scholarly journals Investigation on the Influences of Hygrothermal Aging on the Indentation Size Effects and Micro-Indentation Measurements of PMMA. Part I: Experimental Results

2020 ◽  
Vol 10 (16) ◽  
pp. 5454 ◽  
Author(s):  
Hui Lin ◽  
Lin Lv ◽  
Tao Jin
Keyword(s):  
Elastic Modulus ◽  
Aging Time ◽  
Size Effects ◽  
Companion Paper ◽  
Strain Rates ◽  
Indentation Size ◽  
Hygrothermal Aging ◽  
Shear Transformation ◽  
Micro Indentation ◽  
Indentation Strain

The polymethyl methacrylate (PMMA) subjected to hygrothermal aging was applied to nanoindentation tests under different indentation strain rates. The influences of hygrothermal aging on the indentation behaviors of PMMA are discussed. Results show that the indentation elastic modulus and hardness decrease with increasing aging time. Furthermore, the indentation size effects (ISE) can be observed in aged PMMA specimens as they are sensitive to aging time as well as to the indentation strain rate. The quantitative analysis of ISE is proposed on the basis of shear transformation-mediated plasticity and was presented in our companion paper.

scholarly journals Indentation Size Effect in Pressure-Sensitive Polymer Based on A Criterion for Description of Yield Differential Effects and Shear Transformation-Mediated Plasticity

Polymers ◽  
2019 ◽  
Vol 11 (3) ◽  
pp. 412 ◽  
Author(s):  
Hui Lin ◽  
Tao Jin ◽  
Lin Lv ◽  
Qinglin Ai
Keyword(s):  
Size Effects ◽  
Indentation Depth ◽  
Yield Criterion ◽  
Strain Rates ◽  
Depth Range ◽  
Pressure Sensitivity ◽  
Indentation Size ◽  
Strength Differential ◽  
Two Factors ◽  
Shear Transformation

Indentation size effects in poly(methyl methacrylate) (PMMA) were studied through nanoindentation. Two factors of indentation size effects in PMMA, namely yield criterion and shear transformation-mediated plasticity, were analysed in detail. The yield criterion that considers strength differential (SD) effects and pressure sensitivity was constructed by performing the combined shear-compression experiments. The relationship between hardness and normal stress can then be obtained based on Tabot’s relation. Shear transformation-mediated plasticity was also applied to model the measured hardness as a function of the indentation depth at different strain rates. Results show that the yield criterion contains the terms of SD effects and pressure sensitivity gives the best description of the yielding of PMMA. Additionally, the volume of single shear transformation zone calculated through the presented criterion agrees well with simulation and exhibits increases with increasing strain rate. Indentation size effects in PMMA under different strain rates were discussed and an appropriate indentation depth range was suggested for calculating the hardness and modulus.

A study of indentation work in homogeneous materials

2006 ◽  
Vol 21 (6) ◽  
pp. 1363-1374 ◽  
Author(s):  
Mengxi Tan
Keyword(s):  
Plastic Deformation ◽  
Elastic Modulus ◽  
Elastic Energy ◽  
Size Effects ◽  
Unit Volume ◽  
Plastic Work ◽  
Total Work ◽  
Indentation Size ◽  
Scaling Relationships ◽  
Homogeneous Materials

The work of indentation is investigated experimentally in this article. A method of using the elastic energy to extract the elastic modulus is proposed and verified. Two types of hardness related to the work of indentation are defined and examined: Hwtis defined as the total work required creating a unit volume of contact deformationand Hwp is defined as the plastic work required creating a unit volume of plastic deformation; experiments show that both hardness definitions are good choices for characterizing hardness. Several features that may provide significant insights in understanding indentation measurements are studied. These features mainly concern some scaling relationships in indentation measurements and the indentation size effects.

scholarly journals Round Robin into Best Practices for the Determination of Indentation Size Effects

Nanomaterials ◽  
2020 ◽  
Vol 10 (1) ◽  
pp. 130 ◽  
Author(s):  
Ana Ruiz-Moreno ◽  
Peter Hähner ◽  
Lukasz Kurpaska ◽  
Jacek Jagielski ◽  
Philippe Spätig ◽  
...  
Keyword(s):  
Elastic Modulus ◽  
Size Effects ◽  
Nuclear Fission ◽  
Round Robin ◽  
Indentation Hardness ◽  
Martensitic Steels ◽  
Indentation Size ◽  
Single Cycle ◽  
Fusion Applications ◽  
Methodological Bias

The paper presents a statistical study of nanoindentation results obtained in seven European laboratories that have joined a round robin exercise to assess methods for the evaluation of indentation size effects. The study focuses on the characterization of ferritic/martensitic steels T91 and Eurofer97, envisaged as structural materials for nuclear fission and fusion applications, respectively. Depth-controlled single cycle measurements at various final indentation depths, force-controlled single cycle and force-controlled progressive multi-cycle measurements using Berkovich indenters at room temperature have been combined to calculate the indentation hardness and the elastic modulus as a function of depth applying the Oliver and Pharr method. Intra- and inter-laboratory variabilities have been evaluated. Elastic modulus corrections have been applied to the hardness data to compensate for materials related systematic errors, like pile-up behaviour, which is not accounted for by the Oliver and Pharr theory, and other sources of instrumental or methodological bias. The correction modifies the statistical hardness profiles and allows determining more reliable indentation size effects.

