• <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 ?

    A novel modification method for the dynamic mechanical test using thermomechanical analyzer for composite multi-layered energetic materials

    2023-03-28 08:37:34LeQiShilinZhngHoYunZhonglingZhonglingXio
    Defence Technology 2023年3期

    Le Qi , Shi-lin Zhng , Ho Yun , Zhong-ling M ,*, Zhong-ling Xio

    a School of Environment and Safety Engineering, The North University of China, Taiyuan, 030051, China

    b School of Chemical Engineering, The Nanjing University of Science and Technology, Nanjing, 210094, China

    Keywords:Thermo-mechanical analyzer (TMA)Dynamic mechanical analyzer (DMA)Modified Time-temperature equivalence principle

    ABSTRACT Herein, we present a thermo-mechanical analyzer (TMA) and dynamic mechanical analyzer (DMA) of composite multi-layered gun propellant, focusing on thermal expansion coefficients and dynamic thermomechanical properties. The linear thermal expansion coefficient of the prepared energetic material is determined as approx. 0.1800 × 10-4 - 0.2081 × 10-4 K-1. According to DMA test and dynamic thermomechanical properties, the glass transition temperature is also obtained. The tested value is within the range of 223.01-223.50 K,which indicates the lower limit of the energetic material.However,DMA tests reveal temperature changes, which occur due to thermal expansion. Moreover, the geometrical factor decreases with increasing temperature.Therefore,thermal expansion significantly affects the storage modulus and loss modulus.Additionally,the thermal expansion coefficient can be used to modify the storage and loss modulus.The results show that the proposed method provides effective and reliable modified results.

    1. Introduction

    Double-based (DB) gun propellant is produced from mixing nitrocellulose and nitroglycerine with small amounts of other auxiliary materials [1,2]. DB propellants are widely used for medium and small caliber weapons;hence,many studies have focused on improving their combustion performance [3,4]. The composite multi-layered flake gun propellant has good burning progressivity,which can effectively improve the muzzle velocities of the gun's projectile.Additionally,the mechanical properties of the composite multi-layered flake gun propellant are similar to that of general polymers [5,6]. Therefore, a testing method for general polymers can be used for this composite multi-layered flake gun propellant.

    Thermo-mechanical analyzer(TMA)is commonly used to study the thermal expansion of energetic materials. The thermal expansion coefficient of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine(HMX) has been measured over the temperature range of 58-253 K using TMA. Furthermore, the coefficient of thermal expansion (CTE) value is affected by the temperature range and heating rate, and is within the range of 51-66 × 10-6K-1[7].Thermo-mechanical analyzer (TMA) technique has been used to characterize the thermomechanical properties of carbon nanotubes and graphene nano-platelets[8].This approach has proven to be a simple and effective method to measure the glass transition temperature [9]. Victor et al. investigated the nitramine-based amorphous energetics using TMA, and found that the material's softening was associated with the glass transition at approx.323 K[10]. The relaxation transitions, surface tension, and porosity of nitrocellulose have been studied using TMA and dynamic mechanical analyzer (DMA), where three small relaxation transitions of nitrocellulose can be observed, which are contained in gun propellant at 233 K, 308 K, and 353 K [11,12]. CTE of TATB (1,3,5-triamino-2,4,6-trinitrobenzene) based explosives has been measured using TMA within the temperature range of 300-566 K,in which the axial and radical CTE are 2.7 × 10-6K-1and 48 × 10-6K-1, respectively, which indicate a small degree of alignment of TATB molecules under uniaxial compression [13,14].

    The thermo-mechanical properties tests can be divided into TMA and DMA tests. Furthermore, the thermo-mechanical properties of DB gun propellants influence their proper functioning,which has been the critical focus of many studies. In our previous works, linear thermal expansion coefficient of composite multilayered flake gun propellant was measured using TMA method[3,15]. DMA method can also be used to study the thermal expansion coefficient. However, this method is complicated [16]. It is known that the glass transition temperature is related to phase change and can be evaluated using several techniques, which are attributed to the frequency effect.The glass transition temperature obtained using DMA and temperature modulated differential scanning calorimetry (TMDSC) are different [17-19]. The glass transition temperature of automotive coatings has been measured using TMA and DMA. Reports have shown that the correlation between the temperature of midpoint in DSC, the onset temperature of TMA,and the onset temperature of loss modulus using DMA at low frequencies is good. However, this correlation decreases at high frequencies [20,21]. Most glass transition temperatures of energetic materials have been studied using DMA method[22-24],including perfluorosulfonic acid ionomers.The graph between tanδ and temperature shows four distinct peaks. The glass transition temperature of H+from Nafion corresponds to a weak β-relaxation that is centered at 253 K[25].Furthermore,DMA method is widely used in the research of double-based solid propellant to study the glass transition temperature [26,27]. The dynamic mechanical properties of double-based rocket propellant have been studied at 353 K, 358 K, and 363 K, where the storage and loss modulus depend on temperature and time. However, the prediction of the propellant's artificially aged time has been determined to be unreliable above 333 K [28]. The viscoelastic parameters obtained from DMA measurement can be optimized using a genetic algorithm, which are matched with the experimental results at different temperatures, strain rates, and pressures [29]. Additionally,DMA technique can be used to predict the artificially aged time of the propellant by storage modulus [30].

