gordon murray design - lightweight composite seat development

7/27/2019 Gordon Murray Design - Lightweight Composite Seat Development

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Altair Engineering 2013 1

Lightweight Composite Seat Development

Peter BenzieSenior Engineer, Altair Product DesignImperial House, Holly Walk, Leamington Spa, CV32 [email protected]

David JewellSenior Composite and Plastics EngineerGordon Murray Design limitedWharfside, Broadford Park, Shalford, Surrey, GU4 8EP

Abstrac tGordon Murray Design has developed an innovative lightweight thin shelled compositeautomotive seat. The seat design was analysed and developed in collaboration with AltairProductDesign using the non-linear composite analysis tools available within HyperWorks.Technology Strategy Board funding helped the partnership to develop accurate compositematerial models for RADIOSS which were correlated to physical test data, and then enabledthe design process to be supported through predictive CAE. Prototypes were then producedand tested for component safety performance. Excellent correlation was seen between testand analysis. This paper presents aspects of the seat design and analysis process and howRADIOSS can be used to model composite materials for non-linear events with a highdegree of accuracy.

Keywords: Composites, Simulation, Non Linear Materials, Correlation, Radioss

1.0 Introduction

This work was completed as part of a research and development project that was funded bythe Technology Strategy Board. The seat design and development is part of theiStreamDevelopment (iD1) project.

The organisational structure of this project was relatively simple with only two consortiummembers; Gordon Murray Design and Altair ProductDesign. Gordon Murray Design took theproject lead role and were responsible for overall project management, design development

and prototype manufacture. Altair ProductDesign were responsible for the simulationactivities of the material correlation and seat development work packages. The high levelorganisational structure for the project can be seen in Figure 1.
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Altair Engineering 2013 Lightweight Composite Seat Development 2

Figure 1: Project Organisational Structure

1.1 The Need for Lightweight Solutions in Todays Market

Traditionally weight reduction is focused on major metallic systems such as the bodystructure, powertrain and chassis systems. However, as interior mass increases andstructure design becomes more efficient, OEMs need to look at all systems to achieve theirweight reduction targets.

An example of one of these areas is vehicle seating; the next generation of fuel efficientcars currently being developed have a need for compact, lightweight and low volumeseating that meets the same ergonomic, durability and safety standards as currentautomotive seating. iStream is the perfect enabler for developing a better seat and thisproject will deliver a product that can be offered to OEMs and act as a further platformdemonstrating the benefits of iStream.

Application of the iStream technology enables the development of lightweight solutionsthrough the use of composites to replace traditional materials and creating opportunities toreduce complexity by innovative manufacturing techniques.

Simulation plays a key role in the development of these emerging technologies and acurrent barrier to their adoption is the need for correlated material models. Such models arerequired in order to predict the behaviour of the composite materials and to lead the designthrough the use of optimisation techniques. Furthermore the use of composites in safetycritical components requires an understanding of non-linear behaviour of the compositematerials.

It is therefore vitally important to develop correlated composite models in order to be able touse simulation to aid and lead the design process. Further benefits include a reduction intesting and prototype costs as well as reduced time to market through upfront investment inanalysis.

Altair offers a complete simulation toolset in the HyperWorks software environmentincluding the capability to capture non-linear composite material behaviour in the RADIOSSexplicit solver. Altair ProductDesign is able to leverage these tools to provide advancedconsulting services in the development of composite systems.

1.2 iStreamtechnology

Gordon Murray Design (GMD) have developed a new automotive manufacturing processnamed iStream. A standard iStream structure uses a combination of large diameter,


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thin-walled, manipulated steel tubes and low cost sandwich construction compositematerials, which when bonded together form a very strong and stiff structure with uniquelylow cost and investment requirements.

This flexibility means that the chassis can be used as a standard platform to deliverdifferent vehicle types and model variants e.g. car, urban delivery van, taxi,emergency support vehicle.

Combining this flexibility with the separate chassis and assembly lines, means that

the same factory could be used to manufacture different variants. Entirely new model variants can be produced with significantly reduced lead times

from concept to market.

Pre-painted body panels mean that there is no need for a paint shop in the assemblyplant which removes the complications associated with vox emissions.

Mechanical fixing of body panels is quick and low-energy. It also makes futurerepairs relatively simple as replacement panels are quicker and easier to fix.

