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The siliceous structure that protects diatoms, called frustule, is the main component of diatom sedimentary soils. These particles' physical and mechanical characteristics are challenging, given their geometric conditions of only a few microns. For this evaluation, specialized tools must be used, such as the Scanning Electron Microscope (SEM), the Atomic Force Microscope (AFM) and X-ray dispersion (XRD), among others. The bibliographic references show significant variability in the "load-deformation" behavior in frustules, diatoms or their organic components. Technical background information usually presents information on a single type of species. This research demonstrated the characterization and micromechanical evaluation of frustules of three morphologically distinguishable species of diatoms (Colombian, Mexican and Peruvian origin). The results showed similarities in the chemical composition of the three samples. The displacement records are variable depending on the species for the same load range. The location of the load application points by AFM on the different types of frustules is presented. The most significant deformation in the Mexican species and the regularity in the results of the Peruvian species stand out. Young's moduli were also calculated by applying the Hertz Model, which had the highest values in the Colombian sample. [ABSTRACT FROM AUTHOR]

Over the past few years, there has been an increased focus on offshore pipeline safety due to the development of offshore oil and gas resources. Both onshore and offshore pipelines may face significant geological hazards resulting from active faults. Pre-excavated soil can be used as backfill for trenches to prevent major pipeline deformations. Since these backfill materials have been heavily remolded, they are softer than the native soil. Therefore, the difference in shear strength between the backfill and native ground may have an effect on the interaction between the pipeline and the backfill. In this paper, the pipeline–backfill–trench interaction is investigated using a hybrid beam–spring model. The P-Y curves obtained from CEL analysis are incorporated into a 3D beam–spring model to analyze the pipeline's response to lateral strike-slip faults. Additionally, the nonlinearity of pipeline materials is considered to study pipeline failure modes under strike-slip fault movements. A series of parametric studies were conducted to explore the effects of fault intersection angle, pipe diameter, buried depth of the pipe, and soil conditions on the failure modes of buckling pipelines. The developed method can be used to analyze and assess pipeline–backfill–trench interaction when subjected to strike-slip fault displacements. [ABSTRACT FROM AUTHOR]

The siliceous structure that protects diatoms, called frustule, is the main component of diatom sedimentary soils. These particles’ physical and mechanical characteristics are challenging, given their geometric conditions of only a few microns. For this evaluation, specialized tools must be used, such as the Scanning Electron Microscope (SEM), the Atomic Force Microscope (AFM) and X-ray dispersion (XRD), among others. The bibliographic references show significant variability in the “load-deformation” behavior in frustules, diatoms or their organic components. Technical background information usually presents information on a single type of species. This research demonstrated the characterization and micromechanical evaluation of frustules of three morphologically distinguishable species of diatoms (Colombian, Mexican and Peruvian origin). The results showed similarities in the chemical composition of the three samples. The displacement records are variable depending on the species for the same load range. The location of the load application points by AFM on the different types of frustules is presented. The most significant deformation in the Mexican species and the regularity in the results of the Peruvian species stand out. Young’s moduli were also calculated by applying the Hertz Model, which had the highest values in the Colombian sample.

Over the past few years, there has been an increased focus on offshore pipeline safety due to the development of offshore oil and gas resources. Both onshore and offshore pipelines may face significant geological hazards resulting from active faults. Pre-excavated soil can be used as backfill for trenches to prevent major pipeline deformations. Since these backfill materials have been heavily remolded, they are softer than the native soil. Therefore, the difference in shear strength between the backfill and native ground may have an effect on the interaction between the pipeline and the backfill. In this paper, the pipeline–backfill–trench interaction is investigated using a hybrid beam–spring model. The P-Y curves obtained from CEL analysis are incorporated into a 3D beam–spring model to analyze the pipeline’s response to lateral strike-slip faults. Additionally, the nonlinearity of pipeline materials is considered to study pipeline failure modes under strike-slip fault movements. A series of parametric studies were conducted to explore the effects of fault intersection angle, pipe diameter, buried depth of the pipe, and soil conditions on the failure modes of buckling pipelines. The developed method can be used to analyze and assess pipeline–backfill–trench interaction when subjected to strike-slip fault displacements.

