Specimen Preparation Methods Research Articles

Empirical Model for Shear Strength of Artificial Rock Containing a Single Nonpersistent Joint

Abstract This paper proposes an empirical equation to evaluate the shear strength of rock mass with nonpersistent joints. A novel specimen preparation method is proposed and is used to created plas...

Optimizing the SEM specimen preparation method for accurate microanalysis of carbon nanotube/nanocluster hybrids.

Scanning electron microscopy (SEM) integrated with energy-dispersive X-ray spectrometry (EDS) are scientifically used to characterise the morphology, chemical composition and elemental distribution of powder samples. Upon an accessible analytical instrument, the specimen preparation method directly affects the quality and accuracy of the observation and analysis. In this paper, three preparation methods were utilised to characterise the carbon nanotubes (CNTs) based materials, and their strengths as well as the limitations are discussed. Thus, a characterisation strategy was established by comparing the obtained three measurement together with the derived sample information. To the end, we proposed to acquire the backscattered electron (BSE) images of nanoscale heavier nanoclusters grafted CNTs, typically for wide functional applications such as energy conversion and storage. Our proposed optimum method works particularly on the clarification of powder samples with small particle sizes and low atomic numbers, which underscores the involved contribution of SEM backscattered electron images.

Nanomechanical testing of freestanding polymer films: in situ tensile testing and Tg measurement

A method for small-scale testing and imaging of freestanding, microtomed polymer films using a push-to-pull device is presented. Central to this method was the development of a sample preparation technique which utilized solvents at cryogenic temperatures to transfer and deposit delicate thin films onto the microfabricated push-to-pull devices. The preparation of focused ion beam (FIB)-milled tensile specimens enabled quantitative in situ TEM tensile testing, but artifacts associated with ion and electron beam irradiation motivated the development of a FIB-free specimen preparation method. The FIB-free method was enabled by the design and fabrication of oversized strain-locking push-to-pull devices. An adaptation for push-to-pull devices to be compatible with an instrumented nanoindenter expanded the testing capabilities to include in situ heating. These innovations provided quantitative mechanical testing, postmortem TEM imaging, and the ability to measure the glass transition temperature, via dynamic mechanical analysis, of freestanding polymer films. Results for each of these mentioned characterization methods are presented and discussed in terms of polymer nanomechanics.Graphic

Quantitative nuclear DNA content and cell cycle analysis of a mixotrophic dinoflagellate by image cytometry

AbstractThe goal of this work was to develop and demonstrate the utility of microscope‐based image cytometry (ICM) as a method for quantifying nuclear DNA content and cell cycle phase distribution in microalgae both in culture and in natural blooms, as an alternative to flow cytometry (FCM). To do so, aliquots from the same samples of the dinoflagellate Karlodinium veneficum were examined using both ICM and FCM. ICM specimen preparation and data acquisition methods were optimized to improve precision and agreement between the two techniques. Accuracy and precision of DNA measurements by ICM were significantly higher using the DNA fluorophore DAPI compared to SYBR® Green I. Milli‐Q H2O was found to be superior to Tris‐EDTA as a staining and slide preparation solution for ICM analyses. Lower‐powered objective magnification (10x, 20x) in image acquisition for ICM produced higher precision in nuclear DNA measurements. Overall precision of ICM analysis of DAPI‐stained K. veneficum cells was comparable to FCM, with respective 1C DNA peak coefficients of variation as low as 6.2%. Cell cycle distributions of mid‐log culture samples analyzed by both ICM and FCM were in agreement (two‐way ANOVA; p = 0.93); while distributions analyzed in a field sample were similar but not identical (Z‐test; p < 0.001). Overall, the results show the feasibility of ICM as a useful tool for microalgal cell cycle analysis, with the potential for more flexible application to mixotrophic/phagotrophic species and complex field populations.

An improved specimen preparation method for marine shallow gas-bearing sand sediments and its validations

