Co-reporter:Weiwei Yu;Dunji Yu;Hongbo Gao;Fei Xue
Journal of Materials Engineering and Performance 2017 Volume 26( Issue 9) pp:4442-4449
Publication Date(Web):31 August 2017
DOI:10.1007/s11665-017-2882-5
Accelerated thermal aging tests were performed at 400 °C for nearly 18,000 h on Z3CN20.09M cast stainless steel which was used for primary coolant pipes of nuclear power plants. A series of Charpy impact tests were conducted on Z3CN20.09M after different long-term thermal aging time. The test results indicated that the Charpy impact energy of Z3CN20.09M cast stainless steel decreased rapidly at an early stage and then almost saturated after thermal aging of 10,000 h. Furthermore, J-resistance curves were measured for CT specimens of longitudinal and circumferential pipe orientations. It showed that there was no obvious difference in the fracture characteristics of Z3CN20.09M in different sampling directions. In addition, the observed stretch zone width (SZW) revealed that the value of initiation fracture toughness JSZW was significantly lower than that of fracture toughness JIC, indicating a low actual crack initiation energy due to long-term thermal aging.
Co-reporter:Junfeng Zhang, Dunji Yu, Zizhen Zhao, Zhe Zhang, Gang Chen, Xu Chen
Materials Science and Engineering: A 2016 Volume 667() pp:251-260
Publication Date(Web):14 June 2016
DOI:10.1016/j.msea.2016.04.064
A series of uniaxial strain-controlled fatigue and creep-fatigue tests of the bainitic 2.25Cr1Mo steel forging were performed at 455 °C in air. Three different hold periods (30 s, 120 s, 300 s) were employed at maximum tensile strain and compressive strain under fully reversed strain cycling. Both tensile and compressive holds significantly reduce the fatigue life. Fatigue life with tensile hold is shorter than that with compressive hold. A close relationship is found between the reduction of fatigue life and the amount of stress relaxation. Microstructural examination by scanning electron microscope reveals that strain hold introduces more crack sources, which can be probably ascribed to the intensified oxidation and the peeling-off of oxide layers. A modified plastic strain energy approach considering stress relaxation effect is proposed to predict the creep-fatigue life, and the predicted lives are in superior agreement with the experimental results.
Co-reporter:Haichao Cheng, Gang Chen, Zhe Zhang, Xu Chen
Journal of Nuclear Materials 2015 Volume 458() pp:129-137
Publication Date(Web):March 2015
DOI:10.1016/j.jnucmat.2014.12.028
•Uniaxial ratcheting behaviors are conducted on Zr-4 tubes under various loading at 400 °C.•Zr-4 shows cyclic stable and hardening behaviors at 400 °C.•Loading history has significant influence on the uniaxial ratcheting behaviors.•The higher temperature leads to less ratcheting under same normalized stress.A series of uniaxial tensile, incremental cyclic and uniaxial ratcheting tests were conducted at 400 °C on Zr-4 tubes to investigate the mechanical behaviors under various loading conditions. The experimental results show that this material features cyclic softening at room temperature (RT), and cyclic stable and hardening at 400 °C. Uniaxial ratcheting strain increases with the increase of mean stress and stress amplitude, and decrease with the increase of loading rate. Loading history has significant influence on the uniaxial ratcheting behavior. Lower stress level after a loading history with higher stress level leads to the shakedown of ratcheting. Higher loading rate after a loading history with lower loading rate brings down the ratcheting strain rate. The sequence of stress rate appears to have no effects on the final ratcheting strain accumulation. The ratcheting strain is sensitive to temperature, and the higher temperature leads to less ratcheting under same normalized stress (σ‾=σ/σ0.2).
Co-reporter:LiLan Gao, Xu Chen, Hong Gao
Microelectronics Reliability 2015 Volume 55(Issue 7) pp:1089-1096
Publication Date(Web):June 2015
DOI:10.1016/j.microrel.2015.04.004
•Analytical model considering the nonlocal deformation of assembly was developed.•Interfacial stresses of short and long ACF assembly were predicted.•Analytical expression of chip cracking stress was obtained.The interfacial stresses and chip cracking stress produced because of thermal and mechanical mismatch in layered electronic assembly are one of main reasons for the failure of electronic packages. The analytical model considering the nonlocal deformation of assembly was developed and applied to predict the interfacial stresses produced due to temperature variation for the short and long anisotropic conductive adhesive film (ACF) bonding assembly. The conditions of zero shear stress at the free ends and self-equilibrated peeling stresses were satisfied. Simultaneously the interfacial stresses of ACF assembly were also predicted by the corrected Suhir’s model, Wang’s model, Ghorbani’s model, local model and finite element model (FEM), which were compared with the results by the present model. In addition, the analytical expression of chip cracking stress was also obtained for layered electronic assembly. The approach is mathematically straightforward and can be extended to include the inelastic creep behavior.
Co-reporter:Yansong Tan;Xin Li;Gang Chen;Yunhui Mei
Journal of Electronic Materials 2015 Volume 44( Issue 2) pp:761-769
Publication Date(Web):2015 February
DOI:10.1007/s11664-014-3553-z
Evolution of creep damage in nano-silver sintered lap shear joints was investigated at 325°C. Non-destructive x-ray three-dimensional (3D) visualization clearly revealed the crack-growth behavior of the joint; this could be divided into three stages. In the initial stage, little development of cracks occurred. In the second stage, cracks propagated at a consistent rate. In the final stage, rapid extension of the cracks led directly to fracture of the joint. Three-dimensional volume-rendered images and fractographic analysis showed that the growth of macroscopic initial cracks at the interfaces dominated the creep fracture process. Initial failure of nano-silver sintered lap shear joints often occurred at interfacial nano-silver paste layers. Both the size and position of the initial interfacial cracks had significant effects on the final creep failure of the joints, and higher stresses led to greater porosity and earlier failure.
