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     

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.     

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.     

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.     

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.     

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.