Comparison of Experimental Results with FEM for Impact Response by rjj75795

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									                                                                                                  ISSN 0386-1678

                   Report of the Research Institute of Industrial Technology, Nihon University
                                                Number 90, 2007




 Comparison of Experimental Results with FEM for Impact Response
 Behavior of CFRP Tubes and CFRP/Al Hybrid Beams for Absorbing
    Impact Energy in Full-lap and Side Collisions of Automobiles

                          Hyoung-Soo KIM*, Goichi BEN** and Nao SUGIMOTO***


                                            ( Received March 30, 2007 )


                                                       Abstract

       Carbon fiber reinforced plastic (CFRP) laminates are used in various industrial fields because they
    have excellent properties of a specific strength and a specific stiffness. The CFRP has a potential of weight
    reduction in the automotive structure which can contribute to the improvement of mileage as well as the
    reduction of carbon dioxide. On the other hand, the safety issue in case of collision should be also clarified
    when employing the CFRP as automotive structures. In the automotive industry, try and error systems are
    adopted to design automobiles. This system is disadvantageous concerning cost and time. Therefore, the
    reliable simulation technology has been required. The objective of this study is to establish the simulation
    technology for impact response behavior of rectangular CFRP tubes and Al guarder beams reinforced with
    the CFRP under full-lap and side collisions. We adopted drop weight impact tests to investigate impact
    response behavior and impact energy absorption characteristics. Impact tests were carried out by dropping
    the impactor from the height of 12 m. Impact speed was approximately 55 km/h just before the impact. A
    finite element (FE) model was also developed by using a nonlinear, explicit dynamic code LS-DYNA and
    PAM-CRASH to simulate the impact response behavior of the rectangular CFRP tubes and Al guarder
    beams reinforced with the CFRP under impact load. In case of the rectangular CFRP tubes, the comparison
    of experimental results with that of FEM for the load-displacement curves was favorable. The maximum
    load, absorbed energy and final displacement calculated by FEM model were in good agreement with the
    average values of the impact test results. Furthermore, the experimental relations of impact load to the
    displacement for the CFRP/Al hybrid members with different thicknesses of CFRP showed good agreement
    with those of numerical results. These results show that the numerical method developed here is useful for
    estimating the impact response behavior of CFRP/Al hybrid beams.

    Keywords: Impact response, Rectangular CFRP tube, CFRP/Al hybrid beam, Collision experiment, FEM
              analysis



* Part-Time Lecturer, Department of Mechanical Engineering, College of Industrial Technology, Nihon University
** Professor, Department of Mechanical Engineering, College of Industrial Technology, Nihon University
*** Master’s Course, Mechanical Engineering, Graduate School of Industrial Technology, Nihon University


                                                      –1–
                                     Hyoung-Soo KIM, Goichi BEN and Nao SUGIMOTO



