Issue 35

R. Sepe et alii, Frattura ed Integrità Strutturale, 35 (2015) 534-550; DOI: 10.3221/IGF-ESIS.35.59 538 displacements and the applied loads are measured respectively by linear position transducers and load cells, located along the cylinder axes. Both this devices generate analogical signals accepted by control system. Figure 4 : Mechanical components of the machine. Figure 5 : Shear load introduction system. Test procedure Four types of load controlled tests have been carried out:  T1: Mono-axial static test - P y = 400 kN, with loads applied with a ramp of 1 kN/sec;  T2: Mono-axial static test - P x = 250 kN, with loads applied with a ramp of 0.62 kN/sec;  T3: Bi-axial static test - P x = 250 kN and P y = 400 kN, with loads applied with a ramp of 0.62 kN/sec in X direction and of 1 kN/sec in Y direction;  T4: Fatigue test - A fatigue load P ymax = 400 kN, (frequency equal to 1 Hz) has been applied in the normal direction to the longitudinal joint with a load ratio R = 0.01 while a static load P x = 200 kN has been applied in the joint direction. During fatigue test visual inspections were carried out every 10˙000 cycles. No cracks were found in the joint region during the test. The first significant failure was detected at 164˙292 cycles. This failure initiated in a hole of the web of one of the frames as shown Figs. 6 and 7. The cracks were easily visible with the unaided eye and were located approximately half-length of the frame. The extension of the crack to the size shown occurred in a single cycle. Note that, while the three undamaged frames continued to transmit load, the failed frame did not. Immediately following the failure of the frame,