lab 1_write up_7_18_2013 (1)

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[Company name]

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AbstractThe purpose of this experiment is to test and compare the strengths of welds in the transverse and

longitudinal directions and to compare two common welding processes: stick welding and MIG

welding. Three configurations of welds were tested in tension until the welds failed. The results

were compared to two different sets of calculations obtained from the AISC manual which

calculated the strengths of the welds in both the longitudinal and transverse directions. This test

showed that a weld laid in the transverse direction will be stronger than welds of the same length

orientated in the longitudinal direction because stress concentrations will occur at the corners of

the longitudinal weld. In comparing the two different welding processes, it was concluded that

stick welding and MIG welding have comparable strengths.

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Table of ContentsAbstract ......................................................................................................................................................... 1

Table of Tables .............................................................................................................................................. 3

Table of Figures ............................................................................................................................................. 4

1. Background ............................................................................................................................................... 5

1.1 MIG Welding ....................................................................................................................................... 5

1.2 Stick Welding ....................................................................................................................................... 5

2. Test Setup ................................................................................................................................................. 5

3. Observations ............................................................................................................................................. 6

3.1 Specimen 1-S ....................................................................................................................................... 6

3.2 Specimen 2-S ....................................................................................................................................... 7

3.3 Specimen 3-S ....................................................................................................................................... 7

4. Calculations ............................................................................................................................................... 9

5. Summary of Results ................................................................................................................................ 10

References .................................................................................................................................................. 15

Appendix A: Drawings ................................................................................................................................. 16

Appendix B: Calculations............................................................................................................................. 17

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Table of TablesTable 1: Calculated Weld Strengths .............................................................................................................. 9

Table 2: Actual Weld Strengths ................................................................................................................... 10

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Table of FiguresFigure 1. The 300 kip Southwark Emery Universal Testing Machine ............................................................ 6

Figure 2. Fractured weld in Specimen 1-S..................................................................................................... 7

Figure 3. Specimen 2-S with 45 degree fracture ........................................................................................... 7

Figure 4. Fracture initiating at the weld in Specimen 3-S ............................................................................. 8

Figure 5. Failure in Specimen 3-S caused by stress concentrations at welds ............................................... 9

Figure 6. Weld Orientation ......................................................................................................................... 11

Figure 7: Load vs. displacement graph of stick weld specimens compared to 1/2" and 1/4" coupons ..... 12

Figure 8. Stress lines in a longitudinally loaded section ............................................................................. 12

Figure 9. Stress lines in a transversely loaded section ................................................................................ 12

Figure 10: Load vs. Displacement graph of Stick welds with coupon of 1/4" plate ................................... 13

Figure 11: Load vs. displacement graph of flux core weld specimens compared to 1/2" and 1/4" coupons

.................................................................................................................................................................... 14
http://c/Users/Dan/Documents/Lehigh/CEE%20419%20-%20Structural%20Behavior%20Lab/Lab%201%20-%20Weld%20Strengths/Lab%201_Write%20up_7_18_2013%20(1).docx%23_Toc361989605http://c/Users/Dan/Documents/Lehigh/CEE%20419%20-%20Structural%20Behavior%20Lab/Lab%201%20-%20Weld%20Strengths/Lab%201_Write%20up_7_18_2013%20(1).docx%23_Toc361989606http://c/Users/Dan/Documents/Lehigh/CEE%20419%20-%20Structural%20Behavior%20Lab/Lab%201%20-%20Weld%20Strengths/Lab%201_Write%20up_7_18_2013%20(1).docx%23_Toc361989606http://c/Users/Dan/Documents/Lehigh/CEE%20419%20-%20Structural%20Behavior%20Lab/Lab%201%20-%20Weld%20Strengths/Lab%201_Write%20up_7_18_2013%20(1).docx%23_Toc361989605

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1. BackgroundTwo of the most common forms of welding are Metal Inert Gas (MIG) welding and Shielded Metal Arc

Welding (SMAW). MIG welding is more common in fabrication centers and structures lab due to the

large dimensions of the welding machine and the close proximity that the welding machine has to be to

the welding surface. On the other hand, the shielded metal arc welding allows the fabricator to be

farther away from the machine which allows for more practical uses of welding members together in

large structures.

