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Research Papers

The Contribution of Different Fracture Modes on Drilling Delamination Crack Propagation

[+] Author and Article Information
Mohammad Reza Vaziri Sereshk

Caspian Faculty of Engineering,
College of Engineering,
University of Tehran,
Rezvanshahr 43861-56387, Iran
e-mail: m.vaziri@ut.ac.ir

Hamed Mohammadi Bidhendi

Mechanical Engineering Department,
University of Kashan,
Kashan 87317-53153, Iran
e-mail: hamed.mohamadi89@gmail.com

1Corresponding author.

Manuscript received March 25, 2016; final manuscript received August 26, 2016; published online September 29, 2016. Assoc. Editor: Laine Mears.

J. Manuf. Sci. Eng 139(1), 011013 (Sep 29, 2016) (8 pages) Paper No: MANU-16-1181; doi: 10.1115/1.4034719 History: Received March 25, 2016; Revised August 26, 2016

Delamination as the main defect created during drilling of composite laminate is principally a crack nucleation and propagation phenomenon. The fracture-based investigation is performed to identify the significance of different modes involving in this process. The sensitivity analysis is implemented to evaluate magnitude and importance of each mode. As a result, mode I is a dominant mode while drill point removes the material; however, the crack continues to propagate under pure mode III for a while after drilling due to contact of flutes with spalls. This paper investigates the crack formation process for wide variety of drilling conditions and tool geometries. It is demonstrated that although mode III contributes, its minor effect might be neglected if comparing with fracture mode I. Therefore, it may be vanished as a tool design strategy. It is indicated that chisel edge plays a great role in crack propagation under major mode I; therefore, any further design approach which limits or eliminates opening action of chisel edge decreases delamination significantly. Material removal starting from hole perimeter as well as implementing small predrilled holes (such as action of primary cutting lips in step drill) are examined as solutions based on this approach.

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References

Figures

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Fig. 1

Fracture modes in three regions

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Fig. 2

Sensitivity analysis in three regions

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Fig. 3

Setup of the experiment

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Fig. 4

Conventional twist drill

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Fig. 5

Drill force versus time for the entire drill cycle

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Fig. 6

Drill torque versus time for the entire drill cycle

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Fig. 7

Delamination for drilling condition as (a) n = 1500 (rpm), f = 0.08 (mm/rev); (b) n = 1500 (rpm), f = 0.15 (mm/rev); and (c) n = 1500 (rpm), f = 0.25 (mm/rev)

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Fig. 8

Drill force versus time for the entire drill cycle

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Fig. 9

Drill torque versus time for the entire drill cycle

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Fig. 10

Delamination for drilling condition as (a) n = 160 (rpm), f = 0.25 (mm/rev); (b) n = 565 (rpm), f = 0.25 (mm/rev); (c) n = 950 (rpm), f = 0.25 (mm/rev); and (d) n = 1500 (rpm), f = 0.25 (mm/rev)

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Fig. 22

Drill force versus time for the entire drill cycle

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Fig. 21

Single flute twist drill bit

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Fig. 20

Delamination for drilling condition as (a) n = 565 (rpm), f = 0.25 (mm/rev); (b) n = 1500 (rpm), f = 0.25 (mm/rev)

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Fig. 19

Drill torque versus time for the entire drill cycle

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Fig. 18

Drill force versus time for the entire drill cycle

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Fig. 17

Schematic of final stage of drilling process with step drill: (a) beginning of cutting with second lips and (b) end of cutting with second lips

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Fig. 15

Delamination for drilling condition as (a) 13 deg flute angle, n = 1500 (rpm), and f = 0.25 (mm/rev); (b) 40 deg flute angle, n = 1500 (rpm), and f = 0.08 (mm/rev)

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Fig. 14

Drill torque versus time for the entire drill cycle

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Fig. 13

Drill force versus time for the entire drill cycle

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Fig. 12

Twist drill bit with (a) 13 deg helix angle and (b) 40 deg helix angle

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Fig. 11

Schematic of the cutting lips

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Fig. 23

Drill torque versus time for the entire drill cycle

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Fig. 24

Delamination for drilling condition as (a) n = 1500 (rpm), f = 0.25 (mm/rev); (b) n = 1500 (rpm), f = 0.08 (mm/rev)

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Fig. 25

Torque corresponding to one cycle rotation of spindle: (a) conventional twist drill bit and (b) single flute drill bit

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Fig. 26

(a) n = 1500 (rpm), f = 0.25 (mm/rev); (b) n = 1500 (rpm), f = 0.08 (mm/rev)

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