To evaluate the room-temperature hydrogen embrittlement susceptibility(HES) of high-pressure hydrogen storage vessels, a modified slow-strain-rate tensile(MSSRT) testing method was proposed for effectively aligning wi...To evaluate the room-temperature hydrogen embrittlement susceptibility(HES) of high-pressure hydrogen storage vessels, a modified slow-strain-rate tensile(MSSRT) testing method was proposed for effectively aligning with their actual operating conditions. The effectiveness of the MSSRT testing method in evaluating the room-temperature HES of steels under high pressure was validated by comparing the results obtained using the conventional slow strain rate tensile(SSRT) and proposed MSSRT testing methods for 30CrMo steel, which is widely used for manufacturing high-pressure hydrogen storage vessels. The tensile properties and fracture morphologies of 23Cr2Ni4MoV steel were then examined using the MSSRT testing method under 35 MPa hydrogen and nitrogen at room temperature. Results indicate that 35 MPa hydrogen exerted a marginal effect on the tensile properties of 23Cr2Ni4MoV steel at room temperature when considering the MSSRT testing method;moreover, the test specimen basically exhibited macroscopic ductile fracture. Furthermore, obvious surface cracking was observed on the fractured specimen tested under hydrogen, whereas surface cracking was not observed on the fractured specimen tested under nitrogen. Hence, the relative reduction of area and surface cracking are necessary criteria for evaluating the room-temperature HES of steels using the MSSRT testing method. Overall, 23Cr2Ni4MoV steel might be unsuitable for manufacturing high-pressure hydrogen storage vessels.展开更多
The tensile properties of three different carbonfiberreinforced carbon composites (C/C), mat C/C, 2D laminate and 4D C/C, were investigated under the combined influence of temperature and loading rate. From the experi...The tensile properties of three different carbonfiberreinforced carbon composites (C/C), mat C/C, 2D laminate and 4D C/C, were investigated under the combined influence of temperature and loading rate. From the experiments the following could be concluded: loading rate between 10-1-10 mm/min was valid; the fracture stress of the three kinds of C/C composites increased with increasing temperature in the range from room temperature to 1900, and the initial modulus of 2D laminate C/C composites increased with the increase of temperature up to 2000.展开更多
The reduced-activation ferritic/martensitic(RAFM)steel CLF-1 has been designed as a candidate structural material for nuclear fusion energy reactors.For engineering mechanical design,the effects of temperature on the ...The reduced-activation ferritic/martensitic(RAFM)steel CLF-1 has been designed as a candidate structural material for nuclear fusion energy reactors.For engineering mechanical design,the effects of temperature on the strain distribution of CLF-1 steel during uniaxial tensile tests were explored within the temperature range from room temperature to 650°C using uniaxial tensile tests combined with in situ digital image correlation analysis.Strain-concentrated regions alternately distributed±45°along the tensile direction could be attributed to the shear stress having the maximum value at±45°along the tensile direction and the coordinated deformation of the microstructure.The total strain distribution changed from a normal distribution to a lognormal distribution with increasing deformation owing to the competition between the elastic and plastic strains at all test temperatures.Strain localization has a strong relationship with temperature at the same engineering strain because of the temperature effects on dynamic strain aging(DSA).The stronger the DSA effect,the stronger the strain localization.With increasing temperature,the stronger the strain localization at the same strain,the weaker the plasticity,that is,DSA-induced embrittlement,and the slower the strength decline,that is,DSA-induced hardening.展开更多
The mechanical properties of the SiC fiber-reinforced Mg-Al metal matrix composite materials have been studied on internal microstructure by (scanning electron microscopy) SEM in-situ tensile test. The emergence and p...The mechanical properties of the SiC fiber-reinforced Mg-Al metal matrix composite materials have been studied on internal microstructure by (scanning electron microscopy) SEM in-situ tensile test. The emergence and propagation of the crack, and the fracture behavior in materials have been observed and studied. It is found that in the case of the tensile test, the crack emerged in SiC fiber initially. In the case of the strong cohesion of the fiber-metal interface, the crack propagated in the fiber, meanwhile the fibers in the neighborhood of the cracked fiber began to crack and the Mg-Al metal deformed plastically, and at last the material fractured. Otherwise the toughness of the materials grows in the case of the lower cohesion of the fiber-metal matrix interface.展开更多
An investigation on the plastic behavior of AZ31 magnesium alloy under ultrasonic vibration（with a frequency of 15 kHz and a maximum output of 2 kW） during the process of tension at room temperature was conducted to...An investigation on the plastic behavior of AZ31 magnesium alloy under ultrasonic vibration（with a frequency of 15 kHz and a maximum output of 2 kW） during the process of tension at room temperature was conducted to reveal the volume effect of the vibrated plastic deformation of AZ31.The characteristics of mechanical properties and microstructures of AZ31 under routine and vibrated tensile processes with different amplitudes were compared.It is found that ultrasonic vibration has a remarkable influence on the plastic behavior of AZ31 which can be summarized into two opposite aspects：the softening effect which reduces the flow resistance and improves the plasticity,and the hardening effect which decreases the formability.When a lower amplitude or vibration energy is applied to the tensile sample,the softening effect dominates,leading to a decrease of AZ31 deformation resistance with an increase of formability.Under the application of a high-vibrating amplitude,the hardening effect dominates,resulting in the decline of plasticity and brittle fracture of the samples.展开更多
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...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.展开更多
