币形裂纹纤维桥联效应力学分析

本文基于Castigliano's定理和界面剪滞模型,得到了含界面相效应的复合材料币形裂纹纤维桥联增韧和裂纹张开位移控制方程。并按照第二类Fredholm积分方程的迭代解法给出其数值结果。为便于分析界面相参数对增韧效果等影响,寻求了该控制方程的近似解,对近似解进行了误差估计。在此基础上得到了界面剪切模量、裂纹长度、界面厚度、纤维半径,纤维体积分数以及材料性质等参数对币形裂纹桥联效应的影响。     

Model and mesh generation of cracked tubular Y-joints

In this study, the methods for constructing accurate and consistent geometrical and finite element (FE) models for general cracked tubular Y-joints are described. Firstly, geometrical analysis of welded tubular joint is given and it is then extended to the modelling of general cracked Y-joints. The concept of crack surface and a simple mapping approach are suggested to model either through-thickness or surface cracks which can be of any length and located at any position along the brace-chord intersection. Secondly, the geometrical model developed will be used in the generation of consistent FE meshes. The basic concepts used for the design and generation of three-dimensional FE meshes will be described. This will include the meshing procedures for discretization of tubular joints with through-thickness and surface cracks which are frequently regarded as one of the most difficult steps in the construction of tubular joint models. Finally, some mesh generation examples for uncracked and cracked Y-joints will be presented to demonstrate the use of the purposed geometrical model and mesh generation scheme developed.     

On the linear three-dimensional behaviour of composite beams

This paper describes a method of evaluating the linear stiffness matrix of a three-dimensional beam which accounts for all the possible couplings involved in the use of composite laminations appropriate to satisfy design requirements. The starting point of the procedure is represented by a complete evaluation of the beam cross section properties by use of a two-dimensional finite element analysis. A mass matrix of the beam is also evaluated as well as the external forces, to account for overall thermal deflections.

Some examples are presented and the results are compared either with their theoretical counterparts or with numerical results obtained by means of a full three-dimensional finite element analysis.     

变角度复合材料单元型近场动力学模型

变角度复合材料具有优异的力学性能和更强的可设计性,研究变角度复合材料结构的力学行为和损伤特性对工程应用和结构设计具有重要科学意义。单元型近场动力学(Element-based peridynamics,EBPD)理论基于积分-微分方程,处理不连续问题时不存在奇异性问题,相比于经典连续介质力学方法可以方便处理断裂等破坏问题。通过虚拟单元积分点的位置与纤维角度的对应关系,提出了EBPD变角度复合材料单层板模型。通过对具有不同边缘初始角度含中心圆孔的变角度复合材料单层板变形模拟验证了模型的可靠性,并预测不同角度单层板的裂纹扩展路径。提出的模型可以准确表征变角度复合材料单层板的变形以及破坏模式,为其强度评估及结构设计提供理论指导。     

Curvature determination in the bending test of continuous fibre reinforcements

Bending deformation is one of the main deformation modes in the forming of continuous fibre reinforcements. It is very specific compared to the classical continuous materials. In most textile material forming simulation models, bending stiffness is neglected, but taking into account it would give a more accurate predication, particularly the shape of wrinkles. In the deformation, fibres constituting the reinforcement can slide to each other, resulting in the bending stiffness of reinforcement is not directly related to its in‐plane tensile modulus as the classical continuous materials. Consequently, it is necessary to determine the bending stiffness by the experimental method. A cantilever bending stiffness test approach was proposed to measure the bending stiffness of continuous fibre reinforcements. A CCD camera was used to take the bending deflection shape. To calculate the curvature of bending deflection curve, uniform quartic B‐spline curve was chosen. A detailed process of curvature calculating of deflection curve was given in this paper. A single bending test gives the bending moment as a function of curvature from zero to the maximum value. Bending tests were conducted to validate the capacity of the proposed approach. A smooth curvature plot along the bending deflection curve was obtained for different types of reinforcements, and the non‐linear bending deformation behaviour can be identified with the proposed bending test method.