Numerical Simulation on Welding

esidual Stress and its Effects on

Loading Behavior of Extended Arm Structure

Ang Ji

, Minggang Chen

, Liping Zhang

, Binbin Zhang

and Le Gao

XCMG Research Institute Co., Ltd,Xu Zhou, China

XCMG Fire-fighting Safety Equipment Co., Ltd, Xu Zhou, China

State Key Laboratory of Intelligent Manufacturing of Advanced Construction Machinery, Xu Zhou, China

Keywords: Extended arm structure, welding residual stress(WRS), numerical simulation, welding deformation, loading

behaviour.

Abstract: In this article, the numerical simulation method was utilized to investigate the welding deformation and

residual stress of the extended arm structure. Then the distortion and stress distribution of extended arm

structure under loading state were calculated with and without considering the welding residual

stress(WRS). The results show that the welding residual stress around weld toe is very high and the

maximum Von Mises stress in weld zone is up to 550MPa, which is more than 3 times higher than that of

middle area. When welding situation is taken into consideration, the Von Mises stress around the weld area

reaches the yield strength of base metal while the Von Mises stress apart from the weld area decreases on

account of the offset by WRS. The welding deformation is the main part of the structural deformation in X

and Z direction under welding&static situation and the deformation in Y direction is 38.28mm, which is the

stack of welding deformation and down warping with static load.

1 INTRODUCTION

Residual stresses are self-equilibrating stresses that

are present within a structure when no external

forces are applied[1-3]. Typically, kinds of material

processing and fabrication techniques create a

residual stress in workpiece. One of the most

common and high residual stress is caused by

conventional welding process near the welding

region in metallic structures, where extremely

uneven plastic deformation, temperature change and

phase transformation in different degree occur[4].

During the serving process, the actual stress is very

complicated based on the stack of WRS and working

stress, which is bound to have a certain effect on the

loading behavior and fracture resistance[5].

Many scholars have studied the WRS and its

influence on the bearing capacity of the structure. Li

Yanjun et al.[6] analyzed the influence of WRS on

the load bearing capacity of the container y-shaped

ring joint by using the finite element analysis

method. The results showed that the axial tension

stress was obviously enlarged by the combined

action of WRS and internal pressure and the

maximum stress of the Y-ring under loading also

enlarged a little. Xiao Qi[7] set the air cylinder as

research object and analyzed the influence of WRS

on the result of air cylinder structure strength

calculation, finding that the existence of WRS could

lead to the change of weak link location of structural

strength in cylinder body and the bearing capacity

decreased obviously.

XuLei[8] investigated the influence of WRS in

welding zone of spherical shell on the ultimate

bearing strength and come to a conclusion that WRS

played little or no role in the ultimate bearing

strength which provided certain reference on the

post weld stress relief treatment. Takeshi

MIYASHITA[9] researched the load-carrying

capacity of joint between I shaped girder and thick

plate by stress free method and the test results

confirmed that the slope of stress distribution in the

plate thickness direction increases as the thickness of

the plate increases and the residual stress in the thick

plate does not affect the load-carrying capacity for

the bending of steel girders.

The extended arm is a commonly used welding

structure in the field of engineering machinery, and

its bearing capacity is directly related to the

construction and safety performance of the whole

machine[10]. During the static load calculation of

the general preliminary structure design, the

designer mainly ensure the safety by expanding the

safety factor, and there is no specific analysis on the

influence of residual stress on the structure loading

behavior. Therefore, based on the extended arm as

the research object, the influence of WRS on the

loading behavior is analyzed through the finite

element simulation method so as to provide certain

reference for the design of whole structure and

welding process.

Fig.1 The geometrical model and section form of the extended arm.

Fig.2 Grid model of extended arm structure.

2 PHYSICAL MODEL OF

EXTENDED ARM STRUCTURE

The extended arm structure is set as the research

object of welding and structure finite element

analysis in this article. The WRS and its influence

on loading behavior is the main investigation

contents, hence the finite element model only

includes the upper and lower cover plate, left and

right side plate as well as fillet welds. The

geometrical model and section form of the extended

arm are shown in Fig.1.

