ASTM D6068 Determining J-R Curves of Plastic Materials

Scope

A J-R curve created using ASTM D6068 defines the fracture development resistances of a wide range of polymers and polymer blends (1-5)4 that aren’t available in large enough sizes or thicknesses. A J-R curve can be used for blend or alloy design, material selection, materials processing, and quality assurance. The J-R curve can examine the stability of cracks in structures in the presence of ductile tearing while keeping in mind that laboratory tests and field circumstances may differ.

Procedure

In ASTM D6068, succession of specimens loaded using a crosshead or displacement control to various displacements. The crack fronts that develop are marked, and the crack extensions from the fracture surface are measured. The specimen loaded to a displacement level produces a crack extension in a desired spot on the J-R curve, then the specimen is unloaded. The original crack length a0, and the individual crack extensions, Dap, were also measured. 

Specimen size

To calculate the total energy absorbed by the specimen, measurements of applied load and load-line displacement are required.

Data

J = ήU/B(W – a₀)

Where B, W, and a₀ are specimen thickness, width, and original crack length, respectively.

Conclusion

A J-R curve created using ASTM D6068 defines the fracture development resistances of a wide range of polymers and polymer blends.