基于均匀设计的UHMWPE纤维拉伸蠕变性能的测试方法

以1 555 dtex超高相对分子质量聚乙烯(UHMWPE)纤维为例,采用均匀设计探讨了UHMWPE纤维蠕变性能测试方法,通过DPS分析软件对其结果进行多项式回归分析。结果表明:拉伸蠕变性能测试结果的回归模型相关系数为0.996 8,由模型得到的测试参数优化值分别为蠕变载荷210 N(纤维断裂载荷的50%),拉伸速度为197.670 5 mm/min,蠕变时间为70.917 2 min,测试长度为200.481 9 mm,蠕变伸长率为7.301 5%;在蠕变载荷为纤维断裂截荷的50%,拉伸速度为200 mm/min,蠕变时间为70 min,纤维测试长度为200 mm的实测条件下,测得纤维的蠕变伸长率为7.012%,与模型预测值有较好的对应,回归模型有较好的拟合性和稳定性。     

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。     

HTPB固体推进剂蠕变损伤模型研究

为研究HTPB推进剂的蠕变特性，开展了0.15～0.35MPa应力下推进剂的单轴拉伸蠕变试验；结合线性黏弹性理论和连续损伤力学理论，建立了HTPB推进剂蠕变损伤模型；根据试验数据，确定了不同应力水平下蠕变损伤模型的参数，并获取了应力对各参数的影响规律，最后利用蠕变应力0.2MPa下的试验数据对模型进行了验证。结果表明，HTPB推进剂存在明显的衰减蠕变、稳定蠕变和加速蠕变三阶段过程；建立的蠕变损伤模型结合Burgers模型的特征和连续损伤力学理论，串联含损伤的黏壶元件，克服了Burgers模型无法反映蠕变破坏阶段特性的不足。提出的蠕变损伤模型与试验值拟合度高，误差在3%以内，可以准确地描述推进剂在不同应力水平下的全过程蠕变特性。     

连续纤维复合材料环形试样蠕变行为研究

对连续玻璃纤维复合材料进行了拉伸蠕变试验研究,为了模拟复合材料在压力容器中的受力状态并减少夹具加持力对试样的影响,采用环形复合材料试样拉伸蠕变试验方法。对复合材料环形试样的拉伸强度及不同应力等级下的拉伸蠕变性能进行了研究,并基于时间?应力等效原理,通过双对数法拟合出压力容器50年使用寿命时复合材料的最大蠕变应力,为复合材料压力容器的设计提供支持。并基于时间?应力等效原理,通过双对数法拟合出压力容器50年使用寿命时复合材料的最大蠕变应力应低于其拉伸强度的44.4 %。     

拉伸蠕变仪改造与应用研究

根据聚合物拉伸蠕变原理和光电原理,设计并制造了光电拉伸蠕变仪。该仪器实验精度、准确性较高,仪器误差和人为误差较小;可测试在标准和非标准条件下聚合物的拉伸蠕变性能。试验结果表明,蠕变与湿度成正比,本体黏度与湿度成反比。     

UHMWPE纤维拉伸蠕变性能的测试方法

以线密度1 776 dtex超高相对分子质量聚乙烯(UHMWPE)纤维为例,采用电子式拉力机测试纤维的拉伸蠕变性能,探讨了操作条件对测试结果的影响。结果表明:UHMWPE纤维的预伸长率和蠕变伸长率随蠕变载荷、蠕变时间和拉伸速度的增大而增大,随纤维测试长度的增大而减小,其中,拉伸速度对纤维的蠕变性能测试有很大影响;建议对GB/T 19975—2005进行修改,对其中的拉伸速度、夹持长度进行限制。     

国外有关塑料助剂研究的期刊文摘(纳米填充剂)

<正>聚甲基戊烯-二氧化硅纳米复合物的拉伸蠕变行为[Polymer International,2010,59(6):719]为了研究纳米填料的表面积和功能化反映在拉伸性能特别是拉伸蠕变行为上的作用,首次通过熔融复合的方法制备了含有2%体积比的气相二氧化硅-聚(4-甲基-1-戊     

热-力耦合环境下结构胶粘剂强度退化试验研究

本研究设计了Araldite~?2015型结构胶粘剂热-力耦合环境下的老化试验及试验所需的加载夹具。通过测量胶粘剂老化过程中的蠕变伸长量,获得了该胶粘剂试件的蠕变特性参数,为建立蠕变有限元模型提供试验依据。另对老化后的胶粘剂试件进行准静态拉伸试验,获得了胶粘剂试件的失效强度随老化时间的增加出现先稍微升高然后迅速降低的强度退化趋势。     

