PMMA变温松弛模量获取方法的实验研究

聚甲基丙烯酸甲酯(PMMA)在不同温度条件下进行拉伸应力松弛实验,获取了恒温条件下的松弛模量曲线,并对其进行温度修正,建立折合模量-时间对数曲线图。利用最小二乘法平移原理计算出时温等效因子,确立WLF方程参数。对其参考温度下的松弛模量进行了基于Prony级数的拟合,建立了材料Wiechert黏弹性参数模型,且实验结果与仿真结果吻合性比较好,为后续的数值仿真和实验研究提供了理论的指导作用。     

模内微装配成型二次充填熔体应力松弛特性研究

模内微装配成型二次充填熔体的冷却收缩自紧特性是保证界面可运动性能的关键影响因素,聚合物材料的应力松弛特性可以使微装配界面上的收缩自紧压力逐渐恢复。以线性黏弹性力学理论为基础,Prony级数形式描述黏弹性积分核函数,对模内组装成型低密度聚乙烯(LDPE)/不锈钢(STEEL)运动副界面收缩自紧应力松弛进行了研究。研究表明,以结构单元所采用的Prony级数形式适用于模拟运动副界面收缩自紧的应力松弛现象;同时经应力松弛后,运动副界面收缩自紧力呈现下降趋势,下降程度高达60%左右。     

隔振橡胶材料基于简单应变模式的 蠕变特性研究

对隔振橡胶材料的单轴拉伸应力松弛试验数据进行归一化处理,应用Prony级数模型对其应力松弛试验数据进行拟合,获得对应的粘弹本构参数。将表征粘弹特性的Prony级数因子引入Ogden超弹本构方程,获得隔振橡胶材料基于时间效应的本构方程,进而分析单轴拉伸、双轴拉伸和平面拉伸模式的蠕变特性,最后采用沙漏弹簧进行蠕变仿真与试验验证。该蠕变仿真预测方法为隔振橡胶材料的粘弹试验、蠕变计算和工程应用提供一种新思路。     

PE80聚乙烯管道焊接接头的应力松弛模型验证及安全评价

采用实验方法研究聚乙烯（PE）管道焊接接头在机械载荷条件下的应力松弛行为,通过松弛试验得出用Prony级数表示的PE管道焊接接头的本构模型。结果表明,PE管道焊接接头的松弛曲线与PE管道木材的松弛曲线相似;结合有限元分析软件Abaqus,建立PE80焊接接头的裂纹缺陷模型,导入PE管道焊接接头与PE管道母材的Prony级数,对含裂纹缺陷PE管道的应力强度因子进行计算;借鉴GB/T 19624—2004金属管道的评定标准,给出适合PE材料的断裂判据,比较PE材料的临界应力强度因子（KIC）及计算得出的应力强度因子(KI)的大小,进而通过断裂判据对含缺陷PE管道进行安全评价。     

各向异性导电胶应力松弛力学行为

对固化后的各向异性导电胶（ACF）,利用动态力学分析仪进行了单频和多频温度扫描试验,确定了ACF的玻璃化转变温度,得到玻璃化转变温度与频率的关系式.在不同温度和应变下进行了应力松弛实验,实验发现：在一定（25、80、120℃）的温度下,随着应变值的增加,初始应力和在任一时刻的松弛应力都增加;随着温度的提高,应力松弛的松弛率在增加,并且在不同应变下的松弛曲线变得接近;当温度达到玻璃化转变温度附近时,ACF的应力松弛曲线与应变无关.并进行了湿热老化对ACF应力松弛力学行为的实验研究.     

EPDM发泡材料应力松弛行为的数值模拟

利用两种发泡加工工艺,在相同EPDM橡胶基本配方基础上调节发泡剂用量,制备出四种密度不同的发泡材料.通过单轴压缩实验得到了EPDM发泡材料的应力松弛数据,采用理论推演建立的四单元变参数Maxwell模型,模拟EPDM发泡材料的应力松弛行为,拟合结果表明不同发泡程度的橡胶基材,其应力松弛时间和表观松弛强度略有差别,而气体...     

