Specimen Shape Research Articles

Specimen size and shape effect on the compressive strength of concrete

The results of the investigation of the specimen size and shape effect on concrete strength indicators are presented in this paper. Research on the strength of concrete specimens in the form of cubes (150x150x150 mm) and cylinders of different diameters (50 mm, 100 mm and 150 mm) and heights (100 mm, 200 mm and 300 mm), under compression are carried out on Matest testing machine with Servo-Plus Evolution servo-drive control unit. Three specimens of each type are tested. Control specimens are made according to such ratios of materials that concrete corresponds to the strength class C16/20. All specimens are visually inspected for the presence of any defects, such as large pores, chips, or shrinkage cracks. After that, the actual measurements of all specimens are carried out. They showed minimal deviations from the planned size, which is considered acceptable. In order to check the reliability of the results, after the research of each type of specimen, calculations are carried out to determine the actual strength and the concrete grade. The actual dimensions of the faces and the results of the certain batch research are taken. The data obtained from the concrete specimens research on the test press are analyzed. Due to the formulas and data obtained after the investigation, the actual strength class of concrete for all specimens is determined. According to the results of the research, fracture graphs of all types of control specimens are constructed. The results show that the laboratory measurements are consistent with the literature results, namely that the compressive strength decreases with the specimen size increase. In the case of the smallest, non-standardized specimens (cylinders with 100 mm height and 50 mm diameter), the deviation of compressive strength tests is higher compared to other specimens. The graph is presented for visualizing the specimen type and size effect on concrete strength.

The issue of residual stresses in additive technologies

The paper considers the issue of residual stresses in 3D-printed plastic models. Most additive technologies create residual stresses in products. Residual stresses occur in the printed material due to its expansion when heated and contraction when cooled. Residual stresses and their intensity depend on the printing technology and technique. The paper discusses the impact of printing techniques and various printing nozzle diameters and model shapes (rectangular, circular) on the occurrence of residual stresses in specimens. As part of the study, in transparent models, residual stresses were detected using a PPU-7 polarization-projection unit. Two series of six specimens each have been printed. The first and second series models had the shape of a parallelepiped and a disk, respectively. The frequency-division multiplexing technology was chosen. In the study, the models were manufactured from a polyethylene terephthalate-glycol plastic filament. This material has a high optical sensitivity. Nozzles of two diameters (0.4 and 1 mm) were used to print specimens. Shell-less and singleand double-shell specimens were printed. The dependence of residual stresses on the specimen shape, the printing nozzle diameter, and the model shell thickness has been estimated. The study is focused on finding a technique for printing models from plastic filament, completely free of residual stresses in the specimen material. This is dictated by the photoelasticity requirements for piezo-optical materials, including some transparent plastics used in 3D printing.

Comparative Study of The Asphalt Mix Stiffness Modulus Using Selected Test Methods – 2-Point Bending Test, 4-Point Bending Test and Indirect Tensile Test

The stiffness modulus of the asphalt mixture is a fundamental parameter in the understanding of the mixture strain behavior. It is also an essential design parameter of asphalt pavements. According to the European standards EN 12697-26, various test methods can be performed in order to determine this criterion. These tests are varying according to the loading type and the specimen dimensions and shape. The present paper deals with the study of three test methods: the 2-point bending test on trapezoidal specimens (2PB–TR), the 4-point bending test on prismatic specimens (4PB–PR), and the indirect tension test on cylindrical specimens (IT CY) used on three asphalt mixtures representing different structural pavement layers. The results show that the dual comparison of these tests, i.e., IT-CY and 4PB-PR, and 4PB-PR and 2PB-TR have indicated good correlation between each other. However, the comparison between the three tests did not substantiate to any general correlation.

Established but not spreading: the tropical invasive snail Melanoides tuberculata in a geothermally warmed channel in temperate Southern Pampas

Melanoides tuberculata is a freshwater snail native to Old World tropical areas but has invaded tropical and subtropical regions around the world. In Argentina, populations established in natural environments were reported from northeastern tropical provinces. Here we report for the first time the presence of M. tuberculata in a geothermally warmed channel in temperate Southern Pampas. We mapped its distribution in the channel, searched for its presence in five nearby basins, estimated the risk of establishment and expansion in Argentina with distribution models and analyzed shape variation through geometric morphometrics. Melanoides tuberculata was recorded exclusively in the channel in sites with temperatures between 20 and 40°C, with almost no overlap with other snails. No evidence of M. tuberculata was found in nearby basins. The distribution model predicted that only northernmost areas from Argentina are suitable for this species, where it could impact snail communities and food webs if introduction through the aquarium trade is not prevented. The absence of males indicates parthenogenetic reproduction and probably a recent invasion. Shell shape variation in this population, 15 % of which is attributable to allometry, encompasses the shapes of specimens from other South American populations, suggesting that all belong to the same lineage.

