FINE MECHANICAL TESTING AT OLEM /IMEX/

Evgeni Ivanov

Open Laboratory of Experimental Mechanics (OLEM)Institute of Mechanics (IMech)

Bulgarian Academy of Sciences (BAS)Sofia, Bulgaria

Open Laboratoryon Experimental Micro and Nano Mechanics (OLEM)

at the Institute of Mechanics, Bulgarian Academy of Sciences

1. Research field:RHEOLOGICAL, MICRO AND NANOMECHANICAL STUDY OF REINFORCINGEFFECTS OF NANOFILLERS IN POLYMERS:We Develop and Characterize Polymer Nanocomposites based on Graphene, Carbonnanotubes, and Metal Oxides.

2. Fine mechanical testing:Expertize in: Characterization of materials and parts for Electronics, Dental and Medical applications, and Engineering.

Well equipped Laboratory for Macro- Micro and Nano Mechanical testing

3. Spin-off “Nano Tech Lab”:.

OLEM researchers has found a spin-off company Nano Tech Lab Ltd., which is the first nanotechnology company, in Bulgaria specialized in polymer nanocomposites fabrication, characterization andapplication.

4. OLEM is worked mostly on projects supported by EC and national funds.

Fine Mechanical Tests at OLEM:

CONTENTS

Nano Indentation with Integrated Inline Imaging.AFM indentation.

Tribology, Scratch, Friction and Wear, Coefficient of Friction

Macro Mechanical tests: Deformation and Fracture; Fatigue; Creep

Surface Scanning – AFM and 3D Profilometry

Rheology of Polymer Nanocomposites, Cements and Liquids

Nano Indentation with Integrated Inline Imaging (AFM) of

Dental and Biomedical Materials

Nanoindentation with Integrated Inline Imaging

Nanoindentor (Bruker)Atom Force Microscopy (Ambious Technology)Optical Microscope3D ProfilometerMicrotom

• Instrumented nanoindentation is an accepted technique fordetermining the local mechanical properties of a material from itsmeasured indentation load–displacement response. This involvesindenting a specimen with a small load and recording the load anddisplacement continuously.

• Elastic modulus, E, and hardness, H, are the two mechanicalproperties most commonly measured using load and depth-sensing indentation techniques.

• Possible application of nanoindentation is evaluation of thenanohardness and elastic modulus of dental resin-composites.tooth tissues and materials has been reported in the dentalliterature.

Nanoindentation

Each testing cycle consisted of: (a) the loading segment, (b) the peak load holdingsegment, (c) the unloading segment and (d) the holding segment at 10% of themaximum load.Multicycle Graph and Summary Graph for series of 96 (8x12; spacing betweenindents is 80 µm) indentations with increasing force in the range from 3 to 50 mNfor a pure polymer sample.Data collection and analysis are conducted using the Oliver and Pharr methodVariety of paired parameters can be determined: Hardness, Young’s Modulus,Contact Stiffness, Contact Depth, Contact Area, etc.

Single and Multiple Nanoindentation Tests

Each subsequent indentation from one line is done with increasing force in the rangefrom 3 to 50 mN (3, 5, 7, 10, 15, 20, 25, 30, 35, 40, 45, 50 mN).

There are options for visualization of impressions with optical microscope, AFM andPRO500 3D Profilometer.

Optical micrographs for the series of 96 indentations (8 lines x 12 indentations) for a pure bulk epoxy resin sample

This technique allows mapping the materials with different features on thesurface and analyzing the obtained results for the specific local nanomechanicalproperties (for example Young’s modulus and hardness for a certain interfacialsurface).

AFM images of imprints made with Berkovich nanoindenter on the aforementioned bulkepoxy resin sample at load of: 5 mN and 45 mN, (4th row, 2nd indent and 8th row, 11th

indent, respectively, from the optical images

Examples for Dental ApplicationNanomechanical properties of intertubular and peritubular dentin

Heonjune Ryou, Elaine Romberg, David H. Pashley, Franklin R. Tay, Dwayne Arola. Nanoscopic dynamic mechanical properties of intertubular and peritubular dentin. Journal of the Mechanical Behavior of Biomedical Materials, Vol. 7, 2012, Pages 3–16

Study in collaboration with Medical University ofPlovdiv , Bulgaria (Dental Faculty)

Examples for Dental Application Microindentation on dental cements treated with a chemical solution

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The treatment of the samples with appropriate solution at a specific conditions is strengthen the testing cements (increase of Hardness and Young’s modulus)

Study in collaboration with Medical University of Sofia,Bulgaria (Dental Faculty)

Nanomechanical testing of multilayered materials (including dental structures)

If the sample is composed of several layers of different materials typedensity, the multiple partial unloading tests are ideal to identify thesecoating layers. The multiple partial unloading tests may characterize thehardness, elasticity and thickness of each layer, comprised ofmultilayer structures.