    The purpose of this work is to provide a fundamental background on the method of modifying the dynamic mechanical test results using thermo-mechanical analyzer for energetic materials,which provides a modified reference for DMA method. TMA and DMA tests are used to describe the thermo-mechanical properties of the energetic material. Moreover, frequency sweep curves are obtained using DMA. According to the thermal expansion coefficient, modification of the storage and loss modulus is an effective and reliable method.

    2. Theoretical backgr ound

    In DMA the dynamic mechanical behavior of a material acts as a function of frequency and temperature. The sample mounted in DMA is subjected to a predefined mechanical oscillation program,defined by the frequency and amplitude,and temperature program.The dynamic displacement of the sample during the mechanical oscillation program is measured.The phase lag angle δ between the applied stimulus and the response is also obtained using the displacement measurement.Additionally,a force signal is produced based on the force exerted on the sample by the drive motor.

    The force and displacement are denoted as F and L,respectively.The complex modulus E*can be calculated using Eq. (1).

    where the ratio F/L is defined as the stiffness S, and g is known as the geometrical factor, which is calculated from the sample's dimensions. Both S and g are calculated using Eq. (2) and Eq. (3),respectively.

    where g is the geometrical factor for three-point bending specimen,and l, w, and b are the geometric dimensions of the sample identified in Fig.1.A schematic diagram of DMA test is shown in Fig.1.

    Fig.1. Schematic of functional principle of DMA.

    During DMA method, as temperature increases, the thermal expansion of specimens affects their geometry. The probe's pressure on specimens is 0.05 N in TMA method,whereas in the case of DMA method there is 1 N pressure on the upper clamp bar to ensure the assumed amplitude value can be 10 μm.The geometrical factor(g) can be corrected by the thermal expansion coefficient of the specimen during the heating process at the same heating rate and temperature range.

    Therefore, a method is required that is suitable for composite multi-layered flake gun propellant, which is easy to apply and calculate.The purpose of this paper is to describe such a method to correct for the effect of temperature on geometrical factor.Thermal expansion of the specimen in the thickness direction is considered,and the linear thermal expansion coefficient of the specimen is defined as α. When combined with the definition of thermal expansion coefficient,the thickness of the specimen at temperature T is expressed as Eq. (4).

    where b0(T0) is the original thickness of the specimen, and b(T) is the thickness of the specimen at temperature T.Eq.(3)can also be rewritten as Eq. (5).

    The complex modulus E*is expressed as Eq. (6).

    Therefore, the modulus can be corrected by thermal expansion coefficient.

    3. Experiment

    3.1. Materials

    All samples described herein were composite multi-layered flake gun propellant. The gun propellant had a layered structure.Both the inner and outer layers were composed of double-base propellant. The main component of the inner layered material was 1# double-base absorbent propellant (NC:68.2%, NG:31%,C2:0.8%, where NC is nitrocellulose, NG is nitroglycerin, C2 is centralite, the nitration level is 13.00%). The main component of the outer layered material was 2# double-base absorbent propellant(NC:88.26%, NG:10.04, C2:1.7%, the nitration level is 12.76%). The structure of the composite multi-layered flake gun propellant is shown in Fig.2,inner layer was coated by outer layer,and the inner layer was twice as thick as outer layer, the corresponding geometrical size of the samples is shown in Table 1. And the solubility parameters of nitrocellulose and alcohol/acetone mixed solvents (1:1) are similar, therefore, alcohol/acetone mixed solvents are used as solvent.

    Table 1 Geometrical size of the samples composite multi-layered flake gun propellant.

    Fig. 2. The structure of composite multi-layered flake gun propellant.

    3.2. Thermo-mechanical analyzer (TMA)

    The theory of CTE comprises the deformation of materials was determined as the temperature changes. In some temperature ranges, the linear CTE was constant. When the temperature changed, TMA measured the change in length of materials. The linear CTE of materials was calculated by measuring its deformation within a specific temperature range. The instrument's sensitivity was 0.1 μm.

    Furthermore, the composite multi-layered flake gun propellant belongs to double-based gun propellant, which turns soft above 300 K. In order to reduce the influence of probe on the thickness measurement, a flat probe 3 mm in diameter was used to reduce the pressure of probe on the specimens. TMA results showed that 0.007 MPa causes false negative expansion of the sample above 300 K;however,in DMA test,the specimens were subjected to the same pressure. ΔL values were obtained at various temperature from ΔL-T curves; hence, the thickness of the specimens were modified by ΔL-T curves in DMA test.

    A smooth part of the composite multi-layered flake gun propellant sample (double-base propellant) was selected. The sample was a flake shaped cuboid with the length,width and thickness of 0.5 cm, 0.5 cm, and 0.3-1.0 mm, respectively. The thermal expansion coefficient of the sample was measured using TMA-Q 400(TA instruments, USA) with 2 K/min heating rate under dry nitrogen atmosphere over the temperature range of 213-323 K. The linear CTE can be expressed using Eq. (7).

    where α, Δb, b0, and ΔT are the linear CTE, change in dimension,original thickness of the material, and corresponding temperature change, respectively. The linear CTE (α) is average linear thermal expansion coefficient for the sample in the temperature range of T2to T1.

