Papers by Author: Jia Qu

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Authors: Jia Qu, Guang Ping Zou
Abstract: Concrete is a type of engineering composites which is widely used in military and civil structures. The static performance of concrete can not be used to estimate the variation of concrete under high strain rates under dynamic loads. By introducing the three point bending test under static and dynamic loads, the plane strain fracture toughness KIC and KId were measured. Using the application of experimental-numerical method a three-dimensional model has been established by FEM software Ansys/LS-DYNA, to carryout transient analysis, and the response curves of stress intensity factor-time through the opening displacement of fracture. Thus, with obtaining the cracking time by the method of strain-gauge, the dynamic plane strain fracture toughness KId can be determined. By comparing KIc and KId we could conclude the result which meant concrete was more liable to crack under dynamic load.
Authors: Jia Qu, Guang Ping Zou, Pei Xiu Xia
Abstract: A split tensile test methodology has been established for the concrete spheriform specimens with the principal stress ratio of σ1:σ2:σ3=0.24:0.24:-1 in order to study the tensile-tensile-compressive tri-axial strength. Using a Universal Material Testing Machine and Split Hopkinson Pressure Bar, the quasi-static and dynamic spliting tensile tests have been conducted for the concrete spheriform specimens consisting of 1% steel fiber. In the quasi-static test, the average strain rate of the steel fiber reinforced concrete specimens was 8.3×10-5s-1 and the split tensile strength was found to be 0.77MPa, which is consistent with the existing literature. In the high strain rate tests, the average strain rate was 170s-1 and the split tensile strength was found to be 1.01MPa. When compared with the quasi-static testing results, it is seen that the split tensile strength of the steel fiber reinforced concrete increases with increasing strain rate. The split tensile test methodology established in the present paper is simple and inexpensive, while the strength obtained located on the meridian plane of tension and compression, has practical significance.
Authors: Jia Qu, Geng Chen, Yu Wei Yang
Abstract: In this paper, hyper-elastic constitutive models of rubber material have been summed up based on constitutive relation and the Mooney-Rivlin model has been pay more attention. Then through the tension experimental test, data of sealing material under axial experimental are obtained, and M-R model parameters C10 and C01 are fitted by ANSYS. After obtaining the material parameters, compression deformation behavior and the distribution of stress field and resilience behavior of the seal ring are simulated by using ANSYS/LS-DYNA software under different loading conditions.
Authors: Li Hong Yang, Jia Qu, Guang Ping Zou
Abstract: In this paper, a finite strain constitutive model was proposed by the additive decomposition of the logarithmic strain rate and the generalization of small deformation constitutive model and a complete analysis was made for an isotropic hardening J2 flowing finite strain constitutive model based on torsion experiments. Logarithmic strain and Jaumann stress rate were discussed in solid circular shaft torsion deformation. Utilizing the results obtained from solid circular shaft torsion experiments, the plastic rigidity function in constitutive model was determined. The simple shear problem was studied by using the constitutive model given in this paper. The results shows that the plastic rigidity function corresponding to logarithmic strain was different from one to Green strain and finite strain constitutive model should be analyzed by logarithmic strain and torsion experiments.
Authors: Geng Chen, Jia Qu, Chun Yu Tian
Abstract: LNG storage tank is an important department in the gas receiving station. LNG in the tank is flammable and explosive medium, once the tank damaged, disasters may be happened. So researching the dynamic response analysis is very necessary. In this paper, modal analysis of LNG outside tank were performed by ANSYS Workbench, the first six orders of mode shapes and their frequencies of LNG outside tank were concluded. Contrast vibration mode and natural frequency of the LNG storage tanks with ring beam and no ring beam, the influence of ring beam of LNG tank mode has been discussed. Conduct a series experiment by change the parameters of the ring beam, Parameters for ring beam effect on the inherent frequency and vibration mode of LNG outside tank has been researched. This research has provided the provided the reliable basis for the safety using of tanks and has built the base of the further dynamic response analysis.
Authors: Li Hong Yang, Jia Qu, Yun Zeng He
Abstract: The logarithmic strain is more suitable for analyzing large strain problems because the volume invariability condition in small deformation is equivalent to volume invariability condition in large deformation when using the logarithmic strain. Large simple shear deformation has always been used in the analysis of large strain problems. In this paper, elastic large strain constitutive model was introduced based on the logarithmic strain and large simple shear deformation was analyzed by using the constitutive model given in the paper. The stress responses to large simple shear deformation were derived corresponding to four objective rates of tensors. The results show that normal stresses may maintain good monotonicity, but there exists different levels of oscillation of shear stress corresponding to various objective rates, and there was the most severe oscillation of stress when adopting Jaumann rate. The objective rate should not be the only factor bringing about oscillation of shear stress.
Authors: Jia Qu, Geng Chen, Guang Ping Zou
Abstract: In order to make the specimen deformed under a constant strain rate and the stress in the specimen kept homogeneous, the wave shaper technology was adopted to modify the incidence waves of the normal Split Hopkinson Press Bar. A method of changing the shape of the bullet was suggested to be applied on the SHPB. Bullets with different length and different curvature have been researched in this paper. And the effection of the button head bullet about incidence pulse was simulated with Lagrange method by ANSYS/LS-DYNA. It is shown in the results that changing the curvature of the bullet impact the rising edge of incidence waves, and the peak stress increase with the speed of the bullet increase, the peak stress and length of incidence waves increased with the length of the button head bullet, when the peak stress reached a certain strength, increasing the bullet length could make the stress peak value lasted longer. Due to the reason that the button head bullet was based on the elastic wave theory, the wave length and the max stress of the shaped wave would be controlled conveniently and avoid the shortcoming that the analogue specimens could not be recycled in the normal pulse shaper technology.
Authors: Guang Ping Zhou, Jia Qu
Abstract: When the KId (dynamic fracture toughness) of the three point bending components is tested on the SHPB device, the signals of reflected waves obtained have been elongated because the end of the incidence pole is generally made by wedge shape. Through the conduction theory based on one dimension stress wave theory, the reflection and transmission phenomena of waves on the surface of the wedge have been analyzed. In the present paper, the loads acting the components have been modified, by removing the stress wave part among incidence and reflection waves reflected by the wedge surface.
Authors: Li Hong Yang, Guang Ping Zou, Jia Qu
Abstract: A modified Hill yield criterion considering tension-shear stress coupling was given and material parameters of nickel-based single crystal in this criterion was determined by the Least Square Method. Crack tip plastic zones of nickel-based single crystal plate were analyzed by using this modified yield criterion and the plastic zones corresponding to mixed mode I, II crack, were derived. The crack tip plastic zones of nickel-based single crystal were compared to that of isotropic material. The influences of tension-shear stress coupling, compound ratio of mixed mode I, II crack and temperature on crack tip plastic zones were discussed. The results obtained in this paper indicate that the increasing rate of crack tip plastic zones with compound ratio in the plane stress condition is greater than that in the plane strain condition for nickel-based single crystal and the temperature has greater influence on the size of crack tip plastic zones.
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