Experimental research on creep behaviors of sandstone under uniaxial compressive and tensile stresses

The consideration of time dependence is essential for the study of deformation and fracturing processes of rock materials, especially for those subjected to strong compressive and tensile stresses. In this paper, the self-developed direct tension device and creep testing machine RLW-2000M are used to conduct the creep tests on red sandstone under uniaxial compressive and tensile stresses. The short-term and long-term creep behaviors of rocks under compressive and tensile stresses are investigated, as well as the long-term strength of rocks. It is shown that, under low-stress levels, the creep curve of sandstone consists of decay and steady creep stages; while under high-stress levels, it presents the accelerated creep stage and creep fracture presents characteristics of brittle materials. The relationship between tensile stress and time under uniaxial tension is also put forward. Finally, a nonlinear viscoelastoplastic creep model is used to describe the creep behaviors of rocks under uniaxial compressive and tensile stresses.

IMPROVING MATERIAL REMOVAL RATE OF BRITTLE CERAMICS THROUGH HONING INCIDENTAL TENSILE STRESSES

The stress intensity factors and stress conditions of machining cracks are analyzed by fracture mechanics on the basis of honing characteristics and of brittle ceramic mechanical behavior.Because the honing incidental tensile stresses effectively decrease the critical grinding stresses and increase the stress intensity factors of machining cracks,the honing process can be carried out easily.The results show that honing can be an efficient machining method for brittle materials.

Analysis of stresses at the center of transversely isotropic Brazilian disk

This article presents the stresses at the center of a Brazilian disk(BD)for transversely isotropic rocks.It is shown that the solution of stresses at the center of an anisotropic disk is a function of the disk radius and the magnitude of applied load,as well as the material orientation with respect to the load axis and two dimensionless ratios with specific physical meanings and limitations.These two dimensionless parameters are the ratios of Young’s modulus and apparent shear modulus,although the ratio of apparent shear modulus will be eliminated if the Saint-Venant assumption is considered.Considerable finite element simulations are carried out to find the stresses at the disk center concerning the material orientation and the two dimensionless parameters.Also,an approximate formula obtained from analytical results,previously proposed in the literature for solving the tensile and compressive stresses at the disk center,is re-written and simplified based on these new definitions.The results of the approximate formula fitted to the analytical results are compared to those obtained from numerical solutions,suggesting a good agreement between the numerical and analytical methods.An approximate equation for the shear stress at the disk center is also formulated based on the numerical results.Finally,the influence of the assumptions for simplification of the proposed formula for the tensile,compressive,and shear stresses at the disk center is discussed,and simple and practical equations are proposed as estimations for the stresses at the center of the BD specimen for low to moderate anisotropic rocks.For highly anisotropic rocks,the reference plots can be used for more accuracy.

TENSILE PROPERTIES AND CREEP RESISTANCE OF AZ91 ALLOY CONTAINING ANTIMONY

Small amount of antimony addition to the Mg-9Al-0.8Zn-0.2Mn(AZ91) alloy results in the obvious increase of tensile strength at both ambient and elevated temperatures. The creep resistance at the temperatures up to 200°C is also improved significantly by antimony addition. Microstructural observations revealed that the addition of antimony modifies morphology of the β(Mg17Al12) phase and causes the formation of some rod-shaped precipitates Mg3Sb2 at grain boundaries. These precipitates have high thermal stability and play an important role for strengthening grain boundaries at elevated temperatures.

Film-induced Tensile Stress during CorrosionProcess for α-Ti

The α-Ti foil with protective layer in one side bended to corrosion surface gradually during corrosion process in 0.1 mol/L H2SO4, while the passive film was formed, i.e., a tensile stress was developed in the surface layer of the sample. The extra tensile Stress grew gradually, whose maximum value is =313 MPa (average of 5 samples), which is near or reaches the yield stress. The extra tensile stress would be added to the load Stress during SCC to facilitate the emission and motion of dislocation, so that SCC cracks could nucleate in lower Stress(or lower KI).

EFFECT OF TENSILE STRESS AND RESIDUAL STRESS ON THE SPONTANEOUS STRAY FIELD SIGNALS FROM THE SURFACE OF 0.45%C STEEL

In order to explore the quantitative method of metal magnetic memory testing（MMMT） and clarify the relationship between Hp（y）, the normal component of spontaneous stray field, and applied stress or residual stress, the static tensile tests of 0.45%C steel sheet specimens are carried out on a servo hydraulic MTS810 machine. Hp（y） values are measured during the test process by an EMS-2003 metal magnetic memory diagnostic apparatus and a non-magnetic electric control displacement instrument. Residual stresses of some points on the surface of a specimen are measured by a Stress Tech X-Stress 3000 X-ray diffraction instrument. The results show that the same variation rules of Hp（y） value versus applied tensile stress are presented under the different conditions of load-on and load-off. However, the same rule does not exist between the Hp（y） value and residual stress. The variation of Hp（y） value reflects the history of applied tensile stress.

