@article{rahman_ngaile_hassan_2021, title={Non-contact temperature control and stereo digital image correlation for high-temperature testing of miniature tubular specimens}, volume={92}, ISSN={["1089-7623"]}, url={https://doi.org/10.1063/5.0055718}, DOI={10.1063/5.0055718}, abstractNote={Component failures very often occur due to high temperature and multiaxial stress states arising at critical component locations. To imitate such loading conditions, a multiaxial miniature testing system (MMTS) with axial, torsional, and internal pressurization capabilities for high-temperature testing of miniature tubular specimens has been developed. Among many challenges of developing the MMTS, uniform heating, temperature measurement and control, and surface strain measurement on a miniature tubular specimen at high temperatures have significant difficulties. This paper addresses two significant challenges: first, the development of a non-contact temperature control system using infrared thermography to uniformly heat a miniature specimen of 1 mm outer diameter (OD), and second, the development of a stereo digital image correlation (stereo-DIC) setup for strain measurement on the miniature specimen subjected to high temperature. The developed control system maintains the test temperature through a closed feedback loop and employs a fail-safe mechanism to protect the MMTS load frame components against unanticipated temperature rises. The thermocouple wire-size effect on the measured temperature was examined for three different wire sizes: 0.05, 0.25, and 0.5 mm for accurate emissivity determination required for infrared thermography. Emissivities of the specimen surface at different high temperatures were experimentally determined. Inherent error analysis of the developed high-temperature stereo-DIC setup showed acceptable strain measurement uncertainty. The effectiveness of the developed non-contact temperature control system and high-temperature stereo-DIC setup has been verified by performing tensile testing of a 1 mm OD specimen at 500 °C.}, number={11}, journal={REVIEW OF SCIENTIFIC INSTRUMENTS}, author={Rahman, Farhan and Ngaile, Gracious and Hassan, Tasnim}, year={2021}, month={Nov} }
 @article{rahman_ngaile_hassan_2021, title={Optimized stereo digital image correlation setup for miniature round specimen: framework development and implementation}, volume={144}, ISSN={["1873-0302"]}, DOI={10.1016/j.optlaseng.2021.106555}, abstractNote={For the advancement of micro- and nano-technologies, multiaxial material testing at a small length scale is imperative. A novel multiaxial miniature testing system (MMTS) is under development for testing a tubular specimen of outer diameter (OD) as small as 1 mm. Because of the small specimen size of MMTS, stereo-Digital Image Correlation (DIC) is the preferred strain measurement technique. Although theoretically, stereo-DIC is length-scale independent, the implementation of stereo-DIC, particularly for miniature testing, faces experimental setup related challenges. For this reason, although stereo-DIC is strongly recommended over 2D DIC, researchers are sometimes compelled to use the latter. It is shown in the present study that the experimental setup related difficulties, particularly for miniature round specimen testing, can be overcome by a systematic development of a mathematical framework for stereo-DIC implementation. This framework addresses all setup decisions concerning stereo-DIC implementation, such as selections of stereo angle, speckle size, camera position, camera sensor size, lens focal length, dimensions of camera and lens bodies, calibration grid size, etc., as well as stereo-DIC analysis parameters, such as subset and step size. Besides serving the need of building a stereo-DIC setup for MMTS, since the developed mathematical framework treats all stereo-DIC setup decisions as variables, it can be used to develop an optimized stereo-DIC setup for any application. Examples of two general cases are reported. Since this general framework serves as a tool to solve the stereo-DIC experimental setup related challenges, the developed framework will contribute to the wider adoption of stereo-DIC over 2D DIC.}, journal={OPTICS AND LASERS IN ENGINEERING}, author={Rahman, Farhan and Ngaile, Gracious and Hassan, Tasnim}, year={2021}, month={Sep} }
