• <tr id="yyy80"></tr>
  • <sup id="yyy80"></sup>
  • <tfoot id="yyy80"><noscript id="yyy80"></noscript></tfoot>
  • 99热精品在线国产_美女午夜性视频免费_国产精品国产高清国产av_av欧美777_自拍偷自拍亚洲精品老妇_亚洲熟女精品中文字幕_www日本黄色视频网_国产精品野战在线观看 ?

    Effect of void size and Mg contents on plastic deformation behaviors of Al–Mg alloy with pre-existing void: Molecular dynamics study

    2022-06-29 08:57:30NingWei魏寧AiQiangShi史愛(ài)強(qiáng)ZhiHuiLi李志輝BingXianOu區(qū)炳顯SiHanZhao趙思涵andJunHuaZhao趙軍華
    Chinese Physics B 2022年6期
    關(guān)鍵詞:趙軍

    Ning Wei(魏寧) Ai-Qiang Shi(史愛(ài)強(qiáng)) Zhi-Hui Li(李志輝)Bing-Xian Ou(區(qū)炳顯) Si-Han Zhao(趙思涵) and Jun-Hua Zhao(趙軍華)

    1Jiangsu Key Laboratory of Advanced Food Manufacturing Equipment and Technology,Jiangnan University,Wuxi 214122,China

    2China Aerodynamics Research and Development Center,Mianyang 621000,China

    3National Laboratory for Computational Fluid Dynamics,Beijing 100191,China

    4National Graphene Products Quality Supervision and Inspection Center,

    Keywords: Al–Mg alloys,molecular dynamics,nanovoid,plastic deformation

    1. Introduction

    Al–Mg alloys exhibit excellent specific strength, corrosion resistance and fatigue resistance, which is widely used in aviation,[1,2]lightweight automotive,[3,4]marine[5,6]and defense fields. However, micro defects such as voids and cracks are generated inevitably during the process of materials formation.[7–9]Irradiation damage also causes voids easily in metals and alloys.[10]Numerous experimental studies[11–13]have found that the growth and coalescence of the voids inside Al alloys are the main reasons for fracture. As crucial engineering materials,the mechanical properties of Al–Mg alloys have been affected by voids extensively.With decreasing sizes of materials, the effect of voids becomes more significant.For example, the failure of the Al-or Cu-based films used as radiation tolerant media brings about a significant reliability concern in microelectronic devices.[14]Hence, it is of great significance to study the evolution of voids in metal materials for better understanding the plastic deformation of metals and to improve the reliability of microelectronic devices.[15]Although the process of void growth and coalescence can be observed byin situtransmission electron microscopy(TEM),it is inconvenient to explore the dynamic mechanism of void evolution completely, such as dislocation nucleation, phase transition and dislocation slippage. Meanwhile,as the size of voids is close to nanoscale, the finite element method to capture the dislocation emission and phase transition during the void growth becomes challenging severely.[16]Alternatively,molecular dynamics(MD)based on a reliable empirical interaction potential enables detailed understanding of microscopic defects at the atomic scale,building a foundation to study the deformation mechanism of nano void.

    In recent years, extensive research using MD simulations has been conducted to probe mechanical behaviors of nanoporous materials and the effect of voids.[17–19]Shanget al.investigated the size-dependent effect of pre-void in the Ni/Ni3Al interface on tensile strength,and found that the small void disperses the local energy caused by lattice misfit at the interface, generating higher yield stress than the defect-free structure.[20]Guanet al.simulated the dynamic response of Al containing spherical void under different loading patterns.The results show that the response of the sample is slightly dependent on the loading patterns under weak loadings.[21]Xinet al.reported spinodal strengthened ultralightweight Mg–Al alloys with specific yield strengths surpassing almost every other engineering alloy, and revealed that the lattice mismatch at the diffuse transition region between the spinodal zones and matrix is the dominating factor for ultrahigh specific strength using the computational simulations.[22]Jinget al.reported evolution mechanism of a spherical void in polycrystalline copper under uniaxial tensile loading, proposing a criterion that there exists a critical void diameter dependent on grain size.[23]Moreover,the interaction between grain boundary and void in twin-crystal copper depending on temperature is reported.[24]The dynamic damage behaviors of single crystal HCP-Zr are examined,and the results reveal that the preference of void nucleation and phase transition is dominated by temperature and strain rate.[25]The effect of hard phase Ti and soft phase Mg nanoclusters in Al matrix on the tensile strength of materials is investigated.[26]Effect of layer thickness and strain rate on mechanical properties of Ti/Ni multilayered nanowires is reported.[27]Bahramyanet al.simulated the interaction between edge dislocation and void in pure Al and Al–Mg alloys.[28]Moreover,void growth in high entropy alloys has also been studied.[29,30]

    Mg is the primary alloying element of Al alloys. Although the mechanical behaviors of Al–Mg alloys have been extensively reported,a systematical study on the plastic deformation mechanism of pre-void Al–Mg alloys is still lacking.In this paper, MD simulations are utilized to analyze the influences of Mg content,void size and temperature on the void evolution and tensile strength of Al–Mg alloys. These results may have significant implications for understanding the plastic deformation mechanism of voids in Al–Mg or other alloys.

