Direct shear behavior of gravel-rubber mixtures: Discrete element modeling and microscopic investigations

In this paper, a newly developed 3-dimentional discrete element model (DEM) for gravel-rubber mixtures (GRMs), namely DEM4GRM, that is capable of accurately describing the macro-scale shear response (from small to large deformation) of GRMs in a direct shear box apparatus is presented. Rigid gravel grains are modelled as simple multi-shape clumps, while soft rubber particles are modeled by using deformable 35-ball body-centered-cubic clusters. Mixtures are prepared with different volumetric rubber content (VRC) at 0, 10, 25, 40 and 100%, statically compressed under 30, 60 and 100 kPa vertical stress and then sheared, by closely simulating a reference laboratory test procedure. The variation of micro-scale factors such as fabric, normal and tangential force anisotropy is carefully examined throughout the shearing process and described by means of novel micro-mechanical relationships valid for GRMs. Moreover, strong-force chains are scrutinized to identify the transition from rigid to soft granular skeleton and gain insights on the load transfer and deformation mechanisms of GRMs. It is shown that the development of the fabric and force anisotropy during shearing is closely related to the macro-scale shear strength of GRMs, and strongly depends on the VRC. Besides, strong-force chains appear to be primarily formed by gravel-gravel contacts (resulting in a rigid-like mechanical behavior) up to VRC = 30%, and by rubber-rubber contacts (causing a soft-like mechanical response) beyond VRC = 60%. Alternatively, at 30% < VRC < 60%, gravel-rubber contacts are predominant in the strong-force network and an intermediate mechanical behavior is observed. This is consistent with the behavioral trends observed in the macro- and micro-mechanical responses.     

天然橡胶/顺丁橡胶/丁苯橡胶自润滑喷蜡橡胶材料的性能

在天然橡胶(NR)/顺丁橡胶(BR)/丁苯橡胶(SBR)为基体的自润滑喷蜡橡胶材料中加入芥酸酰胺,考察芥酸酰胺作为润滑剂时对NR/BR/SBR自润滑喷蜡橡胶材料的硫化特性、力学性能、门尼黏度、摩擦系数及耐老化性能的影响。结果表明,与未加芥酸酰胺的胶料相比,当芥酸酰胺用量为10份时,胶料转矩减小,焦烧时间和正硫化时间缩短,扯断伸长率从388%增加至523%,拉伸强度降低了21.36%,邵尔A硬度、压缩永久变形分别下降5.56%和8.74%,动、静摩擦系数分别减小23.46%和24.82%,门尼黏度降低20.89%,耐热氧老化性能下降。硫化胶拉伸100%停放5 min后,表面出现明显的白色润滑膜,胶料流动性变好,各组分分散得更均匀,断面更光滑。     

New ways to improve the damping properties in high‐performance thermoplastic vulcanizates

The incorporation of viscoelastic materials represents an effective strategy to reduce the vibratory level of structural components. Thermoplastic vulcanizates (TPVs) are a special type of viscoelastic material that combines the elastomeric properties of rubbers with the easy processing of thermoplastics. In the present work, we propose innovative ways to improve the damping properties of high‐performance TPVs by using rubbers with carboxylic functionalities. For that, TPVs from physical blends of carboxylated hydrogenated acrylonitrile butadiene rubber (XHNBR) and polyamide 6 (PA6) were prepared. The chain dynamics of different mixed crosslink systems containing peroxide, metal oxides and hindered phenolic antioxidants were investigated in order to find the most suitable strategy to design a high‐performance TPV system with upgraded damping properties. The results indicate that the damping performance of the TPV system can be tailored by controlling the type and magnitude of the bonding interactions between the mixed crosslink system and the XHNBR rubber phase. Therefore, this study demonstrates the potential of TPV systems containing carboxylic rubbers as high‐performance damping materials. © 2020 Society of Chemical Industry     

混炼方式对螺旋纳米碳纤维增强天然橡胶复合材料力学性能的影响

采用干法和湿法两种混炼工艺制备了螺旋纳米碳纤维(HCNFs)/炭黑(CB)/天然橡胶(NR)复合材料,通过扫描电镜、拉伸试验机和应变扫描仪分别对所制备复合材料的界面形貌、力学性能和Payne效应进行了测试分析,考察了混炼方式对复合材料宏观力学性能及Payne效应的影响。结果表明,与纯CB填料相比,在干湿两种混炼方式下,添加适量的HCNFs(1～6份)能提高HCNFs/CB/NR复合材料的300%定伸应力、扯断伸长率、拉伸强度和硬度。与干法混炼相比,湿法混炼能明显增强HCNFs/CB/NR复合材料的Payne效应,并提升在HCNFs高添加量(2～6份)条件下的拉伸强度和扯断伸长率,这主要源于湿法混炼能够有效改善HCNFs在橡胶基质中的分散性。     