Effect of specimen shape on microbubble filling cleaning

Effect of specimen shape on microbubble filling cleaning

Assessment of color stability of shade less composite resin: an in-vitro study

Objective: This study aimed to assess the color stability of omnichroma composite resin after immersion in coffee, cola and iced tea. Methods: A total of 30-disc shape specimens of omnichroma, 10mm diameter and 2mm thickness, were made in a Teflon mold. The samples were washed and stored in artificial saliva for 24 hours in a 37°C incubator. The top surfaces of specimens were polished with polishing disks (Sof-lex; 3M ESPE). Samples were divided randomly into 3 groups, and each group contained 10 discs. Groups were immersed in 15 ml of 3 different storage media (cola, iced tea and black coffee). Immersion groups were stored in an incubator at 37 °C. Color assessment was carried out by VITA Easy shade 2.0 spectrophotometer color assessment device according to the CIE L*a*b*system, against a gray background to measure baseline records for the samples. After 4 weeks, a second record was taken for the samples after they were gently rinsed with distilled water and dried. The experimental data were statistically evaluated using the Wilcoxon sign rank test with a significance level < 0.05%. Results: The highest color change was reported with coffee (ΔE=20.16) followed by cola (ΔE=19.6) and iced tea (ΔE=4.75). Conclusion: All assessed drinks resulted in discoloration of the shade less composite resin material above the clinically acceptable level (ΔE>3.3) after 30 days of immersion. Coffee has the highest staining among the three drinks, followed by cola, and then iced tea.

Functional gradation of aluminum alloy by impact of ballistics as severe plastic deformation process

In the present effort, impact of bullets fired at high speeds on a stationary target was used as a high strain-rate plastic deformation method to generate Functionally Graded Materials (FGMs). The bullet-shaped Aluminum alloy Al5052 specimens impacted the UHMWPE target at different projectile velocities ranging from 100 m/s to 750 m/s, to study the effect of the impact speed. Moreover, few of the projectiles impacted along the longitudinal axis whereas the remaining projectiles impacted with an obliquity to investigate the effect of leading-edge shape. The metallography of the projectile specimens fired at 750 m/s shows grain refinement from 70 ± 3 μm at the rear/ un-deformed point to 10 ± 1 μm at the front/ severely deformed point which is in the impact zone. Similar but of less magnitude variations were observed at other impact speeds also. The hardness variation was 45% (70 ± 3 HV at the rear surface to 102 ± 2 HV at the front face) at 750 m/s. Moreover, least variation in hardness and grain size was observed for projectile impacted at lowest velocity tested (100 m/s). Further, functionality in hardness and grain refinement was seen in graded direction due to shape of the projectile specimens, impact velocity, and target material. Depending upon the impact angles, axisymmetric (impacted normal to the longitudinal axis) or unsymmetrical (impacted at an angle) variation of grain refinement and hardness was observed.

Cryptic persistence and loss of local endemism in Lake Constance charr subject to anthropogenic disturbance.

