Analysis Of Temperature Distribution Of Different Welded Joints In ShipBuilding

Analysis Of Temperature Distribution Of Different Welded Joints In ShipBuilding

Analysis Of Temperature Distribution Of Different Welded Joints In ShipBuilding**

G.Janakiram1 , S.Vijay2, Dr.M.Venkateswara Rao3

1* PG Student, Department of Mechanical Engineering, Bapatla Engineering College, Bapatla, Guntur, India 2 Lecturer, Department of Mechanical Engineering, Bapatla Engineering College, Bapatla, Guntur, India 3Professor and Head of the Mechanical Department, Bapatla Engineering College, Bapatla, Guntur, India

ABSTRACT:

Different materials are prone to distortion and cracks due to thermal stresses induced during welding .This project gives the information about the temperature induced in a joint due to welding in ship building . Simulation was carried out on a plate made of Aluminium and Cast-iron having dimensions 0.05×0.05×0.005 meters .The type of welding chosen is Gas tungsten arc(GTA) welding . Single pass welding was carried out . Simulation values calculated were taken as input for the analysis in ANSYS software.

A model was generated in ANSYS12( A general purpose FEA software) using SOLID Tet 10 node 87(3D solid element with temperature dof) . A refined mesh is made based on the convergence criteria and the analysis is performed to estimate the temperature distribution .Firstly a transient thermal analysis was carried out by giving heat flux as the time varying input to estimate the temperature variation .The non linear material properties are fed for the heat flow solution to get the thermal stress .The variation of the temperature with time , and thermal stress are obtained . The variation of these are reported and discussed.

The results of the present analysis is used in thermal stress analysis of the welded joints in ship building by using ANSYS parametric design language (APDL).

Keywords: Gas tungsten arc(GTA) welding , Temperature field, Weld dimension, Finite element analysis, Thermal modeling.

INTRODUCTION:

Welding is extensively used in the construction of s h i p b u i l d i n g , a e r o s p a c e a u t o m o t i v e , c h e m i c a l , electronic, and power generation industries. In fusion welding, parts are joined by the melting and subsequent solidification of adjacent areas of two separate parts. Safety and reliability of the welded joints depend on the weld metal geometry, composition, and structure. Heat flow during welding is of great interest to welding engineers and metallurgists. It not only controls the size of the fusion, but also affects the properties of the resultant weld. The gas tungsten arc (GTA) welding is a process in which a coalescence of metals is produced by heating them with an arc between a tungsten electrode and the work piece. A good quality weld is characterized by material composition, joint condition, relative position of the welding arc to the joint and welding parameters such as arc current, arc voltage, and torch travel speed, etc.. Therefore, choosing an appropriate set of welding parameters becomes one of the most important tasks in GTA welding process.

The analytical solution to the steady state, two dimensional heat flow problem of thin-plate welding was first derived by Rosenthal. Due to some unrealistic assumptions, heat flow and solidification in the weld pool can not be predicated, and poor agreement exists between calculated and experimental results in the area immediately adjacent to the weld pool. Solving a transient three- dimensional heat conduction equation with convection boundary conditions at the surfaces of the weld element, Boo and Cho obtained the transient temperature distributions in a finite thickness plate during arc welding. A series of GTA welding experiments for various conditions is performed to verify their solutions. Oreper et al. and Oreper and Szekely formulated a mathematical model on the transient fluid flow and temperature fields in a liquid pool generated by a spatially distributed surface heat flux on an initially solid metal block. In the formulation, allowance was made for electromagnetic, buoyant and surface tension force, and the resultant equations were solved numerically. For GTA welding of pipes, Grill studied heat flow during girth welding by the finite difference method. A heat source was assigned to each grid point in the work piece, and the solution was obtained by using the alternating direction implicit scheme. Later, Kou and Le investigated the heat flow during the welding of pipes. Both steady state heat flow during seam welding and unsteady state heat flow

during girth welding were theoretically calculated and experiment tally verified.

Considering arc parameters, radioactive and convective heat losses and the temperature dependent thermal properties, Sharir et al. employed the finite difference method to calculate the unsteady heat flow during the fusion welding of thin tantalum sheets. Based on the measured shape of the weld pool, Pavelic et al. calculated the temperature distribution in a thin plate of steel using the finite difference method. Neglecting heat conduction in the welding direction, Friedman used the finite element method to calculate the temperature and stress distribution in a thin plate being welded. Kou developed a model to describe the steady state, two-dimensional heat flow during the welding of thinplates. The heat of fusion, the size and distribution of the heat sources , the temperature depends of thermal properties , the heat conduction in the welding direction and the surface heat loss during welding were taken into account.

Gas Tungsten Arc Welding (GTA) Process Description:

Gas Tungsten Arc Welding (GTAW), also known as tungsten inert gas (TIG) welding is a process that produces an electric arc maintained between a non consumable tungsten electrode and the part to be welded. The heat-affected zone, the molten metal and the tungsten electrode are all shielded from atmospheric contamination by a blanket of inert gas fed through the GTAW torch. Inert gas (usually Argon) is inactive or deficient in active chemical properties. The shielding gas serves to blanket the weld and exclude the active properties in the surrounding air. Inert gases such as Argon and Helium do not chemically react or combine with other gases. They pose no odour and are transparent, permitting the welder maximum visibility of the arc. In some instances Hydrogen gas may be added to enhance travel speeds.