Co-reporter:D. Yu, K. An, Y. Chen, X. Chen
Scripta Materialia 2014 Volume 89() pp:45-48
Publication Date(Web):15 October 2014
DOI:10.1016/j.scriptamat.2014.06.021
Real-time in situ neutron diffraction was performed on an austenitic stainless steel under cyclic loading at room temperature. The evolutions of individual phase stresses during martensitic transformation were derived from the lattice parameters and volume fraction based on Rietveld refinements and Hooke’s law, while the phase-specific dislocation densities were elucidated by the single peak broadenings. Both results reveal that the increasing content of martensite phase, instead of individual phase strengthening, should be accounted for the remarkable secondary cyclic hardening.
Co-reporter:Shouwen Shi;Dan Liu;Dazhi Liu;Patrick Tae;Carrie Y. Gao;Lei Yan;Ke An
Polymer Engineering & Science 2014 Volume 54( Issue 10) pp:2215-2221
Publication Date(Web):
DOI:10.1002/pen.23770
In this study, mechanical tensile stress–strain response and microstructure changes of proton exchange membranes (PEM) in immersed conditions are studied. The effects of water pretreatment and immersion time on stress–strain responses of Nafion®−212 membranes are discussed. It is found that in the water immersion it took 24 h for the membrane to reach saturation equilibrium. Compared with dry membrane, immersed Nafion membrane shows a lower stress level at 30°C, but a higher stress level at 70°C. In situ small angle neutron scattering (SANS) experiments show that with the increase of temperature and water uptake, domains of the membrane become ordered and stay stable at around 60°C. Based on the observation, the relationship between the microstructure and mechanical properties is explained. POLYM. ENG. SCI. 54:2215–2221, 2014. © 2013 Society of Plastics Engineers
Co-reporter:Shouwen Shi, Gang Chen, Zhenfeng Wang, Xu Chen
Journal of Power Sources 2013 Volume 238() pp:318-323
Publication Date(Web):15 September 2013
DOI:10.1016/j.jpowsour.2013.03.042
The effect of hygrothermal aging on proton exchange membrane (PEM) is a critical issue because the membrane is always subjected to high temperature and humidity under operation conditions. In this study, the mechanical responses of the Nafion 212 membrane subjected to hygrothermal aging are investigated experimentally through uniaxial tensile, stress relaxation and creep-recovery tests. Higher modulus and tensile strength are obtained for longer membrane aging because of the formation of crosslinks during the aging process. The creep strain is divided into three components to quantitatively assess the effect of hygrothermal aging on the mechanical responses of the membrane, and the predominant creep strain component changes as the hygrothermal aging time increases. In general, hygrothermal aging significantly affected the viscous flow strain and delayed elastic strain in correspondence to chain disentanglement and slippage, respectively. In addition, the effect of temperature on the creep behavior of the membrane aging for various times is also studied. The delayed elastic strain increases significantly as the aging time increases, while the instantaneous strain is least affected.Highlights► The effect of hygrothermal aging on mechanical responses of PEM is investigated. ► Higher modulus and tensile strength are obtained for hygrothermal aging PEM. ► The effect of hygrothermal aging on the creep strain of PEM is quantitatively assessed.
Co-reporter:Hua Li, Mingjian Wen, Gang Chen, Weiwei Yu, Xu Chen
Journal of Nuclear Materials 2013 Volume 443(1–3) pp:152-160
Publication Date(Web):November 2013
DOI:10.1016/j.jnucmat.2013.06.052
A series of monotonic tensile, compressive and uniaxial ratcheting tests are conducted at room temperature on Zircaloy-4 (Zr-4) tubes to investigate the mechanical behaviors under various loading conditions. The experimental results show that the ratcheting strain is sensitive to mean stress, stress amplitude and mean stress direction. It is found that the material features anisotropy both in monotonic tests and uniaxial ratcheting tests with different mean stress directions. The difference of mechanical properties under tensile and compressive loading, especially the yield stress, is believed to contribute to the anisotropic ratcheting behavior of the material. In order to describe the anisotropic nature of the uniaxial ratcheting behavior of Zr-4, an anisotropic Ohno–Wang (OW) constitutive model introducing an initial back stress is developed. The results predicted show reasonable agreement with the experimental data.
Co-reporter:Shouwen Shi, Dunji Yu, Lilan Gao, Gang Chen, Jian Chen, Xu Chen
Journal of Power Sources 2012 Volume 213() pp:40-46
Publication Date(Web):1 September 2012
DOI:10.1016/j.jpowsour.2012.03.082
Co-reporter:LiLan Gao, Xu Chen, Hong Gao
International Journal of Adhesion and Adhesives 2012 Volume 33() pp:75-79
Publication Date(Web):March 2012
DOI:10.1016/j.ijadhadh.2011.11.007
The shear strength behaviors of Anisotropic Conductive Adhesive Film (ACF) joints were investigated experimentally with various environments. The shear tests of ACF joints were performed at different constant temperature conditions. It is found that the shear behaviors of the ACF joints are strongly dependent on testing temperature, and the shear strength decrease and the maximum displacement increases with increasing temperature. The shear strength of ACF joints was also investigated under hygrothermal aging and thermal cycling. The results show that the shear strength of ACF joints gradually decreases at first, then quickly decreases and finally the rate of decrease slows down again with increasing hygrothermal aging time. However the shear strength of ACF joints after thermal cycling increases firstly and then decreases with increasing thermal cycling time.
Co-reporter:Chao Li, Gang Chen, Xu Chen, Weihua Zhang
Computational Materials Science 2012 Volume 57() pp:43-47
Publication Date(Web):May 2012
DOI:10.1016/j.commatsci.2011.09.003
16MnR steel is widely used in pressure vessel in China and its ratcheting and fatigue behavior have attracted numerous interest during the past years. In this study, a series of experiments were performed on the uniaxial ratcheting deformation of 16MnR steel. The effects of stress amplitude and mean stress on the ratcheting strain were discussed under uniaxial asymmetrical stress cycling. It shows that ratcheting strain and ratcheting strain rate increase with mean stress and stress amplitude increased under the same stress amplitude and mean stress. At the same time, the increasing ratcheting strain causes fatigue damage, which reduces fatigue life of the material. With the mean stress increased, the fatigue life decreases correspondingly. The fatigue lives obtained from the fully reversed uniaxial loading are also compared with the ratcheting-fatigue experiment results. Finally, the modified model based on Ohno–Wang model by Chen and Jiao is used to predict ratcheting strain. The modified model predicts the uniaxial ratcheting strain of 16MnR steel till 400 cycles very well.Highlights► A series of uniaxial ratcheting-fatigue experiments were performed on the 16MnR steel. ► The increasing ratcheting strain reduced fatigue life of the material. ► The modified cyclic plasticity model was used to predict ratcheting strain till 400 cycles.
