USE OF HIGH EFFICIENT ENERGY ABSORPTION FOAM IN SIDE IMPACT PADDING Gerhard Slik
Dow Automotive
Germany
圣诞节祝福语英文Gavin Vogel
Dow Automotive
USA
Paper Number 07-0185
ABSTRACT
In side impact events padding is often utilid to not only absorb energy but also push the dummy into motion. The padding is usually applied in the pelvic, the abdomen and the thorax area. The amount of absorption versus push load is important to obtain acceptable levels of the injury parameters as stipulated by legislation (e.g. ECE R95, FMVSS 214) and consumer tests (e.g. EURO/US-NCAP and IIagile
HS). Practice shows many types of foam padding designs which fulfil the requirements, often in combination with side airbags.
In this paper the advantage of applying high efficient energy absorption foams in padding is prented. This enables designers of passive safety systems not only to save space, weight and cost but also increa safety (ratings) by having a better defined and more easily tune-able loading system on the dummy during side impact crashes. Computer Aided Engneering (CAE) simulation methodology can be ud efficiently to optimi part design. A ca showing the benefits of high efficient energy absorption foam padding is discusd.
INTRODUCTION
Side impact crashes are one of the most vere accidents and account for roughly 30% of all fatalities in road accidents involving pasnger cars and light trucks. For this reason, in many countries legislation has been put into place with minimum requirements for injury parameters in side impact crash tests. On top of this, consumer test ratings like Euro-NCAP and insurance testing have generally put higher requirements on side impact crash performance of cars. For example the recent upgrade of the IIHS side impact test in which the deformable barrier impactor has comparable
dimensions to tho of the front of a light truck, giving a much more vere impact collision than it ud to be with the old barrier.
In addition, an increasing consumer awareness of safety is allowing automakers to utilize consumer and insurance test reports as a powerful marketing tool.
In view of all this, the trend of increasing level of passive safety measurements is clear. Even in the lower end vehicle gments, airbags are incorporated more often for frontal and side impact protection. In higher end vehicle gments, active safety systems are being introduced to the market and have found their application. However there is still a large number of vehicles built without side airbags, in specific regions such as North America and emerging markets. Therefore it is still necessary to engineer passive energy absorbing countermeasures utilizing foams solutions to provide occupant protection during side impact collisions.
Since the layout of safety systems greatly influences the design and styling of a vehicle it is important to know the performance of such systems and have a reliable tool for evaluation early in the design stage.
In the prent study the advantage of using high efficient energy absorption foam in side impact prot
ection is prented. First, an example of a recently developed energy absorbing foam is discusd. Then the development of the material models to accurately simulate this material in LS-DYNA is described. Subquently a ca is prented and conclusions are listed.
HIGH EFFICIENT ENERGY ABSORPTION FOAM
The foam considered in the prent paper is a clod cell, styrenic foam, specially developed for energy absorption in automotive applications. It is produced via an extrusion manufacturing process and commercialid under the trade name IMPAXX™ energy absorbing (EA) foam. The continuous extrusion production process ensures a constant quality and a high level of consistency of the material properties. Foam boards are formed in the extrusion process from which parts (pads) can be cut by hot wire or abrasive wire cutting technology. This fabrication technique offers the additional benefit of eliminating the need for
™ IMPAXX is a trademark of The Dow Chemical Company and its subsidiaries.
expensive forming tools associated with traditional foam solutions.
A typical quasi-static stress-strain characteristic
of the foam is depicted in Figure 1.
0123456789100
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
1
Compressive Strain [mm/mm]
C o m p r e s s i v e S t r e s s [M P a ]
Figure 1. Quasi-static stress-strain curve for IMPAXX™ foam.
The stress ramps up rather fast and then remains constant, up to 70~80% compression. From then on the material densifies and the stress increas rapidly. Due to this behaviour, the material can be categorid as high efficient energy absorbing since the stress-strain curve is nearly a block curve and an ideal absorber would show a square wave respon.
In Figure 2, a comparison is given between IMPAXX™, expanded Polypropylene (ePP) and mi-rigid Polyurethane (PUR) foam, all of similar densities.
Figure 2. Compression curves of IMPAXX™ in comparison with ePP and PUR foam for equal density.
Due to the square-wave respon of IMPAXX™ foam it is clear that it is a more efficient solution compared to ePP and PUR foams. This is illustrated in Figure 3 where the efficiency curves of the mentioned materials are shown.
Figure 3. Comparison of efficiency curves.
Increasing the density of ePP or PUR to achieve the same compressive strength of IMPAXX™ foam would, not only increa the effective weight of the EA part, but also speed up the densification, thereby further decreasing their efficiencies. Therefore, besides maximising the energy
absorption and minimising the packaging-space required to absorb a given amount of energy using IMPAXX TM foam, significant weight savings can be realized as well.
Another positive attribute is the stable performance over a wide temperature range as illustrated in Figure 4.
Figure 4. Normalid compressive stress over temperature.
It shows that over a wide temperature range from -35 o C up to 85 o C IMPAXX TM has a constant performance.
