LAUSR

Raw load-displacement data from the uniaxial compression test are shown to be contaminated by both machine deflection and seating effects at the specimen surface. Machine displacement is found to be a nonlinear and reversible function of applied load, insensitive to the displacement or loading rate, but sensitive to environmental conditions such as temperature. An empirical function is proposed which provides an accurate fit to machine displacement data. Specimen seating effects alter the measured load-displacement data by introducing additional nonlinearity, reducing the elastic loading slope, and shifting the load data to higher displacement. These effects are shown to originate from non-ideality of the specimen geometry and are independent of friction. A simple analytical model to predict specimen seating effects was proposed. The model was then used to determine a robust method for determining the proper correction to compensate for specimen non-ideality. A new method for compression test data reduction is proposed that accounts for both machine compliance and specimen seating effects.