聚碳酸酯的应力松弛实验及数据处理分析

以黏弹性力学理论为基础,选用广义Maxwell模型作为聚碳酸酯(PC)黏弹性的力学模型。在120℃温度场下以不同的初始应变进行应力松弛试验,得到应力松弛过程中作用力与时间的实验数据。利用ABAQUS软件拟合得出不同初始应变下的黏弹性模型的prony参数,再结合Origin软件优化得出广义Maxwell黏弹性模型在参考温度为120℃时的普适prony级数参数,来供ABAQUS调用分析,为有限元仿真分析奠定理论基础。     

FRP筋应力松弛试样端部锚夹方法研究

将FRP筋作为预应力筋使用,必须了解其应力松弛特性.要测定FRP筋的应力松弛特性,关键是要找到一种有效的试样端部锚固方法.FRP筋一般的锚具系统应用于松弛特性测试时存在这样或那样的缺陷,为此本文提出了一种创新的测试FRP筋应力松弛特性的试样端部加强锚固的方法,实现了松弛试验时端部近似为零的滑移,保证了试验段应变的恒定,从而可准确测定FRP筋的应力松弛性能.     

浮法玻璃退火过程中应力变化的数值模拟

浮法玻璃内部在退火过程中产生的应力是应力松弛和结构弛豫共同作用的结果.基于粘弹性理论,采用波尔兹曼叠加原理,并考虑应力松弛和结构弛豫两种因素影响的应力本构方程是一组复杂的积分方程.利用梯形积分法、拉格朗日差值函数并采用离散化的方法可以对其进行数值模拟求解.计算结果同实验数据的吻合度较好,为浮法玻璃退火过程中应力离线实验仿真计算或在线控制运用提供了一种解决方案.     

金属波齿柔性石墨复合垫片蠕变-应力松弛性能研究

垫片的蠕变-应力松弛特性对螺栓法兰密封连接系统的可靠性有显著的影响.作者按照GB/T19066.3的实验条件对标准规格为D 65.5 mm×50.5 mm×2.5mm 3种不同几何尺寸的金属（06Cr19Ni10＋柔性石墨）波齿复合垫片进行蠕变-应力松弛实验研究,从而找出应力松弛特性影响因素及其规律,为工程实践提供科学指导.     

Mechanical characterization and modeling stress relaxation behavior of acrylic–polyurethane-based graft-interpenetrating polymer networks

The stress relaxation behavior of acrylic–polyurethane (PU)-based graft-interpenetrating polymer networks (IPNs) was characterized via dynamic mechanical analysis (DMA) and modeled using finite element method (FEM) analysis. Stress relaxation of glassy IPN specimens was experimentally studied under flexural testing, while rubbery IPN specimens were tested in tension. The effects of varying the styrene content in the acrylic copolymer phase, compatibility of the two phases in IPNs, and changing the concentration of acrylic copolymer and PU were studied. A higher percentage of styrene content resulted in higher homogeneity of IPN specimens, and decrease in initial modulus for acrylic copolymer specimens. Additionally, glassy IPN specimens with 90% styrene shows resistance to relaxation as high as acrylic copolymer samples. Experimental results were used to develop a numerical model to study stress relaxation response of specimens. While polymer systems have been studied computationally, numerical modeling of IPN systems is still in its infancy. A three-dimensional FEM model was developed using the Generalized Maxwell model and four-term Prony series constants, which were extracted from the stress relaxation experiments. With four terms in the Prony series, a good match was observed between experimental observations and results from the FEM model.     