                     1. Introduction                              2. Impact Response Behavior of Rectangular
                                                                      CFRP Tubes for Front Side Members
   It is well known that CO2 emitted from passenger
                                                               2.1 Experiment
vehicles is one of major causes of global warming. The
most effective method to reduce CO2 is to manufacture
                                                                  Rectangular CFRP tubes with two ribs were manu-
fuel efficient automobiles. Improvement of the auto-
                                                               factured from unidirectional prepregs (P3052s-20, Toray
mobile fuel efficiency can be realized by reducing the
                                                               Industries, Inc.) by using the sheet winding method.
automobile weight using lightweight materials such as
                                                               Configuration of the rectangular CFRP tube is shown
composite materials. Carbon fiber reinforced plastics
                                                               in Fig. 1. Stacking sequences of the main and rib parts
(CFRPs) have been widely used in aerospace industries,
                                                               in the rectangular CFRP tubes were [(0/90)6 /0]S and
industrial goods and other application fields because of
                                                               [0], respectively. An initial imperfection with an exter-
their high specific strength and high specific modulus
                                                               nal bevel type was introduced in order to get a stable
compared with conventional metals. This means that
                                                               progressive failure behavior.
the CFRP can contribute to reduce the weight of auto-
                                                                  We adopted drop weight impact tests to investigate
mobiles significantly.
                                                               impact response behavior and impact energy absorp-
   Besides reducing the weight, the safety of auto-
                                                               tion characteristics of the rectangular CFRP tubes. The
mobiles is also a very important issue which needs
                                                               impact tests were carried out by dropping the impac-
to be investigated along with the reduction of weight.
                                                               tor from height of 12 m (Fig. 2(a)). The mass of the
Collision safety of the automobile was evaluated by
                                                               impactor was 105 kg. Also, the impactor speed was
full-lap frontal crash, offset frontal crash and side impact
                                                               approximately 55 km/h just before the impact. The
tests. In the frontal crash test, it is possible to absorb
                                                               impact load was measured from a load cell under the
energy by large deformation of the front and the rear
                                                               specimen which was mounted on metallic base (see
parts of automobiles. With increasing interests in reduc-
                                                               Fig. 2(b)). In order to investigate the progressive failure
ing the automobile weight and securing the safety of
                                                               mechanism of the rectangular CFRP tubes, a high speed
passengers, extensive research was performed in the
                                                               camera was employed.
recent years for front and rear collision impact1) ~ 6).
However, in the case of the side impact test, it is hard
to absorb energy in the same way as the frontal crash,
because the survival space of passengers is very narrow.
Present door guarder beams made of steel are used
inside the door for absorbing impact energy and their
deformation is limited to about 150 mm.
   In this study, we developed rectangular CFRP tubes
with two ribs and CFRP-Al hybrid beams as impact en-
                                                                            Longitudinal direction




ergy absorption members for full-lap and side collisions.
                                                                                                     Initial imperfection
Drop weight impact tests were carried out to investigate          300mm                                                     Rib : r =5mm
impact response behavior and impact energy absorp-
tion characteristics of the rectangular CFRP tubes and                                                       50mm
                                                                                                             50mm
                                                                                                                              115mm
                                                                                                                              115mm
CFRP-Al hybrid beams. A finite element (FE) model
                                                                                                        5mm
                                                                                                        5mm
was also developed by using the nonlinear, explicit
dynamic code LS-DYNA and PAM-CRASH to simulate
the impact response behavior and absorbed energy of
the rectangular CFRP tubes with two ribs and CFRP-Al           Fig. 1 Configuration of the rectangular CFRP tube with
hybrid beams under impact loading.                                    two ribs




                                                           –2–
    Comparison of Experimental Results with FEM for Impact Response Behavior of CFRP Tubes and CFRP/Al Hybrid Beams
                         for Absorbing Impact Energy in Full-lap and Side Collisions of Automobiles




                                                                                   2.2 Finite element modeling

                                                                                   2.2.1 Details of FEM model
           Added
           mass


                                                                                      In our previous study7), to simulate the progressive
                                     Impactor
                                                                                   failure behavior and absorbed energy of the rectangular
                                                                                   CFRP tubes with two ribs under impact loading, a finite
                                                                                   element (FE) model was developed by using the nonlin-
                          (a)                                                      ear, explicit dynamic code LS-DYNA. In our previous
                                                                                   FEM model (designated as Model 1), the rectangular
             Specimen
                                                                                   CFRP tube with two ribs was modeled by 24 and 44
                                                                                   layers, respectively. Stacking sequences of the main
                                                                                   and rib parts were [(0/90)6/0]S and [010/(0/90)6/0]S,
                                                                                   respectively. There were 8,125 elements and 8,316
                                                                                   nodes in the Model 1.
                                                                                      In this study, in order to actually model the rectangu-
                                     Load cell
                                                                                   lar CFRP tube with ribs, a T-shape rib part is modeled as
                          (b)                                                      shown in Fig. 3 (designated as Model 2). Furthermore,
Fig. 2 Tower drop impact test setup (a) impactor (b)                               the FEM model improved the Model 2 is revised as
       mounted specimen                                                            shown in Fig. 4 (designated as Model 3). The stacking