    2. Model and simulation method

    The desired Al–Mg alloys are constructed by replacing a selected percentage of Al atoms with the same ratio of Mg atoms at the same locations,[31,32]as shown in Fig.2(a). The initial size of the simulation box is approximately 2.4×16.2×20.2 nm3and the orientations of [100], [010], and [001] are taken inx,y, andzdirections, respectively. After the defectfree samples are established,a circular void is introduced into the center of the samples by deleting atoms. The embedded atom method (EAM) interatomic potential developed by Liuet al.[33]is used to described Al–Al, Al–Mg and Mg–Mg interactions in our simulations, which has been proven to predict the mechanical properties of Al–Mg alloys[26,34]in recent years with high accuracy. In this work, MD simulations are carried out using the large-scale atomic/molecular massively parallel simulator(LAMMPS).[35]

    Periodic boundary conditions are applied in all threedimensional directions. Before the relaxation and tensile simulation, all samples are accomplished by adjusting the atom coordinates for energy minimization, where force and energy tolerances are 10-12. Then, the models are conducted to relaxation(60 ps)using NPT ensemble(Nose/Hoover isobaricisothermal ensemble) at 300 K and 0 bar with time steps of 0.001 ps. The structures are optimized when the system potential energy converges. Subsequently, the uniaxial tensile loading is carried out (z-axis) with a constant strain rate of 0.001 ps-1, which is a typical value in MD simulations. Thexandydimensions remain unchanged to deform freely and maintain the stress near 1 atm in these two directions. Meanwhile,the temperature is maintained at 300 K by rescaling the velocities of the atoms explicitly during the tensile process.After the tensile simulations, the methods of dislocation extraction algorithm (DXA)[36]and construct surface mesh[37]of the open visualization tool (OVITO)[38]are utilized to reveal and analyze the variation of dislocation and void volume.

    To verify the reliability of the calculation results,the simulations on the defect-free pure Al models are carried out firstly, and the results are shown in Table 1. Young’s modulus is obtained by linear fitting of the stress–strain curve in the elastic stage.[39]The results are well consistent with the literature.[40]Due to the difference of the potentials used,the results using potential developed by Liuet al.[33]are slightly lower than those in the literature,[40]and Young’s modulus is consistent with the experiment.[41]

    κ (GPa) γ (GPa) Potential Zhu et al.[40] 60 7.8 Mishin et al.[42]This work 1 59 7.8 Mishin et al.[42]This work 2 75 7.2 Liu et al.[33]

    3. Results and discussion

    3.1. Effect of Mg contents on mechanical properties

    We first examine the strain rate effects on mechanical properties of pure Al. The yield stress is obtained with different loading strain rates ranging from 106s-1to 5×1010s-1,as shown in Fig.1. It shows that the yield stress increases with strain rate, which is consistent with that reported by Mayeret al.[43]and its trend becomes steep when strain rate is over 5×109s-1. The yield stress is added by 4.1%from strain rate of 106s-1to 109s-1. Considering the simulation consume,the strain rate of 109s-1is employed in the present study.

    Mg content of Al–Mg alloys ranges from 2% to 5%,[44]and Fig.2(b)shows the typical stress–strain curves of the samples with void diameter 12 °A.To some extent,the stress–strain curve can reflect the overall mechanical properties of materials. As seen in Fig.2(b),the curves of all the samples show a linear increase in the initial stage of deformation and then enter the plastic stage.Here,the peak point of the stress–strain curve is defined as the yield stress. Figure 2(c)shows the yield stress and Young’s modulus of the samples with different Mg contents. As seen in the figure,the yield stress decreases slightly with Mg increased. These results agree well with those of Samiriet al.[45]and Kumaret al.[46]on the mechanical properties of Al–Mg alloys. The reason for the phenomenon opposite to macroscopic solid solution strengthening may be the transition from plastic deformation dominated by dislocation slippage at macroscopic quasi-static low strain rates to dislocation nucleation dominated failure mechanism at microscopic extreme high rates,[31]which was reported by Nitolet al.[31]In dislocation-starved nanoporous alloys,the distortion of the host lattice by solute atoms can retard dislocation glide, but aid dislocation nucleation. Compared with pure Al, the yield stress and Young’s modulus of Al-5%Mg alloy drop by 10.5%and 7%, respectively. It can be seen that the yield stress is more sensitive to Mg content than Young’s modulus.

    To further verify the reliability of the simulation results.We choose the pure Al with void diameter 12 °A as the representative sample, as shown in the inset of Fig. 3(b), and calculate the stress componentσzof the atoms in various regions under uniaxial tension at 300 K. The stress–strain curves are obtained in Fig.3(a). Seen from Fig.3(b),y0is equal to 81 °A,ais void radius,andyiwithibeing the number of the atomic regions denotes the distance between the atoms in different regions and the center of the void,where yield stress is obtained when the strain of the curve is 8% in Fig. 3(a). According to the elastic theory, the stress componentσzofyi/y0can be derived using the existing Kirsch’s solution. In Fig. 3(b), the MD results are in good agreement with those of Eq.(1),where the yield stress decreases monotonically as risingyi/y0and approaches to a stable value of the far-field tensile stressq(q=5.98 GPa here). The reliability of the simulation results is verified.

