Comparative investigation on nanomechanical properties of hardened cement paste

Three types of nanomechanical methods including static nanoindentation, modulus mapping and peak-force quantitative nanomechanical mapping (QNM) were applied to investigate the quantitative nanomechanical properties of the same indent location in hardened cement paste. Compared to the nanoindentation, modulus mapping and peak-force QNM allow for evaluating local mechanical properties of a smaller area with higher resolution. Beside, the ranges of elastic modulus distribution measured by modulus mapping and peak-force QNM are relatively greater than that obtained from nanoindentation, which may be due to a result of the shaper probe and local confinement effect between multiple phases. Moreover, the average value of elastic modulus obtained using peak-force QNM were consistent with those obtained by modulus mapping, while the different in modulus probability distribution could be related to the different nanomechancial theories and contact forces. The probability distributions of elastic modulus measured using nanomechanical methods to provide a basis for the different types of phases existing in cement paste. Based on the observation with high spatial resolution, cement paste can be likely found as nanocalse granular material, in which different submicron scale or basic nanoscale grain units pack together. It indicates that the peak-force QNM can effectively provide an effective insight into the nanostructure characteristic and corresponding nanomechanical properties of cement paste.     

跨尺度模拟硬化水泥净浆力学性能:微观物相的影响

采用纳米压痕实验测量硬化水泥净浆中未水化物、水化产物和孔隙等微观物相的力学性能,并基于背散射电镜（BSE）图像的灰度分析计算各微观物相的含量。在得到各微观物相含量和力学性能的基础上,针对水泥净浆的弹性模量进行均一化建模,并讨论各微观物相及其模量的选取对跨尺度模拟硬化水泥净浆力学性能的影响。通过微米压痕的实测净浆模量验证模型及参数选取的可靠性。提出在硬化水泥净浆力学性能的多尺度模型中,需要选取12 GPa作为孔隙有效模量,并将水化产物划分为低密度的水化硅酸钙凝胶（LD-CSH）和高密度的水化硅酸钙凝胶（HD-CSH）两种物相,而不同种类的未水化物可被视作一种物相。在此基础上,使用Mori-Tanaka模型或自洽模型计算得到的净浆模量与实测净浆模量吻合。     

Experimental and numerical analysis of nanoindentation of Ti-6246 alloy

Titanium and its alloys exhibit a very desirable set of mechanical properties like high strength-to-density ratio, high corrosion resistance, and the ability to work safely in extreme temperature conditions. In this work, nanoindentation technique was used to evaluate the mechanical properties of Ti-6246 alloy. The response of material to the indentation load was checked with light microscopy, and scanning electron microscopy (SEM) imaging was done to study the area around the indents for any sinks-in or piles-up. The light microscopy and SEM images are presented in this work and discussed in detail. In this work it was found that nanoindentation can be successfully used to evaluate the mechanical properties of high-strength material like Ti-6246. The hardness values and Young’s modulus values obtained in this work were found to be in close agreement to that reported in literature. A finite-element model was developed for the nanoindentation processes of the studied alloy using commercially available finite-element software DEFORM 3D. The model was used for parametric analysis of the nanoindentation process, and results obtained from FEA model were in good agreement with the experimental results.     

Finite element simulation for the effect of loading rate on visco‐hyperelastic characterisation of soft materials by spherical nanoindentation

