Local Elastic Modulus Research Articles

Dynamic and quasi-static evaluation of stiffness properties of CLT: longitudinal MoE and effective rolling shear modulus

Cross-Laminated Timber (CLT) is an engineered wood product composed of solid layers of glued sawn timber. In this study, essential material stiffness parameters for CLT made from Norway spruce and Scots pine are evaluated. Specifically, the longitudinal modulus of elasticity (MoE) for longitudinally oriented layers and the effective rolling shear modulus for transversely oriented layers are the focus. By combining finite element (FE) analysis with four-point, out-of-plane bending tests using digital image correlation (DIC), a robust assessment of the effective rolling shear modulus of CLT layers is achieved. Additionally, eigenvalue analysis, applied to an FE model, along with resonance frequencies obtained from dynamic excitation of CLT, enables stable and simultaneous assessment of the dynamic longitudinal MoE and effective rolling shear modulus. Notably, while the dynamic MoE of longitudinal CLT layers is only 4% higher than the quasi-static local MoE, the dynamic effective rolling shear modulus of CLT layers is 40% higher than the quasi-static effective rolling shear modulus. This finding indicates a tangible viscoelastic behavior of wood concerning rolling shear.

Influence of Number and Strength of Hydrogen Bonds on Fracture Property and Microscopic Mechanisms of Associative Hydrogen-Bonded Polymers via Molecular Dynamics Simulation.

A coarse-grained model combining the acceptor-hydrogen-donor 3-body potential is first developed in this work to explore the fracture property and microscopic mechanisms of associative hydrogen-bonded polymers (AHBPs). Next, a triaxial deformation mode is performed to reveal that the fracture toughness of AHBPs initially improves and then is reduced as the number of active groups increases. By characterizing the stress decomposition, the strong hydrogen bond (HB) network improves the maximum stress but reduces the elongation. The destructive process of the HB network is described by quantifying the broken number and reduced energy of HBs. Interestingly, the strength of a single HB first decreases and then rises with strain. The initial decrease is mainly caused by the disruption of strong/moderate HBs, while the following rise is due to the further breakage of weak HBs and partial recovery of strong/moderate HBs. Meanwhile, the formed clusters of HBs due to the self-attraction act as the physical cross-links, whose evolution process is recorded by analyzing their number and size. Following it, the orientation degree and asphericity factor are calculated with strain to reflect the change in chain configuration, which is influenced by the HB network. Subsequently, the nucleation and growth process of voids is quantified. More than 90% of voids are nucleated in the polymer region, while others are in the HB region, which can be proved by the local elastic modulus and snapshots. The growth and coalescence rate of the voids can be suppressed by the strong HB network. Finally, the fracture toughness of AHBPs exhibits a continuous increase with improving strength of HBs due to the strong HB network. In summary, our work presents a clear and novel comprehension of the fracture property of AHBPs at the molecular scale.

