Tensile Testing Machine - Testing the Strength, Ductility and Elasticity Properties of Metals
The Tensile Testing Machine determines the tensile strength, elasticity, and ductility of the metal.
The sample in the form of a round bar is turned in a lathe, leaving an accurate, predetermined diameter section in between two un-machined larger sections with the finished shape being similar to that of a dumbbell.
The tensile testing machine grips the sample vertically between two vertical circular chucks. Once the sample is securely gripped by both chucks pressure is applied to stretch the sample.
A graphic display which also produces a printout of all the process is visible to the operator and a typical curve is shown below to explain the different stages in the testing process.
As the load is increased the sample starts to elongate directly proportion to the applied load in the elastic stage, until it reaches point A.
From here the sample will continue to elongate without any further load being applied. Point A is known as the Yield Point, and if the load is removed from the sample, it will return to its original length.
The curve between A and B represents the plastic stage and if the load is removed between at point B the sample will retain its elongation.
From point B the load is increased again until it reaches point C where the sample will break. The ultimate load at this point is divided by the original cross-section- area of the machined sample. This calculation provides a figure for the ultimate tensile strength (UTS) of the metal in Newtons/square millimetre (N/mm2)
Dividing the load at point A by the original CSA of the sample will give a very important figure – the metal’s yield point. This figure is used in many design calculations.