Small-sized Specimens Research Articles

Mechanical responses of Ti-6Al-4V cuboctahedral truss lattice structures

Ti-6Al-4V cuboctahedral truss lattice structures were manufactured via a combined approach of snap-fitting and vacuum brazing. By varying the strut length l from 7.7 to 22 mm, structures of relative densities in the 1.5–7.5% range were fabricated and mechanically tested in compression. Lattice collapse mode transformed from elastic to inelastic truss buckling at a relative density ~ 2.5%, corresponding to a strut aspect ratio t/l ~ 0.09. The mechanical properties are found to be sample size dependent, and are significantly knocked down in small-sized specimens by the soft edges. A low nodal connectivity Z=8 of the cuboctahedral truss topology makes it less efficient to attain the maximum mechanical performance, and nodal fractures preceded the attainment of numerically anticipated lattice peak strength. Nonetheless, mechanical properties of cuboctahedral structures are competitive with existing topologies and materials, and the full-potential performance could be achieved in structures with large numbers of in-plane cells.

Crack Growth Evaluation for Cracked Stainless and Carbon Steel Pipes Under Large Seismic Cyclic Loading

Abstract Some Japanese nuclear power plants have experienced several large earthquakes beyond the design basis ground motion. In addition, cracks resulting from long-term operation have been detected in piping systems. Therefore, to assess the structure integrity and to evaluate the fragility of cracked pipes taking the occurrence of large earthquakes into account, it is very important to establish a crack growth evaluation method for cracked pipes that are subjected to large seismic cyclic response loading. In our previous study, we proposed an evaluation method for crack growth during large earthquakes through experimental study using small size specimens and investigation using finite element analyses. In the present study, to confirm applicability of the proposed method to pipe, crack growth tests were conducted on both stainless and carbon steel pipe specimens with a circumferential through-wall crack, considering large seismic cyclic response loading with complex waveforms. The predicted crack growth values are in good agreement with the experimental results and the applicability of the proposed method was confirmed.

Ethno-knowledge and attitudes regarding snakebites in the Alto Juruá region, Western Brazilian Amazonia

BackgroundThe Alto Juruá region, located in the extreme western part of the Brazilian Amazonia, possesses an indigenous and riverine population which is involved in agricultural and forest extraction activities, and is a region that stands out for its high incidence of snakebites. ObjectivesTo assess the attitudes of the victims, the characteristics of the snakes and the circumstances of the snakebites which occurred in a region where human populations are highly exposed to snakes. MethodsThe study was conducted at the Regional Hospital of Juruá in the Municipality of Cruzeiro do Sul (Acre), which regularly attends victims of snakebites in the Alto Juruá region. The snakes that caused the envenomations were identified from clinical and epidemiological diagnosis of the symptoms and signs that patients presented during hospital, and by enzyme immunoassay for venom detection using serum samples of the patients, or by identification of the snake responsible for the envenomation when it was taken to the hospital or photographed. People who suffered or witnessed the snakebite were interviewed to assess the circumstances of the bite, the attitude adopted after the accident and whether they recognized the species of snake that caused the envenomation. ResultsThere were 133 cases of snakebite (76.24/100.000 inhabitants), mainly involving male individuals living in the rural area and who had a low level of education. The most affected groups were farmers (48%) and children and teenagers (39%). It was observed that 8.3% of them presented a history of recurrence for bites. The lower limbs were the most affected anatomical region (84%). The Bothrops atrox snake, mainly small specimens (mostly juveniles), was the main species involved in the envenomations (83.4%). Snakebites occurred mainly in forest areas, backyards of houses in rural areas and near to aquatic environments, during activities (walking, farming, extractivism, hunting). Most of the time, the snake was on the ground and the bite occurred because of the approximation of the individual, either by trampling or by approximation of a hand. Half of the victims performed some kind of inadequate first aid (not drinking water, use of tourniquet, incision at the site of the bite, use of black stone, drinking a compound “Específico Pessoa”). ConclusionsSnakebite is an important cause of morbidity in the Alto Juruá region. Bothrops bites are mostly caused by small-sized specimens, probably due to the greater abundance of B. atrox juveniles, and also because small snakes are more difficult for people to see. People are more often bitten on the lower limbs probably due to the size of B. atrox (small and medium) and because the snakes are usually on the ground in most situations. Many victims resort to ineffective actions that can cause complications and also delay serotherapy. A low level of education is a factor that may contribute to worse outcomes in snakebites since it is associated with a lack of knowledge of preventive and first aid measures.