Anti-Microbial Property of SiO2 or SnO2 Thin Film Coated Resin Nanostructures

Nano and micro patterns in nature show many beneficial properties. For examples, the wings of cicadas and dragonflies have sprawled with nano-sized bumps which express bactericidal and antibacterial property physically. The physical antimicrobial property is a promising new tool to combat antimicrobial resistance (AMR) bacteria. The number of deaths related to AMR infection was estimated over 70,000 which was firstly reported by O’Neil. The value increased to 1,270,000 only 4 years after that report. Therefore, new antimicrobial technologies that are not chemically driven are needed. The bactericidal mechanism of nanostructured surface is complex, but the main mechanism is attributed to the stretching effect, which means that cell membrane between the nanostructures is pulled downward and laterally. This physical stress induces reactive oxygen species (ROS) and autolytic protein activity. Sometime, sharp nanostructure could pierce the cell membrane directly. Many researchers have tried to develop materials with anti-microorganism including inorganic and organic materials. In the meanwhile, resin is fit to mass production using nano-imprint lithography (NIL), which has potential for inexpensive supply.There are some reports of antibacterial and bactericidal properties of resin nanostructures. The wettability of the substrate surface has been shown to affect bacterial adhesion and antibacterial performance. Resin surface usually shows relatively hydrophobic. Nevertheless, the hydrophilic surface would increase the number of attached cells since bacterial cell membrane had hydrophilicity, which means that the hydrophilic surface would kill bacteria because many cells attach to the nanostructures. In addition, mechanical property is also important to achieve high antibacterial performance. The higher elastic modulus resin shows the higher antibacterial performance. Therefore, it needs to tune the surface wettability and mechanical property of resin nanostructures. Even though, there is a limit to how much the resin itself can change those properties. We change the surface characteristics of resin nanostructures depositing SiO2 or SnO2 ultra-thin layer by atomic layer deposition and evaluated the anti-bacterial properties among them.Anodic Aluminum Oxide (AAO) with regular nanoholes was used as a mold to fabricate nanostructures on the surface of a resin film. The surface of an Al plate was flattened by electropolishing, and then anodized and wet-etched to fabricate regular nanoholes of AAOs with various parameters (pitch: 200 nm or 300 nm, depth: 100 nm, 150 nm and 200 nm, diameter: 100 nm and 150 nm). The nanoholes were imprinted to resin (Cyclo orefin polymer: COP) film using thermal nano-imprint lithography. Atomic layer deposition (ALD) was introduced to coat the SiO2 or SnO2 ultra-thin layer (10 nm) on the resin film to change the wettability of the surface, increase the elastic modulus. This is expected to be one of the new processes for mass production of resin nanostructures with antimicrobial properties. We evaluated the antibacterial properties with and without the thin films. In general, ALD can form atomic- or molecular-level layers in a single deposition cycle. Many ALDs need relatively high temperatures up to 100 °C, which would damage the resin. Therefore, we introduced the room-temperature atomic layer deposition method (supported by Cool ALD®) . Surface wettability was evaluated by contact angle, and elastic modulus was measured by Atomic Force Microscopy (AFM).Fig.1 shows SEM and AFM images of fabricated sample, which indicated that fine naonopillars were arranged regularly. The water contact angle (WCA) of the resin nanostructures coated with the thin film changed drastically from 130.2° to 7.2°, showing strong hydrophilicity. The local elastic modulus was larger than that without the thin film. In antibacterial tests, nanopillars coated with SiO2 layers showed antibacterial activity against E. coli; nanopillars coated with SnO2 layers were effective in antiviral tests. These results indicate that thin film coatings have great potential to increase the antibacterial and antiviral effects of polymeric nanopillar arrays. Figure 1

Influences of element M (M=Mo, Cu, and Al) on CoCrFeNiTi-based high entropy alloys by laser cladding under different process parameters

Excellent alloys were prepared to explore the effects of different additions of element M on CoCrFeNiTi-based high entropy alloys by laser cladding under different process parameters. The preset-powder method was used to prepare CoCrFeNiTi_0.5M_0.5 (M = Mo, Cu, and Al) coating in the work. The material properties of high entropy alloys were calculated based on the first principle. After that, the influence mechanism of the addition of M on the CoCrFeNiTi-based high entropy alloy was explored by experiments. The phasing standards of coatings added with M were calculated according to the first principle. It was predicted that CoCrFeNiTi_0.5Mo_0.5 coating and CoCrFeNiTi_0.5Cu_0.5 coating had high hardness and toughness, respectively. All six high-entropy alloys were stable in mechanics. The optimal process parameter coating was selected by the all-factor test based on excellent hardness and shaping quality. The results were consistent with those by theoretical calculations. The cocktail effect of high-entropy alloys was explored by analyzing the effect of different elemental additions on the overall performance of coatings. Results showed that the CoCrFeNiTi_0.5Mo_0.5 coating had high wear resistance and local elastic modulus. The friction mass loss and local elastic modulus were 0.0410 mm3 and 279.0444 GPa, respectively. The CoCrFeNiTi_0.5Cu_0.5 coating had high toughness and corrosion resistance. The resilience and free corrosion potential were 81.6473 nm and −0.730 V, respectively. The CoCrFeNiTi_0.5Al_0.5 coating had good crack resistance. Plastic storage energy was 30071.5097 × 10−15 J. Research results provided a theoretical basis for preparing high entropy alloy reinforced coatings by laser cladding.

