COMPARATIVE STUDY OF SAE 1045 CARBON STEEL AND ALUMINIUM ALLOY 7075-T6 FOR LOWER SUSPENSION

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COMPARATIVE STUDY OF SAE 1045 CARBON STEEL AND ALUMINIUM ALLOY 7075-T6 FOR LOWER SUSPENSION Powered By Docstoc
					  International Journal of Advanced Research in OF ADVANCED (IJARET), ISSN 0976 –
  INTERNATIONAL JOURNALEngineering and TechnologyRESEARCH IN
  6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 2, March – April (2013), © IAEME
             ENGINEERING AND TECHNOLOGY (IJARET)
ISSN 0976 - 6480 (Print)
ISSN 0976 - 6499 (Online)                                                IJARET
Volume 4, Issue 2 March – April 2013, pp. 119-124
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     COMPARATIVE STUDY OF SAE 1045 (CARBON STEEL) AND
   ALUMINIUM ALLOY 7075-T6 FOR LOWER SUSPENSION ARM OF
                       A SEDAN CAR

                                   Prof. Pinank A. Patel1
                          1
                            Department of Mechanical Engineering,
              Marwadi Education Foundations’ Group of Institutions-Rajkot, India,
                                     Vivek G. Patel2
                               2
                          Department of Mechanical Engineering,
              Marwadi Education Foundations’ Group of Institutions-Rajkot, India,
                                     Dr. Shashikant S. Khandare3
                         3
                             Principal B.D. Collage of Engineering-Wardha,


  ABSTRACT

          Automobile parts are subjected to variable amplitude loads; fatigue characteristics
  vary with material and loading conditions. This research focuses on the finite element based
  fatigue life prediction of lower suspension arm subjected to numerous loads. Objectives of
  this analysis are to predict fatigue life of the lower suspension arm using Strain-life approach
  and to discover suitable material for the suspension arm. The CAD model of lower
  suspension arm is developed using ProE (Wildfire4.0); later transferred to Ansys 12.1, where
  finite element analysis for fatigue life analysis was performed employing the Strain-life
  approach subjected to variable amplitude loading. While performing fatigue analysis, two
  types of non-uniform variable amplitude loads are considered including zero mean loading
  (SAEBKT) and positive mean loading (SAETRN). We employed Morrow and SWT Method,
  wherein tetrahedron mesh is applied to the model for fatigue analysis.

  Keywords: Fatigue Life, Strain Life Approach, Aluminum Alloy, Non uniformly Varying
  Load (SAEBKT, SAETRANS)




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International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –
6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 2, March – April (2013), © IAEME

I.      INTRODUCTION

        Recent technological research and efforts have focused on new automobile material
forms. At present, in automotive industry it is very crucial task to produce lighter; cheaper
and more efficient parts can sustain high loads. Every automotive suspension is meant for
two aims; vehicle control and passenger comfort. A good car suspension system should have
satisfactory road holding ability, while providing comfort during riding over bumps and pits
on the road. For the prediction of fatigue life stress and strain life approach can be applied,
due to presence of stress concentrated area stress life can’t give accurate results. For here we
employed strain life approach for the prediction of fatigue life of lower suspension arm.

II.     STRAIN LIFE APPROACH

Strain life method is employed where plastic deformation occurs at critical regions (like
notches). In this method plastic strain or deformation is directly measured and quantified
                           h
because Stress life approach fails to account for plastic strain. Even when the component is
under heavy loading conditions, it is necessary to have a plastic deformation at stress
concentration zone where strain life approach is superior to stress life approach. The local
         fe
Strain Life approach has gained acceptance as a useful method of evaluating fatigue life of a
component.
The Strain-Life Curve can be formed by summing up the elastic and plastic strains.


                                     ∇ε       σ'f
Total Strain, εt = εe + εp                =         (2Nf) + ε'f (2Nf)
                                      2       E


                                                        strain life
The effect of the elastic and plastic components on the strain-life curve is shown in Figure 1.




