ASTM D5766 - Open Hole Composite Fixture

Standard Test Method for Open-Hole Tensile Strength of Polymer Matrix Composite Laminates

Theory:

ASTM D5766 specifies a test for composite tensile testing where the sample has an open hole in the middle. The hole is used to simulate where a fastener or fixture may attach. Wires or temperature sensors may also be threaded through holes of this size in aerospace applications. The open-hole can also be used to simulate a defect in the polymer matrix composite laminate. The weaker open-hole tensile strength from ASTM D5766 is often compared to the ultimate tensile strength of an ASTM D3039 test.

Extensometers can be used to accurately measure elongation data and derive more advanced calculations. Composite materials are used in high and lower temperature environments so they are often tested inside of an environmental chamber. Universal Grip offers Nickel plated grips which can withstand high temperature. Temperatures above 700C can be successfully achieved with water-cooled grips.

Geometry:

The size and cross-sectional area of a standard ASTM D5766 sample is specified in the ASTM D3039 test procedure. The composite tensile grips in the video accomodate specimens which are 1 inch wide. Generally there is a 10 to 1 width to length ratio. Please refer to the official spec for more details.

Solution:

The open hole tensile testing fixture of choice for ASTM D5766 are the wedge grips. Usually hydraulic wedge grips are necessary to avoid any slippage. There are a few different failure modes for this test and it is important that only failures at the center hole location are used as quality data.

This test grip attaches to a Universal Testing Machine that has enough capacity to tear the sample while maintaining a speed of 2mm/min.