Changyi Liu

Chemical composition and antioxidant activity of essential oil from berries of Schisandra chinensis (Turcz.) Baill

Essential oils of Schisandra chinensis seeds and berries without seeds were separately extracted. A total of 55 compounds were identified in the essential oil of berries without seeds (EOB), representing 85.75% of the total content. A total of 52 compounds were identified in the essential oil of seeds (EOS), representing 89.74% of the total content. For EOB, the top three content compounds were α-cis-bergamotene (10.79%), 4,11-selinadiene (5.28%) and α-cadinol (5.19%), while the top three content compounds of EOS were ylangene (10.16%), β-himachalene (9.46%) and di-epi-α-cedrene (8.92%). The antioxidant activity of the essential oil was tested using the DPPH radical-scavenging method. The antioxidant activity of EOB was higher than EOS. The IC50 values of EOB and EOS were 8.4 and 15.8 mg/mL, respectively. This study concluded that EOB and EOS were not only different in extraction yield but also in chemical composition and antioxidant activity.

Novel instrument for characterizing comprehensive physical properties under multi-mechanical loads and multi-physical field coupling conditions

Functional materials represented by ferromagnetics and ferroelectrics are widely used in advanced sensor and precision actuation due to their special characterization under coupling interactions of complex loads and external physical fields. However, the conventional devices for material characterization can only provide a limited type of loads and physical fields and cannot simulate the actual service conditions of materials. A multi-field coupling instrument for characterization has been designed and implemented to overcome this barrier and measure the comprehensive physical properties under complex service conditions. The testing forms include tension, compression, bending, torsion, and fatigue in mechanical loads, as well as different external physical fields, including electric, magnetic, and thermal fields. In order to offer a variety of information to reveal mechanical damage or deformation forms, a series of measurement methods at the microscale are integrated with the instrument including an indentation unit and in situ microimaging module. Finally, several coupling experiments which cover all the loading and measurement functions of the instrument have been implemented. The results illustrate the functions and characteristics of the instrument and then reveal the variety in mechanical and electromagnetic properties of the piezoelectric transducer ceramic, TbDyFe alloy, and carbon fiber reinforced polymer under coupling conditions.

Deformation behavior of micro-indentation defects under uniaxial and biaxial loads.

The microdefects of structure frequently act as the source to generate initial cracks and lead to the fracture failure. Study on the deformation behaviors of embedded defects would be conducive to better understand the failure mechanisms of structural materials. Micro-indentation technique was applied to prepare the initial indentations as embedded surface defects at the gauge length section and central section of a cross-shaped AZ31B magnesium alloy specimen. A novel in situ biaxial tensile device was developed to apply the synchronous biaxial loads. Via the observation by an optical microscope with three-dimensional imaging and measurement functions, the changing laws of the indentation topographies under uniaxial and biaxial tensile loads were discussed. Compared with the gauge length section, the increasing trend of the indentation length of the central section was relatively flat, and the decreasing trend of the indentation depth was more significant. The changes of indentation topographies were explained by the Poisson effect, and the significant plastic tensile stress has led to the releasing of the residual stress around the indentation location and also promoted the planarization of the pileup.

A compact bending device for in-situ three-point bending tests under laser scanning confocal microscope

In-situ testing methods are used to investigate the real-time changing process of materials under different mechanical tests. This paper describes a miniature in-situ three-point bending device, which is compatible with the laser scanning confocal microscope. This device integrates a servo motor, a two-stage worm gears reducer with large reduction ratio and two small lead ball screws. It can realize quasi-static loading mode with a wide rate range from 0.1 µm/s to 0.1 mm/s. The microstructure of the specimen can be observed dynamically during the three-point bending test combined with the force-deflection curve. A calibration method was introduced to calibrate the flexibility of the developed device. The bending experiments were carried out for several different materials with known elastic modulus to verify the feasibility of the calibration method. Finally, the in-situ three-point bending test of red copper was performed to verify the function of the device.

Method for determining the true stress of cross-shaped specimens subjected to biaxial tensile loads

For typical cross-shaped specimens subjected to simultaneous biaxial tensile loads, the specimens’ central section would elongate along different directions under plane stress condition. Consequently, the width of the specimens’ gauge length section would gradually decrease along the tensile direction, and true stress, which is based on the instantaneous width, is different from the values obtained from uniaxial tensile tests. To calculate the true stress of cross-shaped specimens, a horizontal biaxial tensile device was developed to apply the equi-biaxial loads. An optical observation method was adopted to measure the specimen’s true deformation. Then, an exponential fitting method was proposed on basis of the true deformation to describe the nonlinear deformation trajectory of the specimen’s gauge length section. Based on a theoretical model, the calculation method of the true stress was established, and the relationships between the true and engineering stress-strain curves were also discussed.

Modular correction method of bending elastic modulus based on sliding behavior of contact point

During the three-point bending test, the sliding behavior of the contact point between the specimen and supports was observed, the sliding behavior was verified to affect the measurements of both deflection and span length, which directly affect the calculation of the bending elastic modulus. Based on the Hertz formula to calculate the elastic contact deformation and the theoretical calculation of the sliding behavior of the contact point, a theoretical model to precisely describe the deflection and span length as a function of bending load was established. Moreover, a modular correction method of bending elastic modulus was proposed, via the comparison between the corrected elastic modulus of three materials (H63 copper–zinc alloy, AZ31B magnesium alloy and 2026 aluminum alloy) and the standard modulus obtained from standard uniaxial tensile tests, the universal feasibility of the proposed correction method was verified. Also, the ratio of corrected to raw elastic modulus presented a monotonically decreasing tendency as the raw elastic modulus of materials increased.