    3.2.1. Dynamic mechanical analyzer (DMA)

    DMA test was performed using DMA1 analyzer(Mettler Toledo)in 3-point bending mode with the sample dimensions of 60 ± 0.05× 7 ± 0.05 ×b0(0.3-1.0) mm.A liquid nitrogen cooling accessory was used for the experiments. The non-isothermal measurements were conducted within the temperature range of 273-393 K at the heating rate of 2 K/min and loading frequency of 1 Hz. The amplitude of the test sample's deformation was established at ±10 μm. The isothermal measurements were carried out over the frequency range of 100-0.01 Hz with 10 data points for each order of magnitude. Moreover, the amplitude was 10 μm for the temperatures of 228 K, 263 K, and 293 K.

    4. Experimental results and analysis

    4.1. TMA test results

    TMA linear thermal expansion curve of specimens with thickness between 0.3 and 1.0 mm, scanned within the temperature range of 263-283 K,is shown in Fig.3.The obtained results showed that the curves were all linear.Between this temperature range,the linear thermal expansion coefficient lied within the range of 0.1800 × 10-4- 0.2081 × 10-4K-1, whereas the linear CTE increased with increasing sample thickness (see Table 2). The composite multi-layered flake gun propellant expansion during this stage was mainly caused by thermal expansion of nitrocellulose. The specimens were extruded under 5 MPa pressure in the forming process.However,solvent still remained in the specimens,as well as having creep recovery characteristics. In the forming process, as the sample was extruded by smaller export molds, the thickness direction of the sample experienced high pressure. The nitrocellulose was also subject to greater bondage stress. As the stress disappeared,nitrocellulose molecule rebounded greatly,and the solvent in the samples was completely volatilized after a long period of time. Hence, nitrocellulose molecule recovery occurred.During TMA test, as the temperature increased, the thermal expansion rebounding of nitrocellulose molecule in samples of smaller thicknesses was small. Therefore, the linear CTE increases with increasing thickness.

    Table 2 Linear thermal expansion coefficient of composite multi-layered flake gun propellant.

    Table 3 Transition temperature of composite multi-layered flake gun propellant.

    The ΔL-T curves of composite multi-layered flake gun propellant with different thickness values within the temperature range of 233-323 K is shown in Fig.4.There was an obviously turning point on each curve at about 300 K,which indicated that the sample had softened above this transition temperature.Therefore,the thermal expansion coefficient of composite multi-layered flake gun propellant could not be calculated by Eq. (4) at temperatures beyond 300 K. This was due to the sample being compressed because of probe pressure beyond 300 K. As a result, a false negative expansion trend above 300 K was observed. However, ΔL-T curves showed shape variable values of thickness for composite multi-layered flake gun propellant with temperatures above 300 K.

    Fig. 3. Relationship between ΔL and T of composite multi-layered flake gun propellant (263-283 K).

    Fig. 4. Relationship between ΔL and T of composite multi-layered flake gun propellant (233-323 K).

    According to the mechanism of the interaction of nitrocellulose and nitroglycerin, the essence of the interaction between the nitrocellulose macromolecule and nitroglycerin molecule was that nitroglycerin swelled or dissolved nitrocellulose. The gravitational force between nitrocellulose and nitroglycerin decreased with increasing temperature. Below 300 K, the nitrocellulose macromolecular chain froze. Low molecular energy was insufficient to overcome the molecular bond rotation of barrier potential,in which only small molecular units could move.Therefore,it was unable to achieve conformational shift. Above 300 K, most of the molecular chain started to move,and the molecular kinetic energy increased and overcame the molecular bond rotation of barrier potential. It was found that even some part of the molecular chain slipped.This phenomenon was realized with a decrease in stiffness. As a result,the samples turned soft and were not sufficiently stiff to withstand the probe pressure of 0.05 N. Meanwhile, the probe was partially embedded into the sample,and showed a false negative expansion above 300 K.Therefore,there was an obvious turning point on ΔL-T curves.

    The transition temperature decreased with increasing thickness within the range of 0.3-0.7 mm. However, the transition temperature of No.5, No.6, and No.7 was approximately 300 K due to the nitrocellulose molecule in thinner samples being rebounded greatly. Hence, more energy was required to make the molecular chain move. Therefore, the transition temperature decreased with increasing thickness. When the thickness of specimen was greater than 0.7 mm, the content of solvent in the specimens was comparable. Due to the addition of solvent, the swelling phenomenon occurred, which increased the distance of nitrocellulose molecule,and the thicker specimens exhibited similar free volume fraction with thinner specimens. Therefore, No.5, No.6, and No.7 had the same transition temperatures.

    4.1.1. DMA test results

    In Fig. 5, the reference temperatures for loss modulus and loss factor were 223.42 K and 233.59 K, respectively. It is well-known that, the glass transition temperature represents the temperature region of phase transition for materials. Therefore, glass transition temperature is not a strict point. This temperature region can be defined by peak temperature of loss modulus and peak temperature of loss factor as lower and upper limits.This temperature range is the usage temperature limit for the material.

    According to Eq.(6),DMA test curves were modified by thermal expansion coefficient. Fig. 6 shows the modified curve for storage modulus of No.2.As temperature increased, the thickness of specimen also increased above 213 K, and the geometrical factor decreased. Therefore, the modified storage modulus value was lower than the test value.

    Fig. 5. DMA test result for No.2.

