- Email: [email protected]
Monel 400 dissimilar metal welded joints
Materials Today: Proceedings xxx (xxxx) xxx
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Finite element simulation on effect of bevel angle and filler material on tensile strength of 316L stainless steel/Monel 400 dissimilar metal welded joints Cherish Mani ⇑, Sozharajan Balasubramani, R. Karthikeyan Department of Mechanical Engineering, BITS Pilani, Dubai Campus, P.O.Box. 345 055, United Arab Emirates
a r t i c l e
i n f o
Article history: Received 17 October 2019 Received in revised form 5 December 2019 Accepted 26 December 2019 Available online xxxx Keywords: Dissimilar metal welding Gas tungsten arc welding Austenitic stainless steel Monel alloy Tensile strength Numerical simulation
a b s t r a c t In the present study, an attempt has been made to analyze the tensile testing of 316L stainless steel/ Monel 400 gas tungsten arc welded joints. The process parameters considered for the study are filler materials and bevel angle used for butt joints. Finite element simulation of tensile testing is attempted for different bevel angles and filler wires. Transient structural analysis has been used for simulation. Linearized equivalent stress distribution is obtained along the axial length of the specimen. Engineering stress-strain curve has been drawn using the reaction force and displacement. Comparison has been made between the experimental results and numerical solution. The results agree to a greater extent till the ultimate tensile region. Ó 2020 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the 2nd International Conference on Recent Advances in Materials & Manufacturing Technologies.
1. Introduction Austenitic Stainless Steels (ASS) are extensively used in petrochemical, paper making and biomaterials-based manufacturing industries due to their excellent properties such as corrosion resistance, weldability and formability with moderate tensile strength [1]. Since they are being used in several manufacturing equipment, welded joints are essential with similar and dissimilar materials. Dissimilar metal welds (DMW) are frequently used in welded constructions and joint efficiency is related to performance of the whole structure. ASS is often welded to different materials ranging from low carbon steel to nickel alloys [2]. DMW pose greater challenges due to the difference in the physical and metallurgical properties of the parent metals and fillers used for welding. DMW of ASS often lead to formation of d ferrite, r phase, sensitization and stress corrosion cracking. ASS based DMW are more specifically used in energy conversion systems [3]. ASS/Ni alloy based DMW joints find applications boiler feed water heat exchangers in nuclear industries. Gas tungsten arc welding (GTAW) is most commonly used for ASS based for DMW. The microstructure of ⇑ Corresponding author. E-mail address: [email protected] (C. Mani).
such welds witness variation of optical microstructure along different zones of welded joints on either side and the hardness generally increases towards the weldment [1]. The weld strength of GTAW joints depends on different process parameters such as weld current, arc voltage, welding speed and gas flow rate. Extensive literature is available related to analysis of these parameters. Selection of filler wires is an important phase in DMW due to the variation of properties between parent metals. The composition and size of the filler wire decides the geometry and metallurgical characteristics of the weldment which in turn decides the tensile strength and corrosion resistance of the joints. ERNiCrMo-3 and ERNiCrMo-4 are Ni-based fillers are found to perform well for ASS/Monel alloy DMW [4]. Geometry of the welded joints is another important parameter which will influence the stress distribution along the welded joints. In butt welded joints, bevel angles play important role which normally vary between 30 and 45°. The welded joints normally act as stress concentration areas. To analyse the stress distribution along the welded joints, numerical simulation may be used [5]. It is an effective tool to analyse the effect of weld geometry. Different regions of the welded joint can be modelled in finite element analysis and effect of different parameters on the quality characteristics of the welded joints can be assessed [6].
https://doi.org/10.1016/j.matpr.2019.12.353 2214-7853/Ó 2020 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the 2nd International Conference on Recent Advances in Materials & Manufacturing Technologies.
Please cite this article as: C. Mani, S. Balasubramani and R. Karthikeyan, Finite element simulation on effect of bevel angle and filler material on tensile strength of 316L stainless steel/Monel 400 dissimilar metal welded joints, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.12.353
2
C. Mani et al. / Materials Today: Proceedings xxx (xxxx) xxx
The objectives of the present study include the following: Dissimilar metal welding of SS 316L/Monel 400 alloy using GTAW. Effect of filler material and bevel angle in butt weld. Numerical simulation of tensile testing using ANSYS WORBENCH. Comparison of simulation results with experimental results 2. Experimental procedure 2.1. Materials Fig. 1. Weld groove typical section.
