Modelling and computation of curing and damage of thermosets

The curing of thermosets is a complex process involving the transition from a fluid into a (visco-) elastic solid. This phase transition comes along with an increase in stiffness and a volume shrinkage of the polymer. The latter may lead to severe residual strains and stresses, which in turn can cause damage in the final, usually quasi-brittle material. In this contribution a constitutive model is developed which takes into account the curing of a thermosetting material together with the process-induced damage as resulting from curing shrinkage. The curing of the material is governed by a phenomenological hypoelastic constitutive equation which includes temporal evolutions for stiffness and volume shrinkage. Thermal and viscous effects are neglected in the present study. An isotropic gradient-enhanced damage model is adapted to describe the damage evolution. The curing-damage model is implemented into a finite element code and numerical examples for thermosetting materials demonstrate that the proposed model is capable to predict cure-induced damage in thermosets.     

The shape and stability of wall-bound and wall-edge-bound drops and bubbles

The behavior of wall-bound drops and bubbles is fundamental to many natural and industrial processes. Key characteristics of such capillary systems include interface shape and stability for a variety of gravity levels and orientations. Significant solutions are in hand for axisymmetric pendent drops for a variety of uniform boundary conditions along the contact line with gravity acting normal to a planar wall. The special case of a wall-bound drop or bubble that is also pinned at an edge (i.e. a ‘wall-edge-bound’ drop) is considered here where numerical solutions are obtained for interface shape and stability as functions of drop volume, contact angle, fluid properties, and uniform gravity vector. For a semi-infinite zero-thickness planar wall (plate), a critical contact angle is identified below which wall-edge-bound drops are always stable. The critical contact angle is computed as a function of the gravity vector. The numerical procedure, which makes no account for contact angle hysteresis, predicts that such wall-edge-bound drops are unconditionally unstable for any gravity field with a component that is tangent to the wall while inwardly normal to the edge. Select experiments are conducted that support the conclusions drawn from the numerical results.     

Measurement and analysis of elastic and anelastic properties of alumina and silicon carbide

Measurements of dynamic Young's modulus, E, and damping as a function of temperature, T, were made for alumina and silicon carbide. The Young's modulus data were compared with some from the literature, and analysed in terms of a theoretical framework relating the Debye temperature, θD, with the elastic constants. For both materials this analysis yielded a ratio T₀/θ_D which was near 0.4, where T₀ is an empirical fitting constant for the plot of (E(0)−E)/T versus 1/T (E(0) is the value of E at 0 K). The analysis of the damping data in terms of an Arrhenius type dependence led to effective activation energies near kT, where k is Boltzmann's constant. This revised version was published online in November 2006 with corrections to the Cover Date.     

Thin-ship theory and influence of rake and flare

The basic computational task of the thin-ship theory of free-surface potential flow about a ship that advances at constant speed along a straight path in calm water, of large depth and lateral extent, is considered. Specifically, a straightforward method for evaluating the pressure and the wave profile at a ship hull (the wave drag, hydrodynamic lift and pitch moment, and sinkage and trim are also considered) in accordance with Michell’s thin-ship theory is given. A main ingredient of this method is a simple analytical approximation to the local-flow component in the expression for the Green function (associated with the classical Michell–Kelvin linearized free-surface boundary condition) of thin-ship theory. This practical Green function is used to evaluate and analyze steady flow about a four-parameter family of ship bows with rake and flare. In particular, the variations of the bow-wave height and location with respect to the draft-based Froude number, the entrance angles at the top and bottom waterlines, and the rake angle are explored via a systematic parametric study. This parametric study provides estimates—immediately useful for design—of the influence of rake and flare on the height and the location of a ship bow wave, and shows that rake and flare effects can be significant, especially at low Froude numbers.     

Dynamics and stability of unicycles and monocycles

Single-wheel vehicles include the monocycle proposed by Leonardo da Vinci and the more familiar unicycle. Although these vehicles are very simple mechanically, their stability characteristics are complicated and it is believed that they have not been investigated analytically previously. In this paper, a unified analysis applicable to both types of vehicles is presented along with typical calculations and a discussion of their implications     

State of the Art and Perspectives of Hydroforming of Tubes and Sheets

Hollow parts of high accuracy and high strength can be produced by forming methods using liquid media. Hydroforming of tubes has reached a high standard for small parts (volume some 1000 cm(3)) and is further developed for larger parts (volume some 10.000 cm(3)). Processes for hydraulic sheet metal forming are sometimes used for small parts from single sheets. These processes are currently under intensive investigation, which is also true for the processing of double layered sheets. Single,sheets can be formed using membranes which separate the workpiece and the liquid. This results in interesting possibilities for a part and process integration in one step. The forming performance of aluminum alloys can be enhanced by using a heated liquid media when forming without membranes.     