Instabilities of shallow gas-charged seabed are potential geological hazards in ocean engineering. In practice, the conventional field sampling techniques failed to obtain undisturbed gas-bearing sediments from the seabed for laboratory mechanical testing because of sensitive gas exsolution and escape from sediments. However, preparation of representative remoulded gas-charged specimens is a challenging issue, because it is rather difficult to quantitatively control the gas content and obtain uniform distribution of gas bubbles within the specimen. Given the above problems, this work proposes a reliable approach to reconstitute the high-saturation specimen of gas-charged sediments in the laboratory by an improved multifunction integrated triaxial apparatus (MITA). This apparatus is developed based on an advanced stress path triaxial system by introducing a temperature-controlled system and a wave-monitoring system. The temperature-controlled system is used to accurately mimic the in situ environments of sediments in the seabed. The wave-monitoring system is utilized to identify exsolution point of free gas and examine the disturbance of gas to specimens during gas exsolution. The detailed procedure of gassy specimen preparation is introduced. Then, the quality of prepared specimens using our improved apparatus is validated by the high-resolution micro-X-ray computed tomography (μCT) scanning test, from which bubble occurrence and size distribution within the gassy sand specimen can be obtained; and preliminary mechanical tests on gassy sand specimens with various initial saturation degrees are performed. The proposed specimen preparation procedure succeeds in proving the postulated occurrence state of gas bubbles in coarse-grained sediments and accurately controlling the gas content.

Assessment of tamping-based specimen preparation methods on static liquefaction of loose silty sand

Dry and moist tamping methods are widely used for the investigation of sandy soil liquefaction. However, the effect of these two tamping-based reconstitution methods on composite soil liquefaction behavior have been rarely assessed. In this study, the dry and moist tamping methods were assessed using loose silica sand matrix (HN31) containing various amounts of non-plastic silt particles (C500), and by performing a series of undrained triaxial compression tests. Microstructural observations using a high-resolution optical microscope were also performed on loose silty sand specimens that had the similar initial states to those for the undrained triaxial tests. Triaxial results show that for silty sand specimens prepared by dry tamping method, a global dilatant behavior was observed and the undrained shear strength decreased as the fraction of silt particles increased. By contrast, a total reversed phenomenon was observed for those prepared by moist tamping method: all specimens showed more or less limited liquefaction behavior and silt particles mitigated the contractive tendency, which provided beneficial contribution to the undrained shear strength. Microstructural observations show that in the dry tamping method, overall structure formed by the host sand and silt particles was regularly deposited, promoting a more stable strain-hardening response. Moreover, some silt particles were found to be located near sand-sand contact points, significantly loosening the sand matrix. On the contrary, by using moist tamping method, the sand was uniformly covered by bulked silt particles, and the aggregated sand formed the metastable structure, facilitating the occurrence of static liquefaction. Moreover, with the increase of fines fraction, this metastable structure was weakened, characterized by the filling of large inter-sand voids, leading to the increase of undrained shear strength. Thus, a critical value of total fines fraction FcTot equalling to 21% was determined, which theoretically verified the insignificant effect of specimen preparation methods on the undrained shear strength. In that case, the metastable structure in specimen prepared by moist tamping method was expected to disappear and the overall response of specimen changed from the dominance of host sand to that of fines.

Study on influencing factors of unconfined penetration test based on orthogonal design

Tensile strength is one of the most important mechanical parameters controlling the development of cracks in loess plateau. The unconfined penetration test (UPT) is often used as an index for prediction of soil tensile strength properties. However, suffering the influence of the experiment condition, its uncertainty and sensitivity analysis to various experiment parameters was still unknown. Therefore, this study designed orthogonal tests and conducted the sensitivity analysis of influence factors (water content, dry density, steel disk (punch) diameter, height-diameter ratio, specimen preparation method, and loading rate) on the tensile strength of loess by using UPT. The statistical analysis of the test results indicated the order that affects tensile strength of the loess was water content, disk diameter, dry density, sample preparation method, height to diameter ratio, and loading rate respectively. The tensile strength of loess presented a tendency to increase at first and afterward to decrease as the increase of the punches diameter in UPT. The tensile strength reached a maximum value for a 24.72-mm disk diameter. According to the failure mode of the specimen, 12.3 to 20.5 times height-diameter ratio punches diameter range was considered appropriate. Furthermore, in the reconstituting specimen preparation method of disturbed loess, positive and reverse static pressure method was beneficial to the gain on the tensile strength. Maintaining a 1-mm/min loading rate, the variance of tensile strength was optimal. Moreover, the interactions of factors had significant effects on the tensile strength in UPT. The achieved results can provide the references and analytical analysis for standardizing UPT to measure the loess tensile strength.

Study on mechanical properties of 3D printed rock mass samples with photosensitive resin material

3D printing technology can provide an effective method for specimen preparation of rock mass, but the mechanical properties of 3D printed rock mass still need to be further studied. In this paper, uniaxial compression tests are carried out on the intact and jointed rock mass models which are printed by laser rapid prototyping printer with photosensitive resin materials, stress-strain curve and fracture propagation are obtained, and the mechanical properties of 3D printed rock mass are studied. The results show that the intact model of the photosensitive resin material has greater plasticity and stress hardening after the peak strength, while the jointed models have obvious brittle mechanical characteristics, but in general, plastic deformation occurs before brittle failure; that the joint dip angle has an important influence on the physical parameters such as the peak strength of the model, strain at brittle fracture, elastic modulus, and the crack propagation; and that photosensitive resin material can simulate rock fracture, but it is not as good as natural rock or rock-like material. The research results can be used for reference in the study of mechanical properties of photosensitive resin and its application in 3D printing for rock mass.