1.1 MIG Welding

MIG welding is a process in which an electrical arc forms between two pieces of steel, typically a

consumable wire electrode and a piece of steel, and heats the metals causing them to melt and join

together. In the MIG welding process, a shielding gas is applied to the surface, through the welding gun,

to help prevent any contamination in the weld which will then allow for a stronger bond. Typically the

shielding gas is either Argon or Helium and theses gasses prevent atmospheric gasses from entering into

the welding surface which causes defects and porosity within the surface of the weld. These flaws will

cause the weld to become brittle and will prevent the weld from achieving the fully design strength.

1.2 Stick Welding

Shielded metal arc welding, or commonly referred to as stick welding is similar to MIG welding in that an

electric arc is formed between two pieces of steel which cause the welding of those two pieces.

However, unlike the MIG welding process, the shielding of the welding surface comes from the shielding

around the metal arc. Instead of using a shielding gas to protect the weld, the metal electrode is instead

shielded with a flux which gives off gasses as it is melted to protect the weld being created. The flux also

contains deoxidizers which purifies the weld but also leaves behind a thin layer called slag which can be

knocked off with a hammer.

2. Test SetupTo test the strengths of the different types of welds, statics tests were performed using the 300 kip

Southwark Emery universal testing machine located in Fritz Engineering Laboratory at Lehigh University.

To measure the vertical movement of the machine crossheads, a linear potentiometer displacement

sensor was used. The sensor, Model No. 606R6KL.12, was manufactured by BEI Duncan Electronics and

has a total displacement stroke of 6 inches. To acquire the data from the displacement sensor and load

output from the test machine, a Campbell Scientific CR5000 16bit digital data acquisition system was

used. The data was recorded at a continuous rate of two samples per second while tests were

performed.

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Figure 1. The 300 kip Southwark Emery Universal Testing Machine

3. Observations

3.1 Specimen 1-S

The first stick welded specimen (1-S) was loaded at a constant rate. The sample only showed marginal

signs of plasticity, for failure occurred without warning. As shown in Figure 2, failure occurred in one

weld at a load of 64.25 kips. At failure a loud slapping noise was observed. The plates did not yield.

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Figure 2. Fractured weld in Specimen 1-S

3.2 Specimen 2-S

The second stick welded specimen (2-S) was loaded at a constant rate until failure occurred at 63.25

kips. Figure 3 demonstrates the fracture that occurred at a 45 degree angle in two of the welds. A soft

creek noise was observed at failure.

Figure 3. Specimen 2-S with 45 degree fracture

3.3 Specimen 3-S

The third stick welded specimen (3-S) was loaded at a constant rate; after the yield strength of the

quarter inch plate was reached, the load rate was increased in the interest of time. The yield peak was

reached at a load of 70 kips, the load than dropped down and plateaued at 67 kips. The load correlating

to the plateau is the yield strength of the steel. Once the plateau ends, the force continues to increase

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until the member fractures. This specimen exhibited a ductile failure as opposed to the first two

specimens that failed without much warning.

Figure 4. Fracture initiating at the weld in Specimen 3-S

The stress concentrations that were developed due to the welds initiated the fracture, which ultimately

lead to failure at 93.25 kips. Figure 4 demonstrates a weld in specimen 3 that did not fail, however, you

can see that fracture is being initiated at the weld. Figure 5 shows where the specimen failed, the

fracture developed from the weld through the whole plate. The plate exhibited necking of about an

eighth of an inch.

Start of fracture

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Figure 5. Failure in Specimen 3-S caused by stress concentrations at welds

4. CalculationsThe strength of the weld can be estimated by two equations found in AISC 360-10 and the results are

shown in Table 1. It can be observed that a higher weld strength can be calculated using the AISC J2.5

calculation. This will allow the engineer to design a stronger connection with less weld than if the AISC 8-

1 method is used.

AISC J2.5 AISC 8-1

Specimen Weld Strength (k) Weld Strength (k)

S1 59.06 27.84

S2 63.00 44.55

S3 122.06 72.39

S4 185.06 116.94Table 1: Calculated Weld Strengths

The equation found in AISC J2.5 accounts for the orientation of the weld. Specimen 1-S had a shorter

overall length of weld than specimen 2-S, however, specimen 1-S failed at a slightly larger load. From

the results of our testing and the results of this equation is can be determined that the direction of the

weld affects the overall strength.