The biaxial tensile behavior of isotropic Ti-6Al-4 V is characterized in this paper.A novel cruciform specimen was designed and optimized to achieve uniform stress and strain distribution within the gauge area.Biaxial...The biaxial tensile behavior of isotropic Ti-6Al-4 V is characterized in this paper.A novel cruciform specimen was designed and optimized to achieve uniform stress and strain distribution within the gauge area.Biaxial tensile tests were conducted at three different loading ratios by the biaxial testing machine.The Digital Image Correlation(DIC)technique was applied to determine strain distribution,and a high-speed camera was employed to record the fracture process.An Inverse Analysis(IA)approach with a combined experimental and numerical method was proposed to determine the true stresses at the gauge section of the specimen during biaxial tensile tests.The results indicate that the initial yield locus can be described by the Cazacu criterion accurately,whereas the Mises criterion can predict better the strengthening behavior of Ti-6Al-4 V in the first quadrant in the principal stress space.展开更多
In this study, slow strain rate tensile testing at elevated temperature is used to evaluate the influence of temperature and strain rate on deformation behaviour in two different austenitic alloys. One austenitic stai...In this study, slow strain rate tensile testing at elevated temperature is used to evaluate the influence of temperature and strain rate on deformation behaviour in two different austenitic alloys. One austenitic stainless steel （AISI 316L） and one nickel-base alloy （Alloy 617） have been investigated. Scanning electron microscopy related techniques as electron channelling contrast imaging and electron backscattering diffraction have been used to study the damage and fracture micromechanisms. For both alloys the dominante damage micromech- anisms are slip bands and planar slip interacting with grain bounderies or precipitates causing strain concentrations. The dominante fracture micromechanism when using a slow strain rate at elevated temperature, is microcracks at grain bounderies due to grain boundery embrittlement caused by precipitates. The decrease in strain rate seems to have a small influence on dynamic strain ageing at 650℃.展开更多
Co68.15Fe4.35Si12.25B15.25 （at%） amorphous microwires with a smooth surface and a circular cross-section were fabricated by the glass-coated melt spinning method. Their mechanical properties were evaluated through t...Co68.15Fe4.35Si12.25B15.25 （at%） amorphous microwires with a smooth surface and a circular cross-section were fabricated by the glass-coated melt spinning method. Their mechanical properties were evaluated through tensile tests of the glass-coated amorphous mi-crowires, and their fracture reliability was estimated using two-and three-parameter Weibull analysis. X-ray diffraction and transmission electron microscopy results showed that these glass-coated Co-based microwires were mostly amorphous. The coated Co-based microwires exhibit a tensile strength of 1145 to 2457 MPa, with a mean value of 1727 MPa and a variance of 445 MPa. Weibull statistical analysis showed that the tensile two-parameter Weibull modulus of the amorphous microwires is 4.16 and the three-parameter Weibull modulus is 1.61 with a threshold value as high as 942 MPa. These results indicate that the fabricated microwires exhibit good tensile properties and fracture reliability, and thus appear to be good candidates for electronics reliability engineering applications.展开更多
This article focuses on the tensile and compressive characteristics of a Ti-based bulk metallic glass composite （BMGC）. It is found that the yield stress, maximum strength, and fracture strain are 1380 MPa, 1516 MPa...This article focuses on the tensile and compressive characteristics of a Ti-based bulk metallic glass composite （BMGC）. It is found that the yield stress, maximum strength, and fracture strain are 1380 MPa, 1516 MPa, and 4.3% for uniaxial tension, but 1580 MPa, 4010 MPa, and 29% for uniaxial compression, respectively. The composite displays a linear ＂work hardening＂ capacity under compression; however, the ＂work softening＂ behavior is observed in the true engineering stress-strain curve upon tensile loading. The fracture surfaces of specimens also exhibit dissimilar properties under the different loadings.展开更多
The objective of this paper was to predict the residual strength of post impacted carbon/epoxy composite laminates using an online acoustic emission （AE） monitoring and artificial neural networks （ANN）. The lamina...The objective of this paper was to predict the residual strength of post impacted carbon/epoxy composite laminates using an online acoustic emission （AE） monitoring and artificial neural networks （ANN）. The laminates were made from eight-layered carbon （in woven mat form） with epoxy as the binding medium by hand lay-up technique and cured at a pressure of 100 kg/cm2 under room temperature using a 30 ton capacity compression molding machine for 24 h. 21 tensile specimens （ASTM D3039 standard） were cut from the cross ply laminates. 16 specimens were subjected to impact load from three different heights using a Fractovis Plus drop impact tester. Both impacted and non-impacted specimens were subjected to uniaxial tension under the acoustic emission monitoring using a 100 kN FIE servo hydraulic universal testing machine. The dominant AE parameters such as counts, energy, duration, rise time and amplitude are recorded during monitoring. Cumulative counts corresponding to the amplitude ranges obtained during the tensile testing are used to train the network. This network can be used to predict the failure load of a similar specimen subjected to uniaxial tension under acoustic emission monitoring for certain percentage of the average failure load.展开更多
The conventional forming limit diagram （FLD） is described as a plot of major strain versus minor strain. However, FLD is dependent on forming history and strain path. In the present study, a forming limit stress-bas...The conventional forming limit diagram （FLD） is described as a plot of major strain versus minor strain. However, FLD is dependent on forming history and strain path. In the present study, a forming limit stress-based diagram （FLSD） has been adopted to predict the fracture limit of aluminum alloy （AA） 5052-O1 sheet. Nakazima test is simulated by plastic constitutive formula derived from the modified Gurson-Tvergaard-Needleman （GTN） model. An in situ tensile test with scanning electron microscope （SEM） is proposed to determine the parameters in GTN model. The damage evolution is observed and recorded, and the parameters of GTN model are identified through counting void fraction at three damage stages of AA5052-O 1. According to the experimental results, the original void volume fraction, the volume fraction of potential nucleated voids, the critical void volume fraction, the void volume fraction at the final failure of material are assigned as 0.002 918, 0.024 9, 0.030 103, 0.048 54, respectively. The stress and strain are obtained at the last loading step before crack. FLSD and FLD of AA5052-O 1 are plotted. Compared with the experimental Nakazima test and uniaxial tensile test, the predicted results show a good agreement. The parameters determined by in situ tensile test can be applied to the research of the forming limit for ductile metals.展开更多
