Explicit Dynamic Finite Element Analysis Research Articles

PREDICTION OF PROXIMAL FEMORAL FRACTURE IN SIDEWAYS FALLS USING NONLINEAR DYNAMIC FINITE ELEMENT ANALYSIS

Hip fracture incidence caused by sideways falls is increasing year by year. The high morbidity and mortality not only cast a gloom over the life, but also increase the medical cost of the country. From a biomechanical perspective, hip fractures are related to different loading directions. The main purpose of this study is to investigate how different hip fracture types are affected by impact directions. The geometry of a proximal femur was obtained from the CT scan data of a 67-year-old Chinese male. Mimics and Ansys softwares were applied to establish the cortical bone and cancellous bone models. Six different loading cases, i.e., SW1 (α = 120°, β = 0°), SW2 (α = 90°, β = 0°), SW3 (α = 60°, β = 0°), SW4 (α = 20°, β = 0°), SW5 (α = 120°, β = 15°), SW6 (α = 120°, β = 45°) were defined as the angle α with reference to the long axis of the femur in the frontal plane, and β with reference to the femoral neck axis in the horizontal plane. They were established to simulate sideways falls by explicit dynamic nonlinear finite element analyses in ANSYS-LS-DYNA software. The impact speed was 3.17 m/s. Stress and strain analyses with time history of the fracture sites were taken to find the relationships between fracture types and impact directions. SW1–SW4 caused femoral neck fractures, and the maximum principal stresses were 4.5, 6, 5 and 4.8 MPa, respectively. SW5 caused compound fractures including neck fracture and trochanteric fracture, and the maximum principal stresses were 6.8 MPa and 6.5 MPa, respectively. SW6 caused trochanteric fracture, and the maximum principal stress was 4.2 MPa. The maximum principal strains of neck fracture (0.075, 0.135, 0.175, 0.092) and trochanteric fracture (0.045) increased to the maximum values in 10 ms after impact, and were much higher than the ultimate compressive strain of cancellous bone. These results were consistent with the clinical findings. This study showed that falling posture was an important factor leading to different types of fracture. Dynamic simulation was more effective in explaining the fracture mechanism and determining the load direction that caused hip fracture. The study also provided a theoretical basis for more targeted preventive measures for different types of hip fracture in clinics.

Incrementally objective implicit integration of hypoelastic–viscoplastic constitutive equations based on the mechanical threshold strength model

The present paper focuses on the development of a fully implicit, incrementally objective integration algorithm for a hypoelastic formulation of \(J_{2}\)-viscoplasticity, which employs the mechanical threshold strength model to compute the material’s flow stress, taking into account its dependence on strain rate and temperature. Heat generation due to high-rate viscoplastic deformation is accounted for, assuming adiabatic conditions. The implementation of the algorithm is discussed, and its performance is assessed in the contexts of implicit and explicit dynamic finite element analysis, with the aid of example problems involving a wide range of loading rates. Computational results are compared to experimental data, showing very good agreement.

Surface flexible rolling for three-dimensional sheet metal parts

To realize highly effective and continuous fabrication of three-dimensional (3D) sheet metal parts, a new forming method, surface flexible rolling forming, has been investigated. This method takes only two integral flexible rolls as the forming tool. In the forming process, a non-uniform elongation in the rolling direction and a bending deformation in the thickness direction occur simultaneously, and finally three-dimensional surface parts are formed. In this work, the basic principle and forming mechanism of surface flexible rolling are studied. A method to calculate the transversal curvature radius of the arc-shaped roll is brought forward, while the feasibility is verified by the explicit dynamic finite element analysis. An experimental device has been developed and the forming experiments have been performed. Typical 3D surface parts including the convex and saddle surface parts have been obtained. Finite element model of surface flexible rolling is established and the effect of forming parameters such as reduction, velocity, bending radius and friction on the surface shape is analyzed. The forming effects including shape errors and thickness changes are studied by the deviation analysis. The results indicate that the formed surface is quite close to the criteria one; the thickness of the parts changes gradually and keeps within a narrow range. The experimental formed parts are measured and the forming accuracy is investigated. The results show that the accuracy is high, and are consistent with the simulation.