New four-point bending test protocol for the strength grading of timber: relationship between local and global modulus of elasticity (MOE) of maritime pine

ABSTRACT This study focuses on the characterisation of maritime pine according to standards EN408 and EN384 required for timber grading. A comparison of the EN408 bending test setup is performed with a new four-point bending protocol, reducing as much as possible, the effects of the shear force in the span where the deflection is measured. The study highlights difficulties to estimate accurately, the elasticity modulus of wood by using EN408 bending test setup. This is probably due to inaccuracies in the measurements of small curvatures and due to the local heterogeneities of wood. An original four-point bending test is proposed with 75% of the span of the wood beams in pure bending. This configuration clearly exhibits the convergence of measurements, in comparison to EN408 setup. The deformations generated by this new loading protocol allow a better evaluation of the bending modulus E 0. Moreover, the study reveals that the proposed setup supplies an increase of elasticity modulus close to 20%. In addition, dynamic tests are also performed to characterise the Young’s modulus. The experimental results reveal a better agreement between static test, using the new four-point bending configuration and dynamic method, than considering EN408 as a reference.

Characterization and property prediction of fibre structures within discontinuous-fibre reinforced polymer matrix composites using 3D fibre cells assisted by contrastive learning

Fibre-cell-based fibre structure characterization approach was proposed recently to characterize the fibre distribution within discontinuous-fibre reinforced polymer matrix composites (DFR PMCs) over a 2D domain. This approach determines the distribution state of each fibre based on the relative size and topological features of its fibre cell. In this study, the fibre-cell-based approach is extended for 3D fibre domains. A convolutional neural network (CNN) encoder is trained through contrastive learning to quantitatively represent topological features of 3D fibre cells. Subsequently, the feature–property correlations are established using an artificial neural network (ANN). For practical application, the ANN is integrated with an image analysis software to provide in situ predictions of local elastic modulus of a DFR PMC based on its fibre structures observed from micro-CT images. The predictions are also compared with the experimental measurements acquired through microindentation testing, and it shows a good agreement.

On the influence of structural and chemical properties on the elastic modulus of woven bone under healing.

Woven bone, a heterogeneous and temporary tissue in bone regeneration, is remodeled by osteoblastic and osteoclastic activity and shaped by mechanical stress to restore healthy tissue properties. Characterizing this tissue at different length scales is crucial for developing micromechanical models that optimize mechanical parameters, thereby controlling regeneration and preventing non-unions. This study examines the temporal evolution of the mechanical properties of bone distraction callus using nanoindentation, ash analysis, micro-CT for trabecular microarchitecture, and Raman spectroscopy for mineral quality. It also establishes single- and two-parameter power laws based on experimental data to predict tissue-level and bulk mechanical properties. At the macro-scale, the tissue exhibited a considerable increase in bone fraction, controlled by the widening of trabeculae. The Raman mineral-to-matrix ratios increased to cortical levels during regeneration, but the local elastic modulus remained lower. During healing, the tissue underwent changes in ash fraction and in the percentages of Calcium and Phosphorus. Six statistically significant power laws were identified based on the ash fraction, bone fraction, and chemical and Raman parameters. The microarchitecture of woven bone plays a more significant role than its chemical composition in determining the apparent elastic modulus of the tissue. Raman parameters were demonstrated to provide more significant power laws correlations with the micro-scale elastic modulus than mineral content from ash analysis.

