30 Years of Nanoindentation with the Oliver-Pharr Method and Beyond: High Strain Rates and Creep Testing
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Nanomechanical Materials Behavior Committee
Program Organizers: Verena Maier-Kiener, Montanuniversitaet Leoben; Benoit Merle, University Of Kassel; Erik Herbert, Michigan Technological University; Samantha Lawrence, Los Alamos National Laboratory; Nigel Jennett, Coventry University
Monday 2:00 PM
February 28, 2022
Room: 259A
Location: Anaheim Convention Center
Session Chair: Megan Cordill, Erich Schmid Institute of Materials Science; Yang Cheng, University Of Kentucky
2:00 PM Invited
A Mathematical Framework for High Strain Rate Nanoindentation Testing: Sudharshan Phani Pardhasaradhi1; Benjamin Hackett2; Christopher Walker2; Warren Oliver3; George Pharr2; 1ARCI; 2Texas A&M University; 3KLA Corporation
Recent advances in electronics have enabled nanomechanical measurements with very low noise levels at fast time constants and high data acquisition rates. These capabilities open the door for a wide range of ultra-fast nanomechanical testing. Given the inherent dynamic nature of the high-speed testing, a thorough understanding of the instruments’ dynamics and electronics is extremely important for accurate measurements. In this talk, a mathematical framework that includes the mechanical and electronic contributions of the instrument and the material constitutive response is presented to provide guidelines for performing high strain rate nanoindentation testing. Simple closed form solutions that provide insights on the choice of test methodology, test parameters and instrument design will be presented along with the strain rate range over which accurate measurements can be performed with the commercially available nanoindenters.
2:25 PM
Nanoindentation at High Sustained Strain Rates: Recent Improvements and Challenges: Benoit Merle1; 1University Erlangen-Nuremberg (Fau)
Nanoindentation is typically performed at strain rates < ~0.1/s, which precludes it from ballistic applications. Recent years have seen the development of nano-impact testing, which produces much higher deformation rates. However, data from such experiments are challenging to interpret, because the high strain rates are not sustained throughout the experiment.Constant strain rate nanoindentation yields more meaningful data, albeit at the expense of the deformation velocity. The current limitation derives primarily from the plasticity error related to the continuous stiffness measurements (CSM). Here, we explore ways to push this limit by rewriting the standard Oliver-Pharr evaluation method, so as to avoid the need for a measurement of the contact stiffness, e.g. by CSM. With this improvement, the experimental upper strain rate limit is mostly determined by the time constants of the hardware components. A comparison between different commercially available systems will be presented.
2:45 PM Invited
New Instrumentation and Analysis Methodology for Nano-impact Testing: Mario Rueda1; Ben Beake2; Jon Molina-Aldareguia1; 1Imdea Materials Institute; 2Micro Materials Ltd.
The nano-impact test is a technique for high strain rate mechanical characterization of materials at the nano/microscale. However, its use has been limited so far because the dynamic hardness has traditionally been computed using an energy-based approach. This work overcomes this limitation by instrumenting the test device with force-sensing capability by means of a piezoelectric load cell. The methodology was evaluated on six materials covering a wide spectrum of mechanical behaviour. The work shows that the energy-based approach used so far yields significant errors on the determination of dynamic hardness, explaining contradictory results existing in literature, and identifies the main sources of error with the aid of finite element simulations. In parallel, a FEM-based inverse analysis methodology was devised to transform the direct outputs of the combined nanoindentation and nano-impact tests into material parameters needed to calibrate the rate dependent constitutive behavior of a wide range of materials.
3:10 PM
NOW ON-DEMAND ONLY – Work-based Definition of the Strain Rate in indentation: Donald Stone1; Z. Melgarejo1; Abdelmageed Elmustafa2; 1University of Wisconsin; 2Old Dominion University
Plastic deformation is often path dependent. This means that in an indentation test, the hardness at given depth and rate of penetration also depends on how fast the indenter was loaded, prior to measurement. A constant load creep test and a load relaxation experiment should therefore produce different strain rate sensitivity, useful for exploring thermal activation of hardening and softening during deformation. To measure the strain rate sensitivity using indentation, experimenters often rely on (1/h)(dh/dt) to specify the strain rate, where h is the depth of penetration of the indenter. This formula does not work for high hardness/modulus (H/E*) materials because it fails to give consistent results depending on how the experiment is performed even for materials where plastic deformation is not intrinsically path dependent. Here, we employ a work-based argument to derive an expression for the strain rate that works for both high and low H/E* materials.