AISC 8-1

AISC J2.5

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5. Summary of ResultsAfter the conclusion of the tests, the results are tabulated in Table 2.

Specimen Yield Strength (k) Max Strength (k)

S1_S 64.25

S2_S 63.25

S3_S 67 93.25

S1_FC 66 66.24

S2_FC 67 70.65

S3_FC 67 94.02

1/4" Plate 67 93

1/2" Plate 99 133.24Table 2: Actual Weld Strengths

There is a very slight difference in the strength of weld between a MIG weld and the SMAW weld, thus it

can be concluded that the two methods are comparable in strength. The percent differences between

the first two samples of the two methods were on average about 7%. The percent difference for the last

samples was about 0.8%. The main difference was seen in specimen S1_S, S2_S and S1_FC, S2_FC, the

MIG welded specimens (S1_FC and S2_FC) yielded before failure as opposed to the SMAW welded

specimen (S1_S and S2_S) failed right before yielding occurred. A reason for this occurrence is that the

MIG weld might be slightly more ductile than the SMAW weld.

The equations used to calculate the design weld strength yielded a lower value than the actual test

results. The design values are an allowable load that includes a factor of safety to ensure substantial

connections. In this lab, specimens are tested to the ultimate load the weld can withstand. AISC

equation J2.5 is more accurate in determining the weld strengths because it takes the orientation of the

weld into consideration. The test results from specimen S1_S and S2_S proved that orientation counts.

Specimen S1_S had a shorter overall weld length with horizontal welds; whereas specimen S2_S had a

longer overall weld length with vertical welds. Specimen S1_S had a higher ultimate strength because of

the horizontal weld orientation. Figure 6 shows the difference between the horizontal and vertical weld

orientations. The AISC 8-1 equation will provide a more conservative strength. This equation could be

used if the designing engineer is uncertain of the strength of the connection.

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Figure 6. Weld Orientation

When a weld fails, there is no warning, its a brittle failure. Unlike a piece of steel, when a weld fails it

doesnt yield and elongate, it will reach its max strength and break. The weld reduces the ductility of

the steel, in return the weld produces a greater strength. Figure 7 shows specimen S3_S fails at a larger

load than the quarter inch plate coupon, however, it fails with a much smaller displacement value than

the coupon. The half inch plate is not affected in this test because the yield value is much greater than

the welds ultimate loads.

Vertical Weld

Orientation

Horizontal Weld

Orientation

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Figure 7: Load vs. displacement graph of stick weld specimens compared to 1/2" and 1/4" coupons

As the stress is transferred across the plate, it will transfer into the welds which are aligned

perpendicular with where the load is applied as shown in Figure 9. If the weld is parallel with the loadingdirection, then the stress will concentrate at the corners of the weld nearest to the applied load. Figure

8Error! Reference source not found. shows how the stress from the applied load will converge at the

corner of the welds.

Figure 8. Stress lines in a

longitudinally loaded section

Figure 9. Stress lines in a

transversely loaded

section

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Testing the plates without welds shows that the third samples failed because of the stress

concentration. The plate specimens had the same yield strength; however, it experienced more ductility

than the welded specimen. Specimens S3_S and S3_FC experienced a stress concentration similar to

that ofError! Reference source not found.. The fractures in these specimens were initiated at the edge

of the plate at the point of the welds. The results proved that stress concentrations reduce the ductility

of a specimen.

In specimens S1_S and S2_S brittle failure of the weld occurred at 64.25kips and 63.25kips respectively

which occurred below the yield strength of the steel as shown in Figure 10, however, in specimen S3_S,

the steel yielded at 67kips and strain hardening occurred before the weld failed as shown inFigure 10.

The percent difference of the displacements of the third specimen and the quarter inch plate was about

72.6%. The large difference in overall displacements demonstrates the loss of ductility caused by

welding.

Figure 10: Load vs. Displacement graph of Stick welds with coupon of 1/4" plate

Figure 11 shows how the flux core welded specimens compared to the coupon plate specimens.