The properties of austenitic stainless steel are valued to industry owing to high ductility, excellent toughness, strength, corrosion resistance, weldability. The test coupons are made from 3 mm plates of Monel 400 and stainless steel 316L of dimensions 200 mm (L) 20 mm (W) with filler material of SS316, Monel and ENiCrFe-5. Table 1 shows the chemical composition of materials used for specimen preparation by GTAW process.
Table 2 Welding parameter and configuration.
2.2. Welding conditions Gas Tungsten arc welding (GTAW) is referred as the welding process which uses a non-consumable tungsten electrode to produce the weld. Monel 400 plates with stainless steel 316L are welded with filler material ENiCrFe-5, SS 316L and Monel wire by GTAW process. The edge preparation with V grove with different bevel angles of 30°, 35° and 40°, with a root gap of 2 mm fitup was done to carry out weld as shown in Fig. 1. The weld specimens were welded under 3 different bevel angles with the filler wires of ENiCrFe-5, SS316 wire, Monel wire producing 9 weld test coupons are listed in Table 2. The weld current in the range of 80– 85 Amp, polarity as DCEN, shielding gas of Argon 8 LPM and backing gas of argon with a flow rate 5–7 LPM were established by trials in line with the recommendations of filler wire manufacturer and the parameters are listed in Table 2.
Filler wire (3 conditions)
ENiCrFe-5
SS 316L wire
Monel 400 wire
Groove angle (3 Conditions) Bevel angle Welding current Plate thickness Root face thickness Root opening Polarity Welding speed Shielding gas (Argon) Backing gas (Argon) Tungsten size and type
V-type 60°
V-type 70°
V-type 80°
30° 35° 80 amps 3 mm 1 mm 2 mm DCEN 2.5 mm/s 8 LPM 5–7 LPM 1/800 , 2% throated tungsten
40°
3. Finite element simulation 3.1. Geometry modelling Tensile test specimens with 30° bevel angle in the weld zone are modelled in ANSYS SPACE CLAIM, material properties were assigned for different zones namely Monel alloy, weld material and SS 316L stainless-steel alloy. Nonlinear - Bilinear Isotropic hardening properties were provided for these three materials. ANSYS geometry modelled for the study is shown in Fig. 3 and weld zone with respect to 30° bevel angle shown in Fig. 4(a) and (b). Properties of base materials and weld materials in the model are presented in Table 4.
2.3. Tensile test standard The weld test coupons upon completion of weld were further visually checked followed by ultrasonic test as per AWS D1.1 standards for weld flawless and defects. Upon acceptance of the weld coupons, tensile test specimens were prepared by water jet cutting with dimensions in accordance with ASTM E8/E8M-13a, ‘‘Standard Test Methods for Tension Testing of Metallic Materials”. The dimensional sketch of tensile test coupon is shown on Fig. 2 [7].
3.2. Contact and target definitions Bonded contact is provided between weld material and base material on either side. Bonded contact defines no penetration and sliding between the faces or edges. Weld material face defined as contact region and the remaining two material faces act as target regions. In bonded contact, augmented Lagrange formulation is used since small amount of penetration is allowed during welding between different zones. Contact behaviour was assumed to be asymmetric since contact elements are defined on weld surface and target elements defined on the other two surfaces. For
2.4. Plan of experiments The range of variable parameters are listed on Table 3 for the plan of experiments. The experiments were done by varying one parameter at a time. Tensile test on the 5 test coupons based on the different variable parameters were test on SHIMADZU 100 kN servopulser dynamic testing machine.
Table 1 Chemical composition of materials. Material
C
Cr
Fe
Mn
Ni
P
S
Si
Mo
Cu
Ti
Co
Nb
SS 316L Monel 400 ENiCrFe-5
0.03 0.3 0.04
17 – 14–17
65.64 2.5 6–10
2 2 1.0
12 63 70 (min)
0.05 – 0.03
0.03 0.024 0.015
0.75 0.5 0.35
2.5 – –
– 31.676 0.5
– – –
– – 0.12
– – 1.5
Please cite this article as: C. Mani, S. Balasubramani and R. Karthikeyan, Finite element simulation on effect of bevel angle and filler material on tensile strength of 316L stainless steel/Monel 400 dissimilar metal welded joints, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.12.353
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Fig. 2. Tensile test coupon dimensions.