    Fig. 6. Test curve and corresponding modified curve for storage modulus of No.2.

    Fig. 7. Loss modulus curves for different samples.

    Fig. 8. Storage modulus curves for different samples.

    The loss modulus and temperature test curves are shown in Fig. 7. It is worth noting that there were two obvious peaks in the loss modulus curves,which indicated the occurrence of two phase transition processes during the increase of composite multi-layered flake gun propellant within the temperature range of 193-373 K.The first peak temperature corresponds to the glass transition temperature of the energetic material, whereas the second peak temperature occurred due to high elastic transition.Table 3 shows the corresponding glass transition temperature of composite multilayered flake gun propellant with different thickness values,where the glass transition temperature decreased with increasing thickness of composite multi-layered flake gun propellant. This phenomenon may be caused by thermal expansion of specimens due to changes in geometrical dimensions with increasing temperature.The intermolecular distance increased with increasing temperature. According to the free volume theory, the energy required for nitrocellulose molecule movement was relatively low. Based upon the results presented in Table 1, the linear thermal expansion coefficient increased with increasing thickness. Therefore, as the thickness of specimens increased,the glass transition temperature decreased.

    Moreover,a smaller peak was observed in the loss modulus and temperature curve at approx.336.07 K,which was attributed to the secondary transition temperature. Fig. 8 shows that the storage modulus decreased with increasing temperature. As the temperature increased, the molecular motor activity increased, and the spacing between the molecules increased. Additionally, the stiffness of this energetic material and value of storage modulus decreased. Furthermore, the fluidity of the energetic material was enhanced,and the loss modulus became the dominant factor above 336.07 K.This resulted in a small peak being observed in the curves.

    As described in the theoretical background, it was confirmed that the linear thermal expansion coefficient could be used for the modification of DMA test results.The left curves in Fig.9 show the unmodified loss modulus curves and right curves the modified loss modulus curves, and the peak temperatures are shown in Table 4.The first peak temperature in the corresponding curves was comparable, which meant that the glass transition temperature was Due to the frequency sweep being performed at a certain temperature, the effect of thermal expansion was eliminated, hence, the curve and modified E’and temperature curve were mirror images.

    Fig. 9. Unmodified and modified loss modulus curves of different samples.

    Table 4 Glass transition temperature of composite multi-layered flake gun propellant.

    Fig.11 shows the mirror images for E′and temperature and E’and frequency curves,where the storage modulus was the same at 253 K (on left curve) and 1 Hz (on right curve). Under the conditions of 293 K and 0.1 Hz, or 213 K and 10 Hz, the storage moduli were equal.Hence,the storage modulus curve modified by thermal expansion coefficient was proven to be effective.

    5. Conclusions

    (1) A sample of composite multi-layered flake gun propellant has been tested using TMA and DMA methods. The linear thermal expansion coefficient has been determined and lays within the range of 0.1800 × 10-4K-1- 0.2081 × 10-4K-1with the temperature range of 263-283 K.The coefficient of thermal expansion and impact on the use of material is small.DMA test shows that the glass transition temperature of the composite multi-layered flake gun propellant is 222.94 K. This result was obtained by eliminating the effect of thermal expansion.

    Fig.11. Mirror images of E′ and temperature and E′ and frequency curves.

    All the modified glass transition temperatures are presented in Table 4. The modified values were lower than the test values and that the modified value was 222.94 K. This temperature was regarded as the lower limit temperature for the energetic material.

    4.1.2. Verification of modified results

    According to the time-temperature equivalence principle, the same mechanical relaxation phenomenon of polymer can be observed at higher temperature and shorter time (or higher frequency), or at lower temperature and longer time (or lower frequency), which means that E′and temperature curve and E′and frequency curve are mirror images. Based upon this theory, frequency sweep of this specimen was performed at a certain temperature, and E′and frequency curve was obtained. E′and frequency curve and E’ and temperature curve were found to be mirror images.

    The frequency sweep experiments were carried out at 293 K within the frequency range of 0.01-10 Hz. The amplitude of test sample's deformation was established at 10 μm.The obtained curve is shown in Fig.10.

    Fig.10. Modified loss modulus curves for different samples.

    Fig. 10 shows the frequency and E′curve for No.2 specimens.223.01-223.50 K, which conforms to the double-based propellant.

    (2) According to DMA test, geometric dimensions have a great impact on the storage and loss moduli. Furthermore, as the geometric dimensions increase, the loss modulus decreases.Therefore, the thermal expansion in the test process has a certain influence on the storage and loss modulus.According to the time-temperature equivalence principle, this method is an effective and reliable method to modify the storage and loss modulus.