Nanoindentation test performed by atomic force microscopy is highly recommended for the characterisation of soft materials at nanoscale. The assumption proposed in the characterisation is that the material is pure elastic with no viscosity. However, this assumption does not represent the real characteristics of soft materials such as bio tissue or cell. Therefore, a parametric finite element simulation of nanoindentation by spherical tip was carried out to investigate the response of cells with different constitutive laws (elastic, hyperelastic and visco‐hyperelastic). The investigation of the loading rate effect on the characterisation of cell mechanical properties was performed for different size of spherical tip. The selected dimensions of spherical tips cover commercially available products. The viscosity effects are insensitive to the varied dimensions of spherical tip in this study. A limit loading rate was found above which viscous effect has to be considered to correctly determine the mechanical properties. The method in this work can be implemented to propose a criterion for the threshold of loading rate when viscosity effect can be neglected for soft material characterisation.Inspec keywords: atomic force microscopy, viscoelasticity, finite element analysis, nanoindentation, viscosity, biomechanics, indentation, elasticityOther keywords: spherical tip, viscosity effect, viscous effect, soft material characterisation, visco‐hyperelastic characterisation, spherical nanoindentation, nanoindentation test, atomic force microscopy, bio tissue, parametric finite element simulation, loading rate effect, cell mechanical properties, constitutive laws     

Anisotropic nanomechanical properties of bovine horn using modulus mapping

Bovine horns are durable that they can withstand an extreme loading force which with special structures and mechanical properties. In this study, the authors apply quasi‐static nanoindentation and modulus mapping techniques to research the nanomechanical properties of bovine horn in the transverse direction (TD) and longitudinal direction (LD). In quasi‐static nanoindentation, the horn''s modulus and hardness in the inner layer and the outer layer demonstrated a gradual increase in both TD and LD. Laser scanning confocal microscopy revealed microstructure in the horn with wavy morphology in the TD cross‐section and laminate in the LD cross‐section. When using tensile tests or quasi‐static nanoindentation tests alone, the anisotropy of the mechanical properties of bovine horn were not obvious. However, when using modulus mapping, storage modulus (E ′), loss modulus (E ″) and loss ratio (tan δ) are clearly different depending on the position in the TD and LD. Modulus mapping is proposed as accurately describing the internal structures of bovine horn and helpful in understanding the horn''s energy‐absorption, stiffness and strength that resists forces during fighting.Inspec keywords: laser applications in medicine, proteins, molecular biophysics, high‐speed optical techniques, biomedical optical imaging, viscoelasticity, elastic moduli, biomechanics, biological tissues, nanoindentation, laminates, tensile testing, tensile strengthOther keywords: resists forces, stiffness, energy‐absorption, internal structures, loss ratio, loss modulus, storage modulus, modulus mapping, quasistatic nanoindentation testing, tensile testing, LD cross‐section, laminate, TD cross‐section, wavy morphology, microstructure, laser scanning confocal microscopy, hardness, longitudinal direction, transverse direction, modulus mapping techniques, quasistatic nanoindentation, loading force, bovine horns, modulus mapping, anisotropic nanomechanical properties     

Nanoindentation for measuring individual phase mechanical properties of lead free solder alloy

The elimination of lead from electronics due to its detrimental effects to environment and health is pushing component manufacturers to consider lead free solder alloys as the substitute. Application of such alloys requires a better understanding of their mechanical behavior at small volume size and at elevated temperatures. Such information is still lacking for both solder joints and bulk materials. In this study, nanoindentation technique was used to investigate the mechanical properties, namely the hardness and Young’s modulus, of the constituent phases in a near eutectic ternary SAC387 lead free solder alloy. The indentation-induced piling-up of the soft Sn phase was accounted for in the nanoindentation mechanical property calculations using a semi-ellipse method. The modified results agreed well with previous studies on similar alloys. Also, finite element simulation was used to estimate the effect of the complicated network between the eutectic Sn and the intermetallic phases on the mechanical properties acquired, which showed that the tested modulus of the intermetallic phase in the eutectic area exhibited considerable reduction. Vickers tests were also carried out at elevated temperatures, and the hardness of constituent phases dropped 35% from 25 °C to 85 °C.     

