Week 3 Verification of Weld Joints

VERIFICATION OF WELD JOINTS USING ANSYS

OBJECTIVE

1. To simulate three different types of welding using three different weld materials,

1. Case 1: Weld Material used is Stainless Steel. The material of plates and ribs are also Stainless Steel.
2. Case 2: Weld Material used is Aluminium Alloy (high strength, wrought). The material of plates and ribs are Stainless Steel.
3. Case 3: Weld Material used is Cast Bronze. The material of plates is Stainless Steel and ribs is Copper.

2. To run the simulation for a load of 15000 N that is to be applied at the rectangular hole in the small plate for each case.

3. To find out the Directional Deformation and Equivalent Strain experienced by the setup for each case.

4. To Identify the weld joint that experiences the highest Equivalent Stress in each case and compare the results for all three cases.

1. THEORY

1.1 Welding:

Welding is a process in which materials of the same fundamental class or type are brought together and caused to coalesce through the formation of chemical bonds under the combined action of heat and pressure, without or with any filler. Welding is used to fabricate new equipment or structures by building up detail parts into a unitized assembly or weldment. The fundamental types of welds used to accomplish joining include those that are used to make butt joints, corner joints, tee or T-joints, lap joints, and edge joints.

Fig.1.1 Cross section of a hypothetical weldment showing the five fundamental types of joints found in welding.

One of the principal reasons welding is often selected as the preferred process for joining components into an assembly is the high joint efficiency obtained; joint efficiency being the percentage of the strength in the joint compared to the strength of the adjacent joint elements. High joint efficiency by welding is the combination of two key factors: (i) the ability of the weld itself to provide strength comparable to the base metals and (ii) the nearly negligible added weight of a weld to a structure.

The weld materials used for the weld joint assembly in the project are (i) Stainless Steel (ii) Aluminum Alloy (iii) Cast Bronze.

Stainless steels represent a broad family of iron‐based alloys that contain a minimum of approximately 12% chromium. The addition of chromium produces an extremely thin but stable and continuous chromium‐rich oxide film that gives these alloys their stainless and corrosion‐resistant properties.

Aluminum alloys represent a family of widely used engineering materials in applications that usually require a combination of low density (light weight) and corrosion resistance. The corrosion resistance of these alloys results from the rapid formation of an aluminum oxide on the surface, which is relatively stable at ambient temperatures.

1.2. Braze welding:

Braze-welding can be used to join similar or dissimilar metals by using a filler material with a lower melting temperature range than the parent metals being joined. When brazing, the filler material is drawn into a close-fitting joint by capillary attraction. Traditionally, braze-welding was known as bronze welding because the process resembled welding and, originally, the filler material was a copper – tin – phosphorus alloy, that is, a bronze. However, the name is a misnomer because the filler material used nowadays is essentially a copper – zinc alloy, that is, a brass.

2. ANALYSIS SETUP

2.1 Geometry:

Fig.2.1 3D model of weld joint model.

The given 3D model of weld joint model is imported into ANSYS Workbench for static structural analysis.

2.2 Material Properties:

Fig.2.2 Weld material property details.

The following materials are considered for weld and weld joint model i.e.,

Case-1: Weld Material is Stainless Steel as well as for plates and ribs.

Case-2: Weld Material is Aluminium Alloy (high strength, wrought). The material of plates and ribs are Stainless Steel.

Case-3: Weld Material used is Cast Bronze. The material of plates is Stainless Steel and ribs is Copper.

Note: The analysis is carried out for each case separately. The analysis setup of case-1 is demonstrated.

2.3 Contact Details:

a. Contact between big plate and small plate.

b. Contact between big plate and rib 1.

c. Contact between big plate and rib 2.

d. Contact between small plate and rib 1.

e. Contact between small plate and rib 2

Fig.2.3 Contact details of weld joint model.

Contact between (a) big plate (contact body) and small plate (target body), (b) big plate (contact body) and rib 1 (target body), (c) big plate (contact body) and rib 2 (target body), (d) small plate (contact body) and rib 1 (target body), (e) small plate (contact body) and rib 2 (target body), are assigned as frictional contact with coefficient of friction μ = 0.2.

The contact between welds and plates as well as welds and ribs are assigned as bonded contact.

2.4 Meshing:

a. Body sizing of plates and ribs.                                                                      b. Meshed model.

