High rate loading of hybrid joints in a Split Hopkinson Tension Bar

E Cadoni,H Couque,A Cosculluela,E Buzaud,Noah Ledford,Hanna Paul,Matti Isakov,Stefan Hiermaier

doi:10.1051/epjconf/201818302023

E Cadoni, H Couque + Show 6 more

Open Access

https://doi.org/10.1051/epjconf/201818302023

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Abstract

Bonded joints are nowadays seen as one of the preferred joining methods in aerospace applications. However, the difficulty in certifying bond strength and the relatively low energy absorption capability of the joint are barriers to widespread adoption. The use of a hybrid joint, that is, the combination of a mechanical and a bonded joint, allows for a fail-safe design and offers improved performance of the joint. The quasi-static properties of hybrid joints have been investigated by a number of researchers. In contrast, the high rate loading regime has been only sparsely investigated. In this work, hybrid joints are tested in quasi-static and high rate loading in order to analyze their loading rate dependence. The hybrid joint studied is a composite-aluminum double lap shear joint with Sikaforce 7752 adhesive and Hi-Lite-315 countersunk titanium bolts. In order to quantitatively analyze the high rate behavior of the hybrid joints and their respective sub-components, additional tests are carried out on simply bonded and simply bolted specimens. The high rate characterization was performed with a Split Hopkinson Tension Bar. The main challenges for these tests are the relatively large specimen size and complex specimen geometry needed to properly characterize the joint behavior, which both are in contradiction with the assumptions of the classical Split Hopkinson Bar-analysis. In this paper we describe an approach to solve these challenges based on an elastic wave analysis of the system.

Highlights

The ever increasing demand for more efficient structures is bringing multi-material design into the technological forefront
In the current contribution we report high rate loading experiments on mixed material hybrid joints by using the Split Hopkinson Tension Bar (SHTB)-technique
During the high rate tests the specimen was monitored with a high speed camera (Phantom 1610 at 150 kHz and 1024 x 96 pixels) allowing for local strain and displacement measurements based on the 2D Digital Image Correlation (DIC) technique

Summary

Introduction

The ever increasing demand for more efficient structures is bringing multi-material design into the technological forefront. Hybrid joints, which combine mechanical and bonded joints, offer improvements to strength and energy absorption This is achieved by load sharing between the two different joining methods. Fastened joints have been tested at elevated rates of loading by many different authors [3,4,5,6,7,8,9] Based on these studies it can be concluded that the geometry and the material of the components being joined play a major role in determining the failure mode of the joint. The main drawback of servohydraulic machines is that at high enough loading rates the dynamic structural response (natural vibrations) of the test machine itself starts to influence the force measurement. We highlight the aspects in which the current experiments differ from the classical SHB tests on homogeneous solid materials

Test specimens

Specimen preparation

Testing methods

Theoretical analysis of the high rate tests

Results and discussion

Conclusions