University of Trento

1
University of Trento Faculty of Engineering
Department of Materials Engineering and
Industrial Technologies
MECHANICAL CHARACTERIZATION OF METALLIC MATERIALS
BY INSTRUMENTED INDENTATION TESTING
Tutor Prof. Vigilio Fontanari
PhD Student Bernardo D. Monelli
2
Introduction Experimental Part Procedure FE
Model Conclusions
PROBLEM DEFINITION

• small amount of material is available
• destructive testings have to be avoided
• coating characterization

The elastic-plastic stress strain-curve (s-e) of
metallic materials cannot be determined by
standard tensile test
AIM OF THE WORK
Evaluation of stress-strain curve of metallic
material by instrumented spherical indentation
testing
Bernardo D. Monelli
University of Trento
3
Introduction Experimental Part Procedure FE
Model Conclusions
PROBLEM DEFINITION

• Spherical indentation test

L h curve

• Evaluation procedure of stress-strain curve

• Numerical simulation of spherical indentation
  test

FE model

• Experimental and numerical results

• Conclusions

Bernardo D. Monelli
University of Trento
4
Introduction Experimental Part Procedure FE
Model Conclusions
Spherical Indentation Test --- L-h curve
A spherical indenter (WC-Co) is slowly pushed
against the sample which has to be tested
L h curve
h
sample

• L load applied to the indenter

• h cavity depth

Bernardo D. Monelli
University of Trento
5
Introduction Experimental Part Procedure FE
Model Conclusions
Spherical Indentation Test --- L-h curve
Material Al alloy Indenter diameter 2.5 mm
Bernardo D. Monelli
University of Trento
6
Introduction Experimental Part Procedure FE
Model Conclusions
s - e evaluation procedure

• Experimental evaluation of L h curve

• Costitutive law assumption

• Numerical evaluation of L h curve

• Comparison between the two curves
• (L2 Norm)

Bernardo D. Monelli
University of Trento
7
Introduction Experimental Part Procedure FE
Model Conclusions

• Model details
• Two-dimensional axi-symmetric model (four node
  structural elements)
• Isotropic and homogeneus material
• Indenter Tungsten carbide (E2630 GPa, n0.22)
• Indenter radius 1.25 mm
• Contact surface to surface elements
• Frictionless contact

Bernardo D. Monelli
University of Trento
8
Introduction Experimental Part Procedure FE
Model Conclusions
Material Al alloy Indenter diameter 2.5 mm
Bernardo D. Monelli
University of Trento
9
Introduction Experimental Part Procedure FE
Model Conclusions
sy Yield stress
n strain-hardening coefficient
Bernardo D. Monelli
University of Trento
10
Introduction Experimental Part Procedure FE
Model Conclusions
Material Ti Alloy
E1 ? 110 GPa
s ? 1000 MPa
n 0.1
Bernardo D. Monelli
University of Trento
11
Introduction Experimental Part Procedure FE
Model Conclusions
Conclusions

• The stress-strain of metallic materials can be
  reasonably deduced from
• the spherical indentation testing.

• The iterative procedure based on FE modelling of
  spherical indentation testing
• can carefully predict the stress-strain curves
  of metallic materials.

• Hollomons power law can be used to represent
  stress-strain curves for
• some metallic materials (Ti-Alloy).

Future works

• Which is the rule played by material properties
  (anisotropy, texture,)?

• Is there a relationship between the state of
  surface (i.e. roughness and residual
• stresses) and L-h experimental curve?

Bernardo D. Monelli
University of Trento
12
University of Trento Faculty of Engineering
Department of Materials Engineering and
Industrial Technologies
MECHANICAL CHARACTERIZATION OF METALLIC MATERIALS
BY INSTRUMENTED INDENTATION TESTING
Tutor Prof. Vigilio Fontanari
PhD Student Bernardo D. Monelli