Issue 35

O. Demir et alii, Frattura ed Integrità Strutturale, 35 (2016) 330-339; DOI: 10.3221/IGF-ESIS.35.38 336 Figure 11 : Variations of KI, KII and KIII SIF values along crack front for all loading angles. E XPERIMENTAL STUDIES ON MODE - I / II FRACTURE his section deals with experimental studies on mode-I/II fracture tests. In the first subsection, details of the experimental set-up, including materials and equipment used, specimen preparation and testing procedure, are explained. The second subsection contains experimental results in terms of fracture loads, crack lengths and broken samples for all the tests performed. Description of The Experimental Set-Up The experiments are performed on 100 kN "Schimadzu Servo Pulser" axial fatigue test machine and 200 kN "Schimadzu AG-X Plus" tensile test machine. In Fig. 12, overall views of the experimental set-up and the equipment used are shown. As seen from this figure, the test assembly consists of mode-I/II CTS and T-specimen (Al 7075-T651), the loading apparatus (St 4140), the pins (HSS steel) and a camera. Figure 12 : Overall views of the experimental set-up, the equipment and test machines used. Before tensile load application, fatigue pre-cracking is performed under mode-I loading for all CTS specimens according to ASTM E399 standard [19] by using axial fatigue test machine. Pre-crack lengths of all CTS specimens used in experiments are determined as indicated in the standard (Pre-crack Length ≥ 0.025W or 1.3 mm whichever is larger) and crack propagation is monitored and controlled by using a high-zoom camera. Also pre-crack load is determined according to the ASTM condition (K max ≤ 0.8K Q ). After generation of the pre-crack, tensile load is applied to CTS specimens under different loading angles. Tensile load rate is applied by taking account of standard limitations that is given as follows, 0.55 MPa√m/s ≤ ∆K/∆t ≤ 2.75 MPa√m/s. Finally, load-displacement data are taken from the machine and critical fracture load is determined as indicated in the standard. Taking into account the above-mentioned considerations fracture tests are also performed for the T-specimens. Results of CTS Specimen Experiments In this subsection, results from the mixed mode fracture tests of CTS specimen are presented for different loading angles. Tab. 2 summarizes different cases tested. Critical fracture loads are determined from load-displacement curves according T