Volkan Esat

Finite element analysis of springback in bending of aluminium sheets

Abstract Bending is one of the processes frequently applied during manufacture of aluminium components. The bending operation involves springback, which is defined as elastic recovery of the part during unloading. In manufacturing industry, it is still a practical problem to predict the final geometry of the part after springback and to design appropriate tooling in order to compensate for springback. In this paper, commercially available finite-element analysis (FEA) software is used to analyse bending and springback of different aluminium materials of different thickness. The amount of springback, the total equivalent plastic strains and the equivalent von Mises stresses are presented. The FEA results are compared with empirical data.

Viscoelastic finite element analysis of the cervical intervertebral discs in conjunction with a multi-body dynamic model of the human head and neck

Abstract This article presents the effects of the frontal and rear-end impact loadings on the cervical spine components by using a multi-body dynamic model of the head and neck, and a viscoelastic finite element (FE) model of the six cervical intervertebral discs. A three-dimensional multi-body model of the human head and neck is used to simulate 15 g frontal and 8.5 g rear-end impacts. The load history at each intervertebral joint from the predictions of the multi-body model is used as dynamic loading boundary conditions for the FE model of the intervertebral discs. The results from the multi-body model simulations, such as the intervertebral disc loadings in the form of compressive, tensile, and shear forces and moments, and from the FE analysis such as the von Mises stresses in the intervertebral discs are analysed. This study shows that the proposed approach that uses dynamic loading conditions from the multi-body model as input to the FE model has the potential to investigate the kinetics and the kinematics of the cervical spine and its components together with the biomechanical response of the intervertebral discs under the complex dynamic loading history.

Evaluating the effects of size and chirality on the mechanical properties of single-walled carbon nanotubes through equivalent-continuum modelling

Due to numerous difficulties associated with the experimental investigation of the single-walled carbon nanotubes (SWNTs), computational modelling is considered to be a powerful alternative in order to determine their mechanical properties. In this study, a novel three-dimensional finite element model incorporating a beam element with circular cross section is developed based on equivalent-continuum mechanics approach. The beam elements are used as the replacement of C–C chemical bonds in modelling SWNTs. Finite element models are generated for a range of SWNTs and employed for the evaluation of effects of diameter and chirality on the mechanical properties including Young’s modulus, shear modulus, shear strain and Poisson’s ratio of SWNTs. The results of this study are in good agreement with those reported in literature.

Pregnant driver injury investigations through modelling and simulation of full-frontal crashes with and without airbags

Road traffic accidents have become an increasingly important element in maternal deaths. It is important to investigate the injury mechanisms and injury levels that pregnant women may be subjected to in order to improve transport safety. The three dimensional computational model ‘Expecting’, which embodies a detailed multi-body model of a fetus in a finite element model of uterus with a placenta, is developed at Loughborough University. The model is designed to simulate dynamic loading conditions that pregnant occupants may experience. In this study, ‘Expecting’ is used to study the kinematics of pregnant occupants to predict the injury levels to the pregnant driver in frontal crashes. The implications of ‘No Restraint’, ‘Seat Belt Only’ and ‘Seat Belt and Airbag’ cases are investigated for various crash severities, from 15 to 45 kph. Crash analysis injury criteria such as head injury criterion (HIC), 3 ms maximum, combined thoracic index (CTI) and viscous criterion (max VC) are used. The results suggest that the frontal airbag together with the correctly worn seatbelt provide better protection for the pregnant drivers.

Estimating the Effect of Chirality and Size on the Mechanical Properties of Carbon Nanotubes Through Finite Element Modelling

Carbon nanotubes (CNTs) are considered to be one of the contemporary materials exhibiting superior mechanical, thermal and electrical properties. A new generation state-of-the-art composite material, carbon nanotube reinforced polymer (CNTRP), utilizes carbon nanotubes as the reinforcing fibre element. CNTRPs are highly promising composite materials possessing the potential to be used in various areas such as automotive, aerospace, defence, and energy sectors. The CNTRP composite owes its frontline mechanical material properties mainly to the improvement provided by the CNT filler. There are challenging issues regarding CNTRPs such as determination of material properties, and effect of chirality and size on the mechanical material properties of carbon nanotube fibres, which warrant development of computational models. Along with the difficulties associated with experimentation on CNTs, there is paucity in the literature on the effects of chirality and size on the mechanical properties of CNTs. Insight into the aforementioned issues may be brought through computational modelling time- and cost-effectively when compared to experimentation. This study aims to investigate the effect of chirality and size of single-walled carbon nanotubes (SWNTs) on its mechanical material properties so that their contribution to the mechanical properties of CNTRP composite may be understood more clearly. Nonlinear finite element models based on molecular mechanics using various element types substituting C-C bond are generated to develop zigzag, armchair and chiral SWNTs over a range of diameters. The predictions collected from simulations are compared to the experimental and computational studies available in the literature.