Creation and motion of dislocations and fracture in metal and silicon crystals

By making a step on one surface ( ) of a rectangular small paralellepiped copper crystal, dislocations could be created by the molecular dynamic method. The dislocation created was not a complete edge dislocation but a pair of Heidenreich-Shockley partial dislocations. Each time a dislocation was created, the stress on the surface was released. Small copper crystals having a notch were pulled (until fracture), compressed and buckled by use of the molecular dynamic method. An embedded atom potential was used to represent the interaction between atoms. Dislocations were created near the tip of the notch. A very sharp yield stress was observed. The results of high speed deformations of pure silicon small crystals using the molecular dynamics are presented. The results suggest that plastic deformation may be possible for the silicon with a high speed deformation even at room temperature. Another small size single crystal, the same size and the same surfaces, was compressed using molecular dynamic method. The surfaces are {110}, {112} and {111}. The compressed direction was [111]. It was found that silicon crystals are possible to be compressed with a high speed deformation. This may suggest that silicon may be plastically deformed with high speed deformation.     

Exploration of new superconductors and functional materials,and fabrication of superconducting tapes and wires of iron pnictides

Abstract

This review shows the highlights of a 4-year-long research project supported by the Japanese Government to explore new superconducting materials and relevant functional materials. The project found several tens of new superconductors by examining ～1000 materials, each of which was chosen by Japanese experts with a background in solid state chemistry. This review summarizes the major achievements of the project in newly found superconducting materials, and the fabrication wires and tapes of iron-based superconductors; it incorporates a list of ～700 unsuccessful materials examined for superconductivity in the project. In addition, described are new functional materials and functionalities discovered during the project.     

Buckling and collapse of open and closed cylindrical shells

The buckling of a finite section of a cylindrical shell resembling a two-dimensional contact lens, and the collapse of a tubular shell of infinite extent are considered. The deformation is due, respectively, to the application of an edge force or to a negative transmural pressure. In both cases, the shell develops elastic bending moments due to the deformation from a specified resting shape according to a linear constitutive equation, accompanied by in-plane and transverse shear tensions. In the case of a section of a shell with a flat resting shape, classical results due to Euler and Love show that, as the applied edge force is increased beyond a sequence of thresholds, an infinite family of deformed shapes becomes possible corresponding to buckled states that bifurcate from the zero-curvature resting configuration. It is shown here that a corresponding infinite family of shapes is also possible for a finite shell whose resting shape is a section of circle. These shapes, however, no longer arise from bifurcations, but rather constitute disconnected solution branches of a nonlinear boundary-value problem. A closed cylindrical shell whose cross-section has a circular resting shape exhibits similar bifurcations when the difference between the exterior and interior pressure exceeds a sequence of thresholds, but a shell with a non-circular resting shape deforms into a multitude of shapes described by isolated solution branches. The computed two-dimensional buckled shapes are used to reconstruct the three-dimensional shape of a slowly collapsing fluid-conveying vessel. The reconstruction procedure involves stacking together cross-sections at axial positions that are found by integrating the differential equation determining the axial pressure distribution in unidirectional pressure-driven flow, subject to a constant flow rate. The dimensionless coefficient relating the local pressure gradient to the flow rate is computed by solving the Poisson equation governing unidirectional viscous flow using a boundary-element method, and expressing the flow rate as a boundary integral involving the shear stress which is available from the solution of the boundary-integral equation. In an appendix, the energy of the bending state is discussed with reference to specific choices made by previous authors in various branches of science and engineering.     

Polytherms of density and surface tension of bismuth lead and of angle of wetting of high-nickel and ferritic-martensitic steels by the Pb-Bi alloy

The large droplet method (in a graphite cup) was used to study the temperature dependences of density ρ and surface tension σ of bismuth lead (～10% Bi) in the temperature range from its melting point to ～1050 K in a helium atmosphere. It was found that the ρ(T) and σ(T) dependences are close to linear and decrease with temperature. The sessile drop method (on a substrate) was used to study temperature dependences of the angle θ of wetting new high-nickel and ferritic-martensitic pressure-vessel steels by bismuth lead in the above temperature range in a vacuum (0.01 Pa). It is shown that the steel substrates alloyed with aluminum are not wetted in the temperature range studied.     