3:30 PM Break
3:45 PM Invited
Development of a New Method to Measure Surface Mechanical Properties Using In Situ SEM Microshear: Application at High Strain Rate: Gaylord Guillonneau1; Guillaume Kermouche2; Sergio Sao Joao2; 1Ecole Centrale de Lyon; 2Mines Saint-Etienne
When two surfaces in contact are submitted to friction, a shearing is applied between them. Consequently, the measurement of shear properties of these surfaces is necessary. A new method to measure shear properties was developed and will be presented. This method consists in compressing a specific micropillar, whose geometry was modified using Focused Ion Beam in order to induce shear during compression. More especially, the geometry was inspired from a macroscopic test named “Shear Compression Specimen” [1]. This method was applied at low and high strain rate (until 2000s-1), on Fused silica, this material being usually used for calibrations at microscale. The results reveal a good repeatability of the tests, at each strain rate, and that deformation is mainly shear during the compression of the specimen, this phenomenon being validated using numerical simulation. [1] Dorogoy et al., Experimental Mechanics, (2015)
4:10 PM
A New Long-term Indentation Relaxation Method to Measure Creep Properties at the Micro-scale with Application to Fused Silica, PMMA and Amorphous Selenium: Paul Baral1; Gaylord Guillonneau2; Guillaume Kermouche3; Jean-Michel Bergheau2; Jean-Luc Loubet2; 1Université Catholique de Louvain; 2Ecole Centrale de Lyon; 3Ecole Nationale des Mines de Saint Etienne
Nanoindentation test is of great interest to characterize small-scale creep behavior of materials, thus a large literature exists on the field. Based on our previous works, a new procedure is developed to measure strain rate sensitivity m and apparent activation volume V* using nanoindentation relaxation experiments. This procedure is based on the control of the dynamic contact stiffness as measured by the continuous stiffness measurement module. Load decrease is monitored while maintaining the contact stiffness constant. It allows for very stable measurements of load with increasing time (up to 10 hours). The load relaxation data are interpreted using an analogy to uniaxial tests in order to extract representative material's parameters. An excellent agreement with literature is found for a wide range of material going from polymer to metals. Nanoindentation relaxation experiment is proved to be an accurate procedure to extract viscoplastic parameters of materials under very low strain rates.
4:30 PM
Nanoindentation Creep Testing: Advantages and Limitations of the Constant Contact Pressure Method: Karsten Durst1; Christian Minnert1; 1TU Darmstadt
Different loading protocols have been developed in the past to investigate the creep properties of materials using instrumented indentation testing technique. We recently presented a new indentation creep method, in which the contact pressure is kept constant, similar to the stress in a uniaxial creep experiment. In this study, the results of constant contact pressure indentation tests are compared to uniaxial creep experiments on ultrafine grained alloy such as Cu and CuAl5. The constant contact pressure method yield similar stress exponents as the uniaxial creep tests, down to strain rates of 10-6 s-1. Furthermore, a pronounced change in the power exponent at large stress reductions is found for both uniaxial and CCP tests, indicating a change in deformation mechanism of the ultrafine grained materials. The CCP technique thus offers new possibility of performing long-term creep experiments while retaining the contact stress underneath the tip constant.
4:50 PM
NOW ON-DEMAND ONLY – Simulations and Experiments of the Strain Rate Sensitivity Measurements Using Conical and Spherical Indentation Creep: Yousuf Mohammed1; Donald Stone2; Abdelmageed Elmustafa1; 1Old Dominion University; 2University of Wisconsin-Madison
The hardness and flow stress strain rate sensitivities, mH, mσ, in indentation creep with conical and spherical tips is examined. mH/mσ extend previous results for cones in terms of a universal curve that describes mH/mσ as a function of H/E*/ϵH for small H/E*/ϵH (fully plastic ≈1.0) to H/E*/ϵH≈2.5 (fully elastic≈0). For cone, the strain level is determined by the angle β (25.3°,22.5°,19.7°). mH/mσ becomes vanishingly small and the material undergoes full elastic deformation for H⁄E*≈0.23 and 0.18 for β of 23.5° and 19.7° compared to β of 22.5° for which H⁄E*≈0.21. For spherical indentations, the strain is a function of indent radius/indenter radius ratio (a/R). mH/mσ does not maintain unique relation with( H)⁄E* and varies with the increase in (a/R) ratio. The data clustered into a single curve similar to the one produced for conical indentation and that mH/mσ approaches zero for a normalized (H⁄E* ) ⁄ (a⁄R) of ≈0.4.