    In plastic deformation of the samples with defects, void fraction is of great importance, which can exhibit the severity of the deformation of the system. Shown in Fig. 4(a) is the void fraction of samples with different Mg as a function of strain. The process of void deformation can be divided into three stages. Similar results are observed in single crystal copper films containing elliptic voids studied by Suet al.[16]. In the first stage,the void fraction has no significant change and maintains the initial value in the elastic stage, where changes in the shapes of the voids are depicted in Fig.5(a). Compared to the voids withε=0%, shapes of the voids are basically unchanged atε=2%. As the loading progresses, the voids elongate slightly along the loading direction,taking on an elliptical shape. In the second stage,the void fraction increases sharply,which indicates that the samples have yielded and the systems begin to enter the plastic deformation stage.The sharp increase of void fraction is caused by the dislocations nucleated from the void surface. The curves of the samples with different Mg contents show similar trends of void growth,indicating that the growth rate of voids is basically consistent in this stage.In the third stage,after the internal stress is released,the void fraction is at a stable value. In general,the void fraction of pure Al is the lowest,and the addition of Mg increases the void fraction of the system. Interestingly,the void fraction decreases with increasing Mg.

    To explore more details on the deformation mechanism of Al–Mg alloys with defects, we analyze the atomic structure snapshots of samples with varied Mg at different strains(Al-2%Mg alloy is discussed in the study of void size). As shown in the insets of Fig. 6, in the initial stage of emission dislocation, the atoms along they-axis direction around void surfaces of all samples behave disordered(white atoms in the illustrations). It shows that the void has a growth trend, and the reason is that the atomic stress here is much higher than the average stress. Local stress concentration leads to higher energy of the atoms around the void,which should effectively lower the energy barrier of dislocation nucleation. Similar results have also been reported in the dislocation nucleation of polycrystal Cu by Duet al.[47]and creep in nanocrystalline metals by Wanget al.[48]When the average stress reaches the yield point, the void surface starts to emit dislocations to release the stress. According to the type of initial dislocation,Shockley dislocations 1/6〈112〉are observed in all samples,as seen in Figs. 6(a), 6(c), 6(e), and 6(g), indicating that Mg content has no effect on the type of initial dislocation. Dislocations emitted from void surface mean that the system has entered the plastic deformation stage, corresponding to the second stage in Fig. 4(a). In this stage, the dislocations emitted from the void surface propagate rapidly along the slip plane,and with the generation of new dislocations, the stress drops sharply, which leads to the rapid growth of the void. When the stress release is about to end, the disordered atomic regions undergoing plastic deformation first in the sample will rearrange into FCC structure,which will probably impede the increase of the void temporarily. Namely, the void fraction will decrease slightly.

    With further loading,the dislocation density of the system enters a relatively stable value. Meanwhile, the void fraction no longer changes significantly, depicted in Fig. 4(a). Seen from Fig. 6(b), extensive stacking faults are distributed near the void of pure Al in the plastic deformation process,which is consistent with the phenomenon described by Guanet al.[21]in the deformation study of single crystal Al with a spherical void. However, with increasing Mg, the stacking faults distributed near the void decrease obviously and are primarily distributed in the diagonal direction of the simulation box,as shown in Figs. 6(d), 6(f), and 6(h). Compared with the alloy system, a more uniform distribution of stacking faults is generated around the void of pure Al, and the direction of the stacking faults is approximately perpendicular to the amorphous region of void surface in Fig.5(b). The uniform stacking faults impede the growth of void to a certain extent,which is similar to the results of the dual-phase polycrystalline Mg studied by Songet al.[49]Therefore,the void fraction in pure Al is lower than Al–Mg alloys. In Mg 2%–5% considered,the solid solution of Mg leads to the distortion of the ideal lattice, and increasing Mg makes it difficult for the dislocations to slip and propagate in the process of the tensile deformation, which impedes the growth of the void. Yet, the void fraction of Al-5%Mg alloy is still higher than that of pure Al. It is found that the Mg concentrations impede the dislocation movement,leading to a decrease of the proportion of the stacking faults around the voids,which results in a decrease of the stacking faults impeding the expansion of voids. Namely,stacking faults around the void and Mg concentrations impact the growth of the voids together. Voids are more sensitive to the stacking faults, which gives rise to the results of the third stage in Fig. 4(a). In addition, we calculate void fraction of the samples with Mg (1%, 6% and 7%). The result indicates that Mg almost has no effect on the void fraction when Mg is beyond 5%,as shown in Fig.4(b).

    Dislocation density is another vital factor to describe the plastic deformation of the system, where the dislocation density is defined as the total length of the dislocation in a unit volume. Figure 7 shows the dislocation density of all the samples as a function of strain. The dislocation density of Al–Mg alloy is significantly lower than pure Al, and the decrease of the dislocation density is much noticeable when the Mg content is 2%. This indicates that the distortion of the ideal lattice caused by Mg effectively impedes the movement of the dislocation. Yet, the sensitivity of dislocation density to Mg concentrations decreases obviously with increasing Mg. From the insets of Figs.7(a),7(b)for pure Al and 7(c),7(d)for Al-2%Mg, the dislocation lines around the void of pure Al are long and distributed evenly, while the dislocation lines in Al-2%Mg are short and entangled.

    3.2. Effect of void sizes on mechanical properties

    The void size has a close relationship with the mechanical properties and plastic deformation of metals. We study the mechanical properties of the Al-2%Mg alloys with different void sizes(d=1.2 nm,2 nm,2.8 nm,3.6 nm,and 4.8 nm).

    As seen in Fig. 8(a), the peak point decreases significantly with the void diameter increased. Whendis larger than 2.8 nm, the stress release process of the sample behaves gently,where a temporary‘step’phenomenon is observed,as shown in point A of the stress–strain curve. The yield stress and Young’s modulus are derived as shown in Fig. 8(b). By comparison withd=1.2 nm, the yield stress of the sample with voidd=4.8 nm decreases by 41.9%,indicating that yield stress is highly dependent on void size. In addition,void size also affects Young’s modulus,which decreases by 15.4%.

