Nano-indentation for probing mechanical properties of nanocomposites based on ethylene butyl acrylate copolymer and carbon black

Mechanical properties of heterogeneous systems based on carbon black (CB) filled semi-crystalline ethylene butyl acrylate (EBA) copolymer nanocomposites are characterized using nano-indentation technique. The size effect and CB content dependence on the deformation behavior at room temperature were investigated. The phenomenology for hardness response (H) indicates a typical enhancement of the H when the indentation depth (h) decreases as for the usual elastomeric materials. All H–h curves, fitted according to the Meyer's empirical power law and Franck elasticity model, highlight the so-called length-scale-dependent deformation. Similar trend is observed for the elastic modulus. Furthermore, it is evidenced that the increases of CB content increases the mechanical properties of composites, that is, hardness and elastic modulus. This behavior can be mainly related, on the one hand, to the change of the meso-structure, formed by the interconnected network of polymer and the aggregates of CB particles and to the nature of the polymer matrix, on the other hand. The mechanical properties characterized from micro and submicron indentations were compared to that characterized at macroscopic scale to highlight the possible correlations between the two scales. This investigation can interest many applications of polymer composites for rubber technology such as tires industry, soft robotic, and adhesives. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47897.     

Carbon black distribution driven by its concentration and its effect on physico-mechanical properties of styrene butadiene rubber and butadiene rubber miscible rubber blends

This paper discusses the influence of partitioning of carbon black (CB) with its increasing concentration (i.e., 10, 20, 30, 40, and 50 phr) on physical and static mechanical properties of Styrene Butadiene Rubber (SBR)/Butadiene Rubber (BR) rubber–rubber blends (RRB's) in 70SBR:30BR blend ratio. Partitioning of CB towards BR in CB-filled SBR/BR RRB's is quantitatively determined via dynamic mechanical analysis (DMA). DMA confirmed increased partitioning of CB towards BR phase with increasing CB. DMA data on the partitioning of CB towards BR were in good agreement with nuclear magnetic spectra obtained by solid-state nuclear magnetic resonance spectroscopy (SS-NMR spectroscopy). Curing properties, relative density, hardness, tensile test, tear test, and transmission electron microscopy (TEM) on CB filled SBR/BR RRB's were carried out to determine the effect of increasing concentration of CB on physical, mechanical, and dispersion characteristics in comparison to neat SBR/BR RRB's.     

Mechanical properties of individual phases of ZrB2-ZrC eutectic composite measured by nanoindentation

Zr-based ceramics are of interest for applications in aerospace propulsion, owing to their high hardness and stability. Application of these ceramics requires better understanding of their mechanical behavior in small scales and at elevated temperatures. Here, we prepared a ZrB₂-ZrC ceramic eutectic composite, consisting of self-assembled ZrC rods grown within a single-crystalline ZrB₂ matrix, and studied the mechanical properties of the individual eutectic phases using nanoindentation at both room and elevated-temperatures. The Vickers hardness of the eutectic composite was measured at room temperature. These data provide insight into the understanding of the mechanical behavior of the individual phases of non-oxide ceramic eutectic composites for high-temperature applications.     

Analysis of indentation size effect (ISE) in nanoindentation hardness in polycrystalline PMN-PT piezoceramics with different domain configurations

Piezoelectric materials contain microstructural features (e.g., domain walls, interdomain spacing, and grain size) that span across several length scales, i.e., few nm in the case of interdomain wall spacing to several μm in case grain sizes. Recent experimental findings indicated that the domain configurations have more influence on the hardness of these materials than the grain size. In this study, nanoindentation experiments are conducted on polycrystalline PMN-PT (a relaxor ferroelectric material) with a focus to investigate the influence of domain configurations on the indentation size effect (ISE) in hardness, H. Different domain configurations are achieved by selectively annealing the as poled samples above and below the Curie temperature. Nanoindentation hardness is obtained in the load range of 1–5 mN with the maximum penetration depth well below the grain size of the samples. The experimental results reveal that all the samples, albeit to a different order, exhibit strong Reverse Indentation Size Effect (RISE) and normal ISE in H. The observed ISE is then analyzed using classical Meyer's law, the proportional specimen resistance (PSR) model and modified PSR (mPSR) model. The critical analysis of nanoindentation data reveals that the PSR model provides a satisfactory understanding of the genesis of RISE and ISE considering the elastic resistance of test material and frictional resistance at indenter facet/test material.     