In addition, body panels are made from recycled materials and the chassis is potentiallyreusable. The lightweight nature will also reduce wear and tear and consequently therequirement for parts and maintenance. Lifecycle testing of an iStream chassis has

indicated a body life far in excess of the current generation of stamped steel vehicles.

Figure 2: iStreamChassis

Although the original focus has been on the application of iStream for chassis applications

investigations has shown significant opportunities to apply the same approach to otherapplications. This includes the application of iStream to a wider range of road, rail and airvehicles, and from chassis to sub-system and component applications.

The development of an iStream vehicle seat will illustrate in the best way that iStream isa process that can be applied across a wide range of platforms and products, and will resultin a unique package of IP that will be attractive to VMs of small city cars globally.

2.0 Thin Shell Composite Seat

2.1 Introduction to Seat Design Approach


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The work that was carried out on the iStream seat comprised benchmark evaluation,styling, tool design, pattern manufacture, mould manufacture and FEA modelling andcorrelation.

By applying iStream manufacturing methods to a vehicle seat the aim was to produce aproduct that is far lighter and slimmer than anything currently on the market. This is ofparticularrelevance to small city cars which are restricted for internal package space.

GMDs usual rigorous approach was taken to the design process to ensure the resultingproduct was suitable for a production vehicle and has been designed with automotiverestraint loading standards and full ergonomic functionality in mind.

To date, iStream has only been applied to vehicle bodies; the exercise of designing analternative product with it is brand new and will demonstrate the flexibility of iStream as amanufacturing method. The seat that results will also be a genuine enabler toward thedesign of increasingly small and lightweight vehicles throughout the automotive industry,where seat function is increasingly being compromised in order to accommodate thepassenger within a small volume. There is currently no metallic/composite combinationlightweight seat on the market that offers the required range of functionality to replace anautomotive equivalent.

Figure 3: Seat Concept Design

The iStream seat design process creates an efficient design by focusing structure wherethe load paths require it, and eliminating unnecessary material whilst accommodating theback adjustment, fore/aft adjustment, restraint systems and ergonomic supports that are

expected of an automotive seat. The use of simulation tools are vital in this process in orderto provide the design team with data on the performance at the global level down to thedetailed of the stress seen in individual plys.

The resulting design will be available as an off-the-shelf product to vehicle manufacturers,with particular emphasis on those involved with GMD on iStream vehicles. It is expectedthat the seat will significantly enhance the product offering for manufacturers of small citycars and provide a new opportunity for UK manufacturing to contribute to these programs.

Initial estimates suggest that an iStream seat could be 50% of the weight of a currenttypical automotive equivalent, which would bring associated benefits to material use duringmanufacture and vehicle fuel consumption.


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Although this work is automotive focused, the opportunities for development of lightweightseating cover many different industries including transport applications such as aerospaceand rail.

2.2 Design Process

The design process consisted of two design and simulation loops with additional subiterations focusing on the layup detailing in the composite panels. Simulation was used

heavily to develop the design and layup of the composite components to pass theloadcases whilst minimising the component weight.

The process from concept through development to prototype manufacture and testing wascompleted in under 3 months. This compressed timing was made possible due to theavailability of correlated material models and composite analysis methods.

The learning from this project has also highlighted further opportunities to optimise andrefine the design to remove additional weight and complexity from the design. Thesuccessful test prediction adds confidence to the simulation techniques and their applicationon future development activities.

2.3 Loadcases

Five loadcases were developed to assess the structural performance of the seat in order tomeet the regulations that would apply to a full seat system.

I. Applied displacement to the seatback (benchmark test)

II. Moment Load (references ECE Regulation 17), illustrated in Figure 4

III. Deceleration Load (references ECE Regulation 17)

IV. Deceleration Load (references ECE Regulation 17)

V. Lateral Load

The criteria set for loadcases II,III,IV and V was for no rupture to occur in the composite

components.

Figure 4: Moment Loadcase Set Up

A benchmark test was also carried out on a conventional pressed steel seat for additionalcomparison data with the new GMD design. The seat was rigidly fixed via its runners to thebase plate and pulled from behind by a hydraulic ram.

2.4 Materials


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The iSeat is fundamentally constructed from two composite panels. The brackets andrails are made from steel components. The composite panels are made up from multiplelayers of GRP in both CSM and UD fabrics.

