The EikoTwin DIC strain measurement system applies stereo grid DIC technology to measure seat deformation in crash tests and track dummy movements.

Author: Alex Chang, Project Engineer

Article Type: Feasibility Study - Application of EikoTwin Tool in Collision Testing

Keywords: Virtual Testing - DIC Measurement - Comparative Test Calculation

Collision testing is a key part of product development and certification, especially in the automotive, aerospace, and railway industries. These tests simulate collision or impact scenarios to assess the product's resistance and safety. The reverse ejector is one of the most commonly used devices for such tests, which is a device that projects objects at high speed (the objects projected during testing are dummies and their seats), generating force pulses that simulate high-intensity impacts. For a long time, local strain gauges have been used to measure the deformation of seats during collision tests. However, these measuring devices cannot measure the entire deformation field of the seat. Therefore, we propose a solution to measure seat deformation using DIC technology. This measurement scheme can also track the movements of the dummy (by pre-setting markers on certain parts of its body to measure the displacement of the target). It is noteworthy that the same camera system used during the test can measure both seat deformation and human model displacement by tracking the markers. Using stereo DIC technology to measure deformation at different positions of the seat, especially when controlling for possible weak points detected through calculations, allows for adjustments to the dimensions of components based on the measured constraints, and can also provide data for calculations in complex areas to be modeled or simulated.

 

In this case study of collision testing, we created a virtual collision testing environment using EikoTwin Virtual software, pre-positioned the stereo camera system, and recorded images of the test.The EikoTwin DIC software processes the images to calculate the displacement of the dummy and the deformation of the seat.Virtual Testing Principle - Using

 

EikoTwin VirtualCreating Virtual Collision Tests for DIC ExperimentsTo create virtual tests, it is essential to use modeling and 3D rendering software. From this perspective, Blender, originally developed for the animation film industry, has proven to be an excellent tool for our use. With Blender, we can create cameras with all necessary features, position the cameras, and capture and export images rendered with realistic materials and lighting. Although Blender was initially designed for the animation industry, through multiple experiments, we have successfully transformed this software into a tool suitable for DIC measurement and creating virtual tests - EikoTwin Virtual.

EikoTwin Virtual

is composed of the ModelConverter tool and the BlenDIC plugin. The ModelConverter converts models and simulation results created in finite element software (such as Abaqus or Hyperworks) into VTK format that can be imported into Blender. The BlenDIC plugin integrates the tools needed to create virtual tests in Blender.Figure 1: The scene on the left created an aesthetic composite image on the right in Blender.

We created a simplified model of a human sitting on a seat using Abaqus, applying stress to simulate displacements similar to those in collision tests. We then imported this simulation into EikoTwin Virtual.

 

Figure 2: Abaqus Impact Test Simulation

 

 

Speckle & Marking

 

is composed of the ModelConverter tool and the BlenDIC plugin. The ModelConverter converts models and simulation results created in finite element software (such as Abaqus or Hyperworks) into VTK format that can be imported into Blender. The BlenDIC plugin integrates the tools needed to create virtual tests in Blender.First, we created speckles on the seat for deformation measurement using DIC technology. At the same time, markers were fixed on certain areas of the human model (head, shoulders, hips, knees, ankles) to track their movements during the test.Figure 3: Application of Speckles and Markers

 

Camera Positioning

 

When setting the spatial positioning of the two cameras, care must be taken to cover the entire area of interest. The specific angle between the cameras is 30°, and the clarity area is determined.

 

is composed of the ModelConverter tool and the BlenDIC plugin. The ModelConverter converts models and simulation results created in finite element software (such as Abaqus or Hyperworks) into VTK format that can be imported into Blender. The BlenDIC plugin integrates the tools needed to create virtual tests in Blender.First, we created speckles on the seat for deformation measurement using DIC technology. At the same time, markers were fixed on certain areas of the human model (head, shoulders, hips, knees, ankles) to track their movements during the test.The images captured by the two cameras are rendered in real-time on Blender.

 

Blendic:

 

Speckle Size and Resolution

 

Based on the camera's resolution and field of view, the optimal size of the speckles can be determined (here it is 2.5 mm). Special attention needs to be paid to how many points each mesh element has and how many pixels each point has to allow for convergence of image correlation, as seen in the images.

 

is composed of the ModelConverter tool and the BlenDIC plugin. The ModelConverter converts models and simulation results created in finite element software (such as Abaqus or Hyperworks) into VTK format that can be imported into Blender. The BlenDIC plugin integrates the tools needed to create virtual tests in Blender.First, we created speckles on the seat for deformation measurement using DIC technology. At the same time, markers were fixed on certain areas of the human model (head, shoulders, hips, knees, ankles) to track their movements during the test.Figure 7: Typical Size of Speckles

 

Generating Virtual Images for Image Correlation in Collision Testing

 

Figure 8: Virtual Impact Test Images Generated by EikoTwin Virtual

 

The final step in creating virtual tests on EikoTwin Virtual is to generate virtual images and export them.Feasibility Verification of Measurements Using Software

After obtaining the test images, the next step is to use EikoTwin DIC software to assess the convergence of the image correlation calculations. This step is crucial for verifying whether the obtained images can accurately measure the deformation and displacement of the parts. After importing the images and mesh into EikoTwin DIC, camera calibration must be performed. This step calculates the projection matrix of the two cameras based on the images.