Tensile behaviour of strain-hardening cement-based composites (SHCC) with steel reinforcing bars

Strain-hardening, cement-based composites (SHCC) are a group of fibre-reinforced construction materials developed specifically to exhibit pronounced quasi-ductile behaviour and high strain capacity under tensile loading. In structural applications, SH CC are often used in combination with steel reinforcement. The article at hand presents an extensive experimental investigation carried out to analyse the load-bearing behaviour of R/SHCC subject to tensile loading. It includes material characterisation as well as uniaxial tension tests of slab elements with different reinforcement ratios and differing steel bar arrangements. It was shown that the production particularities of large specimens and their size influenced the mechanical performance of the SHCC, including its cracking behaviour, thus leading to a significant reduction of tensile strain capacity of structural elements in comparison with test results on small size specimens. The interaction with steel reinforcement, on the other hand, was found to facilitate multiple cracking and enhance tensile strain capacity during the stage of elastic steel deformations. However, a mutual dependency of SHCC fracture localisation and local plastic deformations of steel bars could be observed in the yielding stage of the steel reinforcement. The experimental results are discussed with respect to their implications for constitutive modelling under consideration of the individual behaviours of SHCC and steel bars as well as their bond interaction.

The study of the brittle fracture resistance in fusion areas between RPV steel 15H2NMFA grade 1 and austenitic padding

Brittle fracture resistance of RPV 15H2NMFA grade 1 steel is investigated. Sets of small-sized testing samples and a set of standard-sizes samples were used in the study. It was demonstrated that application of sets of small-sized specimens in mechanical tests for determining the brittle fracture resistance of RPV 15H2NMFA grade 1 steel makes possible the following: increasing the volume of tests in each batch by 8 times without significant changes in the design of irradiation facility thus ensuring maintaining the initial irradiation parameters during testing; substantially expanding the database of test results for statistical processing. The need for large-scale modeling of process conditions arising in weld joint zones inaccessible for direct testing, such as: (1) the welding zone between the base metal and the corrosion-resistant coating metal, (2) the welding area between the weld metal and the corrosion-resistant coating metal, and (3) the fusion area between the base metal, the weld metal, and the anticorrosive cladding metal, is demonstrated in the paper. Process modeling of the metal in fusion areas up to 0.5 mm wide (each is 100 μm in size) with an experimental electroslag refined (ESR) ingot of up to 300 mm long with similar microstructure and variable chemical composition allows the following: (1) examining not less than 1000 small-sized impact testing samples with continuous distribution of concentrations of chemical elements in accordance with a certain law; and (2) testing these samples and identifying brittle fracture dangerous zones across fusion areas between the base metal and the anti-corrosive padding metal in the initial state or after subsequent irradiation at a given fluence rate and temperature.

In vivo evaluations of hydroxyapatites with small and large grain sizes

ABSTRACTThe effect of grain size of hydroxyapatite on its osteoconductivity was newly investigated. The hydroxyapatite discs, which had small (specimen S) and large grain size (specimen L), were prepared through microwave sintering at 1100°C for 6 and 720 min, respectively. The average grain size of specimen S was about 15 times smaller than that of specimen L. The surface energy of specimen S was about 1.6 times higher than that of specimen L under the same surface roughness. For the osteoconductivity test, porous hydroxyapatite granules were prepared using PEG porogen. The osteoconductivity of specimen S was superior to that of specimen L four weeks after implantation in calvarial defects of New Zealand white rabbits. Taken together, it can be concluded that the hydroxyapatite with small grain size had a higher osteoconductivity compared with the hydroxyapatite with large grain size due to its high surface energy.

