Ball indenter based on FEA solutions for property evaluation

摘要

An automated indentation system based on finite element solutions or performing a non-destructive compression test by loading a compressive indentation load (P) and calculating a elastic modulus (E) and a yield strength (sigma0), and a hardening exponent (n) from measured indentation depth (ht) and indentation load (P), and unloading slope (S). The system comprises a stepmotor control system (1), a measurement instrumentation (2) having a load cell (15), laser displacement sensor (17) for measuring the indentation depth and ball indenter (18), a data acquisition system (3) having an signal amplifier for amplifying and filtering signals from the load cell (15) and laser displacement sensor (17), and a control box (4) pre-stored computer programming algorisms for adjusting and controlling the moving speed and direction of stepmotor (12). The control box (4) enables storing and retrieving the signals of measured data and material properties, and plotting the graphs of load-depth curve and stress-strain curves based on the signal data. The procedure of computer programming algorithm is as follows: First, the Young's modulus E is computed from Eq. (29) by using slope S and initially guessed values of n and epsilon0. Then, c2, epsilonp and sigma are calculated as many as the number of load and depth data. From these, the values of n, K, sigma0 and epsilon0 are calculated from stress-strain relation. And then updated E, d, c2, epsilonp, sigma, n, K, sigma0 and epsilon0 are repeatedly calculated until the updated epsilon0 and n are converged within the tolerance.