Linear viscoelastic properties of HFPE‐II‐52 polyimide

The polyimide HFPE‐II‐52 was developed at NASA Glenn Research Center for use as a matrix in high temperature composite materials. The unique properties of such composites stem largely from the performance of the matrix at high temperature. Thus, as part of a larger effort to study high temperature composite materials, the linear viscoelastic properties of HFPE are measured and a mathematical model of the properties is developed. In particular, storage, loss, and stress relaxation moduli were obtained from cyclic and transient loading experiments. A Prony series was fit to the relaxation modulus data. As a cross check, the fit to the relaxation modulus was converted to storage and loss moduli and compared with those measured directly. Effects of postcuring and of moisture on the properties are investigated as well. These results provide researchers with a constitutive model for HFPE‐II‐52 and provide some insight into the performance of HFPE matrix composites at high temperatures. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3255–3263, 2006     

A continuous test data method to determine a reference curve and shift rate for isothermal physical aging

The mechanical response of a material undergoing isothermal physical aging is governed by a reference curve (typically time-dependent modulus or compliance) and a shift rate (which describes the rate of aging). In the standard analysis approach, these parameters are determined from a series of load/unload creep or relaxation tests, in which only the load portion data is used for property evaluation. In this paper, a new continuous test data (CTD) method is presented to determine these parameters using both the load and unload data from such a test series. This is accomplished by employing effective time theory to predict the full load/unload data set, with the reference curve and shift rate obtained as those which best fit the experimental data. It is demonstrated that the references curve obtained via the standard approach is not capable of predicting the full load/unload data set, while the CTD method using a Prony series fits this same data very well. Several concerns regarding the CTD method are addressed, including the differences in the CTD and standard method shift rate, the effect of vertical shifting or material nonlinearity on the results, and application of the method to other loading scenarios. Results are presented for long-term and variable stress tests. The data used in the study was obtained from polyimide resin and polyimide/carbon fiber composite specimens at several temperatures below T_g.     

Improved models of viscosity and relaxation modulus for epoxy resin during cure

In this work, epoxy resin viscosity was calculated by using reference viscosity and “viscosity‐cure” shift factor which was established to research the dependence of viscosity on curing degree. The predicted results were compared with experimental data and the agreements between them were better than those in reference. Generalized Maxwell model was used to characterize the viscoelastic behavior of epoxy resin and the relaxation modulus was modeled by Prony series. A simple model of stress relaxation times was derived as functions of viscosity and stiffness. The stress relaxation times at different curing degrees were calculated after acquiring the stress relaxation times at the reference curing degree. The relaxation modulus predicted by this method agreed well with experimental data. The above results showed that these models could well be used to predict the viscosity and relaxation modulus of thermosetting resin during cure. POLYM. ENG. SCI., 56:617–621, 2016. © 2016 Society of Plastics Engineers     

复合固体推进剂在石灰石矿山深孔爆破中的应用

通过前期对石灰石矿山露天深孔爆破技术的了解和考察,首次将复合固体推进剂余药应用于石灰石矿山爆破工程,基于原有使用炸药的设计方法,结合现场情况,针对复合固体推进剂设计了一套爆破方案,并不断优化爆破参数,爆破结果表明,复合固体推进剂能够很好的满足石灰石矿山露天深孔爆破的要求,解决了长期以来以焚烧方式进行复合固体推进剂余药的销毁工作,为复合固体推进剂余药的销毁提供了一条新途径。     

HTPB推进剂贮存老化建模及寿命预估研究综述

HTPB复合固体推进剂是火箭发动机的动力之源,其贮存寿命和性能优劣决定了火箭发动机的寿命和作战性能的发挥,因而研究HTPB复合固体推进剂的贮存老化模型及寿命预估具有重要的军事和经济意义。本文对复合固体推进剂贮存老化性能的研究方法进行了介绍,并综述了国内外贮存寿命老化建模的研究进展,针对推进剂实际贮存可能出现的问题对未来贮存寿命预估的发展趋势进行了预测。研究结果表明,现代仪器的运用可以弥补传统仪器在固体推进剂老化性能研究上的不足,但是还存在研究手段单一、测试方法存在误差、没有形成统一的系统等缺点;推进剂的老化过程比较复杂,结构完整性分析和老化试验相结合的方法可以对推进剂贮存性能和寿命预估进行系统性的研究,得到的结果更准确,可靠性更高。分段老化建模作为推进剂寿命预估研究的新方向,具有很大的发展空间。     

Applying modified hyperbranched polyester in hydroxyl‐terminated polyether/ammonium perchlorate/aluminium/cyclotrimethylenetrinitramine (HTPE/AP/Al/RDX) composite solid propellant

