In this study, strip cyclic extrusion-compression was introduced as a modified counterpart of cyclic extrusion-compression process for producing ultrafine grained strips. The strip cyclic extrusion-compression method was applied to the pure aluminum and mechanical properties of the processed strips were investigated. The ultrafine grained strips were successfully processed by applying two cycles of strip cyclic extrusion-compression. The transmission electron microscopy observations revealed that the initial microstructure was refined to 1 µm and 650 nm after the first and second cycles, respectively. The yield strength was increased 3 times and the ultimate strength was enhanced 1.5 times after the application of two cycles. The microhardness of the processed strips was increased to 46 Hv and 58 Hv after the first and second cycles, respectively. Furthermore, the fatigue tests revealed that the fatigue strength was higher in the strip cyclic extrusion-compression processed material than the un-processed one. The microstructure evolution during strip cyclic extrusion-compression was also modeled by means of a dislocation density-based finite element method. The finite element method model predicted that the microstructure was refined to 950 nm and 690 nm after the first and second cycles, respectively.

In the present study, a crystal plasticity finite element model was developed for simulating the microstructure evolution and grain refinement during tube cyclic expansion-extrusion as a severe plastic deformation method for tubular materials. A new approach was proposed for extracting the real deformation history of a representative volume element during severe plastic deformation methods. The deformation history of a representative volume element during four cycles of tube cyclic expansion-extrusion was extracted by the proposed approach. Then, in a crystal plasticity finite element model, the deformation history was applied to a two-dimensional polycrystalline representative volume element with randomly assigned crystalline orientations. The intergranular interactions between grains and the intragranular orientation gradients were successfully simulated by the crystal plasticity finite element model. The distribution of misorientation angles, the evolution of grain boundaries, and the achieved average grain size after different cycles of tube cyclic expansion-extrusion were investigated by the crystal plasticity finite element model. On the other hand, ultrafine grained aluminum tubes were processed by four cycles of tube cyclic expansion-extrusion and the grain size of the processed tubes was studied by scanning electron microscopy observations and X-ray diffraction analyses. The experimental and predicted (by crystal plasticity finite element model) average grain sizes were compared.

This work investigates fracture characteristics of a marble semi-circular bend (SCB) specimen with a pre-defined crack under a compressive loading condition. It aims at evaluating how the fracture toughness can be affected by the crack and span length variation. Numerically, the model is solved using meshless methods, extended to the linear elastic fracture mechanics (LEFM), resorting to radial point interpolation method (RPIM) and its natural neighbor versions (NNRPIMv1 and NNRPIMv2). Alternatively, to validate the meshless method results, the problem is resolved following the finite element method (FEM) model based on the standard 2D constant strain triangle elements. As a result, fracture toughness and the critical strain energy release rate are characterized following the testing method on the cracked straight through semi-circular bend specimen (CSTSCB). A comparison is drawn amongst the theoretical, meshless methods and FEM results to evaluate the capability of advanced numerical methods. Encouraging results have been accomplished leading to validate the supporting numerical methodologies.

No abstract