Effects of Residual Stress on the Measurement of Hardness and Elastic Modulus using Nanoindentation

1994 ◽  
Vol 338 ◽  
Author(s):  
G.M. Pharr ◽  
T.Y. Tsui ◽  
A. Bolshakov ◽  
W.C. Oliver
Keyword(s):  
Finite Element ◽  
Elastic Modulus ◽  
Finite Element Simulation ◽  
Linear Array ◽  
Point Of View ◽  
Hardness Testing ◽  
Standard Methods ◽  
Compressive Stresses ◽  
Element Simulation ◽  
Made In

ABSTRACTThe effects of stress on the measurement of hardness and elastic modulus in aluminum alloy 8009 have been studied experimentally and by finite element simulation. The experiments were performed by making a linear array of nanoindentations on the side of a stressed bend bar, sampling regions of high uniaxial tension, high uniaxial compression, and a variety of stresses in between. When analyzed according to standard methods, the nanoindentation data reveal a decrease in both hardness and modulus with increasing stress from compression to tension. While the decrease in hardness is consistent with previous observations made in conventional hardness testing, the modulus decrease was unexpected. Finite element simulation revealed that the drops in hardness and modulus are not real, but occur because the procedure for determining contact area from the nanoindentation load-displacement data does not account for pileup around the indentation. The finite element simulation shows that large compressive stresses promote pileup while tensile stresses reduce it, and this must be properly accounted for if accurate hardnesses and moduli are to be obtained. Experimental results are presented which further support this point of view.

The Influence of the Substrate on the Mechanical Properties of Si-Doped DLC Thin Films

2008 ◽  
Vol 587-588 ◽  
pp. 839-843 ◽  
Author(s):  
Carlos W. Moura e Silva ◽  
Jose R.T. Branco ◽  
Marta C. Oliveira ◽  
Jorge M. Antunes ◽  
Albano Cavaleiro
Keyword(s):  
Thin Films ◽  
Mechanical Properties ◽  
Finite Element ◽  
Stainless Steel ◽  
Elastic Modulus ◽  
Finite Element Simulation ◽  
Gas Mixtures ◽  
Element Simulation ◽  
Si Doped ◽  
Si Content

In this work, Si-doped DLC films were deposited on stainless steel (316SS) and polycarbonate (PC) substrates by RF-PACVD in gas mixtures of SiH4+CH4, with 2, 5 and 10 vol.% SiH4. The increase of the Si content in the films led to a progressive drop in the hardness from 30 GPa down to 23 GPa whereas the elastic modulus increased from 124 GPa up to 146 GPa, as measured in the SS coated substrates. In the case of coated PC samples pop-in was observed in the loading curve which was interpreted by finite element simulation and nanoscratching techniques.

Effect of Indenter Geometries on Material Properties: A Finite Element Simulation

2011 ◽  
Vol 70 ◽  
pp. 219-224 ◽  
Author(s):  
J.J. Kang ◽  
A.A. Becker ◽  
W. Sun
Keyword(s):  
Finite Element ◽  
Elastic Modulus ◽  
Finite Element Simulation ◽  
Material Properties ◽  
Plastic Strains ◽  
Fe Simulations ◽  
Element Simulation ◽  
Different Types ◽  
Indentation Tests

In this study, numerical indentation tests are carried out to examine the sensitivity of FE solutions with respect to different types of substrate models. Axisymmetric, 3D-quarter and 3D-half geometry substrates with a perfectly sharp indenter are modelled. Numerical evaluations of three different indenters, namely Berkovich, Vickers and conical indenters with perfectly sharp tips are investigated. From the FE simulations, the loading-unloading curves can be obtained. From the slope of the unloading curve, the hardness and elastic modulus can be calculated by using the Oliver-Pharr method. The results are compared to investigate the effects of using different indenter geometries. The equivalent plastic strains and the effects of different face angles of the indenters are analysed.

scholarly journals Nanoindentation of Soft Films On Hard Substrates: Experiments And Finite Element Simulations

1997 ◽  
Vol 505 ◽  
Author(s):  
G. M. Pharr ◽  
A. Bolshakov ◽  
T. Y. Tsui ◽  
Jack C. Hay
Keyword(s):  
Finite Element ◽  
Elastic Modulus ◽  
Film Thickness ◽  
Finite Element Simulation ◽  
Penetration Depth ◽  
Work Hardening ◽  
Element Simulation ◽  
Pile Up ◽  
Indenter Penetration ◽  
Hard Substrates

ABSTRACTExperiments and finite element simulations have been performed to examine errors in the measurement of hardness and elastic modulus caused by pile-up when soft films deposited on hard substrates are tested by nanoindentation methods. Pile-up is exacerbated in soft-film/hardsubstrate systems by the constraint imposed on plastic deformation in the film by the relatively non-deformable substrate. To experimentally examine pile-up effects, soft aluminum films with thicknesses of240, 650, and 1700 nm were deposited on hard soda-lime glass substrates and tested by nanoindentation techniques. This system is attractive because the elastic modulus of the film and the substrate are approximately the same, but the substrate is harder than the film by a factor of about ten. Consequently, substrate influences on the indentation load-displacement behavior are manifested primarily by differences in the plastic flow characteristics alone. The elastic modulus of the film/substrate system, as measured by nanoindentation techniques, exhibits an increase with indenter penetration depth which peaks at a value approximately 30% greater than the true film modulus at a penetration depth close to the film thickness. Finite element simulation shows that this unusual behavior is caused by substrate-induced enhancement of pile-up. Finite element simulation also shows that the amount of pile-up increases with increasing penetration depth, and that the pile-up geometry depends on the work-hardening characteristics of the film. Because of these effects, nanoindentation techniques overestimate the true film hardness and elastic modulus by as much as 68% and 35%, respectively, depending on the work-hardening behavior of the film and the indenter penetration depth. The largest errors occur in non-work-hardening materials at penetration depths close to the film thickness, for which substrate-induced enhancement of pile-up is greatest.

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