APPENDIX IX IMPACT STRENGTH - FRACTURE TOUGHNESS One attractive property of ductile iron is ductility, the ability to bend and stretch as measured by percent elongation in the slow loaded tensile test. An equally attractive property of ductile iron is impact strength, the ability to resist the shock of high velocity stresses. This impact property is more difficult to test and measure because it is influenced by temperature, velocity of impact, size of specimen, and the effect of design angles, casting flaws, etc. Good service performance of many ductile iron verifies its serviceable impact resistance. Many ductile iron castings in service have withstood shock loads that caused failure of gray iron parts. Ductile iron pipe have admirably withstood earthquakes and the "water hammer" impact of valve closings. But, laboratory testing of impact qualities has been more difficult. CHARPY IMPACT TEST An earl y and popular impact test is the Charpy test in which a specimen is broken by a swinging pendulum and energy absorbed in breakage calculated. Small machined specimens are tested either unnotched or with a special V notch. Impact strength is calculated in foot pounds or in Joules and various metric designations in different countries. The Charpy test is easiest to perform, but a disadvantage is the specimen too s mall to represent service performance and the full section. TRANSITION TEMPERATURE Above a certain temperature, irons and steels break with a ductile fracture. Upper shelf energy is higher and increases little with further increases in temperature. a certain low temperature, the fracture is a brittle cleavage fracture and the energy level is much lower. The midpoint temperature where half the fracture is ductile (gray) and half brittle cleavage (white crystalline) is considered the transition temperature. In cold climates, a low transition temperature is desirable where impact is anticipated. CHARPY V NOTCH IMPACT STRENGTHS
APPENDIX IX IMPACT STRENGTH - FRACTURE TOUGHNESS One attractive property of ductile iron is ductility, the ability to bend and stretch as measured by percent elongation in the slow loaded tensile test. An equally attractive property of ductile iron is impact strength, the ability to resist the shock of high velocity stresses. This impact property is more difficult to test and measure because it is influenced by temperature, velocity of impact, size of specimen, and the effect of design angles, casting flaws, etc. Good service performance of many ductile iron verifies its serviceable impact resistance. Many ductile iron castings in service have withstood shock loads that caused failure of gray iron parts. Ductile iron pipe have admirably withstood earthquakes and the "water hammer" impact of valve closings. But, laboratory testing of impact qualities has been more difficult. CHARPY IMPACT TEST An earl y and popular impact test is the Charpy test in which a specimen is broken by a swinging pendulum and energy absorbed in breakage calculated. Small machined specimens are tested either unnotched or with a special V notch. Impact strength is calculated in foot pounds or in Joules and various metric designations in different countries. The Charpy test is easiest to perform, but a disadvantage is the specimen too s mall to represent service performance and the full section. TRANSITION TEMPERATURE Above a certain temperature, irons and steels break with a ductile fracture. Upper shelf energy is higher and increases little with further increases in temperature. a certain low temperature, the fracture is a brittle cleavage fracture and the energy level is much lower. The midpoint temperature where half the fracture is ductile (gray) and half brittle cleavage (white crystalline) is considered the transition temperature. In cold climates, a low transition temperature is desirable where impact is anticipated. CHARPY V NOTCH IMPACT STRENGTHS
Ductile-Iron-Quality-Assurance-Guide-Apendix-3-to-end.docx