    Declaration of competing interest

    The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

    黄片大片在线免费观看| av不卡在线播放| 91九色精品人成在线观看| 一区二区三区激情视频| 国产免费av片在线观看野外av| 精品免费久久久久久久清纯 | 精品欧美一区二区三区在线| 欧美乱码精品一区二区三区| 精品亚洲成国产av| 狠狠婷婷综合久久久久久88av| 欧美日韩一级在线毛片| 免费一级毛片在线播放高清视频 | 精品久久久久久电影网| 丝袜美足系列| 欧美 日韩 精品 国产| 久久中文看片网| 母亲3免费完整高清在线观看| 日韩一卡2卡3卡4卡2021年| 国产99久久九九免费精品| 亚洲欧美激情在线| 国产一卡二卡三卡精品| 免费人妻精品一区二区三区视频| 国产精品一区二区在线不卡| 动漫黄色视频在线观看| 十八禁高潮呻吟视频| 日韩欧美国产一区二区入口| 免费在线观看黄色视频的| 国产欧美日韩综合在线一区二区| 波多野结衣一区麻豆| 可以免费在线观看a视频的电影网站| 搡老乐熟女国产| 欧美久久黑人一区二区| 久久人人爽av亚洲精品天堂| 日本av手机在线免费观看| 国产精品免费大片| 国产精品电影一区二区三区 | 窝窝影院91人妻| 我要看黄色一级片免费的| 国产在视频线精品| 亚洲欧美激情在线| 91字幕亚洲| 丁香欧美五月| 久久久久久久大尺度免费视频| 少妇精品久久久久久久| 久久精品熟女亚洲av麻豆精品| 两个人免费观看高清视频| 国产av一区二区精品久久| 成年人免费黄色播放视频| 国产男女超爽视频在线观看| 国产一区二区三区在线臀色熟女 | 美女视频免费永久观看网站| 黄色 视频免费看| 欧美变态另类bdsm刘玥| 中文字幕人妻丝袜一区二区| 午夜福利,免费看| a级片在线免费高清观看视频| 国产在线免费精品| 国产精品一区二区在线观看99| 国产精品久久久久久人妻精品电影 | 满18在线观看网站| 三级毛片av免费| 伦理电影免费视频| 大片免费播放器 马上看| 日韩中文字幕欧美一区二区| 嫩草影视91久久| 亚洲欧美色中文字幕在线| 在线永久观看黄色视频| 91精品三级在线观看| 一区二区日韩欧美中文字幕| 久久天堂一区二区三区四区| 捣出白浆h1v1| 日本a在线网址| 成人黄色视频免费在线看| 两人在一起打扑克的视频| 老司机午夜福利在线观看视频 | 热re99久久精品国产66热6| 欧美+亚洲+日韩+国产| 亚洲国产看品久久| 黄色视频不卡| 中亚洲国语对白在线视频| 成人黄色视频免费在线看| 久久久久久亚洲精品国产蜜桃av| 亚洲国产欧美网| 久久精品国产a三级三级三级| 色94色欧美一区二区| 国产麻豆69| av电影中文网址| 欧美精品高潮呻吟av久久| 最近最新中文字幕大全免费视频| 国产激情久久老熟女| 黄色成人免费大全| 99国产精品免费福利视频| 男人操女人黄网站| 美国免费a级毛片| 免费少妇av软件| 中文字幕另类日韩欧美亚洲嫩草| 久久久精品94久久精品| 999久久久国产精品视频| 视频区欧美日本亚洲| 18禁裸乳无遮挡动漫免费视频| 久久国产精品人妻蜜桃| 老汉色∧v一级毛片| 成人免费观看视频高清| 欧美一级毛片孕妇| 亚洲五月色婷婷综合| 欧美黄色片欧美黄色片| 久久香蕉激情| 老司机深夜福利视频在线观看| 99re在线观看精品视频| 中亚洲国语对白在线视频| 久久人妻av系列| 亚洲精品中文字幕在线视频| 肉色欧美久久久久久久蜜桃| www.精华液| 黑人巨大精品欧美一区二区mp4| 18禁国产床啪视频网站| 久久久精品国产亚洲av高清涩受| 国产精品国产高清国产av | 十八禁人妻一区二区| 黄色a级毛片大全视频| 每晚都被弄得嗷嗷叫到高潮| 亚洲av第一区精品v没综合| 午夜久久久在线观看| 黑人巨大精品欧美一区二区mp4| 精品少妇黑人巨大在线播放| 欧美人与性动交α欧美精品济南到| 国精品久久久久久国模美| av天堂在线播放| 狠狠狠狠99中文字幕| 法律面前人人平等表现在哪些方面| 亚洲三区欧美一区| 丝袜美腿诱惑在线| 搡老乐熟女国产| 久久久久久人人人人人| 国产成人精品久久二区二区91| 正在播放国产对白刺激| 日韩欧美国产一区二区入口| 一边摸一边抽搐一进一小说 | 午夜精品国产一区二区电影| 欧美激情高清一区二区三区| 久久久久精品国产欧美久久久| 动漫黄色视频在线观看| 黄频高清免费视频| 丰满人妻熟妇乱又伦精品不卡| 婷婷成人精品国产| 天堂中文最新版在线下载| 午夜久久久在线观看| 