热驱动形状记忆聚合物的本构建模方法回顾

形状记忆聚合物的本构关系对于其结构设计和力学行为的预报具有重要意义,但是目前对形状记忆聚合物本构模型的研究仍相对不多。文中通过回顾十几年来国内外对热驱动形状记忆聚合物本构模型研究的发展动态,归纳了形状记忆聚合物本构的建模方法与思想,按照流变学方法、细观力学方法以及二者相结合的方法分别加以介绍和评述,并对形状记忆聚合物本构建模今后可能面临解决的关键问题进行了预测。     

热致形状记忆聚合物的形状记忆机理与性能研究进展

主要分析了热致形状记忆聚合物聚集态结构与形状记忆性能之间的关系(聚合物的聚集态结构大致可以分为3种:可逆相和固定相均为不定形结构;可逆相为不定形结构,固定相为结晶结构;可逆相为结晶结构,固定相为不定形结构)。总结了聚集态结构对转变温度、存储模量、形状固定率/回复率、回复应力和回复速率等的影响。     

Functional Fatigue of Shape Memory Polymers

In the present study the functional fatigue in the commercial SMP Veriflex® which is associated with repeating up to 20 programming/1‐WE cycles has been examined. The material is characterized by a glass temperature T_g of 67 °C, above which it looses all its strength. During tensile testing at 21 °C (T < T_g), stresses steadily increase to 26 MPa as strains approach the rupture strain of 7.6 %. At 80 °C (T > T_g) the material can be strained up to 225 % before rupture occurs while stresses slowly increase to values as low as 0.4 MPa. Thermomechanical cycles including programming, cooling and unloading and heating to trigger the one way effect result in an increase of irreversible strain associated with a corresponding decrease of recovery ratio at the beginning of thermomechanical cycling. In parallel a wavy surface structure evolves during cycling.     

形状记忆聚合物的研究与发展

目的分析并总结近年来关于形状记忆聚合物(SMP)的研究及其在高科技领域的应用进展,并提出今后的发展趋势。方法在分析SMP形状记忆机理的基础上,较为系统地介绍SMP的制备方法和工艺,总结改性方法对SMP材料主要性能的影响,指出其在一些高科技领域的应用潜能和形状记忆生物基聚合物复合材料的发展前途。结论制备工艺是影响SMP的力学性能和记忆性能等的主要因素;采用适当的改性方法可以有效改善SMP材料的延伸性和多功能性,能够拓宽其在智能包装、航空航天、医疗器械和机器人等高科技领域的应用。     

Experimental Study on Characteristics of NiMnGaMagnetically Controlled Shape Memory Alloy

The static and dynamic magnetic controlling characteristics of NiMnGa magnetically controlled shape memory alloy （MSMA） were experimentally studied. The results show that the characteristics of induced strain with respect to the magnetic field are nonlinear with saturation nature, and dependent on the temperature as well as the load applied to the MSMA. The magnetic shape memory effect can be observed only in complete martensite phase at room temperature. The magnetic permeability of MSMA is not constant and reduces with the increment of magnetic field. The relative saturation magnetic permeability of MSMA is about 1.5.     

形状记忆聚合物热力学本构模型研究进展

形状记忆聚合物是一种新型的智能材料,与记忆合金相比它具有密度低、高恢复率、易生产和低成本等优点。由于这些特性,它广泛应用于医疗和航天等领域,其理论研究逐渐得到人们的重视。形状记忆聚合物主要通过热致变形来实现形状记忆和恢复效应,因此热力学本构模型是其材料的形状记忆和恢复功能的关键因素。文中介绍了形状记忆聚合物热力学本构模型的一些理论研究成果,并对其中存在的一些问题作了简要地讨论。     

Comparison between the Methods of Determining the Critical Stress for Initiation of Dynamic Recrystallization in 316 Stainless Steel

Several methods have been proposed to calculate the critical stress for initiation of dynamic recrystallization （σc） on the basis of mathematical methods. One＇ of them is proposed by Stewart et al. in which this critical point appears as a distinct minimum in the （-dθ/dσ vs σ） through differentiating from θ vs σ. Another one is presented by Najafizadeh and Jonas by modifying the Poliak and Jonas method. According to this method, the strain hardening rate was plotted against flow stress, and the value of σc was attained numerically from the coefficients of the third-order equation that was the best fit from the experimental θ-σ data. Hot compression tests were used in the range of 1000 to 1100℃ with strain rates of 0.01^-1 s^-1 and strain of I on 316 stainless steel. The result shows that Najafizadeh and Jonas method is simpler than the previous one, and has a good agreement with microstructures. Furthermore, the value of normalized critical stress for this steel was obtained uc=σc/σp=0.92.     

Unifying Dynamic Temperature Measurements and Methods of Determining Complete Dynamic Characteristics for Primary Standard Water-Flow Thermometers

Instruments and methods are considered for unifying dynamic measurements on water stream temperatures and the transfer of the corresponding unit to fast temperature-pulsation thermometers for water flows.     