                                                                          5 mm
                                    Mass of impactor
                                       : 105 kg                                                 Rib part : 3.9 mm
                                                                                                Stacking sequence: [0]
                                    Drop speed : 55 km/h



                                                                                            y

                                                                                                    x
                                                 Longitudinal direction




                                    300 mm



                                                                                                        [(0/90)6/0]S
                                                                               z
                                                                           y       x

                                                                          Only axial displacement
                                z                                         permitted
                                                                          Perfect clamped
                                     x

                         Fig. 3 Details of the finite element model of 1-layer model (Model 2)




                                (a) Model 2                                                             (b) Model 3
                                    Fig. 4 Details of its top part in Model 2 and Model 3



                                                                          –3–
                                         Hyoung-Soo KIM, Goichi BEN and Nao SUGIMOTO



sequences of the main and rib parts in the Model 2               2.2.2 Boundary and contact conditions and failure
and Model 3 were [(0/90)6 /0]S and [0], respectively.                  criterion
The elements and nodes of the Model 2 and Model 3
were 9,656 and 9,784, respectively. The impactor and                 The mass and initial velocity of the impactor modeled
rectangular CFRP tube with two ribs were modeled by              as a rigid body were 105 kg and 15.27 m/s (55 km/h),
solid and shell elements, respectively.                          respectively. For the boundary conditions of impactor,
   In the all FEM models, the imperfection part was              the displacements along the global axes x and y, and the
introduced to reduce a peak load and to get the stable           rotations for the three global axes were constrained in the
progressive failure behavior from the top edge of the            FE analysis. The displacement of impactor along the z
FEM model to a length of 10 mm below (see Fig. 5).               axis downwards was only permitted. On the other hand,
The FEM models with and without the imperfection                 in the case of the rectangular CFRP tube with two ribs,
parts, were designated as thickness-changed and thick-           the bottom side of the model was perfectly fixed.
ness-constant models, respectively.                                  In this FE analysis, the rectangular CFRP tube was
   The comparison between thickness-constant and                 modeled by using a shell element (MAT_54, mat_en-
thickness-changed models is shown in Fig. 6. The model           hanced_composite_damage) and the Chang-Chang failure
without an imperfection part may produce a high initial          criterion8), 9) was used to determine the failure of element.
maximum load. After that, the impact load drops rapidly.             The mechanical properties used for MAT_54 in
The initial maximum load of the thickness-constant               LS-DYNA are listed in Table 1. Also, we adopted a
model is approximately two times higher than that of             removing element method base on a time-step failure
the thickness-changed model. On the other hand, impact           parameter (Tfail). These analyses were conducted with
load in the propagation region is seen that the thickness-       Tfail parameter equal to 0.3. Two different contact al-
changed model is higher than that of the thickness-con-          gorithms were used throughout FE analysis. The “con-
stant model. Therefore, the thickness-changed method in          tact_automatic_surface_to_surface” contact interface
the imperfection part is chosen. As a result, the tendency       type was used for the boundary between the impactor
of the impact response behavior in the FEM analysis is           and the top part of rectangular CFRP tube. In case of
in good agreement with the impact tests.                         the CFRP tube, the “contact_automatic_single_surface”

                                                                10 mm


          5 mm                                                                                           Reduce a
                                                                                                         thickness

                                                                                                        5 mm


                   Fig. 5 Details of the (a) thickness-constant and (b) thickness-changed models


                                       400
                                                        thickness-changed model
                                       300              thickness-constant model
                           Load [kN]




                                       200

                                       100

                                         00           50            100              150
                                                    Displacement [mm]
  Fig. 6 Comparison of the thickness-constant and thickness-changed models for the load-displacement curve


                                                           –4–
            Comparison of Experimental Results with FEM for Impact Response Behavior of CFRP Tubes and CFRP/Al Hybrid Beams
                                 for Absorbing Impact Energy in Full-lap and Side Collisions of Automobiles



