Stefan Tabacu

Improving the Accuracy of Parts Manufactured by Single Point Incremental Forming

The aim of this paper is to enrich the knowledge related to the single point incremental forming (SPIF) process by evaluating the efficiency of two optimization methods - the response surface method and the neural network method - to improve the accuracy of manufactured parts by prescribing a proper combination of the process parameters. The analysis is performed for a double frustum of pyramid made by stainless steel. It was found a good ability of prediction of both methods, demonstrating their suitability for physical implementation in solving problems associated to the SPIF process.

Computational modelling of vehicle interior components for impact applications: Thickness analysis

This paper presents some modelling techniques useful for the optimisation of numerical models of vehicle interior parts in terms of improving the structural response in impact applications. A procedure regarding the random distribution of thickness of the elements for a selected area within a user-specified tolerance is presented. Procedures implemented in a custom-written code and the algorithms used for the random distribution are also presented. This was required because the parts presented some deviations from the nominal value (of thickness), probably due to the manufacturing process. With experiments performed with equipment constructed according to ECE R21 regulation, the results obtained using three numerical models are compared and solutions for numerical modelling are presented. Results (accelerations: maximum, average, at peaks; time: peak time, time interval between two peaks; coefficient of restitution) obtained using the numerical models were evaluated and compared with the experimental data.

Numerical (analytical-based) model for the study of vehicle frontal collision

This article describes and solves a mathematical model useful to study a vehicles kinematics before and after collision, and the structure behaviour during an impact. The algorithm is based on solving differential equations using Runge–Kutta numerical method. To extract input data, a full-scale numerical model is solved using LS-Dyna. The friction coefficient between vehicle and barrier is evaluated and compared with the input value. The motion of the vehicle is solved and then passengers are added. The acceleration and displacement of the passengers centre of gravity are computed for different cases of impact angle and safety restrain systems stiffness. To extend the capabilities for accident-reconstruction applications, a procedure to construct deformation force pulse is presented. Also, a method for the evaluation of vehicles kinematic parameters using force–deformation curve is presented. The performances of the open architecture of the analytical model are presented and applied for the study of passengers head motion.

Finite element analysis and experimental validation of the wedge rolling process

A numerical model, developed for LS-Dyna solver, aimed to study the wedge rolling process is presented in this article. In addition, a comparison is made between the experimental and simulated results in order to set up the numerical model’s definition and simulation parameters. The computational performances are evaluated throughout this article to identify the best practice parameters for cold rolling numerical analysis using wedge tools. For an evaluation of the performances of the numerical model, an experimental system was developed to analyse the process parameters of the complex profiles with grooves formed by wedge tools. The methodologies used to record and evaluate the experimental results and the capabilities of the technique are discussed. For a complete analysis, the material behaviour is described by using a five-parameter strain-hardening law. Both the radial force (process force) and the micro-hardness were measured using the Vickers method on a radial section of the rolled piece. The issues addressing the numerical simulation can be extrapolated to other processes (e.g. riveting, flow forming) as this article provides the required information for the development of reliable numerical models.

Plug-In Hybrid Vehicle with a Lithium Iron Phosphate Battery Traction Type

To promote in the academic environment the ways for reducing global warming produced by the Sport Utility Vehicles, the grand hamster—electric way 4WD concept has developed within the University of Pitesti. It is a Plug-in Hybrid Vehicle powered in electric/hybrid modes by a Lithium Iron Phosphate (LiFePO4) traction battery technology, 205 V, 12 kWh. The concept is developed on the Dacia DUSTER crossover vehicle, 4 × 2 series version by implementing an electric propulsion system in the rear axle. The objective of this project is to realize a 4WD environmentally-friendly vehicle maintaining the leisure of driving the vehicle in the city using the continuously variable transmission (CVT) in the electric mode and the diesel motorization outside of the town in the thermal mode. The architecture is parallel type and E-4WD with a standard diesel engine 1,5 dCi FAP, 79 kW(107 bhp) and 6 speed manual gearbox in the front, and an asynchronous electric motor 31 kW (41 bhp) coupled with the reduction and differential gearbox unit at the rear. The traction battery is monitored by a battery monitor and charged by an embarked charger. The charging and discharging of the battery is authorized by the Battery Management System. The paper presents the firsts performances of the vehicle on the road tests.