This study aims to measure the pit torus and border to monitor the immediate and short-term degradation of wood surfaces after the concrete is cast and the cement hydration releases heat. The surface morphology and adhesion force curves were measured by atomic force microscopy during the treatments in saturated calcium hydroxide solutions ranging from 1 h to 27 days. The results showed that the pit torus and pit border showed different degradation processes. The adhesion force was sensitive to the type of the surface chemical components exposed during the degradation, while the surface modulus, deformation and jump-off force ratio were sensitive to the surface structural strength. The surface modulus of the pit torus degraded to 0.61–0.66 of the untreated original (95% CI) after 7-h treatments, and degraded almost completely after 48-h treatments. The surface modulus of the pit border degraded to 0.83–0.95 of the untreated original (CI) after 10 days and to 0.20–0.23 of the untreated original (95% CI) after 27 days of treatments. The treatment temperature 50 °C caused a 10-times faster degradation in the torus modulus compared to the temperature 20 °C. [ABSTRACT FROM AUTHOR]

Within the development of a novel high-throughput method for the discovery of new structural materials, a compression test on spherical micro samples is established as a short-term characterization process. In this study, the experimental investigations regarding the elastic–plastic deformation behavior of microspheres are carried out on the bearing steel X46Cr13 in 10 different heat treatment conditions. Characteristic values, so-called descriptors, can be derived directly from continuously measured force–displacement curves or are normalized by taking the sample geometry into account. In addition to micro compression tests with quasi-static loading, load increase tests are performed, in which a spherical sample is repeatedly loaded and unloaded with progressively increasing loads. Loading and unloading phases and the development of the displacement amplitude of the hysteresis are analyzed. New descriptors of load increase tests are extracted and discussed regarding their statistical significance and validity as descriptor showing a high potential for a fast characterization of the material behavior during cyclic loading. The descriptor-based micro compression test proves to be a robust method and is a promising approach for a fast evaluation of different material conditions. [ABSTRACT FROM AUTHOR]

Different retrofitting techniques have been developed and proposed to prevent the masonry infill walls (MIW) out-of-plane collapse. Many other authors confirmed that these types of elements are vulnerable when subjected to earthquake loadings, leading to several casualties and economic losses. Based on this, the present manuscript comprises an experimental campaign of flexure strength tests on small masonry walls to discuss the efficiency of textile-reinforced mortar (TRM) strengthening solutions to improve their out-of-plane behaviour. For this, eighteen flexural strength tests parallel to the horizontal bed joints were carried out. Nineteen masonry infill walls made with hollow clay horizontal brick, eight non-strengthened and the remaining ones strengthened with TRM. The tests were performed according to the EN 1052-2 standard. In this study, the effect of textile mesh (weak or strong) is analysed in parallel with the efficiency of the strengthening solutions. The results are presented and discussed in terms of force-displacement response parameters and damages observations. From the tests, it was observed that the TRM strengthening improved the flexural strength capacity up to 54% and the out-of-plane deformation ability about 7.18 times. [ABSTRACT FROM AUTHOR]

Different retrofitting techniques have been developed and proposed to prevent the masonry infill walls (MIW) out-of-plane collapse. Many other authors confirmed that these types of elements are vulnerable when subjected to earthquake loadings, leading to several casualties and economic losses. Based on this, the present manuscript comprises an experimental campaign of flexure strength tests on small masonry walls to discuss the efficiency of textile-reinforced mortar (TRM) strengthening solutions to improve their out-of-plane behaviour. For this, eighteen flexural strength tests parallel to the horizontal bed joints were carried out. Nineteen masonry infill walls made with hollow clay horizontal brick, eight non-strengthened and the remaining ones strengthened with TRM. The tests were performed according to the EN 1052-2 standard. In this study, the effect of textile mesh (weak or strong) is analysed in parallel with the efficiency of the strengthening solutions. The results are presented and discussed in terms of force-displacement response parameters and damages observations. From the tests, it was observed that the TRM strengthening improved the flexural strength capacity up to 54% and the out-of-plane deformation ability about 7.18 times.

