假人dummy

Finite Element Modeling of the Small Side Impact Dummy: SID-IIs AUTHORS: Fuchun Zhu, York Huang, Steve Moss First Technology Safety Systems, Inc. 47460 Galleon Drive Plymouth, MI 48170 USA Abstract This paper presents the development and validation of the new FTSS finite element model of SID- IIs dummy for both LS-Dyna and Pamcrash solvers. The SID-IIs FE model faithfully represents the current design (level-C) of physical dummy hardware from head to toe. It includes all the hardware components, accelerometers, load cells and linear potentiometers to measure rib deflections. Pro-Engineer CAD data was used in the model geometry creation. Nine common materials were used in the model, and their performance has been proved stable in the other FTSS dummy models. Totally the SID-IIs model consists of about 47,000 nodes and over 65,000 elements (Figure 1). The minimum time step has been controlled as 1.03 µs. Validation of the model has been done on various levels, which includes material and component tests, such as standard SID-IIs head drop test, lateral neck flexion test, Rib drop test, arm drop test, and pelvis plug drop test, and full body calibration tests on different areas, such as shoulder, thorax, abdomen and pelvis. The model was finally validated against the sled test data. The criteria for model validation accuracy were controlled at less than 10% off on component level, and 15% on full body dummy level. The model showed stable and robust performance with reasonable accuracy in prediction. Details about model development and validation will be presented in this paper. Introduction SID-IIs, the small side impact dummy, is the smallest side impact crash test dummy currently available in the market, representing the anthropometry of a small female or a thirteen-year-old child. It is designed specifically to evaluate the performance of advanced occupant protection systems, such as side air bags, in automotive side impact situations. For the past two years the IIHS, Insurance Institute for Highway Safety, has been using the SID-IIs dummies to evaluate the automobile crashworthiness and safety ratings on a wide range of brands, which makes the SID-IIs dummy the hottest topic in the automotive safety industry. The primary objective of this modeling project is to develop and validate a finite element (FE) model of the SID-IIs dummy, which can be used in the safety related automobile industry to accurately predict injury criteria in various crashworthiness and safety applications. With its accuracy, robustness, and repeatability the model should serve a virtual tool for the industry to reduce the lead time and testing cost in the new vehicle development process. Figure 1 Assembled SID-IIs Finite Element Model Modeling Approaches For the past eight years FTSS has dedicated to develop a vigorous modeling methodology for all of its FE dummy models from child to adult dummies. The development of SID-IIs dummy model is an example of this proven methodology [1]. The first and crucial step is the accurate geometry representation of each dummy component, which can be done relatively easier than before by employing CAD surface data, such as Pro-Engineer models. Most of the SID-IIs dummy model components were directly created based on Pro-E surface and line data to ensure the faithful geometric representation. These components include head, neck, ribs, thorax spine box, arm foam and steel insert, pelvis foam and casting, as well as upper leg and lower leg foam. There are a few components which have to be digitized using a 3-D digitizer to get the surface data, such as shoe, foot, and some other parts. Engineering drawings are also used to create some regular shaped components. Hypermesh [2] is the major tool used in this phase of model geometry building. After all the component geometric models have been built and verified, the second step is to assemble them together to form sub-assemblies and then the whole dummy assembly according to specifications required by the relevant sub-assembly and whole dummy. These specifications include: locations and orientations of head CG, neck bracket, pivot joints, H-Point, loadcells and accelerometers, as well as dimensions of dummy seating height, and all the other external dimensions. The third step in dummy modeling is to assign the suitable material models and properties to individual dummy components. The same or similar material modeling concepts have been employed for the SID-IIs model as for the previously developed FTSS Hybrid III family dummy models: all the metal parts except for steel ribs are modeled as rigid bodies such as spine box, pelvis casting, and limb internal bones; all the deformable soft parts such as pelvis molded foam, limb flesh foam, head vinyl