材料测试案例1 - 新拓三维技术（深圳）有限公司

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Hopkinson rod experiment

Measurement purpose

Measure the deformation of Hopkinson bar specimens during tension

Brief introduction of experiment

The Hopkinson rod device is mainly used for testing dynamic mechanical properties of materials with strain rate ranging from 10² ~ 10⁴. The basic principle is shown in the following figure. When the hitting rod (bullet) in the gun barrel is projected into the input rod at a certain speed, an incident pulse is generated in the input rod. The stress wave reaches the specimen through the elastic input rod. Under the action of the stress pulse, the specimen is deformed at a high speed, and the stress wave enters the elastic input rod and the projection pulse enters the output rod through the specimen at the same time. The velocity of a bullet can be obtained by using a tachometer. The dynamic stress and strain parameters of the material can be calculated by using strain gauges attached to the elastic rod and recorded strain pulses.

Hopkinson rod experiment is divided into tension and compression experiments. Compression test specimens are easy to fly out, need the protection glass, need to customize the relevant beam. This experiment is a tension experiment. The specimen does not fly out and does not need the protection glass

Experimental parameters: material:stainless steel, specimen size: Ф4X10mm, acquisition frame frequency: 100000 frames, camera: phantom V1612 resolution 768X96, 256X96, lens: Canon 24-70mm adjustable shutter 9us,aperture 4, trigger mode: post-trigger.

Inspection process

（1）Specimen preparation, place the specimens in the right position and adjust the camera and lens parameters.

（2）Under full width (1280X800), 128x96 calibration board is calibrated with a deviation of 0.02.

（3）The resolution was changed to 256X96 or 768X96, and the experiment was carried out.

（4）After the experiment is completed, the post-trigger data acquisition is adopted.

（5）Computation of data.

调节焦距

相机标定

Data analysis

Data requirement:

（1）Choose three points from left, middle and right to draw true, engineering principal and secondary strain curves and calculate strain rate.

（2）Principal and secondary strain curves along a straight line.

（3）Shear strain nephogram.

（4）Displacement and strain nephogram.

The maximum strain energy is about 60% and the maximum strain rate is about 1800s-1. Different pressure applied to specific experiments can sometimes be pulled off at one time, sometimes several times,and sometimes continuously.

轴向截线上应变分布

Experiment summary

（1）The camera parameters are about 16000 frames with a full resolution of 1M. The camera and lens need to be selected according to the specific requirements of the experiment.

（2）Because of the setting of experimental parameters, the experiment did not break once, but twice.

（3）The 3D displacement field and strain field on the surface of the specimen can be calculated by taking pictures of the deformation process of the specimen with a high-speed camera.