PSI - Issue 13

Yanning Guo et al. / Procedia Structural Integrity 13 (2018) 806–812 Yanning Guo/ StructuralIntegrity Procedia 00 (2018) 000 – 000

807

2

Nomenclature stress strain ̇ strain rate ( ) input wave ( ) reflective wave ( ) transmissible wave cross-sectional area of the bar 0 cross-sectional area of specimen wave speed of elastic wave 0 length of the specimen

As the aeronautical structures are often subjected by dynamic loadings, recently, a number of dynamic tensile studies have completed (2014, 2005). In order to understand the dynamic response of aluminum and accurately determine their elastic modulus, yield stress and strength under high strain rates, tensile split Hopkinson bar (TSHB) technique is commonly used (2016). The experimental results show that aluminum alloy did not indicate rate sensitivity under dynamic impact (2015). Strain hardening behavior is greatly influenced by grain size and dislocation density. As mentioned above, traditional tensile specimens are usually machined perpendicular to the weld line, and each specimen covers the base metal, the heat affected zone, the thermo-mechanically affected zone and the stirred zone (2012, 2008). There is very limited studies on dynamic mechanical behavior of the FSWed joints, especially the effect of welding parameters on the dynamic tensile properties of different zones, have been reported. This work presented here focuses on the dynamic mechanical response of AA2024 FSW welded joints at different welding parameters. And the fracture morphology of specimens was studied by scanning electron microscope (SEM).

2. Experimental setup

2.1. Dynamic tensile properties testing

8.0mm thick 2024-T3 plates were joined by FSW at the same welding speed and the different welding rotation speed, which is 400rmp and 600rmp, respectively. The dynamic tests were performed on a tensile split Hopkinson bar (TSHB) apparatus. The TSHB uses a hollow striker tube which strikes an end cap to generate the tensile impact loading in the input bar. In the TSHB test, the stress, strain and strain rate histories of the specimen can be calculated using the strain signals measured in the middle of the incident and transmitted bars below (1964):

( ( ) A E t 

( ) t

( ) t   r 

( )) t





t 

(1)

i

A

2

0

t

c



( ) t

( ( ) t

( ) ( )) t 

t d

(2)





 

 

i

r

t

t

l

0 0

c t

0 (3) where ( ) , ( ) and ( ) are the input wave, the reflective wave and the transmissible wave respectively. A 0 is the cross-sectional area of the specimen; A is the cross sectional area of the bar; c is the wave speed of elastic wave; l 0 is the length of the specimen. In this study, the incident and transmitted bars are 14mm in diameter, and the speed of the elastic wave is 4866m/s. ( ( )  ( ) t   ( )) t i r  t  l   ( ) t