Fig.2.4 Meshing details of weld joint model.

The weld regions are meshed with default element size. The element size of plates and ribs are set as 5 mm using body sizing option to better capture structural behavior at the welded region while reducing solve time. The total number of nodes and elements generated are 57067 and 10154 respectively.

Note: The academic version of software has the problem size limit of 128k nodes or elements.

2.5 Boundary Conditions:

a. Fixed support assigned to mounting holes.                                                  b. Force applied on the rectangular hole in Y-direction.

Fig.2.5 Boundary conditions.

The five mounting holes in the big plate are assigned with fixed support. The rectangular shaped hole in the small plated is applied with a force of 15000 N in the Y-direction.

3. RESULTS AND DISCUSSIONS

3.1 Results:

Case-1: Weld Material is Stainless Steel as well as for plates and ribs.

a. Directional Deformation.                                                                                b. Equivalent Elastic Strain

c. Equivalent (v-m) stress.                                                                               d. Safety Factor.

Case-2: Weld Material is Aluminium Alloy (high strength, wrought). The material of plates and ribs are Stainless Steel.

a. Directional Deformation.                                                                              b. Equivalent Elastic Strain

c. Equivalent (v-m) stress.                                                                               d. Safety Factor.

Case-3: Weld Material used is Cast Bronze. The material of plates is Stainless Steel and ribs is Copper.

a. Directional Deformation.                                                                               b. Equivalent Elastic Strain

c. Equivalent (v-m) stress.                                                                               d. Safety Factor.

3.2. Comparison of Results:

The results of maximum and minimum values of Directional Deformation, Equivalent Elastic Strain and Equivalent (v-m) Stress are tabulated as shown below.

From the table, it is observed that the maximum deformation in case-3 is 0.38788 mm and case-1 is only 0.33367 mm. Therefore, Stainless steel weldments is less deformed compared to other two cases of weldments. Similarly, comparing the maximum values of equivalent elastic strain, Stainless steel weldments is least strained among other two weldments.

The maximum value of equivalent (v-m) stress developed in stainless steel and cast bronze weldments are 310.08 MPa and 269.72 MPa respectively, but the yield stress values of stainless steel and cast bronze are 207 MPa and 144 MPa respectively. Therefore, the value of maximum equivalent (v-m) stress developed is more the yield stress value hence the welds undergo plastic deformation and eventually fails. The maximum value of equivalent (v-m) stress developed in aluminum alloy is 257.29 MPa which is less than the value of its yield strength i.e., 363 MPa, Therefore, aluminum alloy will not undergo plastic deformation, hence, the weldment is safe.

The minimum values of safety factor for weld materials such as Stainless Steel, Aluminum alloy and Cast Bronze are 0.66757, 1.4108 and 0.53389 respectively. The safety factor value of Aluminum alloy weld is more than 1, hence, the weldment can safely withstand the applied load.

3.3. Animation of Results:

Case-1:

a. Directional Deformation.                                                                            b. Equivalent Elastic Strain

c. Equivalent (v-m) stress.                                                                            d. Safety Factor.

Case-2:

a. Directional Deformation.                                                                            b. Equivalent Elastic Strain

c. Equivalent (v-m) stress.                                                                            d. Safety Factor.

Case-3:

a. Directional Deformation.                                                                            b. Equivalent Elastic Strain

c. Equivalent (v-m) stress.                                                                            d. Safety Factor.

CONCLUSION

1. The simulation of three different types of welding using three different weld materials were done successfully by applying a load of 15000 N on the rectangular hole of the small plate, for the following cases,

1. Case 1: Weld Material used is Stainless Steel. The material of plates and ribs are also Stainless Steel.
2. Case 2: Weld Material used is Aluminium Alloy (high strength, wrought). The material of plates and ribs are Stainless Steel.
3. Case 3: Weld Material used is Cast Bronze. The material of plates is Stainless Steel and ribs is Copper.

2. From the results of Directional Deformation and Equivalent Strain, the stainless-steel weldment experienced least deformation and strain compared to other weldments.

3. The stainless-steel weld joint experienced the highest equivalent stress whereas, Aluminium alloy experienced the least equivalent stress.

4. From the point of design, the Aluminium weld joint is preferred choice, because deformation and strain experienced is less and the maximum equivalent stress developed is less than the yield stress value as well as safety factor is above one.