Numerical model (switchable/dual model) of the human head for rigid body and finite elements applications

In this paper, a methodology for the development and validation of a numerical model of the human head using generic procedures is presented. All steps required, starting with the model generation, model validation and applications will be discussed. The proposed model may be considered as a dual one due to its capabilities to switch from deformable to a rigid body according to the applications requirements. The first step is to generate the numerical model of the human head using geometry files or medical images. The required stiffness and damping for the elastic connection used for the rigid body model are identified by performing a natural frequency analysis. The presented applications for model validation are related to impact analysis. The first case is related to Nahums (Nahum and Smith 1970) experiments pressure data being evaluated and a pressure map generated using the results from discrete elements. For the second case, the relative displacement between the brain and the skull is evaluated according to Hardys (Hardy WH, Foster CD, Mason, MJ, Yang KH, King A, Tashman S. 2001.Investigation of head injury mechanisms using neutral density technology and high-speed biplanar X-ray. Stapp Car Crash J. 45:337–368, SAE Paper 2001-22-0016) experiments. The main objective is to validate the rigid model as a quick and versatile tool for acquiring the input data for specific brain analyses.

Computational modelling of vehicle interior components for impact applications: moulding residual stress

This paper presents methods that can be used to connect and transfer the numerical model from structural applications to moulding analysis. Once moulding numerical analysis is performed stress and strain data are exported to be used as initial conditions for the structural analysis. Also a random distribution of the thickness is embedded into the computational model. The material model makes an important contribution to the quality and reliability of the simulation results and each simulation model was evaluated for different material models. Numerical results are compared with experimental data and a score is assigned to the computational models presented in this study. For the first case, the numerical model includes the fixture according to the experiment while a second case is focused on the stand alone model of the cockpit model. By defining a collaborative simulation that uses manufacturing process results, or using codes that can help solving some uncertainties of the model (random thickness) structural analysis becomes more reliable and may provide accurate results that are in good agreement with measured experimental data.

Fatigue Analysis of Rotating Parts. A Case Study for a Belt Driven Pulley

The present study is focused on the life estimation of a rotating part as a component of an engine assembly namely the pulley of the coolant pump. The goal of the paper is to develop a model, supported by numerical analysis, capable to predict the lifetime of the part. Starting from functional drawing, CAD Model and technical specifications of the part a numerical model was developed. MATLAB code was used to develop a tool to apply the load over the selected area. The numerical analysis was performed in two steps. The first simulation concerned the inertia relief due to rotational motion about the shaft (of the pump). Results from this simulation were saved and the stress – strain state used as initial conditions for the analysis with the load applied. The lifetime of a good part was estimated. A defect was created in order to investigate the influence over the working requirements. It was found that there is little influence with respect to the prescribed lifetime.

Numerical and Experimental Investigations of a Twin Sheet Thermoplastic Structure with Rectangular Frusta

Thin walled structures with rectangular frusta discussed by this study are manufactured using vacuum formed thermoplastic sheets that finally define a unitary structure that is a highly efficient solution providing outstanding performance by means of using small amounts of materials and high-tech, low energy consumption equipment. Sample parts formed by 2 × 2 cells with a cell dimension of 10 × 10 mm and a total height of 18.3 mm were tested in compression. Average crushing force and energy absorbed were calculated. Numerical models of the structure were developed and solved using Ls-Dyna explicit and implicit capabilities. Generally, both implicit and explicit solver provided good results in terms of crushing force and energy absorbed, while the failure pattern was better reproduced by the implicit solver. The implicit solver requires longer runtimes and this may add some constrains, thus for the explicit solution the simulation time was investigated in order to setup a parametric analysis. It was found that by using smaller cells the total energy absorption can be increased with respect to the available design volume, yet a limitation is added by the manufacturing process regarding the depth of the shape, draft angle and thickness of the part.

Concept Design of Twin-Sheet Thermoplastic Cellular Structures for Vehicle’s Bumper System

The 2013 World Health Organization’s Report on road safety shows that from 1.24 million fatalities recorded each year there are 270,000 pedestrian related events. Although the most severe injuries are produced when the pedestrian’s head is striking the bonnet or the area surrounding the windshield, lower limbs injuries do commonly result. The present study is focused on the development of an energy absorbing structure based on cellular configurations manufactured by vacuum forming thermoplastic sheets that finally define a unitary part. A parametric analysis is performed in order to evaluate internal energy accumulated during deformation. The numerical model of the front end structure of 2001 Ford Taurus model with the EC No 78/2009 specialised legform impact was investigated and the results discussed. Two configuration for energy absorber were defined and investigated using numerical simulation. The first configuration uses a single layer of four rows of cellular structures, while the second configuration uses a double layered structure of twin sheet cells on three rows. For the first case of cellular structure the bending angle of the impactor recorded a value of 19° while for the second case the value decreased to 14°. In all cases the shear displacement was well below the maximum accepted value. The maximum acceleration recorded during simulation using the single layer cellular structure was of 122 g while for the double layered structure the value was of 106 g. Compared to the original solution in both cases there was an improvement of the impactor’s response.