Co-reporter:Dunji Yu, Weiwei Yu, Gang Chen, Fengmin Jin, Xu Chen
Materials Science and Engineering: A 2012 Volume 558() pp:730-736
Publication Date(Web):15 December 2012
DOI:10.1016/j.msea.2012.08.088
Tensile properties and cyclic stress–strain response of Z2CND18.12N austenitic stainless steel were investigated at the strain rate of 1×10−3/s in the temperature range between 293 K and 723 K. Low cycle fatigue tests were also carried out at the strain rate of 6×10−3/s at 293 K and 623 K. SEM and TEM analyses were performed on the fatigue specimens. Tensile strength and ductility were found to reduce drastically with the temperature increasing from 293 K to 423 K but almost remained on the same level in the range between 523 K and 723 K. Serrations occurred during the stress approaching the ultimate tensile strength at 623 K and 723 K. The cyclic stress responses at temperatures ranging from 293 K to 623 K were characterized by a rapid initial hardening to the maximum stress, followed by gradual softening, whereas at 723 K continuous cyclic hardening was present. The maximum cyclic hardening ratio, defined as the maximum peak stress divided by the initial peak stress, increased with increasing temperature in the present temperature range. Phenomenological friction and back stresses were derived from an analysis of hysteresis loop shapes using the Cottrell scheme. The results indicated that the increase of back stress was mainly responsible for the cyclic hardening. Fatigue life decreased with increasing strain amplitude at both 293 K and 623 K. Transgranular fracture failure mode was observed at both temperatures. TEM observations revealed that the dislocation structure changed from the cellular structure at 293 K to the planar slip band at 623 K. Dynamic strain aging has been believed to play a significant role in tensile properties, cyclic deformation and fatigue behavior of the material.
Co-reporter:Xu Chen, Lei Yan, Zhenfeng Wang, Dan Liu
Journal of Power Sources 2011 Volume 196(Issue 5) pp:2644-2649
Publication Date(Web):1 March 2011
DOI:10.1016/j.jpowsour.2010.11.071
The thermal effects and mechanical effects on the durability of proton exchange membranes (PEMs) have been studied extensively in the literatures. However researches on the thermo-mechanical coupling behavior of PEMs are very limited. In this study, the interaction of mechanical and thermal effects in Nafion® NRE-212 was investigated using experimental methods. The thermo-mechanical coupling experiments were conducted following the in-phase proportional loading path, where the maximum/minimum mechanical loads and temperatures occur simultaneously and out-of-phase non-proportional rectangular loading paths where a phase difference of 90° existed between thermal and mechanical loads. During the creep processes under a variable temperature in out-phase profiles, the creep strain was found to be history-dependent in the membrane. The effect of initial temperature on the creep was significant in the first cycle. Moreover, temperature cycles were applied as thermal loading conditions and the history-dependence was also observed for thermal stresses. The maximum thermal stress did not occur at the lowest temperature.Research highlights▶ The mechanical properties of PEM under thermo-mechanical coupling loading were studied in this study. Very few data were reported on the issue. ▶ Under the proportional loading, the deformations of the membrane were resulted from thermal expansion, the cyclic ratcheting strains and creep strain caused by non-zero ambient stress. ▶ In the cases of rectangular path loading, the elastic behavior of the membrane at the low temperatures can be explained by the freezing of water content in the material and the transition of the non-ionic matrix. ▶ In the case of thermal loading tests, the thermal stress is history-dependent with temperature, i.e. the thermal stress is different in the warming process and the cooling process at the same temperature.
Co-reporter:Li-Lan Gao, Lei Wang, Hong Gao, Gang Chen, Xu Chen
Microelectronics Reliability 2011 Volume 51(Issue 8) pp:1393-1397
Publication Date(Web):August 2011
DOI:10.1016/j.microrel.2011.03.032
The shear fatigue lives of Anisotropic Conductive Adhesive Film (ACF) joints were evaluated experimentally and theoretically under different testing conditions. The shear fatigue tests of ACF joints were performed with different loading amplitudes. It is found that the fatigue lives of ACF joints decrease with increasing loading amplitudes and Basquin’s equation is fit to predict the fatigue lives of ACF joints. Hygrothermal aging and thermal cycling tests were conducted to investigate the shear strength and lives of ACF joints. The results show that the shear strength and lives of ACF joints decrease with increasing hygrothermal aging time, however increase firstly and then decrease with increasing thermal cycling time. The fatigue life model considering aging damage is proposed and the predictions of the fatigue life agree with the experimental results at different aging time for ACF joints.
Co-reporter:Youliang Guan, Xu Chen, Fengqin Li, Hong Gao
International Journal of Adhesion and Adhesives 2010 Volume 30(Issue 2) pp:80-88
Publication Date(Web):March 2010
DOI:10.1016/j.ijadhadh.2009.09.003
In order to provide more experiences on the application of electrically conductive adhesive (ECA), die attachment performance of Ag-epoxy electrically conductive adhesive (Ag-ECA) was systematically investigated by shearing tests. The specimens used in the tests were prepared with different processes, paste thicknesses, and base metal with or without plating layers. The results of the shearing tests show that heating and cooling rates do not affect the adhesive strength evidently. Thinner Ag-ECA and Cu–Cu substrate-chip couples can provide higher shear strength. The effect of hygrothermal aging and thermal cycling on the adhesive strength is also carefully analyzed. Both processes make the decrease of the shear strength of the Ag-ECA. Compared with thermal cycling, moisture invasion have more damage to the die-attachment of Ag-ECA.
