填充型EVA复合材料蠕变行为的研究

以典型球形填料Ca CO3与乙烯-醋酸乙烯共聚物(EVA)制备填充型EVA复合材料。通过对复合材料试样进行拉伸蠕变试验,研究球形填料填充的EVA复合材料在不同的温度下的短期蠕变行为。结果表明,四元件蠕变模型可以很好地模拟填充型EVA材料的实际蠕变形变曲线,相关系数R在0.98以上。填充型EVA复合材料的高弹模量和黏度表现出温度的依赖性。根据时-温等效原理,依据短时期测得的复合材料蠕变数据可预测材料长时间的蠕变行为,可为EVA复合材料长期使用的稳定性和有效性评价提供了参考依据。     

玻纤增强阻燃PBT长期弯曲蠕变行为预测

采用万能电子拉力机测试了不同应力下玻纤增强阻燃PBT(PBT-RG301)的短期蠕变数据,并采用时间应力等效原理、Burgers模型以及Findley指数定律预测了长期蠕变行为.结果发现:依据时间应力等效原理可预测10000h后体系的蠕变数值,在4000s实验时间内Burgers模型和Findley指数定律均可很好的拟合实验结果,但Burgers模型预测的长期蠕变数据高于Findley指数定律和时间应力等效原理预测数值,实验时间14h的跟踪数据也证实了该结果.     

塑料土工格栅蠕变性能测试方法探讨

研究了塑料土工格栅蠕变性能与拉伸强度之间的关系,并证明了塑料土工格栅蠕变行为符合时温等效原理,应用时温等效原理可在较高温度下试验得到较低温度下更长期的设计强度。     

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。     

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。     

PBX 9501炸药动态增强因子的预测公式

为量化应变率效应对PBX炸药力学性能的影响,引入动态增强因子的概念。以PBX 9501炸药为研究对象,总结并收集了其在不同温度和不同应变率下的压缩强度和拉伸强度数据,利用WLF时温等效原理将不同温度下的数据换算成室温条件对应应变率下的值,补充了缺少的强度数据。基于实验数据,分别拟合了PBX 9501炸药压缩强度和拉伸强度的动态增强因子的预测公式。结果表明,随着应变率的变化,PBX 9501炸药的压缩强度和拉伸强度在双对数坐标下均呈现双线性增长趋势,但是压缩强度和拉伸强度的变化趋势是不同的。在给定的应变率范围内,压缩动态增强因子的最大变化值超过40,而拉伸动态增强因子的最大变化值小于10。用这些经验公式,可预测不同应变率下PBX 9501炸药的强度变化,便于工程应用。     

涤纶高密双轴向经编增强PVC膜材粘弹性本构关系

对涤纶高密双轴向经编增强PVC膜材开展蠕变和应力松弛试验,探究拉伸速率和初始应力水平对材料粘弹性行为的作用规律,得到了松弛模量和蠕变柔量并绘制了其随时间变化的曲线。试验结果表明:涤纶高密双轴向经编增强PVC膜材存在典型的粘弹性行为;膜材在试验时长内已达到稳态松弛阶段;应力水平对PVC膜材的静态粘弹性有显著影响,尤其是蠕变现象随着初始应力水平的增大而出现堆积,而拉伸速率对试样的应力松弛行为起一定作用,但并不明显。通过比较可知,运用金属材料的时效蠕变与时效应力松弛关系原理推导的涤纶高密双轴向经编增强PVC膜材的蠕变和应力松弛长期转化关系式与试验结果存在偏差。     

纤维缠绕玻璃钢环形试样测试方法补充说明

本文就纤维缠绕玻璃钢环形试样(NOL环)试验方法中的几个问题进行探讨,并通过一些试验数据加以说明。 一、关于环形试样的制备 纤维缠绕玻璃钢环形试样制作方法的不同,对其拉伸强度和拉伸弹性模量、弯曲强度和剪切强度有一定的影响,需要统     

塑料土工格栅长期蠕变行为的预测

建立塑料土工格栅蠕变性能测试室,测试了格栅试样的蠕变应变随时间的变化情况。测试在一定温度、湿度条件下进行,并对各试样加载了不同的载荷。从得到的时间-应变关系图中发现,当载荷水平较低时,蠕变发展缓慢;载荷水平较高时,蠕变发展较快且应变较大,并在测试周期内发生断裂。采用时间-温度等效和时间-应力等效相结合的叠加方法,预测了格栅的长期蠕变行为。根据叠加结果得出,格栅在温度为15℃、载荷水平为20％的使用环境下,使用寿命可达100a以上。测试的格栅试样在低于20％载荷水平下使用是安全的,而当载荷水平高于40%时,很可能在短时间内发生断裂。     

