Thermal vibration of functionally graded porous nanocomposite beams reinforced by graphene platelets

The thermal vibration of functionally graded(FG)porous nanocomposite beams reinforced by graphene platelets(GPLs)is studied.The beams are exposed to the thermal gradient with a multilayer structure.The temperature varies linearly across the thickness direction.Three different types of dispersion patterns of GPLs as well as porosity distributions are presented.The material properties vary along the thickness direction.By using the mechanical parameters of closed-cell cellular solid,the variation of Poisson’s ratio and the relation between the porosity coefficient and the mass density under the Gaussian random field(GRF)model are obtained.By using the Halpin-Tsai micromechanics model,the elastic modulus of the nanocomposite is achieved.The equations of motion based on the Timoshenko beam theory are obtained by using Hamilton’s principle.These equations are discretized and solved by using the generalized differential quadrature method(GDQM)to obtain the fundamental frequencies.The effects of the weight fraction,the dispersion model,the geometry,and the size of GPLs,as well as the porosity distribution,the porosity coefficient,the boundary condition,the metal matrix,the slenderness ratio,and the thermal gradient are presented.

Postbuckling analysis of functionally graded graphene platelet-reinforced polymer composite cylindrical shells using an analytical solution approach

An analytical approach is proposed to study the postbuckling of circular cylindrical shells subject to axial compression and lateral pressure made of functionally graded graphene platelet-reinforced polymer composite (FG-GPL-RPC). The governing equations are obtained in the context of the classical Donnell shell theory by the von K′arm′an nonlinear relations. Then, based on the Ritz energy method, an analytical solution approach is used to trace the nonlinear postbuckling path of the shell. The effects of several parameters such as the weight fraction of the graphene platelet (GPL), the geometrical properties, and distribution patterns of the GPL on the postbuckling characteristics of the FG-GPL-RPC shell are analyzed.

A comparative study of polymer nanocomposites containing multi-walled carbon nanotubes and graphene nanoplatelets

Featuring exceptional mechanical and functional performance, MWCNTs and graphene(nano)platelets(GNPs or Gn Ps;each platelet below 10 nm in thickness) have been increasingly used for the development of polymer nanocomposites. Since MWCNTs are now cost-effective at US$30 per kg for industrial applications, this work starts by briefly reviewing the disentanglement and surface modification of MWCNTs as well as the properties of the resulting polymer nanocomposites. GNPs can be made through the thermal treatment of graphite intercalation compounds followed by ultrasonication;GNPs would have lower cost yet higher electrical conductivity over 1,400 S cmthan MWCNTs. Through proper surface modification and compounding techniques, both types of fillers can reinforce or toughen polymers and simultaneously add anti-static performance. A high ratio of MWCNTs to GNPs would increase the synergy for polymers. Green, solvent-free systhesis methods are desired for polymer nanocomposites. Perspectives on the limitations, current challenges and future prospects are provided.

Preparation of Functionalized Graphene Nano-platelets and Use for Adsorption of Pb2+ from Solution

Functionalized graphene nano-platelets(FGN) were obtained via treating graphene nanoplatelets(GN) with HNO3, and served as adsorbent for the removal of Pb2+from solutions. We investigated the FGN adsorption capacity for Pb2+at different initial concentrations, varying pH, contact time and temperature. The characterization results of scanning electron microscopy(SEM), thermal analysis(TG/DTG), Fourier transform infrared spectroscopy(FT-IR) and Brunauer-Emmett-Teller(BET) method indicated that FGN layers were thin and possess large specific area with oxygen-containing functional groups grafted onto their surface. Meanwhile, the determined equilibrium adsorption capacity of FGN for Pb2+was 57.765 mg/g and adsorption isotherms well confirmed to Langmuir isotherms models. The results reveals that the FGN has better effect of water treatment.

Nonlinear free vibration of graphene platelets reinforced composite corrugated plates

The nonlinear vibration of graphene platelets reinforced composite corrugated(GPRCC)rectangular plates with shallow trapezoidal corrugations is investigated.Since graphene platelets are prone to agglomeration,a multi-layer distribution is adopted here to match the engineering requirements.Firstly,an equivalent composite plate model is obtained,and then nonlinear equations of motion are derived by the von Kármán nonlinear geometric relationship and Hamilton’s principle.Afterwards,the Galerkin method and harmonic balance method are used to obtain an approximate analytical solution.Results show that the unit cell half period,unit cell inclination angle,unit cell height,graphene platelet dispersion pattern and graphene platelet weight fraction and geometry play important roles in the nonlinear vibration of the GPRCC plates.