Ultrasonic vibration can reduce the forming force, decrease the friction in the metal forming process and improve the surface quality of the workpiece effectively. Tensile tests of AZ31 magnesium alloy were carried ou...Ultrasonic vibration can reduce the forming force, decrease the friction in the metal forming process and improve the surface quality of the workpiece effectively. Tensile tests of AZ31 magnesium alloy were carried out. The stress–strain relationship, fracture modes of tensile specimens, microstructure and microhardness under different vibration conditions were analyzed, in order to study the effects of the ultrasonic vibration on microstructure and performance of AZ31 magnesium alloy under tensile deformation. The results showed that the different reductions of the true stress appeared under various ultrasonic vibration conditions, and the maximum decreasing range was 4.76%. The maximum microhardness difference among the 3 nodes selected along the specimen was HV 10.9. The fracture modes, plasticity and microstructure of AZ31 magnesium alloy also were affected by amplitude and action time of the ultrasonic vibration. The softening effect and the hardening effect occurred simultaneously when the ultrasonic vibration was applied. When the ultrasonic amplitude was 4.6 μm with short action time, the plastic deformation was dominated by twins and the softening effect was dominant. However, the twinning could be inhibited and the hardening effect became dominant in the case of high ultrasonic energy.展开更多
For understanding acoustic emission （AE） activity and accumulation of micro-damage inside rock under pure tensile state, the AE signals has been monitored on the test of directly tension on two kinds of marble speci...For understanding acoustic emission （AE） activity and accumulation of micro-damage inside rock under pure tensile state, the AE signals has been monitored on the test of directly tension on two kinds of marble specimens. A tensile constitutive model was proposed with the damage factor calculated by AE energy rate. The tensile strength of marble was discrete obviously and was sensitive to the inside microdefects and grain composition. With increasing of loading, the tensile stress-strain curve obviously showed nonlinear with the tensile tangent modulus decreasing. In repeated loading cycle, the tensile elastic modulus was less than that in the previous loading cycle because of the generation of micro damage during the prior loading. It means the linear weakening occurring in the specimens. The AE activity was corresponding with occurrence of nonlinear deformation. In the initial loading stage which only elastic deformation happened on the specimens, there were few AE events occurred; while when the nonlinear deformation happened with increasing of loading, lots of AE events were generated. The quantity and energy of AE events were proportionally related to the variation of tensile tangent modulus. The Kaiser effect of AE activity could be clearly observed in tensile cycle loading. Based on the theory of damage mechanics, the damage factor was defined by AE energy rate and the tensile damage constitutive model was proposed which only needed two property constants. The theoretical stress-strain curve was well fitted with the curve plotted with tested datum and the two property constants were easily gotten by the laboratory testing.展开更多
Silicon carbide nanoparticle-reinforced nickel-based composites（Ni–Si CNP）,with a Si CNPcontent ranged from1 to 3.5 wt%,were prepared using mechanical alloying and spark plasma sintering.In addition,unreinforced pu...Silicon carbide nanoparticle-reinforced nickel-based composites（Ni–Si CNP）,with a Si CNPcontent ranged from1 to 3.5 wt%,were prepared using mechanical alloying and spark plasma sintering.In addition,unreinforced pure nickel samples were also prepared for comparative purposes.To characterize the microstructural properties of both the unreinforced pure nickel and the Ni–Si CNPcomposites transmission electron microscopy（TEM） was used,while their mechanical behavior was investigated using the Vickers pyramid method for hardness measurements and a universal tensile testing machine for tensile tests.TEM results showed an array of dislocation lines decorated in the sintered pure nickel sample,whereas,for the Ni–Si CNPcomposites,the presence of nano-dispersed Si CNPand twinning crystals was observed.These homogeneously distributed Si CNPwere found located either within the matrix,between twins or on grain boundaries.For the Ni–Si CNPcomposites,coerced coarsening of the Si CNPassembly occurred with increasing Si CNPcontent.Furthermore,the grain sizes of the Ni–Si CNPcomposites were much finer than that of the unreinforced pure nickel,which was considered to be due to the composite ball milling process.In all cases,the Ni–Si CNPcomposites showed higher strengths and hardness values than the unreinforced pure nickel,likely due to a combination of dispersion strengthening（Orowan effects） and particle strengthening（Hall–Petch effects）.For the Ni–Si CNPcomposites,the strength increased initially and then decreased as a function of Si CNPcontent,whereas their elongation percentages decreased linearly.Compared to all materials tested,the Ni–Si CNPcomposite containing 1.5% Si C was found more superior considering both their strength and plastic properties.展开更多
The tensile strength at the rock-concrete interface is one of the crucial factors controlling the failure mechanisms of structures,such as concrete gravity dams.Despite the critical importance of the failure mechanism...The tensile strength at the rock-concrete interface is one of the crucial factors controlling the failure mechanisms of structures,such as concrete gravity dams.Despite the critical importance of the failure mechanism and tensile strength of rock-concrete interfaces,understanding of these factors remains very limited.This study investigated the tensile strength and fracturing processes at rock-mortar interfaces subjected to direct and indirect tensile loadings.Digital image correlation(DIC)and acoustic emission(AE)techniques were used to monitor the failure mechanisms of specimens subjected to direct tension and indirect loading(Brazilian tests).The results indicated that the direct tensile strength of the rock-mortar specimens was lower than their indirect tensile strength,with a direct/indirect tensile strength ratio of 65%.DIC strain field data and moment tensor inversions(MTI)of AE events indicated that a significant number of shear microcracks occurred in the specimens subjected to the Brazilian test.The presence of these shear microcracks,which require more energy to break,resulted in a higher tensile strength during the Brazilian tests.In contrast,microcracks were predominantly tensile in specimens subjected to direct tension,leading to a lower tensile strength.Spatiotemporal monitoring of the cracking processes in the rock-mortar interfaces revealed that they show AE precursors before failure under the Brazilian test,whereas they show a minimal number of AE events before failure under direct tension.Due to different microcracking mechanisms,specimens tested under Brazilian tests showed lower roughness with flatter fracture surfaces than those tested under direct tension with jagged and rough fracture surfaces.The results of this study shed light on better understanding the micromechanics of damage in the rock-concrete interfaces for a safer design of engineering structures.展开更多
