GAP-ETPE基高能固体推进剂的蠕变性能

为研究GAP-ETPE基固体推进剂的蠕变性能,通过压延工艺制备了GAP-ETPE/Al/RDX/AP/GAPA高能固体推进剂,分析了加载应力、环境温度对推进剂蠕变性质的影响;使用Matlab软件对GAP-ETPE基推进剂在不同加载应力、不同环境温度下的数据进行拟合,对其长期蠕变行为进行预测。结果表明,推进剂的蠕变应变、残余应变随加载应力和温度的增加而增大,室温及1.4MPa加载应力下蠕变应变为4.9%;56℃及0.5MPa加载应力下蠕变应变为4.0%;恒定蠕变速率随加载应力增加显著增大,但是在加工温度附近出现了极值点;对比发现GAP-ETPE基推进剂的抗蠕变性能优于常见的热固性推进剂;广义的Kelvin模型对各组蠕变数据的拟合程度达到0.995以上,能够很好地描述GAP-ETPE基推进剂的蠕变行为;建立的蠕变柔量主曲线将考察时间扩展到10^8.1s,可用于GAP-ETPE基推进剂蠕变性能的长期预测及实际应用。     

PEEK复合材料高温蠕变性能研究

对3种不同的聚醚醚酮( PEEK)复合材料进行高温蠕变实验研究,根据蠕变曲线和蠕变速率曲线获得了不同PEEK复合材料的抗蠕变能力,探讨了不同PEEK复合材料的蠕变机理.     

Al2O3f/Mg-6Al-0.5Nd-1Gd复合材料的高温压缩蠕变行为研究

研究了Al_2O_(3f)/Mg-6Al-0.5Nd-1Gd复合材料的高温蠕变行为。结果表明:随着蠕变温度由483K升高到513K,外加应力从60MPa增大到90MPa,复合材料的稳态蠕变速率增加,压缩蠕变性能变差;复合材料的蠕变行为主要受到位错攀移控制;复合材料中由于Al_2O_3短纤维增强相的添加,提高了材料的蠕变表观激活能Q_c和蠕变表观应力指数n;复合材料在载荷恒定时,随着蠕变温度由483K提高到513K,复合材料材料的蠕变门槛应力由57.2MPa降低为32.3MPa。     

高密度聚乙烯的应力-光氧老化开裂研究

通过显微镜观察、蠕变量测定、凝胶含量测定、表面全反射红外光谱分析的手段研究了高密度聚乙烯(HDPE)的应力-光氧老化开裂行为。实验结果表明,HDPE的老化开裂主要与表面辐照层的性能恶化和样条的蠕变有关,而应力对表面层的光氧老化进程无明显影响。样品的开裂时间随应力的增加而减小,与施加应力呈反S曲线关系,在7 MPa附近存在一个临界应力,该处开裂时间的减小速率最大,该临界应力与蠕变密切相关,是样条蠕变的分界点,在此之前,材料的蠕变速率相对较慢,样条的尺寸稳定性较好,样条应变10%,在此之后,样条的应变迅速增加至700%~800%,甚至超过1 000%。     

羽绒棉纤维的性能测试及其静态热性能研究

测试了羽绒棉纤维(细旦涤纶)的直径、纤度、强力,分析了纤维的应力松弛和蠕变性能对时间的依赖性及定伸长变形性,比较了其与木棉纤维的静态热性能,结果表明:羽绒棉纤维纤度平均值为0.8 dtex;60 s内应力松弛和蠕变率增加,对时间依赖性强;羽绒棉纤维的塑性变形率高;与木棉纤维相比,羽绒棉纤维在较高温度区域的导热性比木棉纤维的好,而降温速率明显低于木棉纤维。     

疲劳／蠕变复合作用下聚碳酸酯的时温等效关系

研究了疲劳／蠕变复合作用下聚碳酸酯的时温等效关系。试验条件随加载最大应力、最大应力保持时间和温度而变化，但是都得到一致的试验结果：随最大应力保持时问延长或试验温度升高，聚碳酸酯断裂寿命下降；最大应力保持时间t-断裂寿命Nf的关系曲线与试验温度T-断裂寿命Nf关系曲线十分相似；疲劳／蠕变复合作用下的聚碳酸酯时温等效关系仍然适用。     

