CTOD Metal Testing - Crack-Tip Opening Displacement

CTOD stands for Crack-Tip Opening Displacement. It is the displacement between the crack tip and 90° intercept. This CTOD test is carried out to test the Fracture toughness in order to check whether a material is appropriate for strenuous (vigorous) working conditions or not. CTOD is to measure the deformation prior to failure in a pre-cracked sample. Method for determination of Klc, critical CTOD and critical J values for weld in metallic materials.

• ASTM E1290 Crack-Tip Opening Displacement Fracture Toughness Measurement
• Supervision of loading
• ASTM E1820 Measurement of Fracture Toughness (JIC-CTOD Measurement)
• BS 7448 Fracture mechanics toughness tests.

CTOD Test is practiced on those materials which undergo plastic (irreversible) deformation before undergoing failure. The testing material resembles the original one, but the dimensions can be reduced proportionally.

• The test specimen is placed on the work table and a notch is created at the center.
• The crack should be generated such that the defect length is about half the depth.
• The critical load and strain gauge measurements at the load are noted and a graph is plotted.

The crack tip opening can be calculated from the depth of the crack and opening at the mouth of the notch. Depending on the material used, the fracture can be brittle or ductile that can be concluded from the graph.