16:10   Session 15: Advanced materials and innovative structural concepts Chair: Michel Guillaume 16:10 20 mins Study on fatigue and crack propagation of titanium alloy laminated structure Tianjiao Zhao, Zhinan Zhang, Jipeng Zhang, Haichao Cui, Yuan Zhao, Bintuan Wang Abstract: Titanium alloy laminate structure is a kind of interlayer hybrid composite material, which is made up of titanium alloy laminate and graphite fiber, and solidified under certain temperature and pressure. Compared with the fiber laminate with aluminum alloy, the titanium alloy laminate structure can improve the strength, modulus and notch impact resistance of the laminate, it also have wide temperature range, good corrosion resistance and better fatigue resistance of the laminate. In this paper, an analytical model considering fatigue crack propagation under lamination is established based on the judgment criterion of laminated crack of composite materials and the law of fatigue crack propagation of metal, and the crack growth rate of titanium alloy laminated structure under different lamination forms is predicted. The accuracy of the analytical method and model is verified by comparing with the experimental data. It provides an effective way to calculate the crack propagation of titanium alloy laminated structure, and has important theoretical significance and engineering application value for making full use of the potential of this kind of material to design and evaluate the safety life. 16:30 20 mins TI-6AL-4V additive manufacturing mechanical properties as indication to measure of quality Carmel Matias Abstract: Airframe industry has not yet adopted Additive Manufacturing (AM) technology for primary load carry structural production. This is mainly due to lack of generic economic quality control methods to detect manufacturing defects that compromise fatigue strength. This study done for Ti-6AL-4V Powder Bed Fusion (PBF), Selective Laser Melting (SLM) technology presents an approach of allowed defects characterization to be used for quality control criteria. 16:50 20 mins High strength and ductility across size scales: 3D printed metal materials with microscale heterostructure Zhijie Yu, Jingfeng Xue, Qixing Sun, Jin Zhou, Yanfei Wang Abstract: Low-weight design is pursued by aeronautical manufacturing since the very beginning. Additive Manufacturing (AM, also known as 3D printing) provides a method to build novel composite materials as well as high-performance structures from conventional materials. AM makes it possible for aeronautical structures to bear large loads with a low weight (examples shown in figures below). However, due to the microscale heterogeneity caused by AM process, AM metal materials exhibit different mechanical properties from conventional cast/wrought materials. The heterogeneity of AM metal products is nearly unavoidable, even if the printed materials is designed to be homogeneous. This phenomenon extensively occurs from microscale (grain boundaries, domain of different grain sizes) to mesoscale (structural or periodical micro-design) or even macroscale (product structures). These heterogeneities, especially the micro and mesoscale ones, always involve significant size-effect of materials. The author applies numerical simulations based on a modified strain gradient theory to find the strength-ductility relationships of heterostructured metal materials [1], the simulation result coincides well with the experiment and literature. Both statistically stored dislocations and geometrically necessary dislocations are combined in a mechanism-based theory to depict the mechanical response across size-scales. The Taylor stress and back stress are found dominating the high mechanical performance of materials with heterogeneous structures. And a hetero-zone boundary affected region, whose width seems to be a constant depended on the materials of the two phases, is revealed to be the key factor of such microscale heterogeneous materials. Results show that heterostructured metals possess superior mechanical properties exceeding the prediction by the rule-of-mixtures. Though the AM materials cannot achieve the performance of conventional manufactured ones in many cases, these efforts indicate that there is an opportunity for AM materials to bridge this gap and even get better. Many related researches together shed lights on the mechanisms of the strength-ductility of heterostructured materials across size scales, and this will help promote the design and manufacture of aeronautical AM structures to a higher level.

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