Direct Visualization of Stress Distribution Related to Adhesive through Mechanoluminescence

Abstract

Elasticoluminescent material is a novel ML functional ceramic powder (controllable size: 10 nm―100 μm, representative and the most efficient ML material: SrAl2O4:Eu2+) and it can emit intensive light repeatedly accompanied by mechanical stress such as deformation, friction, impact, even in elastic deformation region. The ML intensity is proportional to strain energy of the material. Thus, when dispersedly coated onto a structure, each particle acts as a sensitive mechanical sensor, while the two-dimensional (2D) emission pattern of the whole assembly reflects the dynamical strain/stress distribution inside the structure and the mechanical information around the defect and crack or the in-visible tip. This ML visualization technique provides a novel way of diagnosing the structural health, especially in early detection for safe & security measure. Actually, the ML sensor has been applied to real social infra-structure such as bridge, building, welding point of pipeline and high pressure vessel, and successfully demonstrated the ability to detect active crack including likelihood for growth, real crack propagation and mechanically weak points etc. Meanwhile, recently NEW advanced material such as CFRP, high tensile strengthen steel and non-steel metal for light weight vehicle are strongly required from the viewpoint of energy saving and environment. Accordingly, joint & adhesive technologies especially for different kinds of materials and the non-destructive evaluation have been investigating for application of these materials and the reliability in use. Especially, as to adhesion, kissing bond and weak bond, in which strengthen of the bonding is nothing or weak respectively without void and crack, have been remaining as challenge for the application and has been vigorously investigated in the field of non-destruct evaluation so far. In the presentation, we would like to report on suitability of the ML sensing for diagnosing (1) a stress distribution in adhesive, (2) visualization of mechanical distribution related to adhesive condition. In fact, as the result of (1), we succeeded to directly visualize stress distribution in adhesive for the first time through mechanoluminescence. We will discuss the results with the result of conventional FEM analysis, simulation of mechanical stress distribution. In addition, as the result of (2), we succeeded to visualize strass/strain distribution of adherend, clearly find out the stress/strain distribution are related to adhesion condition and also find out the area of pseud kissing bond through mechanoluminescence for the first time. [Acknowledgement] The research was partially supported by Innovative Structural Materials Association (ISMA), program for the promotion of scientific research with a view to creating intellectual resources through New Energy and Industrial Technology Development Organization (NEDO), AIST Strategic budget 2015 and KAKENHI, Grant-in-Aid for Scientific Research (B).