Table 3 Experimental plan. Specimen No
1
2
3
4
5
Filler wire Bevel Angle
ENiCrFe-5 30°
ENiCrFe-5 35°
ENiCrFe-5 40°
Monel wire 30°
SS 316 wire 30°
Fig. 3. Geometry modelling of tensile test specimen.
Fig. 4. (a) Weld zone with 30° bevel angle; (b) Meshed model with tetrahedron element.
Table 4 Materials properties of base material and weld material. 650
MONEL 400
SS 316L
ENiCrFe-5
Density (kg/m3) Young’s Modulus (GPa) Poisson Ratio Yield Strength (MPa) Tangent Modulus (MPa) Ultimate Strength (MPa)
8800 179 0.3 240 1450 550
8000 193 0.31 205 1800 515
8500 190 0.3 275 1750 630
asymmetric behaviour, only the contact surfaces are constrained from penetrating the target surfaces.
600
Linearized Equivalent Stress, MPa
Material Properties
550
500
450
400
350
3.3. Meshing Entire model was meshed using quadratic 3D tetrahedrons elements (Fig. 4b). Tetrahedron element has less degrees of freedom
300 2000
6000
10000
14000
18000
Number of Elements
Fig. 5. Mesh convergence curve for weld specimen.
Please cite this article as: C. Mani, S. Balasubramani and R. Karthikeyan, Finite element simulation on effect of bevel angle and filler material on tensile strength of 316L stainless steel/Monel 400 dissimilar metal welded joints, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.12.353
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Fig. 6. Loading and boundary conditions.
Fig. 7. Linearized equivalent stress.
700
500
WELD MATERIAL 30DEG WELD MATERIAL 35DEG WELD MATERIAL 40DEG MONEL 30DEG SS316L 30DEG
600
450 400 350
Stress,MPa
Linearized Stress,MPa
500
400
300
300 250 200
200
150
FEM WELD MATL 30DEG FEM WELD MATL 35DEG FEM WELD MATL 40DEG FEM MONEL 30DEG FEM SS316L 30DEG
100
100
50 0 0
20
40
60
80
100
120
140
160
180
200
Length, mm
0
5
10
15
20
25
30
Strain
Fig. 8. Linearized equivalent stress for all specimens.
Fig. 9. Engineering stress-strain curves generated from FEM simulation.
compared to hexa-hederal elements and to provide solution at a faster rate. It is necessary to have fine mesh density mainly in the areas of high stress gradients and coarser mesh density in areas of low stress gradients or where the magnitude of the stresses is not of much interest. The effect of sphere of influence has been used to get fine mesh density in the critical areas. Pinch control has been used to merge mesh nodes in close proximity after meshing using a given tolerance which removes the bad elements from the model results more refined meshing. Mesh convergence study (mesh sensitivity analysis) in finite element analysis, is normally done to determine the optimum
number of elements to increase the accuracy of the solution with less computational time. For the present case, the analysis was performed based on the maximum linearized equivalent stress. Element size is varied from 5 mm to 2 mm in whole body and 1.5 mm to 0.5 mm for critical areas. The number of elements were increased from 2847 to 17,522. After that mesh convergence, an element size of 2 mm has been used for the whole body and element size of 0.5 mm has been used for in the critical areas (weld and near weld zones) by using sphere of influence. Fig. 5 shows the mesh convergence curve for the linearized equivalent stress.
Please cite this article as: C. Mani, S. Balasubramani and R. Karthikeyan, Finite element simulation on effect of bevel angle and filler material on tensile strength of 316L stainless steel/Monel 400 dissimilar metal welded joints, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.12.353
C. Mani et al. / Materials Today: Proceedings xxx (xxxx) xxx
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be inferred that, as the bevel angle increases, the stress values were decreased due to increase in area. ENiCrFe-5 (weld material) possess maximum strength when compared to Monel alloy and SS 316L alloy. Hence the stress values are maximum for weld material when compared to the other two filler wires.
500 450 400
Stress,MPa
350 300
4.2. Stress-strain curve
250 200 150
WELD MATL 30DEG WELD MATL 35DEG WELD MATL 40DEG MONEL 30DEG SS316L 30DEG
100 50 0
5
10
15
20
25
30
Strain Fig. 10. Experimental engineering stress-strain curves.
