Finite Element Analysis of Airbag

 

• ABSTRACT :

CAE approaches are increasingly being utilised in the automobile sector to anticipate different functional performance qualities (noise and vibration, crashworthiness, etc.) and adjust the design based on the results of virtual simulations, such as numerical Finite Element (FE) models. This eliminates the need for costly physical prototypes, lowering design costs and speeding up time to market. The final confirmation on a single physical prototype is still the last stage. If problems are still discovered at this late stage, CAE approaches can help with diagnosis, refinement engineering, countermeasure development, and optimization. In the low and medium frequency range, the Finite Element Approach (FEM) has become the main method for modal analysis and interior acoustics. Large FE model sizes are essential for accurate forecasts up to higher frequencies, limiting the number of design iterations in a given period. Furthermore, as the influence of uncertainty and variability (in geometric dimensions, material qualities, etc.) becomes increasingly relevant, it is necessary to integrate their effect in the modelling and simulation process for accurate performance (range) forecasts. Many non-deterministic approaches are based on assessing the influence of uncertainty and variability on the vehicle response using a deterministic "core" method. Faster deterministic design iterations can help with both of these problems since they allow for the evaluation of more design variations, a larger-scale optimization, and a more complete uncertainty assessment in a shorter amount of time. This work discusses two vibro-acoustic design methodologies: Wave-Based Sub structuring (WBS) for effective local re-design and Modal Modification for quick forecasts of the influence of panel thickness and damping changes. Finally, the latter method is utilised to accelerate a non-deterministic analysis utilising the Fuzzy Finite Element method, which is used to examine the influence of panel uncertainty on the NVH response.

• INTRODUCTION :

Vehicles employ an increasing number of components. These components have a functional design that satisfies a variety of standards, including passive safety. Any control adaptations installed to allow disabled individuals to drive should also meet these requirements. While the primary purpose of these changes is to allow people with various disabilities to drive, their use does not have to imply a reduction in vehicle passive safety. Recycling these components in accordance with recognised environmental policies should also be considered. These components may be redesigned to suit functional needs while also increasing the level of passive safety for disabled drivers. The effects of the materials and methods used in design and manufacture on the environment are also taken into account. To carry out such a redesign, the many scenarios that could occur are examined, as well as the passive safety measures now installed in automobiles. The load hypothesis is investigated from both a functional and passive safety standpoint. Airbags and steering modifications have a significant impact on a vehicle's passive safety level, which is examined in this article.

• OBJECTIVES :

The project starts with a number of research stages, with the ultimate goal of recovering the materials utilised when the vehicle parts approach the end of their useful life.The various loads to which these modifications are subjected must be evaluated in order to analyse their behaviour in normal service as well as in the case of an accident.The levels of force to which these modifications are subjected in typical use will be verified in this study. This will lead to the development of multiple loading hypotheses, which will make it easier to design these adaptations from a functional standpoint, with the applied loads being the worst from a functional standpoint.

Furthermore, loads induced by passive safety systems installed on the vehicle should be mentioned during the redesign of these adaptations. In addition to determining how these adaptations are affected, it is critical to determine whether these adaptations compromise the vehicle's passive safety. In the case of an accident, an increasing number of devices are being installed to avoid injury. As a result, the construction of these devices must be scrutinised to see if it affects passive safety. Airbags in the steering wheel are a good example. High loads can be applied on adjustments in these devices, causing deformation or fracture. Furthermore, if these adaptations encroach into the passenger safety cell, they may compromise the airbag's safety function.

• COMPARISON OF VIRTUAL AND PHYSICAL EXPERIMENTS :

In the past, testing was a key aspect of product development. Testing could reveal a design's flaws before the product reached the hands of the client.

However, the ability to conduct a comprehensive examination of many aspects of a design using computer-assisted engineering (CAE) tools has advanced to the point where "virtual" product development is a viable option.

Virtual experiments have several advantages, including the ability to control the experiment, the repeatability of performance and results, the ability to perform accelerated tests, the experiment's safety, the ability to simulate real-world conditions, the ability to optimise the experiment's implementation, and the specific experiment implementation plan. One of the most difficult tasks is the creation of a new product.

• APPLICATON OF CAE TECHNOLOGY IN DESIGING A VEHICLE :

Advanced technologies have a major role in designing vehicles in the automotive industry because it is possible to accurately model the desired shape of a vehicle. With the use of these technologies we have an overview in the design phase, because creating 3D parts in the space provides an ideal insight into geometry, keeping in mind that the body of the vehicle itself has a large number of parts, the defined elements are easily grouped into assemblies and subassemblies.

Advanced technologies have a major role in designing vehicles in the automotive industry .Because it is feasible to correctly model the intended shape of a vehicle, advanced technologies play a significant role in vehicle design in the automobile industry. Because producing 3D parts in space provides an optimal insight into geometry, and because the body of the vehicle has a significant number of parts, the defined elements are readily grouped into assemblies and subassemblies, we have an overview in the design phase with the use of these technologies.

