Development of a compact biaxial tensile tester with DIG technique for viscoelastic strip

Problems in which boundary itself and boundary conditions varies with time are called non-proportional. When it comes to viscoelastic media, the problem becomes more and more complicated. Up to date, very few researches have carried out on the analysis of stress field under non-proportional loading conditions. At first step in this research, a compact biaxial tensile tester is designed and fabricated in order to realize non-proportional loading conditions. The biaxial tensile tester is equipped with four independent motors controlled by a computer, thus various biaxial tensile conditions are enabled. The cross head speed of each grip can be changed in 1000 times range. In addition, load in each direction is measured by a load cell of 2000N capacity, and displacement is estimated from the rotation of screw axis. Also, in order to evaluate the 2D stress and displacement fields in a cross type specimen, various optical techniques are adopted such as the digital image correlation, photoviscoelasticity and etc. With this tester, proportional loading experiments was firstly conducted before proceeding to non-proportional loading problem. The tester and measuring techniques adopted are very effective both for proportional and non-proportional analyses of elastic strip.