Co-reporter:Zhe Zhang, Xu Chen, Yanping Wang
Polymer Testing 2010 Volume 29(Issue 3) pp:352-357
Publication Date(Web):May 2010
DOI:10.1016/j.polymertesting.2010.01.001
A series of uniaxial ratcheting experiments has been carried out on cold compaction polytetrafluoroethylene (PTFE) specimens. All the tests were performed under stress control at elevated temperature. The effects of mean stress, stress amplitude, applied temperature and their histories on the ratcheting behavior of PTFE were studied. It is shown that, as the applied temperature was raised, the elastic modulus of PTFE declined rapidly. The ratcheting strain increased as the mean stress, stress amplitude and temperature increased. Especially, when the temperature was over 100 °C, the ratcheting strain accumulated rapidly. Furthermore, the loading histories also play an important role in the progress of ratcheting. Previous cycling with higher mean stress and stress amplitude greatly restrains ratcheting strain of subsequent cycling at lower ones. Such a phenomenon is due to the enhancement of the material deformation resistance caused by the previous loadings. As the applied temperature changes, the ratcheting strain still accumulates along the direction of mean stress.
Co-reporter:Li-Lan Gao, Xu Chen, Hong Gao, Shu-Bao Zhang
Materials Science and Engineering: A 2010 527(20) pp: 5115-5121
Publication Date(Web):
DOI:10.1016/j.msea.2010.05.002
Co-reporter:Xinjian Zhang, Lu Huang, Xu Chen, Peter K. Liaw, Ke An, Tao Zhang, Gongyao Wang
Materials Science and Engineering: A 2010 527(29–30) pp: 7801-7807
Publication Date(Web):
DOI:10.1016/j.msea.2010.08.072
Co-reporter:Tao Wang, Gang Chen, Yanping Wang, Xu Chen, Guo-quan Lu
Materials Science and Engineering: A 2010 527(24–25) pp: 6714-6722
Publication Date(Web):
DOI:10.1016/j.msea.2010.07.012
Co-reporter:Ning Bai, Xu Chen, Hong Gao
Materials & Design (1980-2015) 2009 Volume 30(Issue 1) pp:122-128
Publication Date(Web):January 2009
DOI:10.1016/j.matdes.2008.04.032
The uniaxial tensile inelastic deformation behavior for three types of lead-free solders, Sn–3Ag–0.5Cu, Sn–3.5Ag and Sn–0.7Cu, were simulated by a unified viscoplastic constitutive model, the Anand model. To obtain the material parameters for the Anand model, a series of constant true strain rate and temperature tests were conducted on three types of lead-free solders at various strain rates from 1 × 10−4 s−1 to 1 × 10−2 s−1, over a wide temperature range from 25 °C to 150 °C. A modified Anand model, in which h0 was set to a function of strain rate, was proposed. The comparison of the experimental and simulated results showed that the modified Anand model improved the simulation capability.
Co-reporter:Zhe Zhang, Xu Chen
Polymer Testing 2009 Volume 28(Issue 3) pp:288-295
Publication Date(Web):May 2009
DOI:10.1016/j.polymertesting.2008.12.012
A series of multiaxial ratcheting experiments have been performed on polyteterafluoroethylene (PTFE) solid cylindrical specimens. All the tests were conducted under cyclic shear strain with a constant axial stress at room temperature. The effects of axial stress, shear strain range, shear strain rate and their histories on the ratcheting behavior of PTFE were studied. It is shown that the ratcheting strain depends on the constant axial stress, cyclic shear strain range and shear strain rate. The ratcheting strain increases more rapidly as the constant axial stress or shear strain range become larger, or the shear strain rate is reduced. Furthermore, the loading histories also play an important role in the progress of ratcheting. The prior cycling with higher axial stress, larger strain range or lower strain rate greatly restrains ratcheting strain of subsequent cycling at lower strains. Such phenomenon is due to the enhancement of the material deformation resistance caused by the prior loadings.
Co-reporter:Gang Chen, Shi-Chao Shan, Xu Chen, Huang Yuan
Computational Materials Science 2009 Volume 46(Issue 3) pp:572-578
Publication Date(Web):September 2009
DOI:10.1016/j.commatsci.2009.03.015
High-nitrogen steel X13CrMnMoN18-14-3 has been used in manufacturing expanding metallic stents with 0.1 mm diameter, and such medical implant is subjected to complicated and asymmetrical cyclic loading during service. But there is no test data published for the thin wire of the material under cyclic loading. In this study, a series of tests were conducted on X13CrMnMoN18-14-3 stainless steel under uniaxial cyclic loading with mean tensile stress. The yield stress and ultimate strength were higher than that of large size specimen with diameters of 5 mm and 7 mm. The effects of stress amplitude, mean stress, loading history and stress rate on the ratcheting behavior of high-nitrogen steel were analyzed, respectively. It can be concluded that the ratcheting strain amplitude and ratcheting strain rate of X13CrMnMoN18-14-3 steel increases with increasing stress amplitude or mean stress correspondingly. At the meantime, experimental results reveal that the material exhibits a strong memory of the previous loading history, the stress cycling with higher stress amplitude or mean stress greatly restrains the ratcheting of subsequent stress cycling with lower ones. The ratcheting strain rate was very sensitive to the applied cyclic stress rate, and the accumulation of ratcheting strain under stress rate of 21.2 MPa/s is much faster than that under stress rate of 106 MPa/s. In addition, comparison of the fatigue life between bulk specimen and thin wire indicates that the size effect has significant influence on fatigue properties of the material. In the case of the test conducted under stress amplitude of 400 MPa, the fatigue life of small specimen is approximately ten times longer than that of bulk specimen under the same loading conditions.
Co-reporter:Li-Lan Gao, Xu Chen, Shu-Bao Zhang, Hong Gao
Materials Science and Engineering: A 2009 Volumes 513–514() pp:216-221
Publication Date(Web):15 July 2009
DOI:10.1016/j.msea.2009.02.002
Stress relaxation test and uniaxial tensile test of anisotropic conductive film (ACF) were conducted on DMA-Q800. A nonlinear relaxation behavior of ACF was observed. The relaxation rate became large and the stress relaxation curves at different strains became close with the increase of temperature. The stress relaxation curves were strain independent near glassy transition temperature (Tg). Strain rate and temperature dependent nonlinear stress and strain curves were obtained. The tensile strength and Young's modulus decreased with the increase of temperature, and specially were reduced more between 80 and 120 °C, however, ultimate strain of ACF increased with the rise of temperature. A nonlinear viscoelastic constitutive model of ACF was proposed to simulate stress relaxation under different strains. It showed good agreement between experimental data and simulation.
