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A concrete-filled fiber-reinforced polymer-steel composite tube column consisting of inner concrete and an exterior fiber-reinforced polymer-steel tube was studied in this paper. A total of 22 specimens were tested under axial compression to investigate the performance of the circular concrete-filled fiber-reinforced polymer-steel composite tube columns. The main experimental parameters were the thickness of the steel tube, the number of fiber-reinforced polymer layers, the type of fiber-reinforced polymer, and the hybridization of fiber-reinforced polymer, in which basalt-fiber-reinforced polymer was used to manufacture concrete-filled fiber-reinforced polymer-steel composite tube columns and was compared with carbon fiber-reinforced polymer. The test results showed that local buckling of the steel tube can be suppressed and even prevented effectively with fiber-reinforced polymer strengthening, and the compressive strength of the concrete-filled fiber-reinforced polymer-steel composite tube specimens is enhanced by the external fiber-reinforced polymer confinement compared with that of the concrete-filled steel tube specimens. With the increase in the number of fiber-reinforced polymer layers or with a larger ultimate tensile strain in the fiberreinforced polymer, the peak axial strain corresponding to fiber-reinforced polymer fracture increases accordingly. A new model that considers composite action was developed for strength prediction of concrete-filled fiber-reinforced polymer-steel composite tube columns, and the analytical results agree well with the experimental results.

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An effective pathway was explored to design and select proper bonding agents that could effectively improve the interfacial interactions between bonding agents and solid particles, with three novel synthesized alkyl bonding agents, dodecylamine‐N,N‐di‐2‐hydroxypropyl‐acetate (DIHPA), dodecylamine‐N,N‐di‐2‐hydroxypropyl‐hydroxy‐acetate (DIHPHA) and dodecylamine‐N,N‐di‐2‐hydroxypropyl‐cyano‐acetate (DIHPCA), as examples. Molecular dynamics simulation was applied to compare unit bond energies of these bonding agents with the [110] crystal face of ammonium perchlorate (AP) and the [120] crystal face of hexogen (RDX). The infrared test was used to characterize the interfacial interactions of these bonding agents with AP or RDX. XPS test was applied to calculate the adhesion percentage of the bonding agents on the surface of precoated AP or RDX particles. All of the above results indicated that these three bonding agents have strong interfacial interactions with AP or RDX in the order of DIHPCA>DIHPHA>DIHPA. The prepared three bonding agents were used in HTPB/AP/RDX/Al propellants, and their effects on tensile strength (σ), elongation under maximum tensile strength (εm), elongation at breaking point of the propellant (εb) and adhesion index (Φ) of the propellant were studied. The results show that the bonding agents improve the mechanical properties of the propellant in the order of DIHPCA>DIHPHA>DIHPA. The methods found from theoretical design, materials synthesis, and mechanistics studies up to practical application show effective guiding significance for choosing the proper bonding agent and improving the interfacial interactions between the solid particles and binder matrix.