Bending and stress analysis of polymeric composite plates reinforced with functionally graded graphene platelets based on sinusoidal shear-deformation plate theory

The bending and stress analysis of a functionally graded polymer composite plate reinforced with graphene platelets are studied in this paper.The governing equations are derived by using principle of virtual work for a plate which is rested on Pasternak’s foundation.Sinusoidal shear deformation theory is used to describe displacement field.Four different distribution patterns are employed in our analysis.The analytical solution is presented for a functionally graded plate to investigate the influence of important parameters.The numerical results are presented to show the deflection and stress results of the problem for four employed patterns in terms of geometric parameters such as number of layers,weight fraction and two parameters of Pasternak’s foundation.

双功能梯度石墨烯片增强金属-陶瓷基圆柱壳的行波振动分析

采用Halpin-Tsai微观力学模型和传递矩阵方法,开展了旋转态双功能梯度石墨烯片增强复合材料圆柱壳体的行波振动特性研究。描述了金属-陶瓷功能梯度基体和5种石墨烯片分布模式的材料属性,基于Love壳理论和传递矩阵方法,考虑转速影响推导了任一截面状态向量的常微分方程和整体传递矩阵关系。以固支-自由(悬臂)边界条件为主,对动力学微分方程进行求解计算,验证了分析方法的合理性。结果表明:低阶模态以轴向半波数为1和周向模态的振动为主,转速引起的科氏力使行波曲线出现分离现象;行波频率随着石墨烯质量分数的增加而增大,分布模式对振型顺序的影响较小,基体体积分数指数对振动特性的影响较大,而石墨烯片层数对振动特性的影响很小,不同倍频激励对共振特性的影响不同。

功能梯度三相复合材料圆柱壳固有振动特性分析

本文以一种石墨烯与碳纤维协同增强三相复合材料圆柱壳为研究对象,研究了在任意边界条件下该新型功能梯度三相复合材料圆柱壳的自由振动特性.首先,基于一阶剪切变形理论、Von-Karman几何非线性关系和Hamilton原理,推导了三相复合材料圆柱壳结构运动控制方程.然后,应用Galerkin法离散求解三相复合材料圆柱壳的固有频率和模态振型.最后通过将本文方法与Abaqus仿真结果进行对比,验证了本文方法的准确性.此外,本文进一步分析了石墨烯质量分数、功能梯度形式和边界条件等不同因素对新型三相复合材料圆柱壳固有振动特性的影响.

功能梯度石墨烯增强复合材料梁的屈曲及后屈曲精确解

采用精确解析求解方法研究石墨烯片(GPL)增强功能梯度梁的非线性屈曲及后屈曲力学行为。研究中假定GPL均匀地分布在梁的每一层,但其重量分数沿厚度方向呈梯度或均匀变化,导致结构的物性参数沿厚度方向连续梯度变化,并根据Halpin-Tsai力学模型和混合率法则得到材料的等效物性参数。同时基于Euler-Bernoulli梁理论和Von-Kármán非线性应变位移关系由能量变分法获得石墨烯片增强功能梯度梁的非线性控制方程,对此方程进行精确解析求解获得临界载荷、屈曲模态以及后屈曲变形的解析表达式。并进行参数研究分析了GPL的重量分数、几何形状及尺寸和分布方式对该复合材料梁非线性屈曲和后屈曲的影响。

活化石墨烯微片对聚β-羟基丁酸酯结晶性能和热性能的影响

采用溶液浇铸法制备了聚β-羟基丁酸酯(PHB)/活化石墨烯微片(GONPs)复合材料,并研究了GONPs对PHB晶体结构、非等温结晶性能、热分解温度和热加工稳定性的影响。结果表明:GONPs加快了PHB的非等温结晶,但不会改变PHB的晶体结构;PHB的结晶度和热分解温度均随GONPs用量的增加而提高;GONPs对PHB热加工稳定性的影响不显著,但PHB自热解发生后,PHB/GONPs复合材料的热降解程度较纯PHB变缓。

