Vijay Kumar G S
. IJRIT-210 International Journal of Research in Information
Technology (IJRIT)
www.ijrit.com ISSN 2001-5569
Static And Model Analysis of Harness Mass Electrical Disconnect Bracket Used In Aerospace
Vijay Kumar G S, M Tech Student, Department Of Mechanical Engineering Name, Ballari Institute of Technology & Management, Visvesvaraya Technological University, Belgaum, Karnataka, India
Asst Prof, Manjunatha T H, Department Of Mechanical Engineering Name, Ballari Institute of Technology
& Management, Visvesvaraya Technological University, Belgaum, Karnataka, India
Abstract
Brackets are simple rigid structure in the shape of an L, Angle brackets, square brackets and curly brackets, the one arm of which is fixed to the vertical surface the other surface is supported from the base of the electrical disconnect Bracket which supports to the Electrical Harness and this Harness mass is transferred from bracket to aircraft fuselage structure.
The purpose of present work is to investigate the static and model analysis of bracket to withstand the electrical harness mass of a wire using hyper mesh and Nastran tool
Present work is focused on the study of strength behavior and mechanical behavior of bracket of material 2024 T3 is carried pre-processing with Hypermesh and Post processing with Nastran tool software’s ,normal mode analysis of the bracket has been carried out using Nastran, to find the natural frequency and its corresponding modes.
The natural frequency analysis is carried out to ensure the first natural frequency of the bracket as well as the natural frequency of the primary structure.
The Finite Element Analysis is implemented using the hyper mesh for pre-processing and NASTRAN as solver for both static and frequency analysis Electrical disconnect bracket and theoretical calculations all together constitute a major portion of this work. The Finite Element Analysis results are validated with theoretical calculations by strength of material approach.
Keywords: Static and Model Analysis of Harness Mass Electrical disconnect Bracket which support to the.
1. INTRODUCTION
An Electrical Disconnect bracket design concepts for the installation of systems. Since the bracket installation zone is almost around the frame area (Fig. 1) attached to fuselage structure, and it is very necessary to know about some basic structural elements of Aeroplane through which the routing of air ducts and cable bundles takes place. The Electrical Disconnect Bracket is installed on fuselage area covering its entire sections of the fuselage in Aeroplane. Fuselage is a main structure of any or Aeroplane.
Fuselage is a tunnel type structure both ends are closed and provides space for passengers, control unit, cargo unit, accessories and other equipment. In some s it also provides housing space for power plant.
Fuselage is the combination of lots of structural members in Aircraft
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. IJRIT-211
Fig 1.1 Fuselage Frame
1.2 Types of Brackets used Depends on Application
The Types of Bracket are normally in Triangular, Square; Rectangular in shape and also Bracket types depends on application and force
1.2.1 Triangular Bracket
Figure 1.2 Triangular Bracket Figure 1.2(a) Triangular Bracket
1.2.2 Square Bracket
Fig 1.3 Bracket Holds Harness Mass
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The required geometry or model is created by using CATIA V5 modeling software and then imported to HYPERMESH Software for further processing. Here entire electrical harness bracket is considered for analysis. As it satisfies the all the requirements. The detailed drawings of the CAD models created for analysis are shown in Appendix II. Figure 4.1 shows typical CAD models created for analysis purpose.
Fig 2.1 Isometric view of an Electrical Disconnect Bracket
2.1 Material Properties
The Bracket is made of with material Aluminum 2024 T3 sheet which is selected as per Aerospace material standards. The mechanical properties of the material used for analysis are described in table 4.1.
Table 1
Properties Value Unit
E 72.394×10^5 MPa
G 25.579×10^5 MPa
µ 0.33 --
σy 324 MPa
Ρ 2767.9 Kg/m3
2.2 Loading Conditions
Loads are applied as per the Aerospace Co-Ordinate System Definition and same has been described. In finite element analysis loading is prerequisite to obtain the solution. Here the standard loading conditions are followed as per Aerospace Requirements.
Take off, Landing and Emergency Loading conditions .
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Electrical disconnect bracket are designed to withstand the ultimate flight and ground equipment acceleration load factors. The acceleration load factors are A/C Model specific and vary with fuselage station. Flight and ground acceleration loads are analyzed independently and are to be combined with any other load conditions.
Acceleration load factors for the exact bracket location obtained by interpolating the values between the fuselage station locations. The lateral and vertical load factors for FS 0.0 to FS 1.400 and the ultimate values obtained by multiplying the interpolated value with the ultimate factor of 1.5. These loading conditions are considered based on the report which has been designed for safety regulations for Aerospace vehicles system.