Spatial distribution of local elastic moduli in nanocrystalline metals

Elastoplastic properties of nanocrystalline metals are nonuniform on the scale of the grain size, and this nonuniformity affects macroscopic quantities as, in these systems, a significant part of the material is at or adjacent to a grain boundary. We use molecular dynamics simulations to study the spatial distributions of local elastic moduli in nanograined pure metals and analyze their dependence on grain size. Calculations are performed for copper and tantalum with grain sizes ranging from 5 to 20 nm. Shear-modulus distributions for grain and grain-boundary atoms were calculated. It is shown that the noncrystalline grain boundary has a wide shear-modulus distribution, which is grain-size independent, while grains have a peaked distribution, which becomes sharper with increasing grain size. Average elastic moduli of the bulk, grains, and grain boundary are calculated as a function of grain size. The atomistic simulations show that the reduction of total elastic moduli with decreasing grain size is mainly due to a resulting larger grain-boundary atoms fraction, and that the total elastic moduli can be approximated by a simple weighted average of larger grain elastic moduli and a lower grain-boundary elastic moduli. Published by the American Physical Society 2024

Investigation of Flexural Strength of African Copalwood (Daniella Oliveri) as Reinforcement in Concrete Slab

This study investigates the potential of African Copalwood as a reinforcing material in concrete slabs. The timber rods were randomly selected from the timber market because there is always variation in timber properties with position in stem, location and soil condition. Various test specimen were prepared according to the Code of practices BS EN 408:2003 using structural size specimens. Thirty (30) slabs of size 75 mm x 300 mm x 700 mm were cast in five sets (1 to 4%) for Timber-reinforced concrete slab (TRCS) and Steel-reinforced slab (SRS) with a mix ratio of 0.5:1:2:4 denoting water-cement ratio, cement, fine and coarse aggregate respectively. Longitudinal bars were varied in 1% to 4% slab cross-sectional area in different TRCS samples while the transverse bar was restricted to be 3% by standard and made constant in all the slab samples specimen. A 10 mm diameter steel bar is used as reinforcement in the SRS. Findings revealed that the mean failure stress for Tensile strength parallel to grain was 41.80 N/mm2, Bending strength parallel to grain was 37.05 N/mm2, Compression parallel to grain was 13.48 N/mm2, Compression perpendicular to grain was 8.88 N/mm2, Local Modulus of Elasticity (MOE) was 3800.17 N/mm2, Apparent MOE was 59.42 N/mm2. Also, with regards to TRCS, the flexural strength test at 28 days for 1% to 4% reinforcement in concrete slabs is 3.61, 5.29, 5.49 and 7.22 N/mm2 respectively. The SRS has a flexural strength of 11.54 N/mm2 at 87.5% composition in slabs. These findings indicate enhancement in the strength properties of the concrete slabs with the incorporation of the African Copalwood reinforcement.

Homogeneous films from amphiphilic hyaluronan and their characterization by confocal microscopy and nanoindentation

Self-supporting films from amphiphilic hyaluronan are suitable for medical applications like wound dressings or resorbable implants. These films are typically cast from water/alcohol solutions. However, when the mixed solvent evaporates in ambient air, convection flows develop in the solution and become imprinted in the film, potentially compromising its properties. Consequently, we developed a novel film manufacturing method: drying in a closed box under saturated vapour conditions. Using this approach, we prepared a series of optically clear lauroyl-hyaluronan (LHA) films with uniform thickness and compared them to their air-dried counterparts. We first evaluated swelling ratios and elastic moduli for LHA films with varying degrees of substitution. The box-dried films swelled significantly less and were 1–2 orders of magnitude stiffer than air-dried films from the same LHA sample. Confocal microscopy revealed that box-dried films exhibited a regular microstructure, while air-dried films displayed a pore-size gradient and strong microstructure modulation due to convection flows. Local elastic modulus variations arising from these microstructures were assessed using nanoindentation mapping. Importantly, achieving the desired film stiffness requires much lower polymer modification when box-drying is used, enhancing the biological response to the material. These findings have implications for all polysaccharide formulations that utilize mixed solvents.

Understanding tightened muscle in knee osteoarthritis and the impacts of Fu's subcutaneous needling: A pilot trial with shear-wave elastography and near-infrared spectroscopy.

