双轴拉伸下高聚物的时间-应力等效原理试验研究

时间-应力等效原理(TSSP)能有效简化高聚物的黏弹性本构模型和力学性能测试。以往研究主要集中在单向应力状态,但工程构件通常处于双向或三向复杂应力状态。为此,首先利用有限元方法对双轴十字型试样进行合理设计与优化,使试样中心测试区的应力和应变基本满足均匀分布,并依此加工出硅橡胶试样。然后,对硅橡胶试样进行不同应力水平及应力比的双轴蠕变试验,获得一系列短期蠕变试验曲线。基于柯西应力和左柯西-格林变形张量定义合适的应力度量和变形度量以探讨双轴拉伸下的TSSP。按照主曲线移位方法,将不同应力水平下的短期性能曲线沿对数时间轴移位构建出宽广时域的主曲线。利用应力移位因子方程对移位结果进行非线性回归分析,获得相应的方程参数。研究结果可为复杂应力状态下黏弹性高聚物的长期力学性能加速表征和长期寿命预估提供理论基础和重要参考。     

环糊精-高聚物超分子类生物材料的研究进展

系统地综述了近年来有关环糊精和高聚物形成的包合物的相关研究现状.着重从生物材料研究的角度对环糊精-高聚物超分子的制备方法、包合物的特殊性质、表征方法和应用领域进行分析.     

高聚物/金属界面微观的表征方法

为了提高胶粘剂、有机涂层、缓蚀剂的性能,了解高聚物/金属界面的结构和性能是非常必要的.目前常用的表征表面的方法直接测定界面层结构尚有困难,因为界面层不能孤立出来直接研究.着重介绍了与有机膜层/金属粘接界面相关的表征方法.衰减全反射红外光谱(ATR-IR)不仅能分析高聚物表面结构信息,还可分析不透明的材料表层及含水材料信息.反射吸收红外光谱(RA-IR)则对研究金属表面涂层分子取向、金属表面化学反应比较有效.X射线光电子能谱(XPS)能较好地表征金属与高聚物间的相互作用.拉曼光谱法与电化学方法相结合可以原位表征金属表面在分子水平上的信息.通过比较认为FTIR与XPS相结合是相对理想的表征界面的方法.     

海藻酸钠/聚乙烯醇共混膜的制备及表征

用溶液共混法制备海藻酸钠/聚乙烯醇(SA/PVA)共混膜,并对其进行了IR、DSC表征和吸水率、透气率、力学性能等测定.结果表明,在这种由两种可生物降解的高聚物共混而成的共混膜中,PVA与SA分子链间有一定的相互作用,相容性好;共混膜有较高的抗水性和较好的综合力学性能.     

材料前沿测试表征技术及其在船舶材料领域的应用展望

材料测试表征技术是了解材料宏观和微观特征、剖析材料科学问题、进行材料应用评价的基础,测试表征技术的发展极大地加速了材料科学重大发现和重要理论创新的进程,密切跟踪测试表征技术前沿动态并尝试在科研生产中加以运用是材料研究的主要创新途径。通过了解材料基础研究和工程应用所关注的关键性能特征(如力学性能、化学成分、微观特征、疲劳性能、腐蚀性能等)的测试表征技术的发展现状,并分析前沿测试表征技术在船舶材料中的应用前景,为船舶领域的材料研制和工程应用研究提供参考。     

非线性粘弹性高分子材料长期蠕变行为的加速测试技术

时间-温度-应力等效原理是时间-温度等效原理的延伸,可用于材料力学行为的加速表征,通过短期实验来预测材料的长期力学性能。针对PMMA试件在不同温度、不同应力水平条件下的蠕变实验,分析PMMA蠕变行为的非线性特性。本文应用时间-温度-应力等效原理,得到相应的温度移位因子、应力移位因子和温度-应力联合移位因子,构建了参考温度和参考应力水平条件下的蠕变柔量主曲线。理论和数值计算表明,较高温度和应力水平下的PMMA短期蠕变实验可用于预测其在较低温度和应力水平下的长期蠕变行为。     

紫外光辐照对羊毛结构与性能的影响

运用紫外光辐照的方法对羊毛纤维表面进行处理,采用场发射扫描电镜(SEM)、X射线衍射仪对样品的形貌和结构进行了表征,并测试了样品的力学性能和色差.结果表明,随着辐照时间的延长,羊毛纤维的失重严重,表面刻蚀、糙化程度增大,结晶度和力学性能下降,泛黄加重.     

