DIC Experiment - Design and Validation of Laser Shock Testing

2007Since then, the headquarters has been located at the Optical and Laser Technology Center in Talence.ALPhANOVand leaders in the European defense sector.MBDAFrom2019Since the year, a joint laboratory for laser and material interaction has been established, consisting of a chamber equipped with high-power infrared sources. It features a flexible and durable architecture, complex experimental equipment, rapid reconfiguration capabilities, and is highly instrumented, making it very safe and reliable for staff. A safety automatic device is used to continuously monitor the status of the chamber, key sensors, and whether shooting is authorized, while another automatic device controls the laser, robots, and optical heads.ALPhANOVThe human-machine interface is used to program test procedures. The instrument, including infrared and visible high-speed cameras and thermometers, is synchronized with clock signals. Finally, all recorded videos and simulated data are replayed in the same interface.

This research is conducted in collaboration withEikoSimandMBDA,ALPhANOVand the Laboratory of Mechanics and Technology (ENS Paris Saclay) with a primary focus on the steel plates subjected to laser irradiation at the center of the laser chamber. The aim is to quantify the thermal-mechanical effects on the plates by measuring the displacement field using digital image correlation.

Digital pre-research

Designing tests using imaging technology in a complex experimental environment is a challenge. In fact, when studying parts in narrow and crowded spaces (such as the laser chamber), it is difficult to predict the ideal position of the camera to ensure visibility of the research area during the experiment.The use ofBlender makes it possible to overcome this issue.The use ofis an open-source3Dcomputer graphics software primarily used in the film industry. It allows the creation of a scene where users can choose the position of the camera around the research part, and then images of reference configurations and distorted configurations can be generated using the results of preliminary numerical simulations. These images can then be processed using image correlation software to estimate the expected measurement performance (in terms of measurement uncertainty) that the software user can anticipate under these ideal conditions.

In this study, considering the limited space of the laser chamber, we placedThe use ofcameras in the scene, ensuring that they do not interfere with or damage the experiment, and they cannot be in the path of the laser beam striking the center of the plate almost horizontally. Therefore, the following view was adopted (see Figure4).1Figure

– The positions of the cameras in the laser chamber (1cameras represented by pyramids,4cameras represented by rectangular prisms)2个由金字塔表示，2个由长方体表示）

通过使用EikoTwin DIC软件对The use of生成的理想图像进行后处理，对于这种特定情况，可以估计平面内组件的位移测量不确定度约为5µm，平面外组件的位移测量不确定度约为15µm。

设置测试

测试仪器配备有两台数码相机的立体视觉装置，辅以NIT出借的红外相机和对数响应相机。ALPhANOV将它们放置在EikoSim在预研究期间确定的位置（见图2），并在大约一天内准备好实验环境。

– The positions of the cameras in the laser chamber (2-测试仪器

– The positions of the cameras in the laser chamber (3–支架上的斑点板

测试活动期间，在一天半的时间内，我们在之前有斑点的纸上进行了10次以上的激光拍摄，以便为数字图像相关创建足够的对比度（见图3）。使用EikoSim提供的拓扑结构创建散斑图案的两种工艺：传统工艺（通过绘画）和创新工艺（通过激光纳米加工冲击表面，ALPhANOV工艺）。

立体相关测量结果

不确定性量化

为了估计试验过程中的不确定度，在每次拍摄前，我们都对一组30张静止图像进行位移测量。因此，可以测量采集噪声对这些图像的预期（零）位移的影响。无论方向如何，不确定度水平都非常接近预研究期间的估计值。

位移场

数字图像立体相关通过从两台数码相机在测试期间拍摄的图像来非接触式测量零件的三维表面位移场。该技术基于图像灰度守恒的假设。测量场直接表示在用于有限元模拟的三维表面模型上。测量分析显示板材有三步变形：

1.激光激活后，冲击区域中的板材沿激光方向膨胀。

2.然后冲击区域的薄板以与激光相反的方向膨胀（见图4Figure

3.激光失活后，板材在冷却时部分返回其原始位置。

数字图像相关提供了测量网格上任意点位移随时间的函数。通过将数字位移传感器放置在薄板网格的一个点上（见图4confirmed the behavior observed in the displacement field (see figure5Figure

– The positions of the cameras in the laser chamber (4- distortion+The second step of the displacement sensor alongZaxis (out of plane) maximum displacement field (green)

– The positions of the cameras in the laser chamber (5- out-of-plane displacement variation over time, measured by the digital sensor in the figure4measured in the figure

Summary of experience

This work has demonstrated数字图像相关the feasibility of the experimental method and achieved encouraging results. This is just the first step in using digital image correlation to explain the phenomenon of strong laser interaction with matter.

Editor:C.Minguet,F.Mathieu-EikoSim;E.Chalumeau- Arfano;F.Hilde-Paris-Saclay University, Paris-Saclay University,CNRS;R.Peiffer,S.Carpier-MBDACompany