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In order to meet the requirements of large downward force and high stiffness performance for the friction stir welding process, this paper proposes a 5 degree-of-freedom hybrid manipulator as friction stir welding robot. It is composed of a 3 degree-of-freedom redundant parallel module and a 2 degree-of-freedom rotating head. Semi-analytical stiffness model of the hybrid manipulator is firstly established by compliance models of the two substructures. Virtual work principle, deformation superposition principle and twist/wrench mapping model are applied to this compliance modeling process. A novel instantaneous stiffness performance index is then proposed on the basis of instantaneous energy defined by reciprocal product of external payload screw and corresponding deformation screw. It solves the problems of inconsistent physical unit of linear/angular stiffness and is able to evaluate overall and worst-case stiffness performance. Next, stiffness/compliance experiments are carried out to verify the stiffness model and the novel instantaneous stiffness performance index. Finally, stiffness performance of 5 degree-of-freedom hybrid manipulator is thoroughly discussed in terms of engineering requirements, worst-case stiffness performance and stiffness singularities. It can be summarized that the semi-analytical stiffness model and the novel instantaneous stiffness index are effective in analyzing and evaluating stiffness performance of the 5 degree-of-freedom hybrid manipulator.

Syntactic foams with fly ash cenospheres or commercial microballoons as fillers have been widely used in various applications ranging from aerospace to marine and automotive industry. However, these two extensively...

Charged domain walls may have lower energy than charge neutral walls when large amount of aliovalent doping are present or when there are substantial amount of charged defects in the system. Charged domain walls can produce much larger contribution to functional properties than charge neutral domain walls because they are energetically less stable. If there are regions of charged domain walls in ferroelectric ceramic, it can enhance the extrinsic contribution to the piezoelectric and dielectric properties. We have performed a theoretical analysis on charged domain walls based on the time dependent Landau-Ginzburg model, assuming there are charge defects from aliovalent doping to locally stabilize such charged domain walls. Using BaTiO 3 and PZT as examples, we have studied the stability of charged walls with defect density and found that piezoelectric properties can be greatly enhanced by charged walls if the charge density q is lower than the charges needed to produce local charge balance. If the charge density is equal or more than the amount needed for electrical balance, the walls are pinned, which causes the reduction of piezoelectric effects.

Active Sites Modulation In article number 2200996, Wahyu Prasetyo Utomo, Hao Wu, and Yun Hau Ng report the active site modulation over oxygen‐deficient TiO2 by copper loading, which enhances the electrocatalytic nitrogen reduction reaction to ammonia. Both oxygen vacancies and copper nanoparticles serve as the active sites. The strong metal–support interaction between them also leads to the better activation of N2 molecules.

To meet the evolving requirements of material designability, sustainability, and eco-friendliness, the development of syntactic foams puts great emphasis on filler optimization and matrix selection. Here, we present a novel...

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Biological materials such as conch shells with crossed-lamellar textures hold impressive mechanical properties due to their capability to realize effective crack control and energy dissipation through the structural synergy of interfacial modulus mismatch and lamellar orientation disparity. Integrating this mechanism with mechanical metamaterial design can not only avoid the catastrophic post-yield stress drop found in traditional architectural materials with uniform lattice structures but also effectively maintain the stress level and improve the energy absorption ability. Herein, a novel bioinspired design strategy that combines regional particularity and overall cyclicity is proposed to innovate the connotation of long-range periodicity inside the metamaterial, in which the node constraint gradient and crossed-lamellar struts corresponding to the core features of conch shells are able to guide the deformation sequence with a self-strengthening response during compression. Detailed in situ experiments and finite element analysis confirm that the rotated broad layer stacking can shorten and impede the shear bands, further transforming the deformation of bioinspired metamaterial into a progressive, hierarchical way, highlighted by the cross-layer hysteresis. Even based on a brittle polymeric resin, excellent specific energy absorption capacity [4544 kJ/kg] has been achieved in this architecture, which far exceeds the reported metal-based syntactic foams for two orders of magnitude. These results offer new opportunities for the bioinspired metamaterials to substitute the widespread syntactic foams in specific applications required for both lightweight and energy absorption.