Effects of Table Design in Railway Carriages on Pregnant Occupant Safety

This paper focuses on safety investigations for pregnant occupants, in particular, on their interactions with an interior feature, fixed bay tables, in railway vehicles. The computational pregnant occupant model Expecting has represented pregnant travellers in railway vehicle environments. Expecting is a computational pregnant occupant model developed at Loughborough University, in order to investigate the dynamic response of pregnant women to impacts. It has been successfully utilised by the authors in earlier studies, in various automobile crash investigations, such as frontal impacts with real and simplified crash pulses. In this study, a model of a network train carriage is generated and used together with Expecting to assess the suitability of fixed bay table designs for pregnant occupants. Investigations of potential injuries in this paper are believed to contribute to the design of more suitable interior features and hence improve safety and quality of life for pregnant women as travellers in railway vehicles.

Pregnant driver injury investigations in oblique crashes

Kinetics and kinematics of an oblique impact are different when compared with frontal collisions. The objective of this research is to simulate various oblique crash scenarios that pregnant drivers may experience by using the computational pregnant occupant model, Expecting and investigate potential injuries that pregnant drivers may suffer. Half-sine acceleration pulses representing crash speeds, 15 to 45 kph are used in the simulations. Oblique impact simulations are conducted both from the nearside and the farside (offside) of the vehicle. The placental abruption and hence foetus mortality risks during oblique crashes are compared with the full-frontal impact cases.

Polarization independent triple-band (5,4) semiconducting carbon nanotube metamaterial absorber design for visible and ultraviolet regions

Abstract. Various metamaterial absorber designs operating in the microwave, infrared, visible, and ultraviolet frequency regions have been proposed in the literature. However, only a few studies have been done on the metamaterials that absorb in both visible and ultraviolet solar spectra. A triple-band polarization-insensitive metamaterial absorber structure with semiconducting single-walled carbon nanotube as the dielectric layer is proposed to efficiently absorb the incident electromagnetic radiations in visible and ultraviolet frequency regions. A unit cell of this design comprises three basic components in the form of metal–semiconductor–metal layers. The metallic part of the structure is aluminum, and the (5,4) single-walled carbon nanotube is used as the semiconducting material. The electromagnetic response of the proposed design is numerically simulated in the visible and ultraviolet regions with the maximum absorption rates of 99.75% at 479.4 THz, 99.94% at 766.9 THz, and 97.33% at 938.8 THz with corresponding skin depths of 13.0, 12.8, and 12.9 nm, respectively. Thus, solar cells based on this metamaterial absorber can offer nearly perfect absorption in the suggested frequency regions. The simple configuration of the design provides flexibility to control geometric parameters to be used in the solar cell and possesses the capability to be rescaled for other solar spectrum.

Structural crashworthiness analysis of a ladder frame chassis subjected to full frontal and pole side impacts

ABSTRACT Automobile chassis is a major element of structural crashworthiness in road motor vehicles. Various chassis geometry and topology research studies have been conducted to improve crash energy absorption characteristics of the chassis. In side impacts, crashworthiness of an automobile body depends not only on the chassis geometry and topology, but also on the design and reliability of other structural members such as B-pillar and side panels. This study aims to contribute to the investigations on the effects of chassis geometry over crashworthiness, particularly focusing on the structure of a ladder frame chassis subjected to full frontal and pole side collisions. Preliminary work has been conducted to evaluate the behaviour of steel beam profiles under impact loading through finite element (FE) modelling, which helps understand the mechanics of the particular beams chosen as chassis elements. Another FE model is developed utilising a previously generated mesh of a pickup truck with a ladder frame chassis. The FE model is employed to simulate full frontal and pole side crash test scenarios on the isolated chassis as well as on the whole body of the vehicle. Crash energy absorption results and reaction forces are collected for different thicknesses and beam profile cross sections of the vehicle chassis to be utilised in several proposed design improvements aiming to enhance crashworthiness. Computational results exhibit good agreement with experimental findings.

Thin film (6,5) semiconducting single-walled carbon nanotube metamaterial absorber for photovoltaic applications

Abstract. A wide-band (6,5) single-walled carbon nanotube metamaterial absorber design with near unity absorption in the visible and ultraviolet frequency regions for solar cell applications is proposed. The frequency response of the proposed design provides wide-band with a maximum of 99.2% absorption. The proposed design is also simulated with (5,4), (6,4), (7,5), (9,4), and (10,3) chiralities, and results are compared to show that the proposed design works best with (6,5) carbon nanotube (CNT) but also good for other chiral CNTs in the visible and ultraviolet frequency region. The geometric structure was carefully analyzed for its contribution to the absorption behavior. The absorber design is highly flexible and capable of keeping the wide-band with high absorption. Due to the excellent symmetric characteristics of the proposed design, which provides polarization independency under normal incidence (transverse electromagnetic mode), the proposed metamaterial absorber is a good candidate for the solar cell application, where absorbance can be kept high with respect to the polarization angle.