جستجوی مقالات مرتبط با کلیدواژه « ls-dyna » در نشریات گروه « مکانیک »

Helmet liners are employed to prevent or reduce head injuries caused by impact loads. Liners minimize the collision damage by impact shock attenuation and absorbing the collision energy. In order to improve crashworthiness characteristics of helmet liner, in the present study, an innovative structure designed by a combination of Polyurethane (PU) foam and auxetic lattice structure is suggested to replace the conventional EPS foams usually employed in the liner section. The baseline liner section is divided into two main layers. In one layer, PU foam is used instead of EPS and in the second layer, an arrowhead pattern auxetic structure is used to improve energy absorbing capacity. By employing three kinds of PU foam with different densities and four 3D printable materials for the lattice structure, 6 combinations of the modified liner are presented. An explicit finite element method is employed to model the innovative helmet structure under impact loading and results are compared with the conventional case based on the trend of acceleration, energy absorption, weight, and Head Injury Criteria (HIC) factor.

Top-hat hollow-section beams are widely used in passenger vehicle’s body-in-white structure because of their proper shape for the montage process and also crashworthiness advantages. Hollow section beams with top-hat cross-section are mostly employed in structures like B-pillar, rocker sill, and roof rail which are engaged in side impact collisions. In the present investigation, simplified top-hat beams are developed based on a conventional B-pillar with the aim of improving energy absorption characteristics. Reinforcements are conducted by employing fiber glass-epoxy composite material. Three types of reinforced beams are presented which are either improved by composite-laminating, or by installation of an extra composite-made internal reinforcement. Experimental tests are performed in quasi-static three-point bending condition and based on results, a FE simulation is developed using LS-Dyna explicit code. Specimens are compared based on peak load, total energy absorption (TEA) and specific energy absorption (SEA) amounts. Also, to illustrate the extent of improvements, a not-reinforced top-hat beam is experimentally subjected under three-point bending test. Results depict a significant difference between the performance of beams reinforced by different methods. Comparison between specimens, considering their respective load-displacement diagram and crashworthiness characteristics, show that applying composite laminates to the inside surface of a hat-shaped beam would produce a beam with satisfying flexural behavior.

The phase field method integrates the Griffith theory and damage mechanics approach to predict crack initiation, propagation, and branching within one framework. No crack tracking topology is needed, and complex crack shapes can be captures without user intervention. In this paper, a detailed description of how the phase field method is implemented with explicit dynamics into LS-DYNA is provided. The displacement field and the damage field are solved in a staggered approach and the phase field equation is solved every Nth time step (N is refered to as calculation cycle) to save computational time. An N value smaller than 1/400 of the total time step numbers is suggested. Several simulations are presented to demonstrate the feasibility of this solving scheme.

In this paper, a novel approach is proposed to investigate the progressive collapse damage of prismatic thin walled metal columns with different regular cross sections, under the action of axial quasi-static and impact loads. The present work mainly focuses on implementation of some important factors which have been neglected in other studies. These factors include the effect of reducing impactor velocity and inertia effect during collapse, a mixed collapse mode for crushing mechanism, and consideration of a realistic elasto-plastic model for material. Taking all these factors into account, the analysis led to some parametric algebraic equations without a possible general solution in terms of collapse variables. Consequently, a new theoretical approach was proposed based on previously offered Super Folding Element (SFE) theory, to obtain the closed form explicit relations for the static and dynamic mean crushing forces and collapse variables. The proposed approach considers an analytic-numeric discretization procedure to solve these equations. To evaluate the results, a detailed finite element analysis on square mild steel models was conducted under an axial impact load, using LS-DYNA and ANSYS software programs. Comparison of the experimental results that are available in the literature with those of finite element analysis, shows the applicability of this approach in predicting the collapse behavior in such structures.

In the present research, the influence of cap geometry on the collapse of thin-walled aluminum-made energy absorbers with various section geometries was investigated. For this purpose, a total of 35 different absorbers were subjected to axial quasi-static loading. In this respect, five different section types and seven different cap configurations were considered for the absorbers and their caps, respectively. The analyses were performed in both experimental and numerical methods. The numerical simulations were conducted using LSDYNA Software and experimental tests were performed to verify the numerical investigations. Good agreement was obtained between the experimental data and numerical results. The results indicated that, in all cases, the application of the cap enhanced the crush force efficiency while lowering maximum force at collapse. In the final stage of the research, optimal absorbers for the cases with open-ended and close-ended caps were proposed using Minitab Software based on the response surface methodology.

In this paper, numerical simulation of FRP composite cylinder tubes progressive crushing processes is conducted using LS-Dyna. Details on the numerical modeling strategy are given and discussed. It is found that triggers introduced in the numerical simulation can effectively model the bevel trigger at the end of the tubular specimens. It is also found that two-layer finite element model based on the TsaiWu failure criteria is effective in representing the crushing failure mode of the tubular composite specimens and energy absorption characteristics. Employing GEvoM software, two meta-models are then obtained for modeling of both the absorbed energy (E) and the peak crushing force (Fmax) with respect to geometrical design variables using input output data obtained from the finite element modeling. Comparison between obtained meta-models and numerical results in both of training and testing sets show good approximation by using obtained polynomial models.