Study on influencing factors of void fraction of asphalt mixture based on grey correlation

grey relational analysis method has been widely used because it is applicable to small samples, irregular samples and has a small amount of calculation. For the study of shear compaction forming factors affecting air void of asphalt mixture, this paper studies a set of shear compaction meter uniform specimen preparation methods, and based on this through the grey relation analysis method the study type of asphalt, asphalt content, shear compaction times and fine aggregate level matching specimen void fraction, and it is concluded that the factors impact on the specimen void fraction size. The results show that the grey correlation method is an analytical method suitable for studying the influencing factors of the voidage of asphalt mixture. Among the influencing factors, the shear compaction times, the ratio of oilstone and the mass fraction of particle size <0.075mm are the three main factors affecting the voidage of shear compaction specimens. The research results have certain guiding significance for asphalt mixture design and construction quality control.

Influence of Specimen Preparation on the Liquefaction Behaviors of Sand and Its Mesoscopic Explanation

AbstractSpecimen preparation methods and the resulting fabric can significantly influence the mechanical behavior of sand. To clarify the influence of specimen preparation methods on liquefaction b...

Polymer-assisted TEM specimen preparation method for oxidation-sensitive 2D materials

By structural and analytical TEM and scanning electron microscopy experiments we show that atomically-resolved structural characterization of oxidation-sensitive two-dimensional material is strongly hindered when the final step of the preparation process, the transfer to the TEM grid, is performed with a wet etching method involving bases or acids, interacting with the highly reactive sample surface. Here we present an alternative polymer-assisted and mechanical-exfoliation-based sample preparation method and demonstrate it on selected oxidation-sensitive transition metal phosphorus trisulfides and transition metal dichalcogenides. The analysis, obtained from the samples prepared with both of the methods clearly show that oxidation is the origin of discrepancy, the oxidation during the final preparation step is strongly reduced only when the new method is applied, and atomically-resolved structural characterization of the pristine structures is now possible.

An optimized TEM specimen preparation method of quantum nanostructures

Electron transparent TEM lamella with unaltered microstructure and chemistry is the prerequisite for successful TEM explorations. Currently, TEM specimen preparation of quantum nanostructures, such as quantum dots (QDs), remains a challenge. In this work, we optimize the sample-preparation routine for achieving high-quality TEM specimens consisting of SrRuO3 (SRO) QDs grown on SrTiO3 (STO) substrates. We demonstrate that a combination of ion-beam-milling techniques can produce higher-quality specimens of quantum nanostructures compared to TEM specimens prepared by a combination of tripod polishing followed by Ar+ ion milling. In the proposed method, simultaneous imaging in a focused ion-beam device enables accurate positioning of the QD regions and assures the presence of dots in the thin lamella by cutting the sample inclined by 5° relative to the dots array. Furthermore, the preparation of TEM lamellae with several large electron-transparent regions that are separated by thicker walls effectively reduces the bending of the specimen and offers broad thin areas. The final use of a NanoMill efficiently removes the amorphous layer without introducing any additional damage.

In-situ SEM based method for assessing fiber-matrix interface shear strength in CFRPs

Accurate assessment of fiber-matrix interface shear strength may play key role in understanding structural strength behavior of polymer-matrix composites, and provide additional flexibility for enabling high-performing material designs. This work presents a method for assessment of fiber-matrix interface strength in carbon fiber reinforced polymers (CFRPs). The method uses in-situ scanning electron microscopy (SEM) imaging while pushing individual fibers out of 20–30 μm thick membranes. Femtosecond laser machining has been utilized to address standing challenges associated with manufacturing high-quality fiber push-out specimens. To ensure that the specimen preparation method used did not affect the properties of the composite, a thorough study has been conducted using benchmark specimens. The benchmark specimens are prepared using a conventional lapping/polishing process. Results for two CFRPs compare fiber-matrix interface shear strength generated using free-standing samples (conventional lapping/polishing preparation) and femtosecond laser-machined specimens. Both specimen types exhibit similar strength. However, load-displacement response of the free-standing samples is overly compliant, representing specimen response rather than fiber-matrix interface material behavior. The excessive compliance is caused by inherent imperfections in the contact of the sample and the test fixture. The femtosecond laser-machined samples are free of such imperfections. Finite element analysis has been accomplished to better understand the load-displacement response.