skin and neck rubber, are represented by nine common material models. Revolute joints or spherical joints are employed to represent each of the dummy physical joints. In the SID-IIS dummy model the condyle joint is a special one, which has stiffness characteristics. All the other joints are 1-G friction joints. Loadcells have been simplified as BEAM (in LS-DYNA) or SPRING (in Pamcrash) elements to measure all six possible channels of load, namely three moment outputs and three force output. Accelerometers are defined as ELEMENT _SEATBELT_ACCELEROMETER (in LS_DYNA) or through local coordinate node output blocks THLOC (in Pamcrash). Rigid BEAM or BAR elements are extensively used to represent local coordinate axis of loadcells, accelerometers and joints for better visualization. Special positioning tree structures have also been created for the following Pre-Processors: Hypermesh, Easicrash [3] and Primer [4]. Users can easily position the whole dummy or just limbs by using any one of the above mentioned Pre-processors. The next step of the dummy modeling is to first validate the sub-assembly models against test data, then the whole dummy assembly. This is the stage when the fine tuning of the material model/properties has to be performed to get better correlations between dummy model predictions and test data. The following section will describe the details of testing and validations. Test Designs In addition to the standard certification tests, special tests for FE modeling had to be carefully designed to collect data in terms of material properties and component performances. Based on these collected test data the dummy component models are to be validated. These tests were designed to be as simple as possible to avoid introducing complication to the model validation process. • Material tests There are three types of commonly used soft materials in a physical dummy: Ensolite foam, molded rubber, and molded vinyl. Material properties have to be extracted for all these materials. A set of tests with three different drop speeds were conducted to test out the soft Ensolite foam. Based on the sample size, drop head force and drop head displacement, the engineering stress/strain curve was constructed, which would be used in the FE model as the Ensolite foam was defined as low density foam material. The visco-elastic behavior of the rubber and vinyl had to be determined through dynamic frequency sweep tests, stress relaxation tests and shear tests. From all these test data the long term and short term shear modulus can be determined. Since SID-IIs dummy shares many parts with the Hybrid III 5th percentile (h3-05) female dummy such as head, neck, upper leg, lower leg, foot, shoe and ensolite foam pad, the material testing results for above mentioned three materials of h3-05 dummy can be used for SID-IIs dummy model. These shared components can be directly imported into the SID-IIs model from the previously developed and validated h3-05 dummy model. Of course the validation still has to be done to fulfill the specific requirements of the SID-IIs dummy. • Head Drop Test The Figure 2 shows the SID-IIs head drop test setup. This is a standard certification test [5]. Figure 2 SID-IIs Head Drop Test setup The head is released from a height of 7.87 inches (200 mm) to impact onto a rigid flat surface with a speed of 2 m/s. The major criterion of this test is that the head CG resultant acceleration falls between 115 and 145 g’s. Please note that there is an angle of 35 degrees between the horizontal plane and the head sagittal plane. • Neck Calibration Test The lateral neck pendulum impact test is also a standard calibration test. The Figure 3 shows the test fixtures and test setup. Figure 3 SID-IIs Neck Calibration Test Setup In this test a head form has to be used instead of the real SID-IIs dummy head. The head form is designed to have the same moment-inertia properties as the real dummy head. In this way the instrumentation can be easily mounted onto the head form. Since the dummy neck is not symmetric about the impact middle plane, this lateral impact test will observe the neck twisting mode instead of pure bending mode. The test performance specifications include impact velocity, timing of pendulum pulse, maximum D-plane rotation, neck moment, and others. For more details please refer to the SID-IIs dummy user manual [5]. The following four tests are specially designed for the FE model development purpose. More details regarding these tests can be found in the SID-IIs FE model component report [6]. • Arm Drop Impact Test The simplified SID-IIs upper arm is constructed of a steel weldment tube molded with foam and vinyl layers. The arm will often get caught between vehicle door trim and dummy upper torso in a side