SHARP CRACK TO DETERMINE FRACTURE TOUGHNESS
As there are more complicated welding joints for heavy steel plates used in large boilers, pressure vessels or ship hulls and decking, the CTOD test is used to determine the fracture toughness of a material with a crack. Fracture toughness is the critical stress intensity factor of a sharp crack where propagation of the crack suddenly becomes rapid and unlimited.
CTOD testing measures the resistance of a material to the presence of a flaw in terms of the load required to cause brittle or ductile crack extension (or to reach a maximum load condition) in a standard specimen containing a fatigue pre-crack. The result is expressed in toughness parameters such as KIc, critical J or CTOD.
PTS have advanced testing equipment to measure the material’s fracture toughness for two primary types of configuration: Single-Edge Notched Bend (SENB) and Compact Tension (CT).
The Crack Tip Opening Displacement or CTOD Test measures the resistance of a material to the propagation of a crack. CTOD is used on materials showing some plastic deformation before failure occurs. Accurate measurement of this displacement is one of the essentials of the test.
Single-Edge Notched Bend (SENB) or Single-Edge Notched Tension (SENT) are the most common specimen geometries used. It is often tested according to BS ISO 12135 and BS 7448.
The ASTM E1820 specification has been developed to provide a standard method for determining all applicable toughness parameters from a single test. The J integral is a popular method of determining a material’s toughness by measuring the energy required to propagate a crack. Edge Notched Bend (SENB) and Compact tension (CT) are commonly used in J-integral testing following ASTM E1820.
Linear-Elastic Plane-Strain Fracture Toughness KIC of Metallic Materials is often tested according to ASTM E 399 specifications. The KIC test is used to determine the brittle fracture toughness of metallic material.
It measures the resistance of a material to crack extension under low toughness conditions when there is little to no plastic deformation occurring at the crack tip.
Compact tension (CT) and Single-Edge Notched Bend (SENB) are the most common specimen geometries. Due to its economical use of material, the CT specimen is the more commonly employed.
FATIGUE CRACK GROWTH RATE (NEW TEST IN 2023)
Fatigue Crack Growth Rate (da/dN) Testing is used to determine the crack propagation rate once it is initiated under specified loading conditions.
PTS uses advanced crack measuring techniques known as Direct Current Potential Drop (DCPD) to measure the change in resistance of a specimen, which correlates directly with crack growth. The graph of Cyclic Stress is plotted against the Crack Growth Rate, with stress intensity being the controlling variable.
The client specializes in the fabrication of offshore structures, and previous had done material testing with PTS.
The client bought an 80mm steel plate with non-compliance with API Specification 2W additional requirement SR 9 for pre-production qualification.
PTS provide the client with a one-stop solution for pre-qualification, including welding inspection and CTOD testing.
PTS give professional advice during the welding inspection and CTOD testing. They are willing to share technical information so that we can have a better understanding of CTOD testing.
Application of CTOD test
Determine fracture toughness (fracture resistance) of a material with an artificial crack
Single specimen method was used
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