Table 5 Mean absolute error for the stress-strain curves. Filler and bevel angle
Weld, 30°
Weld, 35°
Weld, 45°
Monel 400, 30°
SS 316L, 30°
Mean absolute error, MPa
0.4147
7.8247
11.5192
7.7624
7.7417
The reaction force from simulation and the corresponding displacements were recorded for different specimens and using those values, engineering stress-strain curves were drawn. The simulation readings were obtained till ultimate tensile strength region and presented in Fig. 9. The ENiCrFe-5 (weld material) possess higher stress values when compared to filler wires made of parent materials (Monel and SS 316L) since the strength of weld material is higher than both alloys. The increase in bevel angle resulted in decreased stress level for ENiCrFe-5 (weld material). The simulated results may be compared with the experimental results which are presented in Fig. 10. It can be seen for all the cases considered, the simulated stress strain curves are close to experimental curves. The mean absolute error calculated between experimental and simulated values are presented in Table 5. Trend of the curves are almost similar, however, the values are little different due to the material model considered for the study. The FEM analysis proposed may be used for prediction of stress strain curves for tensile testing. However, the fracture behaviour cannot be predicted by this analysis since the fracture criterion has not been defined which has been left for future study.
3.4. Loading and boundary conditions 5. Conclusion One end of the specimen (Monel alloy side) was fixed and the end of the specimen (SS 316L side) was subjected to displacement in X direction as per experimental boundary conditions (Fig. 6). Analysis was performed in transient structural analysis up to 70 steps with 0.2 mm displacement periodic increments till 14 mm. The maximum displacement was chosen based on experimental observation. End of each time step is 1 sec. Applied displacement may result in geometry nonlinearity and hence large deflection was provided during analysis. 4. Results and discussions The proposed simulation was carried out for all the experimental conditions specified in Table 3 and the performance was compared. Linearization stress along the length of the weld has been recorded to study the effect of bevel angle and filler material. For ENiCrFe-5 all three angles were considered for other two filler wires, 30° bevel angle was used. The stress strain experimental results were compared with the FEM results. The analysis is limited to simulation of stress distribution up to ultimate strength level and fracture behaviour is not considered.
Finite element simulation of tensile testing of Monel/SS 316L has been performed using transient structural analysis. The effect of bevel angle and filler wire on stress-strain behavior and linearized stress distribution are analyzed. The stress strain curves generated using FEM simulation were compared with experimental results and are found to be close. The weld material ENiCrFe5 has higher strength than the filler wires made up of the base materials. The increase in bevel angle decreased the linearized stress. FEM simulation can be used for prediction of stress-strain curves and further analysis is required to analyze the fracture behavior. Implicit/Explicit dynamics may be performed to simulate the fracture of the tensile test carried out. Consideration residual stress due to thermal loading during welding will improve the accuracy of prediction which has not been attempted.
CRediT authorship contribution statement Cherish Mani: Investigation, Resources. Sozharajan Balasubramani: Software, Formal analysis. R. Karthikeyan: Conceptualization, Supervision.
4.1. Linearized equivalent stress Stress linearization is a technique to decompose actual stress distribution across thickness into membrane (average) stress and bending (linearly varying) stress, so that net force and moment across the thickness remains same. Fig. 7 shows the linearized stress distribution along the axial length of the specimen. The joint region has maximum stress on either side of the weld since the bonded connections exist along these regions which hold the base materials with weldment. Value of stress in SS 316L side is lesser than Monel side due to difference in strength. The linearized stress distribution has been plotted for all the simulations in Fig. 8. It can
Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgement Authors are grateful to BITS Pilani, Dubai campus for the encouragement and support for the research work.
Please cite this article as: C. Mani, S. Balasubramani and R. Karthikeyan, Finite element simulation on effect of bevel angle and filler material on tensile strength of 316L stainless steel/Monel 400 dissimilar metal welded joints, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.12.353
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C. Mani et al. / Materials Today: Proceedings xxx (xxxx) xxx
References [1] M. Sabzi, S.M. Dezfuli, J. Manuf. Process 33 (2018) 74–85. [2] A.B. Verma, S.U. Ghunage, B.B. Ahuja, 5th International & 26th All India Manufacturing Technology, Design and Research Conference IIT, Guwahati, Assam, India, 2014, pp.302-1–302-6. [3] A. Handa, V. Chawla, J. Mech. Eng. 66 (2016) 27–36. [4] B. Yelamasetti, S. Kumar, B. Sridhar Babu, T. Vishu Vardhan, V.R. Gunda, Mater. Today: Proc. (2019), https://doi.org/10.1016/j.matpr.2019.06.759.