Moiré method analysis for tensile strain field of 2024 aluminum alloy welded joint

Using experimental mechanics method of moiré analysis, strain field distributions of 2024 aluminum alloy welded joints under different conditions were investigated. The results show that moiré stripes of welded joint without trailing peening just before fracture are not only few and scattered but also uneven, and the stress mainly concentrates on the poor position welded toes during the tensioning process with the relatively poor mechanical properties of welded joints; When the method of welding with trailing peening is adopted, moiré stripes of welded joint just before fracture are relatively thick and even due to the strengthening welded toes during the welding process, and fracture position transfers from the welded toes to weld, at the same time the mechanical properties of welded joints are improved greatly than conventional welding which can show that the technology of trailing peening is effective to strengthen welded joints of aluminum alloy with high strength.

Tensile Stress Induced Phase Transformations in Zn-Al Alloy

Both furnace cooled and as-cast eutectoid Zn-Al alloys were investigated under external tensile stress at 100℃. It was observed that the external tensile stress caused decomposition of two metastable phases η'T and η'S which derived from both original state of the alloy, and a phase transformation, αf +ε→T' +η， in both furnace cooled and as-cast eutectoid Zn-Al alloys. Also spheroidized structure formed partially during tensile testing. Superplasticity of the alloy has been discussed correlating with the phase transformations and microstructural changes.

Distribution of Reinforcement in Tensile Flanges of Concrete T-shape Continuous Beam

In this paper the analysis of tensile stress distribution in flexural continuous T- beam has been presented. The observed damages in carrying deck of RC bridge over the Wieprz River in Baranow indicate that over pillar zones are not protected enough. The results of numerical analysis have shown that tensile stress in T- section beam appears not only in a web but in flanges as well. Thus reinforcing bars should be distributed within the whole effective width. This fact is mentioned in building codes, for example, in Eurocode 2： ＂Design of concrete structures＂, both in part 1.1 ＂General rules and rules for building＂ and in part 2 ＂Reinforced and prestressed concrete bridges＂, but there are not detailed rules how to place the bars in flanges of T-section.

Numerical Simulation of Stress Field in Physical Tempering Process of Flat Soda Lime Silica Glass

Based on the analysis of different theory for glass tempering process,the“structural theory”with stress relaxation and structural relaxation effects was selected to investigate the tempering of flat glass quantificationally.The geometrical model with small size and non-homogeneous mesh were considered to build the finite element models according to the characteristics of stress field.The tempering process of flat glass with12 mm thickness was calculated with the verified finite element model.The transient and permanent stress of the central area,edge and corner end of the flat glass are obtained and analyzed.From the calculation results of basic case,the transient tensile stress at the upper surface of the central area,the center point of edge,the edge of edge,the edge of corner were 14.30,18.94,40.76 and 34.75 MPa,respectively.The transient tensile stress at these points were dangerous to promote the glass to break during the tempering.In addition,the point at the diagonal line of symmetry plane in the thickness direction,which is 14 mm from corner,has the maximum permanent tensile stress about 70.01 MPa in the flat glass after tempering.Thus,it is indicated that the corner is the weakest region in the tempered glass.

Chloride Resistance of Concrete under Complex Stress and Environment

The presence of stress is shown to have a significant impact on chloride ions in concrete. Reinforced concrete is usually durable and cost-effective which has resulted in its widespread use for construction, however, the concrete subjected to environment and load has become increasingly apparently that attacked by aggressive agents such as chloride ion. In this study, the coupling influences are stress effects and environmental problems on the coastline concrete durability have been investigated. A series of cyclic of a wet-dry cycle and submersion tests were performed onto the stressed concrete to obtain an understanding of the physical mechanisms causing the accumulation of chlorides in the interior pores of concrete under different stress types and exposure environments, based on the same duration. Specimens were prepared and subjected to NaCl solution in a wet-dry cycle and submersion, the chloride in the tension zone is gradual with increasing the stress level, as well as the chloride ion in the wet-dry cycle, is increasing the number of cycles. The apparent diffusion coefficient of each specimen was calculated respectively, the profile of concentration at a different section of tension and compression zones were presented in influence factors of the number of cycles, the length of drying phase, and periodic wetting cycles with sodium solution was discussed. After employed Fick’s second law, the results suggested Da in a wet-dry cycle is much higher than the Da in submersion zones.