抗蠕变天然橡胶支座

蠕变现象在橡胶或其他高聚物中屡见不鲜,为了在一定程度上阻止蠕变现象,保证产品尺寸的稳定性,往往在橡胶制品中加入入骨架材料,骨架材料同时也起着增强作用。文中主要侧重于从配方上对天然橡胶支座用的胶料进行抗蠕变研究,通过不同的配方设计,研究胶料的抗蠕变性能,描述橡胶拉伸蠕变和压缩蠕变的试验过程,并对蠕变试验数据利用外推滩法加以分析处理,从而预测15年后的蠕变值。     

炉管蠕变损伤的随机计算模型

炉管服役寿命的预测问题一直受到人们关注。由于蠕变问题的随机性研究较困难,过去的研究主要集中在确定性蠕变损伤问题上。本文提出了新的蠕变损伤随机计算模型。通过 Ｍｏｎｔｅ Ｃａｒｌｏ 方法与蠕变损伤随机计算模型结果的比较,验证了蠕变损伤随机计算模型的正确。蠕变损伤随机性的描述为今后炉管蠕变损伤可靠性的评估奠定了基础。     

Nonlinear viscoelastic model for the prediction of double yielding in a linear low‐density polyethylene film

Tensile testing and tensile creep experiments for linear low‐density polyethylene in a thin‐film form were examined and analyzed in terms of a nonlinear viscoelastic model. The proposed model, based on two distinct thermally activated rate processes (Eyring models), was proved to describe the double‐yield‐point tensile behavior of the material tested. The required model parameters were evaluated from the corresponding creep‐strain curves, and this revealed the relationship between the main aspects of the inelastic behavior of polymers, that is, the monotonic loading and creep response. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3519–3527, 2004     

Interphasial viscoelastic behavior of CNT reinforced nanocomposites studied by means of the concept of the hybrid viscoelastic interphase

In this study the effect of carbon nanotubes content as well as of the tensile stress level applied upon the linear viscoelastic creep response of carbon nanotube polymer nanocomposites was investigated. Experimental findings were modeled by means of the newly developed hybrid viscoelastic interphase model, which constitutes an extension of the previously developed hybrid interphase model. According to this model, the viscoelastic interphase thickness has not of constant value but is dependent upon the property considered at the time as well as on the creep time. In addition, the parameter of imperfect bonding is introduced through the degree of adhesion. Experimental findings combined with analytical results gave a better understanding of the viscoelastic response of epoxy resin carbon nanotubes nanocomposites. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Tensile creep of a long‐fibre glass mat thermoplastic (GMT) composite. II. Viscoelastic‐viscoplastic constitutive modeling

In Part I of this article, the short‐term tensile creep of a 3‐mm‐thick continuous long‐fibre glass mat thermoplastic composite was characterized and found to be linear viscoelastic up to 20 MPa. Subsequently, a nonlinear viscoelastic model has been developed for stresses up to 60 MPa for relatively short creep durations. The creep response was also compared with the same composite material having twice the thickness for a lower stress range. Here in Part II, the work has been extended to characterize and model longer term creep and recovery in the 3‐mm composite for stresses up to near failure. Long‐term creep tests consisting of 1‐day loading followed by recovery were carried out in the nonlinear viscoelastic stress range of the material, i.e., 20–80 MPa in increments of 10 MPa. The material exhibited tertiary creep at 80 MPa and hence data up‐to 70 MPa has been used for model development. It was found that viscoplastic strains of about 10% of the instantaneous strains were developed under load. Hence, a non‐linear viscoelastic–viscoplastic constitutive model has been developed to represent the considerable plastic strains for the long‐term tests. Findley's model which is the reduced form of the Schapery non‐linear viscoelastic model was found to be sufficient to model the viscoelastic behavior. The viscoplastic strains were modeled using the Zapas and Crissman viscoplastic model. A parameter estimation method which isolates the viscoelastic component from the viscoplastic part of the nonlinear model has been developed. The model predictions were found to be in good agreement with the average experimental curves. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Modeling for prediction of restrained shrinkage effect in concrete repair

A general model of autogenous shrinkage caused by chemical reaction (chemical shrinkage) is developed by means of Arrhenius' law and a degree of chemical reaction. Models of tensile creep and relaxation modulus are built based on a viscoelastic, three-element model. Tests of free shrinkage and tensile creep were carried out to determine some coefficients in the models. Two-dimensional FEM analysis based on the models and other constitutions can predict the development of tensile strength and cracking. Three groups of patch-repaired beams were designed for analysis and testing. The prediction from the analysis shows agreement with the test results. The cracking mechanism after repair is discussed.     

Comparison of Bend Stress Relaxation and Tensile Creep of CVD SiC Fibers

Three different CVD SiC fibers were tested for bend stress relaxation (BSR) and tensile creep over a wide range of temperatures, times, and stresses. Primary creep was always observed, even for creep strains on the order of 2%. The BSR and tensile creep results were compared using simple linear viscoelastic principles. It was found that BSR results could predict the same time and temperature dependence as tensile creep; however, BSR-predicted creep strains usually overestimated the magnitude of tensile creep strain. The time, temperature, and stress dependence were determined for all the fibers for the experimental conditions of this study. Some of the primary creep behavior can be explained by load-sharing effects between the core and the CVD SiC substrate and some microstructural changes; however, the extent of primary creep cannot fully be accounted for from this work.     

