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ASTM E399 | Metallic Materials | Fracture Toughness

ASTM E399 describes the determination of fracture toughness of metallic materials by fatigue tests of precracked specimens having a thickness of 1.6mm (0.063 in) or greater. Force is applied either in tension or three-point bending.

Fracture toughness, KIc, characterizes the resistance of a material to fracture in a neutral environment in the presence of a sharp crack under linear-elastic stress and severe tensile constraint, such that the state of stress near the crack front approaches tritensile plane strain, and the crack-tip plastic zone is small compared to the crack size, specimen thickness, and ligament ahead of the crack.  

Before conducting ASTM E399, it is important to read the entire specification in the relevant ASTM publication.

ASTM E399 | Metallic Materials | Fracture Toughness

  1. Prepare the notched samples as described in the standard. Measure and record the width and thickness. It is recommended to perform at least three tests for each material condition.
  2. Place the specimen in the tensile grips or on the bend fixture. Attach the displacement gauge to the crack opening of the specimen.
  3. Apply the load at a loading rate such that the rate of increase of stress-intensity factor is between 0.55 and 2.75 MPa√m/s (30 and 150 ksi√in/min) during the initial elastic displacement.
  4. Continue the test until the specimen can sustain no further increase in an applied force. Record the maximum force.
  5. Measure the crack size after fracture, at mid-thickness and two quarter-thickness positions on the crack front, as well as at the intersection of the crack front with the specimen surface. Record load vs. crack mouth opening displacement (CMOD).
Calculations:
  • Fracture toughness, KIc
  • Yield Strength

ASTM E399 | Metallic Materials | Fracture Toughness

ASTM E399 Recommended Equipment
Testing System
Fixturing
Accessories
  • Double-cantilever displacement gauge
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