Issue 45

L. Zou et alii, Frattura ed Integrità Strutturale, 45 (2018) 53-66; DOI: 10.3221/IGF-ESIS.45.05 58 Welding process MIG welding method with the Austria Fronius welding machine is used in the experiment here. The T-welded joints specimen has K type groove, the groove angle is 55°, without leaving blunt edge, the interval is 1-2mm, tests of the T- joints made of 5083 and 5A06 aluminum alloy with different thickness are carried out respectively. X - ray flaw detection is carried out after welding, and three-point bending fatigue experiment of 5A06+5083 T-joint and 5A06+5A06 T-joint are made. The relevant welding parameters of the T-joints are shown in Tab.5. Material Thickness /mm Groove form Layers Welding current /A Welding voltage /V Welding speed /mm/s Gas flow /L/min X ray flaw detection rating 5A06+ 5083 16+10 K 1 210 24.2 7.0 20 Ⅱ 2 240 24.8 7.45 20 3 220 26.6 4.61 20 4 220 26.6 4.56 20 5A06+ 5A06 35+16 K 1 220 26.6 7.29 20 Ⅰ 2 236 24.8 7.78 20 3 220 26.6 5.93 20 4 220 26.6 5.30 20 5 220 27.4 5.30 20 6 220 27.4 4.86 20 Table 5 : Welding parameters of T-welded joints . Three-point bending fatigue test of T-joint The experiment is carried out in accordance with JB/T7716-95. Size and shape of the specimen in the three-point bending fatigue test are shown in Fig. 3. The thickness of the T-welded joint expressed as in Fig. 3. In this work, the nominal value of is 8.6mm for the 5A06+5083 T-joint and it is 14.9mm for the 5A06+5A06 T-joint. PLG-100 microcomputer controlled high frequency fatigue testing machine is used for the three-point bending fatigue test of T-joint. Other technical specifications in the test are: the precision of the static load is ±1%, the average fluctuation of dynamic load is ±1%, the amplitude fluctuation of dynamic load is ±2%. The loading mode of the three-point bending fatigue test is shown in Fig. 4. Span of fulcrum of the 5A06+5A06 T-joint is 100mm, and that of the 5A06+5083 T-joint is 60 mm. Vibration frequency for 5A06+5A06 T-joint is 170HZ, and for 5A06+5083 T-joint, it is 160HZ. During the test, when the crack size at the weld toe is large enough causing the load not to go up, automatically unload and stop vibration, then record the cycle times. The cyclic stress ratio used in the test is R=0.1, and the designated cycle life is 1×10 7 . Ten 5A06+5A06 and ten 5A06+5083 T-joints specimens are used in the three-point bending fatigue test. Fatigue life data of the specimens obtained in the test are shown in Tab. 6. Figure 3 : Size and shape of the three-point bending fatigue specimen . a a