Ultrafine-grained aluminum alloys (UFG AA) show great potential in the design of fatigue-resistant lightweight alloys, and the methodology to assess low-cycle fatigue (LCF) life remains to be studied. In this work, a micromechanics-based LCF life prediction model is presented by conducting crystal plasticity finite element simulation (CPFEM). The fatigue indicator parameter (FIP) of maximum accumulated equivalent plastic strain energy, modulated by triaxiality, is developed to assess the material damage in the microstructure. Particularly, a new multiaxial strain parameter is proposed by considering the combined influence of the mean strain and non-proportional cyclic additional hardening effect, and then directly embedding into the cyclic J-integral. Finally, the reformulated Manson-Coffin relationship is theoretically constructed by correlating the crack tip opening displacement to the crack propagation equation. The results show the scatter fatigue life of UFG AA6061 is not only related to the inhomogeneous evolution of plastic deformation but also to the local stress state. Since the proposed approach considers both the deformation mechanisms at the micro-scale and the corresponding macroscopic responses, it can predict the LCF life of UFG AA with reasonable accuracy.

Traditional shipbuilding crane manipulator is widely used in the process of block lifting and erection of ships, but there are generally problems, such as inflexible output trajectory, limited workspace and low working efficiency. In order to solve above problems, a novel hybrid shipbuilding crane manipulator with closed-chain structure and weakly-coupled characteristics based on multi-DOF (Degree-of-Freedom) mechanism is proposed. Then, a systematically structural and kinematic modeling and analysis method is presented to describe the coupling degree, singular configurations, workspace, motion trajectory, dexterity capacity and static stiffness performances of this type of closed-chain structure mechanism. Results of the numerical examples verify the correctness, accuracy and efficiency of the proposed method. Meanwhile, compared with the traditional shipbuilding crane manipulator, the proposed novel manipulator can finish lifting and transportation operation more efficient, which can also be applied in fields such as: innovative design of oil and gas drilling platforms, deck machinery, construction machinery and other engineering equipment.

The existing gantry ship welding robot mechanism is mostly in series, which has the problems of large motion inertia at the end and joint error accumulation.A kind of ship welding robot with hybrid structure is designed. The platform control mechanism and rotary mechanism adopt the form of planar parallel mechanism, which can effectively increase the rigidity and error compensation ability of the actuator.And the adjusting mechanism of welding torch adopts series structure and keeps the flexible output ability.The kinematics model of the welding actuator is established by combining the closed-loop vector method, complex vector method and D-H four-parameter method.The positive solution of the mechanism is given, and the velocity and acceleration are analyzed based on it.Through simulation analysis, we get the workspace and kinematic characteristics curve of some components under given trajectories to verified the feasibility of the proposed mechanism.