A force displacement curve is drawn from experimental value and finite element analysis.
Figure 61 shows the force and displacement relation curve and it represents that the results are following the same pattern.
Figure 61. Experimental result and Finite element result
0
The experimental value and theoretical capacity of weld are summarized in the following table 13. For nominal throat thickness (3.12 mm), the load bearing capacity is 260 kN; where for effective throat thickness (3.7 mm), the load bearing capacity is 307 kN. The calculation is done using equation no 8. The experimental results show the capacity are 386 kN and 343 kN for -40 °C and room temperature respectively.
Table 13. Load carrying joint, theoretical and experimental capacity Specimen ID Experimental
environment
Theoretical capacity (kN) According to equation 8
Experimental
The failure angle of the specimen is measured from the macro view and done roughly. In figure 62 and figure 63, two specimens (namely ST11_X20 and ST11_X21) were examined in two different temperatures (-40 °C, and room temperature, respectively) showed that the failure angle for ST11_X20 specimen is around 71 and for specimen ST11_X21 it is 18.The failure angle is depicted by the FE model shown in figure 64 and the failure angle is 27.
Figure 62. ST11_X20, failure angel examined in -40 °C temperature
Figure 63. ST11_X21, failure angel examined in room temperature
Figure 64. FE model load carrying joint depicts the failure angle
9 DISCUSSION
This test program is performed to analyze the material behavior and weld performance according to Eurocode 3. The material is Strenx1100 Plus and material certificate values are 1112 MPa yield strength and 1143 MPa ultimate strength. Basically, three types of joints were tested (namely butt joint, T joint, X joint) with FE analysis, an experimental test. The study covers the comparison of joint performance between the analytical, experimental and FEA results. Slightly undermatching filler material Union X96 is used for this experimental test.
Material behavior is analyzed by assessing engineering and true stress and strain curve. A base material was tested for getting engineering and true stress-strain curve. An FE analysis for similar kind of base material is done to validate the used material parameters.
Load carrying joint design by fillet weld type, X-joint, is investigated to verify the validation of the design rules for fillet weld rules presented in Eurocode 3. The geometry of the weld is crucial regarding load carrying capacity, where it was tested at room temperature and -40
C temperature. The ultimate capacity of the load carrying joint is 343 KN (minimum) at room temperature and 386 KN at -40 C temperature. The results illustrate that the load carrying capacity determines by the Eurocode 3 is adequate. The critical failure plane is determined by Von Mises theory. A symmetry fillet weld is used for load carrying joint.
From the experimental result failure angle is either 18 (specimen tested at room temperature) or 71 (specimen tested at -40 C temperature) and for FE analysis the critical plane locates at 27. Two of the load carrying joint design with large throat thickness which summarized that if the weld capacity is big enough than the base material then it will act as a non-load carrying joint.
The non-load carrying joint is being analyzed to understand the heat input, cooling rate effect. The specimens were tested at room temperature as well as -40 C. Almost all specimen results exhibit that the failure occurs in the base material with an angle of 30. The strength of the non-load carrying joint material can vary for fillet weld due to the softening effect. Slow cooling have softening effect in the material, where high cooling rate causes
very hard zone near to the fusion line. It is possible that a large throat thickness (also plate thickness or other joint dimensions) causes slow cooling in HAZ and makes softening in the material. Usually conventional steel and most of the high strength steel shows the softening effect in the HAZ. However, Strenx 1100 Plus did not follow the pattern and has a good hardness in HAZ. While considering cost effective process it is recommended to keep small throat thickness as well as to remove the softening effects. In addition, the heat affected zone containing the high hardness value is presented by hardness measurement. Furthermore, hardness value distribution is almost identical to all over that makes Strenx 1100 Plus material become a sustainable strength maintaining material in different conditions.
10 CONCLUSION
The conclusion derived from the experimental results and other observation is applicable to the material quenched and tempered Strenx 1100 Plus. The material exhibits good weldability and heat effect sustainability that may differ to other ultra-high strength steel.
Although the number of the specimen for load carrying joint was rather low, however detail observation bolstered the conclusion with Eurocode 3 standard in respect that the capacity of the weld is sufficient. Regarding non-load carrying joint, sufficient number of specimens was observed. In conclusion:
There is a resemblance in the results obtained from the theoretical, experimental and finite element analysis.
Eurocode 3 able to define the weld capacity for load carrying joint.
The base material has good toughness and ultimate capacity.
Hardness distribution is quite smooth in all cases.
There is no significant effect of heat input in the material.
Failure model of the specimens was ductile
Except for the load carrying fillet welded joints with throat thickness of 3 mm specimens fail in the base material, follow the von Mises stress theory, except ST11_X12 follows the maximum stress theory.