3. Static and Model Analysis of Electrical Disconnect Bracket
Static analysis is used to determine displacement, stresses, strains, etc. under static loading. In the analysis of steady loading and response conditions are assumed that, the load and structure’s response are assumed to be very slowly with respect to time. The static analysis can be either linear or nonlinear. The gravity loading is considered for static analysis. The kind of loading that can be applied in a static analysis includes the following.
Gravity Load in all the 3 directions
Self-weight of the Electrical Disconnect Bracket applied at CG point.
Here static analysis of the Electrical Disconnect Bracket is carried out to check the section Strength, hence Von Mises failure criteria is applied here. The analysis results are discussed in detail as below.
3.1 Displacement Plot for Take-Off Condition
Fig 3.1(a) Displacement plot For Take-Off Condition.
The maximum displacement obtained in this case is 0.01 mm at the extreme end as shown in the fig 3.1(a) and it is shown by different colors fringes where blue color showing minimum magnitude of displacement and red color will show maximum magnitude of displacement as 0.01mm.
3.2 Displacement Plot for Landing Conditions
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Fig 3.1(b) Displacement plot for landing Condition
The maximum displacement obtained in this case is 0.0398 mm at the extreme end as shown in the fig 3.1(b) and it is shown by different colors fringes where blue color showing minimum magnitude of displacement and red color will show maximum magnitude of displacement as 0.0398mm.
3.3 Displacement Plot for Emergency Landing Conditions
Fig 3.1(c) Displacement plot for Emergency Landing Condition
The maximum displacement obtained in this case is 0.0597 mm at the extreme end as shown in the fig 3.1(c) and it is shown by different colors fringes where blue color showing minimum magnitude of displacement and red color will show maximum magnitude of displacement as 0.0597mm.
3.4 Stress Plot for Take-Off Condition
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The stresses for Electrical Disconnect Bracket are calculated According to Von-Mises theory yielding would occur when total distortion energy absorbed per unit volume due to applied loads exceeds the distortion energy absorbed per unit volume at the tensile yield point. The Von-Mises theory gives the below equation.
The detailed drawing of the model is considered for this analysis is shown in fig B.1 of appendix B. The Take-Off load Condition is applied at CG point were RBE-2 element is applied and static analysis is carried out. The detailed pre-processing required for analysis is discussed in chapter 4. Von Mises stress plots obtained are shown in figure 3.2(a).
Fig 3.2(a) Von Mises stress plot Take-off Condition.
The Von Mises plots obtained are shown in above figure 3.2(a).The maximum von mises stress obtained for take-off condition of Electrical Disconnect Bracket in this case is 2.89 MPa as shown in fig 3.2(a), the obtained stress is much less than the design stress of the Electrical Disconnect Bracket hence it is considered as safe design
3.5 Stress Plot for Landing Condition
Fig 3.2(b) Von Mises stress plot Landing Condition.
The Von Mises plots obtained are shown in above figure 3.2(b).The maximum von mises stress obtained for Landing condition of Electrical Disconnect Bracket in this case is 7.922 MPa as shown in fig 3.1(b),
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. IJRIT-216
the obtained stress is much less than the design stress of the Electrical Disconnect Bracket hence it is considered as safe design
3.6 Stress Plot for Emergency Landing Condition
Fig 3.1(c) Von Mises stress plot for emergency Landing Condition.
The Von Mises plots obtained are shown in above figure 3.2(c).The maximum von mises stress obtained for Emergency Landing Condition of Electrical Disconnect Bracket in this case is 11.79MPa as shown in fig 3.1(c), the obtained stress is much less than the design stress of the Electrical Disconnect Bracket hence it is considered as safe design
3.7 Summary of Static Analysis Results
From static FEA analysis results maximum stress induced in the Bracket is 3.41MPa, 7.92MPa &
11.79MPa for all three loading conditions which is less than the permissible (Design/Allowable) stress of the Electrical Disconnect Bracket is 440 MPa, since design criteria for ductile material is yield stress (strength) of the material, from these FEA results we can conclude that Bracket design is safe under given gravity loading conditions.
From static FEA analysis results maximum deformation in the Electrical Disconnect Bracket is 0.0597mm for Emergency Landing loading case, which is so small that it will not clash with any of the surrounding components even after deformation, from these FEA results we can conclude that design of Electrical Disconnect Bracket is Safe and all the stresses for all Loading conditions are within permissible stress limit
3.8 Frequency Analysis
Modal or Frequency analysis is the study of dynamic properties of structures under vibrational excitation. Frequency analysis is the field of measuring and analyzing the dynamic response of structures and when excited by an input. Both the natural frequency (which depends on the mass and stiffness distributions in my structure) and mode shapes are necessary for proper functioning of the structure.
