Abstract
The friction stir welding (FSW) technology has been widely applied in aircraft structures. The heterogeneity of mechanical properties in weld and the hole in structure will lead the crack to turn. Peridynamics (PD) has inherent advantages in calculating crack turning. The peridynamic theory is applied to study the crack turning behaviour of FSW joints in this work. The compact tension (CT) samples with and without a hole are designed. The crack propagation testing under quasistatic and fatigue loads are performed. The peridynamic microplastic model is used and a three-stage fatigue calculation model is developed to simulate the quasistatic fracture and the fatigue crack growth. The results predicted by the peridynamic models are compared with the experimental ones. The effects of welding direction on quasistatic and fatigue crack propagation behaviours are investigated and the effect of hole position on crack path geometry is also studied. It is shown that the crack turning in FSWed CT samples can be captured by the peridynamic microplastic and the three-stage fatigue calculation models. The peridynamic crack growth rates agree with the experimental results. For CT specimen without a hole, the crack turns into the weld zone where the material is softer. The effect of welding direction on crack growth rates is not obvious. For CT sample with a hole, the crack propagation direction has been mainly controlled by the hole location and the welding direction has a slight effect on crack path.
Highlights
E propagation of cracks in friction stir welding (FSW) joints has been studied by finite element method (FEM) in [18, 19]
The crack can only propagate between elements. e accuracy of crack trajectory predicted by cohesive zone elements (CZE) is not satisfying. e scaled boundary finite element method (SBFEM) is presented to calculate mixed-mode crack propagation in [23]. e remeshing algorithm is still required in SBFEM even though the changes of the global mesh are very small
E crack growth of FSW joints is investigated by XFEM as well [24]. e XFEM permits crack to extend through elements without any remeshing process [25], but the extra computational techniques such as the local enrichment functions, the level set method, and the fracture criterion are still required during analysis. e boundary element method (BEM) was applied to model crack propagation
Summary
E micromodulus c can be obtained by matching strain energy density in peridynamics and its value in classical continuum mechanics. E relation of yield stress and bond yield strain can be obtained by integrating the peridynamic force density within the horizon. E de nition of bond yield strain for plane stress is [43]. Where ε is the cyclic bond strain range and for linear elastic materials it is defined as ε s+ − s− (1 − R)s+. Silling and Askari [37] derived the relationship between the stress intensity factor and the core bond strain. En, the relation of the core bond strain and the peridynamic fatigue crack growth rates can be expressed as da dN βA2εmc 2. E volume correction [31] is involved. e energy method [47] is applied to implement surface correction
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