Nonlinear Transient Dynamic Finite Element Research Articles

Three-dimensional Non-linear Finite Element Analysis of Impact Response and Damage in Laminated Composite Shells

The impact response and the impact-induced damage in curved composite laminates subjected to transverse impact by a metallic impactor are studied using three-dimensional non-linear transient dynamic finite element formulation. A layered version of isoparametric eight-noded hexahedral element with incompatible modes is developed which incorporates geometrical non-linearity based on total Langragian approach. The non-linearity of both strain displacement relation and contact loading are simultaneously solved using Newton-Raphson incrementaliterative method. Impact-induced damages (matrix cracking and delamination) are predicted using appropriate three-dimensional stress-based failure criteria. Some example problems of graphite/epoxy laminated cylindrical shells with variation of important parameters such as impactor velocity, shell curvature, laminate dimension and fibre orientation of plies are solved and the influence of geometrical non-linear effect on both impact response and resulting damages is demonstrated.

Assessment of the Blasting Efficiency of a Long and Large-Diameter Uncharged Hole Boring Method in Tunnel Blasting Using 3D Numerical Analysis

Cut blasting is one of the most essential processes to reduce blast-induced vibration in tunnel blasting. The long and large-diameter uncharged hole boring (LLB) method is an example of one of the cut blasting methods, which utilizes large-diameter uncharged holes drilled in the tunnel face. In this study, blasting simulations were performed to analyze its blasting mechanism, and the LLB method and the traditional burn-cut method were simulated to compare their blasting efficiency. A 3D numerical analysis using LS-DYNA code, a highly non-linear transient dynamic finite element analysis using explicit time integration, was used to simulate the blasting process, and a Johnson–Holmquist constitutive material model, which is optimal for simulating brittle materials under dynamic conditions, was used to simulate the rock behavior under blasting. The modified LLB method showed a 3.75-fold increase in the advance per round compared to the burn-cut method, due to the increased formation of long and large-diameter uncharged holes compared to blast holes. This modified LLB method used 30% less explosives, so its failure range was approximately 1.25 times less than that of the burn-cut method, but its advance was approximately 4 times larger than the burn-cut method, which was similar to the original LLB method. This confirmed that the modified LLB method is significantly more efficient in terms of increased blasting efficiency (particularly the advance per round) as well as reduced blast-induced vibration, compared to the traditional cut blasting method.

Computational simulation of pacifier deformation and interaction with the palate.

ObjectivesThe objective of this study is to demonstrate that computational finite element models can be used to reliably simulate dynamic interaction between a pacifier, the palate, and the tongue during nonnutritive sucking (NNS). The interactions can be quantified by the results of finite element analyses which include deformation, strain, stress, contact force, and contact area.Materials and MethodsA finite element model was created based upon CAD solid models of an infant pacifier and palate. The silicone pacifier bulb is represented by a hyperelastic constitutive law. Contact surfaces are defined between the pacifier and palate. A time and spatially varying pressure load is applied to the bulb representing peristaltic interaction with the tongue. A second time‐varying, periodic pressure representing NNS is applied to the model simultaneously. A large displacement, nonlinear transient dynamic analysis is run over two NNS cycles.ResultsResults from the finite element analysis show the deformed shape of the bulb with maximum principal elastic strain of 0.23 and a range of maximum principal stress on the palate from 0.60 MPa (tensile) to −0.27 MPa (compressive) over the NNS cycles. The areas of contact between the pacifier and the palate are shown in surface contour plots.ConclusionsA nonlinear transient dynamic finite element model can simulate the mechanical behavior of a pacifier and its interaction with the tongue and contact with the palate subject to NNS. Quantitative results predicting deformation, strain, stress, contact force, and contact area can be used in comparative studies to provide insight on how pacifiers cause changes in dental, orthognathic, and facial development.

Numerical Analysis of Shock Initiation on Highly Energetic Material LX-04

The paper presents investigation of shock initiation effects on highly energetic material LX-04, an HMX based one, by a blunt brass projectile using numerical modelling methods implemented in LS-Dyna software. Multi – Material Arbitrary Lagrangian Eulerian (MM-ALE) formulation has been used to provide the possibility of fulfilment of the elements with multiple materials accordingly to multiple phases of the composition detonated. The work is focused on LS-Dyna’s equation of the state keyword *EOS_IGNITON_AND_GROWTH_IN_HE. Proper comparison with experimental data is presented. The introduction into the subject of highly nonlinear transient dynamic finite element analysis, possibilities, and superiority of this kind of modelling are being discussed. Reasons of sustaining the need of data by numerical solutions rather than experimental handling in military applications are given. Some of typical technical issues, occurring during such a fast-performing phenomenon, and the need of experimental validation of the models are typed together with detonation-state determination’s observation capabilities.