功能梯度石墨烯增强复合材料旋转梁强迫振动

研究了功能梯度石墨烯增强复合材料(Functionally Graded-Graphene-Platelets-Reinforced Composite,FG-GPLRC)旋转梁的非线性强迫振动。首先采用修正Halpin-Tsai微观力学模型和混合理论得到FG-GPLRC的有效弹性模量;考虑旋转效应并引入von Kar man几何非线性假设,基于Hamilton原理建立了FG-GPLRC旋转梁的运动控制方程。然后使用Galerkin法和多尺度法求得主共振响应的渐近解析解。最后通过数值分析讨论了石墨烯片(GPLs)含量、分布方式及几何性质对旋转梁强迫振动行为的影响。结果表明:填充GPLs能够同时提高梁的线性刚度和非线性刚度,但两者对共振响应的影响是相反的,在耦合作用下梁的共振响应随着GPLs质量分数的增大而减小;旋转运动造成的离心刚化效应增加了线性刚度但不能改变非线性刚度,从而使共振响应增大。

弹性介质中多孔石墨烯增强复合材料截锥壳的振动

为研究弹性介质中含内部孔隙的石墨烯增强功能截锥壳的振动特性,根据孔隙的分布假定孔隙的体积组分,用混合率和Halpin-Tsai微观力学模型计算石墨烯增强材料的物性参数。基于Donnel经典薄壳理论和Hamilton变分原理建立了振动的控制方程并求解,讨论了孔隙、石墨烯和弹性介质对振动特性的影响。结果表明:与孔隙分布类型相比,孔隙系数对振动频率和动力响应的影响更大。在孔隙分布同为中间多、内侧和外侧少的情况下,石墨烯质量分数从0%提高到0.6%时,石墨烯为内外侧多、中间少分布的最大动挠度减小45.66%,而外侧少、中间多分布的最大动挠度减小36.83%。可见,为提高圆锥壳的有效刚度,石墨烯纳米片应该更多地布置在圆锥壳的内侧和外侧部位。

PBT用多层石墨烯/碳纳米管复合导电剂的制备

利用膨化石墨原位气相沉积制备多层石墨烯／碳纳米管复合粉体。以膨胀石墨为基体，以硝酸铁、碳酸铵等物质对其进行修饰．结合化学气相沉积工艺，原位制备出多层石墨烯／碳纳米管复合粉体材料；探讨不同的修饰液相对复合粉体比例，微观形貌及分散性的影响。利用扫描电镜对复合粉体进行表征。结果表明：多层石墨＇N／碳纳米管复合粉体材料可批量制备；其中多层石墨烯为透明薄片，其厚度为10～30nm；通过控制工艺参数，可以实现多层石墨烯的质量比为15％～50％；复合粉体中碳纳米管的分散性明显优于一般化学气相沉积方法制备的碳纳米管：加入质量分数5％复合粉体的聚对苯二甲酸丁二醇酯（PBT）的表面电阻显著降低。

PBT/石墨烯/碳纳米管复合材料的制备及其导电性能研究

以膨胀石墨为基体,用硝酸铁、碳酸铵等物质对其进行修饰,结合化学气相沉积工艺,原位制备出石墨烯/碳纳米管复合粉体材料;利用扫描电镜对复合粉体进行了表征。采用熔融混炼的方法制备PBT/石墨烯/碳纳米管复合材料并测试了其表面电阻。研究结果表明:该方法可以制备出性能优异的石墨烯/碳纳米管复合粉体材料,将该复合粉体加入到PBT中所制备的复合材料具有优良的电性能;当复合粉体加入量为5%时,PBT/石墨烯/碳纳米管复合材料的表面电阻可达到106Ω。

石墨烯/铝复合材料热挤压过程组织演变

采用冷等静压后热挤压变形工艺制备高含量石墨烯增强6061Al复合材料,研究热挤压变形过程中复合材料显微组织的演化特征。结果表明：冷等静压后坯锭的致密度达到92.5%,在挤压温度480℃、挤压比25∶1的条件下,复合材料棒材的致密度达到99.7%。随着塑性变形量的增大,石墨烯团聚体逐渐被打散,并沿挤压方向呈不连续状分布;由于热挤压保温温度远低于热压烧结温度,热挤压态复合材料中石墨烯与铝合金未发生界面反应;冷等静压后进行高温塑性变形可获得高致密度的复合材料,同时避免了石墨烯与铝合金之间生成Al_4C_3的界面反应。