The stress state in a rock mass is complex. Stress redistribution around underground excavation may lead to various failure modes, including compressive-shear, tensile-shear, and tensile failures. The ability to perfo...The stress state in a rock mass is complex. Stress redistribution around underground excavation may lead to various failure modes, including compressive-shear, tensile-shear, and tensile failures. The ability to perform laboratory tests with these complex stress states is significant for establishing new strength criteria. The present paper introduces a new rock testing system with “tensile-compressive-shear”loading functions. The device includes bi-directional and double-range hydraulic cylinders, auxiliary loading equipment, and roller rows that can perform direct compressive-shear tests, direct tensile tests,and direct tensile-shear tests. The testing system provides maximum vertical and lateral loading forces of2000 k N and allows testing cubical rock specimens with dimensions of 0.5 m × 0.5 m × 0.5 m. The performance of the testing machine was evaluated by testing a rock-like material based on cement mortar under compressive-shear, tensile, and tensile-shear stress states. The failure process and deformation characteristics were monitored during loading using acoustic emission(AE) transient recorder,piezoelectric AE sensors, a high-speed camera, and a thermal infrared camera. The failure mechanism was investigated by analyzing AE counts, AE amplitude, strain, and temperature changes on the rock specimen surface. The test results confirmed that the testing system could successfully simulate the abovementioned stress path. The AE counts and amplitude responses were influenced by different failure modes. The temperature response during the compressive-shear test indicated the development of a high-temperature band on the rock specimen surface. In contrast, a negligible temperature change was observed during the tensile and tensile-shear tests. The newly developed multifunctional rock testing system allows laboratory tests under various failure modes. The monitoring results of multiple variables during rock failure tests provide valuable information on failure characteristics.展开更多
This paper focused on the effect of pre-strain on forming limit curves(FLC)of 5754-O aluminum alloy sheet through utilizing biaxial tensile approach.Based on Swift model and Yld2000-2 d yield criterion,the dimensions ...This paper focused on the effect of pre-strain on forming limit curves(FLC)of 5754-O aluminum alloy sheet through utilizing biaxial tensile approach.Based on Swift model and Yld2000-2 d yield criterion,the dimensions of cruciform specimen was optimized through applying finite element method for increasing the strain at specimen center.After that,with the recommended specimen size,the cruciform specimen was tested under various stroke ratios to experimentally characterize the limit strains under different pre-strain levels.Subsequently,the biaxial tensile tests were simulated by Abaqus to obtain the limit strains and validate the material models.It can be observed in both experiments and simulations that the pre-strained uniaxial tension followed by plane tension or equi-biaxial tension can improve the formability of sheet metals.Besides,the strain path change affects the trend of first derivative of strain rate difference between neighboring points with respect to time.An early increase occurred and then fell back to the stable value,the steady evolution continued until to a new increase reaching the critical value.The M–K prediction approach was simulated to verify the influence of pre-strain on FLC.It can be found that the early increase peaks of the major strain incremental ratio rose with the amplitude of pre-strain.Finally,the phenomenon of pseudolocalization caused by the strain path change was explained through evolution of stress state inside the groove.展开更多
Additive layer manufacturing （ALM） of aerospace grade titanium components shows great promise in supplying a cost-effective alternative to the conventional production routes. Complex microstructures comprised of col...Additive layer manufacturing （ALM） of aerospace grade titanium components shows great promise in supplying a cost-effective alternative to the conventional production routes. Complex microstructures comprised of columnar remnants of directionally solidifiedβ-grains, with interior inhabited by colonies of finerα-plate structures, were found in samples produced by layered plasma welding of Ti-6Al-4V alloy. The application of in-situ tensile tests combined with rapid offline electron backscatter diffraction （EBSD） analysis provides a powerful tool for understanding and drawing qualitative correlations between microstructural features and deformation characteristics. Non-uniform deformation occurs due to a strong variation in strain response between colonies and across columnar grain boundaries. Prismatic and basal slip systems are active, with the prismatic systems contributing to the most severe deformation through coarse and widely spaced slip lines. Certain colonies behave as microstructural units, with easy slip transmission across the entire colony. Other regions exhibit significant deformation mismatch, with local build-up of strain gradients and stress concentration. The segmentation occurs due to the growth morphology and variant constraints imposed by the columnar solidification structures through orientation relationships, interface alignment and preferred growth directions. Tensile tests perpendicular to columnar structures reveal deformation localization at columnar grain boundaries. In this work connections are made between the theoretical macro- and microstructural growth mechanisms and the observed microstructure of the Ti-6Al-4V alloy, which in turn is linked to observations during in-situ tensile tests.展开更多
