Parametric Study of Moderately Loaded Beams_V1 0

8/12/2019 Parametric Study of Moderately Loaded Beams_V1 0

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Ms. Priya P

M.Tech 3RD

SEMInternal guide:

Mr. K. G. Subramanya

Assistant Professor

Department of Civil Engineering

GSKSJTI

Bangalore

External guide:

Mr. S.S. Subramanya Sastry F.I.E.AGM (Technical)

InfoTech Enterprises Limited

Hyderabad

Date: DD/MM/2013 Venue: Srinivasan College of Engineering 2


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In this paper, a systematic study of the various the factorsaffecting the margin of safety of a typical beam with

cutouts are presented.

It is to be noted that the beams are assumed to be

sufficiently stiff and stable so that the strength, stiffnessand stability are accounted in the design.

This paper concentrates the studies on the moderately

loaded beams.

Two Aluminum alloys 7075-T6 and 2024-T4 are selected

for the studies.

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1. King K. M., Rings used for shear web holereinforcement, Aero Digest, Aug 1955

2. Niu, Airframe stress analysis and sizing, Second edition

1999.

3. Paul Kuhn, The strength and stiffness of shear webswith round lightening holes having 450flanges.

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The aircraft structure needs to be designed

accommodating many cutouts of variable sizes.

These cutouts are required to provide access to control

rods / cables, hydraulic lines, electrical lines etc.

The beams are classified into three classes namely,

lightly loaded, medium load and heavily loaded beams.

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Moderately Loaded beams

This is the second class of beams where the beam

carrying shear characterized by a flanged hole with web

stiffeners between the flanged holes.

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The beam considered for the study at present isdescribed below.

Type of the beam: Simply supported beam

Length of the beam: 39.37 inch (1 m)

Shear flow in the web: 570 lb/in (99843.88 N/m)

Height of the web: 12 in (0.3048 m)


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The beam under study is assumed to be a simply supported

beam. This beam represents typical beams like

Flap beams

Control surface beams

Ribs and formers

Floor supports beams

The loading on the beam is assumed in the form of a shear

flow.

This shear flow is a typical characteristic of a class of beams

called shear beams.

Shear beams are short beams which fail primarily by shear than

bending.


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The beam under study is assumed to be made of two

different materials.

Aluminium alloy 7075T6

Aluminium alloy 2024T4

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The analysis is carried out for the following limiting

conditions.

(Height of web / Thickness of web): 115< (h/t)


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Table showing the various parameters with margin of safety (2024-T4)

Table showing the various parameters with margin of safety (7075-T6)


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0%

10%

20%

30%

40%

50%

60%

0 50 100 150 200 250

M.S%

Ratio of spacing between the stiffeners to the thickness of webbs / t

For H/T =210 and D=4.2in

M.S % v/s Bs/T

2024 T4

7075 T6

Graph showing the comparison of margin of safety

between 2024-T4 and 7075-T6


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0

5000

10000

15000

20000

25000

30000

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8

AllowablewebstressFo(psi)

Correction factor K2 for aluminium alloy webs with stiffeners andflanged lightening holes

For H/T =210 and ALUMINIUM 2024 T4

Fo (psi) v/s K2

2024 T4

7075 T6

Graph showing the comparison of correction

factor K2between 2024-T4 and 7075-T6


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Graph showing the comparison of correction factor

K2between 2024-T4 and 7075-T6

0%

10%

20%

30%

40%

50%

60%

0 5000 10000 15000 20000 25000 30000

M.S%

ultimate allowable web stress of a beam without holes (Fo)

For H/T =210 and D=4.2in

M.S % v/s Fo(psi)

2024 T4

7075 T6


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The study is presented for a constant diameter of the cutout of

4.2 in (106.68 mm).

From Table 1 and 2, it is observed that as (bs/t) increasescorrection factor K2, increases. But, Fo(ultimate allowable web

stress without hole) decreases.

Product of K2 and F0 also reduces. This means that as the

cutout size increases, the corrected ultimate allowable stressdecreases.


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The induced stress in the web remains constant. Hence

margin of safety decreases because corrected ultimate

allowable stress decreases.

As the (bs/t) decreases, the stiffness of the beam increases

because the number of stiffeners increases. This will also

increase the weight of the beam.

It is observed that in general for short shear web applications,such as that under study, 7075-T6 gives higher margin safety

as compared to 2024-T4.


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In moderately loaded (short shear) beams for aircraft

applications, it is recommended to use 7075-T4 for

moderately loaded beams.

Proposed procedure in literature gives acceptable results

which show significant reduction in weight of the

structure.

Hence this procedure is adopted in the design of short

beams in aircraft parts.

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Mr. M. Lakshmana Rao,

VP, Engineering Vertical,

Infotech Enterprises Limited, Hyderabad

Dr. M.B. Patil,

Professor and Head,

Department of Civil Engineering,

GSKSJTI, Bangalore


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