 

Once this step is completed, the simulation mesh can be projected onto the images to measure the displacement and deformation on the parts.

 

is composed of the ModelConverter tool and the BlenDIC plugin. The ModelConverter converts models and simulation results created in finite element software (such as Abaqus or Hyperworks) into VTK format that can be imported into Blender. The BlenDIC plugin integrates the tools needed to create virtual tests in Blender.First, we created speckles on the seat for deformation measurement using DIC technology. At the same time, markers were fixed on certain areas of the human model (head, shoulders, hips, knees, ankles) to track their movements during the test.Figure 9: Calibration and Reprojection of the Simulation Mesh

 

Results of Image Correlation Measurement in Collision Testing

 

Displacement Calculation | Results

 

Figure 10: Projection of Displacement Field on Camera ImagesThe EikoTwin DIC software processes the images to calculate the displacement of the dummy and the deformation of the seat.Figure 11: Changes in Seat Displacement Field and Marker Displacement Over Time

The EikoTwin DIC software processes the images to calculate the displacement of the dummy and the deformation of the seat.Figure 12: Changes in Seat Displacement Field Over Time

Figure 13: Evolution of Seat Deformation Field Over Time

 

Comparative Test/Calculation | Displacement

图9：模拟网格的校准和重新投影

 

碰撞试验图像相关性测量结果

The EikoTwin DIC software processes the images to calculate the displacement of the dummy and the deformation of the seat.：位移计算|结果

 

 

图10：位移场在摄像机图像上的投影

 

图11座椅位移场和标记位移随时间的变化

 

图12：座椅位移场随时间的变化

图13：座椅变形场随时间的演变

 

The EikoTwin DIC software processes the images to calculate the displacement of the dummy and the deformation of the seat.First, we created speckles on the seat for deformation measurement using DIC technology. At the same time, markers were fixed on certain areas of the human model (head, shoulders, hips, knees, ankles) to track their movements during the test.对比试验/计算|位移

Using EikoTwin DIC software, the displacement difference field between testing and simulation can be visualized directly. Since the virtual test is created based on the simulation, theoretically, the difference should be zero. Therefore, this difference tells us about the accuracy of the measurements and the minimum uncertainty that may be encountered in actual testing.

Figure 14 shows the variation of the seat displacement difference field over time (video)

 

Figure 14: Variation of the seat displacement difference field over time

 

Figure 15: Variation of the seat deformation difference field over time

 

EikoTwin DIC:Tracking of markers

The EikoTwin DIC software processes the images to calculate the displacement of the dummy and the deformation of the seat.Another interesting feature of the software is the tracking of markers. In the first step, we place markers on the human model to measure its motion. By importing images into EikoTwin DIC, the position of the markers in each image can be indicated, and their displacement over time can be measured.

In the software interface, the calculated points and result curves of the markers can be seen in a three-dimensional view. The results of the head markers are plotted as displacements along the X and Z axes as a function of time, as well as the head trajectory by plotting Z displacement as a function of X displacement. Test results and calculated results can be compared on the chart.

Figure 16: Marker tracking

 

HyperworksExport

The EikoTwin DIC software processes the images to calculate the displacement of the dummy and the deformation of the seat.The final step is to export the results. The results can be exported in different formats to accommodate various modeling software. The results can then be imported into HyperWorks, as shown below.

Figure 17: Importing DIC measurement fields into HyperWorks

 

Schedule

 

For the impact testing experiment, we wrote this schedule, which shows the communication between testing and calculation.

The schedule has two stakeholders: the design office and the testing laboratory. The design office has already simulated the collision test and wants to verify and improve the results of its model. Therefore, they need the laboratory to conduct a real collision test. Measurements are made with several cameras. To avoid the difficulty of positioning these cameras in the actual test, the design office and the laboratory conducted a pre-study together.is composed of the ModelConverter tool and the BlenDIC plugin. The ModelConverter converts models and simulation results created in finite element software (such as Abaqus or Hyperworks) into VTK format that can be imported into Blender. The BlenDIC plugin integrates the tools needed to create virtual tests in Blender.This step allows for pre-setting testing activities and reducing risks, and only one experiment needs to be executed. On the day of the test, an additional step is added to the process: applying speckles for image correlation.

 

Then, the laboratory sends the images to the design office for post-processing of the data and uses EikoTwin DIC to compare the real test with the simulation. Finally, the design office can use the test results for verification and update the simulation with EikoTwin DigitalTwin if necessary.

Figure 18: Communication dialogue between testing and calculation - schedule

 

Conclusion

 

In summary, this paper presents a feasibility study on using EikoTwin tools for collision testing. The use of stereo DIC technology allows for measuring the entire seat deformation field and tracking the dummy by measuring and determining its displacement through pre-set markers on certain parts of the dummy's body. The virtual tests created using EikoTwin virtual are used to simulate displacement images similar to collision tests, which are imported intoThe EikoTwin DIC software processes the images to calculate the displacement of the dummy and the deformation of the seat.the software for high-precision measurement of seat deformation and dummy displacement.

The results obtained are promising and demonstrate the potential of EikoTwin tools in improving the efficiency and accuracy of collision testing in the automotive, aerospace, and railway industries. Using these tools can lead to a better understanding of product deformation and failure mechanisms, reducing development costs and time.

In a nutshell, this feasibility study marks a significant step towards the broader application of EikoTwin tools in industry and opens up new opportunities for innovation in collision testing.