与应用疲劳与蠕变复合作用下聚碳酸酯的断裂行为

研究了疲劳／蠕变复合作用下聚碳酸酯(PC)的断裂行为。研究表明：其疲劳／蠕变曲线与纯蠕变曲线十分相似。在疲劳—蠕变复合作用下，随施加最大载荷的保持时间越短，即蠕变载荷比例越小，疲劳载荷比例越大，PC结束普弹应变阶段的应变越小，延迟弹性变形的平台应变也减小。每一次循环中的最大载荷加载保持时间延长，PC断裂寿命减小。以最大载荷为恒载荷一直加载的纯蠕变曲线，平台最高，断裂时间最早；而最大载荷加载作用时间t＝0的纯疲劳曲线，平台最低，断裂时间最迟。     

疲劳/蠕变复合作用下聚苯乙烯的时温等效关系

研究了疲劳／蠕变复合作用下聚苯乙烯的时温效关系。试验条件加载最大应力，最大应力保持时间和温度而变化，但是都得到一致的试验结果：即随最大应力保持时间的延长或试验温度的升高，聚苯乙烯的断裂寿命下降；最大应力保持时间t和断裂寿命Nf的关系曲线与试验温度T和断裂寿命Nf的关系曲线十分相似；疲劳／蠕变复合作用下的聚苯乙烯，时温等效关系仍然适用。     

基于十字交叉法的陶瓷胶粘剂剪切蠕变性能研究

本研究设计了“十字交叉法”陶瓷胶粘剂剪切蠕变试验装置,选取刚性环氧树脂及柔性硅酮结构胶进行剪切蠕变试验,研究了环境温度、剪切应力、粘结面积等因素对胶粘剂剪切蠕变的影响,通过模型拟合对胶粘剂的剪切蠕变行为进行了分析和预测,探究了两种胶粘剂的蠕变破坏模式。结果表明:采用十字交叉法能够准确便捷地测试陶瓷胶粘剂的蠕变性能。增大胶粘层柔性、提高环境温度、增大剪切应力都会加速蠕变的发展,但粘结面积对蠕变速率无明显影响。刚性环氧树脂胶粘剂试样的蠕变失效形式为粘结层内聚破坏及界面脱粘,符合时间硬化模型;柔性硅酮结构胶试样失效形式为粘结层内聚破坏,符合Burgers模型。     

超高相对分子质量聚乙烯长丝蠕变性能的研究

通过悬挂重物一定时间后测试纤维蠕变伸长和用蠕变仪直接测量的方法分别测试了超高相对分子质量聚乙烯长丝和高强涤纶工业丝这两种高强纤维的蠕变性能。从试验中得出超高相对分子质量聚乙烯长丝具有比高强涤纶工业丝更高的断裂强度和弹性模量。两种纤维随悬挂重物时间的延长及重物重量的增加,其断裂强力总体上呈下降趋势,但程度不同。悬挂重物相同时间下,超高相对分子质量聚乙烯长丝伸长较高强涤纶工业丝小,且其形变在外力撤除后难以恢复,产生较大塑性变形,大大影响其力学性能。     

涤纶低弹网络丝拉伸断裂性能表征

研究在不同的夹持距离、不同拉伸速率条件下涤纶低弹网络丝机械性能 ,从实验结果得知 ,在相同拉伸速率下 ,断裂强力随夹持距离的增加呈对数关系减少。在相同夹持距离下 ,随着拉伸速率的提高 ,平均断裂强力提高 ,断裂伸长增大 ,断裂比功也增大。     

Short term flexural creep behavior of wood-fiber/polypropylene composites

Short term flexural creep tests were conducted to investigate the creep behavior of wood-fiber polypropylene composites. Three experimental parameters were selected: the addition of a wetting agent, temperature, and wood-fiber concentration. All creep curves are presented in terms of relative creep as a percentage of instantaneous (initial) strain. The creep power law model was used to accurately fit the creep data. The addition of a wetting agent greatly reduced the creep at high stress, but had little effect at a lower stress level. The extent of relative creep increased with increasing temperature. It was found that the slope of the power law model was directly proportional to the temperature. The addition of wood-fibers into pure polymer greatly improved the creep resistance of the matrix polymer. The relative creep of the composites decreased with an increase in wood-fiber concentration. However, the composite showed relatively large creep compared with that of solid wood. It was found that both the time exponent and slope of the power law model were inversely related to wood-fiber concentration. The flexural modulus of the composites also had an inverse relationship with the time exponent.     

