ABSTRAT In the present study, the 0Cr13Ni8Mo2Al precipitation hardening high strength steel was selected as the experimental material, and the fracture morphologies and the relevant mechanisms of fracture toughness specimens with different sizes were studied. Results show that, according to the difference of fracture mechanisms, the tensile fracture region of fracture toughness specimens can be divided into crack slow propagation zone (cleavage zone) and fast propagation zone (dimple zone); and the fracture energy is mainly consumed in the crack slow propagation zone. A small size specimen evaluation method for fracture toughness K_IC was established in this study, and the relative error between the fracture toughness K_IC value obtained with this method and that with the standard specimen is 9%. This means that the fracture toughness K_IC value of the metallic materials obtained with the small size specimen evaluation method is very reliable.

The honeycomb absorbing composites with light weight, high strength and broadband absorbing property had been designed by combination of aramid honeycomb and lossy frequency selective surface composite. The effect of the thickness of honeycomb and the configuration of lossy frequency selective surface on electromagnetic performance was investigated, while the electromagnetic absorbing principle of the lossy frequency selective surface with traditional aperture was analyzed by the equivalent circuit method, and of which the deficiency in broadband absorbing was also proposed. In order to resolve the structure with none equivalent capacitance, slots were made on the lossy frequency selective surface with traditional aperture. Consequently, there have been another absorption peak in low frequency, and the high frequency absorption performance kept unchanged. Correspondingly the low frequency absorption performance was greatly improved, thus the whole absorbing performance of the very configuration was greatly improved, and the absorbing bandwidth had been broadened more than one time. Through calculating the equivalent capacitance and inductance by matlab, it follows that as the width of square ring changed,the equivalent inductance varied accordingly,but the equivalent capacitance remain unchanged; The high frequency absorption peaks were mainly affected by the equivalent inductance, and the low frequency absorption peaks were mainly affected by the equivalent capacitance. The thickness of honeycomb mainly affected the low frequency absorption peak and the position of high frequency absorption peak. According to the above characteristics, a thickness of 6mm broadband honeycomb absorbing composites had been designed with the slotted lossy frequency selective surface in front of the honeycomb medium, which presented an absorbing bandwidth 14 GHz of -10 dB. The actual test result basically accorded with the design expectation.

The effect of the minor addition of Mo, Nb, Ti, and Zr on the second-phase precipitation and microhardness of Fe-Cr-Al serial alloys were investigated. Ternary composition of [Al-(Fe₁₂Cr₂)](Al_0.5Cr_0.5) was first determined by the cluster formula approach, based on which a minor amount of alloying elements was added to form new alloys. Alloy ingots were prepared by vacuum arc melting, then solid-solution treated at 1200℃ for 2 h, and finally hot-rolled at 800℃ into plates. The plates were further aged at 800℃ for 24 h. The designed alloys were characterized by means of XRD analysis, OM , SEM and microhardness tester. Results showed that both the type and quantity of minor-alloying elements affect the second-phase precipitation. Specifically, when the atomic ratio of Mo:Nb=2:1 the second-phase particles presented as fine precipitates and distributed uniformly in the ferritic matrix, which results in the higher hardness of about 250 HV. While the addition of Ti decreases the volume fraction of precipitated particles in Mo/Nb/Ti-modified alloy obviously, in which the particle size is increased slightly, corresponding to the lower microhardness about 240 HV. The addition of Zr accelerates the segregation of precipitates and coarsens the particle size, but the Mo/Nb/Ti/Zr-modified alloy still showed a relatively-higher microhardness (about 246 HV).

The flame retardant of melamine-bis[tetrakis (hydroxymethyl) phosphonium] sulfate (MTHPS) was synthesized via reflux reaction with tetrakis hydroxymethyl phosphonium sulfate and melamine as raw materials and then characterized by FTIR and NMR. Beads of pre-expandable polystyrene (EPS) were coated with the MTHPS containing thermosetting phenolic resin, and then with which as raw material, the halogen-free flame retardant EPS foam was prepared via steam foaming and molding process. The effect of MTHPS-content on the flame retardancy, mechanical properties and thermal conductivity of the EPS foams were assessed. It is found that the flame-retardant EPS foam with 50 phr MTHPS presents a limiting oxygen index 34.0% and a V-0 rating for vertical flammability test according to the UL 94 standard. The compressive strength and flexural strength of the flame retardant foam increase with the increasing MTHPS content.

In order to understand the deformation mechanism and energy dissipation of solid buoyant material with different ratio of height to diameter under uniaxial compression loading, the desired experimental tests and numerical simulation were conducted. Firstly, the uniaxial compression test of solid buoyant material specimens with five different ratios of H to D is conducted by means of MTS-45 universal testing machine, while the mechanical response characteristics and failure modes are analyzed. Secondly,the simulation model of the solid buoyant material is proposed based on the results of uniaxial compression test and the macroscopic mechanical property of the solid buoyant material is described with ABAQUS finite element software. Results show that the bearing load stress circles of the solid buoyant material expand at the beginning of plateau stage and the dominant deformation mode is plastic compression during the plateau stage. As densification stage starts, the deformation mode transfers from symmetric biconcave disks to asymmetric slip deformation with the increasing ratio of H to D. The solid buoyant material is apt to shear failure, while the amount of absorbed energy of the failure process increases with the decreasing ratio of H to D, which presents plastic shear failure characteristics. On the contrary, with the increasing ratio of H to D, the material is apt to compression fracture failure．

N-doped porous carbon (C2) was prepared by simple carbonization process with MgCO₃ as template, synthesized polyaniline (PANI) as carbon source and polyethylene glycol (PEG) as binder. Meanwhile, PANI was directly carbonized to prepare (C1) for comparison. The morphology, structure and composition of the prepared porous carbon were characterized by scanning electron microscopy, transmission electron microscopy, N₂ adsorption, thermogravimetry, Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray powder diffraction and X-ray photoelectron spectroscopy. Results show that specific surface area of C2 is 249.8 m²/g, far higher than that of C1 (19.8 m²/g). The N-contents of the two porous carbons were similar i.e. 5.48% (C1) and 4.8% (C2), respectively. Both of the high specific surface area and certain amount of N-doping endowed C2 with good electrochemical capacitive properties. The specific capacitance of C2 is 268 F/g by current density of 1 A/g. Besides, the N-doped porous carbon (C2) exhibited excellent stability after 8000 cycles of charge-discharge by current density of 4 A/g.

