Transient Dynamic Finite Element Simulation Research Articles

Selective guided wave mode transmission enabled by elastic metamaterials

This article presents the selective guided wave mode transmission enabled by elastic metamaterials. The metamaterial unit cells are comprised of Locally Resonant (LR) cylinders arranged in a periodic pattern bonded on an aluminum plate. Via a careful design, the band structure of the metamaterial system displays a complete bandgap for either symmetric wave modes or antisymmetric wave modes within different frequency ranges. A numerical-based effective medium approach is adopted to calculate the effective dynamic mass densities for in-plane and out-of-plane wave motions under the subwavelength requirement. The finite element harmonic analysis of a chain model further substantiates the selective mode transmission capability via the frequency spectrum of the transmitted wave modes. Finally, a coupled-field transient dynamic finite element simulation is carried out to acquire the dynamic response of the structure. The frequency-wavenumber analysis of the transmitted wave field illuminates the successful achievement of the selective mode transmission behavior. Experimental demonstrations are also presented to validate the numerical predictions. The proposed selective wave mode transmission control capability may possess great application potential in Nondestructive Evaluation (NDE) and Structural Health Monitoring (SHM). The paper finishes with summary, concluding remarks, and suggestions for future work.

Transient dynamic finite element simulation for prediction of surface integrity induced by waterjet peening

This paper aims to develop and validate the transient dynamic finite element three-dimensional simulation of a waterjet peening process to predict surface properties (residual stresses, plastic strains, surface roughness, and superficial damage). The finite-element model considers an impingement of multisets of droplets, which strike the treated surface by impact pressures over the corresponding contact regions at high velocities. The impact pressures and their durations are modelled by using the liquid impact theory combined with an impact velocity law depending on the main parameters of the process. The behavior law of the material is an elastoviscoplastic law coupled to the Johnson–Cook damage criterion. The effectiveness of this simulation is discussed in two cases: (i) a linear mono-set of droplets and (ii) multisets of droplets using the experimental results of a waterjet-peened Al7075-T6 aluminum alloy. The predictive results of surface properties obtained by simulation with multi-sets of droplets appear more realistic than those obtained by simulation with a single set of droplets and more close to the experimental surface properties.

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.

Modification of Residual Stresses in Laser Additive Manufactured AlSi10Mg Specimens Using an Ultrasonic Peening Technique.

Ultrasonic peening treatment (UPT) has been proved to be an effective way of improving residual stresses distribution in weld structures. Thus, it shows a great potential in stress modification for metal parts fabricated by additive manufacturing technology. In this paper, an investigation into the ultrasonic treatment process of AlSi10Mg specimens fabricated by selective laser melting (SLM) process was conducted by means of experimental and numerical simulation. The specimens were prepared using a SLM machine, and UPT on their top surface was carried out. The residual stresses were measured with an X-ray stress diffraction device before and after UPT. Meanwhile, a finite element simulation method for analyzing the influence of UPT on the residual stress field of specimens was proposed and validated by experiments. Firstly, the thermal mechanical coupling numerical simulation of the SLM process of the specimen was carried out in order to obtain the residual stress distribution in the as-fabricated specimen. Then, the transient dynamic finite element simulation model of the UPT process of the specimen was established, and the UPT effect analysis was implemented. In the UPT simulation, the residual stress was applied as a pre-stress on the specimen, and the specimen’s material mechanical property was described by the Johnson–Cook model, whose parameters were determined by Split Hopkinson Pressure Bar (SHPB) experiment. The residual stress distribution before and after UPT predicted by the finite element model agree well with the measurement results. This paper concludes with a discussion of the effects of ultrasonic peening time, as well as the frequency and amplitude of the peening needle on residual stress.

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.

Finite Element Simulation of Damage Detection of Stiffened Plate under Temperature Variation

Lamb waves are ultrasonic elastic waves that travel inside and along thin plates and is frequently used as diagnostic tools to detect damage in plate-like structures. In this paper, a transient dynamic finite element simulation of Lamb wave with piezoelectric transducers for damage detection in a stiffened plate under different temperature condition is carried out on the commercial finite element code ANSYS platform. Simulations are conducted over a temperature range. The changes in temperature-dependent material properties are used to measure the differences in the response signal’s waveform. The baseline selection method and baseline signal stretch method are used to compensate the temperature influence on Lamb wave propagation. The results of the numerical simulation demonstrate the effectiveness of the temperature compensation approach and the simulated damage on the stiffened plate can be defected effectively under elevated temperatures environment.

Finite Element Simulation of Lamb Wave with Piezoelectric Transducers for Composite Plate Damage Detection

Structural health monitoring (SHM) is an emerging research area with multiple applications. Lamb waves are ultrasonic elastic waves that travel inside and along thin plates and is frequently used as diagnostic tools to detect damage in plate-like structures. In this paper, a transient dynamic finite element simulation of Lamb wave with piezoelectric transducers for damage detection in a composite plate is carried out. The embedded cross-shaped piezoelectric active sensor arrays were used to generate and receive guided Lamb waves propagating in the plate structure. A full-scale FEM model for the laminate was created using three-dimensional eight-node layered structural solid element and piezoelectric active sensors were created using coupled field elements on the commercial finite element code ANSYS platform. The beam forming technique of Lamb waves is used to locate damage in the plate .The results of the numerical simulation demonstrate the effectiveness of the approach.