Verification of Welded Joints

Verification of Welded Joints

Objective: To analyze the Directional Deformation, Equivalent Stress and Equivalent Strain as well as identify the highest stress regions in the welded assembly, by assigning different materials to the assembly components as well as the welded joints.

Geometry: The geometry is imported into Ansys Space Claim and no alterations are made to it. The geometry consists of two plates and two ribs assembled together through several welded joints.

Meshing: The two plates of the assembly are provided a body sizing of 6mm, after performing a grid test and determinimg the lowest mesh size that can be assigned without breaching the license limits.

The ribs and the weldments are meshed by the program controlled default mesh size.

Contact Definition: In addition to the Bonded Contacts for the welded joints, five Frictional contacts are defined for the simulation, with a co-efficient of friction of 0.2.

The behaviour and formulation \"Program Controlled\". The interface treatment is set to \"Add Offset, No Ramping\", although no offset value is fed.

Analysis Settings: The simulation is run with the load/force being applied in a single step. The step end time is 1s so the analysis time is also 1s.

Since the loading is linear in nature, no non-linear settings are manually defined. The output controls are also left to their default setting.

Boundary Conditions: The five holes on the big plate are provided with a fixed support to simulate the plate being bolted to a frame or a wall.

The surfaces of the square slot on the small plate is provided with a Constant Force of 15000N (over the 1s step) in the Y-direction.

Material Definition: The working material for the plates, ribs and the weldments are changed for each simulation.

Case1

In this case the weldments, the plates and the ribs are assigned the same material-Stainless Steel, whose isotropic properties are as follows:

Sl. No	Particulars	Magnitude
1.	Density	7750kg/mm3
2.	Young’s Modulus	1.93E+05MPa
3.	Shear Modulus	7.3664E+04MPa
4.	Bulk Modulus	1.693E+05MPa
5.	Poisson’s ratio	0.31
6.	Tensile Yield Strength	207MPa
7.	Tensile Ultimate Strength	586MPa

Case2

The weldments are assigned Aluminium Alloy (high strength, wrought) as the working material. The plates are assigned Stainless Steel as the material.

Sl. No	Particulars	Magnitude
1.	Density	2770kg/mm3
2.	Young’s Modulus	73800MPa
3.	Shear Modulus	2.7599E+04MPa
4.	Bulk Modulus	7.546E+04MPa
5.	Poisson’s ratio	0.337
6.	Tensile Yield Strength	363MPa
7.	Tensile Ultimate Strength	449MPa

Case3

This case is run to simulate the process of Brazing. For this, the welded joints are assigned Bronze (cast) as the working material and the Ribs are assigned Copper (cast) as the working material. The working material of the plates remain Stainless Steel.

Sl. No	Particulars	Cast Bronze	Cast Copper
1.	Density	8810kg/mm3	8940kg/mm3
2.	Young’s Modulus	80000MPa	1.25E+05
3.	Shear Modulus	2.9740E+04MPa	4.6468E+04
4.	Bulk Modulus	8.6022E+04MPa	1.3441E+05
5.	Poisson’s ratio	0.345	0.345
6.	Tensile Yield Strength	144MPa	33.5
7.	Tensile Ultimate Strength	267MPa	152

The simulations are run and the results are plotted.

Results: The Equivalent Strain, Equivalent Stress, Directional Deformation and the Von-mises Stress on the welded joints, for all the cases have been tabulated below

Particulars	Case 1	Case 2	Case 3
Max Directional Deformation (mm)	0.35162	0.36572	0.39644
Max Equivalent Stress (MPa)	358.08	362.79	368.6
Max Equivalent Strain	1.9455e-03	3.3992e-03	3.2801e-03
Max Equivalent Stress on the Welded joints (MPa)	301.23	250.61	262.02

1) Directional Deformation: The maximum directional deformation is observed at the edge of the small plate (along the Z-direction) in all the cases, with the Brazing scenario exhibiting a maximim magnitude.

2) Max Equivalent Stress: Maximum magnitude of Von-Mises Stresses are developed at the corners of the square slot on which the Force was applied. This is observed in all the cases and is a fairly expected behaviour as the sharp corners serve as geometric discontinuities where localised or concentrated stresses develop.

3) Equivalent Elastic Strain: For Case1 as there is a material continuity in between the plates, the ribs and the welds, the equivalent strain is the highest at the corner of the square slot (same region as that of max von-mises stress).

For Case2 and Case 3, the maximum change in dimension within the elastic region takes place at the welded joint closest to the region of force application and along the positive X-direction.

4) Equivalent Stress on the welded joints: The maximum Von-Mises Stress on the welded joints is observed in Case 1 where Stainless Steel has been assigned as both the plate and the weld material. The welded joint experiencing the maximum stress is the same in all cases though.

Inference:

All simulations terminate successfully. Since the load was applied in a single step, the convergence time for all the solutions was under a minute.

From the results obtained, the follwing inferences can be drawn:

• The maximum deformation takes place in Case3 where the ribs have been assigned Copper and the welds have been assigned Bronze. This behaviour can be attributed to the low Yield Strength of Bronze and Copper which causes the ribs and the welded joint (closest to the region of application of load) to deform more and also faster.
• The maximum Von-Mises or Equivalent stress is observed in Case3 where Brazing has been simulated. This is on account of the high value of Yield Strength of Stainless Steel (material of the region where max stress is observed) as well as the material discontinuity among various parts which leads to high localised or concentrated stresses.
• The material discontinuity between the welded joints and the ribs and/or plates in Case2 and Case3 leads to high stresses and consequently high strains within the elastic region. The region of maximum equivalent strain also shifts from the corner of the square slot (Case1) to the edge of the welded joint closest to the application of load (Case2 and Case3).
• The welded joint that experiences the highest amount of Von-Mises Stress is the one that is located closest to the region of application of load and in the positive X-direction. Consequently the safety factor in this joint is also the least.

• The highest Equivalent Stress in the welded joints is observed in Case1 where all the components have been assigned Stainless steel as the material. The high value of Yield Strength of Stainless Steel accounts for this. The Equivalent stress in the welded joints in Case3 is higher than in Case2 due to a similar difference in the vale of Young\'s Modulus between Bronze and Aluminium Alloy.