Papers by Author: Jin San Ju

Abstract: The numerical simulation studies on flexural behavior of casing joint of square steel tube were carried out by using finite element analysis software ANSYS/LS-DYNA with consideration of geometric nonlinearity, material nonlinearity and contact nonlinearity. On this basis, the effects of tube wall thickness, tube edge length, and inserting depth on failure mode, ultimate flexural capacity and deformation of casing joint of square steel tube was discussed. The results show that there are two types of failure modes, i.e., inside tube yield failure and outside tube shear failure, when the joints are subjected to lateral concentrated load. Ultimate flexural capacity and rigidity of casing joint of square steel tube increased with the inserting depth increasing. The ultimate flexural capacity of the joint is proportional to tube shear strength, tube wall thickness, inserting depth, and tube edge length. The fruits are useful to the design and application of casing joint of square steel tube.

Abstract: The study on tension behavior of casing and dowel joint of square steel tube was carried out by using finite element analysis software ANSYS/LS-DYNA with consideration of geometric nonlinearity, material nonlinearity and contact nonlinearity. On this basis, the effects of inside tube wall thickness, main tube wall thickness, and inserting depth on failure mode, ultimate tensile load and deformation of casing and dowel joint of square steel tube was discussed. The results show that there are three types of failure modes, i.e., bolt failure, inside tube failure and main tube failure, when the joints are subjected to axial tension force. Compare to the joint with the same wall thickness of inside tube and main tube, the reduction of wall thickness of inside tube or main tube will weaken greatly the ultimate tensile load of the joint. The ultimate tensile load of casing and dowel joints is proportional to bolt shear strength, tube wall thickness, inserting depth, and tube edge length. The fruits are useful to the design and application of casing and dowel joints of square steel tube.

Abstract: This paper primarily presents the automation computational analysis techniques to determine the dynamic stress intensity factor for the stiffened damaged aircraft fuselage subjected to triangle blast load. 3-dimention panel models can be created using parameterization and the dynamic stress intensity factor can be obtained in the procedure of the blast automatically. A typical stiffened curved panel model which consists of 7 frames and 8 stringers is calculated. The calculation results show that the peak SIF value of the crack in the panel with strips under blast load is always smaller than that without strips for all longitudinal crack lengths; the strips can slow down the crack growth markedly and the effect of the strips on SIF is most obvious when the crack tips are close to the edge of strips; the blast load time has effect on the SIF peak value, and the effect is most significant when the load time is about 25 milliseconds for the panel with strips.

Abstract: A new strategy of finite differences method is proposed for analysis of notched cross-section bars under elastic-plastic torsion. Relation curves of the elastic-plastic torque responding with different positions, angles and lengths of the notches in one section are obtained by numerical tests. It can be seen that these relation curves exhibit obvious nonlinearity. Meanwhile, the stress intensity factors can also be easily calculated by utilizing the results of above finite differences method. It provides an effective way for solving such elastic-plastic fracture mechanics problem.

Abstract: This paper primarily describes the development and application of substructure computational analysis techniques in two-step hirarchical strategy to determine stress intensity factors for the stiffened damaged panels subjected to fatigue internal pressure. A program based on substructure analysis technique and global-local hierarchical strategy has been developed for the fracture analysis of curved aircraft panels containing cracks. This program may create superelements in global and local models, and obtain fracture parameter of the crack in local model by expanding results in superelements automatically. The technique is applied to the analysis of a cracked panel with 7 frames and 10 stringers. SIFs of four cracks in it with different crack lengths are obtained efficiently.

Abstract: A new technique, Analytical Trial Function Method (ATFM), is proposed to formulate new finite element models for analysis of plane crack/notch problems. A new analytical finite element, named ATFM-CN, is successfully constructed. Furthermore, in order to determine the eigenvalues of the crack/notch problems, which utilized in above analytical trial functions, a modified sub-region accelerated Müller method is also suggested. Numerical examples show the present approach exhibits excellent performance in the analysis of stress-singularity problems.

Abstract: The explicit numerical method is used to trace the impact procedure of the tube columns impacted by a rigid body. The bar and rectangle tube models are both used to simulate the tube column. The elastic and elas-plastic impact load with different mass ratio and impact speed are obtained. The calculation results show that: for elastic models, the bigger the mass ratio and the higher the rigid body speed, the bigger the peak value of elastic impact load; at the same time, the more obvious the reduction effect of local buckling of rectangle tube on the peak value of impact load and the longer the contact time of tube model; so the peak value of impact load of the rectangle tube is not proportional to the rigid body speed. The stress wave in the tube causes a little difference between the load curves of tube model and bar model. For elas-plastic models, the higher the rigid body speed and the smaller the mass ratio, the bigger the peak value of impact load and the longer the contact time. The higher the rigid body speed, the bigger the difference between elastic and elas-plastic impact load peak value due to the expanding of plasticity. Because of the effect of local buckling, the peak value of elas-plastic impact load of rectangle tube is always lower than that of bar.

Abstract: Nonlinear finite element model analysis of the casing plug joints of steel tubular has been realized by ANSYS software. The law of load-carrying capability and stiffness of joint are separately gained by changing the ratio of length and diameter (R/L) and the ratio of the casing length and the main tube length (l/L). The influence of the casing thickness on the load-carrying capability and stiffness are also discussed. The results indicated that the load-carrying capability and stiffness of the joints both increase with the ratio(R/L) increment and the ratio of the casing length and main tube length (l/L). When the main tube thickness is equal to casing thickness, the load-carrying capacity of joints achieves the most.

Abstract: This paper primarily describes the development and application of substructure computational analysis techniques to determine stress intensity factors for the damaged panels subjected to fatigue internal pressure. A program based on substructure analysis technique has been developed for the fracture analysis of curved aircraft panels containing cracks. This program may create whole model which consists of substructure superelements and obtain fracture parameter of the crack by expanding results in superelement automatically. For instance, a typical test curved panel model consists of 7 frames and 8 stringers is calculated. This numerical approach has been validated through comparison between the calculation SIF results and available experimental data of a typical test panel with a longitudinal crack. The technique that has been established here is also applied to the other analysis of a test series of cracked panel with 7 frames and 10 stringers. SIFs of four cracks in it with different crack lengths are obtained efficiently.

Abstract: This paper primarily presents the development and application of automation computational analysis techniques to determine the dynamic stress intensity factor for the damaged aircraft fuselage subjected to triangle blast load. A program based on automated procedure to simulate cracked fuselage is developed. It may create 3-dimention panel model using parameterization. The stress around the crack tips will be captured and the dynamic stress intensity factor can be obtained at every moment of the blast automatically. A typical curved panel model which consists of 7 frames and 8 stringers is calculated. The calculation results shown that the form of the dynamic SIF curve is similar to that of the triangle load curve while the peak point of dynamic SIF curve occurs a little later than that of the load curve due to the inertia effect. The longer the crack is, the more obvious the effect is. The peak SIF value of the crack under blast load is bigger than that under the static load for certain crack length. The longer the crack is, the bigger the difference between the dynamic peak SIF value and static SIF is. At the same time, the load time has effect on the dynamic SIF curve and its peak value. These results show good agreements with theoretical principles.