国产无遮挡羞羞视频在线观看| 午夜福利免费观看在线| svipshipincom国产片| 国产亚洲一区二区精品| 欧美日韩亚洲综合一区二区三区_| 一级片'在线观看视频| 女同久久另类99精品国产91| 国产精品九九99| 国产精品亚洲av一区麻豆| 97人妻天天添夜夜摸| 国产精品二区激情视频| 少妇的丰满在线观看| 国产精品1区2区在线观看. | 亚洲av第一区精品v没综合| 伦理电影免费视频| 成人国产一区最新在线观看| 一级片免费观看大全| 国产精品一区二区免费欧美| 啦啦啦免费观看视频1| 汤姆久久久久久久影院中文字幕| 欧美日韩国产mv在线观看视频| 在线观看免费视频网站a站| 国产精品偷伦视频观看了| 午夜福利视频精品| 91麻豆精品激情在线观看国产 | 欧美亚洲 丝袜 人妻 在线| 国产av国产精品国产| 精品亚洲成国产av| 国产欧美日韩一区二区精品| 亚洲色图av天堂| 中文字幕人妻丝袜一区二区| 最新在线观看一区二区三区| 老司机靠b影院| 国产精品av久久久久免费| 国产亚洲午夜精品一区二区久久| 亚洲专区中文字幕在线| 一边摸一边抽搐一进一小说 | 老熟女久久久| 十八禁人妻一区二区| 亚洲国产欧美网| 少妇被粗大的猛进出69影院| 国产成人免费观看mmmm| 亚洲精品中文字幕在线视频| 母亲3免费完整高清在线观看| 亚洲 欧美一区二区三区| 亚洲国产毛片av蜜桃av| 视频在线观看一区二区三区| 精品久久久精品久久久| 国产一区二区三区综合在线观看| 国产成人啪精品午夜网站| 亚洲国产成人一精品久久久| 中亚洲国语对白在线视频| 国产免费视频播放在线视频| 久久中文看片网| 国产97色在线日韩免费| 亚洲国产成人一精品久久久| 国产成人影院久久av| 欧美日韩国产mv在线观看视频| 久久毛片免费看一区二区三区| 一区二区av电影网| 精品一区二区三区视频在线观看免费 | 国产在视频线精品| 久久久久精品人妻al黑| 国产精品欧美亚洲77777| 飞空精品影院首页| 高清毛片免费观看视频网站 | 免费不卡黄色视频| 建设人人有责人人尽责人人享有的| 精品久久久久久久毛片微露脸| 法律面前人人平等表现在哪些方面| 老熟妇仑乱视频hdxx| 亚洲国产精品一区二区三区在线| 大片免费播放器 马上看| 久久毛片免费看一区二区三区| 精品久久久久久电影网| 国产精品久久久久久精品古装| 久久精品国产亚洲av高清一级| 精品国内亚洲2022精品成人 | 精品少妇黑人巨大在线播放| 亚洲精品国产一区二区精华液| 大型黄色视频在线免费观看| 久久午夜亚洲精品久久| 国产精品99久久99久久久不卡| 成人亚洲精品一区在线观看| 国产精品一区二区在线不卡| 成年动漫av网址| 欧美日韩福利视频一区二区| 手机成人av网站| 五月开心婷婷网| 免费av中文字幕在线| 国产深夜福利视频在线观看| 男女之事视频高清在线观看| 夫妻午夜视频| 操美女的视频在线观看| 交换朋友夫妻互换小说| 黄色a级毛片大全视频| 欧美成人午夜精品| avwww免费| 久久久久久久精品吃奶| 99精品久久久久人妻精品| 亚洲成a人片在线一区二区| 精品高清国产在线一区| 国产亚洲精品第一综合不卡| 亚洲九九香蕉| 首页视频小说图片口味搜索| 夜夜骑夜夜射夜夜干| 一个人免费看片子| 黄频高清免费视频| 国产亚洲欧美精品永久| 不卡av一区二区三区| 日韩精品免费视频一区二区三区| 久久久久久久久久久久大奶| 久久久精品94久久精品| 成人特级黄色片久久久久久久 | 亚洲人成电影观看| 成年版毛片免费区| 久久人妻熟女aⅴ| 国产成人免费无遮挡视频| 久久久欧美国产精品| 一本色道久久久久久精品综合| 老汉色∧v一级毛片| 中亚洲国语对白在线视频| 成人永久免费在线观看视频 | 高清欧美精品videossex| 精品人妻熟女毛片av久久网站| 国产精品欧美亚洲77777| 一个人免费看片子| 国产区一区二久久| 亚洲伊人色综图| 波多野结衣一区麻豆| 久久国产精品影院| 亚洲av欧美aⅴ国产| av电影中文网址| 19禁男女啪啪无遮挡网站| av天堂久久9| 天天影视国产精品| 亚洲免费av在线视频| 少妇粗大呻吟视频| 国产av又大| 精品福利观看| 免费观看人在逋| 中文字幕av电影在线播放| kizo精华| 中文字幕最新亚洲高清| 搡老岳熟女国产| 菩萨蛮人人尽说江南好唐韦庄| 久久久久久免费高清国产稀缺| 国产精品 国内视频| 国产在视频线精品| 香蕉丝袜av| 丝袜美足系列| 露出奶头的视频| av国产精品久久久久影院| a级片在线免费高清观看视频| av网站在线播放免费| 