    Figure 9 shows the curve of the yield stress and theR/b,

    wherebis the Burgers vector. The yield stress decreases distinctly withR/bincreased,and MD results agree well with the analytical results of the Lubarda model. This model proposed by Lubardaet al.[50]is to describe the void growth caused by dislocation emission under tensile loading,where the analytical results are obtained by

    Here,we assume that the Mg atoms in the alloy are dilute sufficiently so that alloy-induced changes in elastic properties and Burgers vector magnitude are negligible. Hence,σcrrepresents the critical stress of dislocation emission, shear modulusG=26 GPa, Burgers vectorb=2.86 °A, Poisson’s ratioν=0.33,material parameterρ=1.

    In order to capture the deformation mechanism depending on void size,we emphasize the plastic deformation of the Al-2%Mg alloys with different void sizes(d=1.2 nm, 2 nm and 2.8 nm). Figure 10 shows the atomic structure snapshots of the samples with varied void diameters at different strains.From the insets of Fig.10,the atoms along they-axis direction around the void surface behave disordered at the beginning of deformation. As the diameter of the void rises, the stress required to emit the dislocations from the void surface decreases,and the sample with a larger void emits the dislocations preferentially. However, it is interesting that at the same strain interval after the beginning point of deformation, the plastic deformation of the sample with a larger void is remarkably less sharp than that with a small void in Figs.10(b),10(d),and 10(f). In addition, the dislocation density also confirms what we observed. As illustrated in Fig. 11, the model with a relatively small void has a higher dislocation density, indicating that the deformation degree of the model is more severe.From the perspective of the dislocation trend,the larger the void size is, the slower the growth trend of the dislocation density is,which means that the stress release process is longer. Consequently, it shows a slow decline in the stress–strain curves.Moreover,when the dislocation density of the system remains stable,the dislocation line around the void also maintains relatively stable,as shown in Figs.11(a)and 11(b). For the transient‘step’phenomenon at point A in the stress–strain curve.The reason probably is that numerous stair-rod dislocations 1/6〈110〉are generated around the void withd=2.8 nm, as seen in Figs. 10(f) and 11(c). Because the stair-rod dislocations are relatively stable, dislocation density of the sample with voidd=2.8 nm maintains stable when the strain is 7.6%–8.6%in Fig.11,which results in the slow deformation of the system during the loading process.

    3.3. Effect of temperatures on mechanical properties

    It is well known that temperature holds an essential effect on the mechanical properties of nanometals. The mechanical response of Al-2%Mg alloy with voidd=2 nm is investigated at different temperatures(10 K,100 K,300 K and 500 K).As shown in Fig. 12(a), all the curves increase linearly. Beyond the peak stress in the stress–strain curves, the materials enter the plastic deformation stage. In Fig. 12(b), the effect of temperature on the yield stress and Young’s modulus is significant.At temperature of 10–500 K,the yield stress and Young’s modulus decrease sharply from 6.43 GPa and 78.98 GPa to 4.09 GPa and 66.55 GPa,respectively. As the temperature increases,the yield stress and Young’s modulus decrease due to more phonons absorbed by lattice, the increased atomic mobility and the rapid diffusion of free volume.

    Hence, the atoms can be displaced more easily at higher temperature when the external loading is applied.Figure 12(c)shows the void fraction of Al-2%Mg alloy with voidd=2 nm at different temperatures.As the temperature increases,the beginning point of void growth becomes earlier. Similar results are described in the void study of single crystal zirconium.[25]After the stress release is completed,the void fraction remains relatively stable value below 300 K, while the void fraction continues to increase at 500 K.It is reasonable that when the temperature rises, the atoms in equilibrium position vibrate more violently, resulting in the instability of the lattice structure. The stress required for the atoms to leave the equilibrium position decreases,which leads to the further increase of void fraction.

    4. Conclusions

    In summary,the effects of Mg content,void size,and temperature on the deformation properties of cylindrical pre-void Al–Mg alloys under uniaxial tensile loading are systematically analyzed by MD simulations using stress–strain curves, void fraction, atomic configuration, and dislocation density. The results are as follows:

    (1)Mg impedes the void growth effectively by deforming the lattice. The lattice distortion caused by Mg has obviously influences on the growth of the void.

    (2) The void fraction of Al–Mg alloy decreases with increasing Mg content until it reaches a plateau at 5%of Mg.

    (3) The critical stress required for dislocation emitted from void surface decreases with void size increased,leading to the lower yield stress of the sample with a larger void,which is in good agreement with the Lubarda model. The stress release process of the system with a larger void behaves longer,which is generated by the slow growth rate of dislocation in plastic deformation.

    (4) The growth of void is sensitive to the background temperature,and the void growth occurs preferentially at high temperature. The yield stress and Young’s modulus decrease with temperature.

    Acknowledgements

    Project supported by the National Natural Science Foundation of China (Grant No. 11502217), the Fundamental Research Funds for the Central Universities(Grant Nos. 2452015054, 2452017122, and JUSRP121042),the China Postdoctoral Science Foundation (Grant Nos. 2015M570854 and 2016T90949), the Projects of the Manned Space Engineering Technology (Grant No. 2020-ZKZX-5011), Development of Large-Scale Spacecraft Flight and Reentry Surveillance and Prediction System, the Open Fund of Key Laboratory for Intelligent Nano Materials and Devices of the Ministry of Education (NUAA) (Grant No. INMD-2019M08), and Jiangsu Key Laboratory of Advanced Food Manufacturing Equipment and Technology(Grant Nos.FMZ202001 and FMZ202009).

