递进式凸轮加载的中等应变率实验技术

研制了一种可以实现多次加载的凸轮递进式中应变率压缩实验系统。该实验装置采用伺服电机驱动蓄能飞轮转动，后蓄能飞轮带动加载凸轮压缩加载杆的方法，实现对试样中应变率的压缩；同时在一级压缩即将结束时步进电机迅速推动蓄能飞轮贴近加载凸轮，实现多级压缩。试样的动态压缩载荷通过两侧杆上粘贴的应变片所记录的应变信号得到；试样变形过程通过激光干涉测速系统测得的试样两侧杆端的运动速度信号得到。以纸蜂窝试样为例，基于研制的中应变率实验系统，并结合高速摄影图片，研究了厚度10 mm、直径14.5 mm的纸蜂窝试样在应变率3.5 s^-1下的动态压缩力学性能，得到了单级压缩和两级压缩过程中纸蜂窝试样的应力-应变曲线和变形过程，并讨论了该实验系统的可靠性。此实验系统可以实现多级递进式中应变率加载；纸蜂窝试样在中等应变率下的峰值强度和平台应力对高应变率下的动态压缩实验数据和低应变率下的准静态实验数据进行了较好地衔接；试样的失效模式主要为准弹性变形后的外壁屈曲和面内剪切。

An experimental technique for medium strain-rate loading by a progressive cam

A medium strain rate compression experimental system based on a progressive cam was developed to realize multiple medium strain rate loading. The developed experimental system uses the servo motor to drive the energy storage flywheel to rotate at a certain speed, and when the clutch is started, the energy storage flywheel can drive the loading cam to rotate. The loading cam pushes the loading guide bar and the input bar to compress the sample. When the loading cam rotates one circle, a single medium strain-rate compression is completed. At the same time, when the first stage compression is about to end, the stepper motor rapidly pushes the energy storage flywheel close to the loading cam for the next compression, and the cycles repeat to achieve multiple medium strain rate compression. The load and deformation of the material during compression were measured by strain gauges and a velocity?interferometer?system?for?any?reflector (VISAR), respectively. The strain gauges were affixed to the input bar and the support bar, respectively. The strain signals of the bars during compression were recorded by the strain gauges and the forces exerted on the sample were obtained based on these strain signals. Two fiber optic probes of the VISAR system were used to measure the velocities of the input bar and the support bar during compression. Based on the two velocity curves measured, the velocity difference curve between the two ends of the sample was obtained, and then the deformation of the sample was gained by integrating the velocity difference. The stress-strain curves were obtained from the load- and deformation-time curves. Taking the paper honeycomb sample as an example, the reliability of the developed medium strain rate experimental system was discussed based on the high-speed images. The dynamic compressive mechanical properties of the paper honeycomb samples with the thickness of 10 mm and the diameter of 14.5 mm at the strain rate of 3.5 s?1 were studied. The stress-strain curves and deformation processes of the paper honeycomb samples during single compression and double compression were obtained. The experimental system could realize multistage progressive medium strain rate loading. The peak strength and plateau stress of the paper honeycomb samples at medium strain rates well connect the dynamic compression results at high strain rates with the quasi-static compression results at low strain rates. The failure modes of the samples are mainly out-of-plane buckling and in-plane shear after quasi-elastic deformation.