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Development of Advanced Dummy and Barrier Models for Passive Safety
Simulation
Conference Paper · August 2011
DOI: 10.13140/2.1.4840.6401
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2011 中国汽车安全技术国际研讨会
Development of Advanced Dummy and Barrier Models for Passive Safety
Simulation
Marc Schrank, Sridhar Sankar
Dassault Systèmes Simulia Corp., Providence, RI, 02886, USA
marc.schrank@3ds.com, sridhar.sankar@3ds.com
Abstract: The role of design simulation in the Automotive industry is becoming increasingly important,
necessitated by economic and competitive pressures as well as more demanding design requirements, and fueled
by the ever-growing availability and capacity of high performance computing accompanied by the increasing
sophistication of simulation software. Passive safety simulation already plays a prominent role in vehicle design,
at most Automotive OEMs already consuming the majority of cpu cycles available for structural design
simulation. However, the need to further improve passive safety simulation persists, to meet more stringent
passive safety regulations while also further reducing the reliance on physical prototypes and associated testing.
Crash test devices, such as crash test dummies and deformable barriers, play important roles in assessing a
vehicle’s crashworthiness, and hence accurate models for these devices are needed in order to achieve the overall
required level of design simulation accuracy. Two examples are discussed, including technical highlights from
each that enable accurate, yet efficient simulation for these devices under crash loading conditions.
Keywords: Passive Safety Simulation; WorldSID; Dummy Model; Barrier Model; Crashworthiness
1
Introduction
Automotive passive safety requirements continue to evolve, with stricter requirements to protect both
occupants and pedestrians being enacted throughout the world [1] [2]. Simulation has served an
important role in achieving the level of safety in modern cars and light trucks; Spethman et al. point
out that certain developments in the area of passive safety would not have been possible without the
availability of simulation [3]. Various factors, including economic and competitive pressures, are
causing a greater reliance on simulation in the design of vehicles. For example, BMW Group have set
an objective to largely eliminate physical prototypes and associated physical tests from the vehicle
design and development process, and in order to do so, the “predictiveness” of passive safety
simulation is a key factor [4].
Crash test devices, such as dummies, barriers, and other impactors, play important roles in assessing
passive safety. For instance, instrumentation built into a crash test dummy accumulates data from
dozens of sensors in the dummy during the crash test, and these data directly contribute to the safety
rating assigned for the vehicle being tested. Hence it is clear that in order to achieve what is now being
required from design simulation, all components in the simulation, including models representing the
crash test devices, must be of high fidelity. Any “weak link” in the simulation will compromise the
overall accuracy and predictiveness that is required. Two examples (dummy model, barrier model) are
presented in which the level of fidelity achieved is commensurate with the vehicle model itself.
2
WorldSID 50th Percentile Dummy Model
The WorldSID family of hardware dummies has been developed for the purpose of achieving
technologically advanced side impact dummies which exhibit greater biofidelity than presently
available side impact dummies, and which will eventually replace existing side impact dummies used
in testing regulations around the world[5] [6]. WorldSID 50th, representing a 50th percentile male,
incorporates advanced materials and constructions in order to attain the desired higher level of
biofidelity; for example the super-elastic alloy, Nitinol, is incorporated in the rib cage construction in
order to better approximate behavior of the human rib cage due to loading in a side crash event.
In 2006 the Partnership for Dummy Technology and Biomechanics (PDB), a consortium comprised of
the German automobile manufacturers (Audi, BMW, Daimler, Porsche, Volkswagen), initiated a
project to develop a finite element model for the WorldSID 50th dummy in conjunction with the
developers of three crash simulation software packages. Dassault Systèmes SIMULIA have
collaborated with the PDB to develop the WorldSID 50th model for Abaqus/Explicit [7].
The sophistication of the WorldSID hardware, along with the strong requirement to create a high
fidelity model for the dummy, have necessitated a large suite of physical calibration tests to be
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2011 中国汽车安全技术国际研讨会
designed and executed. In all, nearly 300 separate physical calibration tests have been carried out,
ranging from material coupon tests, to component, subassembly and full dummy tests; more than 150
of these tests have been for the component level and higher.
Certain advanced features in Abaqus/Explicit have been invoked in the WorldSID 50 th model in order
to provide for accurate, yet efficient simulation of pertinent behaviors in the hardware dummy. Two
examples are highlighted below.
