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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are surface treatment of the steel, synthesis of steel with GFRP in the prepreg process, and finishing of the specimens by cutting them into the final dimensions. The label #GB identifies the mechanically treated specimens by means of grid blasting. Accordingly, the labels #Si and #Ti identifies the chemically treated specimens by means of silane and titanium dioxide primers and the label #GFRP identifies the pure GFRP specimen that serves as reference. The setup of the pressing process leads to a fiber volume content of approximately 60 % within the GFRP constituents. Two variants of specimens are prepared for mechanical testing, namely (i) the as manufactured specimens and (ii) the aged specimens. Ageing of the specimens happens by depositing them into water at an elevated temperature for one week. The term “ aged ” identifies these variants of specimens. Well defined tensional and shear loads, respectively, are straining the intrinsic hybrid laminate specimens by means of specific material tests. A modified DCB test according to ASTM D 5528-01 serves to determine the fracture toughness of the interface. An EST according to Weidenmann et al. (2015) delivers the shear strength . Testing generally happens in dry conditions at room temperature (RT) and at an elevated temperature within a convection chamber, respectively, 3.1. Fracture Toughness for GFRP, respectively. A thin anti-adhesion film between the layers of GFRP and steel establishes an initial crack of the length during the prepreg process. A length scale on one side of the intrinsic hybrid specimens serves to record the total crack length by means of an external camera system. Load blocks at each layer transmit the load F. The speed of the quasi-static, displacement-controlled test is . 3. Experimental Setup The dimensions of the double cantilever beam specimen are and (s. Fig. 1). The bending stiffnesses of both cantilevers are the same by choosing a thickness of the layers for steel and

b)

a)

average fiber alignment

GFRP steel

t GFRP t steel

length scale

F

F

d

l DCB

a

a 0

F

w

F

F = load, w = width, l DCB = effective length, t = thickness, a 0 = initial crack length, a = total crack length, d = crack opening displacement

Fig. 1. Specimen for the DCB-Test a) unloaded b) loaded

3.2. Shear Strength

The upper limit of the length of the specimen is so that it fails due to the shear stress and not and the width are the dimensions of the intrinsic hybrid laminate specimens (s. Fig. 2). Two pressure plates with an offset are straining the specimens. The upper pressure plate strains the steel component and the lower plate the GFRP component. The speed of the quasi-static, displacement-controlled EST is . due to excessive pressure. Therefore, the length