The document discusses how drilled "crack stopper" holes can reduce stress concentrations at crack tips in structural parts and delay fatigue failure. It explains that drilling a hole at the crack tip changes the stress pattern, which FEA analysis shows is effective. As a case study, FEA models of a simple steel bar under tension and torsion loading were analyzed. The results found that a drilled crack stopper hole reduced maximum stress at the crack tip by 94.6% under tension and 25.4% under torsion, demonstrating how the technique can increase fatigue life.

1. How does a “crack stopper” drilled
hole feature reduce crack tip
stress and delay fatigue failure of
a structural part ?
8/03/2017 rev A
Don Blanchet
3B Associates
dwb3298@verizon.net 1
Tapped hole with
threaded plug

2. Background
 Various methods of attempting to halt
the progression of cracks in metal
parts have been attempted.
 One of the simplest is to drill a hole
that includes the crack tip.
 This changes the stress concentration
pattern.
 FEA is very useful in studying the
effect of “crack stoppers”.
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3. Crack defect
3

4. ‘Crack stopper’ simple
drilled hole at crack tip
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5. Case study : a simple bar
in tension
5
Simple steel bar
Loaded in tension
1.75 x 1.00
Cross section
Load = 4500 lbs

6. Case study : a simple bar
in torsion
6
Simple steel bar
Loaded in torsion
Load = 100 inch- bs

7. Stress contours @ crack tip
bar under tension
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8. Results
in tension
with
stopper
8
24,760 psi max

9. Torsion Stress contours with stopper
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10. Results Summary
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Load type
max
Stress
With
crack
Psi
max
Stress
With
Crack
stopper
Psi
%
Stress
reduction
tension 46120 2476 94.6
torsion 2145 1600 25.4

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