• METHODOLOGY :

Furthermore, loads induced by passive safety systems installed on the vehicle should be mentioned during the redesign of these adaptations. In addition to determining how these adaptations are affected, it is critical to determine whether these adaptations compromise the vehicle's passive safety. In the case of an accident, an increasing number of devices are being installed to avoid injury. As a result, the construction of these devices must be scrutinised to see if it affects passive safety. Airbags in the steering wheel are a good example. High loads can be applied on adjustments in these devices, causing deformation or fracture. Furthermore, if these adaptations encroach into the passenger safety cell, they may compromise the airbag's safety function.

Fig.1 Modelling an airbag deployment

One of the most crucial aspects of passive safety is an airbag. There are numerous airbag systems in use, but one of the most essential is the frontal impact airbag. The simulation of this airbag's deployment is an important part of the adaption evaluation process (Figure 1). A three-dimensional model of the driving position was developed in the first phase of the process utilised to create this simulation. This work was completed using a professional 3D software design application. A finite element model was imported and a finite element mesh was created once this activity was completed (see Figure 2). Finally, the model's primary restrictions were established in dynamic simulation software, including materials and their properties, contact interfaces, gas expansion models, airbag folding technique, and so on.

Fig.2 Model of a steering wheel with a double knob

To begin, a simulation of a standard airbag deployment on a steering wheel was created without any modifications. This allowed for the measurement of the lengths occupied by an expanding airbag as well as the timeframes. Figure 3 displays a dynamic finite element simulation of a steering wheel airbag deployment process.

Fig.3 Modelling an airbag opening

The distance is measured from the halfway line or the outside edge of the airbag when the airbag inflates, using the centre flat surface of the steering wheel as a reference. When the various gadgets being evaluated are mounted to the steering wheel, this measurement serves as a benchmark for subsequent analysis. If no adaption is installed, the airbag's outside edge is parallel to the central surface of the steering wheel, and the distance is constant in all positions. After the adjustments are installed, the lowest and maximum distances from the central surface of the steering wheel are measured to establish how far the airbag has moved.

• DRIVER AND PASSENGER FRONTAL AIR BAGS :

The whole vehicle model included finite element (FE) air bags for driver and passenger occupant frontal crash protection. Frontal impact air bags for the driver and passenger were modelled, validated, and integrated into the occupant compartment. Following the vehicle standards, the driver air bag was installed on the steering wheel, and the passenger air bag was installed on the passenger side instrument panel brackets. To evolve in a reasonable manner.

The air bag model validations were carried out in the following steps to ensure accurate air bag models for realistic occupant frontal crash simulation.

1. Tear down air bag

2. Scan air bag fabrics (or cushion) for FE modeling

3. Conduct inflator tank test

4. Conduct drop tower test

5. Build FE models of air bags including air bag folding

6. Simulate the drop tower test and correlate the air bag characteristics

Disassembling the air bags from the air bag containers and scanning the parts, air bag cushions, and capturing the tether attachment data and tether size were all part of the tear-down and scanning process. The folding patterns for FE folding of the air bags were captured while scanning the air bag cushions. The goal of the inflator tank test was to record the deployment pressure, volume, and triggering time of the inflator, as well as the gas compositions. To determine air bag force-deflection properties, a drop tower test was done with the steering wheel. Appendix A contains the results of the tests conducted by KSS.

• DRIVE AIR BAG MODELING :

For accurate deployment and smooth contact, the driver air bag FE model was created using scanned CAD data with 5 mm elements. Figure 4 shows how the first driver air bag was modelled as a flat air bag on a bench and then folded using DynaFold simulations.

For each fold, simulations included thin folding and flattening. The folded bag was then fitted into the air bag container (or housing) using the housing simulation technique after all thin folds were accomplished. Figure 5 depicts the completed folded driver air bag.

                 Fig.4 Drive Air Bag FE Model Before Folding

Fig.5 Folded Drive Air Bag

• DRIVE AIR BAG VALIDATION :

The drop tower test was reproduced with the folded bag supported on the steering wheel sub-system and the inflator data collected from the tank test during the validation procedure. The drop tower test result was compared to the air bag force characteristics. Figure 6 depicts the drop tower test arrangement as well as the FEA model setup.

Fig.6 Drive Air Bag Drop Tower Test Setup and FEA Model Setup

•  CONCLUSION :

We investigated various combinations of airbag expansion and deployment in order to acquire the time/pressure curve created in the airbag's interior. The geometry of the airbag's explosive opening is clearly indicated by this curve. Reliable models have been obtained for comparison with actual data, allowing an analysis of the level of passive safety provided to physically handicapped drivers.According to the findings, the interference of control adjustments in the area of airbag deployment has a substantial impact on the airbag's location after a collision. As a result, installing such changes reduces the passive safety of disabled drivers significantly. The forked knob and double knob are the adaptations that encroach the most on the space occupied by a deployed airbag, resulting in the airbag's poorest location.