The material used for extended arm is Q550 and

the carbon dioxide gas shielded welding method is

utilized for four fillet joints with the welding power

Fronius TPS5000. There is no groove on the plate

and the weld shall be cleaned before welding. The

welding process parameters are shown in Table 1.

Table.1 Welding process parameters.

Name Current I/A Voltage U/V

Velocity

(

mm·s

-1

)

Value 170~180 19~20 9

3 FINITE ELEMENT ANALYSIS

MODEL OF EXTENDED ARM

3.1 Generation of Extended Arm Grid

Model

The geometrical model of extended arm is

partitioned into solid grid model with 8 nodal

hexahedral element[11]. The base mental is divided

into 2~3 layers in order to ensure the accuracy of

calculation and the size of grid around weld and

HAZ is controlled at 2mm so as to improve the

calculation speed, while the size of grid remote from

welding zone is 12mm. Two element transitions are

adopted in the width direction among the above-

mentioned regions to ensure the accuracy of

calculation and reduce the number of elements. As

shown in Fig.2, the element number of grid model is

344294.

3.2 Material Property Parameters

Q550 is a typical high strength structural steel used

in engineering machinery field. It is assumed that the

whole model has the same thermal physical property

parameters with the change of temperature. The base

metal and welding wire are set to have isotropic

properties: poisson's ratio is 0.33, mass density is

7870 kg/m3, and the other parameters such as

thermal conductivity, specific heat, elastic modulus,

thermal expansion coefficient with the temperature

change are shown in Fig.3.

Fig.3 The relationship between heat-force parameters and

temperature of Q550.

3.3 Boundary Conditions and Loads

In the process of establishing the welding finite

element model, the Goldark double ellipsoid heat

source is selected as the boundary condition of the

welding heat source[12]. Since there is a temperature

difference between the workpiece surface and the

surrounding environment during the actual welding

process, the Newton's law and boltzmann's law are

taken into consideration respectively in the process

setting of the convection and radiation dissipation

between workpiece and external environment[13].

In the model calculation of welding process, the

solid-state phase transformation and work hardening

of low carbon steel are ignored for the reason that

both of them have little influence on welding

residual stress and deformation. The extended arm is

in a free state during the welding process, and the

mechanical boundary conditions are set to prevent

the rigid body displacement of the model.

In the static analysis of the extended arm, the

condition that the extended arm is in the horizontal

state and the load in the arm head is 2000N is taken

into consideration in this paper. As shown in Fig.4,

the element of the arm head is connected by RBE2

unit and the load in Y direction is set as 2000N. In

actual situation, the main constraint boundary

conditions at the end of arm are contact constraints

with the follow arms, which is most accurate.

However, owing to the influence of WRS on the

loading behavior of the extended arm is mainly

discussed in this calculation, the other RBE2 rigid

connection is added to impose a direct displacement

constraints at the end of the extended arm.

Fig.4 Boundary condition of extended arm static analysis.

4 COMPARISON AND ANALYSIS

4.1 Analysis of Welding Deformation

and Residual Stress

Based on the above-mentioned welding boundary

conditions, the model is set and the welding load is

solved. After the calculation is completed, the

welding deformation and welding residual stress of

the extended arm are extracted. The welding

deformation contours in X, Y and Z direction are

shown in Fig.5, from which some results can be

achieved that the extended arm is mainly contracted

in X direction and the total shrinkage is 6.12mm,

while In Y direction, the extended arm is down

warped and the downward deflection is 1.15mm.

The main reason for above distortion is that the

welding seams of the upper cover plate and the

lower cover plate are on the different planes and the

distance between two weld seams on the upper cover

plate is less than that on the lower cover plate. The

deformation of extended arm in Z direction is

mainly the contraction deformation along the section

direction and the amount is very small. Fig.6 shows

the VONMISES stress contour of extended arm

structure. It can be seen that the largest equivalent

stress occurred in the weld region and the largest

equivalent stress is up to 550 MPa which has

reached the yield strength of base metal.