Co-reporter:Dun-ji Yu, Xu Chen, Gang Chen, Guo-quan Lu, Zheng-qiang Wang
Materials & Design 2009 30(10) pp: 4574-4579
Publication Date(Web):
DOI:10.1016/j.matdes.2009.04.006
Co-reporter:Yanping Wang;Weiwei Yu;Lei Yan
Polymer Engineering & Science 2009 Volume 49( Issue 3) pp:506-513
Publication Date(Web):
DOI:10.1002/pen.21314
Abstract
Multiaxial ratcheting characteristics of vulcanized natural rubber (NR) at room temperature were studied experimentally. The effects of axial stress, shear strain amplitude, shear strain rate, and their histories on ratcheting behavior were discussed. It is shown that the ratcheting strain depends on the axial stress and cyclic strain range. The ratcheting strain increases more rapidly as the constant axial stress or shear strain amplitude become larger. The ratcheting behaviors of the rubber exhibit nonsensitivity to the applied cyclic stress rate except initial axial strain. Furthermore, the loading histories also play an important role in progress of ratcheting. The prior cycles with higher axial stress, larger strain range or lower strain rate greatly restrains ratcheting strain of subsequent cycling with lower ones. Influence of creep on ratcheting behavior can not be neglected and its value reaches 87% of ratcheting strain. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers
Co-reporter:Zhe Zhang;Tao Wang
Polymer Engineering & Science 2008 Volume 48( Issue 1) pp:29-36
Publication Date(Web):
DOI:10.1002/pen.20813
Abstract
Pure polyteterafluoroethylene (PTFE) were prepared by using the process of cold pressure and sintering. A series of unaxial cyclic compression tests were carried out on solid cylindrical specimens of pure PTFE. The focus of study was to investigate time-dependent ratchetting behavior of PTFE under cyclic loading. It is shown that the stress–strain hysteresis loops exhibit pronounced nonlinearity with high stress range. The cyclic hardening is rate and stress range dependent. However, mean stresses have less effect on cyclic hardening than stress ranges. It is shown that viscoelasticity is obvious in the beginning cycles. The same stress range produces almost the same viscoelastic delay at the beginning of the compression cycles. A modified universal ratchetting model (URM), which is rate dependent is employed to predict the ratchetting strain under compressive cyclic loading condition at room temperature. POLYM. ENG. SCI., 48:29–36, 2008. © 2007 Society of Plastics Engineers
Co-reporter:Ning Bai;Zhou Fang
Journal of Electronic Materials 2008 Volume 37( Issue 7) pp:1012-1019
Publication Date(Web):2008 July
DOI:10.1007/s11664-008-0445-0
The tensile properties of Sn-3Ag-0.5Cu, Sn-3.5Ag, and Sn-0.7Cu lead-free solders were investigated on small-scale specimens and compared with those of Sn-37Pb eutectic solder at various strain rates from 1 × 10−4 s−1 to 1 × 10−2 s−1 and over a wide temperature range from 25°C to 150°C. The tests were under true strain-rate-controlled conditions. The ductility of each lead-free solder is relatively constant while that for Sn-Pb eutectic solder strongly depends on strain rate and temperature. The strain rate sensitivity index m for lead-free solders is relatively stable and showed little dependence on temperature, whereas the values of m for Sn-37Pb increased linearly with increasing temperature.
Co-reporter:Weiwei Yu;Yanping Wang;Lei Yan ;Ning Bai
Polymer Engineering & Science 2008 Volume 48( Issue 1) pp:191-197
Publication Date(Web):
DOI:10.1002/pen.20953
Abstract
Most of rubber engineering components endure cyclic loading during their service, and a nonzero mean stress during cyclic loading may cause an accumulation of strain which is known as ratchetting phenomenon. In order to study the ratcheting effect of rubber, a series of uniaxial ratchetting experiments were conducted on vulcanized natural rubber (NR). The effects of cyclic stress amplitude, mean stress and their histories on ratchetting behavior were studied, respectively. The uniaxial ratchetting behavior of natural rubber depends greatly on the stress amplitude and mean stress. The ratchetting strain rate greatly increases with the stress amplitude or mean stress increased. Experimental results reveal that the rubber material exhibits a strong memory of the previous high loading history, and such memory plays a significant role on the subsequent ratchetting. The ratchetting behaviors of the rubber exhibit little sensitive to the applied cyclic stress rate except for the initial strain. POLYM. ENG. SCI., 48:191–197, 2008. © 2007 Society of Plastics Engineers
Co-reporter:Xu Chen;Rong Li;Kun Qi;Guo-Quan Lu
Journal of Electronic Materials 2008 Volume 37( Issue 10) pp:
Publication Date(Web):2008 October
DOI:10.1007/s11664-008-0516-2
The mechanical behaviors of partially sintered thick films of a nanoscale silver paste used for attaching semiconductor chips are studied. The films, about 150 μm thick, were made by repeatedly stencil-printing the paste on a ceramic substrate and sintering by a recommended heating profile suitable for device attachment. The partially sintered films were lifted off the substrate, and their tensile behaviors, i.e., stress–strain curves, were measured at temperatures between −60°C and 300°C using a dynamic mechanical analyzer (DMA). The elastic modulus and tensile strength of the sintered silver films decreased with increasing temperature. Ratcheting behaviors of the films under cyclic tension at 150°C were also tested by using the DMA by examining the effects of loading rate, mean stress, and stress amplitude. The ratcheting strain grew with increasing mean stress or stress amplitude and with decreasing loading rate.
Co-reporter:Tao Wang;Guo-Quan Lu;Guang-Yin Lei
Journal of Electronic Materials 2007 Volume 36( Issue 10) pp:1333-1340
Publication Date(Web):2007 October
DOI:10.1007/s11664-007-0230-5
Traditional materials used in chip-level interconnections are not compatible with the high-temperature operation of wide-bandgap high-power semiconductor devices; therefore, this paper studies sintered nano-silver as a novel interconnect material mounting semiconductor devices onto metallized substrates. A low-temperature sintering process was employed in the preparation of a sintered nano-silver die-attachment. The physical mechanisms in volatilization and burnout of the added organic components employed in nano-silver paste were analyzed primarily by thermal gravimetric analysis (TGA) to obtain a reasonable temperature-controlling profile. The shear strength of sintered nano-silver joints was investigated, and the evolution of microstructure in the nano-silver paste sintering process was observed using a scanning electron microscope (SEM) in this process. The effects of sintering temperature, heating rate, and holding time during the sintering process were analyzed according to the densification mechanism. The microstructural observations and shear strength tests showed that a sintering temperature of 285°C, heating rate of 10°C/min, and holding time of 60 min were the best conditions for using this kind of silver paste.