用不同催化剂制备石墨烯碳纳米管复合粉体

研究利用膨化石墨制备石墨烯/碳纳米管复合粉体技术。以膨胀石墨为基体,以硝酸铁、硝酸钴等物质为催化剂,结合化学气相沉积工艺,原位制备出石墨烯/碳纳米管复合粉体材料;研究了不同催化剂对复合粉体微观形貌的影响,利用扫描电镜对复合粉体进行了表征。研究结果表明:以正己烷为碳源,用2号催化剂,在750℃时所制备的复合粉体中,碳纳米管和石墨烯的质量最好。

石墨烯纳米片对碳纤维增强金属层板层间力学性能的影响

提出一种新的方法,用来改善碳纤维增强金属板(CARALL)的层间黏结强度。将不同质量分数(0,0.1%,0.3%,0.5%和1.0%)的石墨烯纳米片(GnPs)利用超声分散的方法使其均匀分散于环氧树脂中,并利用湿法铺层方法完成CARALL的制作。进行Ⅰ型断裂韧性的测试,探究GnPs对CARALL层间性能的影响,并进行CARALL的拉伸与弯曲性能测试,研究GnPs对CARALL力学性能的影响。通过SEM与光学图像观察GnPs的增强机制与CARALL试件的失效模式。结果表明,当GnPs的添加量为0.5%时,CARALL具有最佳的层间黏结强度与力学性能。当添加0.5%GnPs时,Ⅰ型断裂韧性提高79%;拉伸强度、弹性模量与断裂应变率分别提高14.5%,11.0%和15.5%;弯曲强度与弯曲应变率分别提高23.9%和81.5%。这是由于添加GnPs到环氧树脂中可以分散CARALL所承受载荷,并利用自身的断裂、拔出和脱黏等机制吸收能量,进一步改善CARALL的层间力学性能。

石墨烯/碳纳米管复合粉体制备工艺的研究

研究了利用膨化石墨制备石墨烯/碳纳米管复合粉体技术。以膨胀石墨为基体,利用硝酸铁、碳酸铵等对其进行修饰,结合化学气相沉积工艺,原位制备出石墨烯/碳纳米管复合粉体材料;研究了不同的修饰液相、不同沉积工艺对复合粉体比例、微观形貌的影响。利用扫描电镜对复合粉体进行了表征。结果表明,实现了石墨烯/碳纳米管复合粉体材料的批量制备;其中石墨烯为透明薄片,其厚度最小可达到10nm;通过控制工艺参数,可以实现碳纳米管/石墨烯的质量比在0.625～8.250之间变化;并初步获得了最佳修饰液相和最佳工艺。研究结果表明该方法可以制备出性能优异的石墨烯/碳纳米管复合粉体材料。

羧基离子注入石墨烯的血液相容性研究

为解决石墨烯不亲水、不亲脂、难于在溶剂中稳定分散的缺陷,运用了离子注入的方法,分别将剂量为1×1017、5×1017和1×1018 ions/cm2的羧基离子(COOH+)注入到石墨烯表面.利用X线光电子能谱(XPS)、扫描电子显微镜(SEM)和水接触角(CA)分析证明注入可引入含氧官能团,如C—O、O—C=O等;并显著提高了材料的含氧量,从而使石墨烯表现出优异的亲水性,这可能是生物相容性改善的主要原因.血小板黏附实验、溶血实验和与红细胞相互作用实验表明:羧基离子注入后,石墨烯的溶血率降低,注入几乎没有对红细胞产生破坏,且显著抑制了血小板的黏附、聚集和活化.研究结果表明羧基离子的注入可显著提高石墨烯的血液相容性.

石墨烯片增强纳米复合材料微米圆柱壳的振动和稳定性

基于一阶剪切变形壳理论和应变梯度弹性理论(strain gradient elasticity theory,SGET),研究石墨烯片增强纳米复合材料(graphene platelets-reinforced nanocomposite,GPLRNC)微米圆柱壳的稳定性和自由振动。首先,通过Hamilton变分原理得到系统模型的控制微分方程。其次,利用Navier法获得GPLRNC微米壳的固有频率和临界屈曲载荷的解析解。结果表明:石墨烯片(graphene platelets,GPLs)的充填质量和分布模式影响微米壳的稳定性和振动特性。当壳体内部石墨烯片的质量分数给定时,微米壳在石墨烯片的O-GPLRNC分布下具有最高的固有频率和临界屈曲载荷,在X-GPLRNC分布下则反之。此外,材料长度尺度参数、石墨烯片几何尺寸和微米壳几何尺寸对GPLRNC微米圆柱壳的稳定性和自由振动具有重要影响。