    猜你喜歡
    趙軍
    “章節(jié)起始課”的教學(xué)觀察與比較
    俺們村的“貼心人”
    種樹(shù)協(xié)議(原創(chuàng))
    隔離的松風(fēng)
    金秋(2019年14期)2019-10-23 02:11:34
    落魄富豪殺子:自己生的垃圾能“退貨”嗎
    抓住整體巧妙代入
    七分審題三分做
    趙軍 藏石欣賞
    寶藏(2017年3期)2017-05-09 03:21:45
    七彩夜明珠
    求和與求援
    免费观看a级毛片全部| 欧美zozozo另类| 亚洲欧美一区二区三区国产| 真实男女啪啪啪动态图| 黄色配什么色好看| 欧美bdsm另类| 免费看美女性在线毛片视频| 欧美丝袜亚洲另类| 亚洲欧美成人精品一区二区| 纵有疾风起免费观看全集完整版 | 国产免费视频播放在线视频 | 日韩精品有码人妻一区| 少妇裸体淫交视频免费看高清| 男人爽女人下面视频在线观看| 精品人妻一区二区三区麻豆| 国产老妇女一区| 美女大奶头视频| 国产精品精品国产色婷婷| 久久久色成人| 中文字幕人妻熟人妻熟丝袜美| 白带黄色成豆腐渣| 亚洲av男天堂| 2021少妇久久久久久久久久久| 久久精品国产鲁丝片午夜精品| 熟妇人妻久久中文字幕3abv| eeuss影院久久| 一个人免费在线观看电影| 麻豆精品久久久久久蜜桃| 99久久精品一区二区三区| 寂寞人妻少妇视频99o| 亚洲国产精品专区欧美| 高清欧美精品videossex| 老女人水多毛片| 波野结衣二区三区在线| 亚洲美女视频黄频| 69av精品久久久久久| 国产精品伦人一区二区| 国产黄片美女视频| 七月丁香在线播放| 久久久久九九精品影院| 啦啦啦韩国在线观看视频| 身体一侧抽搐| 淫秽高清视频在线观看| 欧美3d第一页| 久久久久久久久久久免费av| 免费电影在线观看免费观看| 国产淫片久久久久久久久| 亚洲在线观看片| av天堂中文字幕网| 亚洲av福利一区| 国产精品熟女久久久久浪| 国产色爽女视频免费观看| 精品国产一区二区三区久久久樱花 | videossex国产| 久久久久久久久久久丰满| 岛国毛片在线播放| 高清日韩中文字幕在线| 国语对白做爰xxxⅹ性视频网站| 伊人久久国产一区二区| 欧美区成人在线视频| 日韩制服骚丝袜av| 18禁在线无遮挡免费观看视频| 蜜桃久久精品国产亚洲av| 国产毛片a区久久久久| av国产免费在线观看| 一区二区三区四区激情视频| videos熟女内射| 在线天堂最新版资源| 日日撸夜夜添| 国产精品一区www在线观看| 成人一区二区视频在线观看| 久久久久久九九精品二区国产| 床上黄色一级片| 人妻少妇偷人精品九色| 国产探花极品一区二区| 成人国产麻豆网| 91精品伊人久久大香线蕉| 免费黄网站久久成人精品| 国产黄片美女视频| 一级片'在线观看视频| 国产精品熟女久久久久浪| 日韩电影二区| 中文欧美无线码| 啦啦啦中文免费视频观看日本| 女的被弄到高潮叫床怎么办| 夜夜看夜夜爽夜夜摸| 亚州av有码| 国产精品嫩草影院av在线观看| 国产免费又黄又爽又色| 国产爱豆传媒在线观看| 综合色丁香网| 天堂影院成人在线观看| ponron亚洲| 激情五月婷婷亚洲| 蜜桃亚洲精品一区二区三区| 一个人看的www免费观看视频| 国产成人91sexporn| 午夜免费激情av| 免费少妇av软件| 色网站视频免费| 亚洲精品色激情综合| 成年人午夜在线观看视频 | 免费电影在线观看免费观看| 最近的中文字幕免费完整| 亚洲欧美成人精品一区二区| 亚洲熟女精品中文字幕| 一个人观看的视频www高清免费观看| 丝瓜视频免费看黄片| 亚洲成人av在线免费| 色吧在线观看| 秋霞在线观看毛片| 免费无遮挡裸体视频| 99热网站在线观看| 国产老妇伦熟女老妇高清| 午夜免费观看性视频| 亚洲精品久久久久久婷婷小说| 一级二级三级毛片免费看| 成人鲁丝片一二三区免费| 国产毛片a区久久久久| 久久久久久久久大av| 国产亚洲精品久久久com| 日韩电影二区| 日韩欧美精品v在线| av在线播放精品| 亚洲国产精品国产精品| 国产乱人视频| 日本免费a在线| 中文字幕免费在线视频6| 夫妻性生交免费视频一级片| 97在线视频观看| 久久精品久久久久久久性| 国产毛片a区久久久久| 色吧在线观看| 婷婷色av中文字幕| 在线天堂最新版资源| 亚洲欧洲日产国产| 欧美极品一区二区三区四区| 国内精品美女久久久久久| 狂野欧美激情性xxxx在线观看| 99热这里只有是精品在线观看| 国产毛片a区久久久久| 最近最新中文字幕免费大全7| 麻豆成人午夜福利视频| 伦精品一区二区三区| 亚洲欧洲国产日韩| 最近2019中文字幕mv第一页| 国产精品1区2区在线观看.