                          Table 1 Material properties of rectangular CFRP tube used in the FE analysis

                                              Material property                    Symbol                 Values
                                      Longitudinal Young’s modulus                   Ea                  140.0 GPa
                                      Transverse Young’s modulus                     Eb                    9.0 GPa
                                      Minor Poisson’s ratio                          ν ba                  0.0219
                                      Shear Modulus in plane (ab)                   Gab                    4.0 GPa
                                      Shear Modulus in plane (bc)                   Gbc                    2.0 GPa
                                      Longitudinal tensile strength                  XT                    2.6 GPa
                                      Longitudinal compressive strength              XC                    1.5 GPa
                                      Transverse tensile strength                    YT                   0.07 GPa
                                      Transverse compressive strength                YC                   0.05 GPa
                                      Shear strength in plane (ab)                   SC                   0.09 GPa

                                                ※ These values were provided by Toray Industries, Inc.



contact interface type was adopted.                                            the maximum load, the maximum displacement and the
                                                                               absorbed energy obtained from the experimental tests
2.3 Results and discussion                                                     are listed. Here, the absorbed energy was obtained from
                                                                               load-displacement curves.
2.3.1 Impact test results                                                         Fig. 8 shows the photographs of failed CFRP tube
                                                                               with ribs after impact test. It is seen that the crush zone
    Fig. 7 shows the load-displacement curves of the                           spread out towards inside and outside of the rectan-
rectangular CFRP tube with ribs under impact loading.                          gular CFRP tube wall. Tearing failure mode was also
It is seen that the same tendency of the impact response                       seen in all of the rectangular CFRP tubes at the corners.
behavior was obtained in the all test specimens. In Table 2,                   Photographs recorded with a high speed camera system

            200
                                             No. 1            No. 4
                                             No. 2            No. 5
            150                              No. 3
Load [kN]




            100

             50

              0
                  0              50                100                 150
                            Displacement [mm]

Fig. 7 Load-displacement curves for all test specimens



            Table 2 Summary of the experimental results

                         No. 1 No. 2       No. 3    No. 4     No. 5   Ave.

  Max. load [kN]         179.0 173.1 170.9         160.8      180.3   172.8
  Absorbed
  energy [kJ]             11.7    13.7     12.7      13.1     12.9     12.8
  Maximum                                                                      Fig. 8 Photographs of impact tested rectangular CFRP
  displacement [mm] 128.0 142.6 138.3              146.8      134.6   138.1
                                                                                      tube with two ribs



                                                                             –5–
                                         Hyoung-Soo KIM, Goichi BEN and Nao SUGIMOTO



 during impact tests are shown in Fig. 9. From the results,        of FEM results, for Model 1, Model 2 and Model 3. It is
 the stable progressive failure behavior was observed.             seen that their tendency of the impact response behavior
                                                                   was relatively the same in the all FEM models.
 2.3.2 Comparison between impact test results and                      Fig. 11 shows the comparison of experimental results
       FEM results                                                 with that of Model 3 for the load-displacement curves.
                                                                   It is seen that the comparison of the impact response
            Fig. 10 shows the impact load-displacement curves      behavior was favorable.




                       (a) t = 0 msec                 (b) t = 2.08 msec                   (c) t = 2.92 msec




                     (d) t = 6.25 msec                 (e) t = 8.33 msec                 (f) t = 10.42 msec
                          Fig. 9 Photographs recorded with a high speed camera system (specimen No. 2)


                                                                              200
            250
                                                                                                EXP           FEM
                                          Model 1                                                             (Model 3)
            200                                                               150
                                          Model 2
                                          Model 3
                                                                  Load [kN]
Load [kN]




            150
                                                                              100
            100
                                                                               50
              50

               0                                                               00        50            100             150
                0            50            100           150
                           Displacement [mm]                                           Displacement [mm]
 Fig. 10 Load-displacement curves obtained from the FEM            Fig. 11 Comparison of experimental and FEM (Model 3)
         analysis                                                          load-displacement curves



                                                            –6–
    Comparison of Experimental Results with FEM for Impact Response Behavior of CFRP Tubes and CFRP/Al Hybrid Beams
                         for Absorbing Impact Energy in Full-lap and Side Collisions of Automobiles