                                 Figure 1 : Strain Life Curve

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International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –
6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 2, March – April (2013), © IAEME


                                           σ'f - σo
          s
   Morrow’s Strain Life Equation: εa =                (2Nf) + ε'f (2Nf)
                                            E


Smith-Watson-Topper (SWT):       σmax εa E = (σ'f ) (2Nf) + ε'f ε' E (2Nf)




III.   CAD MODEL, BOUNDARY CONDITION AND MESHED MODEL

       Figure shows CAD model of lower suspension arm and its bounding box dimensions
are mentioned in table.


                                                             Direction      Length       Unit
                                                                X           436.03       mm
                                                                Y           363.52       Mm
                                                                 Z           65.00       Mm


                 Figure 2 : Cad Model

      Figure 3 shows the meshed model of lower suspension arm with 2.0 mm of mesh size
and 10node Tetrahedron element (TET10) were considered for the analysis. Figure 3 shows
boundary condition applied to the Lower suspension arm.




                     Figure 3 : Meshed Model and Boundary Condition


IV.    MATERIAL PROPERTIES

        Fatigue behavior of any material is highly dependent on its tensile strength; higher the
tensile strength, material will have high fatigue life. The mechanical properties of C45 & AL
      T6
7075-T6 (Aluminum alloy) are shown in Table


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International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –
6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 2, March – April (2013), © IAEME

                                  Table 1: Material Properties
                     Properties                Unit        C45         AL 7075-T6
           Strain-Life Parameters
                       Strength Coefficient     Pa    1099000000        876323996
                        Strength Exponent                -0.11           -0.0751
                      Ductility Coefficient              0.52             0.4664
                        Ductility Exponent               -0.54           -0.7779
                Cyclic Strength Coefficient     Pa    1402000000        943203168
                  Cyclic Strain Hardening
                                                          0.201            0.0966
                                  Exponent

V.        LOADING CONDITION

        The standard ultimate loading cases what we considered are as shown in Table 2. For
prediction of fatigue life of lower suspension arm we considered two non-constant varying
load SAEBKT (Bracket History) and SAETRANS (Transmission History) as shown in
Figure 4&5.

                                  Table 2: Loading Condition
           Conditions                                X               Y              Z
      A    Pothole brake limit load               5688.2           −60.4         −4801.2
      B    Oblique kerb limit load               -9579.7           238.3         2382.1
      C    Lateral kerb strike limit load          549.7           845.9         12218.3




                                Figure 4: Sae Bracket History




                             Figure 5: Sae Transmission History


VI.       RESULTS


        From the following results it is being clear that fatigue life of lower suspension arm is
considerably increased by employing AL7075-T6 aluminum alloy as a lower suspension arm.
Lateral kerb limit is the highest loading condition.




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International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –
6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 2, March – April (2013), © IAEME




 Figure 6: Lateral kerb strike limit load /            Figure 7: Lateral Kerb Strike Limit Load /
         Bracket / AL7075-T6                                         Bracket / C45




   Figure 8: Lateral kerb strike limit load                   Figure 9: Lateral kerb strike limit
        /Transmission/ AL7075-T6                                  load/Transmission/ C45



                                                          Strain Life
         Load Cases                           C45                            AL 7075 T6
                                 SAEBKT         SAETRANS            Bracket        Transmission
     Pothole brake limit
   1                               32232            124833           111763           123848
     load
     Oblique kerb limit
   2                              923866            3404196        175206502        444289956
     load
     Lateral kerb strike
   3                               2268               1058             805              1197
     limit load


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International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –
6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 2, March – April (2013), © IAEME

CONCLUSION

      From the analysis of lower suspension arm it is concluded that if Al alloy (Al 7075-
T6) will give comparative higher fatigue life then C45. Hence, weight of the component
made up from Al Alloy (Al 7075-T6) is subsequently reduced (Approx 60%).
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