The structural principle of extensometer in universal material testing machine

The extensometer is composed of a dial gauge and a set of lever mechanisms composed of a ball hinge as a fulcrum. Hold the ball hinge extensometer with your hand, put the sample into the gauge fork, and clamp the specimen with a pointed screw to make the upper and lower gauge forks and the specimen integrated. Under the action of tension, the sample is elongated ΔL. During the deformation of the sample, the upper gauge distance fork does not rotate, while the lower gauge distance fork rotates at a slight angle due to the action of the ball hinge. The distance from the center of the ball hinge to the axis of the dial gauge rod is equal to twice the distance from the center of the ball hinge to the axis of the sample. Therefore, the deformation reading of the dial gauge is twice the length of the specimen axis within the gauge distance. Since the magnification of the dial gauge is 1000, the magnification of the extensometer is 2000. That is, when the ball-hinged extensometer dial gauge is moved one grid, the sample is stretched by 1/2000mm.

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