Frequency analysis of Electrical Disconnect bracket is done for first six modes of natural frequency.
The response of the structure are different at each of the different natural frequencies. These deformation patterns are called mode shapes.
Modal analysis has been used to identify natural frequencies, damping characteristics and mode shapes of model. Modal analysis is the most common method used to characterize the dynamics of mechanical system and it produces very illustrative and easy interpretable results. Modal analysis has also been used to identify approximate mode shapes associated with the dominating deflection direction only.
First Mode Frequency
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A mode of vibration is characterized by a modal frequency and a mode shape. It is numbered according to the number of half waves in the vibration. For example, if a vibrating beam with both ends pinned displayed a mode shape of half of a sine wave (one peak on the vibrating beam) it would be vibrating in mode 1. If it has a full sine wave (one peak and one valley) it would be vibrating in mode 2.
Each mode is entirely independent of all other modes. Thus all modes have different frequencies (with lower modes having lower frequencies) and different mode shapes.
Fig 3.3(a) First mode of frequency for Electrical Disconnect Bracket
The first mode frequency occurs at 50.26 Hz with a maximum displacement of 3.339 mm is shown in fig 3.3 (a).
3.9 Summary of Frequency Analysis
Normal mode analysis of the bracket has been carried out using NASTRAN, To find the natural Frequency and corresponding modes. The natural frequency analysis is carried out to ensure the first natural frequency of the bracket is well above the natural frequencies of the primary structure, such as wing, horizontal tail, fuselage, etc. Thereby ensuring the integrity of the primary structures.
The first natural frequency of the bracket is FEA Result is 50Hz,the guidance value of the first mode frequency is 40Hz.As the first natural frequency of the disconnect Bracket is above the 40Hz ,Hence it may be assumed that the first natural frequency of the bracket will not cause any determinant effect on primary structure.
3.10 Stress Validation Table.
The below Table.2 shows the percentage difference in stress results between FEA stress results and analytical or theoretical stress calculation results, for All the above loading cases. The Analytical Stress is calculated with some Assumptions like Small holes are neglected in Calculation, Stresses are assumed to be within elastic limit and Uniform Plate thickness is considered.
Table.2
Sl No Loading Cases FEA Stress Results in Analytical Stress Results
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. IJRIT-218
MPa in MPa
A Take-Off Load Case 3.41 4.03
B Landing Load Case 7.922 8.07
C Emergency Landing Load Case
11.79 12.108
4.
Conclusion 4.1 Static case
From static FEA analysis results maximum stress induced in the structure is 11.79 MPa which is less than the permissible (Design/Allowable) stress of the structure 324 MPa (Electrical Disconnect Bracket), since design criteria for ductile material is yield stress (strength) of the material.
From these FEA results we can conclude that design of Fuel Filter Bracket Assembly is safe under given gravity loading conditions.
4.2 Frequency case
From FEA frequency analysis results the first mode shape occurs at a natural frequency of 50.26 Hz which is greater than the aerospace fuselage natural frequency of structure is 45Hz, so it will not create any resonance.
From frequency analysis results we can conclude that Electrical Disconnect Bracket Assembly design is safe as it avoids the resonance.
4.3 Scope for Future work
The conclusion drawn from the FEA results is induced stress values are well within the permissible/allowable stress value for material under consideration.
There is a scope for optimization of Electrical Disconnect Bracket by reducing the thickness of the component wherever stress values are less.
We can reduce the weight of the assembly to some extent by optimizing.
There is scope to use a composite material instated of metals.
5. REFERENCES
[1]
“A Text Book of Practical Finite Element Analysis” First Edition by Nitin S gokhale, Sanjay S deshpande, Sanjay V Bedekar, Anand N Thite. Published by Finite to Infinite, Pune.[2]
Shih, R. (2004). Introduction to Finite Element Analysis using I-DEAS 11. Oregon Institute of Technology.[3]
Heinze P. & Schmidt I. (eds.) (2012). Finite Element Method an Introduction. Hochschule Wismar.[4]
Chandrapatla, "introduction to FEA, 3rd edition, 2008.[5]
nptel.ac.in/.../Strength%20of%20Materials/course_strength%20of%20ma...contents/IIT%20Kharagpur/Structural%20Analysis/New_index1.html.
[6] Practical Stress Analysis for Design Engineers, Jean-Claude Flabel, Lake City Publishing Company, 1997.
[7] Strength of Materials by Timoshenko.
