as the simplest model among several contact mechanics between elastic bodies.However,the preexisting methods based on this theory do not consider the adhesive interaction in principle,which cannot be neglected in the ambient condition.A new analytical method was introduced...

Influence of nano-mechanical evolution of Ti_(3)AlC_(2) ceramic on the arc erosion resistance of Ag-based composite electrical contact material

Al-containing MAX phase ceramic has demonstrated great potential in the field of high-performance low-voltage electrical contact material.Elucidating the anti-arc erosion mechanism of the MAX phase is crucial for further improving performance,but it is not well-understood.In this study,Ag/Ti_(3)AlC_(2) electrical contact material was synthesized by powder metallurgy and examined by nanoindentation techniques such as constant loading rate indentation,creep testing,and continuous stiffness measurements.Our results indicated a gradual degradation in the nano-mechanical properties of the Ti_(3)AlC_(2) reinforcing phase with increasing arc erosion times,although the rate of this degradation appeared to decelerate over arc erosion times.Specifically,continuous stiffness measurements highlighted the uneven mechanical properties within Ti_(3)AlC_(2),attributing this heterogeneity to the phase’s decomposition.During the early(1-100 times)and intermediate(100-1000 times)stages of arc erosion,the decline in the nano-mechanical properties of Ti_(3)AlC_(2) was primarily ascribed to the decomposition of Ti_(3)AlC_(2) and limited surface oxidation.During the later stage of arc erosion(1000-6200 times),the inner region of Ti_(3)AlC_(2) also sustained arc damage,but a thick oxide layer formed on its surface,enhancing the mechanical properties and overall arc erosion resistance of the Ag/Ti_(3)AlC_(2).

Microstructure and nano-mechanical property of cold spray Co-base refractory alloy coating

Co-base refractory alloy coating was prepared on carbon steel substrate by cold spray technology; microstructure and nano-mechenieal property were examined by scanning electron microscope （SEM） and nano indenter individually. The results showed that about 250 μm Co-base refractory alloy coating could be deposited o11 steel substrate by cold spray technique, interface between coating and substrate was combined well, and the refractory alloy particle had a significant plastic deformation during deposition process; mixing Ni powders into Co-base refractory alloy powders could increase the density and decrease the nano-hardness of coating, the nano-hardness and elastic modulus of refractory alloy coating was higher than 6 GPa and 160 GPa, respectively.

Nano-synthesis and nano-mechanics of diamond composites and its petroleum drilling applications

We perform synthesis, characterization, and application of nanostructured diamond composites. The enhancements of the thermomechanical performance of bulk diamond compacts in terms of hardness, fracture toughness, wear resistance, impact strength, and thermal stability are our project objectives. It is to aim at applying an advanced nanosynthesis process for the manufac-turing of superhard and ultratough diamond/SiC nanocomposites with the implementation of nanofiber reinforcement. The R&D re-sults can be used in multi-industrial applications, particularly, for drill bits designed to encounter dynamic impacts for high speed oil/gas drillings, thus to achieve high efficiency and energy saving. Science and technology (S&T) researches on precursors, cata-lyst, reactive sintering, and in-situ/real-time characterization of high P-T neutron/X-ray diffraction studies on phase stability, syn-thesis kinetics, residual strain, and yield strength have been applied to help optimizing the nanomanufacturing process. Our R&D ef-fort in high P-T nanosynthesis of TSP diamond/SiC composites is to achieve superior performance of nanomechanics in resisting dy-namic impact and thermal degradation, while still maintaining the super-hardness and super-abrasiveness of diamond and silicon-car-bide. The improved polycrystalline diamond compact (PDC) bit inserts for drilling, boring, and cutting will be applied in harsh envi-ronments so as to meet the demands of the mining, petroleum, and machinery industries. With success of the proposed project, the expected energy savings and reduction of CO2 emission will be significant and the economic advantages are going to be enormous.

Understanding micro-diffusion bonding from the fabrication of B_4C/Ni composites

A Ni-B_4C macroscopic diffusion welding couple and a Ni-15 wt% B_4C composite fabricated by spark plasma sintering(SPS) were used to understand the micro-scale diffusion bonding between metals and ceramics. In the Ni-B_4C macroscopic diffusion welding couple a perfect diffusion welding joint was achieved. In the Ni-15 wt% B_4C sample, microstructure analyses demonstrated that loose structures occurred around the B_4C particles. Energy dispersive X-ray spectroscopy analyses revealed that during the SPS process, the process of diffusion bonding between Ni and B_4C particles can be divided into three stages. By employing a nano-indentation test, the room-temperature fracture toughness of the Ni matrix was found to be higher than that of the interface. The micro-diffusion bonding between Ni and B_4C particles is quite different from the Ni-B_4C reaction couple.

Bio-inspirations for the Development of Light Materials based on the Nanomechanical Properties and Microstructures of Beetle Dynastes tityus

Dynastes tityus(D.tityus)is a typical beetle whose elytra are light and strong.The primary function of elytra is to protect beetle's hindwings.In this paper,D.tityus elytra were selected as the biological prototype for the investigation to obtain bio-inspirations for the design and development of light materials with high ratio of strength to mass.Firstly,the microstructure investigation and quasi-static nanoindentation tests have been carried out on the ten samples of the selected elytra ofD.tityus to reveal their mechanical properties and microstructures.Secondly,based on the fmdings from the microstructure investigation and nanoindentation tests,three models of bio-inspired materials have been proposed for further study to gain the deep understanding of the relationships between the special mechanical characteristics and microstructures.Then Finite Element Analysis(FEA)simulations have been performed on the three models for harvesting the bio-inspirations for the initial design of light materials.Finally,through comparative analysis of the findings from the microstructure investigation,the nanoindentation tests and the simulations,some meaningful bio-inspirations have been reaped for the future optimization of the design and development of light materials with high ratio of strength to mass.

PERSPECTIVES IN MECHANICS OF HETEROGENEOUS SOLIDS

The Micro- and Nano-mechanics Working Group of the Chinese Society of Theoretical and Applied Mechanics organized a forum to discuss the perspectives, trends, and directions in mechanics of heterogeneous materials in January 2010. The international journal, Acta Mechanica Solida Sinica, is de- voted to all fields of solid mechanics and relevant disciplines in science, technology, and engineering, with a balanced coverage on analytical, experimental, numerical and applied investigations. On the occasion of the 30TM anniversary of Acta Mechanica Solida Sinica, its editor-in-chief, Professor Q.S. Zheng invited some of the forum participants to review the state-of-the-art of mechanics of heterogeneous solids, with a particular emphasis on the recent research development results of Chinese scientists. Their reviews are organized into five research areas as reported in different sections of this paper. ~I firstly brings in fo- cus on micro- and nano-mechanics, with regards to several selective topics, including multiscale coupled models and computational methods, nanocrystal superlattices, surface effects, micromechanical damage mechanics, and microstructural evolution of metals and shape memory alloys. ~II shows discussions on multifield coupled mechanical phenomena, e.g., multi-fields actuations of liquid crystal polymer networks, mechanical behavior of materials under radiations, and micromechanics of heterogeneous materials. In ~III, we mainly address the multiscale mechanics of biological nanocomposites, biological adhesive surface mechanics, wetting and dewetting phenomena on microstructured solid surfaces. The phononic crystals and manipulation of elastic waves were elaborated in ~IV. Finally, we conclude with a series of perspectives on solid mechanics. This review will set a primary goal of future science research and engineering application on solid mechanics with the effort of social and economic development.