   In Table 3, the maximum load, the absorbed energy              On the tension side of the Al beam, a unidirectional
and the maximum displacement obtained by the FE                   CFRP laminate was pasted by using adhesive as shown
analyses and the average values of the experimental               in Fig. 13. The unidirectional CFRP was composed of
results are listed. The results of the Model 3 were in            T700 and epoxy resin and its thickness was changed
good agreement with the average values of the impact              from 0.5 mm to 2.5 mm with an increment of 0.5 mm.
test results.                                                     The 1,000 mm length of hybrid guarder beam was sup-
                                                                  ported by two supporters having a head radius of 15 mm
Table 3 Comparison between the experimental and FEM               and the span between the two supporters was 800 mm.
        results of the rectangular CFRP tube                         In order to evaluate the capacity of crash energy
                    Model 1   Model 2   Model 3
                                                      Exp.        absorption and to show the micro and macro fracture
                                                  (ave. values)
                                                                  behavior of the door guarder beam, a large size of drop
Max. load [kN]       196.0     215.0    174.0        172.8
                                                                  tower facility for the impact test was constructed. The
Absorbed
                      11.8      11.9     12.1          12.8       beam received an impact load generated by a free drop
energy [kJ]
Maximum
                     146.0     136.0    140.0        138.1        weight of 60 kg at an impact speed of 55 km/h. The
displacement [mm]
                                                                  shape of impactor was a half cylinder having a 100 mm
                                                                  radius and a 200 mm width and the hybrid beam was
3. Impact Response Behavior of CFRP/Al hybrid                     fixed by the belts to prevent from scattering (Fig. 14).
           beams under side collision                             The impact load and the displacement of the impac-
                                                                  tor were measured by the load cells attached to both
   We developed CFRP-Al hybrid beams as impact en-                supporters and by a high-speed camera, respectively.
ergy absorption members for side collision as shown in            Fig. 15 shows the relationship between the load and
Fig.12. Such members have the advantages of plastic de-           the displacement of the specimens for the Al beam
formation of aluminum alloy combined with high strength           alone and the hybrid beams with the CFRP of 1 mm.
and lightweight of CFRP. By using a hybrid structure of
aluminum alloy and CFRP, excellent energy absorption is                                                                                  30mm
expected within the limited deformation of 150 mm. The
                                                                                                  Aluminum
goal of this study is to develop simulation technology for
the impact behavior of such hybrid beams.

3.1 Experiment                                                                                                                        CFRP
                                                                  3.0mm

   The square section of Al guarder beam was 30 mm                                                                           1000mm
x 30 mm and its wall thickness was 3.0 mm. The type                       0.5~2.5mm
of aluminum alloy was A7N01S-T5 and its yield stress,
tensile strength, tensile modulus and elongation were             Fig. 13 Hybrid door guard specimen with square section
373 MPa, 416 MPa, 70 GPa, and 16.7 %, respectively.                       of Aluminum




                                                                               a


                                                                                        Ca           Adhesive Aluminum
                                                                                          ro
                                                                                            uts
                                                                                               ide                      Car outside
                                                                               a
                                                                                            CFRP tape
                                                                    Door guarder beam
                                                                                                         Section: a-a


                                   Fig. 12 Door guard beam and hybrid door guard beam



                                                              –7–
                                 Hyoung-Soo KIM, Goichi BEN and Nao SUGIMOTO



        Impactor
       Mass=60kgf
                                                                Supporter

                            200                              Head radius=15mm
                                                   0
                                                10
                                           R



                                          800

                                         Support Length
 R15
                 Fig. 14 Hybrid door guard beam and fixtures in experiment



                            25
                                                                            Aluminum
           Load (kN)




                            20
                            15
                            10
                            5
                            0
                                0                 50         100       150       200     250
                                                            Displacement (mm)

                            25
                                                                            CFRP-1mm
                                                       Fiber break
           Load (kN)




                            20
                            15
                            10
                            5
                            0
                                0           50           100     150      200     250    300
                                                           Displacement (mm)

                            25
                                                                            CFRP-1.5mm
                            20                         Fiber break
           Load (kN)




