摩擦动力系统中两种非光滑现象及其算法研究

摩擦引起的振动在很多工业应用中都是很严重的问题,因此是目前国内外普遍关注的问题之一。讨论摩擦动力系统中的两类非光滑现象:stick-slip运动和碰摩现象,并对其进行比较细致的描述。采用事件驱动方法对实例进行数值分析,并与其他通用数值方法进行比较。结果指出采用方法的优越性。     

Monotonic tension behavior of 2D woven oxide/oxide ceramic matrix composites at ultra-high temperature

The research on mechanical behavior and failure analysis of oxide/oxide CMC at ultra-high temperatures can broaden its application scope. The present work studied monotonic tension behavior of the oxide/oxide CMC at 800 °C～1200 °C and two tensile rates (i.e. 5 mm/min and 0.5 mm/min). The uniaxial tensile test, fracture morphology characterization and finite element analysis were preformed to reveal the deformation and failure mechanisms of the oxide/oxide CMC at ultra-high temperature. The results show that the mechanical properties of the oxide/oxide CMC are sensitive to the temperatures and tensile rates. The stress-strain curves are almost linear at the high tensile rate and nonlinear at the low tensile rate. The ultimate tensile strength decreases significantly at low tensile rate and for temperatures higher than 1100 °C. The mechanical properties of the material are principally determined by oxide fiber/oxide matrix interface strength under low temperature and high-stress conditions, while by interlayer bonding strength under high temperature and low-stress conditions.     

缝合夹层结构复合材料树脂传递模塑成型工艺充模仿真

对复合材料与金属经缝合连接形成的夹层结构板的树脂传递模塑成型（RTM）工艺进行了充模模拟研究。首先通过实验和数值计算的方法,分别获得缝合夹层结构织物和芯层孔洞的渗透率;随后,建立能够反映缝孔内流动情况的二维和三维简化模型,进行RTM充模仿真,讨论不同工艺参数对成型流动的影响;最后通过成型实验验证工艺的可行性。缝线与孔洞直径之比为0.3~0.8时,孔洞渗透率随缝线直径的增大而减小,预制体织物渗透率与孔洞渗透率相差两个数量级;缝孔内容易产生缺陷,没有缺陷的区域随着注射压力的增加、孔洞密度和芯层厚度的减小而增大,在芯层表面沿每排孔洞单向开槽能够改善树脂在孔洞内的浸润;线注射时,树脂整体流动情况优于点注射,而点注射时,将进胶口设置在一角,能够减少表面干斑。     

非傅立叶模型层状复合陶瓷结构热传导分析

用非傅立叶热传导模型分析层状复合陶瓷结构的温度场,并与单热涂层结构的结果进行比较,同时进一步研究了夹层热物理性能参数对温度场的影响。研究表明：夹层可以有效地减缓内部结构的温度变化,夹层热物理性能参数（如：松弛时间、声速）对结构层的温度场有明显影响。     

Strength design optimization of structural steel members according to Eurocode 3

In order to design a steel member subjected to a bending moment and an axial load, there are an infinite number of possible solutions of I- or H‐steel cross-sections, the doubly-symmetric solution being just one of them. This paper presents a procedure to obtain the optimal steel cross-section from the infinite number of possible solutions. The process is based on the Reinforcement Sizing Diagrams employed in reinforced concrete strength design. The procedure looks for any type of solution regarding compact or non-compact steel sections. All aspects related to local instabilities are taken into account, as well as some special considerations in order to address the global instabilities associated with the slenderness of the steel element.     

Validation of the multiaxial racetrack amplitude filter

Amplitude filters are a most important tool in practical fatigue analyses to manage their computational cost when, as usual, the measured load history is noisy, oversampled, too long, and/or contains too many non-damaging low-amplitude cycles or events. To reduce the calculation burden, such filters should not only eliminate noise and remove redundant oversampled data from the measured signal, but also neglect small amplitudes that do not cause fatigue damage. The veteran racetrack filter can perform all such tasks efficiently, however it is limited to uniaxial load histories. Multiaxial filtering techniques have been proposed in the past, however they fail to identify the most damaging events in several non-proportional histories, in addition to losing information on the load path shape. In this work, a new, fast, and efficient multiaxial version of the traditional racetrack filter is proposed to solve these issues, synchronously filtering complex loading histories while preserving all their significant reversals and equivalent ranges, and their load path shape as well, a most important feature for multiaxial fatigue analyses. Six and three-dimensional versions of the filter are proposed, respectively for invariant-based and critical-plane damage calculation approaches. The method allows not only the proper filtering of stress/strain histories at a given material point, but also of any history of multi-dimensional quantities such as forces, moments, and/or displacements acting at different points of a structure. The filter efficiency is evaluated from tension–torsion experiments in 316L stainless steel tubular specimens with challenging non-proportional path shapes.     