[5] J. Fohrenbach, Fatigue Life Prediction of High Frequency Mechanical Impact (HFMI) Treated Welded Joints by Numerical Simulation and Damage Mechanics Approaches Master Thesis, Mechanical Engineering, Franhofer, 2015. [6] S.K. Panda, N. Sreenivasan, M.L. Kuntz, Y. Zhou, J Eng Mater-T ASME 130 (2008) 1–9. [7] ASTM E8/E8M-13a, Standard Test Methods for Tension Testing of Metallic Materials.
Please cite this article as: C. Mani, S. Balasubramani and R. Karthikeyan, Finite element simulation on effect of bevel angle and filler material on tensile strength of 316L stainless steel/Monel 400 dissimilar metal welded joints, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.12.353
Contents lists available at ScienceDirect
Materials Today: Proceedings journal homepage: www.elsevier.com/locate/matpr
Finite element simulation on effect of bevel angle and filler material on tensile strength of 316L stainless steel/Monel 400 dissimilar metal welded joints Cherish Mani ⇑, Sozharajan Balasubramani, R. Karthikeyan Department of Mechanical Engineering, BITS Pilani, Dubai Campus, P.O.Box. 345 055, United Arab Emirates
a r t i c l e
i n f o
Article history: Received 17 October 2019 Received in revised form 5 December 2019 Accepted 26 December 2019 Available online xxxx Keywords: Dissimilar metal welding Gas tungsten arc welding Austenitic stainless steel Monel alloy Tensile strength Numerical simulation
a b s t r a c t In the present study, an attempt has been made to analyze the tensile testing of 316L stainless steel/ Monel 400 gas tungsten arc welded joints. The process parameters considered for the study are filler materials and bevel angle used for butt joints. Finite element simulation of tensile testing is attempted for different bevel angles and filler wires. Transient structural analysis has been used for simulation. Linearized equivalent stress distribution is obtained along the axial length of the specimen. Engineering stress-strain curve has been drawn using the reaction force and displacement. Comparison has been made between the experimental results and numerical solution. The results agree to a greater extent till the ultimate tensile region. Ó 2020 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the 2nd International Conference on Recent Advances in Materials & Manufacturing Technologies.
1. Introduction Austenitic Stainless Steels (ASS) are extensively used in petrochemical, paper making and biomaterials-based manufacturing industries due to their excellent properties such as corrosion resistance, weldability and formability with moderate tensile strength [1]. Since they are being used in several manufacturing equipment, welded joints are essential with similar and dissimilar materials. Dissimilar metal welds (DMW) are frequently used in welded constructions and joint efficiency is related to performance of the whole structure. ASS is often welded to different materials ranging from low carbon steel to nickel alloys [2]. DMW pose greater challenges due to the difference in the physical and metallurgical properties of the parent metals and fillers used for welding. DMW of ASS often lead to formation of d ferrite, r phase, sensitization and stress corrosion cracking. ASS based DMW are more specifically used in energy conversion systems [3]. ASS/Ni alloy based DMW joints find applications boiler feed water heat exchangers in nuclear industries. Gas tungsten arc welding (GTAW) is most commonly used for ASS based for DMW. The microstructure of ⇑ Corresponding author. E-mail address: [email protected] (C. Mani).
such welds witness variation of optical microstructure along different zones of welded joints on either side and the hardness generally increases towards the weldment [1]. The weld strength of GTAW joints depends on different process parameters such as weld current, arc voltage, welding speed and gas flow rate. Extensive literature is available related to analysis of these parameters. Selection of filler wires is an important phase in DMW due to the variation of properties between parent metals. The composition and size of the filler wire decides the geometry and metallurgical characteristics of the weldment which in turn decides the tensile strength and corrosion resistance of the joints. ERNiCrMo-3 and ERNiCrMo-4 are Ni-based fillers are found to perform well for ASS/Monel alloy DMW [4]. Geometry of the welded joints is another important parameter which will influence the stress distribution along the welded joints. In butt welded joints, bevel angles play important role which normally vary between 30 and 45°. The welded joints normally act as stress concentration areas. To analyse the stress distribution along the welded joints, numerical simulation may be used [5]. It is an effective tool to analyse the effect of weld geometry. Different regions of the welded joint can be modelled in finite element analysis and effect of different parameters on the quality characteristics of the welded joints can be assessed [6].
https://doi.org/10.1016/j.matpr.2019.12.353 2214-7853/Ó 2020 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the 2nd International Conference on Recent Advances in Materials & Manufacturing Technologies.
