ASTM E399
Fracture Toughness Test Fixtures: Clevis Grips, Bend Fixture and Clip Gage
ASTM E1820 Bend Fixture – Universal Grip Data Sheet (PDF)
ASTM E399 measures the plane-strain fracture toughness, KIc, of metallic materials. A fatigue-precracked compact tension (CT) or single-edge bend (SEB) specimen is loaded while force and crack mouth opening are recorded. Universal Grip supplies the complete setup: clevis grips for CT specimens, a three-point bend fixture for SEB specimens, and a clip-on crack mouth opening gage. The same fixtures serve ASTM E1820 J-integral and CTOD testing.
What ASTM E399 Measures
E399 reports a conditional value, KQ, from the force versus crack-mouth-opening record. KQ becomes a valid KIc only if the specimen is thick enough and the record is linear enough, as set by the size and linearity requirements of the standard. When a material is too tough for a valid KIc, labs move to ASTM E1820, which measures J, K and CTOD, including resistance curves, on the same types of specimens.
How the ASTM E399 Test Works
Machine the CT or SEB specimen and fatigue precrack it to the required crack length.
Attach knife edges at the notch mouth and seat the clip gage.
Load the CT specimen through the clevis pins, or the SEB specimen in three-point bending.
Record force against crack mouth opening at the specified loading rate.
Determine PQ from the record, calculate KQ and check the validity criteria for KIc.
Specimens and Setup
Precrack in fatigue at controlled loads; the precrack must meet the standard's length and straightness limits.
Use clevises with flat-bottom pin holes so the pins can roll and the specimen self-aligns.
Keep the SEB span at four times the specimen width with free-rolling supports.
Check that the clip gage travel suits the expected opening.
Confirm specimen size requirements and loading rate against your copy of the current standard.
Universal Grip ASTM E399 Fixture
CT clevis grips with flat-bottom holes and hardened pins
SEB three-point bend fixture with free-rolling supports and adjustable span (50 kN standard)
Double-cantilever clip gage with full-bridge strain-gage output
Clear access for knife edges and crack-growth instrumentation
Elevated and low-temperature versions on request
Clevis pin or threaded adapters for servo-hydraulic and electromechanical frames
Applications
KIc testing of metals
J-R curve and CTOD testing (ASTM E1820)
Weld and heat-affected zone qualification
Aerospace alloy fracture data
Related Standards and Products
Send us your specimen dimensions, required capacity and machine connection through our contact page and we will quote an ASTM E399 fracture toughness fixture. Request a quote
ASTM E399 FAQ
What is the difference between E399 and E1820?
E399 gives a single plane-strain value, KIc, under mostly linear-elastic conditions. E1820 covers elastic-plastic toughness using J-integral and CTOD, including resistance curves, for tougher materials where a valid KIc is not possible.
Why must the specimen be precracked?
A machined notch is too blunt. Fatigue precracking creates a sharp crack tip so the measured toughness reflects how a real crack would behave.
What is a clip gage used for?
It measures crack mouth opening displacement (CMOD) at the notch. Force is plotted against this opening to find PQ and calculate KQ.
Which specimen should I use, CT or SEB?
Compact tension specimens save material and are common for plate and forgings. Single-edge bend specimens are simple to machine and suit welds. We supply fixtures for both.