Actual shape of the indenter is very important parameter affecting the results and interpretation of nanoindentation tests. In this study, bluntness of the tip was determined by direct (atomic force microscopy) and indirect methods (indentation into reference materials) for different states of the indenter over its lifetime. It was found that the equivalent radius depends on the used analysis method. Moreover, equivalent radius changes with the distance from indenter apex. Axisymmetric 2D sphero-conical and 3D finite element models of the indenter geometry were used to predict force-displacement curves which were compared with experiment. It was shown, that there exists a significant difference between 2D and 3D models caused by the simplifications of actual 3D shape of Berkovich indenter by sphero-conical model. The sphero-conical model can serve as good estimator of indenter bluntness and it is convenient for the description of the indenter wear throughout its lifetime. [ABSTRACT FROM AUTHOR]

Our ‘alternative’ method of determining interfacial strength parameters in the pull-out and microbond test, based on measuring the maximum pull-out force, F max , and the initial post-debonding force, F b , has been extended to the energy-based approach (estimation of the interfacial toughness, G ic , and the interfacial frictional stress, τ f ). The comparison of the G ic values calculated using the proposed method and the traditional one (using the debond force, F d , instead of F b ) for several fiber–matrix systems showed that both methods yielded very similar results. Thus, the new method can be recommended as an additional technique of G ic determination to be used instead of, or together with the traditional approach. [ABSTRACT FROM AUTHOR]

The traditional way of determining the local interfacial shear strength (IFSS), τ d , between the fiber and the matrix in microbond and pull-out test includes the measurement of the debond force, F d , at which interfacial crack initiates, and subsequent τ d calculation using the shear-lag analysis. However, for some fiber–matrix pairs the debond force, which manifests itself as a ‘kink’ in the force–displacement curve, cannot be reliably measured. We propose a new approach, based on measuring the maximum pull-out force, F max , and the initial post-debonding force, F b , which does not require the knowledge of the F d value. The comparison of the τ d values calculated for several fiber–matrix pairs using three different methods of data reduction demonstrated that the new method yielded results very similar to the traditional one. Thus, it can be recommended as an alternative technique if the debond force is indeterminable. [ABSTRACT FROM AUTHOR]

Abstract: Objectives: To determine the contact response and damage tolerance or strength degradation of a range of dental CAD/CAM ceramic materials including novel polymer-infiltrated-ceramic-network (PICN) materials by means of spherical indentations at various loads and indenter radii. Methods: The seven tested materials included Mark II, PICN test materials 1 and 2, In-Ceram Alumina, VM 9, In-Ceram YZ (Vita Zahnfabrik, Bad Saeckingen, Germany) and IPS e.max CAD, (Ivoclar Vivadent, Schaan, Liechtenstein). To evaluate the damage tolerance and role of indenter size, indentations with tungsten carbide spheres (0.5mm and 1.25mm radius) were placed on bending bars with varying loads (1.96–1000N). The indented bending bars were subsequently loaded to fracture in three-point bending. The contact induced damage was analyzed by light microscopy (LM) and SEM. The spherical contact response was measured on polished surfaces. Results: The initial strengths for the individual materials were found to reduce above specific indentation loads, which were a function of the indenter radius. Employing a 0.5mm radius sphere resulted in the following strength degrading loads and ordering of materials: VM9 (98N)

This paper continues our study on the platelet model of the pull-out specimen, in which the matrix droplet shape is approximated by a set of thin parallel disks with the diameters varying along the embedded fiber. Using this model, the fiber tensile stress and the interfacial shear stress profiles were calculated for real-shaped matrix droplets, including menisci (wetting cones) on the fibers, taking into account residual thermal stresses and interfacial friction. Then, these profiles were used to numerically simulate the processes of crack initiation and propagation in the pull-out test and to obtain theoretical force-displacement curves for specimens with different embedded lengths and wetting cone angles. Our simulations showed that the interfacial crack in real-shaped droplets initiated at very small (practically zero) force applied to the fiber, in contrast to the popular ‘equivalent cylinder’ approximation. As a result, the equivalent cylinder approach underestimated the interfacial shear strength (IFSS) value determined from the pull-out test and at the same time overestimated the interfacial frictional stress; the smaller was the wetting cone angle, the greater the difference. We also investigated the effects of the embedded fiber length and interfacial frictional stress in debonded areas on the calculated IFSS. The simulated force–displacement curves for the real-shaped droplets showed better agreement with experimental curves than those plotted using the equivalent cylinder approach. [ABSTRACT FROM AUTHOR]