Please cite this article as: C. Mani, S. Balasubramani and R. Karthikeyan, Finite element simulation on effect of bevel angle and filler material on tensile strength of 316L stainless steel/Monel 400 dissimilar metal welded joints, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.12.353
2
C. Mani et al. / Materials Today: Proceedings xxx (xxxx) xxx
The objectives of the present study include the following: Dissimilar metal welding of SS 316L/Monel 400 alloy using GTAW. Effect of filler material and bevel angle in butt weld. Numerical simulation of tensile testing using ANSYS WORBENCH. Comparison of simulation results with experimental results 2. Experimental procedure 2.1. Materials Fig. 1. Weld groove typical section.
The properties of austenitic stainless steel are valued to industry owing to high ductility, excellent toughness, strength, corrosion resistance, weldability. The test coupons are made from 3 mm plates of Monel 400 and stainless steel 316L of dimensions 200 mm (L) 20 mm (W) with filler material of SS316, Monel and ENiCrFe-5. Table 1 shows the chemical composition of materials used for specimen preparation by GTAW process.
Table 2 Welding parameter and configuration.
2.2. Welding conditions Gas Tungsten arc welding (GTAW) is referred as the welding process which uses a non-consumable tungsten electrode to produce the weld. Monel 400 plates with stainless steel 316L are welded with filler material ENiCrFe-5, SS 316L and Monel wire by GTAW process. The edge preparation with V grove with different bevel angles of 30°, 35° and 40°, with a root gap of 2 mm fitup was done to carry out weld as shown in Fig. 1. The weld specimens were welded under 3 different bevel angles with the filler wires of ENiCrFe-5, SS316 wire, Monel wire producing 9 weld test coupons are listed in Table 2. The weld current in the range of 80– 85 Amp, polarity as DCEN, shielding gas of Argon 8 LPM and backing gas of argon with a flow rate 5–7 LPM were established by trials in line with the recommendations of filler wire manufacturer and the parameters are listed in Table 2.
Filler wire (3 conditions)
ENiCrFe-5
SS 316L wire
Monel 400 wire
Groove angle (3 Conditions) Bevel angle Welding current Plate thickness Root face thickness Root opening Polarity Welding speed Shielding gas (Argon) Backing gas (Argon) Tungsten size and type
V-type 60°
V-type 70°
V-type 80°
30° 35° 80 amps 3 mm 1 mm 2 mm DCEN 2.5 mm/s 8 LPM 5–7 LPM 1/800 , 2% throated tungsten
40°
3. Finite element simulation 3.1. Geometry modelling Tensile test specimens with 30° bevel angle in the weld zone are modelled in ANSYS SPACE CLAIM, material properties were assigned for different zones namely Monel alloy, weld material and SS 316L stainless-steel alloy. Nonlinear - Bilinear Isotropic hardening properties were provided for these three materials. ANSYS geometry modelled for the study is shown in Fig. 3 and weld zone with respect to 30° bevel angle shown in Fig. 4(a) and (b). Properties of base materials and weld materials in the model are presented in Table 4.
2.3. Tensile test standard The weld test coupons upon completion of weld were further visually checked followed by ultrasonic test as per AWS D1.1 standards for weld flawless and defects. Upon acceptance of the weld coupons, tensile test specimens were prepared by water jet cutting with dimensions in accordance with ASTM E8/E8M-13a, ‘‘Standard Test Methods for Tension Testing of Metallic Materials”. The dimensional sketch of tensile test coupon is shown on Fig. 2 [7].
3.2. Contact and target definitions Bonded contact is provided between weld material and base material on either side. Bonded contact defines no penetration and sliding between the faces or edges. Weld material face defined as contact region and the remaining two material faces act as target regions. In bonded contact, augmented Lagrange formulation is used since small amount of penetration is allowed during welding between different zones. Contact behaviour was assumed to be asymmetric since contact elements are defined on weld surface and target elements defined on the other two surfaces. For
2.4. Plan of experiments The range of variable parameters are listed on Table 3 for the plan of experiments. The experiments were done by varying one parameter at a time. Tensile test on the 5 test coupons based on the different variable parameters were test on SHIMADZU 100 kN servopulser dynamic testing machine.