Vacuum distillation of a mixture of LiCl-KCl eutectic salts and RE oxidative precipitates and a dechlorination and oxidation of RE oxychlorides

In this study, a vacuum distillation of a mixture of LiCl–KCl eutectic salt and rare-earth oxidative precipitates was performed to separate a pure LiCl–KCl eutectic salt from the mixture. Also, a dechlorination and oxidation of the rare-earth oxychlorides was carried out to stabilize a final waste form. The mixture was distilled under a range of 710–759.5 Torr of a reduced pressure at a fixed heating rate of 4 °C/min and the LiCl–KCl eutectic salt was completely separated from the mixture. The required time for the salt distillation and the starting temperature for the salt vaporization were lowered with a reduction in the pressure. Dechlorination and oxidation of the rare-earth oxychlorides was completed at a temperature below 1300 °C and this was dependent on the partial pressure of O₂. The rare-earth oxychlorides (NdOCl/PrOCl) were transformed to oxides (Nd₂O₃/PrO₂) during the dechlorination and oxidation process. These results will be utilized to design a concept for a process for recycling the waste salt from an electrorefining process.     

Modeling and simulation of osteoporosis and fracture of trabecular bone by meshless method

Osteoporosis is a skeletal disease characterized by a decrease in bone strength as a result of a decrease of bone mass and a deterioration of bone microstructure. In this work, the imaging data of a CT scanned human femoral neck trabecular bone is directly converted into a meshless model. A model is developed to analyze osteoporosis process. A fracture criterion and the corresponding post-failure are proposed for trabecular bone. The fracture process is modeled and simulated. The simulations show that the fracture stress is not a monotonically decreasing function in the process of fracture, and the microstructure of trabecular bone has a positive effect in preventing progressive failure. The approach in this work may be used to understand the osteoporosis-related fracture and the bone density–strength relationship, and to serve as a way for prognosis of osteoporosis.     

Thermodynamic similarity and prediction of the properties and characteristics of substances and processes

Principles of the theory of thermodynamic similarity are considered in application to all aggregate states of a substance, including phase transitions, and to the change in dissipative structures in open systems.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 53, No. 5, pp. 709–716, November, 1987.     

Fractal Analysis and Synthesis of Fracture Surface Roughness and Related Forms of Complexity and Disorder

Roughness is, among human sensations, just as fundamental as color or pitch, or as heaviness or hotness. But its study had remained in a more primitive state, by far. The reason was that both geometry and science were first drawn to smooth shapes. Thus, color and pitch came to be measured in cycles per seconds, that is, were reduced to sinusoids, in other words to uniform motions around a circle – the epitome of a smooth shape. A study of roughness had necessarily to wait until specific mathematical tools had been discovered and, much later, suitably interpreted. Fractal geometry began when I reinterpreted the flight from nature that had led mathematicians to conceive of notions like the Holder exponent, the Cantor set, or the Hausdorff dimension. They boasted of these notions being ‘monstrous’ but in fact I turned them over into everyday tools of science. I also added further tools that – taken together – made roughness quantitatively measurable for the first time. Acquiring a quantitative measure is the step that moves a field into maturity. And this move instantly led to a striking conjecture. In 1984, ‘Nature’ published an article I wrote with D. A. Passoja and A. J. Paullay on metal fractures. We found that the traditional measures of their roughness range all over. To the contrary, their fractal roughness varies very little not only between samples but also between materials. Last time I checked the “universality” had been extended but not explained. The new intrinsic measure created a major intellectual mystery. The first major new tool that I added to those contributed by the likes of Holder, Cantor, and Hausdorff was multifractality, for both measures and functions. I was motivated by the urge to model the intermittence of turbulence but my first full paper (in 1972) also noted that the same techniques ought to apply to the intermittence in the variation of financial prices. An ancient adage claimed that the City of London is as unpredictable as the weather. I found unexpectedly quantitative truth to this adage by showing that both phenomena can be tackled with essentially the same tools. Roughness is everywhere therefore fractal geometry has little fear of running out of problems. This address will sketch the fractal geometry of roughness and explore some new developments relevant to this Congress.     

