Small Yield Strength Research Articles

The Influence of the Performance Parameters of Bimetal Composite Pipe on the Forming Efficiency

In order to solve the problem of low efficiency in the mechanical drawing process of bimetal composite pipe, a dynamic model of the forming process of bimetal composite pipe is established based on the principle of virtual work and the elastic-plastic deformation criterion. The influence of the material properties of the inner pipe and the outer pipe on the forming success rate is studied. The residual stress of the inner pipe and the outer pipe after forming is taken as the main evaluation object, and the elastic modulus and yield of the material are systematically analyzed The influence of strength on residual stress. The results show that the ratio of the elastic modulus of the inner tube to that of the outer tube is more than 0.6 times of the yield strength when the bimetal composite tube is formed, and the materials with large elastic modulus and small yield strength of the inner tube and small elastic modulus and large yield strength of the outer tube should be selected as far as possible. At last, the theory of material parameter proportion for the successful forming of inner tube and outer tube is put forward. The research conclusion is reasonable and universal, which provides a scientific basis for the selection of composite tube materials, and has engineering practical significance for improving the forming efficiency of bimetal composite tube.

Mechanical responses of coals under the effects of cyclical liquid CO2 during coalbed methane recovery process

Liquid CO2 fracturing technology has been introduced to enhance coalbed methane (CBM) recovery for the decades, under its multiple-effects of phase transition and flooding, by complicating the crack distribution and improving the reservoir permeability. When huge amounts of cryogenic fluids were cyclically injected into the reservoirs, the accompanying effects of temperature shock and adsorption might have some potential impacts on the fracturing results, and their influence degree and the related mechanical deterioration were required to systematically studied. Three different rank coals were chosen and cyclically treated by liquid CO2, and the uniaxial compression behaviors of these affected coals were studied to investigate the destruction patterns, the evolutions of mechanical parameters, and the mechanism of damage failure. Compared to the raw coals, the ones affected by temperature-adsorption coupling effects of liquid CO2 displayed a more complex “separation + spallation” destruction pattern, while the ones treated by the sole effect had a destruction pattern of “spallation” and “separation” respectively. The more complex the destruction pattern, the larger the fractal dimension, and the greater the structure degradation. The affected coals exhibited diverse mechanical responses, for example, the compression strength σc and elastic modulus E had negative correlations with the increasing cyclical parameters, while Poisson’s ratio μ and damage variable Dv positively correlated with the increasing affecting parameters, respectively, which manifested that the accompanying cyclical temperature shock could facilitate the crack growth and the CO2 adsorption aggravated the strength deterioration, finally destroying the coals with the smaller yield strength. A new damage model was established by jointly considering the grain anisotropy from the microscopic aspect and the diversity of mechanical responses from the macroscopic perspective, and the induced unrecoverable deformations greatly weakened the cohesive stress among the grains or matrix skeleton, finally destroying the coal structure by producing amounts of new cracks. Furthermore, the produced new-raw cracks provided amounts of adsorption sites for CO2 molecules, which further decreased the surface energy and accelerated shear failure. The results were helpful to the injection parameters optimization, the low-cost of CO2 injection invests and the potential profit maximization of CBM utilization.

An experimental study on SrB4O7:Sm2+ as a pressure sensor

A pressure sensor of SrB4O7:Sm2+ has been synthesized and the pressure shift of its 7D0-5F0 fluorescence line has been recalibrated at room temperature up to 48 GPa and 127 GPa hydrostatically and non-hydrostatically, respectively. Different from previous study, our results show that the calibrated relation in the quasi-hydrostatic pressure environment is quite different from that in the non-hydrostatic pressure environment. The yield strength of SrB4O7:Sm2+ as a function of the pressure has been determined by the pressure gradient method in a diamond anvil cell. The results show that the yield strength of SrB4O7:Sm2+ increases from 2.85 GPa at a pressure of 7.9 GPa to 4.22 GPa at 25.4 GPa and is much smaller than that of ruby. The relatively small high-pressure yield strength of SrB4O7:Sm2+ is at the same level of the most sample materials. This would result in a small pressure difference with the coexisting sample, thus lead to a small error in the pressure measurement. The smaller yield strength and excellent fluorescent spectral characters of SrB4O7:Sm2+ make it a good substitute for ruby as a pressure scale in high-pressure experiments, especially under non-hydrostatic pressure environments.

Dependence of Yield Strength on Ferrite Grain Size in Ferrite/Cementite and Ferrite/Pearlite Structures of Medium Carbon Steel

Medium carbon steels have low yield ratio (YR). In order to obtain high yield strength (YS) for them, different microstructures including ferrite(F)/cementite(C) and ferrite(F)/pearlite(P) are prepared and the microstructure for high YR as well as its mechanism is clarified. The purpose of this study is, therefore, to elucidate the effect of ferrite grain size on YS in the relationship between F/P and F/C structures having the same tensile strength (TS) level. In case of F/C, YS can be significantly improved through grain refinement with a slight decrease in ductile properties. This is particularly clear by comparison of F/C with a ferrite grain size of 0.6m and F/P, where both structures show the same TS level while the YS level is significantly different; F/P representing much smaller YS than that of F/C. It is also to be noted that F/P microstructure shows low YS compared to its high TS with a generation of dislocations at the interface between ferrite and cementite in its pearlite phase. In conclusion it is necessary to consider the difference in the YS-TS relationship between F/C and F/P in order to make the most of its forging processing.