                            15
                            10
                            5
                            0
                                 0             50         100      150     200    250    300
                                                            Displacement (mm)

                                25
                                                                            CFRP-2.5mm
                                20                          Fiber break
                Load (kN)




                                15
                                10
                                 5

                                 0
                                     0            50       100      150    200     250   300
                                                            Displacement (mm)

Fig. 15 Impact load to displacement curves for hybrid beam with square section of Al



                                                              –8–
   Comparison of Experimental Results with FEM for Impact Response Behavior of CFRP Tubes and CFRP/Al Hybrid Beams
                        for Absorbing Impact Energy in Full-lap and Side Collisions of Automobiles




1.5 mm, 2 mm and 2.5 mm. For the case of Al beam              and the fracture types of each specimen. In the experi-
alone, after the impact load reached the maximum, it          ment, the fracture mode was classified into the following
then instantly dropped to almost zero. Within 50 ms,          three types, 1) fiber breakage over the entire width and
the impact load was recovered to 12.5 kN and became           partial delamination of CFRP [Type A], 2) non fiber
zero when the displacement was about 200 mm. For              breakage and larger delamination of CFRP [Type B] and
the CFRP of 1 mm, the recovered impact load after the         3) partial fiber breakage in the width direction and the
maximum was faster and higher than that of the Al beam        middle delamination [Type C]. The fracture modes for
alone and the higher impact loads continued until the         all the specimens are listed in Table 4. When the CFRP
break of CFRP. For the hybrid beams with the CFRP             was thin, it broke as the Type A, and gradually changed
of 1.5 mm and 2.5 mm, larger displacement and higher          from Type B to Type C according to the thickness of
impact load were observed compared with those of the          CFRP. The impact absorbing energy was calculated
CFRP of 1.0 mm.                                               from the area of the load-displacement curve. When
   Fig. 16 shows the observed fracture modes of CFRP          the thickness of CFRP increased, the impact energy



                        [A] fiber breakage in the entire width and partial delamination of CFRP




                                [B] non fiber breakage and larger delamination of CFRP




                      [C] partial fiber breakage in the width direction and the middle delamination


                                  Fig. 16 Fracture mode of CFRP after impact test



                              Table 4 Classification of fracture modes for all specimens

                                                Thickness of CFRP
                   0.5mm             1.0mm            1.5mm          2.0mm                  2.5mm
                 2-8    A          3-8    B          4-2     C    5-2     C               6-8    C
                 2-9    A          3-9    A          4-3     B    5-3     C              6-11    C
                 2-10   A          3-10   B         4-15     C    5-11    C              6-15    C
                 2-11   A          3-11   A                       5-15    C              6-17    C
                 2-12   A          3-13   A                       5-16    C
                 2-13   A          3-14   A                       5-17    C



                                                        –9–
                                                     Hyoung-Soo KIM, Goichi BEN and Nao SUGIMOTO



    also increased as shown in Fig. 17. The 2.5 mm CFRP                       with the square section and others.
    absorbed 25 % larger impact energy than that of the Al
    beam alone.                                                               3.3 Comparison of both results and discussion


                      2000                                                       Fig. 18 shows the comparison of the experimental
                                                                              and numerical results of the impact load to the dis-
Absorbed energy (J)




