Tensile Test for Polymer Plastics with Extreme Large Elongation Using Quad-Camera Digital Image Correlation 2016-01-0418

Polymer plastics are widely used in automotive light weight design. Tensile tests are generally used to obtain material stress-strain curves. Due to the natural of the plastic materials, it could be elongated more than several hundred percent of its original length before breaking. Digital Image Correlation (DIC) Analysis is a precise, full field, optical measurement method. It has been accepted as a practical in-field testing method by the industry. However, with the traditional single-camera or dual-camera DIC system, it is nearly impossible to measure the extreme large strain.

This paper introduces a unique experimental procedure for large elongation measurement. By utilization of quad-camera DIC system and data stitch technique, the strain history for plastic material under hundreds percent of elongation can be measured. With a quad-camera DIC system, the correlation was conducted between two adjacent cameras. These four camera DIC system could obtain much wider test range without loss of measurement resolution. Moreover, a multiloading stage measurement procedure is developed to solve the painting peeling off problem due to the material large elongation. Between each loading stage, the tensile test machine is paused and the sample is re-painted before the paint peels off from the sample. The strain history for each loading stage is recorded and evaluated by the DIC system. Then the total strain history is calculated depending on the strain values during each loading stage. The basic principle of multi-camera DIC test system, technical challenges and its solution for the measurement of material under extreme large elongation as well as experimental plan and results are elaborately explained in this paper.