1. The hardware dummy itself includes several joints (shoulder, hip, knee,…) intended to
replicate the corresponding joints in the human body. Connectors elements in Abaqus provide
an efficient means to model such joints or mechanisms, in a two-node discrete construction
accommodating for both the relative motion allowed in the joint (such as a hinge), as well as
complex kinetics or constitutive behavior that can be associated with the joint (Figure 1a).
Connector elements are also used to model the instrumentation in the dummy (accelerometers,
load cells,…).
2. The rib cage assembly in the hardware dummy includes a damping material intended to
provide for a more realistic dynamic motion of the ribs when subjected to sudden impact
loading in a crash event. Continuum shell elements are used to model this damping material;
they have the geometry of three-dimensional solid elements, but with kinematic and
constitutive behavior similar to shell elements. This readily allows for one element to be used
to discretize the small, but varying thickness of the damping material (4-7mm), and still
account for contact interactions that can develop in this region of the model.
(a) Connector elements
Fig. 1
(b) Continuum shell elements
Usage of connector elements and continuum shell elements in WorldSID model
Development of the WorldSID 50th model has required validation against the numerous physical
calibration tests previously mentioned. Figure 2 shows a sampling of the subassembly and full dummy
tests carried out.
(a) Rib cage test
(b) Full dummy pelvis pendulum test
Fig. 2
Sampling of WorldSID model validation tests
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(c) Full dummy sled test
2011 中国汽车安全技术国际研讨会
Selected results from one of the full dummy tests are shown in Figure 3. This is also a certification test
for the dummy hardware and hence the measured dummy response in the physical test has to fall
within prescribed corridors (denoted by the orange horizontal lines in the plots).
Fig. 3
Comparison of physical test and simulation results for full dummy shoulder pendulum test
Following nearly four years of development effort, Version 2 of the Abaqus WorldSID 50th model has
been approved by the PDB in late 2010, and the model is presently available to be used in conjunction
with Abaqus/Explicit for production passive safety simulation.
3
European Enhanced Vehicle-Safety Committee Frontal Offset Deformable Barrier
(EEVC ODB) Model
The EEVC ODB is one of several different deformable barriers utilized in frontal, side, and rear crash
testing regulations throughout the world. These barriers are intended to approximate the profile,
“impact stiffness”, and energy absorption characteristics of another vehicle, and are typically
comprised of aluminum honeycomb construction with aluminum cladding bonded to the outer surfaces.
Gross deformations and failure of both the honeycomb and cladding generally characterize the
response of such barriers in a crash test (Figure 4).
Fig. 4
Typical crash barrier deformations
SIMULIA and BMW are collaborating to develop a new generation of crash barrier models in order to
provide for greater accuracy and fidelity. The collaboration also includes design and execution of a
physical calibration testing program, ranging from material tests to component tests and full barrier
calibration tests. The tests are designed to: yield deformations similar to those in vehicle crash
scenarios; demonstrate repeatability; and demonstrate consistency, with separate measurements of
force and acceleration producing similar results.
Due to computational limitations, earlier generations of finite element models for crash barriers
typically used solid elements to represent the honeycomb structure in a “smeared” manner, though the
honeycomb cells themselves are formed by thin aluminum sheet. With the continuing expansion of
computing performance and capacity, it is feasible to revisit the modeling approach for the honeycomb
structure in order to better capture its characteristic deformation behavior in a crash event.
The approach taken in the new generation of barrier models for Abaqus/Explicit is to consider the
honeycomb cell construction using a conventional shell element discretization, However, in order to
achieve a reasonable level of computational efficiency, the honeycomb cell size is considered 3.5x
larger in the model than in the physical barrier.
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2011 中国汽车安全技术国际研讨会
Properties for the honeycomb are calibrated from physical tests of the honeycomb structure (static and
dynamic compression), as well as from component and full barrier test results. For example,
quasi-static compression of a honeycomb block is shown in Figure 5. Experimental data show a
plateau of crushing strength is quickly reached as deformations in the experimental specimen localize.
Further compression propagates the localized deformations, maintaining the crushing plateau until
final compaction of the honeycomb block finally occurs. The finite element model for the honeycomb
is calibrated to produce similar results; localized deformations (depicted in red), along with correlation
against the observed experimental crushing plateau, are shown in Figure 5.
