In-plane tension

For most tensile test methods the approach is similar in that a specimen is gripped at the ends and loaded in uniaxial tension. The principal differences between different test methods are the dimensions of the specimen and the method of load-introduction. For composites the specimen may have a rectangular, round, or tubular of constant or varying cross-sectional area. For straight-sided specimens tabs are often employed and are intended to distribute the load from the grips into the specimen with a minimum of stress concentration at the load introduction point. There are a number of existing or developing standards for in-plane tensile properties of laminated materials. By changing the specimen configuration, many of the tensile test methods are able to evaluate different grades of composite materials including unidirectional laminates, woven materials, and general laminates regardless of the matrix/fibre combination.

The following test methods are available for determining the in-plane tensile properties of composites using straight sided specimens

• ISO 527 (Parts 4 and 5), Plastics --- Determination of Tensile Properties
• ASTM D 3039/D 3039M, Standard Test Method for Tensile Properties of Polymer Matrix Composites
• SACMA RM 4, Tensile Properties of Oriented Fibre-Resin Composites
• SACMA RM 9, Tensile Properties of Oriented Cross-Plied Fibre-Resin Composites
• ASTM D 5083, Standard Test Method for Tensile Properties of Reinforced Thermosetting Plastics Using Straight-Sided Specimens

In all of these test methods, a tensile stress is applied to the specimen through a mechanical shear interface at the ends of the specimen, normally by either wedge or hydraulic grips. The material response is measured in the gauge section of the specimen by either strain gauges or extensometers, and the elastic material properties subsequently determined.

The following test methods are available for determining the in-plane tensile properties of composites using width tapered specimens

• ASTM Standard Test Method D 638, Tensile Properties of Plastics
• SAE AMS "Bowtie" Tension Specimen

The width tapered specimens help drive the highest stressed region of the specimen away from the gripped region into the gauge length. ASTM Test Method D 638 was primarily developed for plastics, however, it is well suited to SMCs, chopped strand mat and non-unidirectional composites. It uses a flat, width-tapered tension specimen with a straight-sided gauge section.

Other tensile tests exist for specific purposes including the split ring tests ASTM Standard Test Method D 2290.