(a) Welding deformation contour in X direction

(b) Welding deformation contour in Y direction

Fig.5 Welding deformation contour of extended arm

structure.

Fig.6 The Von Mises stress contour of extended arm

structure.

4.2 Structure Analysis Without

Considering the Welding Residual

Stress

Based on the above-mentioned static analysis

boundary conditions, the model is set and solved.

After the calculation is completed, the deformation

and working stress of the extended arm are

extracted. As the load is applied in the Y direction,

the main focus is on the displacement of the

extended arm in Y direction. Fig.7 shows the

displacement distribution of extended arm in Y

direction, as can be seen, the maximum structural

deformation of the extended arm occurs in the

position of the arm head, and the deformation

amount is 36.19mm. The maximum deformation of

the upper cover plate in X direction is 0.98mm,

while the maximum deformation of the lower cover

plate in X is -1.09mm. The deformation of extended

arm in Z direction is smaller and negligible since the

effect of side load is not considered. Fig. 8 shows

the overall Von Mises stress contour of the extended

arm structure. As can be seen from the figure that

the maximum Mises stress with its value being

114Mpa is located in the restrained position of the

extended arm.

(a) Displacement distribution contour in X direction

(b) Displacement distribution contour in Y direction

Fig.7 Displacement distribution contour of extended arm

structure.

Fig.8 Von Mises stress distribution of extended arm

structure.

4.3 Structural Static Analysis

Considering the Welding Residual

Stress

Based on the above-mentioned welding and static

analysis boundary conditions, the model is set and

solved. After the calculation is completed, the

deformation and working stress of the extended arm

are extracted. The displacement distribution

contours of extended arm in X, Y and Z direction are

shown in Fig.9, from which some results can be

achieved that the deformation of the extended arm is

still mainly in the Y direction, the largest welding

deformation occurs in the position of arm head, and

the deformation amount is 38.28mm. Besides, the

extended arm is contracted in X direction and the

total shrinkage is 6.6mm. Fig.10 shows the Von

Mises stress contour of whole extended arm

structure. It can be seen that the largest Mises stress

occurred in the weld region and the largest

equivalent stress is up to 550 MPa which has

reached the yield strength of base metal.

(a) Displacement distribution contour in X direction

(b) Displacement distribution contour in Y direction

Fig.9 Displacement distribution contour of extended arm

structure

Fig.10 Von Mises stress distribution of extended arm

structure

4.4 Comparison and Analysis

In order to compare the stress distribution under

different conditions(welding, welding&static, static),

the stress distribution data along the length direction

in position A and B shown in Fig.1 are extracted.

The stress distribution is shown in Fig.11.

Fig.11 Comparison of Von Mises stress under different

conditions.

As can be seen from the diagram, the Von Mises

stress in position B is much higher than that in

position A and the average Von Mises stress around

weld toe is more than 3 times higher than that of

middle area. The reason for the high value of stress

in position B is that the welding toe is located at the

junction of fusion zone and base metal where the

gradient of temperature change is large and the

plastic deformation is very uneven. The Von Mises

stress curves of two positions are basically

coincident under static conditions, the main reason

for this phenomenon is the bending moment of both

positions are almost identical owing to the same

distance to the centroid of extended arm structure.

With the increase of the length of extended arm, the

bending moment caused by the external force

decreases gradually, resulting in the decrease of Von

Mises stress of position A and position B gradually.

The Von Mises stress in position B is still much

higher than that in position A under welding&static

conditions, which has little difference from the value

in welding condition. The main stress in position B

mainly comes from the welding residual stress. In

addition, the Von Mises stress in position A is

smaller than the WRS in welding condition, the

reason for decrease is that the stress in X direction

caused by welding as shown in Fig.12 is pressure

stress which can be offset by the tensile stress in

static condition.