A Novel, Efficient Method for Otolith Specimen Preparation Using UV‐Cured Resins

AbstractOtoliths are calcified structures that are located in the inner ears of fish, as in most vertebrates, that are responsible primarily for the perception of gravity, balance, and movement and secondarily of sound detection. Microstructural and chemical analyses of the inner otolith growth layers, called increments, constitute powerful tools for estimating fish age and elucidate many life history and demographic traits of fish populations. Otolith analyses often require the production of a thin cross section that includes the otolith core and all increments formed from birth (core) until the moment of collection (otolith edge) in the same plane of view. Here we report on the suitability of single‐component UV‐cured resins to obtain otolith cross sections for both microstructural examination and chemical analysis by electron probe microanalysis. Embedding blocks that were produced with UV‐cured resins had transparency that was comparable to that of the commonly used two‐component epoxy resins and provided similar adhesion and mechanical support for the otoliths during grinding or cutting with a precision cutter and analysis. In addition, UV‐cured resins offer on‐demand, extremely rapid (minute‐order) hardening that makes them useful in classroom situations in which time for otolith embedding becomes a constraint.

Effect of Specimen Preparation on Volumetric Behavior of Sands under Cyclic Multidirectional Shear

Abstract Laboratory specimen preparation methods can significantly influence the dynamic shear-induced volumetric response of sands. In this study, a medium dense to very dense Ottawa sand (relative density, DR = ∼60–95 %) was systematically tested using a multidirectional cyclic direct simple shear device to evaluate the influence of specimen preparation on drained cyclic volumetric strain. Both unidirectional and bidirectional cyclic loads were applied to specimens created using four preparation techniques: dry funnel deposition, dry soil raining, dry funnel deposition followed by table vibrations, and dry funnel deposition followed by cyclic shearing. The results indicate that as DR increases, the effect of specimen preparation on volumetric strain decreases. Specifically, the results illustrate that volumetric strain of medium dense sand (DR = 57–74 %) is affected by specimen preparation, which is consistent with the literature. In contrast, dense to very dense specimens (DR &amp;gt; 80 %) exhibited comparable volumetric strain independent of the specimen preparation method. This observation is consistent for both unidirectional and bidirectional cyclic loading.

Effect of specimen gauge reduction on uniaxial tension properties of reinforcing steel

The Standard Test Methods for Tension Testing of Metallic Materials (ASTM E8) mandates a specimen gauge reduction for obtaining the tensile properties of reinforcing steel bars. The standard outlines the specimen preparation requirements and methods to ensure that test results well represent the material properties. On the other hand, some codes differ regarding the approach to specimen preparation. They do not apply gauging, for both deformed and plain steel bars. Thus, the effect of specimen gauge reduction on the tensile properties of reinforcing steel bars was evaluated, and the interconnection of properties to the layer hardness was analysed. The experiment governed a range of deformed hot-rolled bar sizes, tested in tension using precision instruments. The Rockwell hardness test was implemented layerwise on the specimen’s cross section, and the hardness number (HRC) was measured as a function of the layer distance to the centre. A finite element model was constructed to study the stress concentrations induced by a constant indentation, simulating the HRCs, and to numerically construct the stress–strain relationship of ungauged steel bars based on the core properties and the section HRC relationship. Scanning electron microscopy readings were performed to visually and chemically justify the results. It was shown that the specimen gauge reduction significantly influenced the resulting stress–strain behaviour of the material, and the yield and ultimate strengths were reduced. It was also demonstrated that the hardness response is proportional to the distance to the specimen’s axes. The corresponding yield and ultimate strengths thus increased accordingly, from the inner to the outer layers of the bar. Testing a gauged specimen will therefore result in lower strength than that of an ungauged steel bar.

Relating shear-induced evolution in topology of pore networks to sand specimen response

The shear behaviour of sands is investigated through laboratory testing on reconstituted sand specimens and three-dimensional (3D) digital image-based quantitative characterisation of the topology of pore networks. Specimens prepared using air pluviation and moist tamping methods are subjected to axial compression testing. After shearing, the specimens/microstructures are preserved using a resin impregnation process. Subsequent serial sectioning and image acquisition using bright-field microscopy and image stitching when combined with image montage stacking yield a reconstructed 3D high-fidelity digital microstructure. This paper introduces a computational microstructure tool for analysing geometrical tortuosity of pore structures spatially based on topological skeleton extraction, graph theory and a shortest-path searching algorithm. The tool allows for the tortuous attributes of the highly intricate, heterogeneous pore structure to be evaluated which in turn describes all existing convoluted pathways available for pore-scale transport. Shearing response and strain localisation phenomenon are shown to be influenced by the specimen preparation method as well as the mechanical loading condition. The distribution of pore tortuosity provides new insights into the microstructural evolution induced by shearing which is also closely correlated with the inherent variations in the microstructures.

