Grid-stiffened composite structures not only allow for significant structural weight reduction but also are competitive in terms of structural stability and damage tolerance compared with conventional stiffened candidates. As the development of Automated Fibre Placement (AFP) technology matures, a unitized construction of skin and stiffeners is easily manufacturable. In this paper, a curved stiffener layout is optimized to enhance the structural buckling resistance. A linear variation of stiffener angles is used, resulting in the formation of a locally rhombic lattice pattern. Due to the spatial variation of angle and spacing induced by the use of curved stiffeners, analytic solutions for the responses are not generally applicable. Thus, global and local buckling loads are calculated based on finite element models by a previously-developed global/local coupled strategy. Since the stiffeners are not explicitly modelled in the finite element calculations, a fixed mesh is used for gradient-based optimization. Both parametric design and optimization are performed in order to find the optimal curved grid pattern, whose practical performances are assessed by post-buckling analysis. A comparison between the performances of structures with curved stiffeners, with straight stiffeners, and variable-stiffness skins with curved fibres, demonstrates the potential of curved stiffener configurations in improving the structural efficiency.

A Ca₅Ni₄(VO₄)₆ low loss microwave dielectric ceramic with A site deficient garnet structure was prepared via the conventional solid state reaction method. Ca₅Ni₄(VO₄)₆ sintered at 980°C for 4h to a relative density of 96.2% exhibits favorable microwave dielectric properties such as a permittivity of 10.9, a Q×f value of 96,500GHz, and a τ _f value of -63.6ppm/°C. Its large negative τ _f could be compensated by forming a solid solution with LiCa₂Mg₂V₃O₁₂, that led to improved properties with a near-zero τ _f =-3.7ppm/°C, ε _r =10.2, Q×f=59,300GHz for 0.8Ca₅Ni₄(VO₄)₆-0.2LiCa₂Mg₂V₃O₁₂ after sintering at 955°C for 4h. Further on, 0.8Ca₅Ni₄(VO₄)₆-0.2LiCa₂Mg₂V₃O₁₂ proved to be chemically compatible with Ag electrodes, so it might be a possible candidate for LTCC applications.