Finite Element Model:

SOLID87 Element Description:

SOLID87 is well suited to model irregular meshes. The element has one degree of freedom, temperature, at each node. The element is applicable to a 3-D, steady-state or transient thermal analysis.

Fig.5. SOLID87 Element Geometry 2.3.Material Properties

1. Aluminium:

   Thermal conductivity = 155(W/m-k) Specific Heat = 915(J/kg-k)

   Density = 2750 (kg/m3 )

2. Cast Iron:

Thermal conductivity = 12(W/m-k) Specific Heat = 461(J/kg-k)

Density = 7900(kg/m3 )

Loading and Boundary Conditions:

A uniform temperature of 2000 c is applied on the surface of the plates , and a heat flow of 2500W for the present analysis .The welding velocity of GTA is 3~7.24 mm/s. The time is calculated by knowing the distance between the nodes.

For brevity, it is assumed that the arc heat input area is far smaller than that of the plate and can be considered as a point heat source. No heat generates from the plate .Except during the initial and final transients of the welding process, the temperature distribution in a work piece of sufficient length is steady with respect to a coordinate system moving with heat source. Under such conditions the time dependent term in equation (1) vanishes and the process is reduced to a steady state (quasi- stationary state) heat flow problem [2, 3]. For this reason, a new group of variables is given as

Substituting equation (2) into equation (1), the governing equation then becomes

where , thermal diffusivity of the work piece, is equal to k/(c). The power input of the heat source Q describes the heat flux from the arc. It equals EI, where is efficiency of the arc, E is the arc voltage, and I is the welding current. According to Pavelic et al. [14] the heat flux from the arc can be expressed by

where Q, r, and a are the power input, the distance from the center, and the radius of the heat source, respectively. To c omp let e th e ma th ema ti ca l d escri pti o n of th e problem, the boundary condition s are specified as follows:

Table.The Minimum And Maximum Temperature Of Different Welded Joints In Various Materials

Temparature

Fig. Shows The Nodal Temperature Range Of Lap Joint Of Aluminum Material

400

300

200

100

0

1. 0.1 1

   Time

   Cast Iron	202.241	316.593
   Aluminium	203.068	367.155

   Fig.Variation Of Temperature W.r.t Time Of Lap Joint Of Aluminum Material

   200

   300

   400

   500

   Temparature

   Variation of First Node Temperature with respect to Time:

   600

   0.1

   1.4

   Time

   Cast Iron 398.079

   Aluminium 408.521

   472.355

   568.277

   0

   100

   Fig.21.Variation of Temp. W.r.t Time in Lap Joint at First Node(328)

   The Graph.1.. depicts the variation of first node(328) temperature with respect to time .The temperature value increases gradually from time 0.1 to 1.4. It can be observed from the figure in lap welded joint , the material of cast iron temperature is low with respect to time compared to aluminium at first node.

   Fig.22.Variation of Temp. W.r.t Time in T-Joint At First Node

   Temparature

   The Graph.2. depicts the variation of first node temperature with respect to time .The temperature value increases gradually from time 0.1 to 1.0. It can be observed from the figure in T- welded joint , the material of cast iron temperature is low with respect to time compared to aluminium at first node.

   400

   300

   200

   100

   0

   0.1 0.6

   Time

   Cast Iron 200 257

   Aluminium 200 286.3

   Fig.23.Variation of Temp. W.r.t Time in Corner Joint at First Node

   The Graph.2. depicts the variation of first node temperature with respect to time .The temperature value increases gradually from time 0.1 to 0.6. It can be observed from the figure in corner welded joint , the material of cast iron temperature is low with respect to time compared to aluminium at first node.

   Variation of Last Node Temperature with respect to Time:

   500

   400

   300

   200

   100

   0

   0.1 1.4

   Time

   Cast Iron

   Aluminiu m

   199.84

   389.875

   396.578

   203.101

   Temparature

   Temparature

   Fig.24.Variation of Temp. W.r t Time in Lap Joint at Last Node(337)

   The Graph.4. depicts the variation of last node(337) temperature with respect to time .The temperature value increases gradually from time 0.1 to 1.4. It can be observed from the figure in lap welded joint , the material of cast iron temperature is low with respect to time compared to aluminium at last node.

   Temparature

   500

   400

   300

   200

   100

   0

   400

   200

   0

   0.1 0.6

   Time

   Cast Iron 200.298 260.475

   Fig.26.Variation of Temp. W.r.t Time in Corner Joint at Last Node

   The Graph.6. depicts the variation of last node temperature with respect to time .The temperature value increases gradually from time 0.1 to 0.6. It can be observed from the figure in corner welded joint , the material of cast iron temperature is low with respect to time compared to aluminium at last node.

   CONCLUSION:

   1. The temperature distribution of aluminum and cast iron is uniform throughout the entire length of the weld.

   2. The thermal flux distribution is uniform over the surface of aluminum and cast iron plates.

   3. The thermal stresses and material properties of aluminum and cast iron does not change with time.

   4. Thermal stresses developed during welding may be used for thermal analysis and structural analysis of s h i p b u i l d i n g .

0.1 1

199.84

Cast Iron

Time

293.751

385.175

199.997

Aluminiu m

Fig.25.Variation of Temp. W.r.t Time in T-Joint at Second Node

The Graph.5. depicts the variation of last node temperature with respect to time .The temperature value increases gradually from time 0.1 to 1.0. It can be observed from the figure in T- welded joint , the material of cast iron temperature is low with respect to time compared to aluminium at last node.