PSI - Issue 33

R.V.F. Faria et al. / Procedia Structural Integrity 33 (2021) 673–684 Faria et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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small t A and joint rotations. Actually, the XFEM software enforces the user to define the longitudinal axis to promote crack growth, leading to the reported behavior. The present work aims to validate the XFEM design technique to predict the strength of T-peel joints under tensile loads with different configurations (purely welded, bonded and hybrid), considering steel adherends and a ductile adhesive. The study comprises several damage initiation criteria (stress and strain-based) and growth criteria, together with linear and exponential degradation laws. 2. Experimental work 2.1. T-joint and dimensions The T-peel joint is addressed in different topologies: purely welded, bonded and weld-bonded. Fig. 1 shows the geometry and dimensions (given in mm): adherends’ thickness ( t P )=2, joint width ( w )=25, t A =0.2, bond length ( L )=90, radius of curvature ( R )=1 and unsupported length ( c )=22. The weld-nugget is placed according to dimensions a and b (equal to 12.5 mm). a is the length between the weld- nugget’s axis and adhesive termination, while b = w /2 promotes the width-symmetry placement of the nugget. Using only one weld-nugget is a simplification of industrial applications, which consist of structures with several nuggets along the joining length, but is a valid validation choice, and it also simulates a scenario in which a critical weld-nugget is under heavy loads and fails.

Fig. 1. T-joint and dimensions.

2.2. Materials and fabrication/testing procedure

The adherend material is a C45E carbon steel, whose tensile mechanical characterization was previously accomplished by the ASTM-E8M-04 standard (Campilho et al. 2012). The reported properties are presented next: Young’s modulus E =204.3±2.4 GPa; strength in tension σ f =347.5±0.9 MPa and failure strain in tension  f =36.4±2.5%, all obtained from data analysis to the stress-strain ( σ - ε ) curves. The bonded and hybrid joints were fabricated with the adhesive Araldite ® 2015, known as a ductile epoxy that generally works well in bonded joints by absorbing peak stresses. Table 1 provides the acquired properties (mechanical and fracture) of this adhesive (Campilho et al. 2011, Campilho et al. 2013). Fabrication of the T-peel joints was aided by a built jig that enforced the adherends’ al ignment during the curing/welding process. The weld-nuggets (welded and hybrid joints) were manually produced in a CEA ® NKLT-28 equipment with built-in electrodes with conical shape and diameter of 6 mm. Setting of the welding parameters was done according to the material (steel) and manufacturer’s indications: • Squeeze time – electrode closing time before performing the weld (3 cycles in 50 Hz current); • Upslope – time to attain the operator-defined welding current (5 cycles in 50 Hz current); • Welding time – welding duration (35 cycles in 50 Hz current); • Welding current – supplied electric current/capacity of the welding machine ratio (45% of 6.3 kA).