A combined SPM/NI/EDS method to quantify properties of inner and outer C-S-H in OPC and slag-blended cement pastes

To identify the distinct microstructural features and to provide insight into the mechanism by which the phases in hardened paste possess, this study adopts the coupled techniques of quantitative modulus mapping in the form of Scanning Probe Microscopy (SPM) images, nanoindentation (NI), and energy-dispersive X-ray spectroscopy (EDS) for comprehensive investigation on the chemical-mechanical-morphological properties of C-S-H gel in both ordinary Portland cement (OPC) and slag-blended cement pastes. The thickness of the inner C-S-H (IP) layer is precisely measured for the first time by modulus mapping, it varies with the types of unreacted cores as well as the addition of the supplementary cementitious materials. An interface transition zone (ITZ) is found between the unreacted C₃S grain and the surrounding inner C-S-H layer. The mechanical properties of the five types of C-S-H in OPC and the slag-blended pastes are not significantly affected by their chemical compositions. A good correlation between the storage modulus and the indentation modulus of the individual phases is found. The results indicate the significance of SPM-based modulus mapping technique as a powerful tool to characterize the phase in cementitious materials with more attractive features of higher spatial resolution.     

Evaluation of micro-mechanical properties of nonlinear cementitious composite using large-displacement transient nanoindentation analysis

Nanoindentation technique is employed for evaluation of mechanical properties of homogeneous materials at micro-level. Many engineering materials, especially cement and concrete composites, which are extensively used as building materials, exhibit phase heterogeneity and are highly porous. The presence of pores highly influences the response obtained from nanoindentation tests. In this study, mechanical properties of Calcium-Silicate-Hydrate (C-S-H), the primary binding agent in cementitious composites, are investigated using a simulated nanoindentation technique. The influence of presence of pores and its geometrical distribution on the non-linear response of C-S-H phases and the stress distribution are critically analysed.     

An improved method for the measurement of mechanical properties of bone by nanoindentation

Nanoindentation is widely used to measure the mechanical properties of bio-tissues. However, viscoelastic effects during the nanoindentation are seldom considered rigorously, although they are in general very significant in bio-tissues. In this study, a recently developed method for correcting the viscoelastic effects during nanoindentation is applied to mice bone samples. This method is found to yield reliable elastic modulus and hardness results from forelimb and femur cortical bone samples of C57 BL/6N and ICR mice. The creep properties of the samples are also characterized by a novel procedure using nanoindentation. The measured mechanical properties correlate well with the calcium content of the bone samples.     

Nanoindentation study of calcium silicate hydrates in concrete produced with effective microorganisms-based bioplasticizer

The mechanical properties of concrete produced with effective microorganisms (EM)-based bioplasticizer are investigated by means of statistical nanoindentation, and compared to the nanomechanical properties of concrete produced with ordinary superplasticizer (SP). The resort to nanoindentation enables to survey the elasticity, hardness and long-term logarithmic relaxation behavior of calcium silicate hydrates (C–S–H) after few minutes only. For each material, a cluster analysis of the experimental results yields groupings of indents likely performed on C–S–H with distinct packing densities. It is found that the addition of EM-based bioplasticizer improves the strength of C–S–H by enhancing the cohesion and friction of solid nanograins, and decreases the absolute rate of long-term relaxation. The statistical analysis of indentation results also suggests that EM-based bioplasticizer inhibits the precipitation of C–S–H of higher density. The findings of this work corroborate the results of a previous study which attributed an increase of homogeneity and a refinement of the crystalline structure of silicate phases to the effect of a biomodifier similar to EM-based bioplasticizer. The improvement of strength properties of C–S–H is also shown to coincide with a gain of compressive strength measured at the macroscale of EM-based concrete.     

Biomechanical evaluation of regenerating long bone by nanoindentation

It is crucial to measure the mechanical function of regenerating bone in order to assess the mechanical performance of the regenerating portion as well as the efficiency of the regeneration methods. In this study, nanoindentation was applied to regenerating and intact rabbit ulnae to determine the material properties of hardness and elasticity; viscoelasticity was also investigated to precisely evaluate the material properties. Both intact and regenerating bones exhibited remarkable viscoelasticity manifested as a creep behavior during load hold at the maximum load, and the creep was significantly greater in the regenerating bone than the intact bone. The creep resulted in an overestimation of the hardness and Young’s modulus. Hence, during nanoindentation testing of bones, the effect of creep should be eliminated. Moreover, the regenerating bone had lower hardness and Young’s modulus than the intact bone. The nanoindentation technique proved to be a powerful approach for understanding the mechanical properties of regenerating bone.     