在线观看人妻少妇| 久久久久久亚洲精品国产蜜桃av| 女人高潮潮喷娇喘18禁视频| 国产精品秋霞免费鲁丝片| 亚洲精品国产区一区二| 亚洲熟女精品中文字幕| 飞空精品影院首页| 黄片大片在线免费观看| 国产亚洲av高清不卡| 国产成人精品久久二区二区91| 搡老熟女国产l中国老女人| 美女高潮到喷水免费观看| 久久人人爽av亚洲精品天堂| 亚洲男人天堂网一区| 丰满人妻熟妇乱又伦精品不卡| 精品国产一区二区三区四区第35| 日韩大片免费观看网站| tube8黄色片| 一区二区av电影网| 老熟妇仑乱视频hdxx| 如日韩欧美国产精品一区二区三区| 又紧又爽又黄一区二区| 最新的欧美精品一区二区| 老司机在亚洲福利影院| 久久亚洲真实| 下体分泌物呈黄色| 啪啪无遮挡十八禁网站| 9热在线视频观看99| 黄频高清免费视频| 在线十欧美十亚洲十日本专区| 午夜福利在线免费观看网站| 大片免费播放器 马上看| 国产精品九九99| 精品少妇久久久久久888优播| 午夜福利,免费看| av天堂久久9| 他把我摸到了高潮在线观看 | 国产三级黄色录像| 一区二区三区国产精品乱码| 免费高清在线观看日韩| 美国免费a级毛片| 日韩视频一区二区在线观看| 99久久99久久久精品蜜桃| 欧美日韩中文字幕国产精品一区二区三区 | 亚洲专区国产一区二区| 国产精品 国内视频| 欧美乱码精品一区二区三区| 人妻一区二区av| 亚洲成a人片在线一区二区| 欧美激情久久久久久爽电影 | 高清黄色对白视频在线免费看| 91麻豆av在线| 黄色成人免费大全| 国产一区二区激情短视频| 老司机午夜福利在线观看视频 | av有码第一页| 91麻豆av在线| 老汉色∧v一级毛片| 51午夜福利影视在线观看| 成人18禁高潮啪啪吃奶动态图| 精品人妻1区二区| 亚洲人成电影观看| netflix在线观看网站| 久久久欧美国产精品| 日韩一卡2卡3卡4卡2021年| 麻豆乱淫一区二区| 天堂中文最新版在线下载| 午夜91福利影院| 天天添夜夜摸| 夜夜骑夜夜射夜夜干| 久久人妻熟女aⅴ| 免费日韩欧美在线观看| cao死你这个sao货| 又紧又爽又黄一区二区| 国产色视频综合| 欧美日韩黄片免| 日本av免费视频播放| 亚洲精品在线美女| 国产欧美日韩综合在线一区二区| av天堂在线播放| 女人精品久久久久毛片| 国产精品麻豆人妻色哟哟久久| 欧美黄色淫秽网站| 精品视频人人做人人爽| 正在播放国产对白刺激| 一二三四社区在线视频社区8| 一级毛片女人18水好多| 性高湖久久久久久久久免费观看| 久久精品国产综合久久久| 欧美日韩亚洲综合一区二区三区_| 午夜福利视频精品| 亚洲久久久国产精品| 午夜成年电影在线免费观看| 一边摸一边做爽爽视频免费| 黑丝袜美女国产一区| 欧美日韩亚洲国产一区二区在线观看 | 日韩人妻精品一区2区三区| 黄色毛片三级朝国网站| av在线播放免费不卡| 别揉我奶头~嗯~啊~动态视频| 757午夜福利合集在线观看| 五月开心婷婷网| 黑人猛操日本美女一级片| 嫩草影视91久久| 国产精品久久久久久人妻精品电影 | 亚洲 国产 在线| 最新的欧美精品一区二区| av不卡在线播放| 欧美激情极品国产一区二区三区| 中文字幕最新亚洲高清| 久久国产精品男人的天堂亚洲| 国产欧美日韩一区二区精品| 亚洲欧美精品综合一区二区三区| 肉色欧美久久久久久久蜜桃| 午夜激情av网站| 丝袜人妻中文字幕| 在线亚洲精品国产二区图片欧美| 女人精品久久久久毛片| 亚洲精品久久成人aⅴ小说| 丰满人妻熟妇乱又伦精品不卡| 日韩欧美三级三区| 美女福利国产在线| 亚洲欧美一区二区三区黑人| 一级黄色大片毛片| 亚洲一卡2卡3卡4卡5卡精品中文| 十八禁高潮呻吟视频| 777米奇影视久久| 考比视频在线观看| 久久99热这里只频精品6学生| 欧美日韩中文字幕国产精品一区二区三区 | 日本撒尿小便嘘嘘汇集6| 女人高潮潮喷娇喘18禁视频| 熟女少妇亚洲综合色aaa.