Given the scarce reports on the interplay between Fu's subcutaneous needling (FSN), tightened muscle, and therapeutic effects, we developed a clinical research protocol to synchronously collect data on clinical efficacy and muscle characteristics in patients with knee osteoarthritis, exploring the mechanism of FSN action. The primary aim was to assess the feasibility and safety of this protocol, guiding future trials and their sample size calculations. In this prospective, single-blind, self-controlled study, 19 patients with early to mid-stage unilateral knee osteoarthritis underwent FSN therapy on both knees over 1 week (4 sessions, every other day). We measured local elastic modulus, muscle thickness, blood flow volume, and oxygen consumption rate of bilateral vastus lateralis muscles using shear-wave elastography and near-infrared spectroscopy (NIRS) before and after the first and fourth treatments. Additionally, real-time NIRS indicators (oxygenated hemoglobin [O2Hb], deoxyhemoglobin [HHb], total hemoglobin [THb], and tissue saturation index [TSI]) were recorded during these treatments. Pain intensity (visual analogue scale [VAS]), functional status (Western Ontario and McMaster Universities Osteoarthritis Index [WOMAC]), and active range of motion were evaluated before these treatments. All 19 participants completed the trial without serious adverse events. After 3 FSN treatments, significant changes were observed in VAS and WOMAC scores (VAS: P < .001; WOMAC: P < .001), and knee flexion (P < .001) and external rotation (P = .02), except for internal rotation. No meaningful significant differences were observed in muscle characteristics at baseline or between pre- and post-treatment periods. NIRS results during treatments indicated significant increases in local O2Hb and THb post-FSN therapy (First treatment: O2Hb: P = .005; THb: P = .006. Fourth treatment: O2Hb: P = .002; THb: P = .004); however, no significant increases were observed for HHb (First treatment: P = .06; Fourth treatment: P = .28). No linear correlation was found between therapeutic effects and changes in tightened muscle indices. FSN reduces pain and improves joint function in knee osteoarthritis, while also enhancing blood flow and oxygenation in the vastus lateralis muscle of the affected side. Further revisions of this protocol are warranted based on our insights.

Nanoindentation Hardness and Modulus of Al2O3–SiO2–CaO and MnO–SiO2–FeO Inclusions in Iron

AbstractOxide inclusions appear in steel as a subproduct of steelmaking. These are generally detrimental to alloy properties; however, variations exist in the extent to which different inclusions are harmful because their properties vary as a function of their chemical composition. We use nanoindentation to measure the local elastic modulus and hardness of individual oxide particles, produced by precipitation within liquid iron, that belong to the systems Al2O3–SiO2–CaO and MnO–SiO2–FeO. Measured inclusion hardness values are typically in the range of 8 to 13 GPa and can reach 26 GPa for alumina-rich inclusions. Calcium aluminates rich in alumina are significantly stiffer than iron, with elastic moduli that can reach 350 GPa. On the contrary, calcium aluminates that are expected as a result of successful calcium treatment (i.e., with less than about 80 wt pct Al2O3 content) have elastic moduli below that of iron. This is also the case for the wide range of calcium aluminosilicates and of manganese silicates studied here. In addition, silicates containing about 70 to 80 wt pct MnO are observed to have a fine multiphase structure and an elastic modulus of ≈ 180 GPa. Those inclusions thus emerge as possible candidates if one aims to minimise, in loaded steel, stress concentrations associated with matrix-inclusion elastic mismatch.

Long-range correlations in elastic moduli and local stresses at the unjamming transition.

We explore the behaviour of spatially heterogeneous elastic moduli as well as the correlations between local moduli in model solids with short-range repulsive potentials. We show through numerical simulations that local elastic moduli exhibit long-range correlations, similar to correlations in the local stresses. Specifically, the correlations in local shear moduli exhibit anisotropic behavior at large lengthscales characterized by pinch-point singularities in Fourier space, displaying a structural pattern akin to shear stress correlations. Focussing on two-dimensional jammed solids approaching the unjamming transition, we show that stress correlations exhibit universal properties, characterized by a quadratic p2 dependence of the correlations as the pressure p approaches zero, independent of the details of the model. In contrast, the modulus correlations exhibit a power-law dependence with different exponents depending on the specific interaction potential. Furthermore, we illustrate that while affine responses lack long-range correlations, the total modulus, which encompasses non-affine behavior, exhibits long-range correlations.

Mechanical Resistance of the Largest Denticle on the Movable Claw of the Mud Crab.