| 五月玫瑰六月丁香| 国产一级毛片在线| 麻豆久久精品国产亚洲av| 噜噜噜噜噜久久久久久91| 99久国产av精品| 在线a可以看的网站| 亚洲熟妇中文字幕五十中出| 欧美日韩亚洲高清精品| 永久免费av网站大全| 欧美一区二区亚洲| 国产成人a区在线观看| 日日啪夜夜撸| 亚洲高清免费不卡视频| 国产成人午夜福利电影在线观看| 99热网站在线观看| 女人被狂操c到高潮| 国产白丝娇喘喷水9色精品| 爱豆传媒免费全集在线观看| 欧美 日韩 精品 国产| 国产av码专区亚洲av| 激情五月婷婷亚洲| 国产大屁股一区二区在线视频| 国产高潮美女av| 深爱激情五月婷婷| 国产成人a区在线观看| 2021天堂中文幕一二区在线观| 毛片一级片免费看久久久久| 看黄色毛片网站| 3wmmmm亚洲av在线观看| 51国产日韩欧美| 欧美不卡视频在线免费观看| 一级片'在线观看视频| 欧美丝袜亚洲另类| 精品一区二区三区人妻视频| 天天躁日日操中文字幕| 精品久久久久久久人妻蜜臀av| 亚洲精品日韩av片在线观看| 男人爽女人下面视频在线观看| 搞女人的毛片| 精品久久国产蜜桃| 久久精品国产鲁丝片午夜精品| av网站免费在线观看视频 | 国产午夜精品一二区理论片| 99热网站在线观看| 99久国产av精品| 亚洲欧美一区二区三区黑人 | 好男人在线观看高清免费视频| 麻豆av噜噜一区二区三区| 三级男女做爰猛烈吃奶摸视频| 夫妻午夜视频| 国产 一区 欧美 日韩| 国产黄色免费在线视频| 2021少妇久久久久久久久久久| av在线亚洲专区| 我的女老师完整版在线观看| 如何舔出高潮| 婷婷色麻豆天堂久久| 好男人视频免费观看在线| 欧美潮喷喷水| 我的女老师完整版在线观看| 欧美极品一区二区三区四区| 国产三级在线视频| 久99久视频精品免费| 亚洲最大成人中文| 精品一区在线观看国产| 亚洲在线自拍视频| eeuss影院久久| 久99久视频精品免费| 国产精品.久久久| 麻豆国产97在线/欧美| 特大巨黑吊av在线直播| 国产爱豆传媒在线观看| 性插视频无遮挡在线免费观看| 99久久精品一区二区三区| 亚洲欧美成人综合另类久久久| 成人性生交大片免费视频hd| 插逼视频在线观看| 一二三四中文在线观看免费高清| 99久久精品一区二区三区| 国产一区二区三区av在线| 久久国内精品自在自线图片| 看十八女毛片水多多多| 我要看日韩黄色一级片| 青春草视频在线免费观看| 国产不卡一卡二| 乱系列少妇在线播放| 欧美不卡视频在线免费观看| 少妇裸体淫交视频免费看高清| 一级爰片在线观看| 精品一区二区免费观看| 啦啦啦啦在线视频资源| 日韩一本色道免费dvd| av国产久精品久网站免费入址| 欧美日本视频| 有码 亚洲区| 久久精品国产鲁丝片午夜精品| 国产精品国产三级专区第一集| 亚洲综合精品二区| 国产毛片a区久久久久| 欧美另类一区| 欧美97在线视频| 久久精品久久久久久噜噜老黄| 国产精品美女特级片免费视频播放器| 亚洲第一区二区三区不卡| 久久99热这里只频精品6学生| 国产免费又黄又爽又色| 国产 亚洲一区二区三区 | 久久人人爽人人片av| 一级毛片黄色毛片免费观看视频| 天天躁日日操中文字幕| 国内精品一区二区在线观看| 观看美女的网站| 精品国内亚洲2022精品成人| 亚州av有码| 国产91av在线免费观看| 国产午夜精品久久久久久一区二区三区| 日本一二三区视频观看| 国产精品一区二区三区四区免费观看| 亚洲精品国产成人久久av| 国产大屁股一区二区在线视频| 97人妻精品一区二区三区麻豆| 最近的中文字幕免费完整| 夜夜看夜夜爽夜夜摸| 久久6这里有精品| 午夜免费男女啪啪视频观看| 国产黄a三级三级三级人| 久久久久久久久久久丰满| 欧美日韩在线观看h| 麻豆成人午夜福利视频| 大话2 男鬼变身卡| 18禁在线无遮挡免费观看视频| 欧美人与善性xxx| 精品久久久久久久久av| 精品一区二区三卡| 国产成年人精品一区二区| 中文字幕免费在线视频6| 亚洲真实伦在线观看| 中文乱码字字幕精品一区二区三区 | 国产精品日韩av在线免费观看| 极品少妇高潮喷水抽搐| 亚洲美女视频黄频| 精品久久久久久成人av| 男人舔女人下体高潮全视频| 国产v大片淫在线免费观看| 男女边摸边吃奶| 亚洲欧美清纯卡通| 高清午夜精品一区二区三区| 国产精品久久视频播放| 国产精品一区二区在线观看99 | 久久久欧美国产精品| 日韩三级伦理在线观看| 亚洲第一av免费看| 大码成人一级视频| 天天影视国产精品| 久久久久国产一级毛片高清牌| 在线亚洲精品国产二区图片欧美| 99香蕉大伊视频| 国产乱来视频区| 永久免费av网站大全| 亚洲精品国产av成人精品| 国产精品.