Effect of residual stress on spallation of NiCrBSi coating

The impact induced spallation characteristics of two specimens with NiCrBSi coating developed by different treatments are investigated. Two typical spallation patterns corresponding to the two kinds of specimens are observed. Theoretical analysis indicates that the difference in spallation characteristics is due to the residual stress. The initial stress states for the two kinds of specimens are investigated. The outcomes verify that the compressive residual stress within the coating will lead to large buckling region of the coating upon impact

Comments on theoretical foundation of “EM Drive”

The concept of EM Drive has attracted much attention and groups of work have been conducted to prove or verify it, of which the published experimental outcome is criticized in great details while the theoretical foundation has not been discussed. The present essay investigates on the theoretical derivations of the net thrust in the &ldquo;EM drive&rdquo; and reveals the self-contradiction arising at the very start, when the law of conservation of momentum was utilized and opposed simultaneously.The concept of EM Drive has attracted much attention and groups of work have been conducted to prove or verify it, of which the published experimental outcome is criticized in great details while the theoretical foundation has not been discussed. The present essay investigates on the theoretical derivations of the net thrust in the &ldquo;EM drive&rdquo; and reveals the self-contradiction arising at the very start, when the law of conservation of momentum was utilized and opposed simultaneously.</p

Film residual stress assessment method via temporarily thermal relaxation

The concept of temporarily thermal relaxation is extended theoretically to assess the film residual stress. First, the contribution of the initial stress to the observable displacement field is separated with eliminating the thermal expansion effect of the material. Then, the residual stress is inversely derived through the displacement increment. Finally, finite element analysis was carried out to provide numerical description of the partial relieve of the residual stress

局部热载荷诱导热障涂层界面分层断裂问题

以激光辐照对热障涂层面层进行局部加热,模拟超燃冲压发动机燃烧室热障涂层服役的高热流、高温度梯度载荷环境,研究热障涂层的可能破坏模式.首先给出了YAG激光局部加热试验方法、过程和界面破坏的典型形貌;然后,基于理论分析与有限元模型化研究,计算了表面局部受热时热障涂层体系的温度场、变形场和应力场,分析了热障涂层破坏的力学机制.研究结果表明,在这种局部迅速加热的载荷条件下,热障涂层将由于陶瓷层-粘接层的界面分层断裂而失效.参数化模型研究发现热障涂层体系的关键结构参量、性能匹配对界面分层断裂驱动力具有显著影响且存在优化区间

On The Cyclic Bending Behaviour Of A Hard Coating On A Ductile Substrate With Periodic Surface Hardened Regions

A cyclic bending experiment is designed to investigate the interface fracture behaviour of a hard chromium coating on a ductile substrate with periodic surface hardened regions. The unique deflection pattern of the vertical cracks after they run through the coating and impinge at the interface is revealed experimentally. A simple double-layer elastic beam model is adopted to investigate the interfacial shear stresses analytically. A FE model is employed to compute the stresses of the tri-phase structure under a single round of bending, and to investigate the effect of the loading conditions on the deflection pattern of the vertical cracks at the interface. (C) 2008 Elsevier Ltd. All rights reserved

声源激励下的声-振耦合响应分析

监控单元在现代航空航天飞行器中有重要作用,通常置于相对封闭的薄壁容器内。为提高监控单元可靠性,需要准确描述其环境条件,包括其声学、振动状态和热环境,三者存在相互作用,其结构和声响应是耦合的。本文通过一个典型结构模型,建立热-声-振耦合响应分析方法,研究监控及控制单元的多物理环境特征。首先建立考虑热膨胀效应和热软化效应的热-结构动力学控制及有限元模型,其次进行不同声激励下的声-振耦合数值分析;用该耦合方法预测了该盒子壁面的声传递损失,建立了监控单元薄壁容器多物理环境与声-结构响应的数值预测方法

Invariant in variants

The coronavirus Covid-19 mutates quickly in the pandemic, leaves people struggling to verify and improve the effectiveness of the vaccine based on biochemistry. Is there any physical invariant in the variants of such kind of pathogen that could be taken advantage to ease the tensions? To this point, extensive numerical experiments based on continuity mechanics have been accomplished to discover the consistent vibration modes and the range of natural frequency of coronavirus Covid-19. Such invariant could help us in developing some flexible technique to deactivate the coronavirus, like as resonantly breaking the viral spike by ultrasound wave. The fundamental mechanisms governing such process are demonstrated via solving the coupled acoustic wave and elastic dynamic equations, after which the practical strategies are proposed to efficiently realize the technique concept.</p