Current Issue : October - December Volume : 2020 Issue Number : 4 Articles : 5 Articles
The deformation rules and failure types of rock fatigue damage at different temperatures are quite different, and existing\nconstitutive theory cannot describe them quantitatively. A novel rock fatigue damage model considering the effects of temperature\nwas presented based on phenomenology. In this model, the residual strain method was used to define the fatigue damage, and the\nHarris attenuation function was introduced to characterize the cyclic damage evolution. The proposed model has considered the\ninfluence of the initial damage and temperature, and the model parameters can be easily calculated. The accuracy of the model was\nverified by comparing the calculated values of cyclic upper strain and fatigue life with previous test results. The physical significance\nof the model parameters shows that parameter a is related to fatigue stress ratio and lithology, while parameter b is\nrelated to temperature. The study has some reference values for the fatigue damage model of rock considering the influence\nof temperature....
When the membrane material in the air field vibrates, it will drive the movement\nof the surrounding air. The aerodynamic force generated by the moving\nair will act on the membrane material in turn, resulting in the change of dynamic\ncharacteristics such as membrane vibration frequency. In this paper,\nthe additional air mass produced by membrane vibration in air is studied.\nFirstly, under the assumption that the incoming flow is uniform and incompressible\nideal potential flow, the additional air mass acting on the surface is\nderived by using the thin airfoil theory and potential flow theory respectively.\nThen, according to the first law of thermodynamics and the principle of aeroelasticity,\nthe analytical expression of the additional air mass is derived. Finally,\nthrough a specific example, the variation of the additional air mass with\nthe membrane material parameters and pretension, as well as the influence of\nthe aerodynamic force on the vibration frequency and amplitude of the\nmembrane is obtained....
The concrete expanded pile is a new type of pile in the field of foundation engineering, which exhibits improved performance\ncompared to the ordinary straight-hole pile. The expanded technique increases the bearing capacity of the pile, changes the overall\nload-bearing function of the pile body, and offers great development prospects. While the performance of the expanded pile has\nbeen studied for vertical loading, the performance of expanded pile when subjected to horizontal loading is not adequately\nunderstood. In order to investigate the performance of concrete expanded pile in resisting horizontal loads, particularly the antioverturning\ncapacity of rigid and flexible piles, this paper conducts an experimental model test and performs a numerical\nsimulation. In the experiment, an innovative model test method is used for testing small-scale half-face pile with undisturbed soil.\nA custom-made soil extractor and a loading device are used to observe various stages of pile-soil interaction in real-time during\nthe whole process of loading. Meanwhile, finite element simulation analysis is conducted on a pile model and the corresponding\ndata on displacement, load, stress, and strain are collected to verify the experimental results. Based on the horizontal bearing\ncapacity of rigid and flexible piles and the failure states of soil mass around the piles, two calculation models are proposed for the\nhorizontal bearing capacity of rigid and flexible concrete expanded piles. The models will provide reliable theoretical guidance for\nthe application of concrete expanded pile in engineering applications and for the research and development of pile foundation....
The experimental work presents results on the fatigue performance of composite beams in the negative moment region and the\nchanges of stiffness and deformation of composite beams under repeated loads; fatigue tests were carried out on two double-layer\ncomposite beams. The fatigue performance of composite beams with different reinforcement ratios under complete shear\nconnection and the variation of deflection, strain of the reinforcement, strain of steel beam, and crack growth under fatigue load\nwere obtained. The results showed that the fatigue resistance performance of concrete slab with low reinforcement ratio was much\nlower than that of concrete slab with high reinforcement ratio whereas, under the fatigue load, the stress of the welding nail in the\nnegative moment region was small and the slip was almost negligible. The degradation of stiffness and the development of cracks\nwere mainly due to the degradation of bond-slip between the concrete and reinforcement. The fatigue failure mode was the\nfracture of the upper reinforcement in negative moment region. The results obtained in this study are helpful in the design of\ncomposite beam....
An experimental system for liquid nitrogen soaking and real-time temperature measurement was designed and implemented to\ninvestigate the characteristics of temperature field changes in coal under liquid nitrogen soaking. Then, the heat conduction law of\nthe coal in the process of liquid nitrogen soaking and room temperature recovery for dry and water-saturated coal were examined.\nThe microstructure characteristics of the coal before and after liquid nitrogen soaking were analyzed with nuclear magnetic\nresonance (NMR) technology. Theresults showed that, during the liquid nitrogen cold soaking process, the heat transfer law of the\ndry and water-saturated coal samples exhibited a notable three-stage distribution. For the room temperature recovery process, the\ndry and water-saturated coal samples exhibited rapid heating characteristics, and the cooling rate gradually decreased to zero.\nNMR test results indicated that the liquid nitrogen soaking increased the number of micro and small pores in the coal. Thermal\nstress analysis revealed that the thermal stress generated by the dry coal was larger than that produced by the saturated coal, and\nthe damage was primarily caused by thermal stress. However, the permeability of the saturated coal was better than that of the dry\ncoal. The damage on the saturated coal was caused by the volume expansion of pores and fissures caused by water-ice\nphase transition....
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