FINE MECHANICAL TESTING AT OLEM /IMEX/ Evgeni Ivanov

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1 Open Laboratory of Experimental Mechanics (OLEM) Institute of Mechanics (IMech) Bulgarian Academy of Sciences (BAS) Sofia, Bulgaria FINE MECHANICAL TESTING AT OLEM /IMEX/ Evgeni Ivanov

2 Open Laboratory on Experimental Micro and Nano Mechanics (OLEM) at the Institute of Mechanics, Bulgarian Academy of Sciences 1. Research field: RHEOLOGICAL, MICRO AND NANOMECHANICAL STUDY OF REINFORCING EFFECTS OF NANOFILLERS IN POLYMERS: We Develop and Characterize Polymer Nanocomposites based on nanotubes, 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 and application. 4. OLEM is worked mostly on projects supported by EC and national funds. Graphene, Carbon

3 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

4 Nano Indentation with Integrated Inline Imaging (AFM) of Dental and Biomedical Materials

5 Nanoindentation with Integrated Inline Imaging Nanoindentor (Bruker) Atom Force Microscopy (Ambious Technology) Optical Microscope 3D Profilometer Microtom

6 Nanoindentation Instrumented nanoindentation is an accepted technique for determining the local mechanical properties of a material from its measured indentation load displacement response. This involves indenting a specimen with a small load and recording the load and displacement continuously. Elastic modulus, E, and hardness, H, are the two mechanical properties most commonly measured using load and depthsensing indentation techniques. Possible application of nanoindentation is evaluation of the nanohardness and elastic modulus of dental resin-composites. tooth tissues and materials has been reported in the dental literature.

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

8 Each subsequent indentation from one line is done with increasing force in the range from 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 and PRO500 3D Profilometer. Optical micrographs for the series of 96 indentations (8 lines x 12 indentations) for a pure bulk epoxy resin sample

9 This technique allows mapping the materials with different features on the surface and analyzing the obtained results for the specific local nanomechanical properties (for example Young s modulus and hardness for a certain interfacial surface). AFM images of imprints made with Berkovich nanoindenter on the aforementioned bulk epoxy resin sample at load of: 5 mn and 45 mn, (4th row, 2nd indent and 8th row, 11 th indent, respectively, from the optical images

10 Examples for Dental Application Nanomechanical properties of intertubular and peritubular dentin Study in collaboration with Medical University of Plovdiv, Bulgaria (Dental Faculty) 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

11 Examples for Dental Application Microindentation on dental cements treated with a chemical solution Study in collaboration with Medical University of Sofia, Bulgaria (Dental Faculty) The treatment of the samples with appropriate solution at a specific conditions is strengthen the testing cements (increase of Hardness and Young s modulus) Твърдост (GPa) Модул на Юнг (GPa)

12 Nanomechanical testing of multilayered materials (including dental structures) If the sample is composed of several layers of different materials type density, the multiple partial unloading tests are ideal to identify these coating layers. The multiple partial unloading tests may characterize the hardness, elasticity and thickness of each layer, comprised of multilayer structures. Such tests are very useful when the purpose is to know the variations of hardness and modulus values of each layer, as well as the adhesion between layers of a specimen when the indenter penetrates through different layers or reaches the substrate, respectively.

13 Example for Nanoindentation of Multilayered Structures: PP foil coated with different thickness of polytetrafluoroethylene (PTFE) Load-displacement curves and values of apparent elastic modulus and hardness from nanoindentation tests of: (i) polymer foil (PP substrate) with thickness of 40 um; (ii) PP (40 um) + PTFE (15 nm with plasma assisted sputtering) and (iii) UV irradiated PP+PTFE (15 nm). The penetration depths were much higher than the coating thickness. Comparing to PP sample, an increase in both hardness and Young modulus has occurred. For PTFE covered samples, the hardness has increased of about 25% (average), and increase around 30% for aged samples.

14 Examples of AFM Nanoindentation and Nanoscratch Tests of Biomedical Materials Joint study with Sofia University St. Kliment Ohridski Biology Faculty, Prof. Nadia Antonova (Biomechanics, IMECH) and Dr. L. Drozd 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. Z-controlled and force-controlled loading-unloading curve obtained after nanoindentation with applied displacement of 1000 nm and force of 50 nn on erythrocytes R. Krustev. Investigation of morphological and mechanical characteristics of the erythrocyte membrane. Dependance with rheological properties of blood. Master thesis, Sofia University St. Kliment Ohridski, Sofia. 2011

15 Examples of AFM Nanoindentation and Nanoscratch Tests of Biomedical Materials One of the techniques for calculating the Young s modulus is using the Hertz model describing the elastic deformation of the two bodies in contact under loading. AMF scans of the indented red blood cells samples at different magnification

16 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

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

18 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.