Stress relaxation behavior of two turbine bolt steels was evaluated by the manual-controlled tensile stress relaxation test (TSRT) at high temperature. First, feasibility and the procedure of the manual-controlled ten...Stress relaxation behavior of two turbine bolt steels was evaluated by the manual-controlled tensile stress relaxation test (TSRT) at high temperature. First, feasibility and the procedure of the manual-controlled tensile stress relaxation test (TSRT) is discussed and carried out on a general creep testing machine. And then, the experimental results from such type of test were compared to the existing data provided by certain Laboratory U.K. Overall good agreement between the results of manual-controlled TSRT method and the existing data provides confidence in the use of the proposed method in practice. Finally, the experimental results of turbine bolt steels from TSRT were compared with that of bending test. It is observed that great difference exists between the results from two different type stress relaxation tests. It is therefore suggested that the results from TSRT method be adopted in turbine bolt design in engineering.展开更多
基金Supported by National Key Research and Development Program of China (Grant No. 2023YFB3408300)the Doctoral Science and Technology Foundation of Hefei General Machinery Research Institute Co.Ltd.(Grant No. 2023010792)。
文摘To evaluate the room-temperature hydrogen embrittlement susceptibility(HES) of high-pressure hydrogen storage vessels, a modified slow-strain-rate tensile(MSSRT) testing method was proposed for effectively aligning with their actual operating conditions. The effectiveness of the MSSRT testing method in evaluating the room-temperature HES of steels under high pressure was validated by comparing the results obtained using the conventional slow strain rate tensile(SSRT) and proposed MSSRT testing methods for 30CrMo steel, which is widely used for manufacturing high-pressure hydrogen storage vessels. The tensile properties and fracture morphologies of 23Cr2Ni4MoV steel were then examined using the MSSRT testing method under 35 MPa hydrogen and nitrogen at room temperature. Results indicate that 35 MPa hydrogen exerted a marginal effect on the tensile properties of 23Cr2Ni4MoV steel at room temperature when considering the MSSRT testing method;moreover, the test specimen basically exhibited macroscopic ductile fracture. Furthermore, obvious surface cracking was observed on the fractured specimen tested under hydrogen, whereas surface cracking was not observed on the fractured specimen tested under nitrogen. Hence, the relative reduction of area and surface cracking are necessary criteria for evaluating the room-temperature HES of steels using the MSSRT testing method. Overall, 23Cr2Ni4MoV steel might be unsuitable for manufacturing high-pressure hydrogen storage vessels.
文摘The tensile properties of three different carbonfiberreinforced carbon composites (C/C), mat C/C, 2D laminate and 4D C/C, were investigated under the combined influence of temperature and loading rate. From the experiments the following could be concluded: loading rate between 10-1-10 mm/min was valid; the fracture stress of the three kinds of C/C composites increased with increasing temperature in the range from room temperature to 1900, and the initial modulus of 2D laminate C/C composites increased with the increase of temperature up to 2000.
基金supported by the National Natural Science Foundation of China(Nos.12175231 and 11805131)Anhui Natural Science Foundation of China(No.2108085J05)the Collaborative Innovation Program of Hefei Science Center,CAS(No.2022HSC-CIP009)。
文摘The reduced-activation ferritic/martensitic(RAFM)steel CLF-1 has been designed as a candidate structural material for nuclear fusion energy reactors.For engineering mechanical design,the effects of temperature on the strain distribution of CLF-1 steel during uniaxial tensile tests were explored within the temperature range from room temperature to 650°C using uniaxial tensile tests combined with in situ digital image correlation analysis.Strain-concentrated regions alternately distributed±45°along the tensile direction could be attributed to the shear stress having the maximum value at±45°along the tensile direction and the coordinated deformation of the microstructure.The total strain distribution changed from a normal distribution to a lognormal distribution with increasing deformation owing to the competition between the elastic and plastic strains at all test temperatures.Strain localization has a strong relationship with temperature at the same engineering strain because of the temperature effects on dynamic strain aging(DSA).The stronger the DSA effect,the stronger the strain localization.With increasing temperature,the stronger the strain localization at the same strain,the weaker the plasticity,that is,DSA-induced embrittlement,and the slower the strength decline,that is,DSA-induced hardening.
文摘The mechanical properties of the SiC fiber-reinforced Mg-Al metal matrix composite materials have been studied on internal microstructure by (scanning electron microscopy) SEM in-situ tensile test. The emergence and propagation of the crack, and the fracture behavior in materials have been observed and studied. It is found that in the case of the tensile test, the crack emerged in SiC fiber initially. In the case of the strong cohesion of the fiber-metal interface, the crack propagated in the fiber, meanwhile the fibers in the neighborhood of the cracked fiber began to crack and the Mg-Al metal deformed plastically, and at last the material fractured. Otherwise the toughness of the materials grows in the case of the lower cohesion of the fiber-metal matrix interface.
基金supported by the Natural Science Foundation Project of Chongqing Science and Technology Commission,China (No.2009BB4186)
文摘An investigation on the plastic behavior of AZ31 magnesium alloy under ultrasonic vibration（with a frequency of 15 kHz and a maximum output of 2 kW） during the process of tension at room temperature was conducted to reveal the volume effect of the vibrated plastic deformation of AZ31.The characteristics of mechanical properties and microstructures of AZ31 under routine and vibrated tensile processes with different amplitudes were compared.It is found that ultrasonic vibration has a remarkable influence on the plastic behavior of AZ31 which can be summarized into two opposite aspects：the softening effect which reduces the flow resistance and improves the plasticity,and the hardening effect which decreases the formability.When a lower amplitude or vibration energy is applied to the tensile sample,the softening effect dominates,leading to a decrease of AZ31 deformation resistance with an increase of formability.Under the application of a high-vibrating amplitude,the hardening effect dominates,resulting in the decline of plasticity and brittle fracture of the samples.