Co-reporter:Y.C. Lin, Xu Chen, H.J. Zhang, Z.P. Wang
Materials Letters 2006 Volume 60(Issue 24) pp:2958-2963
Publication Date(Web):October 2006
DOI:10.1016/j.matlet.2006.02.024
The epoxy-based anisotropic conductive film (ACF) joints have the potential of being exposed to a hygrothermal environment and susceptible to moisture sorption. The long-term hygrothermal aging will induce the irreversible damages of epoxy resins system due to susceptibility of the polymer to hydrolysis, oxidation, etc. In this study, the hygrothermal environment test was used as an accelerator for the degradation of ACF joints in Chip-on-Glass (COG) assemblies. The effects of aging on the adhesion strengths were measured by shear mode tests and the changes of molecular conformation were analyzed by Fourier Transform Infrared Spectroscopy (FTIR). Results show that the ACF adhesion strengths decrease with aging and there are some chemical modifications to the aged ACF joints.
Co-reporter:Gang Chen, Xu Chen, Chang-Dong Niu
Materials Science and Engineering: A 2006 Volume 421(1–2) pp:238-244
Publication Date(Web):15 April 2006
DOI:10.1016/j.msea.2006.01.052
Uniaxial ratcheting characteristics of 63Sn/37Pb at room temperature were studied experimentally and particular attention was paid to ratcheting behavior under different loading rates. The effects of stress amplitude, mean stress, and loading history on the ratcheting behavior of 63Sn37Pb were analyzed, respectively. It can be concluded that the ratcheting strain amplitude and ratcheting strain rate of 63Sn37Pb increases with increasing stress amplitude or mean stress correspondingly. At the meantime, the loading history and loading sequence were found to have significant influence on ratcheting strain. In addition, the experimental results indicated that the ratcheting strain rate was very sensitive to the applied cyclic stress rate. In the range of 0.4–8 MPa/s, the ratcheting strain rate had an inversely proportional relationship with stress rate, the ratcheting rate under stress rate of 0.4 MPa/s was approximately 120 times as large as that under stress rate of 8 MPa/s.
Co-reporter:Xu Chen, Shucai Hui
Polymer Testing 2005 Volume 24(Issue 7) pp:829-833
Publication Date(Web):October 2005
DOI:10.1016/j.polymertesting.2005.07.006
In this paper, loading rate dependence of stress–strain response and ratcheting behavior under compression for PTFE were studied. The effects of loading rate, mean stress and stress amplitude on the ratcheting behavior of PTFE are discussed. It is shown that PTFE is a rate dependent material, but it is insensitive to loading rate when the rate is higher than 40 N/s. Ratcheting strain increases as the loading rate decreased. When loading rate is higher than 40 N/s, there is little effect of loading rate on ratcheting strain rate. At the same stress amplitude (mean stress), the ratcheting strain and ratcheting strain rate increase as mean stress (stress amplitude) increased.
Co-reporter:Y.C. Lin, Xu Chen
Materials Letters 2005 Volume 59(29–30) pp:3831-3836
Publication Date(Web):December 2005
DOI:10.1016/j.matlet.2005.06.061
Epoxy resins are attractive materials for many engineering applications, as they are low in density, have excellent mechanical properties and are easily fabricated by processes such as injection molding, extrusion and vacuum forming. However, the hostile humid environment can degrade the epoxy system because most epoxies absorb moisture. In this paper, the tensile fracture surfaces have been analyzed by a scanning electron microscopy (SEM) for the initial dry, moisture-saturated (preconditioned under hygrothermal conditions, 85 °C/85%RH) and completely desorbed (dry under thermal conditions, 85 °C) specimens, respectively. Furthermore, fracture surface patterns are simulated by computer, based on the theory that the conic-shaped pattern is due to the intersection between a moving planar crack front and a radically growing circular craze or secondary crack front. From the fractographic analysis and computer simulation results, it can be concluded that there is a close relationship between the velocity ratios u / v and the effect of hygrothermal conditions. Additionally, the transition of brittle/ductile appeared because of the effect of hygrothermal conditions.
Co-reporter:Xu Chen, De-Hua Yu, Kwang Soo Kim
Materials Science and Engineering: A 2005 Volume 406(1–2) pp:86-94
Publication Date(Web):15 October 2005
DOI:10.1016/j.msea.2005.06.013
A series of uniaxial and multiaxial ratcheting experiments have been conducted on 63Sn–37Pb solder alloys. It is shown that eutectic tin–lead solder is cyclic softening under uniaxial, pure torsional and axial/torsional ratcheting loading. Even low-level stress can cause high ratcheting strain. The rate of ratcheting strain remains steady and does not decay rapidly. Under constant axial stress and cyclic shear strain, the axial ratcheting strain and its rate rise with increase of the axial stress and shear strain range, but loading history and its sequence have no clear influence on the ratcheting behavior. The axial ratcheting strain rate is found to be strongly dependent on applied shear strain rates in axial/torsional ratcheting experiments. Axial ratcheting strain rates increase with decreasing shear strain rates.
