Papers by Author: Lei Jiang Yao

Abstract: An experimental study was carried out to study the low-velocity impact characteristics and the influence of impact energy on the damage of plain woven carbon fiber reinforced silicon carbide composite. Visual, ultrasonic scanning, X-ray, industrial CT and infrared thermal imaging were then utilized respectively for Nondestructive Testing of the test specimens after impact test. The results show that the material damage area increase significantly with the increase of the impact energy. But as the specimen is run through, when the impact energy comes to12J, the damage area decrease. Compare the changing curves of the damage areas obtained by different detection methods, we can find that the changing trends of the damage areas obtained by ultrasonic C-scan and infrared thermal imaging are the same with the impact energies, indicating that the damage of the specimen are more credible by the two methods.

Abstract: The aim of this paper is to study the influence of manufacturing defects on coefficient of thermal expansion (CTE) of Plain Weave C/SiC by using the finite element computational micromechanics (FECM) method. Utilizing photomicrographs taken by scanning electron microscope (SEM), we established an accurate representative volume element (RVE) model for the plain weave C/SiC composites with consideration of manufacturing defects, which have different influence on CTE. The study shows that matrix cracks make CTE increase by 2.7% and matrix porosities make CTE decrease by 2.4% compared with the no defects RVE model. The variation law of CTE along with cracks density and porosity volume is also obtained: CTE of plain weave C/SiC is decreasing correspondingly while the speed gradually slows with the increasing of matrix crack density and matrix porosity volume fraction.

Abstract: Utilized photomicrographs taken by scanning electron microscope (SEM), an accurate representative volume element (RVE) model for plain weave C/SiC composites is established. Based on the steady-analysis method, the in-plane and thickness direction thermal conductivity of the C/SiC composites are calculated as 25.6Wm-1K-1 and 12.1Wm-1K-1, respectively. The manufacturing flaws have different effect on thermal conductivity. Compared with RVE without flaws, the result shows that matrix cracks make thermal conductivity decrease by 7.2% in the in-plane direction and have little effect in the thickness direction; matrix porosities have a significant effect on thermal conductivity, which make the thermal conductivity decrease by 16.7% in the in-plane direction and decrease by 25.4% in the thickness direction. The variation law of thermal conductivity along with porosity volume is also observed: as matrix porosity volume fraction is increasing, the thermal conductivity of material shows significant decrease.

Abstract: The aim of this paper is to propose a microstructure modeling for prediction of thermal conductivity of plain weave C/SiC fibre bundles considering manufacturing flaws. Utilized photomicrographs taken by scanning electron microscope (SEM), an accurate representative volume element (RVE) model for carbon fiber bundles is established. Based on the steady-analysis method, the axial and transverse thermal conductivity of the carbon fibre bundles are calculated as 40.32Wm-1K-1 and 11.33 Wm-1K-1, respectively. The manufacturing flaws have different effects on thermal conductivity, the study shows that class A porosity has a significant effect on thermal conductivity, which leads to the thermal conductivity on the axial direction decrease by 13.31% and transverse direction decrease by 20.56% compared with no flaws RVE. While class B porosity has little influence on the k-value. The change law of axial and transverse thermal conductivity along with porosity volume is also observed: as porosity volume fraction is increasing, the thermal conductivity of fibre bundles shows significant linear decrease.

Abstract: Lightweight design was carried out in order to meeting the requirement of long endurance. Structure form was designed based on loading characteristics. Rationality of structure form was verified by finite element method and static tests, which proved deformation of wing measuring up mechanical properties of cell panel. Finite element modal analysis was performed. Then mode test was carried to correcting analysis results. Low order modes by testing are coincided with that computed in finite element method (FEM).

Abstract: Continuous carbon fiber reinforced silicon carbide composite material (C/SiC) is one of the most effective candidate materials for hot structures in aeronautic and aerospace applications. Its performances in the complicated service environments are widely concerned. A database, aiming at optimized design of C/SiC, was developed. The database collected original data on the fabrication, microstructure of C/SiC, as well as abundant data on performance experiments including tension, compression, shear, fatigue, creep, oxidation, high-temperature fatigue, and so on. The logic structure of the database, modeled by unified modeling language, provides a data link that connecting the processing, microstructure and performance of C/SiC, so that users can conveniently create a test result set to build the mathematical model of material design. Efficient software was developed to realize management, browsing and extension of the database.