 @article{rahman_ngaile_hassan_2021, title={Optimized stereo digital image correlation setup for miniature round specimen: framework development and implementation}, volume={144}, url={https://www.sciencedirect.com/science/article/pii/S0143816621000257}, DOI={https://doi.org/10.1016/j.optlaseng.2021.106555}, abstractNote={For the advancement of micro- and nano-technologies, multiaxial material testing at a small length scale is imperative. A novel multiaxial miniature testing system (MMTS) is under development for testing a tubular specimen of outer diameter (OD) as small as 1 mm. Because of the small specimen size of MMTS, stereo-Digital Image Correlation (DIC) is the preferred strain measurement technique. Although theoretically, stereo-DIC is length-scale independent, the implementation of stereo-DIC, particularly for miniature testing, faces experimental setup related challenges. For this reason, although stereo-DIC is strongly recommended over 2D DIC, researchers are sometimes compelled to use the latter. It is shown in the present study that the experimental setup related difficulties, particularly for miniature round specimen testing, can be overcome by a systematic development of a mathematical framework for stereo-DIC implementation. This framework addresses all setup decisions concerning stereo-DIC implementation, such as selections of stereo angle, speckle size, camera position, camera sensor size, lens focal length, dimensions of camera and lens bodies, calibration grid size, etc., as well as stereo-DIC analysis parameters, such as subset and step size. Besides serving the need of building a stereo-DIC setup for MMTS, since the developed mathematical framework treats all stereo-DIC setup decisions as variables, it can be used to develop an optimized stereo-DIC setup for any application. Examples of two general cases are reported. Since this general framework serves as a tool to solve the stereo-DIC experimental setup related challenges, the developed framework will contribute to the wider adoption of stereo-DIC over 2D DIC.}, journal={Optics and Lasers in Engineering}, author={Rahman, Farhan and Ngaile, Gracious and Hassan, Tasnim}, year={2021}, pages={106555} }
 @article{rahman_ngaile_hassan_2019, title={Development of scanning electron microscope-compatible multiaxial miniature testing system}, volume={30}, ISSN={["1361-6501"]}, url={https://doi.org/10.1088/1361-6501/ab1ca6}, DOI={10.1088/1361-6501/ab1ca6}, abstractNote={Knowledge of deformation and failure mechanisms at micro- to nano-length scales is important for the prediction of material behavior as well as the development of new materials with desired properties. In situ multiaxial testing with scanning electron microscopes (SEM) can reveal physical deformation mechanisms under realistic multiaxial loading conditions. Although in situ SEM testing has gained traction in recent years, there is currently no multiaxial in situ SEM testing stage available with axial-torsional loading capabilities which can generally be used in any SEM. In this study, we report the development of a multiaxial miniature testing system (MMTS) with a unique capability for performing axial-torsional testing of a tubular specimen with a 1–2 mm outer diameter, inside most SEMs. The different challenges of developing a multiaxial in situ SEM testing stage, such as small load frame size, appropriate specimen position, high vacuum compatibility of MMTS load frame components, as well as the development of installation accessories, were addressed. A custom SEM stage door was developed for the MMTS load frame. Verification tests have confirmed the successful development of the MMTS for in situ SEM testing. In addition, digital image correlation was used with recorded SEM images during the test to determine the surface strain.}, number={10}, journal={MEASUREMENT SCIENCE AND TECHNOLOGY}, publisher={IOP Publishing}, author={Rahman, Farhan and Ngaile, Gracious and Hassan, Tasnim}, year={2019}, month={Oct} }
 @inproceedings{rahman_hassan_ngaile_2018, place={Portoroz, Slovenia}, title={Development of a 3D Digital Image Correlation Setup for a Multiaxial Miniature Testing System}, url={http://www.4m-association.org/sites/www.4m-association.org/files/Detailed%20Programme_4.pdf}, DOI={10.3850/978-981-11-2728-1_74}, booktitle={World Congress on Micro and Nano Manufacturing}, author={Rahman, F. and Hassan, T. and Ngaile, G.}, year={2018}, month={Sep} }
 @inproceedings{li_rahman_chan_carcaterra_hassan_ngaile_2016, place={Paper#123, UC Irvine, Orange County, California, USA}, title={Development of a multiaxial miniature testing system for in-situ SEM study of micro tubes at various temperature levels}, url={https://conf.papercept.net/conferences/conferences/ICOMM16/program/ICOMM16_ContentListWeb_2.html}, booktitle={11th International Conference on Micro Manufacturing}, author={Li, L. and Rahman, F. and Chan, Y.C. and Carcaterra, B. and Hassan, T. and Ngaile, G.}, year={2016}, month={Mar} }