Thermomechanical Response of Advanced Materials under Quasi Instantaneous Heating
Thermomechanical Response of Advanced Materials under Quasi Instantaneous Heating
复制标题
准瞬时加热下先进材料的热机械响应
DOI：
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发表时间：
2017
期刊：
影响因子：
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通讯作者：
F. Carra
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文献类型：
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作者：
F. Carra
材料对随时间变化的热负荷的热机械响应的研究在工业和研究实验室中广泛采用的各种部件的设计中至关重要。根据加热速率的不同，热机械问题可以分为三种状态：准静态加热、慢瞬态加热和准瞬时加热。这篇博士论文的重点是后一种情况，其中热沉积速率足够高，导致应力波的起源，从局部加热区传播到结构周围，并与准静态应力场叠加。在论文的第一部分中，材料的动态响应准瞬时加热作为所产生的应力波的函数进行评估。在低热能下，应力波在弹性状态下保持低于材料的屈服应力。当波的振幅超过材料的屈服应力时，发生塑性，并且信号被分散成以声速行进的弹性波和以较低速度行进的塑性波。最后，只有在快速加热引起的能量和压力的临界水平上才能达到激波区。这种情况下的特点是温度，压力和密度的急剧不连续性，需要采用有限元代码的解决方案的热机械问题。受冲击材料的流体静力响应取决于状态方程，而偏应力张量的贡献由强度模型控制。失效模型支配断裂机制，由于空聚结，spectrometry和微观spectrometry。文中给出了状态方程的主要类别--强度模型和破坏模型的实例。一种新的方法来探索不寻常的区域的状态方程，基于强烈的等容加热的粒子束驱动，也介绍了。在论文的第二部分中，我们详细讨论了粒子束与物质碰撞产生的准瞬时加热现象。这些现象包括相变、弹性、塑性和冲击区的圆柱形压力波以及空间和微观空间断裂。为了探索这些机制中的每一个，通过隐式和显式有限元代码的数值研究，并结合，当可用时，在粒子加速器设施中进行的分析方法和实验测试。在论文的最后一部分，所进行的研究被应用到设计和工程的CERN HL LHC加速器组件称为准直器。这些部件与射束粒子密切相互作用，可能会受到意外撞击，必须将其对准直器和整个机器的影响降至最低。为了实现这一目标，CERN近年来开发了新的复合材料，以取代目前LHC中采用的碳纤维增强碳（CFC），将金属的良好热和电性能与碳同素异形体（如石墨和金刚石）的高热稳定性相结合。最有前途的是铜金刚石（CuCD）和钼石墨（MoGr）;这些材料进行了充分的表征，以获得EOS和本构模型，这些模型是研究它们在强烈等容加热下的响应所必需的。为了证明这些模型的准确性，并通过实验验证HL LHC设计方案中典型能量密度质子束直接撞击下的准直器阻力，于2015年在CERN HiRadMat设施设计并执行了一项测试。三个准直器颚，在CFC，MoGr和CuCD，广泛的仪器，并提交质子的影响，在不断增加的强度。实验结果的测试和数值预测的比较。
The study of the thermomechanical response of materials to a time dependent heat load is of paramount importance in the design of a variety of components widely adopted in the industry and in research laboratories. Three regimes can be identified in the thermomechanical problem, depending on the heating rate: quasi static, slow transient and quasi instantaneous heating. This PhD thesis focuses on the latter scenario, where the heat deposition rate is high enough to lead to the origination of stress waves, propagating from the locally-heated zone to the surrounding of the structure, and superposing with the quasi-static stress field. In the first part of the thesis, the dynamic response of materials to quasi instantaneous heating is evaluated as a function of the stress waves generated. At low thermal energies, stress waves remain below the yield stress of the material, in the elastic regime. When the amplitude of the wave surpasses the yield stress of the material, plasticity takes place and the signal is dispersed into an elastic wave travelling at the speed of sound, and plastic waves at lower velocity. Finally, the shock regime can be attained only at critical levels of energy and pressure induced by the fast heating. This scenario features a sharp discontinuity in temperature, pressure and density, requiring the adoption of finite element codes for the solution of the thermomechanical problem. The hydrostatic response of shocked materials depends on the equation of state (EOS), while the deviatoric contribution to the stress tensor is controlled by the strength model. Failure models govern fracture mechanisms due to void coalescence, spallation and micro spallation. Examples of the main categories of EOS, strength and failure models, are given in this thesis. A new method to explore unusual regions of the EOS, based on intense isochoric heating driven by particle beams, is also introduced. In the second part of the thesis, the several phenomena induced by a quasi instantaneous heating, due to particle beam impact on the matter, are explored in detail. Such phenomena involve changes of phase, cylindrical pressure waves at the elastic, plastic and shock regime, as well as spallation and micro spallation fracture. To explore each of these mechanisms, numerical studies by means of implicit and explicit finite element codes are presented and combined, when available, with analytical methods and experimental tests performed in particle accelerator facilities. In the final part of the thesis, the studies performed are applied to the design and engineering of CERN HL LHC accelerator components known as collimators. These components, closely interacting with the beam particles, are potentially submitted to accidental impacts, whose consequences on the collimator and on the overall machine must be minimized. With this goal, new composites were developed at CERN in recent years to replace the carbon fibre reinforced carbon (CFC) currently adopted in the present LHC, combining the good thermal and electrical properties of metals with the high thermal stability of carbon allotropes such as graphite and diamond. The most promising ones are Copper Diamond (CuCD) and Molybdenum Graphite (MoGr); these materials were fully characterized in order to derive EOS and constitutive models necessary for the study of their response under intense isochoric heating. To prove the accuracy of such models, and to experimentally verify the collimator resistance under the direct impact of proton beams involving energy densities typical of the HL LHC design scenarios, a test was devised and performed in 2015 at the CERN HiRadMat facility. Three collimator jaws, in CFC, MoGr and CuCD, were extensively instrumented, and submitted to proton impacts at increasing intensities. Experimental results of the tests and comparisons with the numerical predictions are presented.