Abstract: An experimental study of low velocity impact (LVI) was carried out on 2D carbon fabric reinforced silicon carbide (C/SiC) ceramic matrix composites. The C/SiC composite specimens were impacted by using a free-drop impact machine at different energy levels ranging from 1J to 9J and acoustic emission (AE) technique was used to detect the damage process. The results indicated that AE signals could evaluate the LVI damage behaviors of C/SiC composites from the different aspects. By comparing impact load process with AE hits and AE amplitude, the damage process could be determined. In the loading stage, matrix cracking mainly occurred in the composites; when impact load reached peak load, delamination and fiber fracture started to produce; in the unloading stage, the damage modes were mainly delamination and matrix cracking. AE event count fractions could quantify the main damage modes at different impact energy levels. At lower impact energy, matrix cracking was the main damage mode; when impact energy were between 3J and 6J, delamination and matrix cracking became the main damage modes; at higher impact energy, fiber fracture was the main damage mode.

Abstract: Corrosion of ocean engineering structures leads huge economic loses each year. Corrosion protection technology has already become a very important method for design and manufacture of ocean engineering structures. To decrease corrosive loses and guarantee the safety of engineering structures, extensive studies are invested to understand corrosion mechanisms and rules of engineering materials, and to develop technologies on corrosion control and protection. These research projects have produced and are producing a great amount of test data, reports, products, experiences, and so on. If all these data resources can be collected and organized in a unified platform, it will take great advantages for products design or manufacture on corrosion protection. A database, named Database on Corrosion of Ocean Engineering Materials and Structures (CDOSDB), was planned. For a designer or manufacturer, it should be considered in serving environment, corrosion property of material, methods on corrosion protection, and experiences on protection of real engineering structures. So, the CDOSDB is mainly include ocean environmental information, test data in real sea, simulating test data in lab, methods and products on corrosion protection, survey on corrosion status and protection of real engineering structures, corrosion knowledge and corrosion models. Because the related data and information were collecting from different research institutes and publications, in order to make full use of them, a uniform specification are arranged and standardized. A website is designed and the web addresses is http://www.dematers.com. It makes the database sharable.

Abstract: Data is the main subject of enterprise resource planning. It is an important way to enhance economic efficiency and competitiveness, by taking advantage of information technology to implement the data/information management and ensure their objectivity, accuracy and efficiency. In product design and manufacture process, the life time of data resources are divided into production, collection, arrangement, inputting, transmission, using, etc. If data resources information management system and management platform is established, it can record, share and manage data timely and accurately. At the beginning of data management, the clear and reasonable planning is an important foundation to achieve data information management. So, the concrete problems of planning were discussed about management objective, content and mode. In the course of design and manufacture, the data types, data management user and management basic conditions were summarized, and then it was discussed about framework and process of data resource management. Finally, the concrete operation and management measures were discussed on each link of data life cycle. The paper’s idea has a great impact for reference to integration and compromise of product’s data resources, establishment data resources management platform and taking management measures.

Abstract: For high reliability and long-life equipments, regular test on their performance is an effective approach to keep a fine status during the whole life. Because the number of failures increases with the duration of service, it is very important to use a rational testing strategy with unequal testing period instead of equal testing period. If testing period is not suitable, failure cannot be timely found and repaired, early failure or accident may occur. Reliability detection strategy of exponential distribution products is studied. And for every testing period, on the basis of the assumption that products should be tested when the rate of reliability deterioration reaches a certain value, an equal reliability degradation model on testing period is discussed. Furthermore, according to the idea that environment and personnel factors can lead to characteristic deterioration of products, a mathematical model of testing period incorporating reliability, failure rate, cost and testing efficiency is proposed. As the objective function of minimum cost and constraint functions of reliability and testing interval, an optimization model of unequal testing period is put forward. The optimization model is much better than traditional equal testing interval model in maintenance reliability lifetime, for it conforms to the reality that testing period must be shorten when the reliability degrades.