There are many types of testing machines. The most common are universal testing machines, which test materials in tension, compression or bending. The primary use of the testing machine is to create the stress-strain diagram. Once the diagram is generated, a pencil and straight edge or computer algorithm can be used to calculate yield strength, Young’s Modulus, tensile strength or total elongation.
There are two classes of testing machines, electromechanical and hydraulic. The electromechanical machine uses an electric motor, gear reduction system and one, two or four screws to move the crosshead up or down. A range of crosshead speeds can be achieved by changing the speed of the motor. A microprocessor based closed-loop servo system can be implemented to accurately control the speed of the crosshead.
A hydraulic testing machine uses either a single- or dual-acting piston to move the crosshead up or down. In a manually operated machine, the operator adjusts a needle valve to control the rate of loading. In a closed-loop hydraulic servo system, the needle valve is replaced by an electrically operated servo-valve for precise control.
In general, the electromechanical machine is capable of a wide range of test speeds and long crosshead displacements, whereas the hydraulic machine is a cost-effective solution for generating high forces.