Study on the Effects of Joint Inclination and Size Effect on the Failure Process of Rock-like Materials

To explore the effects of joint inclination angle and the size on the mechanical properties and failure process of rock-like specimens, a series of uniaxial compression tests were carried out on rock-like specimens.The specimens are consist of two sizes and contain three parallel joints with various inclination angles. During testing, the variation characteristics of apparent strain field of specimens is recorded by digital image correlation (DIC) system. Testing results reveal the uniaxial compression strength of the specimen decreases gradually with the joint inclination increases from 0° to 60°, while increasing gradually with the joint inclination increases from 60° to 90°. In addition, the peak compression strength of the large-size specimens is obviously lower than that of the small-size specimen when the joint inclination angle is 0°~30°. By contrast, the peak compression strength of the large-size specimens is the same as that of the small-size specimen when the angle is 30°~60°, approximately. But, the peak compression strength of large-size specimen is obviously higher than that of small-size specimen when the joint inclination angle is between 60° and 90°. Finally, five different types of cracks are observed in this work, i.e., tensile crack,airfoil tension crack,pull-shear mixing crack,secondary crack and far field tensile crack.

Methodical approach for studying kinetics of short and long fatigue cracks growth for irradiated reactor materials. Part 1. Statement of problem. The effect of the initial notch acuity on the fatigue crack rate on small-sized specimens

The paper considers methodical issues in the experimental research of fatigue crack growth kinetics when testing irradiated small-sized specimens. The effect of the initial notch acuity is studied on the long crack growth rate. The stress concentration zone sizes are estimated for notches of various types. A brif literature review of the main problems in the study of the growth kinetics of short fatigue cracks has been performed. The tasks of further research are formulated.

Influence of the incorporation of phase change materials on temperature development in mortar at early ages: Experiments and numerical simulation

The present work is focused on a thorough experimental campaign to assess the thermo-physical properties and performance of mortar containing phase change materials (PCMs) with peak melting temperature of 34 °C. This selected melting temperature was targeted to reduce the peak temperature developed in mortar at early ages, induced by heat of hydration of cement. Indeed, 34 °C is well above normal casting temperatures, yet well below peak temperatures normally attained in massive concrete structures: therefore, this choice would represent a somewhat generalizable choice for attenuating peak temperatures. Due to experimental constraints, the tests conducted herein were performed on mortar (smaller size specimens are possible). However, the methods and findings may easily be extrapolated to concrete.New preparation and incorporation protocols have been considered for using PCMs into mortar: (i) grated pristine PCM to be dispersed into mixtures; and (ii) macro capsule core of PCM. Three PCM volume fractions of 0, 10 and 20% using the two above mentioned different strategies of incorporation into the mortar were used to prepare a total of five mortar test prototypes. Furthermore, mechanical tests were then carried out on companion specimens to evaluate the effect of incorporating PCM on the compressive and flexural strengths.The addition of grated PCM (i.e. shredded) in mortar led to enhancement of volumetric heat capacity while maintaining acceptable structural strength. The results revealed that the addition of PCM reduces density, thermal conductivity, and mechanical strength. In respect to the strength reduction, such percentages of incorporation were found to be small enough (<50%) as to not compromise the use of such mixtures for structural application.As expected the tested PCM mortar specimens had a lower peak temperature, as compared to that of the reference specimens (mortar without PCM). Indeed, the 20% dispersed PCM mixture allowed peak temperature to decrease from ∼52 °C to ∼44.8 °C.Complementarily, numerical models were developed and calibrated using the experimental data. The comparison between numerical simulation (using DIANA software) and experimental results revealed a very good agreement of the temperature profiles in the early ages. This allows to validate the capacity of simulating temperature evolution within mortar containing PCM, as well as, to understand the contribution of PCM to reduce the temperature rise coupled with the cement hydration phenomenon. It also represents a baseline methodology for scientists and practitioners to perform parametric analyses for other situations.