Decapod crustaceans have tooth-like white denticles that are present only on the pinching side of the claws. In the mud crab, Scylla serrata, a huge denticle exists on the movable finger of the dominant claw. This is mainly used to crush the shells of the crab's staple food. The local mechanical properties, hardness (HIT) and elastic modulus (Er), of the peak and valley areas of the largest denticle were examined via a nanoindentation test. The microstructure and elemental composition were characterized using a scanning electron microscope and energy-dispersive X-ray spectroscopy. The striation patterns originating from a twisted plywood structure parallel to the surface were visible over the entire denticle. Most of the largest denticle was occupied by a hard area without phosphorus, and there was a soft layer corresponding to the endocuticle with phosphorus in the innermost part. The HIT of the denticle valley was about 40% lower than that of the denticle peak, and the thickness of the soft endocuticle of the denticle valley was five times thicker than that of the denticle peak. The HIT-Er map showed that the abrasion resistance of the denticle surface was vastly superior and was in the top class among organisms. The claw denticles were designed with the necessary characteristics in the necessary places, as related to the ecology of the mud crab.

Gradient porous structures of mycelium: a quantitative structure–mechanical property analysis

Gradient porous structures (GPS) are characterized by structural variations along a specific direction, leading to enhanced mechanical and functional properties compared to homogeneous structures. This study explores the potential of mycelium, the root part of a fungus, as a biomaterial for generating GPS. During the intentional growth of mycelium, the filamentous network undergoes structural changes as the hyphae grow away from the feed substrate. Through microstructural analysis of sections obtained from the mycelium tissue, systematic variations in fiber characteristics (such as fiber radii distribution, crosslink density, network density, segment length) and pore characteristics (including pore size, number, porosity) are observed. Furthermore, the mesoscale mechanical moduli of the mycelium networks exhibit a gradual variation in local elastic modulus, with a significant change of approximately 50% across a 30 mm thick mycelium tissue. The structure-property analysis reveals a direct correlation between the local mechanical moduli and the network crosslink density of the mycelium. This study presents the potential of controlling growth conditions to generate mycelium-based GPS with desired functional properties. This approach, which is both sustainable and economically viable, expands the applications of mycelium-based GPS to include filtration membranes, bio-scaffolds, tissue regeneration platforms, and more.

Influences of Ti and Mo alloying on the microstructure and properties of laser cladding for CoCrFeNi high-entropy alloys

The CoCrFeNiTi_(1-x) Mo_x high-entropy-alloy coating was prepared using a powder presetting method. The work investigated the influences of Ti and Mo addition on the microstructure and properties of CoCrFeNi high-entropy alloys. The first-principles calculation showed that CoCrFeNiTi_(1-x) Mo_x was mainly composed of the FCC phase, BCC phase, and IMCs. The coating exhibited high hardness, and the mechanical stability of the high-entropy alloys of FCC and BCC phases was maintained when x = 0.5. The coating primarily consisted of FCC, BCC, σand CoTi2 phases when x ≤ 0.75. The coating primarily consisted of FCC, BCC, σand Co2Mo3 phases when x = 1. It exhibited high microhardness, elastic modulus, elastic stiffness, and wear resistance when x = 0.5. Its average microhardness, local elastic modulus, and elastic stiffness were 873.28 HV0.5, 265.5606 GPa, and 102.8008 GPa, respectively. Besides, COF and the wear mass loss were 0.7026 mm3 and 0.0410 mm3, respectively. The coating exhibited exceptional corrosion resistance with a self-corrosion voltage of −0.700 V and a self-corrosion current of 5.387e-007 A when x = 1. The results offer practical guidance for preparing high-entropy-alloy coatings with various advantages as well as a theoretical foundation for preparing such alloys by laser cladding.