Tensile creep of a long‐fiber glass mat thermoplastic composite. I. Short‐term tests

This work is part of a larger experimental program aimed at developing a semi‐empirical constitutive model for predicting creep in random glass mat thermoplastic (GMT) composites. The tensile creep response of a long‐fiber GMT material has been characterized for 3‐ and 6‐mm thick material. Tensile tests showed that the variability within and between plaques are comparable with an overall variability of about 6% and 8% for the 3‐ and 6‐mm thick materials, respectively. The thicker material exhibited slightly higher variability and directional dependence due to greater flow during molding of the plaques. Short‐term creep tests consisting of 30 min creep and recovery, respectively, were performed over the stress range between 5 and 60 MPa. Three tests for determining the linear viscoelastic region were considered which showed that the 3‐ and 6‐mm thick GMT are linear viscoelastic up to 20 and 25 MPa respectively. The 6‐mm thick GMT consisting of a higher fiber weight fraction was linear over wider stress range. Furthermore, it was found that plastic strains were accumulated during creep, which suggests that a nonlinear viscoelastic–viscoplastic model would be more appropriate for long‐term creep at relatively high stresses, which will be presented in our companion paper. The magnitude of the plastic strains developed in the creep tests presented here was lower because a single specimen was loaded at multiple stress level over short durations. Hence, a nonlinear viscoelastic constitutive model has been developed for the two thickness materials. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Tensile creep behavior of unidirectional glass‐fiber polymer composites

The tensile creep behavior of unidirectional glass‐fiber polymer composites was studied at three different temperatures, namely 298, 333, and 353 K. Testing was performed on the pure epoxy matrix, the 0° specimens as well as off‐axis at 15, 30, and 60 degrees in respect to the axis of tension. The creep strain rate was negligible at room temperature, while it was considerable at the higher temperatures examined. The materials exhibit nonlinear viscoelastic behavior, and the creep response of the composites was treated as a thermally activated rate process. The creep strain was considered to include an elastic, a viscoelastic and a viscoplastic part. The viscoplastic part was calculated through a functional form, developed in a previous work, assuming that viscoplastic response of polymer composites arises mainly from the matrix viscoplasticity. The model predictions in terms of creep compliances were found to be satisfactory, compared with the experimental results. POLYM. COMPOS. 26:287–292, 2005. © 2005 Society of Plastics Engineers.     

Nonlinear tensile creep of linear low density polyethylene/fumed silica nanocomposites: Time‐strain superposition and creep prediction

The main objectives of the study were (i) to quantitatively describe the nonlinear viscoelastic creep of model nanocomposites, (ii) to construct the generalized compliance curve by means of the tensile compliance vs. internal time superposition for a pseudo iso‐free‐volume state, and (iii) to predict the compliance vs. real time curves for selected stresses. To this end, the free volume theory of nonlinear viscoelastic creep developed for thermoplastics and their blend was successfully employed. Linear low density polyethylene/fumed silica nanocomposites, showing notable enhancement of the creep resistance in proportion to the surface area of incorporated nanofillers, were taken as simple model materials. POLYM. COMPOS., 31:1947–1955, 2010. © 2010 Society of Plastics Engineers.     

A modified creep model of epoxy adhesive at ambient temperature

The paper presents the results of experimental investigations of the creep behavior of epoxy adhesive-hardened samples. The determined creep characteristics for an assumed range of tensile stresses show that the rheological effects in the examined adhesive have already occurred very distinctly at room temperature, for a relatively short time; moreover, the examined adhesive is a nonlinear viscoelastic medium and does not obey the Boltzmann's superposition principle. The obtained results of experimental investigations were subjected to detailed analysis and mathematical treatments. As a result of these actions, the so-called modified Burgers model has been finally developed for the studied adhesive with a constant modulus of elasticity for the non-relaxing part (describing the instant elastic strain) and variables, dependent on the tensile stress, the parameter values for its relaxing part (describing non-linearly viscoelastic properties of this adhesive). The creep deformations calculated for this model have demonstrated a very good consistency with the results of experimental investigations over the assumed range of stresses and the duration time of measurements.     

短纤维增强SiC／Al复合材料在高温下粘弹性拉伸性能的细观力学分析

本文采用细观力学模型和有限元法研究短纤维增强ＳｉＣ／Ａｌ复合材料在高温下的粘弹性行为，着重讨论了纤维体分比和长径比对复合材料总体蠕变性能的影响。结果表明，随着纤维体分比和长径比的增加，纤维能显著抑制复合材料沿轴向蠕变行为。