Modelling strength of cracked friction stir welded panels by means of the crack tip opening angle (CTOA)

The objective of this work is to assess numerically the strength of cracked flat friction stir welded panels for aerospace applications, on the basis of simple experiments made on small coupons of material (Kahn tear test). The transferability from a geometry to another, in particular the results obtained from Kahn tear tests to the prediction of the R-curve of cracked FSW M(T) panels is performed using the crack tip opening angle (CTOA). The Kahn tear test is reproduced first by means of finite element analysis using a debond procedure based on the attainment of a critical CTOA as a function of crack length. The CTOA extracted from Kahn tests is then used to simulate the R-curve of M(T) panels of different widths. The material considered here is a 6013-T 6 aluminium alloy. Two series of values of CTOA are determined: (i) considering the material as homogeneous with strength equal to that of the parent material; (ii) introducing different strengths locally for the weld TMAZ/HAZ and nugget.