Journal of Multiscale Modelling

AA7075-T6 is widely used in the aviation and aerospace industries thanks to its interesting strength-to-weight ratio. The fatigue life of the structural components of aircrafts and rockets can be altered as a consequence of the impact of alien objects. This work investigates the fatigue behavior of an AA7075-T6 hourglass specimen induced by the impact of a steel ball at its minimum cross-section. The specimen is then tested with a rotating bending moment. The stress distributions after impact and during cyclic loading are estimated using the Finite Element (FE) method. The failure mechanism was clarified by the observation of the failed specimen surface.

Lattice materials, such as honeycombs, are remarkable in their ability to combine high stiffness, strength and toughness at low density. In addition, the recent and pervasive development of additive manufacturing technologies makes it easier to produce these cellular materials and opens new possibilities to improve their properties by implementing small modifications to their microstructure. Such developments open new opportunities towards the design of new classes of architectured materials. For example, recent computational studies have shown that honeycombs with lattice density gradients have a fracture energy under tensile loading up to 50% higher than their uniform counterparts. The aim of this study is to provide experimental evidence for these promising numerical results. To achieve this, single-edge notched tension specimens, with a honeycomb lattice structures, were manufactured by stereolithography using a ductile polymer resin. The performances of three different honeycombs were compared: (i) a uniform sparse lattice, (ii) a uniform dense lattice, and (iii) a gradient lattice with alternating bands of sparse and dense lattices. The results indicated that specimens with a density gradient may achieve a work of fracture per unit volume that is up to 79% higher than that of a uniform lattice.

The body force method is an elastic stress analysis method based on the principle of superposition, where the concentrated force is distributed to satisfy the boundary conditions to obtain a highly accurate elastic solution. In the problem of orthotropic inclusions, the strain difference caused by orthotropic inclusions is expressed as a pair of concentrated forces called a force doublet. For this purpose, the interior of the orthotropic inclusion is discretized by triangular elements, and the fundamental solution of the force doublet is calculated by surface integrating inside the elements. The singularity of concentrated force doublet can be easily eliminated by Green’s theorem when distributing force doublet of uniform magnitude inside a triangular element. However, since the stress distribution inside the orthotropic inclusion is represented by a discontinuous function and the magnitude of the force doublet, the stress inside the inclusion cannot be analyzed accurately. By approximating the magnitude of the force doublet in a triangular element with a linear function, it is possible to obtain the internal stress distribution continuously. The method used to analyze the crack problem is applied to deal with the singularity of the concentrated force doublet. The above method was validated by solving the problem of orthotropic inclusions in the vicinity of the stress concentration.