A New Multiaxial Specimen for Determining the Dynamic Properties of Adhesive Joints

Abstract

Adhesive joints are increasingly introduced in industrial structures for bonding critical parts. Their mechanical characterization is a key element for design and is, therefore, necessary. A significant work has been done for the characterization under quasi-static conditions, but techniques are rather limited for dynamic conditions. Indeed, existing dynamic studies characterize adhesive assemblies and not the adhesive joint alone, and do not investigate multiaxial loadings. Thus, this paper proposes an innovative experimental technique for the characterization of adhesive joints under dynamic multiaxial loadings. The experimental method relies on three main components: i) a conventional Split Hopkinson Pressure Bar (SHPB) apparatus, ii) a novel specimen named as DODECA enabling to test three distinct multiaxial loadings with the same methodology and iii) local strain and stress measurements performed by Digital Image Correlation (DIC). The paper exhibits all steps of the experimental procedure as well as underlying preparation and measuring methods. Stress and strain in the adhesive joint are estimated from experimental data directly both during loading and at the failure point. Finally, the dynamic material behavior of the adhesive joint is identified from the data.

Identification of the material behavior of adhesive joints under dynamic multiaxial loadings

“…The experimental apparatus, already discussed in [31,19], consists of three main components, as displayed in figure 1: (i) a conventional Split Hopkinson Pressure Bar (SHPB). (ii) a specimen named DODECA enabling to test three distinct multiaxial loadings (denoted by 15˚, 45˚and 75˚) with the same methodology and whose geometry has been optimized in order to avoid edge effects.…”

“…(iii) local measurements performed by Digital Image Correlation (DIC). Therefore, information is provided either classically from global measurements on the Hopkinson bar system by using the DAVID software developed by [32], or from local optical measurements using a high-speed camera and a Digital Image Correlation (DIC) software to measure local displacements with a micrometric resolution, as described in [19]. The DODECA specimen is actually a sandwich dodecahedron, with two aluminum parts bonded by the adhesive joint.…”

“…Beaks are machined in the aluminum parts at the edges of the joint to avoid end effets such as strain or stress concentrations in the joint [1,2,33]. For more details on different specimen geometries and how the DODECA specimen has been designed, the reader is referred to [19].…”

“…In a previous work [19], we have shown that the measurements extracted from the experiment permit a rough estimate of the material parameters assuming some assumptions are verified. It has been shown that both global (SHPB) and local (DIC) measurements can be exploited to characterize main features of the material behavior of the adhesive joint.…”

“…The aim of this paper is the characterization of adhesive joints under dynamic multiaxial loadings. In previous studies [31,19], we have proposed a novel specific sandwich specimen denoted as DODECA and performed simple material characterization using a Split Hopkinson Pressure Bar system and local strain measurements performed by Digital Image Correlation (DIC). Here, we add to this framework a detailed direct and inverse analysis of the system which will lead to the characterization of the yield and fracture surfaces in the space of equivalent von Mises stress vs hydrostatic stress.…”