Hardware Compensation
Hardware compensation applied during a tensile test ensures that the measured displacement originates from the specimen rather than the machine itself. Applying frame deflection correction involves subtracting the elastic movement of the load frame and grips from the total recorded extension. This process is necessary for high stiffness materials where the sample deformation is comparable to the machine compliance.
The correction factor is determined by loading the system without a sample or by using a high stiffness calibration bar.
Tensile Performance
Applying this adjustment prevents the underestimation of the material modulus during data reduction. If the frame flex is not removed, the resulting stress and strain curve appears softer than the material truly is.
The Method
The software records the load and the corresponding machine displacement to create a compliance map. During an actual test, the computer calculates the expected frame movement for every load point and removes it from the raw data.
Proper Verification
Proper use of an extensometer often bypasses the need for this calculation by measuring the sample directly. When an extensometer is unavailable, the calculated correction must be verified against a known reference material. Reliable data depends on the periodic recalibration of the frame stiffness.