Such tests are very useful when the purpose is to know the variationsof hardness and modulus values of each layer, as well as theadhesion between layers of a specimen when the indenter penetratesthrough different layers or reaches the substrate, respectively.

Load-displacement curves and valuesof apparent elastic modulus andhardness from nanoindentation tests of:(i) polymer foil (PP substrate) withthickness of 40 um; (ii) PP (40 um) +PTFE (15 nm with plasma assistedsputtering) and (iii) UV irradiatedPP+PTFE (15 nm).

The penetration depths were muchhigher than the coating thickness.

Comparing to PP sample, an increasein both hardness and Young modulushas occurred. For PTFE coveredsamples, the hardness has increased ofabout 25% (average), and increasearound 30% for aged samples.

Example for Nanoindentation of Multilayered Structures:PP foil coated with different thickness of polytetrafluoroethylene (PTFE)

R. Krustev. Investigation of morphological and mechanical characteristics of the erythrocyte membrane. Dependance with rheological propertiesof blood. Master thesis, Sofia University “St. Kliment Ohridski”, Sofia. 2011

Z-controlled and force-controlled loading-unloading curve obtained after nanoindentationwith applied displacement of 1000 nm and force of 50 nN on erythrocytes

AFM gives an opportunity not only to study the individual cell’s morphology,but also to evaluate the surface topography of the membrane and its elasticity.

Examples of AFM Nanoindentation and NanoscratchTests of Biomedical Materials

Joint study with Sofia University “St. Kliment Ohridski” – Biology Faculty,Prof. Nadia Antonova (Biomechanics, IMECH) and Dr. L. Drozd

AMF scans of the indented red blood cells samples at different magnification

One of the techniques for calculating the Young’s modulus is using the Hertz modeldescribing the elastic deformation of the two bodies in contact under loading.

Examples of AFM Nanoindentation and NanoscratchTests of Biomedical Materials

Micro &Macro Mechanical Tests

Macro Mechanical test devise (UMT-2, BRUKER)

Tribology, wear, friction and scratch tests;Macromechanical tests of fine samples and small details:

- deformation and fracture;- tensile, bending, compressive and torsion mode;- fatigue, creep and relaxation tests

Microtribological Measurements using Ball/Pin-on-Flat Reciprocating UMT-2M Setup

Applicable for small flat samples. Wear distance up to 10 mm.

Could be used for testing the wear and friction between tooth and implant

Tribology, Friction and Wear, Coefficient of Friction, Scratch and Nanoscratch

Friction and Wear

A linearly increasing load from 20 to 60 N, velocity of 10 mm/s and distance of 10 mm were applied. The friction, together with electric contact resistance data were continuously monitored.Coefficient of friction (COF) values were continuously calculated during the test.

Micro Scratch Test

The applied load can vary in the range of 5 mN to 1000 N. The microscratch test parameters, which can be measured :

Scratch depth of penetrationCOF – coefficient of friction at scratch.

Electric contact resistance (ECR) and Acoustic emission (AE)Sensors are used in parallel

Microscratch testing of polymer nanocomposite coating on a metal substrate

Nanoscratch

• Nanoscratch can be used for testing the human enamel and dentineand biocompatible dental filling materials: polymer nanocomposites,glass ionomer, and silver amalgam.

• Nano-scratch gave critical load determining the adhesion of coating tothe substrate, as well as the resistance to sliding wear.

• These relatively nondestructive mechanical characterisation techniquesmay assist in better understanding the mechanical behaviour of thedental fillers and thus facilitate the design of robust fillers withexcellent mechanical properties.

Macromechanical tests of fine samples and small details

Universal Materials Tester UMT-2M (BRUKER) works incompliance with international standards ISO, ASTM andDIN.The module system allows measuring of macro-mechanicalproperties of small and fine samples, as follows.