久久久| 人人妻人人添人人爽欧美一区卜| 午夜福利,免费看| 国产精品欧美亚洲77777| 午夜影院在线不卡| 在线观看三级黄色| 巨乳人妻的诱惑在线观看| 国产成人免费观看mmmm| 国产亚洲av片在线观看秒播厂| 99热国产这里只有精品6| 亚洲成人一二三区av| 日韩av不卡免费在线播放| www日本在线高清视频| 亚洲成人av在线免费| 毛片一级片免费看久久久久| 人人妻人人澡人人爽人人夜夜| 久久99热这里只频精品6学生| 18禁国产床啪视频网站| 两个人看的免费小视频| 久久亚洲国产成人精品v| 欧美国产精品一级二级三级| 少妇被粗大的猛进出69影院| 欧美另类一区| kizo精华| 国产精品女同一区二区软件| 国产成人一区二区在线| 校园人妻丝袜中文字幕| 黄色配什么色好看| 久久韩国三级中文字幕| 女性生殖器流出的白浆| 精品卡一卡二卡四卡免费| 久久久久国产网址| 一区二区三区四区激情视频| 亚洲中文av在线| 久久精品久久精品一区二区三区| 大香蕉久久网| 大片免费播放器 马上看| 国产欧美亚洲国产| 男男h啪啪无遮挡| 亚洲精品美女久久av网站| 国产日韩一区二区三区精品不卡| 高清视频免费观看一区二区| 亚洲精品久久午夜乱码| 大香蕉久久网| 高清不卡的av网站| 波野结衣二区三区在线| 美国免费a级毛片| 大陆偷拍与自拍| videossex国产| 亚洲人成77777在线视频| 丝袜美足系列| 大陆偷拍与自拍| 好男人视频免费观看在线| 国产精品一区二区在线观看99| 亚洲成人手机| 在线天堂最新版资源| 国产在视频线精品| 亚洲欧美精品自产自拍| 下体分泌物呈黄色| freevideosex欧美| 热re99久久精品国产66热6| 黄片无遮挡物在线观看| 久热久热在线精品观看| 免费在线观看黄色视频的| 蜜桃国产av成人99| 国产国语露脸激情在线看| 18禁观看日本| 国产成人免费观看mmmm| 日韩视频在线欧美| 亚洲欧洲日产国产| 亚洲第一青青草原| 一区二区三区四区激情视频| 久久女婷五月综合色啪小说| 午夜福利影视在线免费观看| 国产成人精品无人区| 中文乱码字字幕精品一区二区三区| 最近最新中文字幕大全免费视频 | 一级毛片我不卡| 久久久久久久久久人人人人人人| 国语对白做爰xxxⅹ性视频网站| 国产熟女欧美一区二区| 中文乱码字字幕精品一区二区三区| 国产成人精品久久二区二区91 | 如何舔出高潮| 久久这里只有精品19| 黑人巨大精品欧美一区二区蜜桃| 日日撸夜夜添| 天天影视国产精品| 男女高潮啪啪啪动态图| 国产伦理片在线播放av一区| 亚洲精品av麻豆狂野| 久久久国产精品麻豆| av国产久精品久网站免费入址| 国产av码专区亚洲av| 日本欧美国产在线视频| 男女啪啪激烈高潮av片| 亚洲成人一二三区av| 欧美日韩精品成人综合77777| 91在线精品国自产拍蜜月| 亚洲在久久综合| 亚洲精品久久午夜乱码| 午夜福利在线免费观看网站| 2021少妇久久久久久久久久久| 男女下面插进去视频免费观看| 国产 精品1| 免费高清在线观看视频在线观看| 晚上一个人看的免费电影| 日韩不卡一区二区三区视频在线| 天天躁狠狠躁夜夜躁狠狠躁| 日本猛色少妇xxxxx猛交久久| 另类亚洲欧美激情| 精品少妇久久久久久888优播| 国产毛片在线视频| 91精品伊人久久大香线蕉| 精品国产一区二区三区久久久樱花| 国产精品久久久久成人av| 亚洲av日韩在线播放| 日韩 亚洲 欧美在线| 一区二区三区精品91| 丝袜在线中文字幕| 亚洲av男天堂| 亚洲精品久久成人aⅴ小说| 久久久久人妻精品一区果冻| 国产欧美亚洲国产| 热re99久久国产66热| 最近中文字幕2019免费版| 又黄又粗又硬又大视频| 日韩人妻精品一区2区三区| 韩国高清视频一区二区三区| 少妇人妻 视频| 国产亚洲av片在线观看秒播厂| 大片电影免费在线观看免费| 1024香蕉在线观看| 一区二区三区四区激情视频| 日本免费在线观看一区| 在线免费观看不下载黄p国产| 如日韩欧美国产精品一区二区三区| 18禁观看日本| 在线观看三级黄色| 亚洲第一青青草原| 寂寞人妻少妇视频99o| 咕卡用的链子| 电影成人av| 啦啦啦啦在线视频资源| 又大又黄又爽视频免费| 免费少妇av软件| 国产视频首页在线观看| 