Composite solid propellants demand fine and stable mechanical properties, creep resistance and stress relaxation performance during their long storage and usage time. In this study, modified hyperbranched polyester (MHBPE) was prepared and introduced into HTPE/AP/Al/RDX (HTPE, hydroxyl‐terminated polyether; AP, ammonium perchlorate; RDX, cyclotrimethylenetrinitramine) solid propellant as an effective additive. The static tensile and dynamic mechanical properties of this propellant before and after the introduction of MHBPE were evaluated. The elevated interfacial interaction by using MHBPE between the binder and RDX fillers improved the toughness and elasticity of the propellant. The enhancement mechanisms were also confirmed by the influence on the fracture surface morphology of the binder which was investigated by SEM. In addition, some influence on the dynamic mechanical properties of HTPE/AP/Al/RDX propellant caused by MHBPE was investigated by dynamic mechanical analysis. The creep behaviors of the HTPE/AP/Al/RDX propellants with and without MHBPE were also investigated at different stresses and temperatures. Reduced creep strain rate and strain were obtained for the modified propellant, implying enhanced creep resistance performance. The creep properties were quantitatively evaluated using a six‐element model and the long‐term creep performance of the propellant was predicted using the time–temperature superposition principle. A creep behavior of nearly 10⁶ s at 30 °C could be acquired in a short‐term experiment (800 s) at 30–70 °C. Moreover, the stress relaxation investigation of the propellants with and without MHBPE at ?40 °C, 20 °C and 70 °C suggested that MHBPE/HTPE/AP/Al/RDX propellant possessed better response ability to deformation. Thus, the application of MHBPE provides an efficient route of reinforcement to enhance the creep resistance and stress relaxation properties. © 2020 Society of Chemical Industry     

丁羟复合推进剂的辐射点火

采用CO2激光点火装置,对丁羟复合推进剂的点火过程进行了实验研究,利用描述固体推进剂物化现象的一维传热模型对复合推进剂的辐射点火特性进行了理论分析。通过最小二乘法拟合实验数据得到了丁羟复合推进剂的点火准则。结果表明,丁羟复合推进剂的点火过程主要包括惰性加热及气相点火过程,惰性加热时间和点火延迟时间随热流密度的增大而减小,且随着热流密度的增大,热流密度的影响逐渐降低。固相传热数学模型能够比较准确地描述复合推进剂的辐射点火特性。     

固体推进剂体积模量试验研究

采用非接触测量体积模量系统,测出了复合固体推进剂在不同温度下的体积松驰模量和体积蠕变柔量,并依据时间—温度等效原理迭加拟合求得了体积模量主曲线和温度移动因子的数学表达式,其结果可为发动机药柱结构完整性分析提供依据。     

Linear Hygrothermal Viscoelastic Characterization of Nafion NRE 211 Proton Exchange Membrane

The tensile relaxation modulus of a commercially available proton exchange membrane, Nafion® NRE 211, was obtained over a range of humidity levels and temperatures using a commercial dynamic mechanical analyzer (DMA). Hygral stress relaxation master curves were first constructed, followed by a hygrothermal master curve using the time temperature moisture superposition principle. The hygrothermal master curve was fitted using a 10‐term Prony series and validated using longer term stress relaxation tests. To validate the results from the stress relaxation experiments, short and long‐term creep compliance was converted into stress relaxation modulus using a well‐known viscoelastic conversion formula, and compared with the relaxation modulus obtained under identical conditions. Good agreement was found between the two datasets. It was evident that relaxation data at 2% RH at the test temperatures was not superposable with the master curves obtained at higher relative humidity (10% < RH < 90%) at the temperature range 70 °C < T < 90 °C. It was observed that the longer term relaxation modulus under humid conditions matched well with the hygrothermal master curve; however, the longer term relaxation modulus under dry conditions was significantly higher than the relaxation master curve obtained under dry conditions, raising the possibility of a physical aging process in the ionomer and/or irreversible morphological changes in the membrane under dry conditions.