Length scale dependent deformation in natural rubber

Strong length scale dependent deformation has been previously observed in the elastomer polydimethylsiloxane by indentation type experiments at micro‐ to nanometer length scales with a sharp conical tip. To examine if other nonsilicone based elastomers exhibit similar length scale dependent deformation behavior, natural rubber has been chosen in this study. Performing indentation type tests with a nanoindentation system, the universal hardness and the elastic modulus are determined at different probing depths ranging from about 90 to 5 μm to characterize length scale dependent deformation behavior in natural rubber. The testing with a Berkovich tip resulted in an amazing increase in the universal hardness with decreasing probing depth indicating that the deformation mechanisms at the micrometer length scales are significantly different as compared to those at the macroscopic length scales. The observed length scale dependent deformation is associated with an increase in rotation gradients with decreasing probing depth. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42683.     

Microstructure and mechanical properties of an alumina–glass low temperature co-fired ceramic

The microstructure and mechanical properties of an alumina–glass low temperature co-fired ceramic (LTCC) have been investigated. The microstructure was studied by using optical microscope, scanning electron microscope, energy spectrum analysis and X-ray diffraction. The Young's modulus, hardness, flexure strength and fracture toughness were measured by three-point bending, indentation and nanoindentation tests. The LTCC can be regarded as a particle-reinforced composite with macroscopically isotropic properties: particles mainly composed of synthetic corundum and matrix mainly of corundum and silica. The particles with irregular shape and an average radius of 0.71 μm are homogeneously dispersed in the matrix. The properties of the individual particle and matrix were successfully measured and further used to obtain the effective properties of the composite by micromechanics methods. The existence of rigid particles improves not only the modulus, hardness and strength but also the fracture toughness of LTCC materials.     

Thermoplastic rubber/PP elastomers toward extremely low thermal expansion

Fine regulation of the microstructure of rubber/polypropylene (PP) alloys could remarkably reduce the coefficient of linear thermal expansion (CLTE) while retaining the mechanical properties similar to those of thermoplastic elastomers. Rubber/PP elastomers with different morphologies were successfully prepared by controlling the appropriate rubber type, viscosity ratio, and processing method. The CLTE of the polymer alloy parallel to the microlayer directions was considerably reduced when the rubber domains were deformed into microlayers and co‐continuous with plastic domains. The thickness of the PP layers played a crucial role on CLTE reduction. The CLTE considerably decreased with reduced thickness of the PP layer. The sample with a co‐continuous microlayer structure exhibited good flexibility, high elongation, low hardness, and permanent deformation. Thus, low‐thermal‐expansion elastomer materials may have wide applications. Stress relaxation and strain recovery of the ethylene–propylene–diene terpolymer/PP (70/30 wt %) blend were investigated to further clarify the influence of co‐continuous microlayer structure on mechanical properties. Anisotropic mechanical properties were consistent with the morphology. Results of the stress relaxation behavior test would provide further support to the mechanism of the low thermal expansion of blends with co‐continuous microlayer structure. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43902.     

Nanoindentation of isotactic polypropylene: Correlations between hardness,yield stress,and modulus on the local and global scales

The correlations between the hardness, yield stress, and modulus of elasticity of isotactic polypropylene (iPP) were evaluated on the local and global scales. Nanoindentation and traditional macromechanical tests were incorporated for this purpose. Thus, local and global mechanical properties were measured at various temperatures and strain rates. A certain relation was found between the local and global mechanical properties. Moreover, Johnson's model (developed according to the expanding cavity model) was also evaluated at various temperatures and strain rates. The Johnson model was valid only for the yield stresses obtained by nanoindentation and compressive tests and also the elastic modulus obtained via nanoindentation. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Control of coefficient of thermal expansion in elastomers using boron nitride

The thermal expansion properties of three commercial elastomers; Pebax®, Estane® and Hytrel® modified with 2.5–10 wt % boron nitride were investigated. The glass transition temperatures of the filled materials were relatively unaffected; however boron nitride did effectively reinforce all the three elastomers as seen by dynamic mechanical analysis and tensile tests. The coefficients of thermal expansion of the composite materials do not obey the rule of mixtures and show a large decrease without the loss of ductility typically associated with filled elastomers. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5153–5161, 2006     