We compared two models of the pull-out specimen - the 'equivalent cylinder' and the plate-let models in which the matrix droplet is represented as a set of thin parallel disks with the diameters varying along the embedded fiber to approximate the real droplet shape. Analytical expressions for the profiles of the fiber tensile stress and the interfacial shear stress have been derived for the matrix droplet in the shape of a spherical segment, including the effects of residual thermal stresses and interfacial friction. Using these expressions, we analyzed the process of crack initiation and propagation in the platelet model and investigated the effect of the specimen shape on the force-displacement curves. The interfacial stress near the loaded fiber end in the platelet model is higher than in the equivalent cylinder model, which gives rise to earlier crack initiation and smoother shape of the force-displacement curve. As a result, the calculated interfacial shear strength values may be underestimated by 10-20%, if the equivalent cylinder is used instead of the real droplet shape. A method of correction to the equivalent cylinder model in order to avoid this underestimation is proposed. [ABSTRACT FROM AUTHOR]

Abstract: Mechanical response and energy absorption of aluminium foam sandwich panels subjected to quasi-static indentation loads were investigated experimentally. These sandwich panels consisted of two aluminium face-sheets and a closed cell aluminium foam core (ALPORAS®). Quasi-static indentation tests were conducted using an MTS universal testing machine, with sandwich panels either simply supported or fully fixed. Force–displacement curves were recorded and the total energy absorbed by sandwich panels was calculated accordingly. Videos and photographs were taken to capture the deformation of top face-sheets, foam cores and bottom face-sheets. Effects of face-sheet thickness, core thickness, boundary conditions, adhesive and surface condition of face-sheets on the mechanical response and energy absorption of sandwich panels were discussed. [Copyright &y& Elsevier]

Abstract: Force–displacement curves have been obtained on two polystyrene samples, having different molecular weight, at various temperatures and probe rates using an atomic force microscope. The force–displacement curves have been analysed using a novel method, which extends continuum elastic contact theories also to the plastic deformations. The Young''s modulus and the yielding force of the two polystyrene samples have been determined as a function of temperature and frequency. It was also possible to calculate the Williams–Landel–Ferry coefficients for measurements above the glass transition temperature, and the viscoelastic activation energy for measurements below the glass transition temperature using the Arrhenius equation. All the calculated coefficients were in very good agreement with the literature values. The measured quantities span a wide range of temperature (85°C) and frequency (eight decades) and the shifts of all the quantities calculated from force–displacement curves obey the Williams–Landel–Ferry and Arrhenius equation with the same parameters. Quantitative and qualitative comparison of the Young''s modulus, of the stiffness in the plastic region and of the yielding force of the two polystyrene samples revealed different viscoelastic behaviour because of the variation in glass transition temperature of the two samples, due to their difference in the molecular weight. [Copyright &y& Elsevier]

We propose a new model for characterization of strength properties of fiber-polymer interfaces by means of a single fiber pull-out test. Our model is based on shear-lag analysis using a bilinear bond law (stress–slip relationship) which, in turn, is a simplified representation of the true stress behavior as a function of strain for cold-drawing polymers. According to this law, the fiber-polymer interface is subjected to the following successive processes: (1) linear loading within the elastic region; (2) yielding and subsequent bond strengthening with increasing strain; (3) local debonding and interfacial crack propagation along the interface; (4) post-debonding friction. Both crack propagation and extension of the yielded zone can be stable and unstable, depending on the values of interfacial parameters and the load applied to the free fiber end. The procedure of construction of theoretical force–displacement curves for a pull-out test is described in detail. Theoretical curves exhibit such features as multiple kinks and non-linear regions, whose positions and shape are related to interfacial parameters. By fitting experimental curves with theoretical ones, these parameters can be determined for each separate pull-out specimen. Practical examples are provided for basalt fiber–polypropylene and glass fiber–polypropylene specimens. [ABSTRACT FROM AUTHOR]

Poly(methyl methacrylate) (PMMA) surfaces have been modified by dynamic plowing lithography. The resulting modified structures, presenting regions of different densities and stiffnesses, have been studied by force–displacement curves. The elasto-plastic response, the stiffness, and the adhesion of the modified samples have been characterized. Force–displacement curves are able to distinguish between unmodified PMMA and two different structures resulting from the lithography, i.e. compressed PMMA and low density PMMA. In particular, the low density regions are made up of cluster-like globular particles, whose elasto-plastic response and adhesion are measured and whose contribution to the total elasto-plastic response and to the adhesion has been studied in detail. [ABSTRACT FROM AUTHOR]