In the welcome circumstance that species believed extinct are rediscovered, it is often the case that biological knowledge acquired before the presumed extinction is limited. Efforts to address these knowledge gaps, in particular to assess the taxonomic integrity and conservation status of such species, can be hampered by a lack of genetic data and scarcity of samples in museum collections. Here, we present a proof-of-concept case study based on a multidisciplinary data evaluation approach to tackle such problems. The approach was developed after the rediscovery, 40 years after its presumed extinction, of the enigmatic Lake Constance deep-water charr Salvelinus profundus. Targeted surveys led to the capture of further species and additional sympatric normal charr, Salvelinus cf. umbla. Since the lake had been subject to massive stocking in the past, an evaluation of the genetic integrity of both extant forms was called for in order to assess possible introgression. A two-step genomic approach was developed based on restriction site associated DNA (RAD). Diagnostic population genomic (single nucleotide polymorphism [SNP]) data were harvested from contemporary samples and used for RNA bait design to perform target capture in DNA libraries of archival scale material, enabling a comparison between extant and historic samples. Furthermore, life history traits and morphological data for both extant forms were gathered and compared with historical data from the past 60-120 years. While extant deep-water charr matched historical deep-water specimens in body shape, gill raker count, and growth rates, significant differences were discovered between historical and extant normal charr. These resulted were supported by genomic analyses of contemporary samples, revealing the two extant forms to be highly divergent. The results of population assignment tests suggest that the endemic deep-water charr persisted in Lake Constance during the eutrophic phase, but not one of the historical genomic samples could be assigned to the extant normal charr taxon. Stocking with non-endemic charr seems to be the most likely reason for these changes. This proof-of-concept study presents a multidisciplinary data evaluation approach that simultaneously tests population genomic integrity and addresses some of the conservation issues arising from rediscovery of a species characterized by limited data availability.

Influence of anisotropy on the deformation behaviour in microtensile 316L steel specimens fabricated by laser powder bed fusion (PBF-LB/M)

Laser powder bed fusion of metals (PBF LB/M) allows fabrication of intricate structures without any need of tools and moulds. In this process the building orientation becomes a significant issue for the complex structures. Here we fabricated small size 316L steel tensile specimens aligned with their loading axis perpendicular and parallel to the building direction by PBF LB/M. Microstructure and mechanical properties were characterized by colour etching, in-situ tensile testing in a scanning electron microscope, nanoindentation and digital image correlation. The orientation of the melt pools has a significant impact on the deformation behaviour of the PBF LB/M specimens. In parallel specimens (polar angle = 90o) the semi-circular melt pools are aligned perpendicular to the loading axis resulting in an accommodation of larger amount of plasticity as compared to the perpendicular specimens (polar angle = 0o). While strain is localized in the case of perpendicular specimens because primary slip lines are aligned perpendicular to the loading axis, strain is homogenously distributed along the longitudinal axis of the parallel specimens because primary slip lines are aligned parallel to the loading axis. Twin-induced-plasticity and transformation induced plasticity are the deformation mechanisms observed on the fractured specimens. Strain hardening rate in stage IV extended to a higher stress value for the perpendicular specimens as compared to parallel specimens because cross slip is confined in the fusion boundaries. The building direction has shown significant influence on the deformation mechanisms of the PBF LB/M steels which may be a significant issue to overcome for the complex shape specimens.

Assessing dynamic compression of AA2024-T351 with split Hopkinson pressure bar simulation

To understand the dynamic compressive behaviour of aluminium alloy AA2024-T351, which is commonly used in maritime and offshore structures, is vital. This is generally achieved using Taylor impact tests, projectile tests and split Hopkinson pressure bars (SHPBs). It can also be obtained in a less expensive way by using a finite-element simulation of an SHPB under different conditions. This paper numerically investigates the effects of striker velocity, striker shape and specimen shape on the dynamic compressive behaviour of AA2024-T351 using a simulated SHPB. The material behaviour was found to be sensitive to strain rates, striker shapes and specimen shapes under various situations.

Load transfer between permanent and dynamic networks due to stress gradients in nonlinear viscoelastic hydrogels

Relaxation experiments are performed on single edge notch tension (SENT) and T shape specimens consisting of different variations of polyampholyte (PA) hydrogels. These specimens share a common feature of containing regions of high and low stress/strain. This feature enables us to probe the load transfer mechanisms between permanent and dynamic networks of different strengths. This load transfer mechanism is connected to viscoelastic behavior. PA gels are nonlinear viscoelastic, with time-dependent behavior controlled by the breaking and reforming of ionic bonds in the dynamic network. In contrast to the prediction of linear viscoelastic theory, the displacement and strain fields during stress relaxation are not fixed but change with time in a complex way depending on the strength of the dynamic bonds and the observation time window. These experimental results are explained by a nonlinear viscoelastic model. Additional physical insights are gained by appealing to the nonlinear rheology of dynamic bonds or stickers. Our result shows that load transfer between networks can be controlled by modifying the strength of dynamic bonds.