| 国产精品麻豆人妻色哟哟久久| aaaaa片日本免费| 欧美日韩黄片免| 狠狠狠狠99中文字幕| 久久国产亚洲av麻豆专区| 精品亚洲成a人片在线观看| 久久午夜亚洲精品久久| 水蜜桃什么品种好| 露出奶头的视频| 一级毛片女人18水好多| 一进一出好大好爽视频| 色综合欧美亚洲国产小说| 十八禁高潮呻吟视频| 亚洲一卡2卡3卡4卡5卡精品中文| 亚洲熟女毛片儿| 夜夜爽天天搞| 我要看黄色一级片免费的| 一个人免费在线观看的高清视频| 一级毛片女人18水好多| 国产伦理片在线播放av一区| 国产精品欧美亚洲77777| 日韩 欧美 亚洲 中文字幕| 久久久久久亚洲精品国产蜜桃av| 日韩制服丝袜自拍偷拍| 久久香蕉激情| 超碰97精品在线观看| 日韩大码丰满熟妇| 777久久人妻少妇嫩草av网站| 欧美精品一区二区大全| 超碰97精品在线观看| 亚洲国产av影院在线观看| 99国产极品粉嫩在线观看| 黄色片一级片一级黄色片| 在线观看www视频免费| 久久亚洲真实| 欧美国产精品va在线观看不卡| 成人免费观看视频高清| 国产高清国产精品国产三级| 中文字幕制服av| 国产黄频视频在线观看| 九色亚洲精品在线播放| 人妻一区二区av| 国产aⅴ精品一区二区三区波| h视频一区二区三区| 狂野欧美激情性xxxx| 天天躁狠狠躁夜夜躁狠狠躁| 日本撒尿小便嘘嘘汇集6| 韩国精品一区二区三区| 99香蕉大伊视频| 每晚都被弄得嗷嗷叫到高潮| 成年人黄色毛片网站| 国产视频一区二区在线看| 18在线观看网站| 黑人巨大精品欧美一区二区mp4| 一级片免费观看大全| 欧美日韩精品网址| 欧美在线一区亚洲| 一边摸一边抽搐一进一出视频| 狠狠婷婷综合久久久久久88av| 91九色精品人成在线观看| 午夜福利免费观看在线| 国产亚洲午夜精品一区二区久久| 大型黄色视频在线免费观看| 18禁黄网站禁片午夜丰满| 又紧又爽又黄一区二区| 午夜福利在线免费观看网站| 亚洲情色 制服丝袜| 免费少妇av软件| 日韩中文字幕视频在线看片| 无遮挡黄片免费观看| 亚洲人成伊人成综合网2020| 99久久人妻综合| 国产成人一区二区三区免费视频网站| 18禁观看日本| 操出白浆在线播放| 自线自在国产av| 精品国产乱码久久久久久小说| 在线亚洲精品国产二区图片欧美| 精品熟女少妇八av免费久了| 成人av一区二区三区在线看| 美女主播在线视频| 纯流量卡能插随身wifi吗| 日本一区二区免费在线视频| 自线自在国产av| 老司机午夜十八禁免费视频| 97在线人人人人妻| 久久久久久亚洲精品国产蜜桃av| 午夜福利视频在线观看免费| 在线av久久热| 国产xxxxx性猛交| 亚洲精品国产一区二区精华液| 欧美黑人精品巨大| 搡老乐熟女国产| 深夜精品福利| 黄片播放在线免费| 一进一出好大好爽视频| 午夜久久久在线观看| 天天影视国产精品| 国产成人免费观看mmmm| 午夜免费成人在线视频| 别揉我奶头~嗯~啊~动态视频| 老司机靠b影院| 美女主播在线视频| 久久久久久久国产电影| 国产成人一区二区三区免费视频网站| 老熟女久久久| 亚洲精品乱久久久久久| 在线观看一区二区三区激情| 国产区一区二久久| 啦啦啦免费观看视频1| www.精华液| a级片在线免费高清观看视频| 50天的宝宝边吃奶边哭怎么回事| www.999成人在线观看| 啦啦啦在线免费观看视频4| 亚洲av电影在线进入| 又黄又粗又硬又大视频| 男女免费视频国产| 亚洲精品一卡2卡三卡4卡5卡| 桃红色精品国产亚洲av| 天堂俺去俺来也www色官网| 久久香蕉激情| 亚洲少妇的诱惑av| 人妻久久中文字幕网| 久热这里只有精品99| 中文字幕最新亚洲高清| 18禁国产床啪视频网站| 国产一区二区 视频在线| 十八禁网站网址无遮挡| 亚洲色图综合在线观看| 捣出白浆h1v1| 国精品久久久久久国模美| 人人妻人人澡人人爽人人夜夜| 一区二区三区乱码不卡18| 久久99一区二区三区| 变态另类成人亚洲欧美熟女 | 欧美中文综合在线视频| 午夜福利,免费看| 亚洲色图综合在线观看| 日本黄色日本黄色录像| 亚洲色图综合在线观看| 国产精品九九99| 看免费av毛片| 国产免费现黄频在线看| 中文字幕高清在线视频| 久久国产精品大桥未久av| 一本综合久久免费| av超薄肉色丝袜交足视频| 热re99久久精品国产66热6| 变态另类成人亚洲欧美熟女 | 欧美久久黑人一区二区| 女人久久www免费人成看片| 我要看黄色一级片免费的| 久久精品91无色码中文字幕| 黄网站色视频无遮挡免费观看| 女警被强在线播放| 少妇精品久久久久久久| 在线播放国产精品三级| 欧美日本中文国产一区发布| 9191精品国产免费久久| 国产成人精品无人区| 亚洲三区欧美一区| bbb黄色大片| tube8黄色片| 黄色丝袜av网址大全| 美女高潮喷水抽搐中文字幕| 国产精品电影一区二区三区 | 精品久久久久久久毛片微露脸| 岛国在线观看网站| 在线看a的网站| 曰老女人黄片| 99riav亚洲国产免费| 国产无遮挡羞羞视频在线观看| 在线观看免费午夜福利视频| 久久久久久人人人人人| 国产成人一区二区三区免费视频网站| 天天影视国产精品| 9色porny在线观看| 精品久久久久久久毛片微露脸| 一二三四在线观看免费中文在|