The effects of the shape of localized defect in ball bearings on the vibration waveform

Ball bearings, one of the most widely used components in rotating machinery, play a critical role in system performance. Localized defects such as pit and spall may develop in ball bearings during service. The vibration waveform of the impulse generated by a ball passing over a defect on the races is determined by the shape and size of the localized defect. Hence, it is important to study the relationship between the localized defect shape and its pulse waveform characteristics in order to diagnose the types of defect in bearings. This study examines the effects of the defect shape, radial load and shaft speed on the pulse waveform characteristics generated by localized defects using the method of explicit dynamic finite element analysis. To validate the proposed model, the results obtained from the experiments have also been provided, and the waveform and the duration of the pulse generated by the defect on the outer race are in good agreement with the simulation results, which shows validation of the proposed model. Both the experimental results and the simulation results have confirmed that the impulse shape generated by the defect on the raceway will be influenced by the contact deformations at the edges of the defect. The results obtained also demonstrate that the explicit dynamic finite element analysis approach can be used to analyze the pulse waveform characteristic generated by localized defects in ball bearings.

Numerical simulation of multi-point forming accuracy for polycarbonate sheet

Multi-point forming is an advanced flexible manufacture technology, which has been used in many fields successfully. In order to provide a flexible method for forming a polymer, multi-point forming is applied to the manufacture of polycarbonate sheet. An optimized DSGZ constitutive model is established to describe the stress–strain relation of polycarbonate sheet, and its parameters are determined according to experimental data. The multi-point forming process of polycarbonate sheet is introduced briefly, and a simple calculating scheme of punch height is developed. Numerical simulations of spherical and saddle-shaped parts are carried out by dynamic explicit finite element analysis, and the effects of punch number and punch radius on the surface accuracy and shape accuracy are studied. The multi-point forming experiments of polycarbonate sheet are done, and the comparisons of shape error between experimental parts and objective parts are conducted, which show that the polycarbonate products have good surface accuracy and shape accuracy.

Optimal design of honeycomb material used to mitigate head impact

This paper presents a study of the impact resistance of honeycomb structure with the purpose to mitigate impact forces. The objective is to aid in the choice of optimal parameters to minimize the thickness of the honeycomb structure while providing adequate protection to prevent injury due to head impact. Studies are presented using explicit dynamic finite element analysis representing the case of an unprotected drop of a rigid impactor onto a simulated floor consisting of vinyl composition tile and concrete. Analysis of honeycomb material to reduce resulting accelerations is also presented where parameters such as honeycomb material modulus, wall thickness, cell geometry and structure depth are compared to the unprotected case. A simplified optimization analysis technique using a genetic algorithm is presented to demonstrate the use of this method to select a minimum honeycomb depth to achieve a desired acceleration level at a given level of input energy. It is important to select a minimum material depth in that smaller dimensions lead toward more aesthetic design that increase the likelihood that the device is used.

Study of multi-point forming for polycarbonate sheet

The multi-point forming (MPF) process of polycarbonate (PC) sheet is introduced briefly, geometrical relationship between objective surface and punch element is determined, and a simple calculation scheme of punch height is developed. Numerical simulations of spherical and saddle-shaped parts are carried out by dynamic explicit finite element analysis; the effects of forming temperature, forming pressure, punch matrix, and punch radius on the forming quality are investigated, and the suitable forming parameters are determined. Then, the MPF experiments of PC sheet for spherical and saddle-shaped parts based on the forming parameters are done, and the comparisons of shape error between experimental parts and object surfaces are carried out. Consequently, the PC products have good shape accuracy, which confirms that MPF used for forming PC sheet is feasible and the forming parameters obtained by numerical simulation are sensible.