                      1500                                                    placement for the Al beam alone. In the experiment,
                                                                              two results were shown due to the scattering of the
                      1000                                                    experiment values. The numerical result showed the
                                         Until Fiber break                    good agreement with the experimental results. For the
                      500                Until displacement of 200mm          maximum load and displacement, the numerical result
                                         Until displacement of 100mm          was found between the two experiment values. The
                        0                                                     value of absorbed energy was also close to the experi-
                             Al   0.5mm 1.0mm 1.5mm 2.0mm 2.5mm
                                                                              mental ones. The results for the experimental failure
                                  thickness of the CFRP (mm)
                                                                              mode was almost the same as the numerical one as
  Fig. 17 Relation of impact absorbing energy to CFRP                         shown in Fig. 19.
          thickness                                                              The experimental results for Al guarder beams with
                                                                              the CFRP thickness of 0.5 mm agreed well with those of
    3.2 FEM analysis                                                          the numerical results as shown in Fig. 20. The fracture
                                                                              mode of fiber breakage in the middle part of the beam
       In the numerical analysis, the dynamic explicit FEM                    and the partial delamination (Fig. 21) was observed in
    solver (PAM-CRASH, 2004) was employed and the                             both results. The numerical and experimental results for
    elastic-plastic 4 nodes shell element for the Al part and                 other hybrid beam with different thickness of CFRP also
    the laminated shell element for the CFRP were used,                       agreed well one another.
    respectively. The total node number was 64,863 and the
    total element number was 56,456. The contact element                                         4. Conclusions
    between the impactor and the upper surface of hybrid
    guarder beam and between the supporter and the lower                      1. It was proven that the rectangular CFRP tubes with
    surface of hybrid guarder beam was Contact Type 33                           two ribs were effective as an impact absorption mem-
    with the friction and penalty coefficients of 0.5 and                         ber under full-lap collision.
    of 0.1, respectively. For the interface of Al guarder                     2. The comparisons of experimental results with FEM
    beam and the CFRP layer, Contact type 32 was used                            ones for the load-displacement curves were favor-
    for modeling adhesion of interface. Table 5 shows the                        able. Especially, the maximum load, the absorbed
    material properties of CFRP (T700), Al guarder beam                          energy and the maximum displacement calculated by


                                      Table 5 Material constants of hybrid beam with square section of Al alloy

                                                                 CFRP          AL             Belt            Jig
                                     E1 (GPa)                     135           72           0.133           207
                                     E2 (GPa)                     8.5           ---            ---            ---
                                     G12 (GPa)                   3.17           ---            ---            ---
                                     G23 (GPa)                   3.04           ---            ---            ---
                                         ν12                     0.34           0.3           0.3            0.3
                                         ν23                      0.4           ---
                                   Density (kg/mm3)            1.60E-06      2.79E-06      7.93E-03        7.90E-06
                                     FL (GPa)                    2.55           ---           ---             ---
                                          εL                     0.017          ---           ---             ---



                                                                          – 10 –
            Comparison of Experimental Results with FEM for Impact Response Behavior of CFRP Tubes and CFRP/Al Hybrid Beams
                                 for Absorbing Impact Energy in Full-lap and Side Collisions of Automobiles



            30                                                             Model 3 were in good agreement with the average
                                            Experiment                     values of the impact test results.
                                             FEM                      3.   The CFRP Al hybrid door guarder beam showed the
Load (kN)




            20                                                             same performance of impact absorbing energy as that
                                                                           of the steel one and its maximum displacement after
                                                                           the impact was smaller than that of steel.
            10                                                        4.   The CFRP-Al hybrid member with the thicker CFRP
                                                                           showed the larger impact failure displacement be-
                                                                           cause its fracture was extended by the thicker CFRP
            0
                 0       50         100         150         200            and then it absorbed more impact energy.
                           Displacement (mm)                          5.   Changing the design parameters of the hybrid door
                                                                           guarder beam may result in larger impact absorbing
 Fig. 18 Comparison of impact load to displacement for
         Al beam only
                                                                           energy.
                                                                      6.   From the comparison of FEM results with the experi-
            30
                                                                           mental ones for both specimens of CFRP Al hybrid
                                              Experiment                   guarder beam with square section of Al, the proposed
                                              FEM                          numerical method was found to be very useful for
Load (kN)




            20
                                                                           analyzing the hybrid door guarder beams.