Design and development of a micro-LDH apparatus to determine formability of sheet metal under hot stamping conditions using Gleeble

In the last few years, demand for hot stamped components has increased in the automotive industry. Determination of formability under hot stamping is challenging due to elevated temperature, fast cooling, and high punch velocity. Although there was various strive for formability determination, but there were limitations with experiments like non-uniform heating of specimen, non-uniform strain, and temperature distribution. Therefore, in this work, an experimental apparatus was developed to determine formability at room temperature, high temperature, hot stamping conditions, and any complex process cycle involving heating and cooling. New specimen was designed to produce different strain paths, uniform, and homogenous temperature distribution with the help of FEM software using thermomechanical and thermoelectrical simulation. A micro hemispherical dome-based experimental apparatus was designed using Solidworks. The designed apparatus was used in conjunction with the thermo-mechanical simulator (Gleeble-3800). Thermomechanical analysis was done in PAM STAMP software to optimize specimen size and shape to get uniform strain distribution and different strain paths. A thermoelectric FEM model was developed using Abaqus 6.14 to optimize the temperature distribution in the specimen. The developed model enables choosing the appropriate polarity of the electrical cable connection to achieve uniform temperature distribution in the specimen. Strain path and temperature profiles for experiment and simulation were compared. Further, a forming limit curve was developed using the designed apparatus to verify the feasibility of the apparatus. For feasibility test of apparatus, hot stamping process was selected. This new design apparatus can be used for a range of temperatures up to 1000 °C, hot stamping conditions, and for different materials (aluminum, magnesium alloys, different grade of steel, etc.). It concludes that the connection of different polarities of electrical cable was critical for homogenous and uniform temperature distribution in specimens.

A comprehensive study on ring shape specimens under compressive and tensile loadings for covering the full range of I+II fracture modes of gypsum material

Using ring-shape specimens containing two aligned cracks on the internal surface of the ring, two test configurations subjected to tensile or compressive loads namely (i) diametrically compressed ring (DCR) and (ii) diametrically tensile ring (DTR) specimens were suggested to investigate the full mixed-mode I/II fracture problem. The fracture parameters, including modes I and II stress intensity factors and T-stress, were determined numerically for these two test specimens with different crack lengths and crack angles. Also, the ability of the specimens was examined by conducting experimental fracture tests on gypsum material. In addition, the direction of fracture kinking was investigated both experimentally and theoretically. The experimental results were then compared and predicted using the mixed mode fracture criteria such as maximum tangential stress (MTS) and generalized maximum tangential stress (GMTS). The normalized fracture toughness (KIIc/KIc) ratios of the tested DCR and DTR specimens were about 0.72 and 0.95, respectively. Such difference was related to the considerable effect of T-stress values and it was shown that the GMTS criterion provides more accurate predictions for the test results of both DCR and DCT samples compared to the MTS criterion.

Design of Multiphase Metal Balls via Maskless Localized Anodization Based on Bipolar Electrochemistry

AbstractNanoporous metal‐oxide films formed on some metals and their alloys during anodization are crucial for both basic research and commercial applications. They are used as important materials for various types of device fabrication due to their distinctive solid‐state shapes, such as nanopores and nanotubes. However, preparing nanoporous films using anodization, which is a surface treatment for plate‐like specimens, requires a direct electrical connection to the workpiece. Developing new materials independent of the specimen's shape and size will vary if the need for direct energization is eliminated. Here, bipolar electrochemistry is employed to fabricate two‐phase (insulator–conductor) and three‐phase (insulator–conductor–insulator) aluminum balls by controlling the redox reaction region in an electric field. The aluminum balls are site‐selectively anodized employing a wireless and maskless operation. The multiphase aluminum balls’ versatility is demonstrated in the site‐selective electroless deposition of copper on their exposed regions. Additionally, it is demonstrated that various types of materials, including aluminum and titanium, can be oxidized simultaneously in the same cell.

