Composite Materials Open-Hole Strength Test Equipment

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Composite Materials Open-Hole Strength Test Equipment

Continued advancements in the design and manufacture of engineered composites has allowed composite materials to work their way into the products we use everyday. By definition, a composite material is simply any material that contains two or more constituent materials. The materials that make up a composite are chosen either to enhance or supplement the material properties of the individual materials. The typical material combination seen in today's composites is a material that performs well in tension (fiber or rebar) paired with a material that performs well in compression (epoxy, ceramic, or cement). The most common modern advanced composites are fiber-matrix composites and they can be manufactured with polymer, carbon, metal, or ceramic matrix and an extremely wide range of reinforcement fiber including, carbon, graphite, boron, aramid, and glass. Most engineering materials are not used in practice in the form they are tested. This is no different with composite materials, as a functional composite part is likely to have cutouts, holes, screws, rivets, or irregular shape. Open-hole tests of composites help to address the real life application of composite materials. The presence of an open hole in a composite component reduces the cross-section area available to carry an applied load, creates stress concentrations, and creates new edges where delamination can occur. Performing standardized open-hole tests for composite materials can provide useful information about how a composite may perform in an open-hole application. However, due to the nature of composites, it is often necessary to also conduct full scale component tests for products, such as airplane fuselages, where holes and irregular geometries are unavoidable.

ASTM D6671 determines interlaminar fracture toughness, Gc, of continuous fiber-reinforced composite materials at various Mode I to Mode II loading ratios using the Mixed-Mode Bending (MMB) Test. This test is most useful for composites with carbon fiber tape laminates. Susceptibility to delamination is one of the major weaknesses of advanced laminated composite structures. ASTM D6671 provides knowledge of the interlaminar fracture resistance of composites which is useful for product development and material selection.