Gait cycle comparions of cruciate sacrifice for total knee design.-explicit finite element

Joint kinematics and contact mechanics dictate the success of current total knee replacement (TKR) devices. Computational contact prediction is a feasible way of evaluating new TKR designs prior to physical testing and implementation. Previous finite element (FE) knee models have generally been used to predict stresses on contact areas and/or areas subjected to static or quasi-static loading. Explicit dynamic FE analyses have recently been used to effectively predict TKR kinematics and contact mechanics during dynamic loading conditions. In this study, we compared the functional load transmission and kinematic performance of two posterior-stabilized designs, standard and post-cam TKR versions, over a standardized loading cycle using three-dimensional contact finite element analysis. Our objective was to develop and experimentally validate an explicit FE TKR model that incorporates femoral-bearing articulations. Finite element-based computational contact pressure predictions were applied to gait cycles using both force-controlled and displacement-controlled inputs. A standard prosthesis showed a reduction in contact pressure compared with post-cam prosthesis components, as it redistributed the knee motion to two articulating interfaces with more linear motions at each interface. In this FE analysis, the wear of TKR bearings was dependent on kinematics at the articulating surfaces and on prosthesis design.

The Effect of Material Parameters on Crashworthiness of Vehicle Steering Column

The drivers were hurt seriously by the vehicle steering column in the frontal collision. So a steering column with well energy-absorbing is very useful for the drivers. In this paper, the crashworthiness of a vehicle steering column is investigated by using the explicit dynamics finite element analysis method. Based on the proposed finite element model, the steering column with different material parameters including elastic modulus and yield strength are analyzed. Moreover, the displacement, velocity and energy absorption is discussed. The simulation results show that the crashworthiness of the vehicle steering column is significantly influenced by the yield strength. However, the elastic modulus has little effect on the crashworthiness.

Research and Application on Automotive Aluminum Bumper Based on Topology Optimization

Based on the explicit dynamic finite element analysis software, the use of hybrid cellular automata (HCA) as an optimization model, the collision of beams in the aluminum front structure optimization design. The 6061 aluminum alloy before the collision of beams to replace a model of the original steel beams, trolley collision simulation and experimental validation of the results show that the aluminum front impact beams than the original steel before the collision beam quality to reduce by 25% and has a higher flexural strength, low-speed collision, aluminum front impact beams than the original steel system energy absorption increased by 45.6%.

Study of Mechanical Deformations on Tough Skinned Vegetables during Mechanical Peeling Process (A Review)

Peeling is an essential phase of post harvesting and processing industry; however undesirable processing losses are unavoidable and always have been the main concern of food processing sector. There are three methods of peeling fruits and vegetables including mechanical, chemical and thermal, depending on the class and type of fruit. By comparison, the mechanical methods are the most preferred; mechanical peeling methods do not create any harmful effects on the tissue and they keep edible portions of produce fresh. The main disadvantage of mechanical peeling is the rate of material loss and deformations. Obviously reducing material losses and increasing the quality of the process has a direct effect on the whole efficiency of food processing industry, this needs more study on technological aspects of these operations. In order to enhance the effectiveness of food industrial practices it is essential to have a clear understanding of material properties and behaviour of tissues under industrial processes. This paper presents the scheme of research that seeks to examine tissue damage of tough skinned vegetables under mechanical peeling process by developing a novel FE model of the process using explicit dynamic finite element analysis approach. A computer model of mechanical peeling process will be developed in this study to stimulate the energy consumption and stress strain interactions of cutter and tissue. The available Finite Element softwares and methods will be applied to establish the model. Improving the knowledge of interactions and involves variables in food operation particularly in peeling process is the main objectives of the proposed study. Understanding of these interrelationships will help researchers and designer of food processing equipments to develop new and more efficient technologies. Presented work intends to review available literature and previous works has been done in this area of research and identify current gap in modelling and simulation of food processes.