Mechanical properties of hybrid computer-aided design/computer-aided manufacturing (CAD/CAM) materials after aging treatments

The purpose of this study was to evaluate and compare the changes in the various mechanical properties of hybrid and conventional CAD/CAM materials after accelerated aging using hydrothermal processes.Five kinds of hybrid and ceramic CAD/CAM blocks were selected. A total of 225 specimens were prepared with highly polished surfaces, in the form of round discs (diameter 12?mm, thickness 1.2?mm), and were divided into three groups (the control group, thermal cycling group, and autoclave group [n?=?15, each]). The nanoindentation hardness and Young's modulus (nanoindenter), biaxial flexural strength (ball-on-ring test system), surface roughness (atomic force microscopy), surface texture (scanning electron microscopy (SEM)), and elemental concentrations (energy dispersive spectroscopy) were evaluated. The Kruskal–Wallis test and Mann–Whitney U test were used to determine statistical significance (P?<?0.05).The nanoindentation hardness and Young's modulus of the hybrid CAD/CAM materials were lower than those of ceramic materials, and they decreased after autoclave treatment. Among the hybrid CAD/CAM materials, Vita Enamic alone showed no significant difference in the Young's modulus after autoclave treatment; it also exhibited the highest nanoindentation hardness and modulus. There were significant changes in the biaxial flexural strength of hybrid CAD/CAM materials after aging. However, there was no change in the biaxial flexural strength of ceramic materials. The surface roughness of all materials, except CeraSmart, changed after aging. The SEM observations indicated a loss of filler particles in Lava Ultimate and morphological changes in IPS e.max ZirCAD, after aging.The ceramic CAD/CAM materials are superior to hybrid CAD/CAM materials in terms of the mechanical properties. The accelerated aging procedure induced changes in the mechanical properties of some hybrid CAD/CAM materials. Therefore, when using hybrid CAD/CAM materials, it is important to understand the behaviors of the various properties of each material as time progresses, and long-term follow up is necessary.     

A combined experimental and modeling study revealing the anisotropic mechanical response of Ti2AlN MAX phase

Ti₂AlN MAX phase with a hexagonal crystal structure exhibits great potential as structural material for operation under harsh environments due to its excellent mechanical performance. For a reliable application, a comprehensive understanding of the mechanical behavior, and in particular of the anisotropic properties is needed. Thus, in this study, we combined nanoindentation and electron-backscatter diffraction experiments to correlate elastic modulus and hardness of Ti₂AlN to the crystallographic orientation. We used two different modeling approaches to better understand, validate, and in the long run to predict the anisotropic mechanical behavior of MAX phase materials. While we observed consistent trends in both experiments and modeling, elastic modulus and hardness showed different dependencies on the crystal orientation.     

The effects of recycling on the structure and properties of carbon nanotube‐filled polycarbonate

Sustainable manufacturing processes are becoming more important in industrial practice. A critical part of the manufacturing process is understanding the recycling behavior of nanocomposite materials, particularly as more recycled plastic nanocomposites are entering the market for a variety of different applications. A common method to recycle thermoplastic composites is by melting and remolding, which often leads to decreased mechanical properties. This work was conducted to investigate the effect of nanofillers on the recycling behavior and structure–property relationships of carbon nanotube (CNT)‐filled polycarbonate (PC). Materials were recycled by repeated injection molding and granulating up to twenty cycles. The effect of recycling on chemical, rheological, and mechanical properties was investigated. The results indicated a general decrease in melt viscosity and mechanical properties (with the exception of Young's Modulus). The CNT‐filled PC shows less resistance to recycling compared to neat PC. POLYM. ENG. SCI., 58:1278–1284, 2018. © 2017 Society of Plastics Engineers     

Mechanical properties of block poly(propylene carbonate‐cyclohexyl carbonate) investigated by nanoindentation and DMA methodologies

