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The critical stress intensity factors Kc for some engineering materials are grouped in the following categories.

Toughness of Metals
Material Kc
(MPa·m1/2)
Yield Strength
(MPa)
Aluminum Alloy    
  2014 18-31 380-470
  2020 19-27 525-240
  2024 21-37 305-455
  2124 21-36 440-460
  2219 28-41 340-345
  7049 21-38 460-510
  7050 25-41 430-510
  7075 16-41 395-560
  7475 33-44 395-515
  7079 24-33 505-540
  7178 17-30 470-540
Ferrous Alloy    
  Cast Iron 6-20 120-290
  Roter Steel (A533) 204-214 -
  Pressure-vessel Steel (HY130) 170 -
  High-Strength Steel 50-154 -
  Mild Steel 140 -
  Medium-Carbon Steel 51 -
  4330V 86-110 1315-1400
  4340 44-91 1360-1660
  D6AC 62-102 1495-1570
  9-4-20 132-154 1280-1310
  18Ni 50-110 1450-1905
  AFC77 79 1530
Titanium Alloy    
  Ti6Al4V 77-116 815-875
Other Metals    
  Beryllium (Be) 4
Toughness of Polymers
Material Kc
(MPa·m1/2)
ABS 4
Epoxy 0.3-0.5
Nylon 3
Polycarbonate 1-2.6
Polyester 0.5
Polyethylene 1-2
Polypropylene 3
Polystyrene 2
PMMA 0.5-1.75
Toughness of Ceramics
Material Kc
(MPa·m1/2)
Electric Porcelain 1
Soda Glass 0.7-0.8
Alumina (Al2O3) 3-5
Toughness of Composites
Material Kc
(MPa·m1/2)
GFRP 20-60
CFRP 23-45
Boron Fiber-Epoxy 46
Wood (along grain) 0.5-1
Toughness of Minerals
Material Kc
(MPa·m1/2)
Shale 0.6
Soda Glass 0.7-0.8
Cement/Concrete 0.2
Granite 3
Toughness of Synthetic Materials
Material Kc
(MPa·m1/2)
Cement/Concrete 0.2
Cement/Concrete, Steel Reinforced 10-15
Silicon Nitride (Si3N4) 4-5
Cobalt Carbite 14-16
Silicon Carbite (SiC) 3
Tungsten Carbite 14-16
Magnesia (MgO) 3
Alumina (Al2O3) 3-5
Glossary