Measurement of the in situ transverse tensile strength of composite plies by means of the real time monitoring of microcracking

Failure of a ply due to transverse loading is one of the mechanisms that was taken into account in physically-based failure criteria, used in composites design. However, experimental data are scarce and the measurement techniques used in the past are time consuming and involve a lot of specimen handling during testing. While some physical information is currently well consolidated (such as the dependence of the strength on ply thickness, or in situ strength), there still remain relevant open questions. This work presents a methodology, which does not interfere with the tensile test, to detect transverse cracks by optical means. Four different configurations of CFRP are considered. The results show that the in situ strength depends on the thickness of the ply and the orientation of the adjacent layers. In the case of thick transverse plies, the strength is controlled by full-width transverse cracks whereas, in thin plies cracking parallel to the specimen’s mid-plane occurs before transverse matrix cracking.     

基于环境激励下的柔度灵敏度损伤识别方法

随着社会的快速发展以及科学技术的不断进步，现代结构特别是基础建设方面的结构逐渐趋向于大型化、复杂化的方向发展。同样，在结构的使用阶段所经受的环境影响也越来越复杂，遇到的冲击也越来越强烈，如地震、强风及暴雨等等各种突发性的灾害，严重后果影响着结构的整体强度，也影响着结构的使用寿命，因此对于正在使用中的结构的损伤检测就显得尤为重要和紧迫。本文将讨论以环境激励下的利用柔度灵敏度的方法识别结构的损伤。     

初探钻杆接头损坏的原因

钻杆接头的优化处理需要从很多方面进行考虑,这就要求在材料和热处理方面必须进行严格的规定。这样才能保证接头的韧性和强度要求,达到延长寿命的要求。本文结合钻杆接头的损坏原因作了一些分析,提出了相应的处理方法,并对钻杆接头进行优化设计,来达到增加钻杆疲劳寿命的的目的。     

Experimental and numerical study of oblique impact on woven composite sandwich structure: Influence of the firing axis orientation

During flight, aircrafts can be submitted to complex loadings. The reliability of their structure is an essential aspect in ensuring passenger safety. In the specific case of helicopters, blades are subjected to impact loading. The following work will focus on the experimental and numerical study of an oblique impact on the skin of the blade. It is equivalent in a first approach to an impact on a sandwich panel comprising a foam core and a thin woven composite skin. This study aims to identify the mechanisms of damage to the skin for different orientations of the firing axis, and to develop a representative model of the damage kinetics adapted to the modeling of the complete structure. Thus, an F.E. semi-continuous explicit model has been developed. It relies on the development of a specific damageable element at the woven mesh scale. Numerical results obtained are accurate, allowing the identification of the damage mechanism of the woven skin for different firing orientations.     

Structural health monitoring system based on multi-agent coordination and fusion for large structure

In practical applications of structural health monitoring technology, a large number of distributed sensors are usually adopted to monitor the big dimension structures and different kinds of damage. The monitored structures are usually divided into different sub-structures and monitored by different sensor sets. Under this situation, how to manage the distributed sensor set and fuse different methods to obtain a fast and accurate evaluation result is an important problem to be addressed deeply. In the paper, a multi-agent fusion and coordination system is presented to deal with the damage identification for the strain distribution and joint failure in the large structure. Firstly, the monitoring system is adopted to distributedly monitor two kinds of damages, and it self-judges whether the static load happens in the monitored sub-region, and focuses on the static load on the sub-region boundary to obtain the sensor network information with blackboard model. Then, the improved contract net protocol is used to dynamically distribute the damage evaluation module for monitoring two kinds of damage uninterruptedly. Lastly, a reliable assessment for the whole structure is given by combing various heterogeneous classifiers strengths with voting-based fusion. The proposed multi-agent system is illustrated through a large aerospace aluminum plate structure experiment. The result shows that the method can significantly improve the monitoring performance for the large-scale structure.     

Damage induced anisotropy of polycrystals under complex cyclic loadings

Motivated by a low-cyclic fatigue micromechanical model proposed recently [1], qualitative and quantitative studies are performed emphasizing the concept of damage induced anisotropy. In this model, the plastic strain and local damage variables are examined at the crystallographic slip system scale for FCC metallic polycrystals. Determined at the macroscopic scale, the elastic behavior is initially assumed to be compressible and isotropic. The anisotropic damaged behavior, caused by activation/deactivation concept, is adopted using a fourth-order damage tensor at the overall scale. Accordingly, the overall behavior, notably the deactivation phase due to the microcracks closure under complex cyclic loadings, is of particular interest in the study.A host of plastic damaged behaviors of metallic polycrystals is predicted underlining the damage activation/deactivation effects on the multiaxial low-cyclic fatigue (LCF) behavior. Actually, the model is tested under strain- and stress-controlled conditions describing the effects of the loading complexity and the mean stress on the polycrystal LCF behavior. Finally, the model can successfully describe the LCF behavior of the Waspaloy at room temperature.     

铸铁均匀压缩和非均匀压缩时破坏方向分析

通过对铸铁试样进行均匀轴向压缩和非均匀轴向压缩实验,结合应力理论以及莫尔强度理论,分析铸铁试样受压时的受力状态,讨论其破坏方向和破坏原因。     

悬臂梁损伤的支持向量机识别研究

针对结构损伤识别中,损伤与其影响因素之间的复杂非线性关系,提出了结构损伤识别的支持向量机方法。支持向量机是一种基于统计学理论的机器学习算法,本文以模态频率作为损伤标识量,通过支持向量机建立了损伤程度和频率之间的支持向量机模型,并以悬臂梁的损伤为例进行了计算分析,结果表明提出的方法是科学,可行的。     

Study of metal barrier deposition-induced damage to porous low-k materials

A unique test structure based on a metal-insulator-semiconductor planar capacitor (Pcap) design was used to investigate several aspects of metal barrier-induced low-k damage. A special term called Effective Damage Thickness was introduced to describe the degree of damage. Ta(N) barrier was deposited on various dielectric films with porosity up to 32%. It has been found that the Effective Damage Thickness increases as the porosity increases. The damage is influenced more by the porosity of low-k films than the film density. Furthermore, the damage was modulated by Ta(N) deposition conditions. More damage was observed when higher target and/or substrate bias power was used, suggesting that the ion energy of the barrier material plays an important role in the low-k damage mechanism. A same degree of damage was observed for Ta barrier as for Ta(N), suggesting that Ta(N) deposition-induced low-k damage was primarily caused by Ta ions not nitrogen. Impact of Ru(Ta) and Cu(Mn) self forming barrier on low-k damage was also investigated. Among all the barriers studied in this work, the Ta-based barriers caused the most damage while the Cu(Mn) self forming barrier had the least damage to the low-k. The atomic masses for Ta, Ru, and Cu are 181, 101, and 64, respectively, corresponding with the observed degree of damage in the low-k material.     

射孔作业中的储层保护技术

射孔完井是一种非常重要的完井方式,针对射孔完井,通过射孔过程、射孔液、射孔参数及射孔压差对油气层的损害情况分析,提出了当前射孔作业中储层保护的技术及措施。