聚合物注塑成型内应力数值计算的非线性模型

为了提高注塑内应力计算的可靠性,利用粘弹性力学理论建立了新的注塑制品内应力计算的四元件串联力学模型,并推导了其瞬态粘弹性响应的非线性本构方程.通过求解流动及保压控制方程,得到内应力计算所需的温度场和压力场,利用回归分析得到了聚合物弹性模量和粘壶系数的计算公式.用新模型对PS平板注塑制件脱模前的内应力进行了模拟计算.计算结果与固体高聚物的结构和力学性能的相关研究结论相一致.     

一个高聚物多相系显微结构强化材料体系的设计初探

通过分析和控制高聚物熔体在流行和凝固过程中的相态变化，理论预测预报了材料的力学性能，并实现了高聚物多相系显微结构强化材料的理论设计。     

MPS程序研究

本文用高斯-柯西复合函数表征高聚物X射线衍射晶态峰,用四种类型函数表征高聚物X射线散射非晶态峰。据此,编写了四种类型高聚物非晶态相干散射峰的拟合子程序,以及四种类型半结晶高聚物X射线衍射重叠谱图的分峰子程序。用“阻尼最小二乘法”求解评价函数极小值,从而计算出各单峰参数。并对所编MPS程序进行了讨论。     

Material Mechanical Properties Necessary for the Structural Intervention of Concrete Structures

Structural intervention involves the restoration and/or upgrading of the mechanical performances of structures. In addition to concrete and steel, which are typical materials for concrete structures, various fiber-reinforced polymers (FRPs), cementitious materials with fibers, polymers, and adhesives are often applied for structural intervention. In order to predict structural performance, it is necessary to develop a generic method that is applicable to not only to steel, but also to other materials. Such a generic model could provide information on the mechanical properties required to improve the structural performance. External bonding, which is a typical scheme for structural intervention, is not applied for new structures. It is necessary to clarify material properties and structural details in order to achieve better bonding strength at the interface between the substrate concrete and an externally bonded material. This paper presents the mechanical properties of substrate concrete and relevant intervention material for the following purposes: ① to achieve better shear strength and ultimate deformation of a member after structural intervention; and ② to achieve better debonding strength for external bonding. This paper concludes that some of the mechanical properties and structural details for intervention materials that are necessary for improvement in mechanical performance in structures with structural intervention are new, and differ from those of structures without intervention. For example, high strength and stiffness are important properties for materials in structures without structural intervention, whereas high fracturing strain and low stiffness are important properties for structural intervention materials.     

Impact of time-dependency on long-term material testing and modeling of polyethylene

Ultra-high molecular weight polyethylene (UHMWPE) has an important role in orthopaedic implants because of its favorable properties as an articulating surface. UHMWPE component testing often focuses on measuring the long-term fatigue or wear response of the material that could be realized during many years of use. However, the impact of time-dependent properties of UHMWPE on such tests is not well characterized. In particular, altering the frequency of loading and allowing for material creep or relaxation can significantly alter the stress/strain state of the material, and therefore affect long-term mechanical properties (e.g. wear, fatigue) that are dependent on the constitutive state. The goal of this work is to use advanced, validated material modeling of UHMPWE that incorporates time-dependent properties to explore the effects of frequency and rest time on the mechanical response of UHMWPE.     

Wood as a bioinspiring material

Wood is one of the natural materials that inspired mankind very early to imitate some of its features to develop new “intelligent” artificial materials. The properties of wood are optimized in various respects and in various areas. It exhibits, for example, excellent mechanical properties together with low density, and both are determined by its structural design. In the present paper, the effects of structural features of wood on selected mechanical properties and especially fracture properties are discussed. Some examples of how man-made materials are tailored by mimicking wood's intriguing optimization principles are provided.     

航天结构材料低温力学性能测试技术

概述了航天结构材料在深温条件下的力学,物理特性及深低温和学性能研究的内容和特点,强调了液氢温度介质条件下,结构材料力学行为的特殊性。介绍了国内外液氢介质条件下力学性能测试技术。     

Hybrid composites based on polyethylene and carbon fibres Part 2: influence of composition and adhesion level of polyethylene fibres on mechanical properties

Combining high performance polyethylene (HP-PE) and carbon fibres as reinforcing elements in so-called hybrid composite structures results in a unique class of structural materials possessing high damping and impact resistance. Mechanical properties of unidirectional HP-PE/carbon-epoxy hybrids have been studied, emphasizing basic mechanical characterization such as tensile, compressive and shear strength, initial as well as long-term modulus, vibrational damping and impact response. This paper describes the influence of overall composition and adhesion level of the HP-PE fibres on the mechanical properties of such hybrids.     