微波胶粉比表面积对橡胶沥青流变性能的影响

通过考察不同微波辐射时间对胶粉活化处理并制备胶粉改性沥青的效果,研究微波辐射对胶粉表观特性与其改性沥青流变性能的影响。采用气体吸附仪、动态剪切流变仪分别测定胶粉活化前后的比表面积及改性沥青的流变性能,并将胶粉的比表面积与沥青流变性能进行关联。在此基础上,结合扫描电镜,从微观角度揭示活化胶粉对沥青流变性能的影响机理。结果表明:在测定时间内,微波辐射使得胶粉表面变得蓬松,孔隙增多,比表面积增长显著;一定时间范围内(60～120s)的微波辐射对胶粉改性沥青的高温抗车辙能力有显著影响;胶粉微波活化后其比表面积与改性沥青流变性能之间有很好的相关性,胶粉比表面积越大,其复数剪切模量越大,相位角越小,沥青的高温抗变形能力越好。     

天然橡胶期货市场回顾及后市展望

2019年天然橡胶期货市场起起落落,沪胶价格继续低位震荡。2020年天然橡胶供大于求的局面仍不会发生根本性改变,由极端天气引发的天然橡胶市场行情变动可能会减小,汽车行业可能会在政策支持下再次振兴,尤其重型卡车市场会成为亮点,轮胎企业继续寻求扩大出口。2020年上半年,天然橡胶期货市场可能还会受到2019年异常天气和病害等的余波作用,胶价会达到一个相对的高点,价格底部抬升,但很难出现持续性上涨的市场行情。2020年下半年,随着天然橡胶产量的季节性增长,胶价可能会再次回落。     

244.5 mm套管三胶筒隔离封隔器研制

为了解决老式隔离封隔器容易出现刮损失效和密封性能差的问题,采用具有不同硬度组合的三胶筒式密封结构,研制了一种适用于海上油田防砂作业的新型隔离封隔器。该隔离封隔器由密封机构、锁紧机构、坐封机构和心轴组成。通过优化胶筒的参数,以及在胶筒两端安装铜环,使胶筒的压缩力更加均匀。室内试验时,正反向验封压力均达到41.4 MPa,坐封后自锁状态稳定。现场应用表明,该封隔器设计合理、性能可靠。     

高温环境下编织-嵌槽型金属橡胶的疲劳特性分析

采用拉-压式组合试验工装，以位移控制的加载方式对编织-嵌槽型金属橡胶进行了疲劳试验，研究了常温（25 ℃）及高温（300 ℃）环境下编织-嵌槽型金属橡胶在不同加载振幅下的疲劳特性，并通过平均刚度、等效黏性阻尼系数及其损伤因子对构件的损伤演化过程进行了表征。结果表明：编织-嵌槽型金属橡胶构件的疲劳损伤形式表现为磨损、断丝以及塑性变形；构件在各种试验条件下的疲劳过程均可分为刚度强化期和刚度衰减期，而构件力学性能的衰减主要发生在刚度衰减期；温度的升高或振幅的增大均会显著增大构件的积累损伤，进而缩短其使用寿命。     

基于ABAQUS的变截面橡胶密封条热应力与密封性分析

研究用于发动机油气分离器的乙烯丙烯酸酯橡胶密封胶条在不同温度下的强度和密封性能。借助于大型有限元分析软件ABAQUS建立橡胶密封胶条与配合壳体的有限元模型,采用Mooney-Rivlin模型,对不同温度下的密封胶条进行热应力计算分析,得到橡胶密封胶条在不同温度下的Von Mises应力、压缩率、接触应力和接触宽度。结果表明:随着温度的升高,密封胶条的Von Mises应力和密封胶条与壳体连续接触面上的接触应力逐渐增加,接触宽度基本不变,密封条的压缩率逐渐减小;密封胶条的Von Mises应力远小于橡胶材料的拉伸强度,满足强度要求;密封胶条连续接触面上的接触应力始终大于油气分离器的工作压力且接触宽度符合要求,橡胶密封胶条满足密封条件。