Cyclic Response of Concrete Beams Reinforced by Plain Bars

There are many reinforced concrete structures throughout the world that have been built in the past decades that lack appropriate seismic details and reinforced by plain bars. To study the behavior of such buildings, seven beams have been tested under cyclic and monotonic load. The specimens include substandard specimens, with deficient seismic details and reinforced by plain bars, specimens designed in accordance with ACI-318-99 but reinforced by plain bars, and standard specimens reinforced by deformed bars. The tests indicate that the substandard specimens sustain relatively large slip of longitudinal bars, separation of specimen relative to foundation and sliding at large deformation phase, low initial stiffness ratio, limited lateral displacement capacity, and loss of nominal yield strength. The specimens reinforced by plain bars in accordance with ACI-318-99 perform almost similar to standard specimens with deformed bars, in terms of elastic stiffness and lateral displacement ductility; but, they sustain larger slip, and smaller yield strength. Failure of all specimens reinforced by plain bars is characterized by flexural cracks without visible shear failure. Residual shear strength of substandard specimens is modeled by dowel action of longitudinal bars to predict a lower limit for lateral strength of the specimens.

Vent geometry and eruption conditions of the mixed rhyolite–basalt Námshraun lava flow, Iceland

We describe the morphology and circumstances of eruption of the mixed rhyolite–basalt lava flow Námshraun in the Torfajökull–Vei∂ivötn area of central Iceland. The unusual location and exposure of the elongate fissure vent permits its length along strike (a total of ∼ 275 m) and the width of the dyke feeding it (up to ∼ 10 m) to be estimated in the field. Using analyses of the heat losses during the rise of the mixed magma through the shallow part of its conduit system, we are able to refine the absolute minimum dyke width estimate to ∼ 1.5 m. The lengths of the two main lava flow lobes, assuming that their advance was cooling-limited, imply that the volume effusion rate of the lava varied between ∼ 2.7 and ∼ 1.5 m 3 s − 1 as different parts of the fissure became active. Prior to its emergence at the surface the magma had at most a small yield strength (probably significantly less than ∼ 3000–4000 Pa) and a near-Newtonian viscosity in the range ∼ 1 × 10 4 to ∼ 5 × 10 6 Pa s. After its eruption, the lava formed flows with marginal levées whose sizes imply a yield strength just less than 30 kPa. The lava in the central channels between the levées can be modeled either as a Newtonian fluid with a viscosity of between 3 × 10 7 and 6 × 10 7 Pa s or as a Bingham plastic. Estimates of the plastic viscosity from the two main flow lobes (< 10 4 to ∼ 6 × 10 5 and 1.2 × 10 7 to 1.8 × 10 7 Pa s) differ by a very large factor (at least 30) and are regarded as unreliable; however, they lead to a much smaller range of apparent viscosities, from ∼ 1.5 × 10 7 to ∼ 5.5 × 10 7 Pa s, values very similar to the viscosities found when the rheology is assumed to be Newtonian. If the field estimate of the dyke width is reliable, these results imply that the viscosity (and yield strength) of the magma averaged over the path from its source to the surface had increased by a factor close to 10 by the time that it emerged from the vent; alternatively the feeder dike may have been almost twice as wide during the eruption and relaxed to the presently exposed width as the eruption ended. The typical advance speeds of the two main flow lobes were less than 4 mm s − 1 and their emplacement times were ∼ 2.5 and ∼ 5 days. The implications for the sizes of the conduits feeding other rhyolitic and mixed lavas in central Iceland are discussed.

On the dynamics of subaqueous clay rich gravity mass flows—the giant Storegga slide, Norway

The Storegga slide, released about 8200 years ago off the western coast of Norway, is a complex system of debris flows which occurred on the remains of previous Pleistocenic slides materials. Following geological mapping and interpretation of data gathered with geological and geophysical methods, the Storegga slide has been interpreted as consisting of a giant slide (volume ≈3100 km 3 and runout of about 400 km) followed by a swarm of progressively smaller events. The flow of the giant slide, object of the present, study, represents a dynamical enigma. Indeed, if one simulates the flow of the giant slide with simple non-Newtonian soil properties constant along the path, extremely small yield strength must be attributed to the material. This finding is incompatible with observations of the smaller slides, where the simplest non-Newtonian soil properties models work well with a yield strength more than one order of magnitude larger. A possible conclusion is that the material has charged its properties during the flow. Numerical simulations are conducted with a newly introduced model where in analogy with soil mechanical models, the material progressively loses strength during the flow. The model gives results comparable to field data if the shear strength decreases by at least a factor of 30 during flow.

The internal structure of lava flows—insights from AMS measurements I: Near-vent a'a

Two small near-vent a'a flows (one from Xitle, Mexico and the other from Mauna Kea, Hawaii) showing a conspicuous pattern of concentric vesicle foliation were used to investigate how anisotropy of magnetic susceptibility (AMS) measurements relates to the internal structure of lava flows. The results show an almost perfect match between the vesicle foliation and the plane containing the maximum and intermediate principal susceptibilities, or plane of magnetic foliation. Both types of foliation can be explained by variations in the relative magnitudes of local shear stresses, assuming a unidirectional velocity within the lava flows. The attitude of the plane of magnetic foliation provides a three-dimensional picture of the dynamic behavior of flowing lava, and might be applicable also in instances when no other foliation is observable. A strong imbrication occurs, marked by the distribution of magnetic foliation parallel to a family of nested cones the axis of which coincides with the flow axis, and the apices of which point down-flow. Flow of lava having, at least in part, a stationary roof and possessing a small yield strength is consistent with the velocity profiles inferred from the orientation of the foliations. A model based on its fluid behavior is proposed to explain the origin of the AMS of lava. At variance with existing qualitative models, our model allows a semi-quantitative systematic explanation of the different circumstances under which any principal susceptibility is parallel to the flow direction.