impact test. So it is important to validate the arm foam properties. In this test the arm was fixed to a rigid flat surface with two pieces of double-sided tape. A drop head weighing 4.56 kg was released from different heights to impact onto the arm vinyl-foam surface at different velocities. The test data were then examined to determine if the maximum compression had been reached before the foam material bottomed out. A stress-strain curve was then generated from the test data of 3.8 m/s speed. The Figure 4 shows the arm drop test setup. Figure 4 SID-IIs Arm Drop Test Setup • Thorax Rib Test This test is designed to determine the stiffness characteristics of the rib sub-assembly with damping material. The rib deflection and drop head acceleration were recorded major parameters. Two series of drop test were performed on a sub-assembly containing the spine box, ribs, damping material strips, rib stiffeners and rib bibs. The first series was to test the single rib (middle thorax rib) with two impact speeds of 3 m/s and 4 m/s. The drop head weight for this series tests was 3.3 kg. The second series was to test the three thorax ribs together also with the same two speeds. The drop head weight for the second series tests was 8.3 kg. The Figure 5 shows the test setup for the three rib drop test. Figure 5 SID-IIs Three-Rib Drop Test Setup • Lumbar Spine Pendulum Impact test As pointed out above the lumbar spine pendulum impact test is also a unique test designed only for the SID- IIs FE model development since the lumbar spine performance calibration test is not required by the SID-IIs dummy specifications. Figure 6 SID-IIs Lumbar Spine Flexion Test Setup Standard neck pendulum test fixtures were used for the lumbar spine flexion pendulum test. The SID-IIs lumbar spine was connected to the pendulum through a loadcell on one end, and connected to a mass structure on the other end. As usual two impact speeds were excised at 3.45 m/s and 5.15 m/s. Loadcell force, moment, pendulum acceleration, and lumbar spine rotation were recorded major parameters. The Figure 6 shows the test setup for the lumbar spine flexion test. • Pelvis Plug Drop Test Pelvis plug is made of low density foam. It is inserted in the pelvis acetabulum hole and transmits load to the acetabulum loadcell upon a side impact. Since it is subject to permanent deformation after the impact, the pelvis plug has to be replaced after each test. This drop tower test was to collect data of force- compression relationship of the pelvis foam plug. A series of drop tests were conducted at different speeds to reach the maximum engineering strain of about 85% before the pelvis plug bottomed out. Drop head acceleration was the only recorded parameter. The test data at 9 m/s were use to construct the stress-strain curve, which is implemented in the model. The Figure 7 shows the setup of pelvis plug drop test. Figure 7 SID-IIs Pelvis Plug Drop Test Setup The following four whole dummy pendulum tests are standard certification tests required by SID-IIs dummy specifications. FTSS test database was used in the model validation tests for all these four standard certifications. The following summarizes the four test setup requirements. For more details about these four tests please refer to the SID-IIs dummy user manual [5]. • SID-IIs Shoulder Pendulum Impact Test The SID-IIs dummy with pants but without jacket sits on top of two sheets of 2 mm thick Teflon supported by a flat rigid surface. The dummy arm has to be positioned 90 degrees relative to the vertical plane. The left side impact pendulum weighing 13.97 kg is to impact at the center point of the shoulder plug at a speed of 4.5 m/s. Major criteria are the shoulder rib deflection and probe force calculated from the product of pendulum mass and pendulum acceleration. The Figure 8 shows the test setup. Figure 8 SID-IIs Shoulder Impact Test Setup • SID-IIs Thorax Pendulum Impact Test The same procedure of dummy preparation and seating as for the shoulder impact test has to be observed in the thorax impact test except that the arm has to be removed and thorax ensolite pad has to be installed. The same impact pendulum is used, and the differences between these two tests are the impact location and impact speed. For the thorax impact test the impact point is on the center of the middle thorax rib, and the impact speed is 4.3 m/s. More performance specifications are required, which include spine accelerations and rib accelerations. The Figure 9 shows the thorax impact test setup. Figure 9 SID-IIs Thorax Impact Test Setup • SID-IIs Abdomen Pendulum Impact Test For the abdomen impact test the impact location is lowered to the center point between two abdomen ribs. The wood impact pendulum head has to be used with a smaller