An energy flow approach for progressive collapse assessment

This paper explains the correlation of energy flow and the rate energy flow to the susceptibility of progressive collapse (PC) for typical mid-rise steel framed buildings. Energy-time histories of structural members were analysed to determine the energy flow behaviour throughout the structural system. All structural elements, including all connections, were represented numerically to (more accurately) determine the building’s susceptibility to PC, including the sequence of failing members. Assessing PC susceptibility with the incorporation of the rate of energy flow for a structure that accounts for the effects of connection resistance functions constitutes a novel approach. Advanced nonlinear transient dynamic finite element simulations were used to reveal the energy flow and its flow rate, and the de facto relationship with building response and failure. In addition, the efficacy of the current DOD approaches for PC assessment are examined in a comparative study with the proposed energy flow approach.

Structural response analysis of slamming impact on free fall lifeboats

The evaluation of impact induced slamming loads experienced by ships and offshore structures using advanced fluid structure interaction methods may be a challenging task involving complex and time consuming engineering solutions. This is the reason why to date the application of well understood and validated quasi-response approaches remains the most rational alternative used by experts for preliminary design assessment. Based on a benchmark study carried out by the International Ship and Offshore Structures Congress Technical Committee II.1 on Quasi-Static Response this paper demonstrates the practical use of “quasi-response” prediction methods for the assessment of impact loads on modern free fall lifeboats. The case study presented is considered relevant in terms of technical background and ship design for safety. Following a brief review rationalising the practical relevance of the engineering solutions examined, the influence of high speed impact is evaluated using linear-elastic and nonlinear beam models, as well as a nonlinear transient dynamic finite element analysis idealisation. Comparisons of the methods presented against experimental results led to the conclusion that the nonlinear quasi-dynamic beam approach accounts for the influence of the dynamic effects of strain by suitably idealising the effects of nonlinear geometric stiffness. It may therefore be more appropriate to employ this approach at preliminary stage, especially when conducting comparisons against simplistic linear methods used for rigid structures (e.g. stiffened steel and aluminium panels), or advanced nonlinear finite element analysis and other multi-physics methods that may be computationally complex and time consuming.

Multilevel design optimisation of a vehicle-dummy model under crash, vibration and injury criteria

A decomposed formulation and solution approach is presented for multidisciplinary vehicle design optimisation under crashworthiness, occupant safety, mass, and vibration design criteria. The vehicle model, equipped with a dummy and occupant restraint system, is used in nonlinear transient dynamic finite element simulations of both full frontal impact (FFI) and side impact (SI) for calculation of multiple injury criteria. A body-in-white vehicle model based on the corresponding crash finite element model is used for vibration analysis. The hierarchically decomposed multilevel optimisation problem consists of an injury criteria minimisation problem at the system level and separate mass minimisation problems subject to FFI and SI criteria at the subsystem level. Key aspects of the multilevel optimisation methodology are presented with the results showing a mass reduction of 8.7 kg in the vehicle model along an 8% improvement in the injury index with no loss of vehicle rigidity relative to the baseline model.

Multilevel vehicle–dummy design optimization for mass and injury criteria minimization

A vehicle–dummy multidisciplinary design optimization problem is treated as a multilevel system composed of structural and occupant restraint system design elements. The vehicle-based responses and the dummy-based responses are obtained from nonlinear transient dynamic finite element simulations of full frontal impacts and side impacts. The wall thicknesses of a set of energy-absorbing components together with the occupant restraint system control parameters associated with the seat belt and the airbag are treated as design variables and used to optimize the multilevel system to minimize both the structural mass and the selected injury criteria. Each element optimization problem is modeled using the augmented Lagrangian with exponential penalty function formulation. A single-loop coordination strategy is used to solve the multilevel optimization problem. To maximize the computational efficiency, surrogate models are used to approximate the vehicle-based responses and the dummy-based responses. The results of the vehicle–dummy design problem are used to examine the computational efficiency and the accuracy of the decomposed multilevel optimization methodology.

Prediction of impact induced failure modes in reinforced concrete slabs through nonlinear transient dynamic finite element simulation

A systematic numerical and analytical approach, to predict the various global failure modes such as flexural, punching shear and mixed flexure-shear failures along with the local failure modes such as crushing, cracking, spalling and scabbing, under impact load is investigated in this study. Numerical simulation on reinforced concrete (RC) slab impacted with cylindrical drop hammer has been carried out using ABAQUS finite element code to obtain the failure modes. Also a comparison has been made to validate the results of numerical simulation with the Zineddin and Krauthammer experimental results. The simulation results are in excellent agreement with the experimental failure modes reported by Zineddin and Krauthammer.The behavior of RC slab under impact load is simulated with the conventional limiting strain criteria as well as fracture energy softening models within the framework of damage plasticity model. It is found that the limiting strain criterion suffers from the limitation of mesh sensitivity and results from the fracture energy approach are close to the actual experimental results. Therefore the fracture energy softening models have been recommended as robust method for these types of studies.Besides the complexities due to concrete heterogeneity, the inelastic concrete and rebar behavior, strain rate effect and mesh sensitivity issues are addressed in the present paper to evolve a robust nonlinear transient dynamic finite element simulation. It is illustrated that the global and local failure modes can be numerically predicted through identifiable and measurable parameters such as the point of inflection, bi-axial failure criteria, strain based failure criteria, shear failure criteria, rebar strain and tensile damage profiles.

