RNL 15 Static Stiffness Scale Methodology Development for IP Head IAC

7/27/2019 RNL 15 Static Stiffness Scale Methodology Development for IP Head IAC

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Simulation Driven Innovation 1

Static Stiffness Scale Methodology Development for IP Head Impact Simulation

in Early Design Phase

Nitinkumar LokhandeManagerCAE

International Automotive India Pvt.

LtdPlot No. 3, Phase 1, Rajiv Gandhi

InfoTech Park,Hinjewadi, Pune411057

[email protected]

Ganesh GondakeInternational Automotive India Pvt.

Ltd

Plot No. 3, Phase 1, Rajiv GandhiInfoTech Park,

Hinjewadi, Pune411057

Jamil ManjurulInternational Automotive India Pvt.

Ltd

Plot No. 3, Phase 1, Rajiv GandhiInfoTech Park,

Hinjewadi, Pune411057

Keywords: Automotive Interior, ECER21/ FMVSS 201, Static stiffness scale, CAE, Radioss Bulk, block

Abstract

Severe competition in current market situation forcing automobile companies and their suppliers to reduce thedevelopment time and development costs. The biggest challenge in design phase is to predict the potential failure asearly as possible and address these failures in initial design. IP design is govern mainly by functional, environmental,safety, personalization and manufacturing aspects of product. ECE R21/ FMVSS201 regulatory requirement addressoccupant safety by limiting 3ms head acceleration response below 80g, when head interacts with IP. The headacceleration response is function of dynamic IP stiffness. Virtual CAE validation of ECER21/ FMVSS201 load casehas shown close agreement with physical tests. The CAE validation process is time consuming because of model size,

time step requirements, material nonlinearities, contact nonlinearities aspects of solution.In this paper two step methodologies is presented which addresses ECER21/FMVSS201 IP dynamic stiffness throughstatic analysis and static stiffness scale. First step is to develop methodology for static analysis to evaluate staticstiffness. Second step is developing methodology to create static stiffness scale. The static stiffness derived from staticanalysis gauged on static stiffness scale to identify the hard points which could fail in ECER21/FMVSS201. Thesemethodologies will allow the designer to identify potential hard points in initial design phase to accelerate initialdesign.

Introduction

Occupant interactions with interior parts such as Instrument panel, console, trims etc are addresses briefly by

regulations ECER 21 and FMVSS201. The main requirement of these regulations to address head injuries andemphasis is given to keep these injuries below target injury. The injury response function is function of stiffness ofInstrument panel. Additionally IP stiffness value should address load cases of NVH, durability, thermal cycling, abuse

loading etc. The virtual validation of IP can be done effectively using Hyperworks tools such as Radioss bulk andblock. It is very important to address the IP characteristics for ECE R 21/FMVSS201 regulations in early design phase

to avoid rework in later phase. The IP stiffness is function of material constants, ribbing structure, part thickness,connection scheme, packaging telematics, safety equipments etc. It is very important to address these variables ininitial design phase to avoid rework due to non compliance of IP with regulatory requirement. The ECE R 21/FMVSS201 test can be effectively simulated using virtual validation tools. The major challenges to perform virtualvalidations are to get material stress strain data for different strain rates, to create detailed non linear contactcharacteristics model, computational cost and time. A close observation of results for ECE R21/FMVSS201 shows thatmaterial elastic characteristics rather plastic characteristics plays important role in head injury function. This

observation leads us to create methodology where linear analysis could generate stiffness data of IP. These stiffness

values could help designer to compare IP stiffness on scale between 0 to 1 and separate points in zone red, green ororange. The Red points are points which will fail dynamic test where as Green points are points which will pass thedynamic test. The Orange points can be the border cases. The designers have to consider Orange and Red points as
mailto:[email protected]:[email protected]:[email protected]


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area need the stiffness corrections. These stiffness corrections need to validate with other load cases mentioned above.Needless to mention that Radioss bulk solver performs static analysis of instrument panel.

Process Methodology

Product validation scope

The detailed DFMEA (Design failure mode effect analysis) study of Instrument Panel will lead to creation of

DVP (Design validation plan). The typical virtual validation is shown in schematic figure 1. These tests are done inseries under heads as linear static, Non linear structural and thermal. Any non compliance resulted in virtual validationtest will call for design modifications. The best practice guidelines followed at design centers will address most offunctional static tests without any issues. The area where inertial forces, material non linearity, contact non linearityoccurs is difficult area to address at early design stage. In this paper an attempt is made to empower design engineersby providing stiffness scale to evaluate the instrument panel design for ECE R 21/FMVSS 201 head impact

requirement.

Fig. 1 schematic diagram of virtual validation for instrument panel

CAE Methodology

Figure 2 shows the functional diagram of head impact model. The headform with mass and velocity 6.8kg and

6.69 m/s respectively impacts on instrument panel. The stiffness of instrument panel will decide time to zero velocity

and accelerations.

