Additive manufacturing (AM) processes are reliable techniques to build highly complex metallic parts. Direct energy deposition (DED) is one of the most common technologies to 3D print metal alloys. Despite a wide range of literature that has discussed the ability of DED in metal printing, weak binding, poor accuracy, and rough surface still exist in final products. Thus, limitations in 3D printing of metal powder and wire indicate post-processing techniques required to achieve high quality in both mechanical properties and surface quality. Therefore, hybrid manufacturing (HM), specifically additive/subtractive hybrid manufacturing (ASHM) of DED has been proposed to enhance product quality. ASHM is a capable process that combines two technologies with 3-axis or multi-axis machines. Different methods have been suggested to increase the accuracy of machines to find better quality and microstructure. In contrast, drawbacks in ASHM still exist such as limitations in existing reliable materials and poor accuracy in machine coordination to avoid collision in the multi-axes machine. It should be noted that there is no review work with focuses on both DED and hybridization of DED processes. Thus, in this review work, a unique study of DED in comparison to ASHM as well as novel techniques are discussed with the objective of showing the capabilities of each process and the benefits of using them for different applications. Finally, new gaps are discussed in ASHM to enhance the layer bonding and surface quality with the processes' effects on microstructures and performance.

This paper presents nonlinear finite element (FE) models to predict time-and tempera-ture-dependent responses of shape memory polymer (SMP) foams in the large deformation regime. For the first time, an A SMP foam constitutive model is implemented in the ABAQUS FE package with the aid of a VUMAT subroutine to predict thermo-visco-plastic behaviors. A phenomenological constitutive model is reformulated adopting a multiplicative decomposition of the deformation gradient into thermal and mechanical parts considering visco-plastic SMP matrix and glass micro-sphere inclusions. The stress split scheme is considered by a Maxwell element in parallel with a hyper-elastic rubbery spring. The Eyring dashpot is used for modelling the isotropic resistance to the local molecular rearrangement such as chain rotation. A viscous flow rule is adopted to prescribe shear viscosity and stress. An evolution rule is also considered for the athermal shear strengths to simulate macroscopic post-yield strain-softening behavior. In order to validate the accuracy of the model as well as the solution procedure, the numerical results are compared to experimental responses of Styrene and Polyurethane SMP foams at different temperatures and under different strain rates. The results show that the introduced FE modelling procedure is capable of capturing the major phenomena observed in experiments such as elastic and elastic-plastic behaviors, softening plateau regime, and densification.

In the present study, the fatigue behavior and tensile strength of A6061-T4 aluminum al-loy, joined by friction stir spot welding (FSSW), are numerically investigated. The 3D finite element model (FEM) is used to analyze the FSSW joint by means of Abaqus software. The tensile strength is determined for FSSW joints with both a probe hole and a refilled probe hole. In order to calculate the fatigue life of FSSW joints, the hysteresis loop is first determined, and then the plastic strain amplitude is calculated. Finally, by using the Coffin-Manson equation, fatigue life is predicted. The results were verified against available experimental data from other literature, and a good agree-ment was observed between the FEM results and experimental data. The results showed that the joint’s tensile strength without a probe hole (refilled hole) is higher than the joint with a probe hole. Therefore, re-filling the probe hole is an effective method for structures jointed by FSSW subjected to a static load. The fatigue strength of the joint with a re-filled probe hole was nearly the same as the structure with a probe hole at low applied loads. Additionally, at a high applied load, the fatigue strength of joints with a refilled probe hole was slightly lower than the joint with a probe hole.

Bonded patches are widely used in several industry sectors for repairing damaged plates, cracks in metallic structures, and reinforcement of damaged structures. Composite patches have optimal properties such as high strength‐to‐weight ratio, easiness in being applied, and high flexibility. Due to recent rapid growth in the aerospace industry, analyses of adhesively bonded patches applicable to repairing cracked structures have become of great significance. In the present study, the fatigue behavior of the aluminum alloy, repaired by a double‐sided glass/epoxy composite patch, is studied numerically. More specifically, the effect of applying a double‐sided composite patch on the fatigue life improvement of a damaged aluminum 6061‐T6 is analyzed. 3D finite element numerical modeling is performed to analyze the fatigue performance of both repaired and unrepaired aluminum plates using the Abaqus package. To determine the fatigue life of the aluminum 6061‐T6 plate, first, the hysteresis loop is determined, and afterward, the plastic strain amplitude is calculated. Finally, by using the Coffin‐Manson equation, fatigue life is predicted and validated against the available experimental data from the literature. Results reveal that composite patches increase the fatigue life of cracked structures significantly, ranging from 55% to 100% for different applied stresses.