The simulation and development of these panels was possible due to the availability ofcorrelated material models that were validated at both coupon and subsystem levels. Thesemodels were developed in a separate work package that is not covered in this report.

Figure 5: iSeat FE Model

2.5 Prototype Seat

A deliverable of the project was the construction of a fully trimmed fully functional prototypeseat. The completed seat can be seen in Figure 6 and was trimmed using state of the artrecycled materials and foam products.

The seat performed well in the three ECE reg. 17 tests. The seat passed the relevantregulatory tests making it suitable for use in a future vehicle with confidence. The seat washalf the weight of the benchmark pressed steel seat. The use of composite materials wasoptimised, encapsulating all iStream principals including the use of recycled andrecyclable materials in the construction of the trim.


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Figure 6: Completed iSeat

3.0 Composite Simulation Techniques

The FE model was constructed from the CAD provided by GMD with the compositesrepresented by shell elements. Pre-processing was completed using both HyperMesh andHyperCrash toolsets.

The composite material cards were populated from the parallel material correlation project.These include the validation of the complex non-linear properties of the composite materialsfrom coupon through to system level analysis. It is also important to consider the influenceof strain rates on the composite and adhesive component materials.

The approach enabled multiple ply layups to be assessed in rapid succession to develop a

lightweight design that was able to meet the performance requirements. This includes theoptimal distribution of UD layers as well as control of the ply thicknesses.

3.1 RADIOSS Material Modelling

The composite materials were modelled using /MAT/LAW25 (COMPSH) with the TSAI-WUformulation. This enables the non-linear orthotropic material properties to be characterised.A wide range of tests and validation work is required to populate all the relevant fields in thematerial card. Correlation using a single common material model was achieved for all testcorrelation items.


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Figure 7: Material Correlation

In order to capture the non-linear behaviour it is necessary to include failure modelling. Inthis case failure was controlled using the /FAIL/CHANG. In this form failure is controlled bystress. It was also possible to control the element deletion options between individual plyfailures or for all layers. This method was used as the acceptance criteria during the plylayup development work.

3.2 Post Processing

To assess composite performance based on individual ply failure in addition to the

conventional element deletion (rupture) approach. Post processing macros were writtenwithin HyperView in order to visualise using a contour plot the individual ply failureinformation that is written to the .out file. The macro is able to plot layer and number of plyfailures for each time step. This is particularly useful in being able to understand which plyand material are driving the material failure.

Figure 8: Composite Stress Plots


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Stress based ply failure with stress distribution per layer was assessed in order todetermine failure. This method was used to highlight regions where material could be addedor removed. This information was used in the ply layup development process.

4.0 Test Correlation

4.1 Test Resul ts

The prototype seat successfully passed the testing which included the moment anddeceleration loadcases. This work was carried out at MIRA UK.

4.2 Moment Test Correlation

In order to correlate to the test a specific FE model was built which captured the loaddistribution of the back form through the foam material. This model can be seen in Figure 9.

Figure 9: Correlation Model Set Up Moment Loadcase

To monitor the deformation during the test, displacement pots were used to measuredisplacement vs time during the complete test. In order to get good correlation to this testthe model had to be run at a very slow rate to avoid dynamic effects in the results. The testsaw a displacement of 72mm and 78mm compared to an analysis value of 72.1mm and78.4mm respectively. This represents an error of less than 1%.

4.3 Deceleration Loadcases Correlation

The prototype tests passed both forward and rearward deceleration loadcases without anydamage. In order to match test an accelerometer was positioned as per test, as shown inFigure 10.


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Figure 10: Correlation Model Set Up Deceleration Loadcases

Excellent correlation was seen between test and analysis as can be seen in Figure 11. Theplots show that in test energy is lost to damping effects that are not included in the FEanalysis model.

Figure 11: Deceleration Correlation Results


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5.0 Conclusions

An innovative seat design was developed in a very compressed timescale that met theperformance and mass targets set out at the start of the project. Advanced simulationtechniques played a vital role in the design process. This was enabled through the creationof correlated material models for the composite components that were able to capture thenon-linear and failure characteristics of the composite parts.

The prototype seats that were produced as part of this project passed the safety tests thatwere carried out and excellent correlation was seen between the test and analysis results.The success of this process demonstrates the capability of simulation within theHyperWorks environment utilising the RADIOSS explicit solver to model compositematerials in safety component applications.

gordon murray design - lightweight composite seat development

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