Modeling for life estimation of HVDC cable insulation based on small-size specimens

The long-term performance of cable insulation has been severely challenged [1–3] by the technological advances of high voltage DC (HVDC) power lines for bulk long-distance subsea or underground transmission worldwide [4–8]. In particular, its life plays an important role in the reliability of the whole transmission system, which has received a great deal of attention and been extensively investigated over many years [1], [9–19]. Several competing life expressions, based on different mechanisms, have been developed with the aim of quantifying relationships between applied stresses (electrical, thermal and mechanical) and time to failure (lifetime). These have been used for theoretical studies and practical engineering applications. In their favor, the mean life data of laboratory tests can be fitted well to the model expressions. Alternatively different endurance characteristics of insulating material candidates can be compared with investigate their performances for a given cable system [1], [10], while providing feedback and insights on power cable design and manufacture.

Study of deformation and fracture of [formula omitted] ceramics by wedge splitting of a chevron-notched specimen

A method for determination of crack resistance of a material based on the test data of small-sized chevron-notched double cantilever beam specimens by wedge splitting is proposed. Specific fracture energy for small-sized chevron-notched double cantilever beam specimens is calculated using analytical expressions derived on the basis of the beam theory with a correction for elastic deformation of the ligament of a double cantilever beam specimen. A proper transition is performed from the pressing force on a wedge to the deflection force of cantilevers with account for the deformation of the ligament of a chevron-notched double cantilever beam specimen and the friction coefficient between the wedge and the specimen. An analytical formula that allows determination of friction coefficient during an experiment is worked out. New data have been obtained when testing ceramics based on ZrO2+3mol%Y2O3. The ceramics’ loading diagrams reveal an extensive inelastic stage of deformation that precedes specimen fracture. It is shown to be associated with the α-β polymorphic transformation in the chevron notch zone. The displacement contributed from inelastic deformation is ⩾21% at the moment of specimen fracture for tested specimens. The obtained evidence indicates the dislocation-free mechanism of inelastic behavior of ZrO2+3%Y2O3 ceramics. In chevron-notched specimens, the α-β transformation is performed under the action of stress concentration without a crack in the chevron notch zone. The paper points out the necessity to use the value of “nonelastic” displacement of chevron notch sides as an additional characteristic of crack resistance of a material when studying and modelling deformation and fracture of small-sized specimens.

Limitations and applicability of a new small-scale measuring setup for sound insulation characterization

The development of soundproofing materials with exceptional acoustic properties has been of great interest in recent years. The acoustic characterization of such materials using full-scale reverberation chambers requires the preparation of relatively large-sized specimens, fulfilling the requirements of the ISO 10140 standards; this is a costly and time-demanding process. Recently, various methods based on the utilization of small-sized specimens have been developed by numerous researchers, so that the acoustic performance of a large selection of materials can be more rapidly assessed in the laboratory. However, such attempts to experimentally characterize soundproofing materials have specific limitations with regard to the validity of the measured sound reduction index. The article addresses the use of a small-scale measuring setup which can be used to study the sound insulation characteristics of a variety of materials, taking into account the limitations and applicability of the setup. The experimental analysis was performed on three materials that are widely used in building and civil engineering applications but have completely different internal structures and mechanical properties. It is shown that the use of the proposed small-scale measuring setup is more appropriate for materials with lower structural stiffnesses and with higher critical frequencies, as well as for porous materials with open pores. © 2019 Institute of Noise Control Engineering.

Length and orientation direction effect on static bending properties of laminated Moso bamboo

Considering the influencing factors length and bending direction, 124 small size specimens and 12 beam specimens of laminated Moso bamboo were manufactured and tested under static loading. Detailed discussions on how the length influences the bending performance of laminated Moso bamboo are presented in this paper. The bending directions have an influence on the strength but not very significant as a whole. No matter how long and which bending direction, each specimen showed a similar tensile failure process with increasing loading. Comparison of the two orientations of the small specimens indicates that the strength and modulus of elasticity values for tangential bending direction had increased over the values for radial bending direction. The length has an influence on the static bending properties of laminated Moso bamboo but not very clear. In addition, the formulas for calculating the ultimate bending moment and ultimate bending deflection were discussed under nonlinear conditions.