Crashworthiness optimisation of vehicle structures with magnesium alloy parts

This paper explores the effects of replacing the baseline steel with lightweight magnesium alloy parts on crashworthiness characteristics and optimum design of a full-vehicle model. Full frontal, offset frontal and side crash simulations are performed on a validated 1996 Dodge Neon model using explicit nonlinear transient dynamic finite element analyses in LS-DYNA to obtain vehicle responses such as crash pulse, intrusion distance, peak acceleration and internal energy. Twenty-two parts of the vehicle body structure are converted into AZ31 magnesium alloy with adjustable wall thickness while the remaining parts are kept intact. The magnesium alloy material model follows a piecewise linear plasticity law considering separate tension and compression properties and maximum plastic strain failure criterion. Six different metamodelling techniques including optimised ensemble are developed and tuned for predictions of crash-induced responses within the design optimisation process. The crashworthiness optimisation problem is solved using the sequential quadratic programming method with most accurate surrogate models of structural responses considering both constrained single- and multi-objective formulations. The results show that under the combined crash scenarios with the selected material models and design constraints, the vehicle model with magnesium alloy parts can be optimised to maintain or improve its crashworthiness characteristics with up to 50% weight savings in the redesigned parts.

Simulation methodology development for rotating blade containment analysis

An experimental and numerical investigation on the aeroengine blade/case containment analysis is presented. Blade out containment capability analysis is an essential step in the new aeroengine design, but containment tests are time-consuming and incur significant costs; thus, developing a short-period and low-cost numerical method is warranted. Using explicit nonlinear dynamic finite element analysis software, the present study numerically investigated the high-speed impact process for simulated blade containment tests which were carried out on high-speed spin testing facility. A number of simulations were conducted using finite element models with different mesh sizes and different values of both the contact penalty factor and the friction coefficient. Detailed comparisons between the experimental and numerical results reveal that the mesh size and the friction coefficient have a considerable impact on the results produced. It is shown that a finer mesh will predict lower containment capability of the case, which is closer to the test data. A larger value of the friction coefficient also predicts lower containment capability. However, the contact penalty factor has little effect on the simulation results if it is large enough to avoid false penetration.

Explicit dynamic finite element analysis of an automated grasping process using highly damped compliant fingers

This paper has been motivated by the need to reduce the number of live animal tests in the development of an automated live-bird transfer system (LBTS) for the poultry meat-processing industry. Simulation-based models have been developed, which carefully address key engineering issues prior to live animal tests so that physical experiments can be focused on understanding reflex issues such as fear and escape behavior. To gain insights into the effects of operational timing on the LBTS handling performance, the multibody dynamics is modeled numerically based on the method of explicit dynamic finite element analysis (FEA) using off-the-shelf FEA packages. The findings also offer information on contact forces and their locations acting on the object’s body and legs by the compliant fingers and grippers respectively for optimizing designs and avoiding damage to the object. Specifically, this paper discusses computational issues such as time-step considerations and highly damped behavior of compliant fingers when modeling using dynamic FEA methods. The FEA model has been validated by comparing simulated handling of an ellipsoidal object by a pair of robotic hands with multiple compliant fingers against published experimental data. It is expected that the FEA-based method presented here can be extended to a spectrum of applications where flexible multibody dynamics involving large deformable contacts and highly damped behaviors plays an important role.

Simulation of Rolling Forming of Precision Profile Used for Piston Ring based on LS_DYNA

The rolling process of precision profile used for piston ring is simulated by large general-purpose explicit dynamic finite element analysis software ANSYS/LS_DYNA. The modeling of finite element models, the selection of material models and element types, the meshing of the model are introduced in detail. The rolling metal flow rulers of each pass are gained. The deformation of rolled piece and distribution of stress field are analyzed deeply. These can provide guidance for the design of forming roller and the optimization of process.

Dynamic Modeling of Damping Effects in Highly Damped Compliant Fingers for Applications Involving Contacts

In many industries, it is often required to transfer objects using compliant fingers capable of accommodating a limited range of object shapes/sizes without causing damage to the products being handled. This paper presents a coupled computational and experimental method in time domain to characterize the damping coefficient of a continuum structure, particularly, its applications for analyzing the damping effect of a highly damped compliant finger on contact-induced forces and stresses. With the aid of Rayleigh damping and explicit dynamic finite element analysis (FEA), this method relaxes several limitations of commonly used damping identification methods (such as log-decrement and half-power methods) that are valid for systems with an oscillatory response and generally estimate the damping ratio for a lumped parameter model. This damping identification method implemented using off-the-shelf commercial FEA packages has been validated by comparing results against published data; both oscillatory and nonoscillatory responses are considered. Along with a detailed discussion on practical issues commonly encountered in explicit dynamic FEA for damping identification, the effects of damping coefficients on contact between a rotating compliant finger and an elliptical object has been numerically investigated and experimentally validated. The findings offer a better understanding for improving grasper designs for applications where joint-less compliant fingers are advantageous.

