Key Engineering Materials Vols. 525-526

Abstract: In the present work, three-dimensional finite element analyses have been conducted to calculate the-stress for semi-elliptical surface cracks in finite thickness plates under remote tension. The-stress solutions are presented along the crack front for cracks with values of 0.2, 0.4, 0.6 or 0.8 and values of 0.2, 0.4, 0.6 or 1.0. The current-stress solutions are suitable to be used as the constraint parameter for the fracture analysis.

Abstract: In order to signify the thermal damage and the influence it has on the fatigue property, a 3D finite element method, as well as experiment investigation, was employed for this research. By the study, it suggests that laser surface scanning can bring about some tensile residual stress and a heat affected zone in the workpiece, so as to lead a fall in fatigue life cycles. Since the fatigue character is affected by the residual stress and the microstructure change, which relate to the laser process parameters, it is expected to draw a scalar variable from stress feature and microstructure parameter to stand the level of thermal damage influence.

Abstract: To build a stress-strain-time relationship of salt rock with unified instantaneous law and creep law, we combine the stress-strain curve with whole process of creep curve, looking for inner relation between softening curve and creep deformation. Finally, the stress-strain-time space surface is obtained. The researching results demonstrated that time and space development law of rock salts can be well reflected by it.

Abstract: Fiber reinforced plastic (FRP) composite which has high strength, high fatigue resistance, low density, and better corrosion resistances is desirable characteristics for bridge applications, especially decks. According to the ACI 440.3R04, Glass fiber reinforced plastic (GFRP) bridge deck samples were immersed into the simulated concrete environment at 60 for 92d (corresponds to the natural environment 25 years). The results show that, with the time increased, the interlaminal shear strength of GFRP bridge decks decreased significantly. After being exposed to the simulated concrete environment for 3.65d, 18d, 36.5d and 92d, the interlaminal shear strength degradation of GFRP bridge decks were 18.69%, 25.90%, 50.93% and 53.74%, respectively. The micro-formation of the GFRP bridge deck sample surface was surveyed under scanning electron microscopy (SEM), which indicated that with the aging time increased, corrosion pits in the surface of GFRP bridge decks became more obviously and the interface between fiber and resin was severely damaged. Therefore, the degradation of FRP under the simulated concrete environment should be considered in the design of FRP bridge decks.

Abstract: The vibration fatigue experiments of cantilever beam structures were performed to investigate the fatigue behavior of 2024-T62 aluminum alloy. Two types of cantilever beams with various natural frequencies under the sinusoidal excitation were investigated. The initial stress of two types of specimens were set in the same amplitude by adjusting the acceleration of electrodynamic shaker. Based on the stress history recorded by the strain gauge in fatigue test and the Miners liner cumulative damage rule, the fatigue damage of the cantilever beam was calculated. The effect of vibration state on the vibration fatigue behavior of the cantilever beam was discussed. The experiment results show that the fatigue life of the cantilever beam, of which the initial vibration state is resonance, is longer than that of non-resonance. The calculated damage results were in accord with the reduction of the natural frequency measured in experiment. The reduction of natural frequency could be used to evaluate the fatigue damage of structures.

Abstract: Most large commercial aircraft engines are hanged below wings. When the aircraft makes an emergent landing process, at the same time, the landing gear cannot work or the centrifugal force becomes unbalanced as the fan blades fly away. In order to ensure safe landing, overall tank crack and fuel leak should be avoid at the crack area. Access to a large number of emergent landing accidents, emergency break-away is essential. In this paper, the break-away position, which locates between the pylon and the wing, is mainly considered. We choose true size in the models of wing, pylon and engine. High strength steel is employed for the bolts which connect pylon and wing. Earth and lake are employed concrete and pure water respectively. SPH method is applied in the case that the aircraft lands on the lake. Whats more, different landing cases have been analyzed. By constantly adjusting the size of pins, a set of conclusions of the emergent landing problem are obtained in the simulation process. The locus of centroid of engine and pylon is obtained, and then the condition which may achieve safe flight and avoid the secondary damage to wings can be chosen, from which we can provide reasonable designing strength of the wing box and accordingly provide reference for the design of aircraft structure.

Abstract: The mechanical behavior of two composites, i.e., CF3031/QY8911 (CQ, hereafter in this paper) and EW100A/BA9916 (EB, hereafter in this paper), under dynamic loadings were carefully studied by using split Hopkinson pressure bar (SHPB) system. The results show that compressive strength of CQ increases with increasing strain-rates, while for EB the compressive strength at strain-rate 1500/s is lower then that at 800/s or 400/s. More interestingly, most of the stress strain curves of both of the two composites are not monotonous but exhibit double-peak shape. To identify this unusual phenominon, a high speed photographic system is introduced. The deformation as well as fracture characteristics of the composites under dynamic loadings were captured. The photoes indicate that two different failure mechanisms work during dynamic fracture process. The first one is axial splitting between the fiber and the matrix and the second one is overall shear. The interficial strength between the fiber and matrix, which is also strain rate dependent, determines the fracture modes and the shape of the stress/strain curves.

Abstract: The residual compressive strength of composite laminates subjected to low-velocity impact (CAI) was analyzed using the ABAQUS/Explicit package through a two-step calculation. The finite element model was composed of solid elements and interfacial cohesive elements. The out of plane low-velocity impact process was simulated in the first step and the results of which were taken as the input for the second step of the in-plane compression, until the collapse of the laminate. The usefulness of the explicit solution algorithm in dealing with the quasi-static procedure of the in-plane compression was investigated by examining the effect of different initial velocities of the compression loading on CAI values. The simulation results agree well with the experimental results.

Abstract: The deposition process and interface properties of electro-thermal explosion sprayed WC/Co coating were studied by numerical simulation and experimental observation in this paper. The variety rule of the deposition particles / metal substrates interface temperature, the critical remelting condition of the substrates surface, and the interface removment speed of deposition particles were numerical simulated by finite element method. Results show that the remelting depth of the substrate increased with increasing spraying particle temperature and particle size. Structures and interface properties of the electro-thermal explosion sprayed WC/Co coating was analysed based on the numerical results. The morphologies, AES patterns, element distributions, TEM micrographs were experimentally observed and compared with the simulatin results. Which show that the finite element analysis is in good agreement with the experimental results, suggesting that the analysis in the present work is reliable.

Abstract: The present work is an effort to provide experimental results focusing on segregation behavior of phosphorus at grain boundary and the intergranular fracture behavio under low tensile stresses. AES (Auger electron spectroscopy) experiments and dynamic analyses on the non-equilibrium grain-boundary segregation (NGS) of phosphorus and the SEM photos of intergranular fracture in Auger specimens in 12Cr1MoV steel were carried out in this paper. The variation of phosphorus segregation level in grain boundary under different low tensile stresses and at different temperature were obtained. Results show that NGS of phosphorus occurred in the experimental steel while subjected to low tensile stresses. Maximum values of phosphorus segregation level were obtained at the critical times. SEM photos of intergranular fracture in Auger specimens of the test steel show that the intergranular fracture rate increased with increasing concentration of phosphorus. The intergranular fracture behavior is accordant with the segregation behavior of phosphorus at grain boundary.