Specimen S1_FC had a brittle failure in the weld at strength of 66.24 kips which occurred right after the

steel yielded. Specimen S2_FC experienced yielding and began to strain harden before eventually failing

at 70.65 kips. Specimen S3_FC acted similar to specimen S3_S as the quarter inch plate yielded and

experienced strain hardening before failure occurred at 94.02 kips.

Specimen S4_S and S4_FC were not tested because they were act very similarly to specimens S3_S and

S3_FC. The third specimens in both methods experienced a fracture that went through the quarter inch

plate. This failure was brought on by the presence of the weld, as the fracture initiated at the edge of

the plate by the weld. The same result would have occurred in specimens S4_S and S4_FC.

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Figure 11: Load vs. displacement graph of flux core weld specimens compared to 1/2" and 1/4" coupons

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ReferencesSalmon, Charles G., John Edwin Johnson, and Faris A. Malhas. "Welding." Steel Structures: Design and

Behavior. 5th ed. Upper Saddle River, New Jersey: Pearson Prentice Hall, 2009. 161-227. Print.

Specification for structural steel buildings. Chicago, Ill.: American Institute of Steel Construction, 2010.

Print.

Steel construction manual. 14th ed. Chicago, Ill.: American Institute of Steel Construction, 2011. Print.

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Appendix A: Drawings

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Appendix B: CalculationsAISC 360 EQN J2.5

Specimen 1:

Weld Strength:

Weld Size:

Length:

Specimen 2:

Weld Strength:

Weld Size:

Length:

Fnw 0.6FEXX 1 0. 5 sin( )1.5

FEXX 70ks

a3

16i

L 5in

2

Fnw 0.6FEXX 1 0. 5 sin ( )( )1.5

630 00psi

Rn Fnw a L 59.06ki

FEXX 70ksi

a3

16i

L 8in

0

Fnw 0.6FEXX 1 0. 5 sin ( )( )1.5

420 00psi

Rn Fnw a L 63ki

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Specimen 3:

Weld Strength:

Weld Size:

Length:

Specimen 4:

Weld Strength:

Weld Size:

Length:

FEXX 70ksi

a3

16in

L1 5i L2 8in

1

2 2 0

Fnw1 0.6FEXX 1 0. 5 sin 1 1.5

630 00psi

Rn1 Fnw1 a L1 59.06ki

Fnw2

0.6FEXX

1 0. 5 sin 2

1.5 420 00psi

Rn2 Fnw2 a L2 63ki

Rn Rn1 Rn2 122.06ki

FEXX 70ksi

a

3

16i

L1 5in L2 16i

1

2 2 0

Fnw1 0.6FEXX 1 0 .5 sin 1 1.5

630 00psi

Rn1 Fnw1 a L1 59.06ki

Fnw2 0.6FEXX 1 0 .5 sin 2 1.5 420 00psi

Rn2 Fnw2 a L2 126ki

Rn Rn1 Rn2 185.06kip

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1/4" Plate:

1/2" Plate:

A0.25 0. 25in 2.5 in 0.63in2

Fy

50ks

Fu 65ks

Ry Fy A0.25 2 62.5kip

Ru Fu A0.25 2 81.25kip

A0.5 0.5in 3 .5 in 1.75in2

Fy 50ks

Fu 65ks

Ry Fy A0.5 87.5ki

Ru Fu A0.5 113.75ki

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AISC 360 EQN 8-1

Specimen 1:

Weld Strength:

Weld Size:

Length:

Unfactored strength of weld:

Factored strength of weld:

Specimen 2:

Weld Strength:

Weld Size:

Length:



Specimen 3:

Weld Strength:

Weld Size:

Length:



Rn 0.6FEXX2

2 a L

FEXX 70ks

a3

16i

L 5in

R FEXX2

2 a L 46.4kip

Rn 0.6R 27.84ki

FEXX 70ks

a3

16i

L 8in

R FEXX

2

2 a L 74. 25ki

Rn 0.6R 44.55ki

FEXX 70ks

a3

16i

L 13in

R FEXX2

2 a L 12 0. 65ki

Rn 0.6R 72.39ki

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Specimen 4:

Weld Strength:

Weld Size:

Length:



FEXX 70ks

a3

16i

L 21in

R FEXX2

2 a L 194 .9ki

Rn 0.6R 116.94ki