The transient response of a functionally graded piezoelectric rod subjected to a moving heat source under fractional order theory of thermoelasticity

The transient thermo-piezoelectric response of a functionally graded piezoelectric rod subjected to a moving heat source is investigated in the context of fractional order theory of thermoelasticity proposed by Sherief. The material properties of the functionally graded piezoelectric rod are assumed to vary exponentially along the length, except for the thermal relaxation time and the specific heat, which are taken to be constant. To solve the governing equations of the problem, Laplace transform is applied, eliminating the time effect; the analytical solutions of the displacement, stress, temperature, and electric field in Laplace domain are obtained. Subsequently, the solutions of the considered variables in time domain are obtained by numerical Laplace inversion and illustrated graphically. In calculation, the effect of the fractional order parameter on the variations of the considered variables is presented.     

Wave propagation in functionally graded nanocomposites reinforced with carbon nanotubes based on second-order shear deformation theory

In the present article, as a first endeavor, the wave propagation in functionally graded nanocomposites reinforced with carbon nanotubes is investigated on the basis of second-order shear deformation theory. Four different types of functionally graded nanocomposites are presented. An analytical method is used to find the circular frequencies and phase velocities. To show the accuracy of the present methodology, our results for the free vibration are compared with the results of functionally graded plates available in the literature. The influences of different parameters are also investigated on the circular frequencies and phase velocities.     

Bending-stretching analysis of thick functionally graded micro-plates using higher-order shear and normal deformable plate theory

In the present article, higher-order shear and normal deformable plate theory together with modified couple stress theory are developed to study the bending analysis of thick functionally graded rectangular micro-plates. One material length scale parameter is used for capturing the size effects. Utilizing the variational approach and also a principle of virtual displacement, a new form of equilibrium equations and the corresponding boundary conditions are derived. It is assumed that material properties vary through the thickness according to the power law function. Finally, an analytical solution for the bending problem of a simply supported FG rectangular micro-plate is presented.     

Fracture investigation of U‐notch made of tungsten–copper functionally graded materials by means of strain energy density

The averaged strain energy density over a well‐defined control volume was employed to assess the fracture of U‐notched specimens made of tungsten–copper functionally graded materials under prevalent mode II loading. The boundary of control volume was evaluated by using a numerical method. Power law function was employed to describe the mechanical properties (elasticity modulus, Poisson's ratio, fracture toughness and ultimate tensile stress) through the specimen width. The effect of notch tip radius and notch depth on notch stress intensity factors and mode mixity parameter χ were assessed. In addition, a comparison based on fracture load between functionally graded and homogeneous W–Cu was made. Furthermore, in this research, it was shown that the mean value of the strain energy density over the control volume can be accurately determined using coarse meshes for functionally graded materials.     

Ti合金插层厚度对反应连接TiB_2基陶瓷/Ti-6Al-4V梯度复合材料的影响

将Ti合金插层引入(Ti+B_4C)反应原料和Ti合金底板之间,研究Ti合金插层厚度变化对超重力反应连接TiB2基陶瓷/Ti-6Al-4V梯度复合材料界面显微组织与力学性能的影响。热力学计算表明:合成反应的绝热温度远超Ti合金的熔点,可以保证不同厚度的Ti合金插层全部熔化。XRD、FESEM及EDS分析结果表明:在陶瓷和Ti合金底板之间形成梯度界面区,且随着Ti合金插层厚度的增加,梯度界面区的厚度也不断增大。自陶瓷基体至Ti合金底板,TiB_2和TiC_(1-x)的体积分数不断减少,而TiB的体积分数先增加而后减少,最终形成以TiB_2、TiC_(1-x)及TiB陶瓷相尺寸和分布为特征的梯度复合结构。而梯度连接区的硬度分布趋势更加平缓,其剪切强度不断提升。     