Bond behavior of superelastic shape memory alloys to carbon fiber reinforced polymer composites

In this research pull-out specimens were tested to investigate the bond behavior of superelastic NiTi (Nitinol) SMA wires to carbon fiber reinforced polymers (CFRP). A total of 45 pull-out specimens were tested monotonically up to failure. The test parameters considered include the wire diameter and embedment length. A digital image correlation (DIC) system was used to identify the onset and propagation of debonding. Based on the experimental observations two debonding mechanisms were observed: complete debonding after the onset of martensitic transformation of SMA wire, and complete debonding before the onset of wire transformation. The former mechanism predominated, while the latter mechanism governed for larger diameter wires with shorter embedment lengths. A 3-D non-linear finite element model (FEM) was developed to predict the pull-out behavior. A cohesive zone model (CZM) was used to model the interface. A parametric study was conducted using the FEM to quantify the parameters of the cohesive zone model. The results demonstrate that the proposed modeling approach can be used to characterize the bond behavior of superelastic SMA wires embedded in FRP composites.     

温度作用下封装材料厚度变化对翘曲影响

主要研究在均匀温度载荷和不均匀温度载荷作用下材料厚度变化对翘曲的影响。研究表明，封装结构各种材料的不同，温度的分布也不同，翘曲的方向和数值也不同，而且均匀温度载荷作用下尺寸变化对翘曲的影响明显比不均匀温度载荷作用下的大。     

Material defects as the basis of fatigue design

Microstructural inhomogeneities can exist in metals, such as precipitates and inclusions. These can be introduced purposely to strengthen the metal matrix (e.g.: CuAl₂ in α-phase aluminium) or by faulty manufacture (e.g.: large inclusions). A major part of the history of metal fatigue has been to eliminate, or at least reduce, detrimental precipitates, inclusions and manufacture defects such as scratches, surface roughness and shrinkages in cast irons since these can initiate fatigue cracks. The deleterious nature of foreign bodies or other forms of inhomogeneities, e.g.: pores or de-bonded zones within a microstructure are related to their size, position, shape, orientation and physical properties.Small sizes of precipitates and inclusions are to be preferred to large ones; such defects being less detrimental inside a grain rather than at grain boundaries where they can simultaneously affect two or three near-neighbour grains. The orientation of a defect is dangerous should it be inclined to the future direction of Stage I and/or Stage II crack growth planes. An important duty of a metallurgist is to reduce the effectiveness of these different forms of micro-defects produced during manufacture whilst a mechanical engineer is required to derive a suitable form of fracture mechanics in order to account for their behaviour in a quantitative fatigue fracture analysis.In this paper, some important types of microstructural defects will be illustrated and discussed in terms of their size, position, shape, orientation and properties, together with their effect on the fatigue resistance of a material. This will be coupled with a fracture mechanics (FMs) approach that quantifies their behaviour in terms of their relationship to fatigue crack propagation. In this approach, the boundary condition between failure and non-failure is explored using FM as a threshold condition for a small crack coupled with the Vickers hardness HV of the material that represents the condition (ΔK_th) for the onset of micro-plasticity (yielding) required for the growth of a crack from the defect and the non-propagation behaviour of the crack.Statistical scatters of microstructures, defects and inclusions are the major factors of statistical scatters of fatigue strength and fatigue life. Directions for optimizing microstructure to improve fatigue strength are explained from the viewpoint of equality control based on the statistics of extremes of defects and inclusions.A new efficient and reliable inclusion rating method for high strength steels based on the statistics of extremes using the phenomenon of hydrogen embrittlement is proposed.     

Fibrous composite matrix characterisation using nanoindentation: The effect of fibre constraint and the evolution from bulk to in-situ matrix properties

The variation of the in-situ matrix properties of a carbon-fibre composite has been investigated using nanoindentation. The aerospace carbon-fibre composite material (HTA/6376) and the bulk matrix (6376) have been co-cured to produce specimens ideal for matrix characterisation. The in-situ matrix has been characterised using fifty indentations in matrix pockets of many different sizes. The fibre constraint effect on in-situ matrix indentations has been characterised experimentally using the continuous stiffness measurement (CSM) technique, showing good correlation with finite element results from a previous study. The co-cured specimens allow the evolution of property change in the matrix material to be observed. The in-situ matrix modulus increases with decreasing matrix pocket size, and is up to 19% greater than the bulk matrix. This property change occurs outside the normal range of the interphase region for CFRP materials, and is statistically significant relative to the experimental scatter associated with the nanoindentation technique.