Foams of Gray Cast Iron as Efficient Energy Absorption Structures: A Feasibility Study

Gray cast iron foams, were produced using a reticulated polyurethane by using a modified investment casting process. To evaluate the attributes of the produced micro‐geometries, foam segments and single struts are investigated by light and electron microscopy in 2D, and synchrotron micro‐computed tomography in 3D. Mechanical properties are determined by macro/micro‐mechanical testing and nanoindentation. In the microstructure of the gray cast iron struts, both flake‐like coarse type A and locally fine undercooled type D graphite particles are observed. The distribution of the two graphite types is heterogeneous and is the likely cause for the large scatter of the mechanical properties of the single struts. The high graphite content and the resulting brittle behavior of the struts lead to strong serrations in the stress‐strain curve of the foams with a negative effect on energy absorption. We found a relatively low energy absorption efficiency of below 50% as compared to 75% in 316L austenitic steel struts. The small specimen size results in scale effects which strongly influence the mechanical properties of the foams. Further improvement in the fabrication of gray cast iron foams is needed to tailor graphite distributions and optimize performance of cast iron‐based foams.

STUDYING THE CHANGES IN THE MECHANICAL PROPERTIES OF NEUTRON-IRRADIATED CHROMIUM-NICKEL STEELS USING THE “SHEAR PUNCH” METHOD

Obtaining mechanical properties of neutron irradiated structural materials is made difficult by the high radioactivity of typical specimen sizes. Developing new mechanical tests which obtain the same properties with far smaller specimen sizes would significantly enhance the speed and safety of performing such tests. In this study, we demonstrate the correspondence in mechanical properties between standard, uniaxial tensile testing and a new “Shear Punch” method, involving the shear-based removal of a small (1 mm) disc of material. Two types of steel, 12Cr18Ni9 and 08Cr16Ni11М3, were irradiated with fast neutrons in the BN-350 reactor up to 23 dpa and shear punch tested between 20…300 °C. Excellent correspondence was found between the 0.2% shear and uniaxial tensile yield stresses, validating this technique as a way to obtain the same mechanical properties with greatly reduced sample size.

An abrasive wear test for thin and small-sized steel blade specimens

An abrasive wear tester was obtained by equipping a polishing machine with a specimen holding system. The test results for SKD11 and SCM440 steels were consistent with the standard pin on disk test. The main objective of developing this tester was to use it on thin and small-sized specimens. Thermal glue was applied to fix these wear test specimens, instead of using nuts or screws, or embedding them into epoxy resin. Influences of the factors specimen size, test time, load, speed, and environment (dry and wet conditions) on wear in the test were studied with both high speed steel (HSS) and high carbon (High C) steel blades. The results show that larger specimens of both materials had less wear, because at a constant loading force the pressure decreased with area of the specimen. Wear increased with testing time, load, and speed, as expected. In addition, wet conditions gave more wear than dry conditions. The HSS blades with 63 HRC hardness had better wear resistance than the high C steel with 43 HRC hardness. The developed test could distinguish between the wear properties of HSS and high C steel blades for thin and small-sized specimens, for which the ASTM standard wear test cannot be applied.

Effects of Density, Temperature, Size, Grain Angle of Wood Materials on Nondestructive Moisture Meters

