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Excavation damage zones that occur around tunnels usually lead to a change in rock permeability, which has an impact on the water inflow into tunnels and even induces water inrush disasters. For a better understanding of the effect of the excavation damage zone, analytical solutions that consider the excavation damage zone are developed based on the review and modification of the solutions that consider linings and grouting circles. Then, both analytical solutions and the finite element method are applied to estimate the water inflow, and the results are in good agreement. The effect of the excavation damage zone on water inflow is analyzed based on an impact factor of the excavation damage zone and evaluated in a real engineering case, and the seepage-preventing effects of grouting are discussed. The results reveal that the water inflow increases with increasing permeability and thickness of the excavation damage zone and that there is a limit for the effects of the excavation damage zone. In addition, the effect is stronger for underwater tunnels with small water inflows and stabilizes gradually as the magnitude of water inflow increases. The increase in the impermeability and thickness of the lining and grouting circle can reduce the effect.

Superalloys have a high tensile strength at elevated temperature, a good stability and reliability in a large range of temperatures. Among these superalloys, GH4169 is widely used as thermal components in the turbojet engine. Traditional welding methods are difficult to adapt to the development of high-tech manufacturing. Laser welding plays an important role in superalloys welding field increasingly for its advantages. In this investigation, superalloy GH4169 plate with a thickness of 1mm was welded utilizing the pulsed laser welding and the mechanical properties of the laser welded joints are analyzed. The maximum tensile strength is 928 Mpa, which is close to the base material tensile strength. The welded joint can meet the requirements of users.

In the midst of highly corrosive marine environment the corrosion damage is very critical in the aircraft structure. Corrosion will reduce the fatigue strength and fatigue life of aircraft structure. The fatigue notch factor is a very important factor, and which directly affects the accuracy of the fatigue life estimation result. The LY12CZ aluminum alloy of aircraft structure was accelerated tested according to equivalent accelerated corrosion testing spectrum based on key environment data, then made a fatigue test. According to the fatigue test data fatigue notch factor was calculated and then the variation law of fatigue notch factor with the corrosion life was studied.

Traditional welding methods are difficult to adapt to the development of welding technology of aluminum alloys. Laser welding plays an important role in this field increasingly for its advantages. In this investigation, LF21 plate with a thickness of 2mm was welded utilizing the pulsed laser welding and the mechanical properties of the laser welded joints are analyzed. The tensile strength of welded joint is in the range of 196 Mpa to 232 Mpa. The maximum tensile strength is obtained at the working current of 250 A, pulse width of 6 ms and pulse frequency of 2 Hz. The maximum tensile strength can reach 87% of base material. The intensity factor of welded joint is in the range of 74% to 87%. The welded joint can meet the requirements of users.

The finite element model of the concrete mixing truck’s frame is builded by using shell as basic element, and the process of building the finite element model of the balance suspension is introduced in detail. Based on this, frame’s stress on five types of typical operating conditions are calculated by using the finite element analysis software, NASTRAN, and results can show the dangerous position and the maximum stress position on the frame. The analysis result on structural strength can provide the basis for further improving the frame structure.

With the extensive use of new materials for aircraft structures, traditional riveting technology has been difficult to meet the demands of aircraft repairs. Laser welding of high concentration of energy is ideal technique for aircraft repair,because of its high welding speed, small heat-affected zone, perfect welding joint and small deformation of the welded structure. This article analyzes the application of laser welding technology in aeronautical aluminum alloys, titanium alloys and superalloys aircraft damage repair.

Recently determination of harmful elements in fertilizer has been paid growing attention. The determination method of cobalt in fertilizer by Wavelength Dispersive X-ray Fluorescence Spectrometry (WD-XRF) is developed. The calibration samples are made of blank compound fertilizer to simulate the matrix. The sample covered with microcrystalline cellulose is pressed at 35t for 60s, and cobalt content is determined by WD-XRF. This method has a good repeatability and accuracy with the linearity in the ranges of 0-2000mg/kg. The relative standard deviation is not more than 2.0%. The results obtained from WD-XRF and ICP-AES showed an acceptable agreement. 43 fertilizer samples are collected from 18 countries and determined. The cobalt contents are all not more than 13mg/kg.

Free damping treatment for a marine life hoist of the helicopter is analyzed in this paper. Based on the pipe structure used in actual life hoist bracket, the complex rigidity method is used to analyze the damping loss factor of the pipe structure. When the temperature is 30°C and the thickness of the damping material is 2.5mm, the damping loss factor of the structure increases by 9.83 times. The damping ratio of the first mode reaches 11.61%. The results indicate that the free damping treatment can obviously increase the damping loss factor and the modal damping ratio of the structure, which can mitigate structural vibration and reduce noise induced by the vibration.

Fatigue life can be divided into crack initiation life and crack propagation life in fatigue damage process. Fatigue crack comes of the initial discontinuity states （IDS） of material, and goes through short crack , long crack and rupture failure. A estimation model based on fracture theory is built, in which includes of IDS, short crack, long crack and rupture failure. A fatigue holistic life (including fatigue life, the residual life and the calendar life ) estimation model was built on the basis of IDS in which the aircraft structures had not been corrosion damage. A lot of fatigue tests with different stress level and different stress ratio are carried out to validate the model. The results demonstrate that the approach is reasonable and feasible.

Generally, the welding HAZ is more sensitive to corrosion. In order to increase the corrosion resistance of the welding HAZ in aircraft structures, the laser surface treatment technology was used to treat the welding HAZ. In this study, the processing parameters of the laser surface treatment were optimized. According to our study, the laser quenching can increase the corrosion resistance property obviously. The laser surface treatment new technique has been used in the maintenance of the airplane structures, which has better application outlook.

In order to improve the effect of isolation structure, the principles and behaviours of the base-isolation system are studied, and the types and characteristics of the base-isolation are also discussed. Compared to the traditional aseismatic structures, the base isolation structures decrease the seismic response obviously: the total structural aseismatic value decrease 1/4-1/32, the seismic shear stress in the upper structure decrease 1/14-1/23. In the huge seism, the structure can have the obvious aseismatic effect.