Table 1 Chemical composition of materials. Material
C
Cr
Fe
Mn
Ni
P
S
Si
Mo
Cu
Ti
Co
Nb
SS 316L Monel 400 ENiCrFe-5
0.03 0.3 0.04
17 – 14–17
65.64 2.5 6–10
2 2 1.0
12 63 70 (min)
0.05 – 0.03
0.03 0.024 0.015
0.75 0.5 0.35
2.5 – –
– 31.676 0.5
– – –
– – 0.12
– – 1.5
Please cite this article as: C. Mani, S. Balasubramani and R. Karthikeyan, Finite element simulation on effect of bevel angle and filler material on tensile strength of 316L stainless steel/Monel 400 dissimilar metal welded joints, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.12.353
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Fig. 2. Tensile test coupon dimensions.
Table 3 Experimental plan. Specimen No
1
2
3
4
5
Filler wire Bevel Angle
ENiCrFe-5 30°
ENiCrFe-5 35°
ENiCrFe-5 40°
Monel wire 30°
SS 316 wire 30°
Fig. 3. Geometry modelling of tensile test specimen.
Fig. 4. (a) Weld zone with 30° bevel angle; (b) Meshed model with tetrahedron element.
Table 4 Materials properties of base material and weld material. 650
MONEL 400
SS 316L
ENiCrFe-5
Density (kg/m3) Young’s Modulus (GPa) Poisson Ratio Yield Strength (MPa) Tangent Modulus (MPa) Ultimate Strength (MPa)
8800 179 0.3 240 1450 550
8000 193 0.31 205 1800 515
8500 190 0.3 275 1750 630
asymmetric behaviour, only the contact surfaces are constrained from penetrating the target surfaces.
600
Linearized Equivalent Stress, MPa
Material Properties
550
500
450
400
350
3.3. Meshing Entire model was meshed using quadratic 3D tetrahedrons elements (Fig. 4b). Tetrahedron element has less degrees of freedom
300 2000
6000
10000
14000
18000
Number of Elements
Fig. 5. Mesh convergence curve for weld specimen.
Please cite this article as: C. Mani, S. Balasubramani and R. Karthikeyan, Finite element simulation on effect of bevel angle and filler material on tensile strength of 316L stainless steel/Monel 400 dissimilar metal welded joints, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.12.353
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C. Mani et al. / Materials Today: Proceedings xxx (xxxx) xxx
Fig. 6. Loading and boundary conditions.
Fig. 7. Linearized equivalent stress.
700
500
WELD MATERIAL 30DEG WELD MATERIAL 35DEG WELD MATERIAL 40DEG MONEL 30DEG SS316L 30DEG
600
450 400 350
Stress,MPa
Linearized Stress,MPa
500
400
300
300 250 200
200
150
FEM WELD MATL 30DEG FEM WELD MATL 35DEG FEM WELD MATL 40DEG FEM MONEL 30DEG FEM SS316L 30DEG
100
100
50 0 0
20
40
60
80
100
120
140
160
180
200
Length, mm
0
5
10
15
20
25
30
Strain
Fig. 8. Linearized equivalent stress for all specimens.
Fig. 9. Engineering stress-strain curves generated from FEM simulation.
compared to hexa-hederal elements and to provide solution at a faster rate. It is necessary to have fine mesh density mainly in the areas of high stress gradients and coarser mesh density in areas of low stress gradients or where the magnitude of the stresses is not of much interest. The effect of sphere of influence has been used to get fine mesh density in the critical areas. Pinch control has been used to merge mesh nodes in close proximity after meshing using a given tolerance which removes the bad elements from the model results more refined meshing. Mesh convergence study (mesh sensitivity analysis) in finite element analysis, is normally done to determine the optimum
number of elements to increase the accuracy of the solution with less computational time. For the present case, the analysis was performed based on the maximum linearized equivalent stress. Element size is varied from 5 mm to 2 mm in whole body and 1.5 mm to 0.5 mm for critical areas. The number of elements were increased from 2847 to 17,522. After that mesh convergence, an element size of 2 mm has been used for the whole body and element size of 0.5 mm has been used for in the critical areas (weld and near weld zones) by using sphere of influence. Fig. 5 shows the mesh convergence curve for the linearized equivalent stress.
Please cite this article as: C. Mani, S. Balasubramani and R. Karthikeyan, Finite element simulation on effect of bevel angle and filler material on tensile strength of 316L stainless steel/Monel 400 dissimilar metal welded joints, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.12.353
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be inferred that, as the bevel angle increases, the stress values were decreased due to increase in area. ENiCrFe-5 (weld material) possess maximum strength when compared to Monel alloy and SS 316L alloy. Hence the stress values are maximum for weld material when compared to the other two filler wires.
