Sachin Patil

An experimental and numerical investigation into the dynamic crash testing of vehicle bumper fabricated using friction stir welding and gas metal arc welding

The advancement in friction stir welding (FSW) technology has provided automotive and aerospace industry with an alternative method in developing structures and assemblies. This study investigates the performance of FSW and gas metal arc welding (GMAW) on road vehicle bumpers. The method of investigation is to weld the bumper to the crash-box, and the assembly is mounted onto a moving deformable barrier before a dynamic crash test is performed. The bumper and crash-box is fabricated from AA6082-T6 and AA6063-T6 extrusions, respectively. In the first part of the study, the full-frontal crash testing of the FSW and GMAW fabricated bumper using experimental method is presented. The FSW and GMAW fabricated bumpers are subjected to 7, 10, 15 and 20 km/hr impact velocities against a rigid wall. The methods used to quantify the results are the post-crash deformation and stress distribution of the bumper as well as crack propagation at the weld joint. The non-linear dynamic software, LS-DYNA, is used exclusively in the second part of this study to replicate the experimental procedures using numerical methods. Finally, a 40% frontal offset test is conducted to evaluate the performance of the bumper when subjected to a different impact condition. It was shown that the FSW fabricated bumper can enhance the structural integrity and performance of the bumper at all impact velocities and configurations.

Preliminary Study on Modeling of the Deformation and Thermal Behavior of FSSW using SPH Approach

Material flow in the solid-state Friction Stir Welding (FSW) is quite a complex process. Investigation of material flow can be carried out either by experimentation or by numerical simulation. However, compared to experimentation, numerical simulation is inexpensive, efficient and convenient, but quite challenging to model. The challenging issue in modeling FSW is to deal with the large deformations of the work piece material. The Lagrangian simulations of FSW show that the severely distorted finite elements are caused due to the large deformation of the workpiece material, which makes the Lagrangian approach inappropriate for modeling FSW. A good alternative is to study it in a SPH environment. SPH formulations are used to overcome the shortcoming of Lagrangian formulations due to its continuous regimes. The basic idea of the SPH approach is that the mesh is obliged to follow material flow. Thereby the excessively distorted elements can be avoided as in Lagrangian formulations. In this paper, we fulfill this aim by using a SPH method.Based on the simulation results, it is concluded that the material motion characteristics on the top surface and through the depth (volume) of friction stir welds have been made for the advancing and retreating sides. The motion trends are consistent with the reported published experimental evidence.

Characterisation and modelling the strength of EHSS steel grade spot weld for automotive joints and its application for frontal impact load-case

ABSTRACT Ever increasing requirements regarding automotive safety have led to major innovations in the field of crash safety. With a greater emphasis placed on weight reduction, the ground vehicle industry has increased the use of higher strength, thinner gauge steels, particularly by using various new grades of high and ultra-high strength steels. Choice of a particular High strength steel HSS will depend upon such factors as cost, formability, fatigue resistance and weldability, in particular spot weldability. A modern car structure may consist of several thousand weld-type connections, and failure in these connections plays an important role for the crashworthiness of the vehicle. Therefore, accurate modelling of these connections is important for the automotive industry. This paper presents the latest investigation of the strength of steel grade spot-weld joints. This study shows a developed simplified spot-weld model in crash simulations to reach the best collision characteristics of the car to meet the Federal motor vehicle safety standards (FMVSS) requirements.

Simulation Study of Spot Weld Material Configurations for Crash Analysis

In engineering practice, spot welds are normally not modeled in detail, but as connection elements which transfer forces and moments. Therefore a proper methodology for the development detailed weld model to study structural response of the weld when the applied load range is beyond the yield strength discussed in this paper. Threedimensional finite element (FE) models of spot welded joints are developed using LS-Dyna. Simple spot weld models are developed based on the detailed model behavior developed earlier. In order to generate testing data, virtual tensile testing simulations are carried out with mesh sensitivity in the necking zone. This high mesh resolution around necking zone is required to capture the steep gradients in the pressure and stress tri-axility, etc. Once the stress strain curves are generated in the simulations examined damage function and evolution to represent failure. Various EHSS steels grades used in this study. The results from this study shows reasonable agreement between the simulations and the test results. Hence, spot weld model obtained should be considered for crash analysis applications to understand behaviors of structural parts.

Vehicle Mass Optimization for Frontal Structure Using I-Sight and Study of Weld Parameterization for Mass Improvement

In order to meet the Federal Motor Vehicle Safety Standards (FMVSS) requirement, the frontal structure of the vehicle needs to be design to maximize energy absorption in the presence powertrain design layout constraint. This needs the basis for structural optimization using a pragmatic approach. With regards to passive safety of a vehicle, there is a constant increase of the requirements to the BIW (Body in White) stiffness in ever greater extent, without a significant increase in vehicle weight. The primary objective of this study is to demonstrate mass optimization in a virtual tryout chain and generate optimized analytical model that can be leveraged in future assessment of a car. For this, a parameter investigation concerning variation of input data is done using I-sight. Simplified model of the bumper subsystem is developed for the offset crash test to serve as a base for the creation of designs by changing design variables. The optimization is carried out using I-sight to explore design space for this subsystem. Finally the effectiveness of optimized bumper subsystem is examined using full vehicle impact test. The focus of the work is further promoting the trend for light weight construction by weld optimization. Overall, this virtual tryout leads in sustainability by lighter transport on road, thus saving fuel and reducing emission.Copyright