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A NbMoTaWVTi refractory high entropy alloy (HEA) has been successfully synthesized by mechanical alloying (MA) and spark plasma sintering (SPS). The microstructure and mechanical properties of this alloy are investigated. It is observed that only two types of body-centered cubic (BCC) solid solutions are formed in the powders after ball milling for 40 h. However, a new face-centered cubic (FCC) precipitated phase is observed in the BCC matrix of bulk material consolidated by SPS. The FCC precipitated phase is identified as TiO, due to the introduction of O during the preparing process of HEA. The compressive yield strength, fracture strength, and total fracture strain of the consolidated bulk HEA are 2709 MPa, 3115 MPa, and 11.4%, respectively. The excellent mechanical properties can be attributed to solid solution strengthening and grain boundary strengthening of the fine-grained BCC matrix, as well as the precipitation strengthening owing to the formation of TiO particles.

In recent years, application of high strength concrete (HSC) has attracted increasing interest in the construction industry due to its significant economic, architectural, and structural advantages, compared to the conventional normal strength concrete (NSC). However, under fire condition, which is one of the most common hazards that attack building structures, HSC members may be subjected to explosive spalling. Strength reduction of structural members may occur, leading to severe consequences such as failure of members or even collapse of the whole structure. A newly designed 2layered cylindrical specimen consisting of an HSC core and an NSC outer layer is proposed to improve the fire performance of HSC members under elevated temperature. The NSC layer is designed to act as an outer layer insulation to reduce the thermal gradient and also serve as a lateral confinement to prevent the HSC core from spalling. Compression and thermal tests were performed on the specimens to investigate their strength and behavior under elevated temperature. Test results preliminarily verify the feasibility of 2-layered design and at the same time provide insights for the applicability of 2-layered columns in practical construction projects.

Various bifurcation phenomena in a nonlinear curved beam subjected to base harmonic excitation, which is governed by a coupled nonlinear equation with both quadratic and cubic nonlinearities, are investigated using the incremental harmonic balance (IHB) method. The nonlinear partial differential equation that governs the motion of the curved beam is given using Hamilton’s principle. A spatially discretized governing equation is derived using Galerkin’s method, yielding a set of second-order nonlinear ordinary different equations. A high-dimensional model that can take nonlinear model coupling into account is derived. Specific attention is paid to the different bifurcation phenomena of frequency responses and amplitude responses of the system without and with an anti-symmetric mode being excited. Numerical results reveal the rich and interesting diverse bifurcation phenomena that have not been presented in the existent literature on the nonlinear vibration of the curved beam system. Saddle-node, Hopf, and period-doubling bifurcations are observed without an anti-symmetric mode being excited. Besides, a symmetry-breaking bifurcation is observed with an anti-symmetric mode being excited. Furthermore, the phase portraits and bifurcation points obtained by the IHB method agree very well with those obtained by the numerical integration using the fourth-order Runge–Kutta method.

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