19 Micro Scratch Test Microscratch testing of polymer nanocomposite coating on a metal substrate 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 penetration COF coefficient of friction at scratch. Electric contact resistance (ECR) and Acoustic emission (AE) Sensors are used in parallel

20 Nanoscratch Nanoscratch can be used for testing the human enamel and dentine and biocompatible dental filling materials: polymer nanocomposites, glass ionomer, and silver amalgam. Nano-scratch gave critical load determining the adhesion of coating to the substrate, as well as the resistance to sliding wear. These relatively nondestructive mechanical characterisation techniques may assist in better understanding the mechanical behaviour of the dental fillers and thus facilitate the design of robust fillers with excellent mechanical properties.

21 Macromechanical tests of fine samples and small details

22 Macro Mechanical properties Universal Materials Tester UMT-2M (BRUKER) works in compliance with international standards ISO, ASTM and DIN. The module system allows measuring of macro-mechanical properties of small and fine samples, as follows. - Deformation and fracture from 5 mn to N. - Tension, bending, twist and compression tests can be done in environmental control chambers: from 20 o C to 200 o C. - Fatigue, creep and relaxation tests

23 Tubing longitudinal tensile strength The purpose of this test is to determine the longitudinal strength of tubing used in the delivery system. Test conditions: Time 60 sec; Speed 25 mm/min; Temperature 37 ± 2 o C ; Displacement 20 mm. The test method describes a tension test on 10 samples of tubes. The aim is to measure force at break or at least the max force which can be reached for each sample. Therefore test pieces have been cut and a displacement has been applied to each test piece until a failure 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 o C. Results: Yield strength (MPa); Ultimate strength (MPa); Elongation at Ultimate strength (%); Toughness (J/mm3); Energy at Yield point (J/mm3).

24 Tubing torsional strength The purpose of this test is to determine the torsional strength of tubing used in the delivery system. Test conditions: Time 305 sec; Speed 10 rev/min (rpm); Number of Revolutions 50; Temperature 37 ± 2 o C The 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 o C. Results: Max Torsion force Tz (Nm); Time (at max Tz); Destruction time (s); Revolutions (at destruction time)

25 Surface Scanning: AFM and 3D Profilometry

26 Example for AFM tests of Multilayered Structures: PP foil coated with different thickness of polytetrafluoroethylene (PTFE) 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. AFM measurements and surface roughness (S a ) calculated from the AFM images for polymer foil (PP substrate) and PP + PTFE (15 nm)

27 3D Profilometry 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 surface topography on micro- and nanoscale. It is a measuring instrument used for two different requirements surface measurements and contour measurements on any kind of materials, e.g. transparent, opaque, specular, diffusive, polished, rough, etc.

28 Rheology of Polymer Nanocomposites, Cements and Liquids

29 Rheology Dentists are subjected to manipulate materials which flow or deform when subjected to stress. 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 impression materials undergo a liquid to solid transformation in mouth. Gypsum products used in fabrication of dies are transformed from slurries into solid structures. Cements used as luting agents and bases

30 Viscosity test related to the structure of nanodispersions

31 OLEM is a partner in EU Projects: Graphene Flagship FP SME-NanoXCT ( ) FP INCO-BY-NanoERA ( ) FP CSA-NaPolyNet ( ) FP CSA-TeAm ( ) COST FP0904 ( ) COST MP1105 ( ) COST MP1202 ( ) COST MP1206 ( ) OLEM Team: Prof. D.Sc. Rumiana Kotsilkova Assoc. Prof. Dr. Evgeni Ivanov Assistant Ivanka Petrova - PhD student Assistant Verislav Angelov - PhD student Assistant Petar Todorov - PhD student Assistant Hristiana Velichkova Open Laboratory for Experimental Mechanics of Micro & Nanomaterials (OLEM), IMech, BAS

32 OLEM Research Team Prof. DSc. Rumiana Kotsilkova Assoc. Prof. Evgeni Ivanov Ivanka Petrova, PhD student Hristiana Velichkova - engineer Peter Todorov, PhD student Verislav Angelov, PhD student Thank you for your attention!