Fig.12 Welding residual stress of extended arm in X

direction.

Tab.2 shows the comparison of extended arm

deformation in different conditions, from which can

we find that the deformation in X direction in

welding&static condition mainly results from the

welding deformation. The deformation in Z direction

in welding&static condition mainly comes from the

welding deformation as well. The deformation value

in Y direction is 36.19 mm under load in static

condition, while the value comes to 38.28 mm in

welding&static condition which mainly results from

the stack of welding deformation and downwarping

with static load.

Tab.2 Comparison of extended arm deformation in different conditions.

min

max

min

max

min

max

Welding -3.11 3.01 -1.15 0.14 -0.28 0.32

Static -1.08 0.98 0 36.19 -0.01 0.01

Welding&stat

-3.85 2.75 0.03 38.28 -0.28 0.33

5 CONCLUSIONS

(1) The welding deformation and residual stress

of the extended arm structure is investigated in the

numerical simulation method. The results show that

the welding residual stress around weld toe is very

high and the maximum Mises stress in weld zone is

up to 550MPa, which is more than 3 times higher

than that of middle area.

(2) The Von Mises stress around the weld zone

in welding&static condition is up to 550 MPa, which

is mainly influenced by the welding residual stress,

while the stress apart from the weld area decreases

on account of the offset by the WRS.

(3) The welding deformation is the main part of

the structural deformation in X and Z direction

under welding&static condition and the deformation

in Y direction is 38.28mm, which is the

superposition of welding deformation and

downwarping with static load.

REFERENCES

1. Flores-Johnson E A, Muránsky O, Hamelin C J, et al.

Numerical analysis of the effect of weld-induced

residual stress and plastic damage on the ballistic

performance of welded steel plate[J]. Computational

Materials Science, 2012, 58:131-139.

2. Nikkarila J P, Manninen M. Introduction to the

characterization of residual stress by neutron

diffraction /[M]. Taylor & Francis, 2005.

3. Lammi C J, Lados D A. Effects of residual stresses on

fatigue crack growth behavior of structural materials:

Analytical corrections[J]. International Journal of

Fatigue, 2011, 33(7):858-867.

4. Cheng Xiaoyu, Wang Xiaomei. The essence and

adjustment of residual stress[J]. Total corrosion

control, 2009, 23(7):33-35.

5. GaoZhanyuan, GuoYanlin.Analysis on Influence of

welding residual stress on ultimate bearing capacity of

Y-joints[J]. Journal of architectual science and

engineering, 2016, 33(6):73-80.

6. Li Yanjun, Wu Aiping, Liu Debo, et al. Numerical

simulation on Y-ring welding residual stress and its

effects on loading behavior of propellant

tank[J].Transactions of nonferrous metals society of

china, 2017, 27(4):701-707.

7. Xiao Qi. Study on numerical method of strength

analysis based on coupling method of welding residual

stress and service load[D]. Beijing Jiaotong

University, 2014.

8. Xu Lei, Huang Xiaoping, Wang Fang. Effect of

welding residual stress on the ultimate strength of

spherical pressure hull [J]. Journal of ship mechanics,

2017, 21(7):864-872.

9. Miyashita T, Inaba N, Hirayama S, et al. Measurement

method for welding residual stress in steel I-shaped

girder with thick flange and its influence on load

carrying capacity for bending[J]. Structural

Engineering, 2015, 3:191-208.

10. Liu Min. Structure analysis and optimization of

autocrane [D]. Chang an university, 2014.

11. Wang Changli. Numerical simulation of welding

temperature distribution and stress variation

[D].Shenyang University of Technology,2005.

12. John Goldak，AdityaChakravarti，Malcolm Bibby．

A new finite element model for welding heat

sources[J]．Metallurgical Transactions B，1984(15)

：299-305．

13. Deng D. Theoretical prediction of welding distortion

in thin curved structure during assembly considering

gap and misalignment [D]. Doctoral Thesis, Osaka

University, 2002.