文摘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.
基金the financial support from National Natural Science Foundation of China(Nos.11922211,11832015,11527803)the 111 Project,China(No.BP0719007)Science Challenge Project,China(No.TZ2018001).
文摘The biaxial tensile behavior of isotropic Ti-6Al-4 V is characterized in this paper.A novel cruciform specimen was designed and optimized to achieve uniform stress and strain distribution within the gauge area.Biaxial tensile tests were conducted at three different loading ratios by the biaxial testing machine.The Digital Image Correlation(DIC)technique was applied to determine strain distribution,and a high-speed camera was employed to record the fracture process.An Inverse Analysis(IA)approach with a combined experimental and numerical method was proposed to determine the true stresses at the gauge section of the specimen during biaxial tensile tests.The results indicate that the initial yield locus can be described by the Cazacu criterion accurately,whereas the Mises criterion can predict better the strengthening behavior of Ti-6Al-4 V in the first quadrant in the principal stress space.
基金supported by AB Sandvik Material Technology in Sweden and the Swedish Energy Agency through the Research Consortium of Materials Technology for Thermal Energy Processes(KME-501)Agora Materiae and the Strategic Faculty Grant AFM(SFO-MAT-LiU#2009-00971)at Linkping University
文摘In this study, slow strain rate tensile testing at elevated temperature is used to evaluate the influence of temperature and strain rate on deformation behaviour in two different austenitic alloys. One austenitic stainless steel （AISI 316L） and one nickel-base alloy （Alloy 617） have been investigated. Scanning electron microscopy related techniques as electron channelling contrast imaging and electron backscattering diffraction have been used to study the damage and fracture micromechanisms. For both alloys the dominante damage micromech- anisms are slip bands and planar slip interacting with grain bounderies or precipitates causing strain concentrations. The dominante fracture micromechanism when using a slow strain rate at elevated temperature, is microcracks at grain bounderies due to grain boundery embrittlement caused by precipitates. The decrease in strain rate seems to have a small influence on dynamic strain ageing at 650℃.
基金financially supported by the National Natural Science Foundation of China(No.51371067)supported by the Japan Society for the Promotion of Science(JSPS) fellowship and Grants-in-Aid for Scientific Research(No.25-03205)
文摘Co68.15Fe4.35Si12.25B15.25 （at%） amorphous microwires with a smooth surface and a circular cross-section were fabricated by the glass-coated melt spinning method. Their mechanical properties were evaluated through tensile tests of the glass-coated amorphous mi-crowires, and their fracture reliability was estimated using two-and three-parameter Weibull analysis. X-ray diffraction and transmission electron microscopy results showed that these glass-coated Co-based microwires were mostly amorphous. The coated Co-based microwires exhibit a tensile strength of 1145 to 2457 MPa, with a mean value of 1727 MPa and a variance of 445 MPa. Weibull statistical analysis showed that the tensile two-parameter Weibull modulus of the amorphous microwires is 4.16 and the three-parameter Weibull modulus is 1.61 with a threshold value as high as 942 MPa. These results indicate that the fabricated microwires exhibit good tensile properties and fracture reliability, and thus appear to be good candidates for electronics reliability engineering applications.
基金supports by the National Natural Science Foundation of China(No.51001008)the Fundamental Research Funds for the Central Universities of China(FRF-MP-10-005B)
文摘This article focuses on the tensile and compressive characteristics of a Ti-based bulk metallic glass composite （BMGC）. It is found that the yield stress, maximum strength, and fracture strain are 1380 MPa, 1516 MPa, and 4.3% for uniaxial tension, but 1580 MPa, 4010 MPa, and 29% for uniaxial compression, respectively. The composite displays a linear ＂work hardening＂ capacity under compression; however, the ＂work softening＂ behavior is observed in the true engineering stress-strain curve upon tensile loading. The fracture surfaces of specimens also exhibit dissimilar properties under the different loadings.
文摘The objective of this paper was to predict the residual strength of post impacted carbon/epoxy composite laminates using an online acoustic emission （AE） monitoring and artificial neural networks （ANN）. The laminates were made from eight-layered carbon （in woven mat form） with epoxy as the binding medium by hand lay-up technique and cured at a pressure of 100 kg/cm2 under room temperature using a 30 ton capacity compression molding machine for 24 h. 21 tensile specimens （ASTM D3039 standard） were cut from the cross ply laminates. 16 specimens were subjected to impact load from three different heights using a Fractovis Plus drop impact tester. Both impacted and non-impacted specimens were subjected to uniaxial tension under the acoustic emission monitoring using a 100 kN FIE servo hydraulic universal testing machine. The dominant AE parameters such as counts, energy, duration, rise time and amplitude are recorded during monitoring. Cumulative counts corresponding to the amplitude ranges obtained during the tensile testing are used to train the network. This network can be used to predict the failure load of a similar specimen subjected to uniaxial tension under acoustic emission monitoring for certain percentage of the average failure load.
基金Aeronautical Science Foundation of China （03H53048）
文摘The conventional forming limit diagram （FLD） is described as a plot of major strain versus minor strain. However, FLD is dependent on forming history and strain path. In the present study, a forming limit stress-based diagram （FLSD） has been adopted to predict the fracture limit of aluminum alloy （AA） 5052-O1 sheet. Nakazima test is simulated by plastic constitutive formula derived from the modified Gurson-Tvergaard-Needleman （GTN） model. An in situ tensile test with scanning electron microscope （SEM） is proposed to determine the parameters in GTN model. The damage evolution is observed and recorded, and the parameters of GTN model are identified through counting void fraction at three damage stages of AA5052-O 1. According to the experimental results, the original void volume fraction, the volume fraction of potential nucleated voids, the critical void volume fraction, the void volume fraction at the final failure of material are assigned as 0.002 918, 0.024 9, 0.030 103, 0.048 54, respectively. The stress and strain are obtained at the last loading step before crack. FLSD and FLD of AA5052-O 1 are plotted. Compared with the experimental Nakazima test and uniaxial tensile test, the predicted results show a good agreement. The parameters determined by in situ tensile test can be applied to the research of the forming limit for ductile metals.
