Evolution of Micro-CT
stimuli. However, in most cases, the experiments have been limited to processes that occur slowly, or there is a require- ment to interrupt the process at certain time points to collect data. Tis is referred to as time-lapse tomography, where data are collected at certain time points, but there is discontinu- ity in the data as no information about what is happening between these discrete points is available. For dynamic CT, a continuous acquisition method is used where imaging is never stopped throughout the process. Tis provides a much more complete picture of the sample evolution and allows for much more flexibility in terms of working with the collected data. Continuous acquisition eliminates the reliance on fixed individual 360o
rotations of data; it is possible to shiſt recon-
struction blocks and, in some cases, overlap reconstruction blocks to provide the most useful information possible in a process called “sliding window reconstruction” [8,12]. Addi- tionally, many time-dependent processes are unpredictable, and capturing the most important aspects of the process may not be possible in an interrupted or time-lapse collection scheme. With dynamic CT, this issue is resolved by collect- ing data throughout the entire process, providing a wealth of information previously unavailable to researchers. To better illustrate the concept of dynamic CT, several case studies are presented.
Dynamic CT Case Studies Uninterrupted compression testing: additive manufac-
turing (AM). 3D printing is a quickly emerging production process for many applications in medicine and the aerospace industry. As with many manufactured parts, AM products can be prone to both external and internal defects. Tese defects, such as voids, cracks, delamination, and contaminants, may influence the mechanical performance of a product. How- ever, the complex geometry possible with AM creates unique challenges for inspection. Micro-CT, which provides non- destructive 3D information about a part, has become essential for detection and analysis of internal imperfections in these intricate parts [13]. Aside from basic quality analysis, it is also essential to understand how these imperfections influence the behavior of the part when they are actually used. Dynamic CT can provide detailed information on a part’s actual performance. As mentioned previously, most lab-based in situ micro-
CT involving loading a part in compression or tension is done in an interrupted form, where the applied force must be held constant during the tomography collection. Tis sometimes creates issues involving sample relaxation and missing infor- mation during the actual loading procedure [14]. Dynamic CT, with continuous acquisition and uninterrupted loading, helps
Figure 3: Example of 3 different plastic additive manufactured (AM) parts that have undergone compression testing while being continuously imaged with dynamic CT. Only 4 images out of 210 collected are shown here.
2021 May •
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