WCA July 2011

The shape of the initial crack was observed using a microscope, and a mother wire with a crack of the same shape was modelled in the FEM analysis. It is clear that the FEM analysis result agrees with the experimental result. As shown in Figure 10 , the crack appears to be removed because side AB is pushed up into the wire; however, side BC of the crack is tilted so that it overhangs side AB, forming an overlapping crack (defect). The three-pass drawing of a mother wire with a surface crack was repeated in the experiment and FEM analysis. The obtained crack deformation behaviour for each drawing pass is also shown in Figure 10 . 4.2 FEM analysis of U-shaped crack deformation behaviour during repeated drawing Next, a wire with a U-shaped crack was modelled and the drawing process was similarly analysed by finite element analysis.

5 Conclusion

Wire breakage was investigated using experimentation and finite element method analysis.

A focus was on wire breakages caused by the presence of a foreign substance, in or on the wire, or by transversal cracks that develop on the surface of wires due to the effect of fatigue, inclusions or surface flaws. The obtained results are summarised below: 1) Surface flaws, foreign materials and excessive drawing stress generated by seizing are the causes of wire breaking. However, many of the causes of breakage in wires with a diameter of 50μm or less are speculated to be due to the presence of inclusions that are formed during casting

Experiment

Analysis

Figure 11 shows examples of crack deformation behaviour for 10mm diameter wires with a crack of breadth (a)=0.73mm and depth (h)=0.10mm (1%) and with a crack of a=0.73mm and h=0.60mm (6%) during repeated drawing at α =6° and R/P=20%. As shown in Figure 11 , under condition I, the bottom of the crack rises during repeated drawing, and thus the surface crack is removed after the first pass. Under condition II with the greater depth, however, the right side of the crack is tilted so that it over- hangs the left side and forms an overlapping crack (defect), indicating that the crack cannot be removed by drawing. Moreover, a deep crack develops in the wire although it appears to be small. Namely, the behaviour of the U-shaped crack during drawing depends on the depth (h). The results for the concave and U-shaped cracks were compared. An overlapping defect develops from the concave crack, regardless of the depth (h), whereas for the U-shaped crack the depth (h) serves as a parameter; that is, the crack with a shallow (h) is removed, but the crack remains on the wire when (h) is greater. It is considered that the shape of both sides of the crack significantly affects its removal under condition I in Figure 11 .

Mother wire

1 pass

Drawing direction

2 pass

3 pass

Distribution of residual stress in X-axis direction - 1400

Figure 10 : Changes of crack after each drawing pass in experiment and analysis

1400 [MPa]

a) Mother wire

b) 1 pass

c) U shape

Drawing direction

b) 1 pass

a) Mother wire

Figure 11 : Deformation behaviour of U-shaped crack during drawing

d) 3 passes

c) 2 passes

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Wire & Cable ASIA – September/October 2007 Wir & Cable ASIA – July/August 11