PSI - Issue 19

M. Duchet et al. / Procedia Structural Integrity 19 (2019) 585–594 Author name / Structural Integrity Pro edi 00 (2019) 000 – 000

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Fig. 9: representative specimens extracted from real components (body mount support of pickup frame).

3.1. Grade of interest, geometries and fatigue test conditions

In the following, the material of interest is a hot rolled complex phase HR CP800 SF (SF for its very good stretch flangeability). The microstructure is composed by a bainitic with ferrite matrix and island of martensite/austenite distributed in the matrix. The tensile strength is higher than 780 MPa with a high yield stress, higher than 680 MPa. This grade exhibits a good elongation as well as very good capacity to sustain severe local straining (hole expansion up to 45%). Thicknesses between Different geometries of demonstrators were investigated. The principle lies on the welding of a U-shape part to a plate to form technological specimens like brackets. Different weld geometries can be used depending on the type of welds as illustrated Fig. 10: T-joint (a), flared joint (b) and lap-joint (c). The T-joint and lap-joint were designed to be loaded in tension and bending whereas the flared joint could only be loaded in tension up today. Different thicknesses of uncoated HR CP800 SF were selected to manufacture demonstrators (from 2 to 3.4 mm). Each demonstrator is welded in homogeneous condition (same grade and thickness for the U-shape and the plate).

(a) T-joint

(b) Flared-joint

(c) Lap-joint (in progress)

Fig. 10: different geometries of demonstrators: (a) T-joint, (b) flared-joint and (c) lap-joint.

A specific clamping line has been developed to test T-joint demonstrators using a standard servo-hydraulic machine equipped with hydraulic grips (Fig. 11): at the bottom, the base of demonstrator is maintained between two plates that are bolted. Then, the upper part of the U-shape is linked to the upper hydraulic grip through a double pivot connection to compensate misalignments and avoid parasite bending moments. Thus, tensile loading can be applied on the specimen. With the similar tooling and by inserting a component that rotates by 90° the base of demonstrator, the