DARHEL BOULINGUI BU IKAPI Louvet， CHEN Huimin()， GE Mengying()， ZHU Chengchao()， YUE Xiaoli ()

College of Mechanical Engineering， Donghua University， Shanghai 201620， China

Abstract： The fabric clip is an important component in textile machine.The creep deformation on the clip body hole at high temperature acted on different pulling forces during a period of 6 240 h was researched by using ABAQUS software. The Norton-Bailey’s with time hardening constitutive equation was used to simulate the creep deformation on the clip body hole made of A380 aluminum alloy at high temperature， and the simulation results showed that for different pulling forces， the creep deformation on the clip body hole increased with an increase in the pulling force. Then， the experimental dimensional changes test was performed on three different specimens of the clip body hole at different service time(1 200 h， 4 800 h， 6 240 h) by using a Global Performance test machine. A comparison between the finite element method (FEM) and the experimental results show a good correlation. The simulation results also indicate that the creep deformation on the clip body hole has an important effect on the relaxation of the blade clamping fastness which leads to fabric clip failure.

Key words： creep analysis; clamping fastness relaxation; dimensional changes; finite element method (FEM)

Introduction

Fabric clip， also called stenter, is widely used in dyeing， mercerizing， stretching and printing machineries. The main function of the stenter is to stretch the fabric widthwise to recover the uniform width[1-2]. The fabric clip is one of the most important assembly components and has a good shaping effect， avoiding the emergence of “l(fā)otus leaf”， “broken edge” and other defects. Therefore， during the stenter process， the structure of the fabric clip has a great influence on the fabric quality[3]. The complex structure of the fabric clip is shown in Fig. 1 and it’s composed of different parts,e.g., the blade， the plate， the clip body， the hammer clip and the shaft.

Fig.1 Structure of the fabric clip assembly

Several parts of the fabric clip are made of different materials，e.g., the shaft， the blade and the plate are made of steel， the hummer clip is made of copper, and the clip body is made of A380 aluminum alloy. During the stenter finishing process， the fabric clip is subjected to different mechanical loads and high thermal loads due to air steam heating system located in every chamber of the stenter[4]. The two factors are responsible for the fabric clip failure[5]. At high temperature 230 ℃ for different pulling forces， the clip body made of A380 aluminum alloy is identified as the part of the fabric clip which experienced the creep deformation. The main factor which principally influences the material deformation on the clip body hole during creep deformation is dependent on temperature， time and mechanical force， and it is important to improve the reliability and the service life of the fabric clip[6]. Creep can be defined as a time deformation resulting by a slow plastic deformation on a solid under the influence of mechanical load and high temperature[7].

Bouzid and Nechache[8-9]investigated the effect of gasket creep relaxation on the leakage tightness of bolted flange joints by using ABAQUS software， with the results showing that the creep deformation on the flange gasket has an important effect on the bolt flange joint. Mackerle[10]explored the finite element method creep fracture/damage of engineering material and structures from theoretical model. Willschützetal.[11]investigated the failure of the reactor pressure vessel and the failure time for a light water reactor. Rajendranetal.[12]studied the life prediction of a high strength steel plate. Kumaretal.[13]published studies one creep life prediction of a simple impulse steam turbine blade by using ANSYS software at high temperature for various mechanical loads. Ivancoetal.[14]used ANSYS software to simulate the creep deformation of spiral strand based on Timoshenko beam theory and Saint Venant torsion theory. Tuetal.[15]analyzed the effect of large deformation on a small specimen due to creep property. Zhouetal.[16]reported the creep behavior and lifetime prediction of polymethyl methacrylate (PMMA) immersed in liquid scintillator by using a new creep test machine at room temperature.

First， we analyze the creep deformation on the clip body hole made of A380 aluminum alloy at 230 ℃ for different pulling forces (100 N， 200 N， 300 N) for a duration time of 6 240 h by using ABAQUS. Then for a constant pulling force of 300 N， determine the blade clamping fastness relaxation effect due to the creep deformation on the clip body hole. And then analyze the dimensional changes and distortions on three specific clip body holes for different period of time (1 200 h， 4 800 h， 6 240 h).

1 Characteristic of the Fabric Clip

1.1 Structure of the fabric clip

The complex structure of the fabric clip is shown in Fig.1 and each component of the fabric clip has different types of contact interaction. Firstly， the shaft component is directly joint to the clip body and the pivoting hammer clip. Secondly， the fabric component is directly in contact with the blade and the plate component. Finally， the different dimensions of each part of the fabric clip were well-matched with the dimension related on the different drawing engineering graphics provided by several manufacturing company.

1.2 Components materials and properties of the fabric clip

The components material and physical properties of the fabric clip are presented in Table 1.