Co-reporter:Dunji Yu, Xu Chen, Weiwei Yu, Gang Chen
International Journal of Plasticity (October 2012) Volume 37() pp:119-139
Publication Date(Web):1 October 2012
DOI:10.1016/j.ijplas.2012.05.001
Monotonic tension, isothermal/anisothermal fully reversed strain cycling and zero-to-tension cyclic tests were conducted within the temperature domain from room temperature to 823 K to investigate the mechanical behavior of Z2CND18.12N austenitic stainless steel under various uniaxial loading conditions. Interesting results were observed from these tests, including obvious rate-dependence at room temperature but lack of rate-dependence at elevated temperatures with the occurrence of serrated flow stress in tensile tests, more cyclic hardening at higher temperature in strain cycling tests, and tendency to reach shakedown condition at elevated temperatures in zero-to-tension cyclic tests. Dynamic strain aging (DSA) effect was presumably believed to contribute to these characteristics of the material. A thermo-viscoplastic constitutive model was proposed to describe the mechanical behavior of the material under uniaxial loading conditions at small strains. Kinematic hardening rule with two components of back stress and isotropic hardening rule incorporating DSA effect are the novel features of the proposed model. The simulated and predicted results show reasonable agreement with the experimental data.Highlights► Tensile and cyclic behavior tests are conducted on Z2CND18.12N austenitic stainless steel. ► Dynamic strain aging effect is observed for Z2CND18.12N steel at high temperature. ► A thermo-viscoplastic constitutive model incorporating DSA effect is proposed.
Co-reporter:Yonghe Yang, Lei Shi, Zhen Xu, Hongsheng Lu, Xu Chen, Xin Wang
Engineering Fracture Mechanics (November 2015) Volume 148() pp:337-349
Publication Date(Web):1 November 2015
DOI:10.1016/j.engfracmech.2015.07.061
•Fracture toughness of welded joint of X80 pipeline steel is studied.•Fracture toughness test is conducted with a new non-contact double-extensometer vision system.•The HAZ is embrittled in different degrees, because of M–A constituents.•It is observed the fusion zone is the fracture risk zone of the X80 steel weldment.The microstructures, mechanical properties and fracture toughness of the materials in different locations of the welded joint of the X80 pipeline steel were studied at room temperature. Elastic–plastic fracture toughness testing of crack tip opening displacement (CTOD) and J-integral of the welding materials and base material were conducted. A new non-contact double-clip gauge measuring system was developed and used in the fracture toughness tests. It was observed the fusion zone (FZ) was the fracture risk zone of the X80 steel weldment; and the occurrence of hard-brittle martensite–austenite (M–A) constituents was a significant because of welding hardening and embrittlement.Download high-res image (105KB)Download full-size image
Co-reporter:Ning Bai, Xu Chen
International Journal of Plasticity (November 2009) Volume 25(Issue 11) pp:2181-2203
Publication Date(Web):1 November 2009
DOI:10.1016/j.ijplas.2009.02.007
A series of tensile tests of Sn–3Ag–0.5Cu and Sn–0.7Cu lead-free solders were investigated at various strain rates from 1 × 10−4 s−1 to 1 × 10−2 s−1 and over a wide temperature range from 25 oC to 150 oC. Two-step strain rate jump tests, three-step short term creep tests with stress jump, and uniaxial ratcheting tests were also conducted. Based on the test data, a new constitutive model was proposed with a simple formulation and only eight material constants which can be easily obtained. The model employs two carefully defined back stress components to simulate the loading/unloading asymmetry phenomenon in uniaxial ratcheting tests. Different evolution rules of short-range back stress were given for loading and unloading stage, which provides the model ability to simulate the asymmetry in hysteresis loops. The proposed model presents good simulation of uniaxial tensile tests, strain rate jump tests, short term creep tests with stress jump, and uniaxial ratcheting tests.
Co-reporter:Xiaohui Chen, Xu Chen
International Journal of Pressure Vessels and Piping (March–April 2016) Volumes 139–140() pp:69-76
Publication Date(Web):1 March 2016
DOI:10.1016/j.ijpvp.2016.03.005
Ratcheting deformation is studied on straight pipe made of Z2CND18.12 N stainless steel with local wall thinning subjected to constant internal pressure and reversed bending using finite element analysis. The local wall thinning is located at the center of straight pipe, whose geometry is rectangular cross-section. The effect of depth, axial length and circumferential length on the ratcheting behavior of straight pipe is studied in this paper. Three-dimensional elastic-plastic analyses with ANSYS employed Chen–Jiao–Kim (CJK) kinematic hardening model is carried out to evaluate structural ratcheting behaviors. Results indicate that ratcheting strain is along the center of straight pipe extending to the two ends. The ratcheting strain occurs mainly at hoop direction. Axial ratcheting strain is relatively small. The effects of the depth, axial length and circumferential length of local wall thinning on the ratcheting response are discussed by CJK model.
Co-reporter:Xiaohui Chen, Xu Chen, Weiwei Yu, Duomin Li
International Journal of Pressure Vessels and Piping (January 2016) Volume 137() pp:28-37
Publication Date(Web):1 January 2016
DOI:10.1016/j.ijpvp.2015.04.016
•Ratcheting behavior of austenitic stainless steel Z2CND18.12N elbow pipe is studied.•Ratcheting strain is compared by with and without isotropic hardening rule.•Ratcheting boundary is determined by FEA with and without isotropic hardening rule.Ratcheting behavior of 90o-elbow pipe is experimentally investigated under constant inner pressure and force-controlled cyclic loading (abbr. cyclic reversed bending). The results indicate that the ratcheting strain occurs mainly in the circumferential direction. It is shown that the ratcheting strain per cycle increases with a reversed bending loading under the same inner pressure or inner pressure under the same reversed bending loading. In addition, the ratcheting behaviors of pressurized elbow pipe characterized by the Ohno-Wang (OW) II model with and without isotropic hardening rule are compared with experiments data. The predicted results show that the OW II model with isotropic hardening rule is slightly better than those without isotropic hardening rule. The ratcheting boundary of elbow pipe is determined by the Elasto-Plastic Finite Element Analysis and OW II model with and without isotropic hardening rule. It is observed that the determined ratcheting boundary of elbow pipe by OW II model with isotropic hardening rule is larger than that without isotropic hardening rule.
