me 307: machine design i dr. a. aziz bazoune king fahd university of petroleum & minerals...

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Dr. A. Aziz Bazoune

King Fahd University of Petroleum & Minerals

Mechanical Engineering Department

CH-9 LEC 41 Slide 1

Dr. A. Aziz Bazoune Chapter 9: Welding, Bonding, and the Design of Permanent Joints

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CH-9 LEC 41 Slide 2


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CH-9 LEC 41 Slide 3


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Fig. 9-17a shows a cantilever welded to a support by fillet welds at top and bottom.

CH-9 LEC 41 Slide 4


9-4 Stresses in Welded Joints in 9-4 Stresses in Welded Joints in BendingBending

A FBD diagram of the beam would show a shear force V and a moment diagram M.

The shear force produces a primary shear in the welds of magnitude

' V

A

The moment M introduces a throat shear stress component of 0.707 τ in the welds.

Treating the two welds of Fig. 9-17b as lines we find the second moment of area to be

2

2ubd

I

(a)

(b)

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The second moment of area I, based on weld throat area, is

The nominal throat shear stress is now found to be

The model gives the coefficient of 1.414, in contrast to the predictions of Sec.9-2 of 1.197 from distortion energy, or 1.207 from maximum shear.

The second moment of area in Eq. (d) is based on the

distance d between the two welds.

CH-9 LEC 41 Slide 5


9-4 Stresses in Welded Joints in 9-4 Stresses in Welded Joints in BendingBending

2

0.707 72

0. 07 uI hbd

Ih

2

2 1.414

0.707 2

M dMc M

I bd hh bd

(c)

(d)

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CH-9 LEC 41 Slide 6


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CH-9 LEC 41 Slide 7


9-5 The Strength of Welded 9-5 The Strength of Welded JointsJoints

The matching of the electrode properties with those of parent metal is usually not so important as speed, operator appeal, and the appearance of the completed joint.

The properties of electrodes vary considerably, but Table 9-3 lists the minimum properties for some electrode classes.

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CH-9 LEC 41 Slide 8


It is preferable, in designing welded components, to select a steel that ill result in a fast, economical weld.

Best results are obtained for steels having a UNS specifications between G10140 and G10230.

All these steels have a tensile strength in the hot-rolled condition in the range of 60 to 70 kpsi.

Permissible stresses are now based on the yield strength of the material instead of the ultimate strength, and the code permits the use of a variety of ASTM structural steels having yield strengths varying from 33 to 50 kpsi.

For these ASTM steels, Sy = 0.5 Su.

Table 9-4 lists the formulas specified by the code for calculating these permissible stresses for various load conditions.

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CH-9 LEC 41 Slide 9


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CH-9 LEC 41 Slide 10


The fatigue stress concentration factors listed in

Table 9-5 are suggested for use. These factors

should be used for the parent metal as well as

for the weld metal.

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Table 9-6 gives steady-load information and minimum

fillet sizes.

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9-6 Static 9-6 Static LoadingLoading

Example 9-2 Example 9-2 (Textbook)(Textbook)

Table A-20, Sy = 27.5 kpsi

h =3/8=0.375 int = 1/2 inl = 2 in

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Example 9-2 Example 9-2 (Cont.’d)(Cont.’d)

h =3/8=0.375 int = 1/2 inl = 2 in

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Example 9-4 Example 9-4 (Textbook)(Textbook)

Table 9-3, Sy = 50 kpsi, Sut= 62 kpsi

Table 9-2, pattern 2, b=3/8 = 0.375 in and d= 2in

Table A-20, Sy = 32 kpsi, Sut= 58 kpsi

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Eq. 6-21Ssy= 0.577 Sy

E6010 electrodeTable 9-3, Sy = 50 kpsi,

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Given n=3

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The conventional methods will be provided here.

In fatigue, the Gerber criterion is best; however, you will find that the Goodman criterion is in common use.

Recall, that the fatigue stress concentration factors are given in Table 9-5.

For Welding codes, see the fatigue stress allowables in the AISI manual.



9-7 Fatigue Loading9-7 Fatigue Loading

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Example 9-5 (Textbook)Example 9-5 (Textbook)

Table A-20, Sy = 32 kpsi, Sut= 58 kpsi

Table 9-3, Sy = 62 kpsi, Sut= 50 kpsi

Table 9-5, Kfs=2.7

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A = 2 x 0.707 x h x l

h = 3/8=0.375 inl = 2 in(7-8) (7-17)

(7-4)

(7-25)

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Example 9-6 (Textbook)Example 9-6 (Textbook)

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(7-4)

(7-25) (7-8) (7-17)

(7-56)

(7-10)

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me 307: machine design i dr. a. aziz bazoune king fahd university of petroleum & minerals...

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