纤维缠绕玻璃钢环形试样测试方法补充说明

本文就纤维缠绕玻璃钢环形试样(NOL 环)试验方法中的几个问题进行探讨,并通过一些试验数据加以说明.一、关于环形试样的制备纤维缠绕玻璃钢环形试样制作方法的不同,对其拉伸强度和拉伸     

Creep and Stress–Strain Behavior after Creep for SiC Fiber Reinforced, Melt-Infiltrated SiC Matrix Composites

Silicon carbide fiber (Hi-Nicalon Type S, Nippon Carbon) reinforced silicon carbide matrix composites containing melt-infiltrated silicon were subjected to creep at 1315°C at three different stress conditions. For the specimens that did not rupture after 100 h of tensile creep, fast-fracture experiments were performed immediately following the creep test at the creep temperature (1315°C) or after cooling to room temperature. All specimens demonstrated excellent creep resistance and compared well to the creep behavior published in the literature on similar composite systems. Tensile results on the after-creep specimens showed that the matrix cracking stress actually increased, which is attributed to stress redistribution between composite constituents during tensile creep.     

复合材料天然气气瓶预紧压力的研究

本文针对铝内衬全缠绕复合材料天然气气瓶,应用ALGOR FEAS有限元分析系统进行了气瓶材料的弹塑性历程分析,设计了气瓶的预紧压力。采用轴对称的应力－应变关系对气瓶金属内衬、复合材料进行了应力分析,确定了气瓶的应力分布状态。研究表明,通过预紧压力设计,降低了铝内衬工作状态下的最大拉应力,实现了提高复合材料气瓶疲劳寿命的目的。     

Improved tensile properties of carbon nanotube modified epoxy and its continuous carbon fiber reinforced composites

Carbon nanotubes (CNTs) were used to improve the tensile properties of an epoxy resin and its continuous carbon fiber (CF) reinforced composites. Micrography picture showed that CNTs has been well incorporated into the composites, and made the fracture cross section more rougher through sharing the stress. For the CNT/epoxy composite, the tensile strength and modulus both increased upon the CNT addition, and at a CNT volume concentration of 2.0%, the maximum enhancements in the tensile strength and modulus were achieved as 26.7% and 21.5%, respectively. For the CNT‐CF/epoxy composite, the maximum enhancement in tensile strength was achieved as 11.6% at a CNT volume concentration of 1.0% and then decreased with the further increase of the CNT addition, but the tensile modulus increased monotonically upon the CNT addition. POLYM. COMPOS., 36:1664–1668, 2015. © 2014 Society of Plastics Engineers     

Carbon fiber/epoxy vitrimer composite patch cured with bio-based curing agents for one-step repair metallic sheet and its recyclability

Vitrimers have gained a great deal of attention from researchers, yet research on its application is still lacking. This study, a novel bio-based vitrimer was developed from epoxy (EP) and bio-based curing agents, that is, cashew nut shell liquid (CNSL) and citric acid (CA), and then reinforced by carbon fiber. The vitrimers with different ratios of acid to epoxy (R ratio) at 0.30–0.40 contained ester and ether linkages. All EP/CA/CNSL vitrimers showed the stress relaxation over 70–100°C due to transesterification. The vitrimers were applied as polymer matrices for the carbon fiber composites and then used as repair patches. By using the carbon fiber-reinforced vitrimer with the R ratio of 0.30, patch repair on a damaged alloy sheet revealed that approximately 98% of the tensile strength of the damaged alloy sheet was recovered. The vitrimer can be dissolved from carbon fiber composite to recover carbon fiber. The recovered carbon fiber retained good tensile strength compared to the pristine composite. Based on this study, the EP/CA/CNSL vitrimers showed the comparable thermomechanical properties with the epoxy vitrimer cured by the petroleum-based curing agent. The vitrimer composite patch could therefore be an alternative new repair method to extend the service life of damaged structures.     

Influence of Loading Frequency on the Room-Temperature Fatigue of a Carbon-Fiber/SiC-Matrix Composite