To extend the practical application of poly(propylene carbonate) (PPC), the chemical methods were used to improve its mechanical properties. In this connection, random copolymer poly(propylene‐cyclohexyl carbonate) (PPCHC) and di‐block copolymers poly(propylene carbonate‐cyclohexyl carbonate) (PPC‐PCHC) were synthesized. Dynamic mechanical analysis (DMA), nanoindentation and nanoscratch test were applied to evaluate their mechanical properties. The storage's modulus, Young's modulus (E) and hardness (H) obtained from DMA and nanoindentation tests showed that the introduction of the third monomer cyclohexene oxide (CHO) can greatly improve the mechanical properties of PPC, and that the block copolymer PPC‐PCHC hand better mechanical properties than the random copolymer PPCHC. The annealing treated PPC‐PCHCs exhibited deteriorated mechanical properties as compared with untreated PPC‐PCHC. From the results of scratch tests, the plastic deformation of PPC‐PCHC was smaller than those of PPC and PPCHC. Meanwhile, the plastic deformations of the heat‐treated PPC‐PCHCs were smaller than the untreated PPC‐PCHC because of the possible rearrangement of the molecular chains of PPC‐PCHC. The scratch hardness (H_s) of the block copolymer PPC‐PCHC is larger than random polymer PPCHC and PPC, but lower than the values of heat‐treated samples indicating that the surfaces' hardness of block polymers increase after heat treatment. These different measurement methodologies provide a more precise assessment and understanding for the synthesized block polymers. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Thermomechanical properties,phase structure,and conductivity of organic/inorganic hybrid material filled with a conductive filler

Novel epoxy‐based organic/inorganic hybrid materials filled with carbon black (CB) were synthesized from an epoxy resin and silane alkoxide via a sol–gel process. The phase structure and thermal and mechanical properties of the hybrid materials were studied in detail. It was revealed by transmission electron microscope observations that the filled CB particles formed a secondary aggregation structure and were uniformly dispersed in the aggregate. The storage modulus in the rubbery region increased and the peak area of the tan δ curve in the glass‐transition region decreased with the hybridization of silica. Moreover, the conductive properties of the CB‐filled hybrid systems were investigated. In the same volume fraction of CB, the conductivity of the hybrid systems was much higher than that of the unmodified system. This result was attributed to the excluded volume effect of the silica network. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1980–1984, 2003     

Nanoindentation of NiTi shape memory thin films at elevated temperatures

The shape memory effect and nanoindentation response of various phases of sputtered NiTi shape memory thin films were investigated as a function of temperature. The phase transformation temperatures of NiTi films were observed to be sensitive to a compositional shift. The mechanical properties of NiTi thin films also presented a significant response to phase transformations. At the same load, the maximum indentation depth for austenite is smaller than for martensite, indicating that martensite is softer than austenite. A martensite thin film was converted to austenite via in situ heating nanoindentation and displayed the mechanical properties similar to the austenite film at room temperature. These results underscore the validity of elevated temperature nanoindentation methods as a means of interrogating the mechanical properties of materials that undergo thermally-induced phase transformations. The details of the load–displacement curves are also described.     

Swelling and mechanical properties of (acrylonitrile‐butadiene rubber)/(hydrogenated acrylonitrile‐butadiene rubber) blends with precipitated silica filled in gasohol fuels

This work studied the effects of hydrogenated acrylonitrile‐butadiene rubber (HNBR) and precipitated silica (PSi) loadings in acrylonitrile‐butadiene rubber (NBR) filled with 60 parts per hundred of rubber (phr) of carbon black (CB) for oil‐resistant seal applications in contact with gasohol fuel. The cure characteristics, mechanical properties, and swelling behavior of HNBR/NBR blends reinforced with PSi before and after immersion in ethanol‐based oils (E10, E20, and E85) were then monitored. This work studied the effects of PSi loading in rubber compounds on the mechanical properties of the rubber blends. The results suggested that the scorch time of CB‐filled NBR/HNBR was not affected by HNBR loading, but the cure time, Mooney viscosity, and torque difference increased with HNBR content. The swelling of the blends in E85 oil were relatively low compared with those in E10 and E20 oils. The recommended NBR/HNBR blend ratio for oil‐resistant applications was 50/50. Tensile strength and elongation at break before and after immersion in gasohol oils increased with HNBR loading, and the opposite effect was found for tensile modulus and hardness. PSi filler had no effect on scorch time, but decreased the cure time of the blends. The swelling level of the blends slightly decreased with increasing PSi content. The recommended silica content for optimum reinforcement for black‐filled NBR/HNBR blend at 50/50 was 30 phr. The results in this work suggested that NBR/HNBR blends reinforced with 60 phr of CB and 30 phr of silica could be potentially used for rubber seals in contact with gasohol fuels. J. VINYL ADDIT. TECHNOL., 22:239–246, 2016. © 2014 Society of Plastics Engineers     

