Metals are hard, strong and tough and by their nature, are malleable, fusible and ductile which means that they can be formed into a vast array of desired shapes without cracking or breaking. Due to their nature they can be treated to alter characteristics and formed to meet the requirements of any number of applications.
Metal Testing Goal:
Testing the mechanical properties of metallic materials determines if it meets the requirements of a desired application. The most common characteristics measured during testing are the modulus of elasticity, yield strength, tensile and compressive strength, and elastic limit. Metals are also tested to measure modulus of rigidity, shear strength, bend strength, flexure strength and fatigue strength as well as the time dependent behavior such as creep and stress relaxation. These values provide an accurate depiction of the behavior that a metal material may be expected to exhibit during loading and the lifetime of its application.
Common Metal Test Methods:
Test methods for metals tend to be very similar as those used for the testing of other materials such as plastics or composites. Flexure, bend, shear and torsion tests are all performed on metals, but the most common tests are the tension, compression and fatigue tests.Tension and compression testing involve the metal sample experiencing a load along one of its axis that either pulls the material apart or pushes it together. These tests are generally run until the sample fails or ruptures but may be stopped at any time.
Shear and torsion tests require that the sample experiences opposing loads at each end that act perpendicularly to the axis of the sample. A shear tests will pull the ends of the sample so it will fail in a sliding motion whereas a torsion test will twist the ends of the sample so it will fail in a turning motion.
A metal sample for flexure and bend tests will experience a load at its midsection while it is supported at its two ends. As the load is increased the sample will be deformed into a “U” or “V” shape depending upon its characteristics.
Fatigue testing measures time and cycle dependent behavior of metals through cyclic loading. These tests measure the number of cycles till failure, the time till failure, and possibly creep and stress relaxation rates of the metal samples.
All of these tests are used to determine if a metal material is suitable for an application and are often combined with each other to create an accurate representation of the stresses a metal material will experience in its lifetime.
Metal Testing Specimens:
Testing specimens made from metal can essentially take any form. They commonly come in the shape of dog bones, dumbbells, rods, bars, cylinders, cubes, bricks, and tubes. The difference between test samples made from metal and test samples made from other materials is in the microstructure. Metals can undergo processes such as heating, quenching, annealing and others that alter its microscopic composition. Specifically the grain size, grain orientation and the dislocations are altered to change the characteristics of the metal such as its strength, toughness, and ductility.