Xiujuan Li

Study of the microstructure and mechanical properties of white clam shell.

The microstructure and mechanical properties of white clam shell were investigated, respectively. It can be divided into horny layer, prismatic layer and nacreous layer. Crossed-lamellar structure was the microstructural characteristic. The extension direction of lamellae in prismatic layer was different from that in nacreous layer, which formed an angle on the interface between prismatic layer and nacreous layer. The phase component of three layers was CaCO3 with crystallization morphology of aragonite, which confirmed the crossed-lamellar structural characteristic. White calm shell exhibited perfect mechanical properties. The microhardness values of three layers were 273HV, 240HV and 300HV, respectively. The average values of flexure and compression strength were 110.2MPa and 80.1MPa, respectively. The macroscopical cracks crossed the lamellae and finally terminated within the length range of about 80μm. It was the microstructure characteristics, the angle on the interface between prismatic and nacreous layer and the hardness diversity among the different layers that enhanced mechanical properties of white calm shell.

One-step fabrication of robust superhydrophobic and superoleophilic surfaces with self-cleaning and oil/water separation function

Superhydrophobic surfaces have great potential for application in self-cleaning and oil/water separation. However, the large-scale practical applications of superhydrophobic coating surfaces are impeded by many factors, such as complicated fabrication processes, the use of fluorinated reagents and noxious organic solvents and poor mechanical stability. Herein, we describe the successful preparation of a fluorine-free multifunctional coating without noxious organic solvents that was brushed, dipped or sprayed onto glass slides and stainless-steel meshes as substrates. The obtained multifunctional superhydrophobic and superoleophilic surfaces (MSHOs) demonstrated self-cleaning abilities even when contaminated with or immersed in oil. The superhydrophobic surfaces were robust and maintained their water repellency after being scratched with a knife or abraded with sandpaper for 50 cycles. In addition, stainless-steel meshes sprayed with the coating quickly separated various oil/water mixtures with a high separation efficiency (>93%). Furthermore, the coated mesh maintained a high separation efficiency above 95% over 20 cycles of separation. This simple and effective strategy will inspire the large-scale fabrication of multifunctional surfaces for practical applications in self-cleaning and oil/water separation.

Effect of Al content on impact resistance behavior of Al-Ti-B4C composite fabricated under air atmosphere

Reaction behavior, mechanical property and impact resistance of TiC-TiB2/Al composite reacted from Al-Ti-B4C system with various Al content via combination method of combustion synthesis and hot pressed sintering under air was investigated. Al content was the key point to the variation of mechanical property and impact resistance. Increasing Al content could increase the density, strength and toughness of the composite. Due to exorbitant ceramic content, 10wt.% and 20wt.% Al-Ti-B4C composites exhibited poor molding ability and machinability. Flexural strength, fracture toughness, compressive strength and impact toughness of 30-50wt.% Al-Ti-B4C composite were higher than those of Al matrix. The intergranular fracture dispersed and defused impact load and restricted crack extension, enhancing the impact resistance of the composite. The composite with 50wt.% Al content owned highest mechanical properties and impact resistance. The results were useful for the application of TiC-TiB2/Al composite in impact resistance field of ceramic reinforced Al matrix composite.

Effects of Bionic Units in Different Scales on the Wear Behavior of Bionic Impregnated Diamond Bits

Based on anti-wear theory of soil animals, the samples of impregnated diamond bit with bionic self-regenerated non-smooth surface were designed and fabricated. Such a bionic surface was characterized by concave-shape units of different scales that continuously maintained their shape and function during the whole working process. Abrasion tests were carried out to investigate the performance of samples. Results showed that the bionic samples exhibit excellent wear resistance and drilling performance under the action of bionic self-regenerated units, especially those with units of 2 mm–3 mm diameter. The particle- trapping mechanism coming from the self-regenerated concaves and the lubricating mechanism coming from the continuously self-supplying of solid lubricant are important reasons for reducing or even avoiding the severe abrasions. The improved drilling performance of bionic samples derives from, on the one hand, the back edge of bionic unit that contributes to exposing new diamond and supplying additional shear stresses to increase the cutting ability, on the other hand, the enhanced load per unit area due to the decreased contact area at the frictional interface. The relationship between the wear behavior and the scale of bionic unit was revealed. The unit of smaller scale on the bionic samples can enhance the shear stress level. Further reducing the scale to a contain extent will diminish the wear resistance of sample. While increasing the scale can lead to the poor lubricating effect.

Dry Sliding Friction and Wear Mechanism of TiC-TiB2 Particulate Locally Reinforced Mn-Steel Matrix Composite from a Cu-Ti-B4C System via a Self-Propagating High-Temperature Synthesis (SHS) Casting Route

An Mn-steel matrix composite locally reinforced with in situ TiC-TiB2 ceramic particulates was successfully fabricated via a self-propagating high-temperature synthesis (SHS) casting route in a Cu-Ti-B4C system with various Cu contents. The effect of the Cu content on wear behavior, wear surface, and wear mechanism of the composite was investigated against an AISI H13 mating disc in similar testing conditions at various applied loads and sliding velocities. Moreover, the phase identification and microstructure of the composite were examined. With the increase in Cu content, the wear resistance of the Mn-steel matrix composite decreases first and then increases. Impressively, the composite with 30 wt% Cu content has the highest wear resistance. The enhanced wear resistance can be attributed to the combination of size of ceramic particulates, number of pores, and strength of the interfacial bonding. The dominant wear mechanisms of the TiC-TiB2 ceramic particulate–reinforced Mn-steel matrix are ploughing grooves and delamination wear associated with more abrasion and adhesion.

In-situ mechanical test of dragonfly wing veins and their crack arrest behavior

In natural biological systems, many insects in complex environments exhibit exemplary mechanical properties. Dragonfly wings are light and strong enough to withstand wind loading. Their rigid veins play supporting and strengthening roles to enhance resistance to fatigue. To explore the effect of veins on arresting cracking in the wing, the costa, subcosta, radius R1, and two areas of dragonfly hind wings were samples for in situ tensile tests. The fracture process of the samples was observed with a high-speed camera and a scanning electron microscope. The mechanical properties of the veins and the results of nanomechanical tests on the wings were analyzed. The costa was stiffer and more resistant to deformation than the subcosta and radius, but it was less tough. The results of this study may provide inspiration for the design of mechanical structures and materials.