PSI - Issue 14

Robert Brandt et al. / Procedia Structural Integrity 14 (2019) 891–899 Robert Brandt/ Structural Integrity Procedia 00 (2018) 000 – 000

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1. Introduction

Intrinsic hybrid materials most frequently consist of a light metal, e.g. aluminum and titanium, and a fiber reinforced polymer like glass fiber reinforced plastic (GFRP) or carbon fiber reinforced plastic (CFRP). Only few approaches of an intrinsic hybrid laminate consisting of steel and CFRP are known from literature by Both (2014), Monden et al. (2016), and Lauter et al. (2010). In this study, a unidirectional GFRP and a high strength steel make up the intrinsic hybrid laminate. A mechanical surface treatment by means of a grid blasting process leads to a weak adhesion between the constituents, but chemical treatments by means of primers are significantly improving the adhesion, s. Monden et al. (2014). These primers comprise a functional group, which links itself to the steel surface, and another group, which links itself to the epoxy resin. Two main load cases serve to characterize the bonding strength of the interface. A double cantilever beam (DCB) provides the data to evaluate the fracture toughness by means of the energy release rate and an Edge-Shear-Test (EST) according to Weidenmann et al. (2015) provides the shear strength . The target materials for these two tests are FRP materials so that modifications are necessary for intrinsic hybrid laminates.

Nomenclature

Crack length Initial crack length Effective shear area Crack opening displacement Correction value for the energy release rate Frequency Load Force at failure Maximum load of cyclic edge-shear-test Energy release rate Fracture toughness evaluated by the extrapolation Fitting parameter Inclination of the Wöhler curve Fracture toughness

Length of the specimen Strengthening exponent Cycles Fitting parameter Thickness of the specimen Stress ratio Temperature Maximum nominal shear stress Static nominal shear strength Cyclic nominal shear strength Speed of the traverse Width of the specimens

2. Specimen Preparation One layer of bainitic steel 51CrV4 and another layer of unidirectional GFRP prepregs, which consist of E-glass fibers and an epoxy resin, make up the intrinsic hybrid laminate specimens. The length , thickness , and width denote the dimensions of each specimen. It is here agreed upon that the direction of the dimension length is pointing into the average alignment of the unidirectional glass fibers. The specimens are manufactured in three steps, which