白炭黑对聚硅氧烷佩恩效应及热弹行为的影响

利用溶解-溶胀实验和流变测试对聚甲基乙烯基硅氧烷(PMVS)-沉淀法二氧化硅Z142的佩恩效应进行研究,利用热弹性分析方法对PMVS-Z142的热弹性行为进行分析。结果表明:随着Z142含量的增大,PMVS中的二级结构增多;在小应变下二级结构遭到破坏发生解聚,导致PMVS-Z142的剪切模量下降,即佩恩效应;随着Z142含量的增大,内能对总应力的贡献愈大,内能是温度的函数,即PMVS的力学行为受温度的影响越大。     

纤维增强复合材料热弹性特性的计算机辅助结构优化

复合材料具有高的比刚度和比强度、低的热膨胀率，并有可能通过设计得到特定的材料性质，因而许多情况下是一种比金属更合适的材料。然而，复合材料层合结构的最优设计较为复杂，尤其当时变热弹性特性也作为设计准则更是如此。本文所介绍的有限元结构优化方法有助于确定复合材料层合结构中的大量自由设计变量。其中工艺约束被作为附加条件加以考虑。由机床制造业呈个部件的例子显示了这一优化方法的效果。     

可分散性纳米二氧化硅增强硅橡胶

采用表面经过硅烷偶联剂原位修饰的纳米二氧化硅增强硅橡胶。通过扫描电子显微镜和Payne 效应考察了纳米二氧化硅在硅橡胶中的分散特性; 用DSC 分析了复合体系的低温结晶行为; 考察了填料对硅橡胶力学性能的影响。结果表明, 由于修饰后纳米颗粒表面非极性有机基团的存在和表面能的降低, 无须加入分散剂, 纳米颗粒就能在硅橡胶中有较好的分散; 在各自最优添加量时, DNS-3 链状纳米二氧化硅增强的硅橡胶相对于气相法二氧化硅增强的硅橡胶在拉伸强度、撕裂强度及断裂伸长率上有显著提高; DNS-2 纳米二氧化硅增强性能与气相法二氧化硅的相当, 但前者混炼胶黏度较小, 有较好的加工性。      

结晶高聚物硬弹性材料的研究进展─—Ⅲ．硬弹性材料的弹性机理

本文综述了解释硬弹性材料形成的两类机理，一类以片晶的弹性形变为基础；另一类以表面能的变化为基础。这两类机理都具有其局限性，完整的机理还需要作进一步的探索和研究。     

结晶高聚物硬弹性材料的研究进展：Ⅲ.硬弹性材料的弹性机理

本文综述了解释硬弹性体材料形成的两种机理，一类以片晶的弹性形变基础，另一类以表面能的变化为基础，这两类机理都具有其局限性，完整的机理还需要作进一步的探索和研究。     

硅灰石制备多孔高比表面积二氧化硅机理探讨

通过对用硅灰石与盐酸反应制备多孔高比表面积SiO2最佳实验工艺条件的研究,确定了最佳试验工艺条件,即反应速度、反应时间、中和速度、反应最终pH值与SiO2比表面积的关系,探讨了其合成的机理。研究结果表明,当pH≤1.0时,硅灰石与盐酸反应生成大量稳定的硅酸溶胶;反应最终(pH＝4.0)使硅酸水解和缩聚以及Si—O与OH基团氢键的形成以适宜的速度进行,形成弱交联、网状、低密度的硅酸凝胶,最终产物SiO2的比表面积增大。     

定常温度热弹性板的精化理论

本文首先给出了定常温度热弹性 Ｂｉｏｔ［１］通解的一种新的简化形式,它看起来与各向同 性弹性力学的Ｐａｐｋｏｖｉｃｈ－Ｎｅｕｂｅｒ 通解十分相象,而后由此出发,由一般的各向同性弹性板推 广到本文的热弹性板问题,研究了热弹性板的问题,在没有任何预先假设的前提下,应用Ｌｕｒ’ｅ 算子法,证明了此通解不失一般性,导出了热弹性板精化理论的控制微分方程。     