Silicate conversion film was prepared on Zn-5%Al hot dip galvanized Q235 steel by dipping in sodium silicate solution with different molar ratio of SiO₂ to Na₂O in the range of 1.0-4.5. The surface morphology and microstructure, as well as the corrosion resistance of the conversion film were characterized by scanning electron microscopy (SEM) with energy dispersive spectrometer (EDS), transmission infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS), as well as electrochemical impedance spectroscopy (EIS). The results show that in the solution of molar ratio 4.0, the prepared film is uniform and smooth with the highest electrochemical impedance up to 204.22 kΩ?cm². However, the film formed in the solution of molar ratio 2.0 exhibits a large number of cracks, which presents the lowest corrosion performance. The silicate conversion film consists of zinc silicate, aluminosilicate, silicon dioxide, aluminum oxide/hydroxide and zinc oxide/hydroxide. Finally, the formation mechanism of silicate conversion film on the Zn-5%Al hot dip galvanized steel was also discussed.

Graphite oxide (GO) was prepared via freeze-drying process of a modified Hummers method and then nitrogen-doped graphene was synthesized by one-step hydrothermal method with hydrazine hydrate, ethylenediamine, ammonia and urea as nitrogen sources and reductants respectively. The microstructure and morphology of the as-produced graphene were characterized by means of Fourier transform infrared spectroscopy, X-ray diffraction, field emission scanning electron microscope, X-ray photoelectron spectroscopy, synchronous thermogravimetric analyzer and nitrogen adsorption-desorption analyzer. The electrochemical performance of the prepared products was assessed by means of cyclic voltammetry, electrochemical impedance spectroscopy, galvanostatic charge/discharge technology. Results show that the four nitrogen-containing agents could effectively reduce GO to produce different graphenes, the corresponding nitrogen content (in mass fraction) of which is 4.99%, 7.7%, 6.35% and 9.18%, respectively. The doped-N atoms coupled into the graphene lattice in forms of "pyridinic N", "pyrrolic N" and "graphitic N". The specific capacitance of the nitrogen-doped graphene prepared with ethylenediamine and urea as reductants could reach 187.6 F·g^-1 and 191.6 F·g^-1 respectively, implying excellent electrochemical performance.

A self-healing CB[7]/PAA hydrogel was prepared with acrylic acid (AA), H₂O, cucurbituril[7] (CB[7]), potassium persulfate (KPS) and NaCl as raw materials. The self-healing process of CB [7]/PAA hydrogel was investigated by means of FT-IR and ¹H NMR techniques. Results show that the hydrogel networks formed during the self-healing of CB [7]/PAA hydrogel are mainly induced by the existence of multiple hydrogen bonds, and after the self-healing, the maximum tensile elongation of CB[7]/PAA hydrogel can reach about 1.73 times of that of the as prepared ones. Within a range of low AA content, the swelling and swelling rate of the hydrogel increase with the increasing AA content, while in a range of high AA content, the swelling and the swelling rate decreases with the increasing AA content; the swelling and swelling rate of the hydrogel in the aqueous solution of pH=7.6 were obviously higher than those in the aqueous solution of pH=10.0 and pH=4.0. The kinetic index n, rate constant K and water diffusion coefficient D of CB[7]/PAA hydrogel were acquired corresponding to non-Fickian diffusion mode. It follows that the swelling of CB [7]/PAA hydrogel is in accordance with the non-Fickian diffusion mode, and the diffusion rate of water molecules is comparable to that of the relaxation rate of chain segments in the hydrogel.

The corrosion kinetics and corrosion product of galvanized steel, which is widely used for making power transmission tower, in a simulated atmosphere of Guangzhou area were investigated by means of wet/dry-cyclic corrosion test (CCT), scanning electron microscopy (SEM), X-ray diffractometer (XRD) and Raman spectroscopy (Raman). Results indicate that, under the present simulated conditions, the corrosion weight loss of galvanized steel after 120 cycles test by CCT is equivalent to that of the same steel exposed to the atmosphere at a designed test site at Guangzhou area for 6 months. The corrosion process of the CCT test can be divided into two stages, and the corrosion rate in the early corrosion stage is relatively higher and the corrosion product scale is thin, loose and porous with poor adhesion to the matrix. With the progress of corrosion, the corrosion rate decreases obviously, and the corrosion product scale gradually becomes thicker and compact with good adhesion to the matrix, while an inner rust layer emerges. In addition, the corrosion product of the Zn-coating consists of ZnO, Zn(OH)₂, ZnCO₃, ZnSO₄, Zn₅(OH)₆(CO₃)₂, Zn₄(OH)₆SO_4·xH₂O, Zn₅(OH)₈Cl₂, and Zn₁₂(OH)₁₅Cl₃(SO₄)_3, however, which present rather low crystallization degree. As the corrosion process proceeds, among others, the proportion of stable phases of Zn₄SO₄(OH)_6·xH₂O and Zn₅(OH)₆(CO₃)₂ increases, while that of the unstable phase of Zn₁₂(OH)₁₅Cl₃(SO₄)₃ decreases.