泡沫金属多向承载行为的研究意义

泡沫金属具有优良的物理性能和综合力学性能,在很多场合都可用作轻质结构材料.在简要介绍该类材料用途的基础上,指出了多向载荷研究对于泡沫金属应用的实际意义,分析了以往工作在该类材料力学性能研究方面的不足,以期推进相关领域的研究者在该方面的突破.在此基础上,提出了一条研究该类材料在多向载荷作用下有关数理关系的思路.     

Structurally Controlled Cellular Architectures for High‐Performance Ultra‐Lightweight Materials

The design and synthesis of cellular structured materials are of both scientific and technological importance since they can impart remarkably improved material properties such as low density, high mechanical strength, and adjustable surface functionality compared to their bulk counterparts. Although reducing the density of porous structures would generally result in reductions in mechanical properties, this challenge can be addressed by introducing a structural hierarchy and using mechanically reinforced constituent materials. Thus, precise control over several design factors in structuring, including the type of constituent, symmetry of architectures, and dimension of the unit cells, is extremely important for maximizing the targeted performance. The feasibility of lightweight materials for advanced applications is broadly explored due to recent advances in synthetic approaches for different types of cellular architectures. Here, an overview of the development of lightweight cellular materials according to the structural interconnectivity and randomness of the internal pores is provided. Starting from a fundamental study on how material density is associated with mechanical performance, the resulting structural and mechanical properties of cellular materials are investigated for potential applications such as energy/mass absorption and electrical and thermal management. Finally, current challenges and perspectives on high‐performance ultra‐lightweight materials potentially implementable by well‐controlled cellular architectures are discussed.     

Time-dependent response of active composites with thermal, electrical, and mechanical coupling effect

The mechanical and physical properties of materials change with time. This change can be due to the dissipative characteristic of materials like in viscoelastic bodies and/or due to hostile environmental conditions and electromagnetic fields. We study time-dependent response of active fiber reinforced polymer composites, where the polymer constituent undergoes different viscoelastic deformations at different temperatures, and the electro-mechanical and piezoelectric properties of the active fiber vary with temperatures. A micromechanical model is formulated for predicting effective time-dependent response in active fiber composites with thermal, electrical, and mechanical coupling effects. In this micromechanical model limited information on the local field variables in the fiber and matrix constituents can be incorporated in predicting overall performance of active composites. We compare the time-dependent response of active composites determined from the micromechanical model with those obtained by analyzing the composites with microstructural details. Finite element (FE) is used to analyze the composite with microstructural details which allows quantifying variations of field variables in the constituents of the active composites.     

Structural nanocrystalline materials: an overview

This paper presents a brief overview of the field of structural nanocrystalline materials. These are materials in either bulk, coating, or thin film form whose function is for structural applications. The major processing methods for production of bulk nanocrystalline materials are reviewed. These methods include inert gas condensation, chemical reaction methods, electrodeposition, mechanical attrition, and severe plastic deformation. The stability of the nanocrystalline microstructure is discussed in terms of strategies for retardation of grain growth. Selected mechanical properties of nanocrystalline materials are described; specifically strength and ductility. Corrosion resistance is briefly addressed. Examples of present or potential applications for structural nanocrystalline materials are given.     

Structural Design Elements in Biological Materials: Application to Bioinspiration

Eight structural elements in biological materials are identified as the most common amongst a variety of animal taxa. These are proposed as a new paradigm in the field of biological materials science as they can serve as a toolbox for rationalizing the complex mechanical behavior of structural biological materials and for systematizing the development of bioinspired designs for structural applications. They are employed to improve the mechanical properties, namely strength, wear resistance, stiffness, flexibility, fracture toughness, and energy absorption of different biological materials for a variety of functions (e.g., body support, joint movement, impact protection, weight reduction). The structural elements identified are: fibrous, helical, gradient, layered, tubular, cellular, suture, and overlapping. For each of the structural design elements, critical design parameters are presented along with constitutive equations with a focus on mechanical properties. Additionally, example organisms from varying biological classes are presented for each case to display the wide variety of environments where each of these elements is present. Examples of current bioinspired materials are also introduced for each element.