Oxidation behavior of Ni-based superalloy GH4738 under tensile stress

Revealing the oxidation behavior of superalloys is crucial for optimizing material properties and extending service life.This study investigated the oxidation behavior of superalloy GH4738 under stress states at 850℃.High-throughput specimens were fabricated to withstand different stresses at the same time.Isothermal oxidation s amples were analyzed using the mass gain method to obtain oxidation kinetic curves.The results show that the external stress below 200 MPa could improve the oxidation resistance of the GH4738.With tensile stress increasing,the oxide layer becomes thinner,denser and more complete,while internal oxidation decreases.The tensile stress alters the structure of the external oxide layer from a two-layer to a threelayer configuration.The Cr_(2)O_(3) oxide layer inhibits the outward diffusion of Ti,leading to Ti enrichment at the oxide-matrix interface and altering the oxidation mechanism of GH4738.

Numerical analysis of crack generation within embankment built on expansive soil foundation

In order to analyze the initial cracking behavior of highway embankment in the regions of expansive soil, the changes in peaks of tensile stress and their location on top of the embankment for a typical highway embankment section were simulated by ABAQUS. The simulation results indicate that the matric suction was a concave distribution on top of the expansive soil foundation and that it induced differential deformation of foundation and embankment. The peaks of tensile stress on top of the embankment are not located at a fixed site, but gradually move towards the shoulder following the evaporation duration. When the evaporation intensity is larger, the peak of tensile stress on top of embankment increases at a faster rate following the evaporation duration,and its location is closer to the shoulder. The thicker expansive soil layer helps the peaks of tensile stress to reach the critical tensile stress quickly, but the embankment cannot crack when the expansive soil layer is no more than 1.5m after 30d soil surface evaporation; the higher the embankment, the smaller the peak of tensile stress occurring on top of the highway embankment, and its location will be further away from the shoulder. Therefore, a higher embankment constructed on a thinner expansive soil layer can reduce the crack generation within the highway embankment.

Mechanical model for failure modes of rock and soil under compression

The failure modes of rock and soil under compression are complex phenomena that have not been explained in a mechanical perspective. However, large amounts of studies indicate that the failure modes of rock and soil samples can be categorized into eight types. In this work, the inner tensile stress and the dissipation and conversion of energy of rock and soil under compression are analyzed, then the effective conversion coefficient of energy is deduced, thus the tensile failure criterion of rock and soil under compression is established. Combined with the shear strength criterion of Mohr–Coulomb, a tensile joint shear strength criterion for rock and soil under compression is built. Therefore, a mechanical criterion model concerning the failure modes of rock and soil under compression is established and verified by tests. This model easily explains the test results in the existing literature and many natural phenomena, such as collapse.

Study on Strength and Life of Anisotropic Single Crystal Blade - Part I: Crystallographic Constitutive Models and Applications

The single crystal blade is one of the key technologies for improving the performance, durability and reliability of aero-engines and ground gas-turbine engines. However, the anisotropic mechanical properties of the single crystal material makes a great deal of difficulties on the development and the application of the single crystal blade, which is a challenge for the engineering application of the single crystal superalloy and the theoretic bases of the application. Some researches on the strength analysis and the life prediction of the anisotropic single crystal blade were carried out by the authors' research team. They are as follows. The crystallographic constitutive models for the plastic and the creep behaviors and the method of the rupture life prediction were established and verified. The tensile or the creep experiments for DD3 single crystal alloy with different orientations under different temperatures and different tensile rates or under different temperatures and different stress levels were carried out. The experimental data and the anisotropic properties at intermediate and high temperatures revealed by the experiments are significant for the application of the single crystal alloy. In addition, the experimental research for a kind of single crystal blade was also made. As the application of the researches the strength analysis and the life prediction were carried out for the single crystal blade of a certain aero-engine. In this part, the constitutive models and their applications are described, and the experimental research work will be described in part II.

Stress and strain analysis on the anastomosis site sutured with either epineurial or perineurial sutures after simulation of sciatic nerve injury

The magnitude of tensile stress and tensile strain at an anastomosis site under physiological stress is an important factor for the success of anastomosis following suturing in peripheral nerve injury treatment. Sciatic nerves from fresh adult cadavers were used to create models of sciatic nerve injury. The denervated specimens underwent epineurial and perineurial suturing. The elastic modulus （40.96 ＋ 2.59 MPa） and Poisson ratio （0.37 ＋ 0.02） of the normal sciatic nerve were measured by strain electrical measurement. A resistance strain gauge was pasted on the front, back left, and right of the edge of the anastomosis site after suturing. Strain electrical measurement results showed that the stress and strain values of the sciatic nerve following perineurial suturing were lower than those following epineurial suturing. Scanning electron microscopy revealed that the sciatic nerve fibers were disordered following epineurial compared with perineurial suturing. These results indicate that the effect of perineurial suturing in sciatic nerve injury repair is better than that of epineurial suturing.

