Papers by Keyword: Dynamic Explicit

Abstract: The fuselage is one of the main component in aircraft to carry payload and passenger. The fuselage enclosed with high weight structure. The fuselage is hollow tube which holds all parts of the airplane together. The shape of the fuselage based on the mission of the aircraft. A supersonic fighter plane will be having streamlined fuselage to reduce the drag force enclosed with high speed flight and similarly the shape vary depend on the velocity. The design of fuselage is very complicated for designers because it takes about 60% of total weight of the aircraft and the contribution of fuselage towards performance and the stability is very decent. This paper investigates the fatigue behavior of the fuselage under dynamic equilibrium state made of both aluminum alloy and Kevlar composite. Those results can be applied to optimize the fuselage structure thereby the better structure can be made.

Abstract: The Finite Element Method (FEM) is today the most widely used in numerical simulation of forming processes, due essentially to the continuous improvement of the FEM over the years and the simplicity of its implementation. However, this method has some limitations such as the distortion of elements under large inelastic deformation and the influence of the mesh on the results in several applications. The simulation of metal forming process with large plastic strain is a classical example where the successive remeshing is often the proposed solution in this case. But the remeshing raises the problems of precision and computing time. In this context and in order to avoid the remeshing process, a Meshless method is experimented in the solving of an elastoplastic problem coupled to the isotropic ductile damage. An Element Free Galerkin (EFG) method based on Moving Least Square (MLS) concept is considered in this proposal. A two-dimensional Mechanical problem was studied and solved by a Dynamic-Explicit resolution scheme where the material behaviour is based on an isotropic hardening fully coupled to ductile damage model. In a first step a parametric study is conducted in order to find the most influent parameters on the accuracy of the results. The effect of the number of nodes, of support nodes, of quadrature points, the effect of the time-step and the support domain size are analysed and optimal values are found. In a second step, the meshless results are compared with those of the finite element method and some concluding remarks relative to the accuracy and the computing time are given.

Abstract: A front bumper of a car is attached to the main vehicle structure by using hollow metals. This paper investigates various cross section profiles that can be used as bumper attachments. Several cross section profiles with the same circumscribe are firstly selected, i.e. round, square, triangular and hexagonal shape cross sections. Each model is then numerically impacted in an axial mode as if it is crashed into a rigid wall with an impacting velocity of 10 m/s or equivalent to 36 m/s. A dynamic-explicit open source software Impact is employed to do the simulation. The displacement results are monitored in the first 1:8ms then compared to the models that can absorb better showing the less displaced in certain examination nodes. The results shows that the triangle cross section performs better compared to other cross sections.

Abstract: Aim of this paper is to present a numerical method for modeling of the so-called “equivalent box section fiber beam concrete element”. By comparing hysteresis curves of specimen of the concrete structure plotted with rebar beam with those plotted with the equivalent box section beam under a set of loading cases, the following conclusions are obtained: 1) The modeling technology of equivalent box section beam can overcome the difficulty which the rebar in beam can only be used in static calculation, and the fiber beam element can be applied to dynamic explicit analysis; 2) By comparing hysteresis curves which are plotted by the rebar beam with those obtained with model of equivalent box section beam, it is found that results are in good agreement for a specific typical loading case; 3) By comparing hysteresis curves of the equivalent box section beam with experimental data under given loading case, numerical results indicate that numerical results obtained with proposed modeling technology can fit the experiment phenomena very well.

Abstract: First stretch bending process of aluminium extrusions given by Norwegian scholars is simulated by using revised model proposed in the paper. That maximum die force calculated is closer to experiment than Norwegian scholars’ one demonstrates that the revised model is rather accurate in forming simulation and lays the foundation for later springback simulation. Then springback is simulated by using dynamic explicit and static implicit FE codes, respectively. The influences on cross-sectional distortion and springback of two codes are compared. It is shown that dynamic explicit FE code can predict cross-sectional distortion accurately and static implicit FE code overestimates it. Neither of two codes can predict springback accurately. Dynamic explicit FE code overestimates it and static implicit one FE code underestimates it.

Abstract: The two methods of artificial damping and artificial stiffness are developed in dynamic explicit FEA code for ring rolling. Advantages and disadvantages of artificial damping method and artificial stiffness method are analyzed. A rectangular section cold ring rolling is simulated. The hourglass energy and the ratio of the hourglass energy to the internal energy are compared between the two hourglass control methods. The hourglass control coefficient criterion of the two methods in the cold ring rolling simulation is proposed.

Abstract: A special elasto-plastic dynamic finite element code named RingForm has been developed to analyze cold ring rolling process. Central difference method was introduced to solve the dynamic explicit finite element equations. Strain state was estimated by the value of yield function of the last and the present time step. To reduce the accumulative error caused by elasto-plastic constitutive relations, the radial return algorithm was employed. In comparison with the experimental results, the cold ring rolling process of a ring with rectangular section has been simulated to verify the accuracy and stability of the system solver.

Abstract: Based on the dynamic analysis method and central difference explicit algorithm, a dynamic explicit finite element code is developed for modeling the hammering deformation processes, in which hammer velocity is calculated by the energy balance principle. The dynamic upsetting processes of copper block under different hammer velocities are simulated using the developed code, and the deformed configuration, the displacement and the equivalent plastic strain distribution are investigated. Then, the calculated results are compared with that obtained by the static implicit program, and the comparison shows that the results obtained by the developed code are nearly identical to that obtained by the static implicit program under a low hammer velocity, and that there is a great difference between them under a high hammer velocity, which can be explained from the viewpoint of inertial effect and stress wave propagation effect. The research results indicate that the developed code adequately considers the dynamic characteristic under drop hammer impact, and can be used to analyze the effect of hammer velocity on the deformation during the hammering deformation process.

Abstract: A new method for modeling the contact between the tool and the metal sheet for the incremental forming process was developed based on a dynamic explicit time integration scheme. The main advantage of this method is that it uses the actual contact location instead of fixed positions, e.g. integration or nodal points. The purpose of this article is to compare the efficiency of the new method, as far as accuracy and computation time are concerned, with finite element simulations using a classic static implicit approach. In addition, a sensitivity analysis of the mesh density will show that bigger elements can be used with the new method compared to those used in classic simulations.