Scope:

ASTM D7905 is limited to composites made of unidirectional carbon-fiber and glass-fiber-reinforced laminates. It determines how strong the products are and how suitable a material is for industrial purposes. Therefore, knowing interlaminar fracture toughness is useful for product design, product development, and quality control.

One of the most common problems of laminated composites is mode II interlaminar fractures—in this mode the layers of a composite have slid against each other, causing a fracture. The fracture reduces the stiffness and load-bearing capacity of the product. The resistance of the material to interlaminar fracture is called interlaminar toughness. 

In ASTM D7905, measurements independent of specimen geometry and method of force are performed. This helps determine damage tolerance—the ability to sustain defects safely until repair can be affected. Both the pre-cracked toughness and after crack toughness is determined so that people can pick composites based on application.

Test Procedure:

The specimen has a non-adhesive insert at the midplane which is used to delaminate the sample. A force is applied to the sample through an ENF fixture under displacement-controlled loading. Delamination growth is not stable in the ENF test. Initiation values of mode II interlaminar fracture toughness are obtained from the pre implanted insert as well as from a pre-crack state. A record of the applied force versus center roller displacement is obtained using an x-y recorder or equivalent real-time plotting device. The compliance calibration (CC) method is used to determine the mode II interlaminar fracture toughness, GIIc.

Sample:

The sample should be rectangular and of uniform thickness. At least five specimens are required. Valid results can be obtained by testing fewer than five samples but this way the results are more accurate.

Data:

The value of applied force and toughness of the sample is indicated.