Papers by Author: Si Ying Chen

Abstract: Airborne 3-D focal imaging LiDAR can take images in a very short gating time (3~5ns), so it can shield background noise instantaneously. Since the area of laser irradiated surface is about when the detected distance is about 3km, to ensure high imaging quality the laser beam needs to be smoothed before it arrives the ground. In this paper, based on self-developed airborne 3-D focal imaging LiDAR system, a beam homogenization device by using lens array method is presented for the detection range from 1km to 3km. The experimental result indicates that the smoothing rate can reach 89%. Subsequent tests in LiDAR system show that the homogenization device is reliable and effective.

Abstract: In this paper, the deformation fields of LY12 crack samples loaded by an SHTB are real-time investigated with the time interval of 10 µs by an optical system, which consists of a high-speed camera, a flash light, a frame grabber and a synchronization device with the delay-time less than microsecond. The cracks are preset by using the three-points bending method in a MTS fatigue machine. The crack is 2mm long with a flare angle of 60 degree. During the experiments, the dynamic deformation images are captured by the high speed camera and analyzed by newly developed software based on Digital Correlation theory. And the displacements fields near crack-tips according to the changes of the flare angle and radius during the impact process are obtained. Experimental results acquired in this paper are proofed, by compared with the theoretical calculations.

Abstract: In this paper, the real-time deformations and failures of LY12 samples loaded by an SHTB are investigated by an optical system, which consists of a high-speed camera, a flash lamp, a frame grabber and a synchronization device with the controlling accuracy of 1 microsecond. The deformation history of LY12 is obtained with a time interval of 10μs and the result is compared with that acquired by classic Hopkinson method at the same time. Besides, two different failure modes and the crack propagation velocity of LY12 specimen are detected in impact tensile process. The fracture textures after working are also surveyed by SEM and it shows that the dynamic fracture mode is affected by the microstructure of materials.

Abstract: In this paper, the mechanical properties of several aluminum alloys are obtained experimentally at different temperatures, from room temperature to about 4000C by using the Gleeble 1500 thermomechanical system. Besides, the thermal softening characteristics, effects of heating rate and temperature holding time are discussed in details. It is found that the strength of LF6, a kind of antirust aluminum alloy, is not sensitive to the heating rate (0.1-1000K/s) and temperature holding time (0-1h). However, the mechanical behaviors of other alloys depend on these factors very obviously. At last, these phenomena are discussed in the viewpoint of the microstructures and techniques of ageing strengthening of these alloys.

Abstract: In this paper, the dynamic behaviors of several kinds of high strength fibers, including Kevlar, UHMPE, glass fibers, carbon fibers etc., are investigated experimentally, with a Split Hopkinson Tension Bar（SHTB）. The effect of strain rate on the modulus, strength, failure strain and failure characteristics of fibers, under impact loading, is analyzed with the relative stress vs. strain curves. At the same time, the mechanism about the rate dependence of mechanical behaviors of various fibers is discussed based on the understanding on the microstructures and deformation models of materials. Some comments are also presented on the decentralization of experimental results, and a new method called traveling wave method is presented to increase the experimental accuracy. Research results obtained in this paper will benefit to understand the energy absorption and to build up the constitutive law of protective materials reinforced by high strength fibers.