Evaluation of rockburst proneness considering specimen shape by storable elastic strain energy

AbstractTo systematically assess the rockburst proneness considering specimen shape, multiple groups of laboratory tests were performed on 5 rock materials in cylindrical and cuboid shapes. The linear energy storage (LES) law of both cylindrical and cuboid rock specimens under uniaxial compressive load was confirmed, and the energy storage coefficient was found to be unrelated to specimen shape. On the basis of LES law, two rockburst proneness indexes, namely the strain energy storage index (Wet) and the potential energy of elastic strain (PES), were modified. Subsequently, the Wet, PES, peak‐strength strain energy storage index (, and peak‐strength potential energy of elastic strain (PESp) were used to assess the rockburst proneness of the cylindrical and cuboid specimens. In addition, the fragment ejection course of specimens under test was recorded by a high‐speed camera. Then, the rockburst proneness judgments obtained from the 4 indexes were compared with the qualitative data during rock destruction. The results show that, under similar stress conditions, specimen shape has an ignorable effect on the rockburst proneness as a whole. The judgment accuracy of the two modified indexes, especially that of the PESp, is favorably improved to evaluate the rockburst proneness of both cylindrical and cuboid specimens. However, misjudgment of and PESp may still occur in the assessment of rockburst proneness as these two indexes only consider the energy state before rock peak strength and the is formulated in a ratio form.

Large deflection resistance and fracture of panels subjected to the lateral penetration

This paper is concerned with the plastic behaviors of a rigid indenter into a typical ship side panel with analytical and numerical studies. The focus is on a more comprehensive framework where panel dimensions, indenter shapes, and material failure properties are allowed to change when predicting panel failure initiation and the deformation resistance force. Therefore, concise analytical solutions are derived by the plastic membrane and fracture based on a global stability criterion for large deflection. The power curve fitting to the analytical solutions brings out the brief-expression where the influence of geometric and material parameters is present clearly. In addition, the shape factor CS is introduced to illustrate the indenter's sharpness and enable the semi-analytical solutions to deal with the indenter with various geometries:Experimental results of specimens with a range of dimensions punched by indenters presented in the previous work are used to validate the proposed analytical solutions. Numerical simulations are supplemented and demonstrate that the penetration to fracture initiation and the large deflection resistance are sensitive to specimen dimensions and shape and can be predicted accurately by the proposed solutions. Moreover, the applied fracture criterion in analysis considered the change of the geometric and material properties shows consistency with the numerical observations that panel fails by localized necking. By the extension based on the deformation assumption, the corrected procedure enables the prediction of stiffened panels.

Numerical Simulation of Failure Behavior of Brittle Heterogeneous Rock under Uniaxial Compression Test.

Rocks have formed heterogeneous characteristics after experiencing complex natural geological processes. Studying the heterogeneity of rocks is significant for rock mechanics. In this study, a linear parallel bond model with Weibull distribution in two-dimensional particle flow code (PFC2D) is adopted to study the mechanical characteristics and brittle failure mode of granite rock specimens with different heterogeneity. Firstly, we selected several combinations of key micro-parameters of the parallel bond model. Then, we subjected them to a Weibull distribution to satisfy heterogeneity, respectively. Finally, we chose one optimal combination plan after comparing the stress–strain curves of heterogeneous rock specimens. We analyzed the simulated results of heterogeneous rock specimens. The crack distribution of rock specimens under peak stress shows different characteristics: a diagonal shape in rock specimens with low heterogeneity indexes, or a rotated “y” shape in rock specimens with high heterogeneity indexes. As for failure mode, the numerical simulation results show high consistency with the laboratory experiment results. The rock specimen breaks down almost diagonally, and the whole specimen tends to form an x-shaped conjugate shear failure or the well-known “hour-glass” failure mode. With the increase of the homogeneity index of the rock specimen, the shear rupture angle becomes larger and larger. Generally, the crack number increases with time, and when the rock specimen reaches the peak failure point, the number of cracks increases sharply. The development of cracks in numerical rock specimens under compression test is a result of the coalescence of many microscopic cracks. Furthermore, tensile cracks formed initially, followed by shear behavior along the macroscopic crack plane. We also preliminarily study the mechanical characteristics of heterogeneous rock specimens with discontinuous structural planes. The discontinuous structural planes are simulated by the smooth-joint model. We can conclude that the discontinuous structural planes and the microscopic structural planes which contribute to the heterogeneity have a mutual influence on each other.