MATERIAL MODELS FOR CAE
Becau computer simulations play a big role in modern vehicle development, it is important that trustworthy material models are available. This ction describes briefly the material model validation of IMPAXX TM EA foam.
Parameters for LS-DYNA material model Type 63 (*MAT_CRUSHABLE_FOAM) [1] were identified for each foam grade from drop tower tests with a flat impactor, e Figure 5, to obtain high strain rate stress-strain curves, e Figure 6.
Figure 5. Drop tower test t-up.
The smoothened average compressive stress-strain curves were ud as input load curves for the material models.
0,0
0,2
0,4
0,6
0,8
minkakelly1,0
Compressive Strain [mm/mm]
C o m p r
e
s
s
i v
e
S
t r
e s
s
[
M
P a ]
Figure 6. Average dynamic compressive stress-
strain respons for IMPAXX™.
Pelvic shaped impactor tests, e Figure 7, were performed for validation of the models.
remember的用法>wacFigure 7. Pelvic impactor test t-up.
The tests were done on veral sample
geometries: blocks, cones and pyramids, e Figure 8.
Figure 8. Sample geometries for the pelvic impactor tests: block, cone and pyramid.
Finite element models for the drop tower test, e Figure 9, and the pelvic impactor test, e Figure 10, were created and the tests were simulated.
Rigid Impactor
Foam Block Rigid Support
Figure 9. Finite element model of the drop tower test t-up.
Rigid Pelvic Impactor
Foam Samplealfie
Rigid Wall
Figure 10. FE Model of the pelvic impactor test t-up.
Figure 11 to Figure 14 show simulation results versus tests for IMPAXX™ 700 of drop tower tests and pelvic impactor tests.
Figure 11. Drop Tower Test vs. Simulation for IMPAXX™ 700.
Figure 12. Pelvic impactor tests vs. simulation on 75 mm thick IMPAXX™ 700 blocks.
Figure 13. Pelvic impactor tests vs. simulation
on IMPAXX™ 700 cone samples.
Figure 14. Pelvic impactor tests vs. simulation on IMPAXX™ 700 pyramid samples.
All cas show a very good correlation of the impactor’s load and displacement level between test and simulation. The models can be ud with confidence.
SIDE IMPACT CAE OPTIMISATION CASE
againstIn many cas car manufactures obtain door modules from a supplier who is then also
responsible for the development with respect to safety. In the cas, the door system is required to give a certain load-intrusion characteristic to a rigid impactor. This characteristic is then defined for the pelvic, abdomen and thorax area and is such that it will achieve the appropriate loads during side impact to the dummy to result in the targeted level of injury parameters. Figure 15 illustrates a typical pelvic impactor load-intrusion requirement for a door panel.
Figure 15. Typical load corridor specified for rigid pelvic impactor.
The door module supplier is required to prove the right load-intrusion characteristic by CAE
simulations and by testing. Testing is defined on the door module as follows. A rigid pelvic shaped
impactor hits the door module with a defined initial velocity and the impactor acceleration is recorded. Acceleration and displacement are calculated from the load and thus obtained load versus
displacement must fit in the defined corridor. The test is usually done on a drop tower or on a sled test t-up. Figure 16 illustrates a drop tower test t-up with a rigid pelvic shaped impactor.
Figure 16. Drop tower with pelvic impactor.
The pelvic impactor test t-up of the discusd door module is modelled, e Figure 17 and contains all components of the door, the door-in-white and the rigid pelvic impactor.
Figure 17. Side impact CAE door model.
Starting with a relatively large foam pad, the optimum shape is found by reducing the size and changing the location. The optimum shapes from fabrication point of view are square parts (blocks). Usually the door trim is rather flat which means that if the pad is attached to that side, it also can be flat. Usually the door-in-white has a complex geometry, however if during a side impact crash the barrier starts pushing the car, the door-in-white is pushed and deforms and will move as a flat surface, even if it is not flat in the original position. This means that also on the side of the door-in-wh
ite, the foam padding can be flat. Usually, the whole part can be kept simple and block shaped. For the ca discusd here, the size of the part was optimid, such that the pelvic load respon was in the corridor, e Figure 18.
Figure 18. Pelvic impactor load respon for an optimid foam pad.
In Figure 19 a cross ction of the simulation model at four stages during the pelvic impact is shown.
五年级上册英语人教版跟读软件>经典英文歌Impactor
Door trim
Foam pad
Body-in-whitetuoci
(1) (2)
(3) (4)
Figure 19. Pelvic impactor intrusion; horizontal cross ction through the H-point.
At stage (1) the impactor has just made contact with the door trim, displacement is 0 mm. At stage (2) the impactor has moved further, the load has ramped up and is going towards 8 kN at 20 mm displacement. At stage (3) the impactor has moved 20 mm and the contact area between impactor and foam pad is maximal. When the impactor moves further, the load does not increa significantly; the compression area is constant and the stress level is constant until the foam enters the densification area at about 70% compression. This means that up to that point a nearly perfect load control is possible, e Figure 18.
This ca illustrates a relatively easy method of optimizing the part design of an energy absorbing foam countermeasure pad using an efficient solution such as IMPAXX TM foam.