聚碳硅烷和二乙烯基苯的交联及纳米SiC陶瓷的制备

碳化硅基复合材料是理想的高温结构材料,以聚碳硅烷(PCS)作为碳化硅陶瓷的先驱体,二乙烯基苯(DVB)为交联体,通过改变二者的配比研究了PCS与DVB的交联反应以及PCS/DVB交联体的热裂解过程。通过傅立叶红外光谱详细研究了PCS/DVB配比变化对PCS与DVB的交联反应和交联体微观结构的影响,PCS/DVB配比最终决定碳化硅陶瓷的产率,当PCS/DVB配比为1∶0.5时,经1500℃热裂解后碳化硅陶瓷产率最高,达到63.1%,热裂解产物为纳米碳化硅,粒径为10-40nm。用SEM和XRD研究了不同PCS/DVB配比交联体热裂解产物的微观结构和相组成,通过热重分析研究了PCS/DVB配比为1∶0.5时交联体的热裂解过程,在400-800℃,PCS/DVB交联体失重显著,在800℃热裂解过程基本完成,PCS/DVB配比为1∶0.5时能够制备出纳米碳化硅基复合材料。     

混凝土结构裂缝及防治

混凝土的裂缝问题是一个普遍存在而又难于解决的工程实际问题，通过对混凝土工程中常见的一些裂缝问题进行探讨分析，并针对具体情况提出了一些预防、处理措施。     

Glaciers and laws of friction and sliding

Summary. Glaciers slide at their base. A deeper understanding of the frictional behaviour and sliding between an ice mass and a rock bed is an important problem in glacier physics. In this study we investigate two approaches to the problem of glacier sliding. The first approach models friction forces between the ice and the bed. The second approach considers various proposals of a sliding velocity. Anisotropy of rock bed topographies is a source of anisotropic tribological phenomena. Therefore, anisotropic and inhomogeneous friction and anisotropic sliding are discussed in detail. Various types of friction anisotropy are distinguished with the aid of linear and nonlinear friction models. Next, anisotropic friction and sliding rules are derived using an elasto-plastic analogy. A sliding law proposed by Hindmarsh is applied in the analysis of anisotropic sliding. Extended forms of the sliding law are given with the aid of anisotropic friction models. Furthermore, stick-slip motions are identified as important in the dynamics of glacier sliding.     

Improvement of metrological provision for methods and means of monitoring internal stresses and strains of components and joints

It is established that in certifying gage blocks in an interference comparator, during which precise placing of the measure on a quartz plate is provided by molecular (adhesion) interaction of their measurement surfaces, the corresponding internal stresses and strains are a functional property of the certification method. __________ Translated from Izmeritel’naya Tekhnika, No. 2, pp. 37–40, February, 2007.     

ECAP变形与材料组织性能控制的研究

等径弯曲通道变形(ECAP)是制备超细晶材料的新工艺,其基本原理是将试样放入横截面形状完全相同、并成一定角度的弯曲通道中,试样在压力作用下通过通道时,在通道弯曲处产生一定量均匀的纯剪切变形,最终获得很高的变形量,使材料组织发生明显细化.详细介绍了ECAP变形工艺路线对晶粒细化的影响,以及ECAP变形制备超细晶材料的显微组织特征及其力学性能.     

转子压缩机与涡旋压缩机的对比与发展

空气源热泵压缩机的性能是适合不同气候条件的热泵的关键。本文回顾了转子与涡旋压缩机的发展历程,早期房间空调器用压缩机为活塞式,后期出现了转子压缩机和涡旋压缩机,压缩机效率得以提升。转子式压缩机和涡旋式压缩机均向适应低环境温度工况的方向发展。介绍了影响这两种压缩机发展的关键技术,改进电机与压缩机的结构来提升压缩机效率,通过变压比、喷气增焓、部分负荷下调节等技术,提升了压缩机系统性能系数COP与综合部分负荷性能系数IPLV(H)。采用直流电机替代交流电机,可提高两种压缩机的电机效率和频率调节范围。通过对涡旋压缩机进行不对称涡旋盘设计,可减小噪音与泄漏量;对转子压缩机的双转子进行对称布置,增大了压缩机的容量。带排气阀的涡旋压缩机可在一定程度上实现变压缩比,而转子式压缩机有排气阀,在变工况方面具有明显的优势。两种压缩机均可采用喷气增焓技术,实现热泵低环境温度较大的压缩比。