Table 1 Components material and physical properties of the fabric clip

1.3 Creep deformation process and law

Creep failure occurs when the accumulated creep-strain values in a component deformation exceeds the designed limit[17-18]. Furthermore， three characteristic periods of time have been observed. The creep rate with time is sequentially decreasing， remaining essentially constant and increasing，which is shown in Fig. 2. These are often called the periods of primary， secondary， and tertiary creep[19].

Fig.2 Three creeps stages at constant stress(σ) and temperature(T)

ABAQUS provides three different creeps laws:the power law with time hardening and strain hardening， the hyperbolic sine law model and creep user subroutine. In ABAQUS software the power law is divided into two specifics parameters as the strain hardening and the time hardening.

In many engineering studies， the power law with time hardening is the one used due to its simplicity and accurate results. However， this method is restricted because the power law with time hardening can only work when the stress remains constant. The power law with time hardening equation is given in Eq. (1).

(1)

According to Eq. (1)， the creep parameter data of A380 aluminum alloy previously reported by Chang and Wang[20]were used in the present work to analyze the creep deformation on the clip body hole at high temperature. The relevant data are shown in Table 2.

Table 2 Creep constant data of A380 aluminum alloy

The specificity of this section is to apply the creep constant data and the plastic deformation on the clip body made of A380 aluminum alloy. In addition， due to the high temperature (230 ℃) of the simulation， the creep deformation does not appear on the parts made of steel and copper but only the clip body made of A380 aluminum alloy，which can be influenced by this high temperature and pulling forces.

2 Computational Model

2.1 Mesh and friction coefficients of the fabric clip

The fabric clip was created by using solid works software and exported to ABAQUS software via a step folder. In addition， half model of the fabric clip component had been created for a better and faster computational calculation，and our fabric clip assembly structure is shown in Fig. 3.

Fig.3 Mesh model of the clip

Due to the complexity of our assembly model， each component is meshed separately for a better simulation accuracy and lower computational period in ABAQUS[21]. The blade， plate， fabric and the shaft part are meshed with hexahedral elements with 8 nodes and three degree of freedom at every node. The element control of the three parts mentioned above is C8D8R， which is an 8-node linear brick reduced integration， hourglass control. The type of element used for the mesh of the hammer clip and clip body is the free mesh quadratic tetrahedral elements. The element control of these two parts is C3D4 which is a basic A-4 node linear tetrahedral.

In this study， four different surface contact interactions of the fabric clip are shown in Fig. 3. The contact interaction is defined using the master-slave algorithm with finite sliding in ABAQUS. The assembly structure is composed of four different materials and the material of each interaction has different friction coefficients. A tie constraint is used between the hammer clip and the blade with a tolerance dimension of 0.01 mm. According to American Society of Metals (ASM) Handbook Volume 2， the value of the friction coefficient between aluminum and steel is 0.35， the one between steel and cooper is 0.36 and the one between two steel material component is 0.15. Therefore， the value of the friction coefficient of the contact interaction between the fabric and the blade and the plate is 0.15[23-25].

2.2 Mechanical load and boundary condition

In this study，the fixed boundary conditions (Ux=Uy=Uz=URx=URy=URz=0) were set at the lower surface of the clip as indicated in Fig. 3. This function means that there will be no node translation and rotation at this area. The boundary symmetry constraints were set to the clip body， shaft， blade and plate while the symmetry was constrained inZdirection. The displacement boundary condition(Uy=0) was applied on the lower surface of the fabric. Finally， the different pulling forces (100 N， 200 N， 300 N) were applied onXdirection and a gravity load (9.8 m/s2) was also applied on the pivoting hammer clip inYdirection.

3 Simulation

3.1 Creep deformations of the clip body for different pulling forces

The creep deformation curves of the clip body hole at constant temperature 230 ℃ for different pulling forces (100 N， 200 N， 300 N) for different time intervals of 6 240 h are shown in Fig. 4. According to cooperate company， the maximum creep deformation occurs on the clip body hole for a time period of 6 240 h.

Fig.4 Creep strain curves of the clip body hole for different pulling forces

The different creeps curves are extracted from the nodes located at the edge surface of the clip body hole and the selected node is the one which experienced the maximum creep deformation during simulation for a time period of 6 240 h. Two specific regions can be observed in Fig. 4 during the creep deformation of the clip body hole at high temperature 230 ℃，such as the primary and secondary creep phase region. The simulation data show that for all the three pulling forces (100 N， 200 N， 300 N)， the primary creep stage starts at the beginning of the analysis and ended when the simulation reaches the time period of 1 000 h.

The secondary creep stage started at the period of 1 000 h and ended at the simulation time 6 240 h. The second region of the creep deformation curve is reached when the material experienced a linear expansion of the creep strain with time. At high temperature 230 ℃ for 6 240 h of creep time period for different pulling forces (100 N， 200 N and 300 N)， the maximum creep strain values were 0.003 2%， 0.006 1% and 0.009 2%. Finally， it can be observed that the trend of the creep curve increases as the pulling force increases in function of time.