Mechanical Properties of Asphalt Pavement Structure in Highway Tunnel

A linear full 3D finite element method (FEM) was performed in order to present the key design parameters of highway tunnel asphalt pavement under double-wheel load on rectangular loaded area considering horizontal contact stress induced by the acceleration/deceleration of vehicles.The key design parameters are the maximum horizontal tensile stresses at the surface of the asphalt layer,the maximum horizontal tensile stresses at the bottom of the asphalt layer and the maximum vertical shear stresses at the surface of the as- phalt layer were calculated.The influencing factors such as double-wheel weight;asphalt layer thickness;base course stiffness modulus and thickness;and the contact conditions among the structure layers on these key design parameters were also examined separately to propose construction procedures of highway tunnel asphalt pavement.

Microstructural,Mechanical,Electrical,and Thermal Properties of the Bi-Sn-Ag Ternary Eutectic Alloy

The development of lead-free solders has emerged as one of the key issues in the electronics packaging industries.Bi-Sn-Ag eutectic alloy has been considered as one of the lead-free solder materials that can replace the toxic Pb-Sn eutectic solder without increasing soldering temperature.We investigated the effects of temperature gradient and growth rate on the mechanical,electrical and thermal properties of the BiSn-Ag ternary eutectic alloy.Bi-47 wt%Sn-0.68 wt%Ag alloy was directionally solidified upward with different temperature gradients（G=2.33-5.66 K/mm） at a constant growth rate（V=13.25 μm/s） and with different growth rates（V=6.55-132.83 μm/s） at a constant temperature gradient（G=2.33 K/mm） in the growth apparatus.The microstructures（λ）,microhardness（HV）,tensile stress（σ）,electrical resistivity（ρ）,and thermal properties（△H,Cp,Tm） were measured on directionally solidified samples.The dependency of the λ,HV,σ,and ρ on G and V was investigated.According to the experimental results,X values decrease with increasing G and V,but HV,λ,and ρ values increase with increasing G and V.Variations of electrical resistivity（ρ） for cast samples with the temperature in the range of 300-400 K were also measured by using a standard dc four-point probe technique.The enthalpy of fusion（△H） and specific heat（Cp） for the same alloy was also determined by means of differential scanning calorimeter（DSC） from heating trace during the transformation from eutectic liquid to eutectic solid.

MECHANICAL ANALYSIS OF CYLINDERS BEING UPSET BETWEEN SPHERICAL CONCAVE PLATEN AND CONCAVE SUPPORTING PLATE

Mechanical analysis of cylinders being upset between spherical concave platen and concave supporting plate is conducted. Rigid-plastic mechanical models for cylinders are presented. When the ratio of height to diameter, is larger than 1, there exists two-dimensional tensile stress in the deformed body, when the ratio is smaller than 1, there exists shear stress in static hydraulic zone. The former breaks through the theory that there is three-dimensional compressive stress irrespective of any ratio of height to diameter. The latter satisfactorily explains the mechanism of layer-like cracks in disk-shaped forgings and the flanges of forged gear axles. The representation of the two models makes the upsetting, theory into correct and perfect stage.

Experimental study on complete stress-deformation curves of larger-size concrete specimens subjected to uniaxial tension

In order to provide parameters for numerical analyses of the huge Three-Gorge concrete dam (2309 m long by 175 m height), complete tensile stress-deformation curves for large-size plain concrete specimens were measured and studied by per-forming uniaxial tensile tests on large-size unnotched specimens (250 mm×250 mm×1400 mm). The specimens were prepared with the three-graded-aggregate materials provided by the client of the Three-Gorge project. To prevent a failure occurring near the ends of the unnotched specimens, both the ends of each specimen (450 mm in length) were cast using a higher-strength concrete than the middle part (i.e., active part). Tensile tests were completed on a specially-designed tensile testing machine, which can be easily re-assembled to accommodate different-size specimens. To make the specimens fail stably, a cyclic loading scheme was adopted after the peak strength was reached. Four of five tests in this study were successful, and four complete tensile stress-deformation curves were obtained. It was found that the post-peak curve of the large-size specimens used in this study is more gradual than those for the small-size specimens reported in the literature.