Selective laser melting (SLM) is a promising additive manufacturing (AM) process for high-strength or high-manufacturing-cost metals such as Ti-6Al-4V widely applied in aeronautical industry components with high material waste or complex geometry. However, one of the main challenges of AM parts is the variability in fatigue properties. In this study, standard cyclic fatigue and monotonic tensile testing specimens were fabricated by SLM and subsequently heat treated using the standard heat treatment (HT) or hot isostatic pressing (HIP) methods. All the specimens were post-treated to relieve the residual stress and subsequently machined to the same surface finishing. These specimens were tested in the low-cycle fatigue (LCF) regime. The effects of post-process methods on the failure mechanisms were observed using scanning electron microscopy (SEM) and optical microscopy (OM) characterization methods. While the tensile test results showed that specimens with different post-process treatment methods have similar tensile strength, the LCF test revealed that no significant difference exists between HT and HIP specimens. Based on the results, critical factors influencing the LCF properties are discussed. Furthermore, a microstructure-based multistage fatigue model was employed to predict the LCF life. The results show good agreement with the experiment.

Solid riveting is the most widely used joining technique in aircraft assembly, and the current key problems affecting practical application and reliable lifting are concentrated on static strength and fatigue. This paper aims to present a practical review on current practice and novel techniques of solid riveting for aircraft applications in order to obtain a thorough understanding of the underlying mechanisms of defect development to assist industrial users to find pragmatic solutions for safe life extension of components. At first, the current status of solid riveting processes is reviewed, and the key influencing factors on static/fatigue failure of riveted joints are identified. Effects of solid riveting design parameters, manufacturing parameters, residual stress, load transfer and secondary bending on static and fatigue strengths of riveted lap joints are discussed, followed by a review of the state-of-the-art solutions that deal with static/fatigue failures. Furthermore the new development in solid riveting techniques, including the use of different materials and riveting processes, is addressed. Finally, future research perspective and applications industrial riveting is presented.

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Understanding the creep failure mechanism depends on identifying the effects of applied load on the evolution of long-term microstructures. Creep tests at elevated temperatures are time consuming and expensive. Thus, it is important to optimize the number of tests needed to reduce the time from the fabrication of new materials to the operation cycle, as well as to extend materials application scenarios. This paper develops a grain/grain boundary microstructure meshing system in compact tension (CT) geometry that is extended to nonequiaxed grains. The model can produce elongated grains and grain boundaries to simulate the columnar grains in material. A continuum remaining multiaxial ductility damage mechanics model (known as a Nikbin, Smith and Webster [NSW] model) is then adopted to simulate the mechanics of creep behavior. Triple intersections of grain boundaries are invariably the weakest points that form voids to allow for microcracks to join and form macrocracks. The cracking is allowed to develop freely from an element following a critical multiaxial strain accumulation limit. The overall trend is that a loading direction perpendicular to the grain elongation direction contributes to slower creep cracking. This paper shows that it is possible to use grain-level finite element method (FEM) modeling to predict grain microstructure sensitivity to creep crack growth. This novel, virtual test method can be developed further using more complex microstructures to assist in quantifying cracking rates and reducing the number of actual tests needed to characterize crack growth in new materials.