Abstract
Instrumented indentation test is a promising non-destructive method to determine mechanical properties. This paper proposes a new approach to determine the plastic properties of bulk metal materials (including yield stress, strain-hardening exponent (n) and strain-hardening rate (K)), which couples an experimental load-displacement curve with finite element method. The load–displacement curve was obtained from continuous instrumented indentation test. Then a hybrid particle swarm optimization was employed to minimize the deviation between experimental and simulated load-displacement curves. As a combination of particle swarm optimization and simulated annealing, the simulated annealing particle swarm optimization is an economical and effective algorithm to identify plastic parameters. It was observed that the maximum error of strain-hardening rate extracted from the macro indentation test was 8.2 percent contrast to that determined by the conventional tensile test, and the maximum error of strain-hardening exponent was 4.7% respectively.
Highlights
Indentation tests have been employed to estimate material characteristics extensively
At large values of T, poor solutions will be accepted high probability; as T decrease, acceptance of poor solutions will become lower; when the value of T approaches 0, poor solutions will not be accepted any more. This feature means that simulated annealing particle swarm optimization (SAPSO) algorithm, compared with PSO algorithm, can help escape from local minima while it still retains an excellent ability in searching global optimum solution
Numerical simulation of indentation test is performed by a commercial code ABAQUS with Young’s modulus and strain strength coefficient (K) and strain hardening exponent (n) deduced from standard tensile test to ensure that the simulation is valid
Summary
Indentation tests have been employed to estimate material characteristics extensively. In 1951, Tabor [1] found that the material constant in equation (1) had a relationship with work-hardening exponent (n) according to a power-law stress-strain behavior and it can be expressed as equation (2) as below: n=β-2 This equation is valid especially when applied load is large enough to form a plastic zone near the indenter. To avoid the effect of pile-up and sink-in on the contact area edges, an intelligent optimization algorithm named a simulated annealing particle swarm optimization algorithm and finite element simulation were employed to derive mechanical properties of materials from P-h curves directly. This novel approach can obtain material characteristics regardless of any inspection of indentation morphology or various definition of representative strain. The uniqueness of identified parameters was discussed and the stress-strain curves were verified
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