diameter. The total weight of the pendulum is still kept at 13.97 kg. The impact speed is 4.5 m/s. Similar performance specifications as for the thorax impact test are required. • SID-IIs Pelvis Pendulum Impact Test The last standard whole dummy certification test is the pelvis impact test. The same pendulum as for the shoulder test is used here. The impact speed is 6.7 m/s, and the impact location is at the center point of the pelvis plug. Only two parameters are required as for the performance criteria: the impact force and pelvis y-axis acceleration. • SID-IIs Rigid Seat Sled Test In addition to above mentioned tests, one last test is to test the whole dummy in the sled situation. The test was conducted at VRTC at impact speed of 6.7 m/s (15 mph). The test severity is very high since no restraint system has been applied to the dummy. High rib deflections are observed. Various data channels were recorded during the sled test. The SID-IIs dummy model was excised to correlate most important injury criteria. Component Validations This section describes the component model validation results such as head, neck, arm, thorax ribs, lumbar spine, and pelvis plug. • Head The SID-IIs head comprises a vinyl skin, which fits over a cast aluminum skull. The rear of the skull is detachable to allow access to the inside of the head. A tri- axial accelerometer is mounted at the center of mass of the head. The skull geometry and the geometry of the external surface of the skin were obtained by scanning physical components. The location of the accelerometer set was taken from drawings. Material properties were derived from FTSS Free Motion Head Form model with modification to fit the calibration test. The skull was modeled as rigid shell elements. The vinyl skin was modeled using two layers of visco- elastic solid elements with a single integration point. There is mesh connectivity between the skin and the skull. The inertia properties of the skull were calculated from a geometrically accurate solid model of the skull. Lumped masses were added to the shell skull model until the mass and inertia properties were correct (Figure 10). Figure 10 SID-IIs Head Model (half cut) The head assembly was then tested under the standard certification test condition: 2 m/s drop speed with an angle of 35 degrees relative to the impact surface. Figure 11 shows the orientation of the model at the beginning of the event. Figure 11 SID-IIs Head Drop Test Figure 12 shows the correlation of acceleration to the test data. The acceleration magnitude is shown here: solid green line stands for test result, and dotted red line represents the model prediction. The acceleration components are measured in the head’s local coordinate system, not in the global coordinate system. Figure 12 SID-IIs Head Drop Test Correlation It is obvious that the model predicted the peak acceleration quite well in both magnitude and timing. But the loading and uploading duration is shorter in the model prediction. The discrepancy was caused by the limitation of VISCO_ELASTIC material model used to define head skin. Now FTSS is working with a more promising material model: OGDEN_RUBBER in both LS-DYNA and Pamcrash to overcome this discrepancy. An updated version of SID-IIs head model will be available in the near future. • Neck The SID-IIs neck, the same as H3_05 neck is a butyl rubber piece and aluminum segmented assembly, with an internal steel cable to limit neck stretching and increase durability. Each rubber disc has a partial-depth horizontal slit on the anterior side. This results in a less stiff response in neck extension (head bends back) than in flexion (head bends forward). Each slit has a different depth. The butyl rubber material properties were modified slightly based on the original H3_05 neck properties, which were derived from the standard H3_05 neck calibration test. When incorporated in the SID-IIs model, these properties gave accurate results in lateral pendulum impact tests. The aluminum discs were modeled as rigid solid elements. The rubber discs were modeled using visco- elastic solid elements with 8-point full integration. The steel cable was modeled as elastic beam elements with contact defined between the cable nodes and segments on the aluminum discs. To represent the diameter of the physical cable, the diameter of holes in the aluminum discs was reduced by adding rigid solid elements. The completed model is shown in Figure 13. The validation of the neck model was performed using the standard SID-IIs neck calibration test (Figure 14). The tests were performed at the standard velocity of 5.61m/s. The deformation of the neck during the lateral test is shown in Figure 15. Figure 16 and Figure 17 show the correlation of loadcell moment and shear forc