亚洲中文av在线| 高清欧美精品videossex| 一级片免费观看大全| 另类精品久久| 性少妇av在线| 成人午夜精彩视频在线观看| 黄色怎么调成土黄色| 国产成人精品在线电影| a级毛片黄视频| 国产黄频视频在线观看| 久久精品国产a三级三级三级| 女人精品久久久久毛片| 精品人妻在线不人妻| 9色porny在线观看| 午夜福利,免费看| 激情五月婷婷亚洲| 国产在线视频一区二区| 一本大道久久a久久精品| 国产男女超爽视频在线观看| 大片免费播放器 马上看| 中文字幕另类日韩欧美亚洲嫩草| 日韩 亚洲 欧美在线| 一区在线观看完整版| 国产亚洲精品第一综合不卡| 国产片内射在线| 免费大片黄手机在线观看| 久久精品国产综合久久久| 男的添女的下面高潮视频| 国产精品久久久久久精品古装| 亚洲综合色惰| 国产精品国产av在线观看| 啦啦啦视频在线资源免费观看| 久久人妻熟女aⅴ| 人妻系列 视频| 久久这里只有精品19| 一区福利在线观看| 看免费av毛片| 免费观看av网站的网址| 建设人人有责人人尽责人人享有的| 日韩不卡一区二区三区视频在线| 日韩精品免费视频一区二区三区| 免费观看性生交大片5| 国产精品av久久久久免费| a 毛片基地| 波多野结衣一区麻豆| av在线老鸭窝| 制服人妻中文乱码| 成人亚洲欧美一区二区av| 亚洲欧美一区二区三区国产| 国产国语露脸激情在线看| 久久狼人影院| 啦啦啦在线免费观看视频4| 亚洲第一区二区三区不卡| 黄网站色视频无遮挡免费观看| 国产麻豆69| 成年动漫av网址| 看免费av毛片| 国产福利在线免费观看视频| 欧美亚洲日本最大视频资源| 久久久久国产一级毛片高清牌| 亚洲男人天堂网一区| 日韩欧美精品免费久久| 丝袜人妻中文字幕| av线在线观看网站| 国产亚洲最大av| 久久女婷五月综合色啪小说| 少妇人妻精品综合一区二区| 菩萨蛮人人尽说江南好唐韦庄| 一区福利在线观看| 日日摸夜夜添夜夜爱| 永久免费av网站大全| 女人被躁到高潮嗷嗷叫费观| 熟女少妇亚洲综合色aaa.| 国产欧美亚洲国产| 久久久久精品性色| 日韩精品有码人妻一区| 精品人妻在线不人妻| 男男h啪啪无遮挡| a级毛片在线看网站| 欧美成人午夜免费资源| 男女国产视频网站| 色94色欧美一区二区| 97精品久久久久久久久久精品| 久久久精品国产亚洲av高清涩受| 久久毛片免费看一区二区三区| 午夜日韩欧美国产| freevideosex欧美| 国产亚洲精品第一综合不卡| 久久综合国产亚洲精品| 午夜福利在线观看免费完整高清在| 久久久久久免费高清国产稀缺| 中文字幕色久视频| 欧美日本中文国产一区发布| 9热在线视频观看99| 亚洲欧洲国产日韩| 国产又色又爽无遮挡免| 性色avwww在线观看| 麻豆av在线久日| 女人高潮潮喷娇喘18禁视频| 国产一区二区 视频在线| 狠狠婷婷综合久久久久久88av| 超碰97精品在线观看| 亚洲av福利一区| 日韩,欧美,国产一区二区三区| 欧美国产精品va在线观看不卡| 日本午夜av视频| 日韩精品免费视频一区二区三区| 国产精品久久久久久av不卡| 日韩av在线免费看完整版不卡| 亚洲少妇的诱惑av| 青青草视频在线视频观看| 大话2 男鬼变身卡| 18禁观看日本| 成人影院久久| 欧美日韩一区二区视频在线观看视频在线| 999精品在线视频| 日韩av免费高清视频| 久久精品人人爽人人爽视色| 国产乱来视频区| 国产一区亚洲一区在线观看| 在线天堂中文资源库| 777久久人妻少妇嫩草av网站| 精品久久久久久电影网| 日韩在线高清观看一区二区三区| 欧美人与性动交α欧美软件| 中文字幕人妻熟女乱码| 少妇的逼水好多| 春色校园在线视频观看| 免费观看a级毛片全部| 日韩欧美一区视频在线观看| 亚洲,一卡二卡三卡| 亚洲激情五月婷婷啪啪| 97在线人人人人妻| 校园人妻丝袜中文字幕| 电影成人av| 91成人精品电影| 亚洲 欧美一区二区三区| 一级,二级,三级黄色视频| 在线观看人妻少妇| av在线播放精品| 1024视频免费在线观看| 久久久国产欧美日韩av| 久久97久久精品| freevideosex欧美| 午夜影院在线不卡| 美女福利国产在线| 国产黄频视频在线观看| 成年动漫av网址| 日韩欧美精品免费久久| 哪个播放器可以免费观看大片| 免费黄频网站在线观看国产| 国产精品三级大全| 亚洲久久久国产精品| 欧美日韩精品网址| 99久久中文字幕三级久久日本| 亚洲精品一二三| av卡一久久| 伊人亚洲综合成人网| 亚洲精品一区蜜桃| 日本爱情动作片www.在线观看| 91午夜精品亚洲一区二区三区|