Studies on the effect of titanate coupling agent (2.0%) on the mechanical properties of flyash‐filled polybutadiene rubber

Flyash, a waste product of thermal power stations, generated in huge quantities, has been posing problems of disposal. Attempts have been made for its utilization as a filler in elastomers and plastics; however, it has been established that untreated flyash does not at all contribute in enhancing mechanical properties of composites. The purpose of this work was to make meaningful utilization of flyash as a filler, by treating it with a titanate coupling agent and to use it as a filler in PBR. The properties under consideration were tensile strength, modulus at 100 and 400%, Young's modulus, hardness, etc. Composites were made with varying proportion of untreated and treated flyash. A two‐roll mill was used for dispersing the filler in the rubber, and a compression‐molding technique was used to cure the compound in sheet form. Tensile properties were measured on a computerized UTM using an ASTM procedure. Comparison of properties of composites filled with treated and untreated flyash established that treatment of flyash imparts better reinforcing properties. Tensile strength was improved by 50%, while modulus at 400% was improved by 400%. Similarly, Young's modulus also was improved by 209%. The Titanate‐coupling agent used here has promoted adhesion between flyash and the PBR. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1293–1298, 2004     

A hybrid model for mechanical spectra of filled and unfilled elastomers

The dynamic mechanical properties of elastomers are of vital importance in determining the product design/performance relationship. Unfortunately, the statistical theory of Gaussian networks, commonly used for the ideal rubbery state, cannot adequately model the moduli of elastomers in engineering applications. The WLF equation, although not originally designed to predict moduli, has a functional form that predicts moduli for the range from T_g to 100°K plus T_g. A hybrid equation which incorporates elements of the WLF equation and the statistical theory of Gaussian networks in an ideal rubbery state has been developed for explaining the mechanical spectrum of elastomeric materials. The new equation satisfactorily models the mechanical properties for both filled and unfilled elastomers. This model shows that filler loading tends to broaden the relaxation spectrum. This finding agrees with a previous study on the viscosity of uncured elastomer-filler systems.     

Synthesis and characterization of the properties of thermosensitive elastomers with thermoplastic and magnetic particles for application in soft robotics

In the currently rapidly developing field of soft robots, smart materials with controllable properties play the central role. Thermosensitive elastomers are soft, smart materials whose material properties can be controlled by changing their temperature. The aim of this work is to investigate the mechanical properties, to analyze the surface, the inner structure, and the heat transfer within the thermosensitive elastomer materials. This should provide a knowledge base for new combinations, such as a combination of thermosensitive and the well-known magneto sensitive elastomers, in order to realize new applications. Thermoplastic polycaprolactone particles were incorporated into a flexible polydimethylsiloxane matrix to produce thermosensitive elastomer samples. With a low melting point in the range of 58–60°C, polycaprolactone offers good application potential compared to other thermoplastic materials such as polymethamethylacrylate with a melting point above 160°C. Test samples of different material compositions and geometries were made to examine temperature-depending material properties. Two useful effects were identified: temperature-dependent change in stiffness and the shape memory effect. In certain examinations, carbonyl iron particles were also included to find out if the two particle systems are compatible with each other and can be combined in the polydimethylsiloxane matrix without disadvantages. Changes in shore hardness before and after the influence of temperature were investigated. Micro computed tomography images and scanning electron microscopy images of the respective samples were also obtained in order to detect the temperature influence on the material internally as well as on the surface of the thermosensitive elastomers in combination with carbonyl iron particles. In order to investigate the heat transfer within the samples, heating tests were carried out and the influence of different particle concentrations of the thermosensitive elastomers with and without carbonyl iron particles was determined. Further work will focus on comprehensive investigations of thermo-magneto-sensitive elastomers, as this will enable the functional integration in the material to be implemented with increased efficiency. By means of the different investigations, the authors see future applications for this class of materials in adaptive sensor and gripper elements in soft robotics.