基金Projects(51375269,51675307) supported by the National Natural Science Foundation of China
文摘Ultrasonic vibration can reduce the forming force, decrease the friction in the metal forming process and improve the surface quality of the workpiece effectively. Tensile tests of AZ31 magnesium alloy were carried out. The stress–strain relationship, fracture modes of tensile specimens, microstructure and microhardness under different vibration conditions were analyzed, in order to study the effects of the ultrasonic vibration on microstructure and performance of AZ31 magnesium alloy under tensile deformation. The results showed that the different reductions of the true stress appeared under various ultrasonic vibration conditions, and the maximum decreasing range was 4.76%. The maximum microhardness difference among the 3 nodes selected along the specimen was HV 10.9. The fracture modes, plasticity and microstructure of AZ31 magnesium alloy also were affected by amplitude and action time of the ultrasonic vibration. The softening effect and the hardening effect occurred simultaneously when the ultrasonic vibration was applied. When the ultrasonic amplitude was 4.6 μm with short action time, the plastic deformation was dominated by twins and the softening effect was dominant. However, the twinning could be inhibited and the hardening effect became dominant in the case of high ultrasonic energy.
文摘For understanding acoustic emission （AE） activity and accumulation of micro-damage inside rock under pure tensile state, the AE signals has been monitored on the test of directly tension on two kinds of marble specimens. A tensile constitutive model was proposed with the damage factor calculated by AE energy rate. The tensile strength of marble was discrete obviously and was sensitive to the inside microdefects and grain composition. With increasing of loading, the tensile stress-strain curve obviously showed nonlinear with the tensile tangent modulus decreasing. In repeated loading cycle, the tensile elastic modulus was less than that in the previous loading cycle because of the generation of micro damage during the prior loading. It means the linear weakening occurring in the specimens. The AE activity was corresponding with occurrence of nonlinear deformation. In the initial loading stage which only elastic deformation happened on the specimens, there were few AE events occurred; while when the nonlinear deformation happened with increasing of loading, lots of AE events were generated. The quantity and energy of AE events were proportionally related to the variation of tensile tangent modulus. The Kaiser effect of AE activity could be clearly observed in tensile cycle loading. Based on the theory of damage mechanics, the damage factor was defined by AE energy rate and the tensile damage constitutive model was proposed which only needed two property constants. The theoretical stress-strain curve was well fitted with the curve plotted with tested datum and the two property constants were easily gotten by the laboratory testing.
基金supported by the China-Australia Joint Research Project (Grant No.2014DFG60230)Knowledge Innovation program of Chinese Academy of Sciences and National Basic Research Program of China (Grant No.2010CB832903 and 2010CB834503)
文摘Silicon carbide nanoparticle-reinforced nickel-based composites（Ni–Si CNP）,with a Si CNPcontent ranged from1 to 3.5 wt%,were prepared using mechanical alloying and spark plasma sintering.In addition,unreinforced pure nickel samples were also prepared for comparative purposes.To characterize the microstructural properties of both the unreinforced pure nickel and the Ni–Si CNPcomposites transmission electron microscopy（TEM） was used,while their mechanical behavior was investigated using the Vickers pyramid method for hardness measurements and a universal tensile testing machine for tensile tests.TEM results showed an array of dislocation lines decorated in the sintered pure nickel sample,whereas,for the Ni–Si CNPcomposites,the presence of nano-dispersed Si CNPand twinning crystals was observed.These homogeneously distributed Si CNPwere found located either within the matrix,between twins or on grain boundaries.For the Ni–Si CNPcomposites,coerced coarsening of the Si CNPassembly occurred with increasing Si CNPcontent.Furthermore,the grain sizes of the Ni–Si CNPcomposites were much finer than that of the unreinforced pure nickel,which was considered to be due to the composite ball milling process.In all cases,the Ni–Si CNPcomposites showed higher strengths and hardness values than the unreinforced pure nickel,likely due to a combination of dispersion strengthening（Orowan effects） and particle strengthening（Hall–Petch effects）.For the Ni–Si CNPcomposites,the strength increased initially and then decreased as a function of Si CNPcontent,whereas their elongation percentages decreased linearly.Compared to all materials tested,the Ni–Si CNPcomposite containing 1.5% Si C was found more superior considering both their strength and plastic properties.
文摘The tensile strength at the rock-concrete interface is one of the crucial factors controlling the failure mechanisms of structures,such as concrete gravity dams.Despite the critical importance of the failure mechanism and tensile strength of rock-concrete interfaces,understanding of these factors remains very limited.This study investigated the tensile strength and fracturing processes at rock-mortar interfaces subjected to direct and indirect tensile loadings.Digital image correlation(DIC)and acoustic emission(AE)techniques were used to monitor the failure mechanisms of specimens subjected to direct tension and indirect loading(Brazilian tests).The results indicated that the direct tensile strength of the rock-mortar specimens was lower than their indirect tensile strength,with a direct/indirect tensile strength ratio of 65%.DIC strain field data and moment tensor inversions(MTI)of AE events indicated that a significant number of shear microcracks occurred in the specimens subjected to the Brazilian test.The presence of these shear microcracks,which require more energy to break,resulted in a higher tensile strength during the Brazilian tests.In contrast,microcracks were predominantly tensile in specimens subjected to direct tension,leading to a lower tensile strength.Spatiotemporal monitoring of the cracking processes in the rock-mortar interfaces revealed that they show AE precursors before failure under the Brazilian test,whereas they show a minimal number of AE events before failure under direct tension.Due to different microcracking mechanisms,specimens tested under Brazilian tests showed lower roughness with flatter fracture surfaces than those tested under direct tension with jagged and rough fracture surfaces.The results of this study shed light on better understanding the micromechanics of damage in the rock-concrete interfaces for a safer design of engineering structures.