Performance of porous asphalt mixture with various additives

The objective of this study is to evaluate the approaches to improve the durability and strength of the porous asphalt through laboratory testing. Porous asphalt specimens were prepared using three types of binders: high-viscosity binder (HVB), PG76-22 and PG70-22. Various additives: fibre, hydrated lime and DBS polymer, were utilised in the porous asphalt. Comprehensive laboratory tests, including strength test, binder draindown test, Cantabro abrasion test, moisture susceptibility test, rutting test, thermal stress restrained sample test, and permeability test, were conducted. It is found that HVB significantly improved the overall performance of the porous asphalt; DBS additive improved its high-temperature performance, but lowered the cracking resistance at low temperature as well as the durability; fibre enhanced its durability and anti-cracking performance at low temperature; hydrated lime improved its moisture stability while weakening its durability. It is concluded that HVB and polyester fibre should be used in all porous asphalt; DBS additive is good for porous asphalt in high-temperature areas, and hydrated lime can be added to porous asphalt in rainy areas.     

Free vibration analysis of functionally graded conical, cylindrical shell and annular plate structures with a four-parameter power-law distribution

Based on the First-order Shear Deformation Theory (FSDT) this paper focuses on the dynamic behavior of moderately thick functionally graded conical, cylindrical shells and annular plates. The last two structures are obtained as special cases of the conical shell formulation. The treatment is developed within the theory of linear elasticity, when materials are assumed to be isotropic and inhomogeneous through the thickness direction. The two-constituent functionally graded shell consists of ceramic and metal. These constituents are graded through the thickness, from one surface of the shell to the other. A generalization of the power-law distribution presented in literature is proposed. Two different four-parameter power-law distributions are considered for the ceramic volume fraction. Some material profiles through the functionally graded shell thickness are illustrated by varying the four parameters of power-law distributions. For the first power-law distribution, the bottom surface of the structure is ceramic rich, whereas the top surface can be metal rich, ceramic rich or made of a mixture of the two constituents and on the contrary for the second one. Symmetric and asymmetric volume fraction profiles are presented in this paper. The homogeneous isotropic material can be inferred as a special case of functionally graded materials (FGM). The governing equations of motion are expressed as functions of five kinematic parameters, by using the constitutive and kinematic relationships. The solution is given in terms of generalized displacement components of the points lying on the middle surface of the shell. The discretization of the system equations by means of the Generalized Differential Quadrature (GDQ) method leads to a standard linear eigenvalue problem, where two independent variables are involved without using the Fourier modal expansion methodology. Numerical results concerning six types of shell structures illustrate the influence of the power-law exponent, of the power-law distribution and of the choice of the four parameters on the mechanical behaviour of shell structures considered.     

基于几何特征和力学特性的自适应网格生成算法

为获得适合有限元分析的满意网格划分,提出了平面域的基于几何特征和力学特性相结合的自适应网络生成方法,实现了应力集中区的网格局部加密及平稳变密度的网格自动剖分,通过实例表明本方法实用性强、效果良好。     

微粘结级配碎石基层沥青路面结构分析

目的 找寻适应重、中交通等级的合理的微粘结级配碎石基层沥青路面结构.方法 拟定微粘结级配碎石沥青路面结构,利用有限元软件计算各结构参数变化对弯沉、沥青层底拉应力等设计指标的影响,给出适应重、中等级交通量的合理路面结构.结果 在重、中交通荷载作用下,推荐级配碎石上基层沥青路面级配碎石层厚度为12～20 cm,面层厚度为5～10 cm,半刚性基层厚度为15～ 20 cm.结论 在重、中交通荷载作用下,提高微粘结级配碎石模量,能很好地改善路面结构受力,合理的微粘结级配碎石基层能够在防治反射裂缝同时,较好地满足交通荷载需求.     

级配集料的分形特性研究AC-16C

为了研究沥青混合料微观结构不均匀性的分布规律,基于分形的理论方法,从沥青混合料中集料的分布状态入手,对10组AC-16C级配类型的沥青混合料采用双对数坐标的方法计算其级配质量分形维数,研究沥青混合料级配质量分形维数的规律.研究结果表明:随着集料级配质量分形维数的增大,集料的空间填充能力增强,沥青混合料的空隙率也越来越小;随着粗集料中针片状含量的减小,集料颗粒被压碎或断裂的机率减小,从而提高了沥青混合料的均匀性.