The influence of cyclic loading frequency on the tensile fatigue life of a woven-carbon-fiber/SiC-matrix composite was examined at room temperature. Tension-tension fatigue experiments were conducted under load control, at sinusoidal frequencies of 1, 10, and 50 Hz. Using a stress ratio (σ_min/σ_max) of 0.1, specimens were subjected to maximum fatigue stresses of 310 to 405 MPa. There were two key findings: (1) the fatigue life and extent of modulus decay were influenced by loading frequency and (2) the postfatigue monotonic tensile strength increased after fatigue loading. For loading frequencies of 1 and 10 Hz, the fatigue limit (defined at 1 × 10⁶ cycles) was approximately 335 MPa, which is over 80% of the initial monotonic strength of the composite; at 50 Hz, the fatigue limit was below 310 MPa. During 1- and 10-Hz fatigue at a maximum stress of 335 MPa, the modulus exhibited an initially rapid decrease, followed by a partial recovery; at 50 Hz, and the same stress limits, the modulus continually decayed. The residual strength of the composite increased by approximately 20% after 1 × 10⁶ fatigue cycles at 1 or 10 Hz under a peak stress of 335 MPa. The increase in strength is attributed in part to a decrease in the stress concentrations present near the crossover points of the 0° and 90° fiber bundles.     

Microwave welding of high density polyethylene using intrinsically conductive polyaniline

The use of intrinsically conductive polymers in welding of plastics and composites offers the possibility of developing new welding methods. Intrinsically conductive polyaniline (PANI) composite gaskets were used to microwave weld high density polyethylene (HDPE) bars. Two composite gaskets were made from a mixture of HDPE and PANI powders in different proportions. Adiabatic heating experiments were used to estimate the internal heat generation and electric field strength in the gasket. During welding, the effects of heating time, heating pressure and welding pressure were evaluated. It was found that increasing the heating time and the welding pressure increased the joint strength. The maximum tensile joint strength was achieved using a 60 wt% PANI gasket with a heating time of 60 sec and a welding pressure of 0.9 MPa; this resulted in a tensile weld strength of 24.79 ± 0.34 MPa, which equals the tensile strength of the bulk HDPE.     

塑料土工格栅力学行为研究--Ⅱ.长周期力学行为的预测

对塑料土工格栅长期蠕变行为进行了预测。预测以有限周期内的蠕变数据为依据,采用适当的数据处理方法来进行。数据处理方法有多种,现采用了一种线性外推的方法来处理数据,得到实验温度下格栅的长周期失效时间和蠕变极限强度数据;然后再根据时温等效原理,采用WLF方程将上述结果扩展到其他温度下。预测结果显示约50~120年后,格栅的蠕变极限强度下降到原来的21%~26%。     

Stress states in plasma-sprayed thermal barrier coatings upon temperature cycling: Combined effects of creep,plastic deformation,and TGO growth

To ascertain material parameter effects on the stress states is beneficial to comprehend the crack growth behavior and delamination mechanism in thermal barrier coatings (TBCs). In this work, numerical models are established to explore the combined effects of material parameters including creep, plastic deformation, and thermally grown oxide (TGO) growth on the stress states upon temperature cycling. For all layers, thermal-physical properties reliant on temperature are incorporated into the model. The process of bond coat (BC) oxidation, namely TGO growth, is materialized by changing material properties with cycles. Based on the principle of a single variable, the residual stress states are explored using many different material combinations. The results indicate that the tensile stress in the ceramic top coat (TC) decreases with the increase in the TGO lateral strain distribution gradient. Increasing the BC yield strength or decreasing the TGO growth stress can reduce the tensile stress in TC if there is no creep in the model. When BC yield strength is relatively high (≥150 MPa), BC creep will strengthen the TC tensile stress. TGO creep can decrease the tensile stress in TC irrespective of TGO growth stress and BC creep. When TGO creep rate is higher than 10B^tgo, an exceedingly small tensile stress can always be achieved. This work could provide significant theory direction for material selection and composition control towards advanced TBCs with prolonged lifetime.     

奥氏体不锈钢压力容器应变强化设计技术探讨

应变强化技术能够有效的提高奥氏体不锈钢的屈服强度,从而减小奥氏体不锈钢压力容器的设计壁厚,减轻容器的重量,降低重容比,减少容器制造与运输过程中的能耗,实现压力容器的轻型化。本文介绍了奥氏体不锈钢压力容器应变强化的基本原理和基本设计思路,并从强度、蠕变、疲劳、均匀腐蚀、应力腐蚀开裂(SCC)等方面综述了奥氏体不锈钢应变强化后的性能变化,并提出进一步研究的方向,以实现奥氏体不锈钢压力容器轻型化设计。     

压力容器垫片密封螺栓静强度安全系数的确定

基于信息熵理论中模糊等效随机的原理,将压力容器垫片密封螺栓的模糊静强度和模糊载荷等效为随机静强度和随机载荷,根据先漏后爆的观点和中国标准,分析了内压容器垫片密封螺栓模糊强度在不同工况时的许用可靠度,建立按许用可靠度确定螺栓静强度安全系数的方法。对于内压容器垫片密封结构,研究表明：①在预紧、正常操作、气压试验与液压试验时...