Fig. 5
Quasi-static honeycomb block compression
Dynamic compression of the honeycomb can cause air entrapment in the honeycomb cells, visible
both in homogeneous compression tests as well as full barrier tests, which can lead to a pronounced
stiffening effect. To account for this stiffening effect, the EEVC barrier model also includes connector
elements in each column of honeycomb cells. These connector elements then incorporate a
constitutive model corresponding to the adiabatic compression law for air, along with nonlinear
damping behavior for rate effects. The connector elements monitor the compression of each column of
honeycomb cells, and apply a resisting force according to the prescribed constitutive model.
Figure 6 shows a sequence of images from the full EEVC barrier calibration test, along with a
comparison of experimental data and simulation results for the time history of normal force exerted by
the barrier on the impacting sled.
Fig. 6
4
EEVC full barrier calibration test
Optimization
Calibration for both the dummy and barrier models provides opportunities to invoke optimization
methods in order to most efficiently arrive at the combination of model parameters that produce
solution results to best match the experimental data. In particular, material model parameters can be
optimized in an iterative and automated manner.
An example is for the WorldSID 50th model, which includes a number of rubber-like materials. These
materials are generally considered as hyperelastic, and in some cases rate dependency is also
important to consider. In such cases, viscoelasticity is used to account for the rate dependency, using a
Prony series expansion for the dimensionless relaxation modulus. Using the Isight software from
Dassault Systèmes, an optimization “sim-flow” is constructed using the Prony series terms as design
variables (Figure 7). A sequence of Abaqus analyses, representing various loading rates both in tension
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2011 中国汽车安全技术国际研讨会
and compression, are inserted in the same Isight optimization sim-flow, and the resulting simulation
responses are matched against the test data using the available “Data Matching” component within
Isight. Various statistical measures are used to quantify the level of correlation between the simulation
and experimental curves and to arrive at the optimal parameters that yield the best correlation.
Fig. 7
5
Optimization workflow for calibration of viscoelastic material parameters
Summary
Greater accuracy requirements for passive safety simulation places associated accuracy requirements
on all components of such simulations, including those for the models used for crash test devices, such
as dummies and barriers. The continuing growth of high performance computing, along with ongoing
advances in the sophistication of simulation software, enables a reassessment of modeling techniques
and construction. The WorldSID 50th percentile dummy and EEVC offset deformable barrier (ODB)
are presented as two examples where modern modeling features are being employed to achieve greater
accuracy.
Connector elements available in Abaqus/Explicit are used for a variety of purposes in the WorldSID
model and EEVC ODB model. They are used for modeling various joints and mechanisms in the
dummy model, as well as for measuring pertinent results, such as forces, accelerations, and intrusions.
They are also used in the barrier model to account for the stiffening effect that air entrapment and its
subsequent compression have on the response of the barrier to impact loads.
For both the dummy and barrier models, optimization methods are employed in order to facilitate the
calibration of material model parameters. Invoking such methods is done in an automated manner, and
is very efficient in arriving at the combination of material model parameters that exhibit the best
correlation between simulation results and experimental calibration data.
Acknowledgements
The authors wish to acknowledge the Partnership for Dummy Technology and Biomechanics (PDB)
for its collaboration in the development of the WorldSID 50th percentile dummy model, and BMW for
its collaboration in the development of the EEVC ODB model.
References
[1]
[2]
[3]
[4]
[5]
[6]
[7]
National Highway Transportation Safety Administration, http://edocket.access.gpo.gov/2008/pdf/E8-30701.pdf.
European New Car Assessment Programme, www.euroncap.com.
Spethmann P., Herstatt C., and Thomke S. (2009), “Crash simulation evolution and its impact on R&D in the
automotive applications”, Int. J. Product Development, Vol. 8, No. 3, pp. 291-305.
Lescheticky J., Hooputra H., and Ruckdeschel D., “Predictive Crashworthiness Simulation in a Virtual Design Process
without Hardware Testing”, SIMULIA Customer Conference, Providence, RI, USA. May 2010.
International Organization for Standardization: Internatinoal Standard 15830; Road Vehicles; Design and performance
specifications for the WorldSID 50th percentile male side-impact dummy; Geneva; 2005.
Louden A., “50th Male WorldSID Test Results in FMVSS214 Test Conditions & ES-2re Comparisons”, February 2009,
http://www.nhtsa.gov/DOT/NHTSA/NRD/Multimedia/PDFs/Public%20Paper/SAE/2009/Louden%202009%20SAE%2
0Worldsid.pdf .
Gehre, C., Taylak E., Oancea V., Stahlschmidt S., Gromer A., Berger A., and Thibaud C., “Development of a
computational model of the WorldSID 50th male, ESV-Paper, Stuttgart, 2009.
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