ARAMIS High-Speed DIC Systems

Digital imaging technology constantly evolves. Next to the resolution, the imaging speed of digital cameras is of great importance for many imaging applications. Typically, digital cameras are categorized as high-speed cameras if they provide imaging speeds of at least 1000 frames per second (fps). The maximum achievable imaging speed is constantly advancing. At the moment, cameras with maximum achievable frame rates of up to several millions of images per second are available.

Many high-speed cameras are equipped with imaging chips that allow cropping. Cropping enables the reduction of the image resolution to achieve higher imaging speeds. Some key factors for high-speed cameras are the imaging speed, specified in frames per second (fps), and the light sensitivity (ISO). The benefit of the imaging speed is obvious. The faster you can record images of dynamic processes of deformation or motion, the more accurately you can study the changes observed. The benefit of the light sensitivity of the imaging chip might not be as obvious in the first place, but it is an important factor as well. Capturing highly dynamic events requires a lot of light to ensure that there is enough contrast in the images later. If you don’t have enough light, your images might be just too dark to analyze them. Having this in mind, the light sensitivity of the imaging chip gets a practical meaning. The higher the light sensitivity, the less light you need to still get images with enough contrast. This is especially useful when it comes to measuring high-speed motion or deformation of material specimens which are typically very small in size. It can get difficult to arrange all the light sources and point them to the small specimen in the confined spaces of a materials laboratory. So, every lamp that you can spare, will make your life easier and the setup of the 3D measuring sensor more convenient.

Another advantage of an image sensor with higher light sensitivity is that exposure times can be kept shorter. Very short exposure times are required especially for high-speed tests in materials research but also for crash tests in the automotive industry. If the exposure times are too long, there is a risk that the rapid movements or deformations that are to be investigated can no longer be imaged sharply. In these cases, the term “motion blur” is used. Such motion-blurred image data is then not suitable for evaluation using the digital image correlation method.

High-speed digital image correlation systems are very versatile tools for studying 3D motion and deformation in mechanical testing. Thus, the possible applications for these sensors are vast. Among other fields of application, high-speed digital image correlation sensors are used for:

• Impact tests in the aerospace industry (bird strike test on airplane’s windshield, NASA return to flight test program for the space shuttle including impact test on the leading edge wing section)
• Airbag deployment tests in the automotive industry
• Vibration analysis tests on components and structures (e.g., measurement of the deflection of a helicopter’s rotor blades)
• Drop tests in the automotive industry to assess the crashworthiness of the chassis and automotive components, like the battery tray of electric vehicles
• High strain rate testing of materials (e.g., Split-Hopkinson Bar tests)
• Head impact tests on the windshields of cars to improve the pedestrian safety
• Biomechanical motion and deformation studies (e.g., pumping of the heart valve)
• Ballistic impact studies (bullet impact on protective helmets or Kevlar vests)
  

ARAMIS is an optical measuring system for the sensing of strains, displacements, velocities, accelerations, rotations and angles in a non-contact way. ARAMIS combines point tracking technology and the digital image correlation approach for capturing 3D coordinates and their derived measures like displacements and strains over time.

ARAMIS can be used in two ways for measuring strains and displacements. Using one camera for the measurement, ARAMIS provides 2D DIC and point tracking capabilities, i.e., you can measure flat specimens or objects and track translations in X- and Y-directions as well as planar strains.

The full power of ARAMIS comes to life when you use two cameras for the measurement of strains and displacements in 3D. You can measure specimens and objects of any shape with a so-called stereo camera sensor and track translations in 3D space. For successful measurements with the optical 3D sensor, it is important to have a stable setup of the two cameras (ideally in a sensor assembly like ARAMIS provides) as well as a calibration of the stereo camera sensor with the help of an appropriate calibration object.