Adsorbed multilayer effects on the mechanical properties in nanometer indentation depth

Nanoindentation is a powerful technique for determining the mechanical properties of a material at the nanometer scale. In this study, the changes induced in the mechanical properties of a thin film by the presence of adsorbed multilayers are examined by performing nanoindentation tests with ultra-low indentation depths. The current findings suggest that the results obtained for the mechanical properties of thin films under nanoindentation will be overestimated if the effects of the adsorbed multilayers on reducing elastic recovery between the indenter and the substrate are not taken into consideration.     

Indenter geometrical effects on sub-micro/nano indentation and scratch behaviors of polymeric surfaces

In this work, we study the indenter geometrical effects on the nanoindentation and scratch behaviors of polymers (epoxy resin and its based nanocomposites) through both experimental and numerical approaches. Two different types of indenter commonly used in nanoindentation tests, Berkovich (i.e., three-sided pyramid-shaped) and conical-shaped, are studied. An indenter (tip) geometry reconstruction procedure is presented and the results are input into finite element models to better understand the mechanisms of the geometrical effects on nanoindentation. The effect of indenter geometry on nanoscratch behavior is also investigated experimentally. Overall, our results show that the corrected Oliver and Pharr's method is applicable to nanoindentation of polymeric surfaces and the indenter geometry plays significant roles in both the nanoindentation and nanoscratch tests. The conical-shaped indenter provides slightly overestimated mechanical parameters for the polymers tested due to the material pile-up. Therefore, for nanoindentation and scratch tests, the type of indenter should always be mentioned and comparisons between tests using different types of indenter should be taken with caution.     

Static and dynamic mechanical properties of polydimethylsiloxane/carbon nanotube nanocomposites

The purpose of this study is to investigate the static and dynamic mechanical properties of polydimethylsiloxane (PDMS) and the mixture of PDMS and carbon nanotubes. The PDMS/CNT nanocomposites were stirred by an ultrasonic instrument to prevent agglomerations. The tested specimens of nanocomposites were manufactured by using the thermoforming method at 150 °C for 15 min. A micro tensile tester was adopted in this testing system with a maximum load of 500 mN and a crosshead extension of 150 mm. The static elastic modulus can be calculated by means of a tensile test and the average elastic modulus of pure PDMS is 1.65 MPa. In addition, the Nano Bionix tensile tester was also used to perform the dynamic mechanical analysis. Its dynamic frequency range is from 0.1 Hz to 2.5 KHz. The dynamic properties of PDMS/CNT nanocomposites such as storage and loss modulus can be obtained by this system. The storage modulus increased with the CNT content and also with the higher frequencies. Finally, the nanoindentation measurement system was employed to characterize the mechanical properties of PDMS and PDMS/CNTs. The measurement results of elastic modulus by a nanoindentation test have the similar trend with the results obtained by the tensile test method.     

Mechanical properties of Bi(x)Sb(2-x)Te3 nanostructured thermoelectric material

Research on thermoelectric (TE) materials has been focused on their transport properties in order to maximize their overall performance. Mechanical properties, which are crucial for system reliability, are often overlooked. The recent development of a new class of high-performance, low-dimension thermoelectric materials calls for a better understanding of their mechanical behavior to achieve the desired system reliability. In the present study we investigate the mechanical behavior of nanostructure bulk TE material p-type Bi(x)Sb(2-x)Te(3) by means of nanoindentation and 3D finite element analysis. The Young's modulus of the material was estimated by the Oliver-Pharr (OP) method and by means of numerically assisted nanoindentation analysis yielding comparable values about 40 GPa. Enhanced hardness and yield strength can be predicted for this nanostructured material. Microstructure is studied and correlation with mechanical properties is discussed.     