Values of different specimen preparation methods for the diagnosis of lung cancer by endobronchial ultrasound guided transbronchial needle aspiration

BackgroundEndobronchial ultrasound guided transbronchial needle aspiration (EBUS-TBNA) has been become an important procedure for the diagnosis and staging of lung cancer. Our research identified the effects of different pathological preparation on the diagnosis of lung cancer for specimens obtained by biopsy.MethodsPatients were clinically considered if lung cancer was accompanied by mediastinal or hilar lymph node enlargement between March 2014 and November 2017. Specimens obtained by EBUS-TBNA were treated by three methods: traditional smear cytology, liquid-based cytology (LBC) and histopathology.ResultsOf a total of 154 puncture sites from 153 patients, the total positive rate of combination for the three pathological treatment types (histopathology, direct traditional smear, and LBC) was 77.3%. The diagnostic positive rate for histopathology was 68.6%, direct traditional smear was 65.6%, and LBC was 60.4%; there was no significant differences among the three single pathological treatment types (P = 0.29), but there was a statistically significant difference between the combination of three treatments and any single pathological treatment type (P = 0.01). The diagnostic sensitivities of histopathology combined with traditional smear and histopathology combined LBC were 94.4 and 92.8%, respectively, the specificities and PPVs were both 100%, and the diagnostic accuracies were 95.5 and 94.2%, respectively; the sensitivities, specificities and diagnostic accuracies above were all higher than those of single specimen treatment and lower than those of the three combined.ConclusionWhen EBUS-TBNA is used for the diagnosis and staging of lung cancer, the use of histopathological sections combined with direct cytological smear should be sufficient and is the most economical choice.

Characteristics of Films on the Surface of Sea Sand and Effects on the Dissolution of Chloride

In this study, the effects of the specimen preparation method, temperature, and duration of the extraction step for the determination of the water-soluble chloride content of sea sand were investigated. The results demonstrated that increasing the heating temperature and duration promoted the dissolution of chloride, where the maximum value was obtained at 80°C and 60 min. Hot water extraction (80°C/60 min) could eliminate the effects of different specimen preparation methods on the final test results. Therefore, a new method was developed with drying at a temperature of 110 ± 5°C and hot water extraction at a temperature of 80°C for 60 min. The suitability of the new method for determining the water-soluble chloride content of sea sand was verified by testing the extracted specimens again. The results indicated that the chloride in sea sand dissolved fully with the new method, and thus it is suitable for testing the water-soluble chloride content of sea sand. Finally, the organic and inorganic compositions of the film adsorbed on the surface of sea sand were studied based on thermogravimetric analysis, inductively coupled plasma atomic emission spectrometry, ion chromatography, and total organic carbon measurements. The results indicated that a layer of substance (a multi-substance film) was adsorbed onto the surface of sea sand. This layer comprised inorganic salts (such as Cl–, Na+, Mg2+, SO42–, and Ca2+) and organic compounds, which were related to the composition of sea water. The multi-substance film greatly affected the dissolution and diffusion of chloride in the sea sand. Hot water extraction accelerated the dissolution of the film and increased the test results in terms of the water-soluble chloride contents.

Statistical analyses of SEM-EDS results to predict the quantity of added quicklime in a treated clayey soil

In the road construction sector, soil treatment is a method for increasing the strength and durability of fine soils that would otherwise be waste: the treatment with lime allows building embankments with clayey soils. However, in-situ and laboratory tests should be carried out to verify the correct addiction of lime during earthworks. This study deals with SEM-EDS analyses in order to identify the most reliable method to prepare specimens and obtain relationship between added quicklime and Calcium content after treatment. A natural clayey soil has been tested: more than one thousand values of Calcium content have been analyzed with statistical approach. The results from one-way and two-way ANalysis Of VAriance (ANOVA) and Tukey’s test confirmed the usefulness of SEM-EDS analyses to verify quickly the quantity of added quicklime in treated soils. The most reliable method for specimen preparation consists of a sequence of procedures similar to those that occur in worksite. The high variability of Ca content in the natural soil did not allow definition of a linear reliable relationship between the added quicklime and the after-treatment Ca content. Therefore, further experimentation is on-going to define a method based on SEM-EDS analyses and valid for clays with non-uniform chemical composition.