- Deformation and fracture from 5 mN to 1 000 N.- Tension, bending, twist and compression tests can

be done in environmental control chambers: from 20oC to200oC .

- Fatigue, creep and relaxation tests

Macro Mechanical properties

Tubing longitudinal tensile strength

• The purpose of this test is to determine the longitudinal strength of tubing used in thedelivery system.Test conditions: Time – 60 sec; Speed – 25 mm/min; Temperature – 37 ± 2 oC ; Displacement – 20 mm.• The test method describes a tension test on 10 samples of tubes. The aim is to measureforce at break or at least the max force which can be reached for each sample. Thereforetest pieces have been cut and a displacement has been applied to each test piece until afailure of the sample. An axial displacement rate of 25 mm/min has been used for all tests.All tests have been performed in environmental test chamber at 37 ±2 oC.• Results: Yield strength (MPa); Ultimate strength (MPa); Elongation at Ultimate strength(%); Toughness (J/mm3); Energy at Yield point (J/mm3).

Tubing torsional strength• The purpose of this test is to determine the torsional strength oftubing used in the delivery system.Test conditions: Time – 305 sec; Speed – 10 rev/min (rpm); Number of Revolutions – 50; Temperature – 37 ± 2 oCThe test method describes a torsion test on 10 samples of tubes. The aim of this report is to measure torsional force at break in Nm. Therefore test pieces have been cut and rotational rates of 10 rev/min (rpm) have been applied for all tests. All tests have been performed in environmental test chamber at 37 ±2 oC.Results: Max Torsion force Tz (Nm); Time (at max Tz); Destruction time (s); Revolutions (at destruction time)

Surface Scanning: AFM and 3D Profilometry

AFM measurements and surface roughness (Sa) calculated from the AFM images for polymer foil (PP substrate) and PP + PTFE (15 nm)

Comparing to PP sample, an increase in surface roughness (Sa) from 32.4 nm to 52.9 nm for PP + PTFE (15 nm). Probable explanation may be the thickness of the deposited layer – 15nm.

Example for AFM tests of Multilayered Structures:PP foil coated with different thickness of polytetrafluoroethylene (PTFE)

Typical surface measurement parameters include flatness, roughness,curvature, peak-to-valley, asperity, texture, thickness, slope and distance.Profilometers are the industry standard method of measuring surfacetopography on micro- and nanoscale. It is a measuring instrument used for twodifferent requirements – surface measurements and contour measurements onany kind of materials, e.g. transparent, opaque, specular, diffusive, polished,rough, etc.

3D Profilometry

Rheology of Polymer Nanocomposites,

Cements and Liquids

Rheology

Dentists are subjected to manipulate materials which flow or deform when subjected tostress. The study of flow characteristics of materials is the basis for the science of rheology.Applications:• Measure viscosity of dental materials.• Materials manipulated in fluid state in oral cavity i.e, materials like cements and impressionmaterials undergo a liquid to solid transformation in mouth.• Gypsum products used in fabrication of dies are transformed from slurries into solidstructures.• Cements used as luting agents and bases …

Viscosity test related to the structure of nanodispersions

OLEM is a partner in EU Projects:Graphene FlagshipFP7-2011-SME-NanoXCT (2012-2015)FP7-2010-INCO-BY-NanoERA (2011-2013)FP7-2009-CSA-NaPolyNet (2009-2012)FP7-2009-CSA-TeAm (2010-2012)

COST FP0904 (2010-2014)COST MP1105 (2012-2016)COST MP1202 (2013-2017)COST MP1206 (2013-2017)

OLEM Team: Prof. D.Sc. Rumiana KotsilkovaAssoc. Prof. Dr. Evgeni IvanovAssistant Ivanka Petrova - PhD studentAssistant Verislav Angelov - PhD studentAssistant Petar Todorov - PhD studentAssistant Hristiana Velichkova

Open Laboratory for Experimental Mechanics of Micro & Nanomaterials (OLEM), IMech, BAS

OLEM Research Team

Ivanka Petrova, PhD student

Verislav Angelov, PhD studentPeter Todorov, PhD student

Hristiana Velichkova - engineer

Prof. DSc. Rumiana Kotsilkova

Thank you for your attention !

Assoc. Prof. Evgeni Ivanov