3.2 Effect of the blade clamping fastness due to the creep deformation on the clip body hole

Figure 5 shows the blade clamping fastness relaxation for constant pulling force 300 N during a period time of 6 240 h. The blade clamping fastness relaxations are extracted on the 244 nodes located on the lower surface of the blade. The maximum contact stress is located at the middle region of the blade part. The simulation results show that as the creep deformation occurs on the clip body hole for a period time of 6 240 h， the maximum blade clamping fastness relaxation value is 52.12 MPa.

Fig.5 Blade clamping fastness relaxation for constant pulling force 300 N

It can be observed that when the operating time increases， the trend of the blade clamping fastness decreases. The blade clamping fastness decreases due to the creep deformation which appears on the clip body hole. In addition， when the blade clamping relaxation decreases in function of time， the friction force between the blade and the upper surface of the fabric decreases also， this phenomenon has an important impact on the fabric quality.

Furthermore， the degree of wear appears also at this stage on the middle area of the blade and the plate， for the maximum fabric pulling force is applied on the fabric motion direction. The apparition of the abradability at this stage is responsible of the fabric clip failure at high temperature 230 ℃. This is also one of the principal reasons of the fabric clip failure and mainly leads to the difficulty of the hammer clip to grip the fabric edge properly.

4 Experiment

4.1 Experimental procedure

A Coordinate Measuring Machine (CMM) Global Performance testing machine(Global 05.07.05 produced by Hexagon Metrology, China) is used to determine the dimensional changes and distortion of the three specifics clip bodies made of A380 aluminum alloy as shown in Fig. 6. The experimental test duration of the three specifics clip bodies were 1 200 h， 4 800 h， 6 240 h and the CMM experiment are performed at room temperature 23 ℃. The creep deformation of the clip body hole occurs when the temperature reached 230 ℃ for different pulling forces，and CMM experiment room temperature doesn’t affect the result because the creep deformation on the clip body hole was already observed during the assembly components working period. The testing machine was located at College of Mechanical Engineering, Donghua University and the displacement of the testing machine is established with a specific maximum permissible error (E0，MPE= 3.5+L/250 μm)，whereLrepresents the length in mm， and the testing standard is done according to Chinese coordinate measurement standard GB/T 16857.2—1997.

Fig. 6 Three different clips bodies’ specimens

Each specimen was fitted and aligned at the middle position of the CMM Global Performance testing machine and the remote control was used to change the position of the sensor probe. During the test， six different points nodes inside each clip body hole at three different positions (lower， middle and upper) circular surface of the clip body hole were selected to extract the dimensional changes and distortions on the clip body hole as shown in Fig. 7. Several measurements (five points) have been made in order to obtain accurate deformation on the clip body holes after the fabric clip process. In order to characterize the amount of distortion on the clip body hole after the process， a fixture made of steel material is used to hold significantly the clip body at center location of the CMM operating platform.

Fig. 7 Different clip body hole nodes locations

4.2 Measurements of dimensional changes and comparison with the finite element method (FEM)

The CMM Global Performance measuring machine was used to measure the dimensional changes and distortion on the clip body hole. The dimensional changes are caused mainly by the creep deformation appearing on this component. The experiment of the clip body holes distortion was done for three different time periods (1 200 h， 4 800 h， 6 240 h )as referred in Fig. 6.Table 3 shows the comparison between the creep strains simulated by FEM and dimensional changes of the clip body hole measured by CMM for different periods of operating service. The elongation of the clip body hole was measured after the appearance of the creep deformation and the wear deformation on the clip body hole. At 1 200 h for a constant pulling force 300 N, the elongation measured on the clip body hole wasd1= 0.009 36 mm. Att= 4 800 h andt=6 240 h， the clip body hole measured changes， but the elongation measured values were almost the same，d2= 0.009 88 mm andd3= 0.012 36 mm. In conclusion， it can be noted that the elongation of the clip body hole increased as the operative time increased. The CMM and the FEM elongation changes of the clip body hole present a good correlation between the two methods.

Table 3 Comparison between the CMM and the FEM results

5 Conclusions

(1)At 230 ℃ and different pulling forces (100 N， 200 N， 300 N)， the creep deformation on the clip body hole is located at edge surface of the clip body hole and the maximum creep strain value are 0.003 2%， 0.006 8% and 0.009 1%. The simulation results show that the creep deformation on the clip body increases as more as the pulling force increases and the creep deformation on the clip body hole has an important impact on the fabric quality.

(2)At high temperature when the creep deformation occurs on the clip body hole， the blade clamping fastness decreases in function of time， which means that the creep behavior on the clip body hole has an important effect on the blade clamping fastness. So we can conclude that the blade clamping fastness relaxation leads to the fabric clip failure.

(3)A Global Performance test machine was used to determine the dimensional changes and distortions on the clip body hole. Three different clip’s bodies were used with various working period time 1 200 h， 4 800 h， 6 240 h. The experimental and computational results were compared with each other and showed a good correlation.