Creep properties of micron-size domains in ethylene glycol modified wood across 4½ decades in strain rate

2008 ◽  
Vol 1132 ◽  
Author(s):  
Joseph E. Jakes ◽  
Charles R. Frihart ◽  
Donald S. Stone
Keyword(s):  
Cell Wall ◽  
Elastic Modulus ◽  
Ethylene Glycol ◽  
Secondary Cell Wall ◽  
High Strain ◽  
Strain Rates ◽  
Creep Properties ◽  
Micron Size ◽  
Indentation Strain ◽  
Modified Wood

ABSTRACTThe hardnesses of secondary cell wall laminae (SCWL) and compound corner middle lamellae (CCML) in wood were measured at indentation strain rates between approximately 7×10-4 s-1 and 20 s-1, using a new method called broadband nanoindentation creep. The wood was subsequently modified with ethylene glycol (EG) and the properties were re-measured. The SCWL and CCML responded differently to this modification: in the SCWL, hardness decreased uniformly by a factor of 3.7 ± 0.3 across all strain rates, whereas in CCML, the modification had a similar effect at low strain rates. However, at high strain rates, hardness was only lowered by a factor of 1.8. The EG modification also lowered elastic modulus of the SCWL and CCML, swelled the SCWL and CCML, and caused previously placed indents to disappear (CCML) or partly disappear (SCWL).

On the origin of indentation size effects and depth dependent mechanical properties of elastic polymers

2016 ◽  
Vol 36 (1) ◽  
pp. 103-111 ◽  
Author(s):  
Chung-Souk Han ◽  
Seyed H.R. Sanei ◽  
Farid Alisafaei
Keyword(s):  
Mechanical Properties ◽  
Elastic Modulus ◽  
Size Effects ◽  
Indentation Depth ◽  
Second Order ◽  
Indentation Size

Abstract Indentation size effects have been observed in both polymers and metals but, unlike in metals, the origin of size effects in polymers is not well understood. To clarify the role of second order gradients of displacements, a model polymer is examined with spherical and Berkovich tips at probing depths between 5 and 25 μm. Applying different theories to determine the elastic modulus, it is found that with a pyramidal tip, the elastic modulus increases with decreasing indentation depth, while tests with the spherical tip yielded essentially constant values for the elastic modulus independent of indentation depth. The differences between these tips are attributed to second order displacement gradients, as they remain essentially constant with a spherical tip while they increase in magnitude with decreasing indentation depth applying a Berkovich tip.

Study on the Aging Rules of Rigid Polyurethane Foams at Indoor Storage and Different Hygrothermal Conditions

2005 ◽  
Vol 24 (4) ◽  
pp. 197-208 ◽  
Author(s):  
Yuan-Jun Liu ◽  
Wen Zhai ◽  
Chuan-Lan He ◽  
Jian-Guo Deng ◽  
Ke-Jian Ji ◽  
...  
Keyword(s):  
Compressive Strength ◽  
Aging Time ◽  
Fire Retardant ◽  
Ester Group ◽  
Polyurethane Foams ◽  
Compressive Modulus ◽  
Glass Beads ◽  
Hygrothermal Aging ◽  
Aging Properties ◽  
Mass Dimension

The aging rules of rigid polyurethane foam (PUR) at indoor storage and different hygrothermal conditions have been studied. Four parameters, which are mass, dimension, compressive strength and compressive modulus were tested. At indoor storage, mass, dimension and compressive strength vary slowly with an increase in aging time, while compressive modulus decreases quickly. PUR is sensitive to relative humidity (RH) verified by accelerated hygrothermal aging, and hydrolysis of ester group is the main reason resulting in the decrease of compressive properties. The filling with fire retardant and glass beads had some effect on hygrothermal aging properties of PUR. The addition of fire retardant increased compressive strength with aging time in the total trend, but it made dimension stability worse. The addition of glass beads slightly improved hygrothermal aging properties.

Local Investigations of the Mechanical Properties of Ultrafine Grained Metals by Nanoindentations

2006 ◽  
Vol 503-504 ◽  
pp. 31-36 ◽  
Author(s):  
Johannes Mueller ◽  
Karsten Durst ◽  
Dorothea Amberger ◽  
Matthias Göken
Keyword(s):  
Mechanical Properties ◽  
Strain Rate ◽  
Strain Rate Sensitivity ◽  
Room Temperature ◽  
Rate Sensitivity ◽  
Strain Rates ◽  
Fcc Metals ◽  
Angular Pressing ◽  
Ultrafine Grained ◽  
Indentation Strain

The mechanical properties of ultrafine-grained metals processed by equal channel angular pressing is investigated by nanoindentations in comparison with measurements on nanocrystalline nickel with a grain size between 20 and 400 nm produced by pulsed electrodeposition. Besides hardness and Young’s modulus measurements, the nanoindentation method allows also controlled experiments on the strain rate sensitivity, which are discussed in detail in this paper. Nanoindentation measurements can be performed at indentation strain rates between 10-3 s-1 and 0.1 s-1. Nanocrystalline and ultrafine-grained fcc metals as Al and Ni show a significant strain rate sensitivity at room temperature in comparison with conventional grain sized materials. In ultrafine-grained bcc Fe the strain rate sensitivity does not change significantly after severe plastic deformation. Inelastic effects are found during repeated unloading-loading experiments in nanoindentations.

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