Determination of Linear thermal expansion coefficient by using digital image correlation

Many materials and certain material applications require detailed preconditioning and specific thermal test schedules to be followed to obtain a correct evaluation of thermal expansion. Since a general test method cannot cover all specific requirements, details of this nature should be contained in the relevant material specification. The standard testing method to measure the linear thermal expansion is based on contact methods (ASTM E228-95, Standard Test Method for Linear Thermal Expansion of Solid Materials with a Vitreous Silica Dilatometer). The Thermal Mechanical Analysis (TMA), measures the change of length of the specimen during heating by using a vitreous silica push-rod or tube dilatometer. A big disadvantage of this method is the restricted size of the specimens. When using the TMA method on fibre reinforced composites; the small specimens required (maximum 5 x 5 mm cross section) are not representative for the behaviour of the composite, so the method is not applicable. In this paper the coefficient of linear thermal expansion will be determined by using a contact (TMA) and a non contact method based on digital image correlation (DIC). This full field optical non contact method measures the in-plane displacements of the object surface [1]. By using software the data of the DIC measurement can be converted to strain values which can be used to calculate the coefficient of thermal expansion. The aim of this study is to use both testing methods on different material in order to calibrate and verify the usability of the method to determine the linear thermal expansion coefficient.