Numerical Investigation of Flexible Holding Technology for Stretch Forming Process

A new type of discrete clamp stretch forming machine based on flexible holding technology was developed to improve the performance of traditional rigid clamp stretch forming machine used for double-curvature metal sheet forming, and its forming characters were illuminated simply. The FE model of flexible discrete clamp stretch forming was set up, and extensive numerical simulations of spherical parts for both the flexible holding mode and the rigid holding mode were carried out by dynamic explicit finite element analysis. The numerical results show that the distribution of stress, strain and thickness were well-proportioned in the flexible holding mode. The larger the spherical radius is, the smaller the minimum transitional length of sheet metal is. The transitional length of 60mm is suitable for flexible discrete clamp stretch forming in the case of considering the forming quality and material utilization. Then, the stretch forming experiment proves that the flexible holding technology is feasible, and the error contrast illustrates the new type of discrete clamp stretch forming machine is practicable.

Linear finite elements with orthogonal discontinuous basis functions for explicit earthquake ground motion modeling

The dynamic explicit finite element method is commonly used in earthquake ground motion modeling. In this method, the element mass matrix is approximately lumped, which may lead to numerical dispersion. On the other hand, the orthogonal finite element method, based on orthogonal polynomial basis functions, naturally derives a lumped diagonal mass matrix and can be applied to dynamic explicit finite element analysis. In this paper, we propose finite elements based on orthogonal discontinuous basis functions, the element mass matrices of which are lumped without approximation. Orthogonal discontinuous basis functions are used to improve the accuracy and reduce the numerical dispersion in earthquake ground motion modeling. We present a detailed formulation of the 4-node tetrahedral and 8-node hexahedral elements. The relationship between the proposed finite elements and conventional finite elements is investigated, and the solutions obtained from the conventional explicit finite element method are compared with analytical solutions to verify the numerical dispersion caused by the lumping approximation. Comparison of solutions obtained with the proposed finite elements to analytical solutions demonstrates the usefulness of the technique. Examples are also presented to illustrate the effectiveness of the proposed method in earthquake ground motion modeling in the actual three-dimensional crust structure. Copyright © 2010 John Wiley & Sons, Ltd.

Transient meshing performance of gears with different modification coefficients and helical angles using explicit dynamic FEA

The gearbox, as the main part of power transmission of many mechanical systems, plays a critical role for the performance of the system. The transient meshing performance of the gears is dependent on their structural parameters like modification coefficient and helical angle among others. In this paper, the effects of modification coefficients and helical angles on the transient meshing performance of the gears are investigated using the method of explicit dynamic finite element analysis (FEA) in an energy point of view. The relationships between the transient meshing performance and modification coefficient or helical angle of gears are obtained by explicit dynamic simulation. The simulation results demonstrate that explicit dynamic FEA can be used for choosing these structural parameters in the design and manufacture of gears to enhance their transient meshing performance.

FEA MODELING OF SCHALLAMACH WAVES

AbstractThe term Schallamach wave is used to describe a wave of detachment that sometimes arises during the frictional sliding of a smooth rubber surface against a smooth rigid surface. Extensive experimental investigations have been made since Schallamach first observed the waves in 1971; however, no successful finite element analysis (FEA) modeling of the behavior has been reported yet. This work uses an explicit dynamics FEA approach to model both the initiation and progression of waves of detachment for the first time. The use of the finite element method allows for the detailed stress and strain analysis at the interface to be examined. Here, the limitations of using a purely elastic solution in plane-strain are explored. To validate the explicit dynamics approach for modeling the Schallamach waves, another biaxial compressive buckling mode has also been modeled.