                                                                                          Acknowledgment
            10

                                                                         This study was conducted as part of the Grant-in-Aid
            0                                                         for Scientific Research (C) (No. 15560081) by JSPS (the
                 0      50         100        150          200        Japan Society for the Promotion of Science) from April
                           Displacement (mm)                          2003 to March 2005 and the authors acknowledge the
 Fig. 19 Comparison of impact load to displacement for                assistance of Toray Industries, Inc. who supplied the
         hybrid beam with square section of Al and CFRP               materials for these test specimens.
         of 0.5 mm




                        Fig. 20 Impact absorbing energy and fracture aspect s after impact for Al beam only




 Fig. 21 Impact absorbing energy and fracture mode of hybrid beam with square section of Al and CFRP of 0.5 mm
         square section



                                                                 – 11 –
                                 Hyoung-Soo KIM, Goichi BEN and Nao SUGIMOTO




                    References                               Exposition (2002)
                                                        6)   H.S. Kim, G. Ben and Y. Iizuka, Proceedings of
1) P.K. Mallick and L.J. Broutman, J. Testing and            11th Japan -US Conference of Composite Materials
   Evaluation, 5, pp. 190, 1977                              (2004)
2) S.S. Cheon, T.S. Lim and D.G. Lee, Composite         7)   H.S. Kim, G. Ben, Y. Aoki and A. Shikada, 5th
   Structures, 46, pp. 267-278, 1999                         Japan-Korea Joint Symposium on Composite
3) D.G Lee, T.S. Lim and S.S. Cheon, Composite               Materials, pp. 95-96, 2005
   Structures, 50, pp. 381-390, 2000                    8)   F.K. Chang and K.Y. Chang, Journal of Composite
4) G. Ben, T. Uzawa, H.S. Kim, Y. Aoki, H. Mitsuishi         Materials, 21, pp. 809-833, 1987
   and A. Kitano, Transaction of JSME Series A, 70      9)   H.S. Kim, G. Ben and Y. Aoki, Proceedings of
   (694), pp. 824-829, 2004 (in Japanese)                    the 12th US-Japan Conference on Composites
5) A. G. Caliska, Proceedings of IME2002, ASME,              Materials, pp. 367-378, 2006
   Internatinal Mechanical Engineering Congress &




                                                  – 12 –
                         CFRP
                                             CO             CFRP
                           CFRP




                                                     CFRP       CFRP/Al


                                                                m
                        km/h                          LS-DYNA        Pam-
Crash   CFRP       CFRP/Al
           CFRP


                       CFRP                CFRP/Al


         CFRP/Al




                                  – 13 –
       Biographical Sketches of the Authors



   Hyoung-Soo Kim is a part-time lecturer of College of Industrial Technology, Nihon
University. He was born in Mokpo, Korea on March 10, 1968. He received his Dr. of
Eng. from the Kyushu University in 2000. He is now a member of the Japan Society for
Composite Materials, Japan Society of Mechanical Engineers and The Japanese Society
for Strength and Fracture of Materials.




   Goichi Ben is a professor of College of Industrial Technology, Nihon University.
He was born in Akita, Japan on November 29, 1945. He received his B.S. from Nihon
University, Japan in 1969, M.S. from the University of Tokyo, Japan in 1971 and Ph.D.
in Engineering from the University of Tokyo in 1974. He joined College of Industrial
Technology, Nihon University in 1974. He has been engaged in the study of strength
and optimum design of light weight structures. The present research is focused on
composite engineering, namely mechanics and strengths of composites, evaluation of
mechanical properties in composites, optimal design of composite structures, fabrica-
tions of composites and so on. Dr. Ben had stayed each one year at the University of
Delaware from 1988 to 1989 and at the University of Colorado from 1996 to 1997 in
the U.S.A. as a visiting associate and full professor, respectively. He is now a president
of the Japan Society for Composite Materials. He is a member of board director of the
Association of Reinforced Plastics in Japan. He is a member of council of the Japan
Society for Computational Engineering and Science and a member of the Japan Society
of Mechanical Engineers, the Japan Society for Aeronautical and Space Sciences, the
Society of Material Science, Japan, Dr. Ben is also a member of AIAA in the U.S.A. and
American Society for Composite Materials.




   Nao Sugimoto was born in February 10, 1984 in Tokyo, Japan. He received his B.S.
from Nihon University, Japan in 2006. He is a master course student of department of
mechanical engineering, graduate school of industrial technology, Nihon University.




                           – 14 –

								
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