回热器工作的热声机理

从热致声的瑞利判据出发，给出了回热器工作的数学模型。据此分析证明了回热器不仅是逆流换热器，而且也是一个热声转换部件，即在纵向声波与横向热量波动的耦合下，可以实现热致声或声泵热或声输热。给出了在理想流体条件下，控制声场条件以调节或控制横向温差，从而改变回热器工作模式的原则方法。进而指出，对于用实际耗散流体的实际回热器，由耗散性质所造成的热声效应截面分布是回热器工作性能的另一决定因素。     

金属材料热腐蚀机理研究的进展

着重介绍了金属材料中常用的基体材料及合金元素的氧化物,在纯Na_2SO_4及其混合盐中溶解度的研究结果,进而从热化学及电化学方面进一步讨论了高温热腐蚀机理。     

Developments in rapid thermoelastic analysis

This paper describes the work carried out by Rover's Experimental Analysis Department on developing the thermoelastic stress analysis technique for use with rapid prototype models. The paper discusses the business issues, which drove the research into a new "rapid" design validation technique, and the detailed work required to ensure the validity of the stress results.     

正弦脉冲激光激发声波的热膨胀机制理论

阐述了激光与液体媒质作用通过热膨胀机制激发平面光声源的理论;针对激光脉冲为正弦波形的情况,求解出δ脉冲和长脉冲分别在约束界面和自由界面下产生声脉冲的解析解,通过仿真得到了声脉冲剖面,并对每种情况下产生的声波进行了对比分析;然后对液体中激光致声的光声转换效率进行了理论研究,对正弦波形δ脉冲和长脉冲激光分别在约束界面和自由界面下产生声脉冲的光声转换效率分别进行了理论分析和仿真,并讨论了液体媒质特性参数和激光参数对转换效率的影响,提出了提高转换效率的方案。     

A Koiter reduction technique for the nonlinear thermoelastic analysis of shell structures prone to buckling

The multi-modal Koiter method is a reduction technique for estimating quickly the nonlinear buckling response of structures under mechanical loads requiring a fine discretization. The reduced model is based on a quadratic approximation of the full model using a few linear buckling modes and their second order corrections, followed by the projection of the equilibrium equations onto the modal subspace. In this article, the method is reformulated for geometrically nonlinear thermoelastic analyses of shell structures. The starting point is an isogeometric solid-shell discretization with an accurate modeling of thermal strains, temperature-dependent materials and general temperature distributions. The equilibrium path is defined as a displacement versus temperature amplifier curve, while mechanical loads are kept constant. The strain energy nonlinearity with respect to the temperature amplifier is the main obstacle in the definition of an accurate reduced model. This task is achieved by coherent asymptotic expansions in mixed form using independent stress variables at the integration points and accurate linear buckling modes obtained by a two-point mixed eigenvalue problem. Structures made of isotropic and multi-layered composite materials, including variable angle tow laminates, are considered to show the accuracy of the proposed method.     

A finite element formulation for thermoelastic damping analysis

We present a finite element formulation based on a weak form of the boundary value problem for fully coupled thermoelasticity. The thermoelastic damping is calculated from the irreversible flow of entropy due to the thermal fluxes that have originated from the volumetric strain variations. Within our weak formulation we define a dissipation function that can be integrated over an oscillation period to evaluate the thermoelastic damping. We show the physical meaning of this dissipation function in the framework of the well‐known Biot's variational principle of thermoelasticity. The coupled finite element equations are derived by considering harmonic small variations of displacement and temperature with respect to the thermodynamic equilibrium state. In the finite element formulation two elements are considered: the first is a new 8‐node thermoelastic element based on the Reissner–Mindlin plate theory, which can be used for modeling thin or moderately thick structures, while the second is a standard three‐dimensional 20‐node iso‐parametric thermoelastic element, which is suitable to model massive structures. For the 8‐node element the dissipation along the plate thickness has been taken into account by introducing a through‐the‐thickness dependence of the temperature shape function. With this assumption the unknowns and the computational effort are minimized. Comparisons with analytical results for thin beams are shown to illustrate the performances of those coupled‐field elements. Copyright © 2008 John Wiley & Sons, Ltd.     