Fig. 2 Functional diagram of head impact model


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Figure 3 shows the Normalized velocity vs. Normalized time diagram. At time equal to 0 second the velocity

of head form is 1 unit. The time at which velocity becomes 0 is denoted as time to zero velocity (TTZ). The slope ofcurve is acceleration of head form. If the time to zero is beyond the line shown in green color, the acceleration level isbelow the required target zone. This zone is denoted as green zone. If the time to zero is less than the line shown in redcolor, the acceleration level is above the required target zone. This zone is denoted as red zone. The zone in betweenthese two zones is marked as orange zone. The three zones are clearly marked on graph namely green zone, red zoneand orange zone. In order to keep the acceleration in green zone the stiffness of Instrument panel should be so used thattime to zero velocity is beyond green dark line point.

Fig. 3 Normalized velocity vs. Normalized time diagram

The methodology to use the static modal for evaluating the headimpact performance of instrument panel is supports withfollowing observations made during virtual validation andphysical testing.

The trend of internal energy shows that internalenergy is of elastic nature.

Many physical test samples do not shows permanentdeformation on plastic part.

Force and moment transfer is through the firmconnections between adjacent parts

The diagram 4 shows the CAE methodology where the static

force is applied to instrument panel model (described in section1.3) at the various locations. The out put parameters are set asdeformation and stresses. The instrument panel stiffness is

evaluated with deformation value.

Fig. 4 CAE methodology flow diagram

This stiffness value is compared with stiffness scale and the point is differentiated in three categories namelyGreen, Orange and Red. The Red point demands the design change where as orange point depending upon its valuemay need design changes.

This methodology is studied with two different configuration of instrument panel model with four head

impact point each are studied. These points are tested for dynamic FMVSS 201/ECE R 21 test. The detailed

comparisons are plotted between the results from static test against dynamic test.


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CAE Model building

The Static analysis model is developed using static model CAE guidelines. The care is taken to modelconnections such as C nut, snaps, locators etc. The variable thickness ribs stiffness is captured using linearinterpolation rule. The static isentropic material properties are assigned with input material constants as Youngsmodulus, poisons ratio and density. The head impact points are identified through section study and head impactmarking procedure described in regulation. It is important to find out the impact angle and area of contact between thehead form and instrument panel. The magnitude of static load is calculated from the desired acceleration level,impactor mass and scale factor function. The force is calculated with following Equation.

Magnitude of Force = Acceleration levelX

mass of impactorX

Scale factor .. Eq. 1

This load is applied to the nodes covering the area of contact. The nodal displacements, nodal stresses arerequested as out put of analysis. The analysis is carried out using Optistruct solver. The stiffness of Instrument iscalculated with following formula,

Stiffness function = (Applied force / Deformation) Xscale factor... Eq. 2

The complete model building, analysis and post processing is carried out using Hyperworks product such asHypermesh 10.0, Optistruct and Hyperview 10.0.

Result Discussion

The following graph presented results of two configuration of instrument panel. On Y axis the normalizedacceleration values corresponding to X axis normalized stiffness are plotted. The blue line shows the stiffness scale.The normalized stiffness is plotted from IP static analysis on the static stiffness scale (shown with blue line) to evaluatenormalized acceleration value. For IP configuration 1 five points are evaluated one point stiffness has normalizedstiffness in red zone, two points are in green zone and two points in orange zone. For IP configuration 2 four points areevaluated one point stiffness has normalized stiffness in red zone, one point is in green zone and two points in orangezone.

The readings from static stiffness methodology are evaluated against virtual FMVSS 201 head impact test.Table 1.1 and 1.2 shows the normalized values in both the test. In addition to this comparison table also addressimportant question judging criteria on scale as Pass or Fail. The results show close agreement between the resultsobtained by virtual dynamic test and results obtained by static scale methodology. The time required to carry out the

static analysis is only 5 % that of dynamic analysis.


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Conclusion

The static stiffness scale methodology shows close agreement with the ECE R 21 dynamic results. Thismethodology can be used successfully in initial design phase where the stress strain curve relation ship at different

strain rates is not available. The advantage computational time offered by static stiffness scale methodology makes iteasy to run DOE with larger matrix in initial level.

Future work

Static stiffness methodology effectiveness can be used in various instrument panel programs to increase itsacceptance in industry. Additionally, physical testing results need to validate with static stiffness methodology.

1.7 References

[1] RADIOSS user manual, Altair Engineering[2] ECE R 21 regulation draft, FMVSS 201 regulation draft

[3] Mechanical Engineering Design by Shigley

[4] IAC internal plastic guide[5] SITA 2010 paper Application of Innovative Numerical Modeling Techniques to Accelerate CAE based

Development Process for Side Pole Impact Test Rig by Atul Rohnge, Nitinkumar Lokhande[6] Burr S., Gras J., Mott J., Jeep Liberty structural IP cockpit module, Presentation on Automotive Cockpit

Modules Conference 2001, March 9 2001, Dearborn, MI, USA.

[7] SAE Paper # 2003-01-1175Interior FittingsA Global View.

[8] SAE J921, June 1965, Instrument Panel Laboratory Impact Test Procedure

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RNL 15 Static Stiffness Scale Methodology Development for IP Head IAC