A novel approach to measuring local mechanical properties via photothermal excitation of an atomic force microscope probe using an optical pump–probe inspired design

Obtaining and improving measurements of mechanical properties at the nanoscale has been made possible through the continuous advancement of atomic force microscopy (AFM) techniques over the past several decades. Among these advancements include implementing multifunctional AFM probes and developing new detection schemes that enable sensitivity to local mechanical properties. In this work, we demonstrate a proof-of-concept for a detection scheme that enables a standard AFM configuration to produce qualitative local mechanical property maps through the use of an optical pump–probe scheme, alleviating a common requirement of incorporating additional piezoelectric actuators. Data from this work are presented for silicon carbide and epitaxially grown graphene on silicon carbide. Through preliminary analysis of resonant frequency maps acquired through dual-frequency resonance tracking, the local stiffness and elastic modulus can be estimated at each point. This work contributes to the field of scanning probe microscopy by providing a new opportunity for AFM systems that are not currently equipped for a mechanical mode to obtain local mechanical property data.

Grading of recovered Norway spruce (Picea abies) timber for structural purposes

An increasing amount of timber is recovered from demolition and can be value-added through reuse or recycling for structural applications. This study investigates the possibilities of using visual and non-destructive parameters to estimate the mechanical properties of recovered timber so that it can be graded for new applications. A batch of nineteen recovered Norway spruce (Picea abies (L.) Karst.) rafters was studied. The application of two visual grading standards produced a rejection of 95% of the specimens. Estimation of modulus of elasticity was performed using ultrasound and vibration NDT techniques, with determination coefficients (R2) of 0.66 and 0.75 respectively. In the case of bending strength estimation, R2 were 0.60 and 0.77 respectively. Visual knottiness parameter was only a statistically significant variable in the estimation model of local modulus of elasticity. Density was estimated using drilling chips extraction and drilling penetration resistance with R2 of 0.66 and 0.58 respectively.

The Constituent Phases and Micromechanical Properties of Steel Corrosion Layers Generated by Hyperbaric-Oxygen Accelerated Corrosion Test.

Hyperbaric oxygen-accelerated corrosion testing (HOACT) is a newly developed method to study in the labor the corrosion behavior of steel bars in concrete. This work aimed to intensively investigate the mechanical properties and microstructures of HOACT-generated corrosion products by means of nano-indentation tests, Raman micro-spectrometry, and scanning electron microscopy. The local elastic modulus and nanohardness varied over wide ranges of 6.8-75.2 GPa and 0.38-4.44 GPa, respectively. Goethite, lepidocrocite, maghemite, magnetite, and akageneite phases were identified in the corrosion products. Most regions of the rust layer were composed of a complex and heterogeneous mix of different phases, while some regions were composed of maghemite or akageneite only. The relationship between the micromechanical properties and typical microstructural features is finally discussed at the micro-scale level. It was found that the porosity of corrosion products can significantly influence their micromechanical properties.

Experimental characterisation of the local mechanical behaviour of cellulose fibres: an in-situ micro-profilometry approach

The accurate mechanical characterisation of fibres of micrometric length is a challenging task, especially in the case of organically-formed fibres that naturally exhibit considerable irregularities along the longitudinal fibre direction. The present paper proposes a novel experimental methodology for the evaluation of the local mechanical behaviour of organically-formed (aged and unaged) and regenerated cellulose fibres, which is based on in-situ micro-tensile testing combined with optical profilometry. In order to accurately determine the cross-sectional area profile of a cellulose fibre specimen, optical profilometry is performed both at the top and bottom surfaces of the fibre. The evolution of the local stress at specific fibre locations is next determined from the force value recorded during the tensile test and the local cross-sectional area. An accurate measurement of the corresponding local strain is obtained by using Global Digital Height Correlation (GDHC), thus resulting in multiple, local stress–strain curves per fibre, from which local tensile strengths, elastic moduli, and strains at fracture can be deduced. Since the variations in the geometrical and material properties within an individual fibre are comparable to those observed across fibres, the proposed methodology is able to attain statistically representative measurement data from just one, or a small number of fibre samples. This makes the experimental methodology very suitable for the mechanical analysis of fibres taken from valuable and historical objects, for which typically a limited number of samples is available. It is further demonstrated that the accuracy of the measurement data obtained by the present, local measuring technique may be significantly higher than for a common, global measuring technique, since possible errors induced by fibre slip at the grip surfaces are avoided.