The aim of this study was to investigate the effects of density, temperature, size, and grain direction on measurement of moisture contents (MC) of wood materials non-destructively. The MC of different sizes of solid wood, glulam, and CLT from larch (larix kaempferi, 560 kg/m3) and pine (pinus koraiensis, 430 kg/m3) were measured using the dielectric type and resistance type meters. The specimens were conditioned in the environmental chamber to be equilibrium moisture content (EMC) of 12 % and 19 %. When density setting in dielectric type meter was increased from 400 kg/m3 to 600 kg/m3, the MCs of specimen (S-L-100-E) were decreased from 13.4 % to 11.3 %. However, when wood group (WG) setting in resistance type meter was changed from WG1 to WG4, the measured MCs were increased from 9.2 % to 12.3 %. When temperature setting in resistance type meters was changed from 0 to 35 °C, the MC was decreased from 17.0 % to 13.0 %. The MCs measured by dielectric type meter for larger specimens (S-L-100-E_11.3 %, G-L-240-E_11.7 % and C-L-120-E_12.8 %) were higher than those of small size specimens (S-L-30-E_8.7 %, G-L-150-E_10.3 %, and C-L-90-E_9.7 %). The MCs measured by resistance type meter for larger specimens (G-L-240-E_11.6 % and C-L-120-E_13.3 %) were also higher than those of small size specimens (G-L-150-E_10.4 %, and C-L-90-E_11.8 %). The resistance type meter was not affected by the grain direction but the dielectric type meter were affected by the grain direction. The MC measured by resistance type meter for G-L-120–E perpendicular to grain direction was 11.5 % and the measured MC parallel to grain direction was 11.3 %. The MC measured by dielectric type meter parallel to grain direction (12.1 %) was higher than that measured perpendicular to grain direction (10.7 %).

Improved backward fatigue statistical inference to the high-speed railway vehicle components

Original backward statistical inference method (BSIM) was improved (here further termed as ISIA) to fit the fatigue probabilistic S-N (P-S-N) curve with finite life data or small sample problem. Based on the search path, the novel scheme captures the optimal parameters that can efficiently establish the quantitative relationship between the life distribution and stress levels. Meanwhile, the equivalent lives at different stress levels can be obtained through the conversion of fatigue life. To formulate the more realistic P-S-N curve of full-size components, the life distribution effect of small-size specimens can be considered when fitting curves. Results show that the slope and intercept of newly-proposed fatigue P-S-N curve by using the ISIA for (X-x-x-x) type life data exhibit a relative error less than 3%, and the predicted fatigue life is approximately 5% of the group method (TGM). On the other hand, the predicted life is only 0.1% of (x-x-x-x) type life data by the classical method (TCM). For the welded structures widely used in high-speed railway vehicles, the present ISIA can achieve more conservative and reliable life predictions. It is thus concluded that the newly-proposed ISIA can not only ensure the accuracy of life distribution particularly during high cycle fatigue regime but also acquire more conservative P-S-N curve as opposed to standard methods such as TGM and TCM.

A comparative morphological investigation of otoliths of six parrotfish species (Scaridae) from the Solomon Islands

A comparative morphological investigation of otoliths from six parrotfish species and two genera, Scarus and Hipposcarus, was conducted to identify taxonomically diagnostic species-specific characters. Ontogenetic trends in otolith morphology were evident: Otoliths of small-sized specimens were most like those of large-sized Scarus oviceps and were least similar to large-sized Hipposcarus longiceps.

Peculiarities of Determining the Physico-Mechanical Characteristics of Brittle Materials on Small-Sized Specimens

The paper presents methods for determining the elastic modulus, sound speed, logarithmic decrement of vibrations (internal friction), tensile, compressive and bending strength, crack resistance, specific work of fracture of small-sized specimens. The specimens of polycrystals of superhard materials, which are prepared in high-pressure apparatuses, or of other expensive sintered materials (boron carbide, silicon nitride, hard alloys), which have a high hardness and elastic modulus, have typically a small size. Most of such materials experience significant dynamic loads during operation in products (metal-cutting tools, armor protection elements). It has been shown that disk specimens of brittle materials 3–15 mm in size can be used to determine strength characteristics under dynamic loading. The use of such specimens makes it possible to avoid oscillations in the loading diagram and to reduce the measurement error of breaking load. Moreover, it is possible to determine on such specimens the specific work of fracture of brittle materials from energy balance in measuring bars. Methods for determining mechanical characteristics under dynamic loading using Hopkinson–Kolsky bars are described, and examples of using procedures for the investigation of hard alloys, polycrystals of superhard materials based on diamond and cubic boron nitride, boron carbide and silicon nitride, obtained by the Bakul Institute for Superhard Materials of the National Academy of Sciences of Ukraine, are given.