Fracture Toughness Testing

Performed to ASTM E399 & ASTM E1820

fatigue test labThe Fracture Toughness Test determines how well a material can resist the growth of a crack under increasing load. It is valuable in determining whether there is a danger of component failure when a flaw is discovered in an existing structure. Fracture Toughness Testing is performed by the experienced staff at Laboratory Testing Inc. in PA (USA).

Scope of Testing

  • Computerized servohydraulic load frames can generate up to 100,000 lbs. force.
  • Temperature chambers, furnaces and instrumentation allow testing to be performed between temperatures of -150°F and 1200° F.
  • We have fixturing to test specimens in a range of sizes, including SE(B) (single edged bend) and C(T) (compact tension) specimens..

Test Methods/Specifications

  • Fracture toughness specimensASTM E399
  • ASTM E1820
  • ASTM E1290 (Superseded by ASTM E1820)

Test Specimens Prepared by LTI

The fracture toughness test requires a precisely machined specimen prepared to specification. The Machine Shop at LTI can prepare specimens for all fracture toughness testing performed at our lab and provides an EDM machined notch. Specimen sizes ranging from Charpy-sized SE(B) bars up to 4.5” W C(T) specimens have been machined.

The Fracture Toughness Test Process

Fracture toughness is an important material property in design applications since the occurrence of flaws is not completely avoidable. Flaws may appear as cracks, voids, inclusions, weld defects or design discontinuities.

A fracture toughness test measures the conditions under which an existing crack in a material will extend by characterizing the resistance of the material to crack extension when a sharp crack is present. The properties are obtained by testing specimens containing preexisting deliberately introduced cracks or notches that are subjected to increasing tensile loading conditions. By measuring the combination of load and displacement as the crack lengthens, the material’s resistance to further crack extension is determined.

ASTM E399 / KIC Test

Fracture toughness testing according to ASTM E399 (Linear-Elastic Fracture Toughness Testing) applies a continuously increasing load to the specimen and determines the critical stress intensity KIc. This method is known as the KIC, K1C or KIC fracture toughness test. 

ASTM E1820

During ASTM E1820 (Linear-Elastic Fracture Toughness Test), a rising load with periodic partial unloading is applied to measure the crack length as the test progresses. ASTM E1820 provides KJIc and JIc. Crack-Tip Opening Displacement (CTOD, δ) is also available from the data analysis.

The “J” integral describes elastic-plastic fracture toughness in more ductile materials which are better able to deform and resist crack growth under load. A Roman numeral subscript added to “K” and “J” indicates which of the three modes of fracture is used in the test. Mode I fracture is most common and is the condition in which a tensile load is applied normal to the direction of the crack plane. When a cracked material under Mode I plane-strain conditions reaches a critical value, denoted as KIc or JIc, the crack will begin to grow. Experimental values of KIc and JIc can be applied to the design of structures to ensure that a component does not fail by brittle or ductile fracture. KJIc is derived from the JIc result.

LTI Capabilities

  • Test Methods – KIc per ASTM E399 and ASTM E1820; JIc, KJIc and CTOD per ASTM E1820
  • Loads  – 40 lbf. to 100,000 lbf.
  • Temperature – between -150° F and +1200° F
  • Fixturing – SE(B) single edge bend and C(T) compact tension specimen geometries in a range of sizes
  • Test Specimens – specimens are prepared in LTI’s Machine Shop according to standard procedures; EDM notch capabilities

Contact us to discuss your test requirements.

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