New measurement method of Poisson’s ratio of thin films by applying digital image correlation technique

• Published in: International journal of precision engineering and manufacturing 2014-05, Vol.15 (5), p.883-888
• Main Authors: Kang, Dong-Joong, Chen, Feifei, Park, Jun-Hyub
• Format: Article
• Language: English
• Subjects: Engineering; Industrial and Production Engineering; Materials Science
• ISSN: 2234-7593; 2005-4602
• DOI: 10.1007/s12541-014-0412-z

This paper describes a new method to measure the Poisson’s ratio of thin films by applying digital image correlation technique. Image regions in region of interest (ROI) before and after deformation are compared to each other for precise measurement. For the microsized sample, a representative sub-pixel registration algorithm is applied which is the Newton-Raphson iteration method combined with bicubic intensity interpolation. The first order derivatives of the intensities in the axial loading direction and the transverse direction to loading axis were solved and Poisson’s ratio is the absolute value of the ratio of transverse strain to the corresponding axial strain resulting from uniformly distributed axial stress below the proportional limit of the material. To verify this method, microtensile tests of BeCu thin film were performed and the micro-tensile properties including Poisson’s ratio of BeCu thin film were measured. To obtain more accurate Poisson’s ratio, the stress-strain curve was divided into several intervals to calculate the Poisson’s ratios of BeCu. And, the average value of the Poisson’s ratios of several intervals came to 0.304. Besides, the ultimate tensile strength, 0.2% yield strength and elastic modulus of BeCu were obtained and came to 1065 MPa, 1037 MPa, 102 GPa, respectively.