Hongya Fu

Mechanical Properties of Thermoplastic Variable-Angle Composite Laminations for Conical Shells

Thermoplastic composite automated fiber placement technology, as one of the extreme manufacturing technologies for large or extra large composite components with complex surface shapes, has been widely used in the field of aerospace vehicles. This paper takes 8 lamination groups with different initial placement angles generated by the conical shell variable angle placement algorithm as research objects. Variable angle placement algorithm for conical shell and finite element model establishment method for thermoplastic composite laminations of variable angle with different initial placement angles are presented. Static, modal and buckling analyses are conducted for each group. The results show that stress-strain relation, modal and buckling strength of variable-angle laminations vary regularly with the initial placement angle.

Parametric Study on Heat Transfer for Tow Placement Process of Thermoplastic Composite

Fiber placement process of thermoplastic material is an in situ consolidation process which can significantly reduce consolidation process time and save costs compared with autoclave consolidation. The heat and crystallization behaviours play very critical role in the quality control during the process. In this work, two dimensional model of finite element is presented to perform heat transfer analysis of fiber placement process. The relationship between heat distribution of lamination and process parameters, including roller velocity, main heating temperature, preheating temperature, preheating length and preheating location, is deeply investigated. The numerical results show that for certain heating temperature there is a safe roller velocity which should not be exceeded, and such parameters as main heating length, preheating length and preheating location could be optimized to obtain better quality of product.

A Heuristic Task Periods Selection Algorithm for Real-Time Control Systems on a Multi-Core Processor

The performance optimization problem is investigated for discrete-time control systems on a multi-core platform. An integrated approach which considers both control performance and real-time scheduling aspects is applied to allocate optimal periods to controller tasks. A real-time control system is modeled as a set of directed acyclic graphs with weighted edges in this paper. The system allows producer/consumer relationship between tasks, and the data dependence relationships between tasks are uncoupled by attaching harmonic constraints to task periods. The period assignment problem is formulated as an optimization problem, which minimizes the system performance loss index under multi-core schedulability constraints. A heuristic search algorithm is proposed to solve this optimization problem and select periods for real-time tasks scheduled by rate-monotonic scheduling algorithm. Experimental results demonstrate that the proposed heuristic algorithm is capable of finding a high quality local optimal solution with fast computing speed. The proposed method is applicable to online failure recovery and reconfiguration in real-time control systems.

A Compensating Method of Gravity Deformation Curve Calculation for the Column of Heavy-Duty Floor-Type Boring and Milling Machine

The inhomogeneity of material is assumed to be the reason that affects the accuracy of FEM simulation of gravity deformation curve for the column of heavy-duty floor-type boring and milling machine. To solve this problem, a compensation method of gravity deformation curve calculation is proposed by discretizing the column into segments based on finite difference method. Equivalent flexural rigidity is utilized to characterize the inhomogeneity of the material. The results of FEM simulation is corrected by the proposed equivalent flexural rigidity based on a correction model. The experimental result shows that the computational accuracy is improved from 19.88% to 62.37%, compared with just FEM simulation.

Uncertainty Analysis Based Geometric Error Detection for Heavy-Duty Machine Tools

In order to measure the geometric errors of heavy-duty machine tools with high efficiency and high precision, an uncertainty analysis method based on Monte Carlo theory is presented to determine the detection of geometric errors for heavy-duty machine tool. It is found that 4-station orderly multilateral method is the preferred method for heavy-duty machine tool geometric error detection through the comparison among the measurement uncertainty of single station method, multilateral method and different station numbers sequentially multilateral method. The experimental results show that 4-stations sequentially multilateral method can improve the detection efficiency, and the errors are similar to the direct measurement of the laser interferometer.

Finite difference method–based calculation of gravity deformation curve for the large-span beam of heavy-duty vertical lathe:

To solve the problem that gravity deformation curve of large-span cast-iron beam analyzed by finite element method simulation is inaccurate due to material imperfection, a discretization calculation considering the inhomogeneity of the material based on finite difference method is proposed. Supposing the flexural rigidity of the beam is different along the length, the continuous beam is discretized into segments based on finite difference method, and equivalent flexural rigidity is presented to characterize the inhomogeneity of the material. Correction model of bending deformation is constructed to revise the results of finite element method simulation applying equivalent flexural rigidity that could be obtained by combining the discretization model and deformation data acquired in a simple self-load experiment in which the beam is simply supported without any assembly process. Finally, flowchart of application is presented, and the approach is illustrated through an example from real case. The experimental results show that the computational accuracy is improved from 73.14% to 88.33%, compared with just finite element method simulation.

Design of simulation system for fiber placement based on CATIA CAA

Fiber placement is one of the most popular processing techniques in fabricating composites in aviation and aerospace industries, due to its capability of placing prepregs or tapes precisely in the exact position when manufacturing complex parts. This paper presents a motion simulation framework for fiber placement, which is critical in validating the fiber placement path and preventing the possible collision and damage among machine, mandrel and operator. The linkage coordinate system was established according to the physical characteristics of a fiber placement machine. The coordinate information of multi-axes which move coordinately to implement the fiber placement path designed in the CAD system, was achieved by an algorithm which decouples the spindle and manipulator. Moreover, three criteria were proposed to check the feasibility of fiber paths and coordinated motion of multi-axes. Finally, the correctness and feasibility of proposed algorithms and fiber placement paths were verified by fiber placement simulation of an airplane inlet.

Simulation of Non-isothermal Crystallization Kinetics of Thermoplastics during Fiber Placement Process

Currently more and more thermoplastic composites are applied in aircraft structures. During automated fiber placement process, thermoplastic composites, which adopted “in-situ consolidation” technology, can be formed and consolidated in several minutes. Therefore, using “in-situ consolidation” technology instead of autoclave technology is more economically. However, some technical indicators of laminates using “in site consolidation” technology are below the autoclave laminates. In order to eliminate the most significant barriers, the automated fiber placement process should be studied. The crystallization rate of thermoplastic in the cooling stage of automated fiber placement is one of the most important factors. In order to obtain the special crystallization, the cooling temperature and cooling time should be strict controlled. According to the coupling phenomena between the non-isothermal crystallization kinetics and the heat transfer in thermoplastic during the cooling stage, a mathematical model has been established. By solving above model, the relationship among cooling temperature, cooling time and relative crystallization rate has been obtained. Above simulated data can guide the cooling stage of automated fiber placement process.