Co-reporter:Xiaohui Chen, Xu Chen, Dunji Yu, Bingjun Gao
International Journal of Pressure Vessels and Piping (January 2013) Volume 101() pp:113-142
Publication Date(Web):1 January 2013
DOI:10.1016/j.ijpvp.2012.10.008
This article presents an overview of recent progresses in experimental investigation and finite element analysis (FEA) of ratcheting behavior of pressurized piping. Ratcheting, namely the cyclic accumulation of plastic deformation, occurs when the structures are subjected to a primary load with a secondary cyclic load if the applied loads are high enough to make the structures yield. Typical piping structures including straight pipes, elbow pipes and piping joints have been investigated experimentally under mechanical or thermal cyclic loading. Finite element analyses with several well-developed constitutive models implemented in the commercial software ANSYS and ABAQUS have been conducted to simulate and predict the ratcheting behavior of pressurized piping. Based on such experimental and FEA research, ratcheting boundaries have been determined with the final aim of aiding the safety design and assessment of engineering piping structures. Some suggestions for structure ratcheting study are proposed.Highlights► Researches on ratcheting behavior of pressurized piping components are reviewed. ► FE implementation of unified Armstrong–Frederic type models is introduced. ► FE analyses on ratcheting behavior & boundary of pressurized piping are discussed.
Co-reporter:Dunji Yu, Gang Chen, Weiwei Yu, Duomin Li, Xu Chen
International Journal of Plasticity (January 2012) Volume 28(Issue 1) pp:88-101
Publication Date(Web):1 January 2012
DOI:10.1016/j.ijplas.2011.06.001
Experimental results of monotonic uniaxial tensile tests at different strain rates and the reversed strain cycling test showed the characteristics of rate-dependence and cyclic hardening of Z2CND18.12N austenitic stainless steel at room temperature, respectively. Based on the Ohno–Wang kinematic hardening rule, a visco-plastic constitutive model incorporated with isotropic hardening was developed to describe the uniaxial ratcheting behavior of Z2CND18.12N steel under various stress-controlled loading conditions. Predicted results of the developed model agreed better with experimental results when the ratcheting strain level became higher, but the developed model overestimated the ratcheting deformation in other cases. A modified model was proposed to improve the prediction accuracy. In the modified model, the parameter mi of the Ohno–Wang kinematic hardening rule was developed to evolve with the accumulated plastic strain. Simulation results of the modified model proved much better agreement with experiments.Highlights► Uniaxial ratcheting behaviors of Z2CND18.12N steel at room temperature were obtained by tests. ► A Visco-plastic constitutive model incorporated with isotropic hardening was developed. ► The parameter mi of the Ohno–Wang model was developed to evolve with accumulated plastic strain.
Co-reporter:Hongrui Shi, Gang Chen, Yong Wang, Xu Chen
International Journal of Pressure Vessels and Piping (February–March 2013) Volumes 102–103() pp:14-23
Publication Date(Web):1 February 2013
DOI:10.1016/j.ijpvp.2012.12.002
Ratcheting deformation is studied on elbow pipe made of Z2CND18.12N stainless steel with local wall thinning subjected to constant internal pressure and reversed in-plane bending under load control. The local wall thinning is located at extrados and crown of elbow. It is shown that local wall thinning has a very pronounced effect on the ratcheting behavior of elbows, as compared to the ratcheting behavior of sound elbow specimen. Three-dimensional elastic-plastic analyses with ANSYS in which Chaboche and Chen–Jiao–Kim (CJK) kinematic hardening model are carried out to evaluate structural ratcheting behaviors. A reasonable agreement has been found between the experimental and the simulated results with CJK model for the ratcheting of the elbows. The ratcheting boundary is determined by evaluating variations in the plastic strain increment with CJK model. The effects of the depth and location of local wall thinning on the ratcheting response are discussed by CJK model.Highlights► Ratcheting deformation is studied on Z2CND18.12N elbow with local wall thinning. ► The local wall thinning causes a significant ratcheting strain rate during the initial cycles. ► Structural ratcheting strains of elbow are evaluated by 3D Elastic-plastic FEA. ► The ratcheting boundary of elbow with local wall thinning is determined.
Co-reporter:Akhtar S. Khan, Xu Chen, Mohammad Abdel-Karim
International Journal of Plasticity (August 2007) Volume 23(Issue 8) pp:1285-1306
Publication Date(Web):1 August 2007
DOI:10.1016/j.ijplas.2006.06.005
A series of experiments has been conducted on oxygen free high conductivity (OFHC) copper hollow cylinders under cyclic free-end torsion and biaxial tension–torsion at large strains. In addition, equations are developed to account for the finite rotation and strains in electrical resistance strain gages. In free-end cyclic torsion experiments with shear strain range equal to 23%, a significant strain in the axial direction is observed and it accumulates with a constant rate cycle by cycle. In the biaxial tension–torsion (multiaxial ratchetting) experiments, in which the primary (constant) axial stress is larger than the initial yield stress of the material, the loading conditions are varied to determine the influence of primary axial stress, cyclic shear strain range, pre-cyclic hardening and loading sequence on multiaxial ratchetting. Some important experimental features are high-lighted and recommended to help modeling efforts later.
Co-reporter:H.S. Lu, Y.H. Yang, G. Chen, X. Chen, X. Wang
Procedia Engineering (2015) Volume 130() pp:828-834
Publication Date(Web):1 January 2015
DOI:10.1016/j.proeng.2015.12.203
API X80 pipeline steels have been widely used in long-distance transportation of oil or natural gas under high pressure due to their high transportation efficiency, low energy loss and low production cost. While the fracture toughness of welded joints are harder to measured. In this paper, J-integral resistance curves of Spiral Submerged Arc Welded (SSAW) joints were examined at different locations of the BM, WM and HAZ. The grain coarsening induced by welding thermal cycling leaded to weaker toughness in WM and HAZ than the BM. The optical microscope (OM) and scanning electron microscope (SEM) were used to analyze the fracture mechanism.
Co-reporter:Z.Z. Zhao, X.Y. Wu, X. Chen
Procedia Engineering (2015) Volume 130() pp:414-422
Publication Date(Web):1 January 2015
DOI:10.1016/j.proeng.2015.12.235
For pressure vessels constructed with low alloy steels which operate at temperatures above 371 ̊C, the fatigue design and exemption rules provided in ASME Boiler & Pressure Vessel Section VIII are no longer applicable. High temperature structure design codes which consider creep effect at elevated temperatures have to be used. An illustration of the assessment procedure of ASME-NH was given in detail based on thermal and structural finite element analysis results of hydrogenation equipment. The influences of primary load, temperature, weldment and the size of transition fillet on creep-fatigue damage evaluations were investigated by numerical analysis.