Pressure dependence of the thermoelastic quotient for three glasses

The interrelationship between the mechanical work done on a material in the elastic range and changes in its thermodynamic properties, that is, between stress and strain, on the one hand, and temperature and entropy, on the other, is known as the Thermoelastic effect. The phenomenon is exactly adiabatic and is characterized by the thermoelastic quotient commonly referred to as thermoelastic constant. The thermoelastic effect can be used for stress analysis by monitoring the stress fluctuations by means of infrared radiometry, Also, it can be applied to study the anharmonicity in materials by measuring the temperature changes associated with adiabatic pressure changes, In this paper thermodynamic expressions are derived for the pressure derivative of the thermoelastic quotient under adiabatic as well as isothermal conditions, The derived expressions are applied to investigate the thermoelastic effect for the three glasses, namely, silica glass, soda-lime silica glass, and lead-silica glass, The isothermal pressure derivative of the thermoelastic quotient is evaluated for the three glasses. The isothermal volume derivative of the Gruneisen function is calculated.     

Mixed-mode thermoelastic fracture analysis of orthtropic composites

This study demonstrates ability to determine the in-plane stress intensity factors, K _I and K _II, simultaneously under mixed-mode conditions in orthotropic composites by the combined use of least-squares, stress representations which are valid away from the crack and distant measured temperatures. Recognizing the stresses near a crack-tip are dominated by the stress intensity factors, it has not been uncommon to neglect the higher-order stress terms when evaluating these factors. However, and among other considerations, it is typically difficult to obtain accurate temperature information very near the crack-tip. It can therefore be advantageous to employ measured data which originate away from the crack and to retain six to eight terms in the stress functions when evaluating the stress intensity factors. On the other hand, errors in K _I and/or K _II can be appreciable if only the r^–1/2 terms are employed with distant input information.     

Evaluation of damage in composites by using thermoelastic stress analysis: A promising technique to assess the stiffness degradation

The stiffness degradation represents one of the most interesting damage phenomena used for describing the fatigue behaviour of composites. A critical aspect of modelling the damage is represented by the simulation of the whole behaviour of the composite and by the assessment of the actual stiffness for the models validation. In this work, the stiffness degradation of quasi‐isotropic carbon fibre reinforced polymer (CFRP) obtained by automated fibre placement has been assessed by means of thermoelastic stress analysis. The amplitude of temperature signal at the mechanical frequency (thermoelastic signal) was considered as an indicator of material degradation and compared with the data provided by an extensometer. The correlation between thermoelastic and mechanical data allowed to build a new experimental model for evaluating and predicting material stiffness degradation by just using thermoelastic data. The proposed approach seems to be very promising for stiffness degradation assessment of real and complex mechanical components subjected to actual loading conditions.     

疏水性白炭黑在硅橡胶海绵中的应用研究

研究了表面疏水处理对白炭黑在硅橡胶及其海绵材料中的分散效果及其增强作用的影响.研究表明:表面疏水处理改善了白炭黑在硅橡胶中的分散均匀性,提高了胶料的可塑性,有利于胶料发泡,使硅橡胶海绵的表现密度降低;而表观密度降低导致硅橡胶海绵的硬度、拉伸强度、延伸率、压缩应力松弛减小.     

Mean stress dependence of the thermoelastic constant

The SPATE 8000 thermoelastic stress analyser has been used to demonstrate the mean stress dependence of the thermoelastic constant. This dependence has potential application in the measurement of residual stress provided the material has not yielded.     

The analysis of thermoelastic isopachic data from crack tip stress fields

A computer program—FACTUS (fracture analysis of crack tips using SPATE)—has been developed for the efficient analysis of thermoelastic data obtained from around a crack tip. The program is based on earlier work for the determination of stress intensity factors (SIFs), and also includes a novel solution procedure for the derivation of the non-singular stress term σ _{0 x} . The program has been used in the analysis of a series of large plate specimens with central or edge slots/cracks. The derived SIFs are compared with independent values. Issues, e.g. crack closure and the extent and effect of the plastic zone, are discussed.