Chapter 16 Measurement of Local Strain Distribution and Its Variation Near Eyes During Blink Using Digital Image Correlation Kasumi Sakai, Yuelin Zhang, Satoru Yoneyama, Yukihiro Miyazaki, Yuko Nagai, and Takanori Igarashi Abstract The strain distribution of the facial skin surface at the local area near eyes at the instant of blinking are measured for evaluating the effect of cosmetics products. The motion of the skin at the local area as well as the whole face is observed using multiple digital high-speed cameras. Images of the typical blink motion are extracted from the mass of the local images by evaluating the blink motion in the whole face images. Two-dimensional digital image correlation is used for measuring strain. Irregularities and textures of the skin near the eyes are utilized as random patterns in digital image correlation. The strain distribution and its variation with time under various condition of skin such as bare skin, skin care, and foundation are obtained. The effect of cosmetic product on the skin behavior is elucidated by performing the series of the measurement for several subjects. Keywords Facial skin · Strain · Digital image correlation · Skin condition · Blink 16.1 Introduction The deformation of the facial skin surface is occurred due to the change of the facial expression, and it is known that the deformation is different under each condition such as moisture level or applied cosmetics [1]. Therefore it is considered that the deformation is potential indicator to know the skin conditions. In this study, the deformation on the facial skin surface of daily life is expressed by strain. Human skin surface is sensitive, so a non-contact and non-invasive method is suitable to measure the strain. There are some methods to measure the strain such as digital image correlation (DIC) [1] and optical coherence topography [2]. The previous study [1] shows that DIC is effective for measuring the strain distribution on the whole face. However, the method can be regarded as a non-contact but not a non-invasive since random pattern is painted on the skin to measure the deformation of the face. To propose the non-invasive method by using DIC, authors attempt to substitute a pattern naturally present on the skin such as textures or irregularities for the paint pattern [3]. The results show that it is effective to measure the time histories of the strain in the local area around the eye (250 μm2). The final goal of this study is to propose a non-contact and non-invasive method to measure the strain of the skin in-site by using DIC. In this paper, to show the effectiveness of the proposed method, the time histories and distributions of strain around the eyes during the blinking under various skin conditions are measured. K. Sakai · Y. Zhang · S. Yoneyama ( ) Department of Mechanical Engineering, Aoyama Gakuin University, Sagamihara, Japan e-mail: yoneyama@me.aoyama.ac.jp Y. Miyazaki · Y. Nagai Makeup Products Research, Kao Corporation, Odawara, Japan T. Igarashi Skincare Products Research, Kao Corporation, Tokyo, Japan © The Society for Experimental Mechanics, Inc. 2019 L. Lamberti et al. (eds.), Advancement of Optical Methods & Digital Image Correlation in Experimental Mechanics, Volume 3, Conference Proceedings of the Society for Experimental Mechanics Series, https://doi.org/10.1007/978-3-319-97481-1_16 113
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