500 450 400
Stress,MPa
350 300
4.2. Stress-strain curve
250 200 150
WELD MATL 30DEG WELD MATL 35DEG WELD MATL 40DEG MONEL 30DEG SS316L 30DEG
100 50 0
5
10
15
20
25
30
Strain Fig. 10. Experimental engineering stress-strain curves.
Table 5 Mean absolute error for the stress-strain curves. Filler and bevel angle
Weld, 30°
Weld, 35°
Weld, 45°
Monel 400, 30°
SS 316L, 30°
Mean absolute error, MPa
0.4147
7.8247
11.5192
7.7624
7.7417
The reaction force from simulation and the corresponding displacements were recorded for different specimens and using those values, engineering stress-strain curves were drawn. The simulation readings were obtained till ultimate tensile strength region and presented in Fig. 9. The ENiCrFe-5 (weld material) possess higher stress values when compared to filler wires made of parent materials (Monel and SS 316L) since the strength of weld material is higher than both alloys. The increase in bevel angle resulted in decreased stress level for ENiCrFe-5 (weld material). The simulated results may be compared with the experimental results which are presented in Fig. 10. It can be seen for all the cases considered, the simulated stress strain curves are close to experimental curves. The mean absolute error calculated between experimental and simulated values are presented in Table 5. Trend of the curves are almost similar, however, the values are little different due to the material model considered for the study. The FEM analysis proposed may be used for prediction of stress strain curves for tensile testing. However, the fracture behaviour cannot be predicted by this analysis since the fracture criterion has not been defined which has been left for future study.
3.4. Loading and boundary conditions 5. Conclusion One end of the specimen (Monel alloy side) was fixed and the end of the specimen (SS 316L side) was subjected to displacement in X direction as per experimental boundary conditions (Fig. 6). Analysis was performed in transient structural analysis up to 70 steps with 0.2 mm displacement periodic increments till 14 mm. The maximum displacement was chosen based on experimental observation. End of each time step is 1 sec. Applied displacement may result in geometry nonlinearity and hence large deflection was provided during analysis. 4. Results and discussions The proposed simulation was carried out for all the experimental conditions specified in Table 3 and the performance was compared. Linearization stress along the length of the weld has been recorded to study the effect of bevel angle and filler material. For ENiCrFe-5 all three angles were considered for other two filler wires, 30° bevel angle was used. The stress strain experimental results were compared with the FEM results. The analysis is limited to simulation of stress distribution up to ultimate strength level and fracture behaviour is not considered.
Finite element simulation of tensile testing of Monel/SS 316L has been performed using transient structural analysis. The effect of bevel angle and filler wire on stress-strain behavior and linearized stress distribution are analyzed. The stress strain curves generated using FEM simulation were compared with experimental results and are found to be close. The weld material ENiCrFe5 has higher strength than the filler wires made up of the base materials. The increase in bevel angle decreased the linearized stress. FEM simulation can be used for prediction of stress-strain curves and further analysis is required to analyze the fracture behavior. Implicit/Explicit dynamics may be performed to simulate the fracture of the tensile test carried out. Consideration residual stress due to thermal loading during welding will improve the accuracy of prediction which has not been attempted.
CRediT authorship contribution statement Cherish Mani: Investigation, Resources. Sozharajan Balasubramani: Software, Formal analysis. R. Karthikeyan: Conceptualization, Supervision.
4.1. Linearized equivalent stress Stress linearization is a technique to decompose actual stress distribution across thickness into membrane (average) stress and bending (linearly varying) stress, so that net force and moment across the thickness remains same. Fig. 7 shows the linearized stress distribution along the axial length of the specimen. The joint region has maximum stress on either side of the weld since the bonded connections exist along these regions which hold the base materials with weldment. Value of stress in SS 316L side is lesser than Monel side due to difference in strength. The linearized stress distribution has been plotted for all the simulations in Fig. 8. It can
Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgement Authors are grateful to BITS Pilani, Dubai campus for the encouragement and support for the research work.
Please cite this article as: C. Mani, S. Balasubramani and R. Karthikeyan, Finite element simulation on effect of bevel angle and filler material on tensile strength of 316L stainless steel/Monel 400 dissimilar metal welded joints, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.12.353
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C. Mani et al. / Materials Today: Proceedings xxx (xxxx) xxx
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Please cite this article as: C. Mani, S. Balasubramani and R. Karthikeyan, Finite element simulation on effect of bevel angle and filler material on tensile strength of 316L stainless steel/Monel 400 dissimilar metal welded joints, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.12.353