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.

Analysis of impact response and damage in laminated composite cylindrical shells undergoing large deformations

The impact behaviour and the impact-induced damage in laminated composite cylindrical shell subjected to transverse impact by a foreign object are studied using three-dimensional non-linear transient dynamic finite element formulation. A layered version of 20 noded hexahedral element incorporating geometrical non-linearity is developed based on total Langragian approach. Non-linear system of equations resulting from non-linear strain displacement relation and non-linear contact loading are solved using Newton-Raphson incremental-iterative method. Some example problems of graphite/epoxy cylindrical shell panels are considered with variation of impactor and laminate parameters and influence of geometrical non-linear effect on the impact response and the resulting damage is investigated.

Feasibility study of a lunar landing area navigation network deployed by impacting micro-probes

Exploration activities on the lunar surface will require precise knowledge of the position of a robotic or manned vehicle. This paper discusses the use of radio beacons as method to determine the position of a mobile unit on the surface. Previous concepts consider the installation of such equipment by the robot itself. A novel idea is discussed here, namely to use miniaturized radio beacons which are deployed (released) during the descent of the lander on the surface. This idea has three major advantages compared to previous proposals: (i) it avoids the time costly and energy consuming installation of the equipment by a rover. (ii) The impact velocities of the probes are in reasonable range since the probes are deployed at low altitude from the main lander that approaches its final landing site. (iii) The probes can take reconnaissance pictures during their free-fall to the surface. This method will therefore deliver charts of the proximity of the landing area with higher resolution than those done by orbital means. Such information will enable scientists and mission operators to precisely plan robotic excursions (and later Extra Vehicular Activity) through the identification of hazardous areas and spots of interest. The paper will study the feasibility of this system from different aspects. The first section will outline the application scenario and the potential outcome of such a system for the coming phase of lunar exploration. A technological readiness review was done to evaluate if the payload instrumentation for these high velocity impacting probes is available. The second section presents the simulation of the impact process of a preliminary probe model in nonlinear transient dynamic finite element analysis using the Lagrangian hydrocode LS-DYNA. The purpose of this simulation was to evaluate if the beacon is able to communicate with the mobile unit even when buried into the soil. The integration of this payload into coming lunar missions will contribute to the international efforts of lunar exploration with a landing site ad hoc navigation system for robotic or manned excursions.

Shape and sizing optimisation of automotive structures with deterministic and probabilistic design constraints

This paper presents the results of a study on the combined shape and sizing optimisation of automotive structures while examining the effects of different design constraints and associated uncertainties on reliability and efficiency of the optimum designs. Nonlinear transient dynamic finite element analysis is used for full- and offset-frontal crash simulations of a full vehicle model. Surrogate models are developed for the intrusion distance and peak acceleration responses at different vehicle locations based on the material and geometric characteristics of the rail component. The obtained solutions provide insight on the effect of uncertainties in optimum design of automotive structures.

Numerical integration of rate constitutive equations under finite deformation

An objective stress rate must be used in the constitutive law to accurately describe material response when large rigid body translations and rotations are present. The choice of a suitable objective stress rate has been the subject of considerable debate. For example, a basic flaw in the well known Jaumann stress rate (J-rate) has been demonstrated using the simple shear problem. A number of alternative objective stress rates have been suggested and developed. Among these is the Eulerian or E-rate in which rate constitutive calculations are performed on material axes coincident with the principal axes. The use of the principal axes technique greatly simplifies the constitutive calculations and resolves the difficulties surrounding the question of objectivity and frame invariance which arise in finite deformation problems. A numerical algorithm is presented which incorporates the principal axes technique for the Eulerian stress rate. The algorithm is intended for use in general purpose two or three dimensional solid mechanics software using the incremental or rate form of constitutive modelling. The algorithm focuses on an efficient method of integrating the material rotation tensor relating the principal axes to the fixed or global axes. The implementation of this algorithm into a general purpose non-linear transient dynamic finite element computer code is included. A number of numerical examples ranging from the simple shear problem to a large scale impact simulation demonstrates the accuracy and salient features of the algorithm.