Instrumented indentation for determining stress and strain levels of pre-strained DC01 sheets

In classical mechanical testing, determining the stress and strain states of complex shape specimens turns out to be very challenging, especially in the most deformed regions. In the latter case, when not enough material is present, non-destructive testing is needed for determining the corresponding mechanical state. In this study, a novel approach, based on the local quasi-non-destructive instrumented indentation technique (IIT) coupled with the inverse analysis technique (IAT), is used to determine the stress and strain levels of pre-strained DC01 specimens using monotonic and non-monotonic loading paths. Monotonic and cyclic shear tests as well as Marciniak tests, in both plane and equi-biaxial strain states, are used to apply different pre-strain levels. For monotonic loading paths, i.e. monotonic shearing and Marcianiak tests, the applied methodology showed very satisfying results in determining the stress and strain states of the pre-strained specimens, especially for pre-strain values close to the representative indentation strain values. A maximum stress error of less than 15% was obtained in the case of the highest applied pre-strain value (29.04%). The purely isotropic Voce hardening law was adopted for determining the hardening behavior of the studied specimens in both cases: as-received and pre-strained. In the case of cyclic shear, a mixed isotropic-kinematic hardening law is to be used to determine the stress and strain states of the pre-strained specimens. Adopting a mixed isotropic-kinematic Chaboche hardening law led to satisfying results where the estimation errors of the applied pre-strain value and corresponding yield stress didn't exceed 6% and 1.3%, respectively. The obtained results show that the proposed indentation-based method can be very useful in estimating the work-hardening level and corresponding plastic deformation of pre-strained parts under various loading paths

Three-Dimensional Mesoscopic Investigation on the Impact of Specimen Geometry and Bearing Strip Size on the Splitting-Tensile Properties of Coral Aggregate Concrete

The use of coral aggregate concrete (CAC) as a novel construction material has attracted significant attention for the construction of reef engineering structures. To investigate the static splitting-tensile behaviors of CAC under the influence of two factors, namely specimen geometry and bearing strip size, a three-dimensional (3D) mesoscale modeling approach with consideration for aggregate randomness in shape and distribution was adopted in this study. We established 12 different specimen models with two specimen shapes (i.e., a cube with an edge length of 150 mm and a cylinder with dimensions of ϕ 150 mm × 300 mm) and six strip widths (i.e., 6, 9, 12, 15, 18, and 20 mm) for calculation. The effects of specimen geometry and strip width on the splitting-tensile properties of CAC, such as failure processes, final failure patterns, and splitting-tensile strength ( f st ), are analyzed and discussed systematically. The results indicate the high reliability of the developed mesoscale modeling approach and reveal the optimal computational parameters for simulating and predicting the splitting-tensile properties of CAC. The f s t values of CAC are associated with both the specimen geometry and width of the bearing strip. The f st values of the cube model are slightly higher than those of the cylinder model for the same bearing strip size, representing geometry effects that can be explained by differences in fracture area. Additionally, the f st value of CAC gradually increases with the relative width of the bearing strip ranging from 0.04 to 0.13. Based on the elastic solution theory, the variation area of CAC f st values with the relative width of the bearing strip was determined preliminarily, which has great significance for studying the tensile performance of CAC.

Effect of LPSO orientation on the compression behavior and workability of the Mg-5Gd-3Y–1Zn-0.5Zr alloy

To investigate the effect of LPSO orientation on the compression behavior and workability of Mg alloys, a Mg-5.3Gd-3.3Y-1.1Zn-0.5Zr (wt%) alloy was extruded to obtain the bimodal microstructure with a certain amount of directionally arranged LPSO phases. The subsequent compression tests indicate that the values of activation energy of deformation (Q) are approaching (180–194 kJ/mol) along different orientations (ED, 45°, and TD), which are much lower compared with the as-homogenized Mg-Gd-Y-Zn-Zr alloys due to the sufficient initial grain boundaries (I-GBs). Enhanced kinking and DRX at kink bands at the higher Zener-Hollomon (Z) parameters result in the slight decrease of Q and the movement of optimal processing domains for the ED orientation. The I-GBs overshadow the effect of LPSO orientation via kinking deformation on the DRX ratio and workability. The increase of Z parameter tends to reduce the DRXed grain size and the homogeneity of both the microstructure and hardness. Different α-Mg and LPSO orientations of the extruded alloy induce the anisotropy of peak flow stress (σp) during compression and the extraordinary elliptical shape of the compressed TD specimens. This work provides useful information for the industrial production of wrought LPSO-containing Mg alloys.