Property investigation of individual phases in cementitious composites containing silica fume and fly ash

In this study, nanoindentation was used to investigate the microstructures of cementitious composites containing silica fume and fly ash. With the help of scanning electron microscope, the mechanical properties (elastic modulus and hardness) of individual phases (like outer product, inner product, calcium hydroxide, remained fly ash particles, residual cement grains) in cementitious composites containing silica fume and fly ash were investigated and analyzed. Additionally, this study examined the differences between the ‘C–S–H’ phases in the different cementitious composites and provided an insight into the influence of mineral admixtures (silica fume and fly ash) on the properties of the ‘C–S–H’ phase.     

Mechanical properties of superhard boron subnitride B<Subscript>13</Subscript>N<Subscript>2</Subscript>

Microstructure and mechanical properties of bulk polycrystalline rhombohedral boron sub-nitride B₁₃N₂ synthesized by crystallization from the B–BN melt at 7 GPa have been systematically studied by micro- and nanoindentation, atomic force microscopy and scanning electron microscopy. The obtained data on hardness, elastic properties and fracture toughness clearly indicate that B₁₃N₂ belongs to a family of superhard phases and can be considered as a promising superabrasive or binder for cubic boron nitride.     

Nanomechanical investigation of the effects of nanoSiO2 on C–S–H gel/cement grain interfaces

In this paper, nanoindentation and viscoelastic modulus mapping were employed to study the influence of nanoSiO₂ on the properties of the interface between C–S–H gel and cement grains. The interface width measured by modulus mapping was around 200 nm as compared to a rough estimation of less than 5 μm by nanoindentation, due to the fact that 2 orders of magnitude increase in spatial resolution can be achieved with modulus mapping. Although the influence of nanoSiO₂ on the interface width was not significant, its impact on nanomechanical properties of the interface was marked. The data suggest an improvement of modulus and hardness of the interface by nanoSiO₂ in early age. This interface, which could be regarded as a layer surrounding cement grains, become denser by the addition of nanoSiO₂.     

Thermomechanical properties of poly(vinyl alcohol) plasticized with varying ratios of sorbitol

The objective of this work is to study the thermal and mechanical properties of films based on blends of poly(vinyl alcohol) (PVA) with different weight percent of sorbitol. Solid-state PVA/sorbitol polymer membranes were prepared by a solution casting method. The characteristic properties of these polymer membranes were examined by thermo-gravimetric analysis (TGA), differential scanning calorimetry (DSC), nanoindentation methods and by Fourier Transform Infrared (FTIR) spectroscopy. It was found that the thermal properties (glass transition, T_g, melting point, T_m and decomposition temperature, T_d) for PVA blends showed a decrease proportional to the sorbitol concentrations. The hardness and elastic modulus obtained from nanoindentation test were also found to decrease with increase in plasticizer concentration. FTIR confirmed the reduction in hydrogen bonding between PVA chains in favour of formation new bonding between the plasticizer and the PVA chains.     

Al2O3/TiO2纳米复合粉体爆炸喷涂层微结构及纳米压痕力学特性

研究了纳米复合涂层(NCC)和传统涂层(MCC)的微观结构及纳米压痕力学性能. NCC孔洞小,具有良好的均质分布特征.MCC中存在多级尺度分布的孔洞及微裂纹等缺陷, 呈现明显的非均质分布特征.NCC中大量晶界、亚晶界和微裂纹使得涂层中Al2O3基质相细化为纳米晶粒,但MCC中存在大量未熔片层颗粒.NCC和MCC具有各向异性的弹性、塑性、硬度和弹性模量.NCC比MCC相应的断面和表面具有更优良的抵抗外加负载性能、弹性恢复能力,更高的纳米压痕硬度和弹性模量.