This presentation is about fracture analysis of US battle tank M107. This case study appears in Hertzberg book.

1. FAILURE ANALYSIS OF 175mm
GUN TUBE
Fracture Mechanics
Metallurgical and Materials Engineering
IIT Kharagpur

2. US ARMY M107 175mm SELF PROPELLED GUN
BREECH END

3. FRACTURE
• Flaw shape : semi-elliptical
• Flaw dimensions : half minor axis=0.94 cm
major axis = 2.79 cm
Small semi-elliptical critical crackSmall semi-elliptical critical crack

4. PREVIEW
• US army gun no.733 catastrophic failure near the breach end
• Gun barrel broke into 29 pieces
• Very little plastic deformation Brittle fracture suspected

5. Gun barrel composition :
AISI 4335 HSS Steel modified with Cr & Mo and 0.14% V.
Gun barrel was manufactured by forging
MATERIAL COMPOSITION AND PROPERTIES

6. BACKGROUND
Gun barrel dimensions:
• Length : 10.5 m
• Inner diameter :17.8 cm
• Outer diameter : 37.3 cm
Loading history:
• 227 rounds at 152 Mpa
• 373 rounds at 345 Mpa
Firing at 2 minutes interval, final round nominal pressure 345MPa

7. INSPECTION
• Possibilities of failure :
1. Overpressure: ruled out on further examination
2. Environment assisted cracking : ruled out due to short time
under service load (20x10-3
sec)
3. Low residual tensile stress
4. Loading rate effects ruled out as HSS was used.
• Cause of failure:
Crack Initiation due to Thermally Induced Cracking : heat
checking
Random network of cracks penetrating upto 0.13 cm below
inner bore surface.
IG fracture and cleavage Enhanced crack propagation rate
due to Temper Embrittlement.

8. • Low fracture toughness
• TE contributed to accelerated fatigue crack propagation

9. • SIF for internally pressurized thick walled tube:
• f=f(a/W, r2/r1, a/c)
• For semi-elliptical crack
K=99MPam0.5
N=2000 cycles
• TE increases crack propagation rate by about 2.5 times  N
decreases
• Taking into account other assumptions N comes down to near
the failure value
Fatigue Life Estimation

10. CONCLUSION
• Guns having Charpy impact energy < 13.5 J removed.
• Reduced service life to 300 rounds from 800 at 345MPa.
• Gun in manufacturing were heat treated to a lower strength
level to increase service life to about 10,000 rounds.
• Autofrettage treatment was done to improve the fracture life.
• Autofrettage tube withstood 20,000 firing cycle.

11. Thank You
Reference:
This case study was taken from the following book:
Case study no.7 : Deformation and Fracture Mechanics of
Engineering Materials - Hertzberg