ASTM D 3518 is used to determine the in-plane shear response of polymer-matrix composite materials tensile test of a ±45° laminate. Composite materials are tested for their shear stress and shear strain properties at temperatures that simulate the planned end-use environment.
In-plane shear response tensile testing method using ASTM D3518 evaluates the shear response of polymeric matrix composites materials. This test measures the shear stress and shear strain properties of a composite material specimen composed of +45° and -45° plies. The physical properties of several materials tend to vary with change in surrounding temperatures, so it becomes necessary to test materials at temperatures that simulate the planned end-use environment.
A universal tester is used, and the specimen is fastened between the grips separated by a specified distance. Next, the specimen is pulled till it fails as per theASTM D3039 protocols for tensile properties of composite materials. Bonded strain gauges are mounted to the specimen to measure strain response during the test if Shear Strain or Shear Modulus of Elasticity data are also required. For standard test specimens, the typical test speed is kept as 2 mm/min.
For non-ambient temperature tests, a thermal chamber is installed on the universal testing machine. The chamber is designed so that the test mounts from the base and crosshead of the testing machine pass through the top and bottom of the thermal chamber. Testing is carried out inside the controlled thermal environment by installing a standard text fixture inside the chamber. The process is similar to as done in the ambient temperature. For high-temperature conditions, the chamber used electric heaters, and for low temperatures conditions, the chamber uses carbon dioxide gas supply as a coolant.
ASTM D 3518 usually takes specimens of constant rectangular cross-section, 25 mm (1 inch) wide and 250 mm (10 inches) long. Tabs can be bonded to the ends of the specimen as an option to prevent gripping damage.