疲劳与蠕变复合作用下PS的应变与寿命

对PS在疲劳/蠕变复合作用下应变与寿命进行了研究。结果表明：其疲劳/蠕变曲线与纯蠕变曲线十分相似。加载时间周期越短和疲劳载荷变化越频繁。结束普弹应变阶段应变越小，进入延迟弹性变形的平台应变阶段越早。在疲劳/蠕变复合作用下聚苯乙烯存在疲劳和蠕变的交互损伤，其断裂寿命比纯疲劳或纯蠕变的断裂寿命低。断裂寿命减小，疲劳/蠕变的交互损伤程度与温度密切相关，PS在较低温度的疲劳/蠕变交互损伤作用大于较高温度的交互损伤作用。随温度升高，疲劳/蠕变断裂寿命下降是疲劳和蠕变各自的单独损伤增加所致。     

Accelerated failure of bisphenol-A polysulfone during electron beam irradiation under an applied stress

Bisphenol-A polysulfone, poly(oxy-1,4-phenylenesulfonyl-1,4-phenyleneoxy-1, 4-phenyleneisopropylidene-1,4-phenylene), PSF (I) showed greatly reduced resistance to electron beam irradiation when subjected simultaneously to an applied tensile stress. The creep rate increased, and the time (dose) to failure of the sample decreased with increasing stress. The failure strain was constant for different applied stresses. Air, oxygen, and moisture caused decreases in radiation resistance compared with a dry nitrogen atmosphere. Increasing the irradiation temperature from 0 to 90°C resulted in substantially decreased radiation resistance.     

In Situ NMR Study of Dislocation Jump Distance During Creep of Pure Sodium Chloride Single Crystals

Nuclear magnetic resonance pulse techniques were used in situ during creep of single crystals of NaCl to evaluate the contribution of mobile dislocations to spin relaxation. ²³Na spin-lattice relaxation rates were measured in the rotating frame ( T _1p) during compression creep of single crystals of NaCl along the [110] direction at 473 K at an applied stress of 20 MPa. The relaxation rates were evaluated from the spin-echo height following π/2, locking, and 64° pulse sequence. We describe here the experimental setup and methodology in evaluating the dislocation jump distance from NMR-creep experiments. The height of the free induction decay decreased as soon as the load was applied followed by a gradual increase until the steady state was reached, at which point a saturation value was observed corresponding to the constant steady-state creep rate. The mean jump distance of the mobile dislocations, evaluated from the ratio of the signal heights without deformation and during creep, decreased with time/strain, reaching a constant value during the steady-state creep regime. The results are compared with the dislocation-dislocation spacing, subgrain size, as well as the jump distance predicted from creep models.     

Enhancement of Creep Properties of TATB‐Based Polymer‐Bonded Explosive Using Styrene Copolymer

In order to investigate the effects of binder component on the creep properties of polymer‐bonded explosive (PBX), three‐point bending creep behaviors of 1,3,5‐triamino‐2,4,6‐trinitrobenzene (TATB)‐based PBX and its styrene copolymer modified formulation were studied by dynamic mechanical analyzer. The experimental results showed that owing to the addition of reinforcing agent (styrene copolymer) with high glass transition temperature and high mechanical strength, the creep resistance performance of the modified formulation was improved with reduced creep strain and constant creep rate and prolonged creep failure time. A six‐element mechanical model was applied to simulate the creep behaviors of TATB‐based PBX and its modified formulation. The constitutive equation of creep curves under different conditions were obtained by nonlinear fit. The predicted theoretical results coincided quite well with the experimental data.     

稠油乳状液屈服特性及环道启动压力预测

针对海上平台稠油管线停输置换、再启动难题,以旅大稠油为研究对象,利用Rheolab QC流变仪测量系统剖析稠油及其乳状液启动过程与初始阶段力学响应特性,讨论含水率、启动温度、静置时间与恒定剪切速率对启动屈服应力的影响作用,自主研制并加工搭建了室内小型再启动环道实验装置,测量与验证再启动压力理论预测值可靠性。实验结果表明：稠油乳状液启动过程可划分为屈服、衰减和平衡3个阶段,启动屈服应力均在反相点附近达到最大值,随着启动温度升高而降低,随恒定剪切速率增大而增大;适当增大启动流量可缩短管线启动时间,但同时也增大了启动压力;基于启动屈服应力的启动压力预测值是环道实验装置测量值的2～3倍,而基于平衡剪切应力的启动压力预测值与实测值吻合较好,平均相对误差为4.5%。