Development of an indentation method for material surface mechanical properties measurement [electronic resource] /
Development of an Indentation Method for Material Surface
Mechanical Properties Measurement
With the utilizing structural materials with small size dimensions (such as MEMS
devices), there are growing need to characterize the mechanical properties of the small
volumes of materials. Tensile test is not possible to be applied to these small volumes.
Indentation technique has emerged as a cost-effective, convenient and non-destructive
method to solve this problem. It is also a promising means of obtaining mechanical
properties for thin films, which were widely used in various industries nowadays.
In this work, finite element simulations of spherical indentation on various
material models were performed to develop a series of methodology, by which the
material surface mechanical properties are to be determined through indentation test.
Finite element mesh and modeling were first verified by both Hertz analytical solution
and experiment results of surface displacement fields from combined Moiré
Interferometry and Twyman-Green Interferometry. Method to calculate elastic
properties through initial unloading indentation stiffness obtained in load depth curve is
verified. Special attention was put to the relationship between the surface displacement
fields (U (in-plane radial displacement) and W (out-of-plane displacement)) and material
mechanical properties. It is discovered that each point on the surface experienced same
equivalent stress strain history governed by input uniaxial stress strain curve. Elasticplastic
boundary corresponds to characteristic point in the W field variation, which
indicated an experimental method to capture the E-P boundary. The yield strength could
be calculated from Hooke’s law by strain fields derived from displacements using
kinematic equations. The strain-hardening exponent is to be obtained by modified
Meyer’s law or Tabor’s relation. Hence, the uniaxial stress strain relation of the material
could be reestablished using indentation method.
Then the micro spherical indentations on thin film – substrate systems were
simulated. The influence of substrate on the load depth curve, surface deformation was
studied for both soft film on hard substrate and hard film on soft substrate cases. Then
different thickness of thin film was simulated and it is concluded that the effect of
substrate is negligible when the indentation depth is less than 10-20% of film thickness.
School:West Virginia University
School Location:USA - West Virginia
Source Type:Master's Thesis
Keywords:thin films finite element method microelectromechanical systems
Date of Publication: