The tensile strength of rock is a crucial parameter for the stability assessment and reinforcement design of rock engineering, which is commonly determined by indirect tension test or uniaxial direct ...tension test. However, the rock in slopes and underground caverns is often in a direct tension stress state under confining pressure, due to the stress redistribution induced by excavation or mining. In this study, the direct tension tests of granite samples under both different confining pressures and tensile loading rates were carried out by an auxiliary apparatus installed in pressure chamber, to investigate the confined tensile strength and fracture surface morphology. High-precision 3D laser scanning was used to obtain the morphology data and the geometrical statistics of asperities on fracture surface, containing the distributions of height, dip angle and dip direction of the asperities. The tensile strength first increases and then decreases with the increase in confining pressure, indicating that the maximum tensile strength of tested granite is not the uniaxial tensile strength and appears in the condition of a certain confining pressure. The tensile strength slightly increases with the increase in tensile loading rate. The fracture surface is smoother as confining pressure increases, while is rougher with the increase in tensile loading rate. As confining pressure goes up, from a micro-point of view, the friction force and the locking force between grains of granite have a similar changing rule to the tensile strength. The roughness of fracture is closely related with both micro-fracture pattern between grains and macro-fracture pattern concerning tensile and shear properties. These provide a reasonable explanation for the correlation of the tensile strength and fracture roughness with confining pressure and loading rate.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The effects of tensile strain rate on the hydrogen-induced mechanical and microstructural features of a twinning-induced plasticity (TWIP) steel were investigated using a Fe-23Mn-0.5C steel with a ...saturated amount of hydrogen. To obtain a homogeneous hydrogen distribution, high-pressure hydrogen gas pre-charging was performed at 423 K. Similar to previous studies on hydrogen embrittlement, the deterioration in the tensile properties became distinct when the strain rate was decreased from 0.6 × 10−3 to 0.6 × 10−4 s−1. In terms of microstructural features, hydrogen-precharging decreased the thickness of deformation twin plates, and it localized dislocation slip. Moreover, facets of the hydrogen-induced quasi-cleavage feature on the fracture surface became smoother with decreasing strain rate. In this study, we proposed that a combined effect of hydrogen segregation, slip localization, and thinning of twin plates causes the hydrogen embrittlement of TWIP steels, particularly at a low strain rate.
•Hydrogen embrittlement is substantially more pronounced at low strain rates.•Introduction of hydrogen decreases the average twin thickness.•Hydrogen enhances the microstructural activities.•Hydrogen charging changes the fracture mode from ductile to quasi-cleavage.•Strain rate dependent hydrogen embrittlement mechanism is proposed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
An equiatomic FeCoCrNi high-entropy alloy is used as an input material for selective laser melting. The material is characterized using X-ray diffraction, scanning electron microscopy, thermal ...analysis and mechanical testing to investigate the feasibility of using high-entropy alloys in additive manufacturing and the resulting tensile properties. Results show that not only does the alloy preserve its single-phase solid-solution state, but it also exhibits high strength and ductility that are comparable to engineering materials like stainless steels.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Knowledge of the critical resolved shear stress (CRSS) values of different slip modes is important for accurately modeling plastic deformation of hexagonal materials. Here, we demonstrate that CRSS ...can be directly measured with an in-situ high energy X-ray diffraction microscopy (HEDM) experiment. A commercially pure Ti tensile specimen was deformed up to 2.6% strain. In-situ far-field HEDM experiments were carried out to track the evolution of crystallographic orientations, centers of masses, and stress states of 1153 grains in a material volume of 1.1 mm × 1 mm × 1 mm. Predominant prismatic slip was identified in 18 grains, where the orientation change occurred primarily by rotation around the c-axis during specimen deformation. By analyzing the resolved shear stress on individual slip systems, the estimated CRSS for prismatic slip is 96 ± 18 MPa. Predominant basal slip was identified in 22 other grains, where the orientation change occurred primarily by tilting the c-axis about an axis in the basal plane. The estimated CRSS for basal slip is 127 ± 33 MPa. The ratio of CRSSbasal/CRSSprismatic is in the range of 1.7–2.1. From indirect assessment, the CRSS for pyramidal 〈c+a〉 slip is likely greater than 240 MPa. Grain size and free surface effects on the CRSS value in different grains are also examined.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
•FRP bars lost up to 55% of their tensile strength at a critical temperature of 325°C.•Concrete-FRP bond was significantly reduced upon exposure to high temperatures.•FRP bars lost up to 81.5% of ...their bond strength at critical temperature of 325°C.•The analytical model, proposed in this study, showed good predictability.
This paper presents the results of an experimental study on the effect of elevated temperatures on the mechanical properties of FRP bars and the bond behavior between FRP bars and concrete. Four types of reinforcement bars namely: basalt fiber reinforced polymer (BFRP), CARBON fiber reinforced polymer (CFRP), glass fiber reinforced polymer (GFRP), and steel bars of 10mm diameter were used. The results showed that the FRP bars suffered significant reductions in their mechanical properties upon exposure to high temperatures of up to 450°C at which the GFRP and BFRP melted and lost their total tensile strength capacity. At a critical temperature of 325°C, the FRP bars lost as high as (55% and 30%) of their tensile strength and elastic modulus, respectively. The percentage reduction in mechanical properties and bond strength was more pronounced in specimens with FRP bars than those with steel bars under elevated temperatures; the percentage reductions in bond strength between concrete and FRP bars reached as high as 81.5% after exposure to 325°C. Based on the experimental results, an empirical model was proposed to predict the post-heating bond stress-slip relationship between the FRP bar and the surrounding concrete: a good agreement was noticed between the experimental results and the proposed model.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
An SEM in situ uniaxial tensile testing setup allowing HR-EBSD acquisition during deformation was used to study the extension twinning mechanism in magnesium (Mg) at the micron scale. Structures were ...fabricated with two different crystal orientations, respectively perfectly aligned with, and at 5° to, the 0001 axis. Limited {101¯2} twin formation was identified in the former case, while twinning was found to largely accommodate the plastic deformation in the latter case. These two different mechanisms are explained by the activation of basal slip when loading at 5° to the c-axis, which triggers {101¯2} twin nucleation and favors twin growth and propagation. The other orientation shows the activation of pyramidal slip together with only limited {101¯2} twin growth. The critical resolved shear stress for {101¯2} twinning has been determined to be ten times higher than in bulk material. 3D HR-EBSD mapping enabled reconstruction of the three dimensional twin structure after deformation. From this, the interaction between the dislocations located ahead of the incoming twin and a pre-existing twin boundary was investigated, where the GND distribution and the local shear stress were determined. The results show plastic accommodation up to ~11% of strain, revealing higher ductility than usually reported for bulk materials.
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•In situ HR-EBSD was used to map the sequence of events that occur during micro-tensile loading of single crystal Mg.•Extension twins occur at the micron-scale when loaded off the c-axis, while limited twins form when loaded along the c-axis.•The critical resolved shear stress for {101¯2} twinning has been determined to be ten times higher than in bulk material.•Basal slip triggers {101¯2} twin nucleation and strongly favors twin growth and propagation.•The 3D structure of the twins was obtained by FIB tomography and HR-EBSD allows associated stress and dislocations analyses.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•Mechanical properties in centrifugal casting ductile iron pipes vary across thickness.•Equations are proposed to evaluate tube properties in ring hoop tension test.•Casting defects cause material ...inhomogeneity in ductile iron pipe walls.•Round bars in pipeline standards tend to overestimate actual pipe behaviour.
Ductile iron pipes are widely used in pipe manufacturing for water and sewage transmission and distribution. In pipeline standards such as EN545, the pipe material is assumed isotropic and its mechanical properties are determined by tensile testing of round bars extracted along the longitudinal direction. This study experimentally examined the mechanical properties of centrifugal casting ductile iron pipes, focusing on the effects of sampling orientation, location, preparation, and test methodology. A ring hoop tension test (RHTT) was designed to evaluate circumferential properties. Force analysis of RHTT was performed and theoretical equation was derived to quantify the friction coefficient that existed between the coupon specimen and the loading fixture. A numerical study was conducted to further validate the effectiveness of the proposed theory. The test results indicated that the pipe mechanical property was inhomogeneous across the wall thickness, being inferior in the internal section and superior in the middle and external sections. This inferior layer would develop crack first and lead to subsequent outward propagation. This phenomenon led to a substantial degradation in the overall mechanical performance of the entire specimens, in comparison to the material in the middle portion. The material exhibited better performance in the circumferential direction compared to the longitudinal direction in terms of its mechanical properties, such as tensile strength and ductility. Flattened specimens showed enhanced strength and reduced ductility compared to the base pipe material. Fractographic and metallographic analyses revealed the existence of casting defects of porosity and agglomerated graphite in the internal section, which were the primary cause of material inhomogeneity. The round bars suggested per EN545 tended to overestimate the actual mechanical behaviour of ductile iron pipes, and may not be a true representation of the finished product of pipes. Flattened specimens as per ASTM E8/E8M were not recommended for ductile iron pipe material assessment, as the flattening process altered the stress–strain characteristics significantly.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Intermetallic γ-TiAl based alloys are promising materials for lightweight high-temperature applications, but their limited room temperature ductility poses an obstacle to the exploitation of their ...full potential. Especially in the case of multi-phase TiAl alloys, such as the β-stabilised TNM alloy of a nominal chemical composition of Ti-43.5Al-4Nb-1Mo-0.1 B (in at.%), an understanding of deformation and load partitioning mechanisms is required that works at all scales and encompasses all phases, including e.g. βo. In the present work, in situ high-energy X-ray diffraction measurements were conducted on a recent TNM sheet to study the load-bearing mechanisms and their sequential order upon tensile loading for the first time on the level of individual lattice planes and phases. Four specific stages of deformation were revealed. The direction-dependent analysis of the diffraction elastic moduli offered insights into the anisotropy of the individual phases and the initiation of intergranular and interphase stresses in the elastic regime. Plastic deformation was found to commence in the γ phase at applied stress levels of roughly 670–690 MPa. Load partitioning between differently oriented grains of the γ phase was observed, followed by a load transfer onto the α2 and βo phase. Further tensile loading entailed the onset of plasticity within favourably oriented α2 grains. The globular βo phase was found to deform elastically until failure. Differently oriented specimens of the weakly textured TNM sheet showed that the macroscopic mechanical properties can be assumed nearly isotropic.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
•Uniaxial tension tests were conducted on a group of grouted-sleeve splices.•The influence of splice geometrical parameters was investigated quantitatively by FEA.•The failure modes of the ...grouted-sleeve splices were studied.
Sleeve grouting technology is widely employed in prefabricated building structures. However, the influence of multiple factors on the mechanical properties of grouted-sleeve splices have not been sufficiently investigated. This study attempts to investigate the failure process of the grouted-sleeve splice while loaded in uniaxial tension. A series of tensile loading tests were conducted on a group of grouted-sleeve splices. The failure mode of rebar fracture was observed in the test, and the result reveals that the grouted-sleeve was in elastic stage during the test. Three-dimension finite element analyses are carried out on the tensile loading test, considering grout plasticity and damage as well as the influence of rebar thread on interaction property of material interface. The influence of the clearance between sleeve and rebar, as well as the anchorage-diameter ratio, is investigated by finite element parametric study. The numerical results reveal that an anchorage-to-diameter ratio greater than 7 is sufficient for preventing the slippage failure at the interface between the grout and rebar. In addition, an exponential relationship exists between the anchorage length and the ultimate bearing capacity. The damage zone always initiates from the sleeve port in spite of different failure modes.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
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