基金funding support from the National Natural Science Foundation of China (Grant Nos. U1806226 and 51979154)。
文摘The stress state in a rock mass is complex. Stress redistribution around underground excavation may lead to various failure modes, including compressive-shear, tensile-shear, and tensile failures. The ability to perform laboratory tests with these complex stress states is significant for establishing new strength criteria. The present paper introduces a new rock testing system with “tensile-compressive-shear”loading functions. The device includes bi-directional and double-range hydraulic cylinders, auxiliary loading equipment, and roller rows that can perform direct compressive-shear tests, direct tensile tests,and direct tensile-shear tests. The testing system provides maximum vertical and lateral loading forces of2000 k N and allows testing cubical rock specimens with dimensions of 0.5 m × 0.5 m × 0.5 m. The performance of the testing machine was evaluated by testing a rock-like material based on cement mortar under compressive-shear, tensile, and tensile-shear stress states. The failure process and deformation characteristics were monitored during loading using acoustic emission(AE) transient recorder,piezoelectric AE sensors, a high-speed camera, and a thermal infrared camera. The failure mechanism was investigated by analyzing AE counts, AE amplitude, strain, and temperature changes on the rock specimen surface. The test results confirmed that the testing system could successfully simulate the abovementioned stress path. The AE counts and amplitude responses were influenced by different failure modes. The temperature response during the compressive-shear test indicated the development of a high-temperature band on the rock specimen surface. In contrast, a negligible temperature change was observed during the tensile and tensile-shear tests. The newly developed multifunctional rock testing system allows laboratory tests under various failure modes. The monitoring results of multiple variables during rock failure tests provide valuable information on failure characteristics.
基金supported by the National Natural Science Foundation of China(Grant No.51875027)the China Postdoctoral Science Foundation(No.2018M630058)assistances of the program for the financial support。
文摘This paper focused on the effect of pre-strain on forming limit curves(FLC)of 5754-O aluminum alloy sheet through utilizing biaxial tensile approach.Based on Swift model and Yld2000-2 d yield criterion,the dimensions of cruciform specimen was optimized through applying finite element method for increasing the strain at specimen center.After that,with the recommended specimen size,the cruciform specimen was tested under various stroke ratios to experimentally characterize the limit strains under different pre-strain levels.Subsequently,the biaxial tensile tests were simulated by Abaqus to obtain the limit strains and validate the material models.It can be observed in both experiments and simulations that the pre-strained uniaxial tension followed by plane tension or equi-biaxial tension can improve the formability of sheet metals.Besides,the strain path change affects the trend of first derivative of strain rate difference between neighboring points with respect to time.An early increase occurred and then fell back to the stable value,the steady evolution continued until to a new increase reaching the critical value.The M–K prediction approach was simulated to verify the influence of pre-strain on FLC.It can be found that the early increase peaks of the major strain incremental ratio rose with the amplitude of pre-strain.Finally,the phenomenon of pseudolocalization caused by the strain path change was explained through evolution of stress state inside the groove.
文摘Additive layer manufacturing （ALM） of aerospace grade titanium components shows great promise in supplying a cost-effective alternative to the conventional production routes. Complex microstructures comprised of columnar remnants of directionally solidifiedβ-grains, with interior inhabited by colonies of finerα-plate structures, were found in samples produced by layered plasma welding of Ti-6Al-4V alloy. The application of in-situ tensile tests combined with rapid offline electron backscatter diffraction （EBSD） analysis provides a powerful tool for understanding and drawing qualitative correlations between microstructural features and deformation characteristics. Non-uniform deformation occurs due to a strong variation in strain response between colonies and across columnar grain boundaries. Prismatic and basal slip systems are active, with the prismatic systems contributing to the most severe deformation through coarse and widely spaced slip lines. Certain colonies behave as microstructural units, with easy slip transmission across the entire colony. Other regions exhibit significant deformation mismatch, with local build-up of strain gradients and stress concentration. The segmentation occurs due to the growth morphology and variant constraints imposed by the columnar solidification structures through orientation relationships, interface alignment and preferred growth directions. Tensile tests perpendicular to columnar structures reveal deformation localization at columnar grain boundaries. In this work connections are made between the theoretical macro- and microstructural growth mechanisms and the observed microstructure of the Ti-6Al-4V alloy, which in turn is linked to observations during in-situ tensile tests.
文摘Stress relaxation behavior of two turbine bolt steels was evaluated by the manual-controlled tensile stress relaxation test (TSRT) at high temperature. First, feasibility and the procedure of the manual-controlled tensile stress relaxation test (TSRT) is discussed and carried out on a general creep testing machine. And then, the experimental results from such type of test were compared to the existing data provided by certain Laboratory U.K. Overall good agreement between the results of manual-controlled TSRT method and the existing data provides confidence in the use of the proposed method in practice. Finally, the experimental results of turbine bolt steels from TSRT were compared with that of bending test. It is observed that great difference exists between the results from two different type stress relaxation tests. It is therefore suggested that the results from TSRT method be adopted in turbine bolt design in engineering.