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APPENDIX I, 1 Hardness graph of non-load carrying joint.
Figure 1. W23 from base metal to the weld
Figure 2. W24 from weld to the base metal
Figure 3. W26 through thickness right side of the front view
200
APPENDIX I, 2 Hardness graph of butt weld.
Figure 4. HP3 from base metal to the weld
Figure 5. HP4 from wed to the base metal
360 380 400
0 1 2 3 4 5 6 7 8
HP3
360 380 400 420 440
0 1 2 3 4 5 6 7 8
HP4
Figure 6. HP6 through thickness
360 380 400 420 440
-7 -6 -5 -4 -3 -2 -1 0
HP6
APPENDIX I, 3 Hardness graph of load carrying joint.
Figure 7. 4A from weld to the base metal
Figure 8. 4D through the weld
0 100 200 300 400 500
0 1 2 3 4 5
0 100 200 300 400 500
-6 -5 -4 -3 -2 -1 0
APPENDIX I, 4 Hardness graph of non-load carrying T joint (NLCT-HiFIT treatment.)
Figure 9. 1 from weld to the base metal
Figure 10. 2 through thickness
200 250 300 350 400 450 500
0 1 2 3 4 5 6 7
365 370 375 380 385
-4.5 -4 -3.5 -3 -2.5 -2 -1.5 -1 -0.5 0
APPENDIX I, 5 Hardness graph of non-load carrying T joint (NLCT Tig).
Figure 11. 1 from weld to base metal
Figure 12. 2 through thickness
370
APPENDIX II Determining yield stress at 0.2% from experiment test and maximum stress.
Figure 1. ST11_B4, yield stress at 0.2%
Figure 2. ST11_X10, yield stress at 0.2%
0
0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04 0.045 0.05
Stress
Figure 3. ST11_X11, yield stress at 0.2%
Figure 4. ST11_X12, yield stress at 0.2%
0
0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04 0.045
Stress
0.000 0.005 0.010 0.015 0.020 0.025 0.030 0.035 0.040
Stress
Strain
ST11_X12 ST11_X12 YIELD
Figure 5. ST11_X13, yield stress at 0.2%
Figure 6. ST11_X18, yield stress at 0.2%
0
0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04
Stress
0 0.005 0.01 0.015 0.02 0.025 0.03
Stress
Strain
ST11_X18 ST11-X18 Yield
Figure 7. ST11_X19, yield stress at 0.2%
Figure 8. ST11_X14, yield stress at 0.2%
0
0 0.005 0.01 0.015 0.02 0.025 0.03 0.035
Stress
Strain
ST11_X14 ST11_X14 yield
Figure 9. ST11_X15, yield stress at 0.2%¨
Figure 10. ST11_X16, yield stress at 0.2 %
0
0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04
Stress
0 0.005 0.01 0.015 0.02 0.025 0.03 0.035
Stress
Strain
ST11_X16 ST11_X16 yield
APPENDIX III
Continues. Welding parameters.
S11_LCX_4 1 11 7.8 220 26.7
2 11 7.8 221 26.7
3 11 7.8 220 26.8
4 11 7.8 222 26.7
S11_LCX_1 latest 1 11.5 20 222 26.3
2 11.5 20 223 26.5
3 11.5 20 224 26.5
4 11.5 20 224 26.5
S11_LCX_2 latest 1 11.5 20 222 26.5
2 11.5 20 224 26.5
3 11.5 20 225 26.5
4 11.5 20 225 26.5
APPENDIX IV Force displacement curves
Figure 1. Force displacement curve. ST11_B4
Figure 2. Force displacement curve. ST11_T9
0
Figure 3. Force displacement curve. ST11_X11
Figure 4. Force displacement curve. ST11_X12
0
Figure 5. Force displacement curve. ST11_X10
Figure 6. Force displacement curve. ST11_X14
0
Figure 7. Force displacement curve. ST11_X15
Figure 8. Force displacement curve. ST11_X16
-100
Figure 9. Force displacement curve. ST11_X19
-100 0 100 200 300 400 500 600 700
-1 0 1 2 3 4 5
Force
Displacement
ST11_X19
ST11_X19
APPENDIX V Specimens’ failure locations
Figure 1. ST11_B4
Figure 2. ST11_B5
Figure 3. ST11_BM
Figure 4. ST11_T9
Figure 5. ST11_X10
Figure 6. ST11_X11
Figure 7. ST11_X12
Figure 8. ST11_X13
Figure 9. ST11_X14
Figure 10. ST11_X15
Figure 11. ST11_X18
Figure 12. ST11_X19
Figure 13. ST11_X20
Figure 14. ST11_X21
Figure 15. ST11_X16