NiTi形状记忆合金基本驱动特性

研究了预应变ＮｉＴｉ形状记忆合金的基本驱动特性，结果表明，加热和冷却过程回复力存在滞后行为；卸载过程中应力与应变具有与加热、冷却过程相关的非线性关系；卸尖力随卸载应变速率增加而降低，此外研究了预应变ＮｉＴｉ合金丝产生回复力后对外应力的响应行为。     

Shape Memory Polymers for Body Motion Energy Harvesting and Self‐Powered Mechanosensing

Growing demand in portable electronics raises a requirement to electronic devices being stretchable, deformable, and durable, for which functional polymers are ideal choices of materials. Here, the first transformable smart energy harvester and self‐powered mechanosensation sensor using shape memory polymers is demonstrated. The device is based on the mechanism of a flexible triboelectric nanogenerator using the thermally triggered shape transformation of organic materials for effectively harvesting mechanical energy. This work paves a new direction for functional polymers, especially in the field of mechanosensation for potential applications in areas such as soft robotics, biomedical devices, and wearable electronics.     

Assessment of Methods for Determining the Impurity Concentration in Mercury Cells

The uncertainty arising from chemical impurities is the principle contribution in the uncertainty budget of primary level temperature measurements. Impurities in any substance generally decrease the freezing (or triple) point temperature of a substance, and their influence is governed primarily by their behavior at low concentrations in the host material. The depression in temperature due to impurities is theoretically expressed by Raoult??s law which, at final analysis, expresses the linearity between ??T (T _observed?T _pure) and the inverse of the melted fraction (1/F). Recently, TUBITAK UME carried out a new project on the construction of new reference mercury fixed-point cells. Within the scope of this study, three different sets of mercury cells with different purity values were fabricated. Three methods were employed to assess the impurity concentration in the cells. The first method is known as the mole fraction sum of impurity components, and the chemical assays form the basis for this kind of assessment. The second method of evaluation is based on a 1/F versus ??T curve, and the slope values obtained from these curves are important. The final method is to directly compare the new cells with a national (or reference) standard mercury cell. The results obtained from three methods of evaluation showed consistency in terms of qualitative analysis.     

热致非晶态形状记忆聚合物的热粘弹性参数及回复行为

分别采用非线性拟合应力松弛主曲线及单个常频率条件下变温动态力学分析(DMA)实验中储能模量与损耗角正切曲线的方式,获取热致非晶态形状记忆聚合物(SMP)多重松弛模型中的热粘弹性参数。结合广义有限变形粘弹性理论和KAHR33参数热变形模型在有限元软件平台研究了该SMP的自由回复与约束回复行为。仿真结果与实验数据相符较好,说明该建模方法的合理性及获取的热粘弹性参数的准确性。相比构建应力松弛和储能模量主曲线而言,单个DMA实验数据更易得到,因此对其拟合能大幅减少实验成本。     

机械合金化制备形状记忆合金的研究

机械合金化技术(MA)是一种制备材料的新工艺,用它可以制备性能优越的形状记忆合金.综述了机械合金化技术在TiNi、Cu-Al-Ni、Cu-Zn-Al、Cu-Al-Nb等形状记忆合金制备上的研究状况.     

Cu－Zn－Al－Mn－Ni－Ti合金的显微组织及力学行为

本文利用电子拉伸试验、扫描电镜、金相显微镜研究了Ｃｕ－Ｚｎ－Ａｌ－Ｍｎ－Ｎｉ－Ｔｉ合金的细化效果、断裂方式、记忆性能及伪弹性。结果表明：试验合金的铸态、轧态和淬火态组织得到明显细化。晶粒细化后合金室温拉伸断裂强度为７５０ＭＰａ，断裂应变为６．６％，同未细化的Ｃｕ基记忆合金相比强度大大提高，塑性也有所改善。低温拉伸时呈穿晶断裂，断口主要为准解理台阶；高温拉伸时呈微孔聚集型断裂。试验合金的室温完全可恢复应变为４．０％，完全伪弹性恢复应变为４．５％，均达到了多晶体材料的理论平均值。     

热塑性聚氨酯/聚己内酯共混物的形状记忆和力学性能

利用简单的熔融共混制备得到不同组分比的热塑性聚氨酯(TPU)/聚己内酯(PCL)共混体系,研究了两相组分比的变化对共混材料相形态、形状记忆性能和力学性能的影响。偏光显微镜观察发现,随着结晶相PCL含量的增加,其逐渐从分散相过渡至连续相再发展为基体相。热性能测试结果表明TPU的加入对PCL的熔融行为影响甚微,整个共混体系基本表现出与PCL一致的熔点。形状记忆性能测试发现共混材料的形状记忆性能表现出明显的组分依赖性,并在组分比为50%/50%性能达到最优(R_r=91%,R_f=96%)。而力学测试结果表明,PCL的加入既不会显著劣化TPU原有的拉伸强度,还能进一步提高其断裂伸长率。