缓冷玻璃态ABS在拉伸应变状态下的老化行为

用万能拉伸实验机和差示扫描量热仪(DSC)对物理老化和应变老化的ABS试样进行研究。力学性能测试结果表明:在相同老化时间内,应变老化试样的屈服应力和弹性模量高于物理老化试样,而断裂伸长率却小于物理老化试样。DSC测试表明:在相同老化时间内,应变老化试样比物理老化试样的热流吸收峰面积更大,说明应变老化试样形成了与物理老化试样不同的结构。     

应变状态下徐冷玻璃态PVC老化现象研究

通过机械拉伸试验和差示扫描量热法(DSC)等手段对物理老化和应变老化的聚氯乙烯(PVC)试样进行研究。力学性能测试结果表明:应变状态下老化试样的屈服应力和弹性模量均大于物理老化试样的屈服应力和弹性模量,而断裂伸长率则相反。这说明PVC试样在应变状态下的老化导致材料脆性增加。DSC测试中,观察到应变状态下老化试样的吸热峰随着时间的增加表现在滞后于物理老化试样。这种现象可以解释为应变状态下老化试样形成了与物理老化试样不同的结构。     

第十四节 橡胶老化性能的测定（拉伸应力松驰试验）

橡胶试样在应变状态下，其应力随时间的变化是物理和化学作用的结果。当薄橡胶试样在高温下较长时间暴露于含氧气氛中时，以化学过程为主。因此，在这种条件下，经过一段时间的暴露老化，可以通过拉伸变形的薄橡胶试样的应力变化，来测定橡胶的老化性能。     

炭黑对丁苯橡胶耐热氧和紫外老化性能的影响

研究了填充不同量炭黑对丁苯橡胶耐热氧和紫外老化性能的影响,测试了各试样的交联密度及物理机械性能,并用扫描电镜观察了其表面形貌.结果表明,丁苯橡胶在热氧老化开始时内部发生了以交联为主的反应,表面氧化缓慢;而在紫外老化开始时表面的变化较大,在老化过程中交联密度出现峰值;热氧和紫外老化120 h后,橡胶的硬度增加,表面变得致密,使热氧和紫外线侵入至橡胶内部变得困难,邵尔A硬度等物理机械性能的变化趋势减缓;炭黑填充量大于20份(质量)时SBR的耐紫外老化性能得到改善,老化360 h后物理机械性能保持率仍然较高,这是因为炭黑对紫外线有很好的屏蔽作用,而炭黑对SBR耐热氧老化性能的影响却相反.     

有机玻璃在盐水条件下老化性能的研究

在盐水（50℃温度,3％NaCl溶液）条件下对有机玻璃做了70d左右的人工加速老化试验,对不同老化时间的有机玻璃试样进行了宏观力学性能测试,并进一步利用凝胶渗透色谱法（GPC）、示差扫描量热法（DSC）等手段分析了老化前后有机玻璃试样的结构和组成差异,结合老化前后有机玻璃力学性能的变化,揭示了有机玻璃在盐水条件下的老化规律和老化机理。实验表明,有机玻璃在温度为50℃,盐质量分数为3％的盐水条件下老化66d,拉伸强度、弯曲强度、弯曲模量都呈现下降趋势。有机玻璃在盐水条件下老化的主要机理是水对有机玻璃的化学作用和物理作用,有机玻璃由于水分渗入的结果影响,降低了分子间的相互作用力（范德华力）从而使材料机械性能下降;同时水对有机玻璃的化学作用没有引起力学性能的变化。     

物理老化对非晶态PET结构、性能以及结晶的影响

采用密度、DSC、应力—应变测量、溶剂诱导结晶和声速测定等方法研究了物理老化对非晶态PET膜和纤维结构与性能的影响.研究结果表明,非晶态PET经物理老化后DSC曲线上的Tg增加,并出现吸热峰,热结晶变慢,溶剂诱导结晶和溶剂扩散速率变慢,初始模量和屈服应力增加,从物理老化引起PET中凝聚缠结增加这一结构变化的角度对上述实验现象进行了解释.     

硅酮结构胶自然曝晒老化试样表征方法研究

对不同厂家的3种硅酮密封胶样品于广东、吐鲁番两地的曝晒场进行曝晒老化试验,对其外观、粘接性、拉伸强度和伸长率等性能进行分析。通过热重分析仪（TG）、傅里叶变换红外光谱仪（FT-IR）、扫描电子显微镜（SEM）等对各种曝晒试样进行测试,对试样老化前后微观内部结构变化进行分析。研究结果表明：老化后的试样A、B的力学性仍然能保持较好,试样C的力学性能下降明显。通过TG法、FT-IR法不能明显地表征出老化前后硅酮密封胶试样物理力学性能的差异变化,而通过SEM表征方法可发现样品老化前后的微观结构变化,所以研究表明后续硅酮结构胶老化的微观结构研究可采用SEM表征方法。     

防老剂AW—P在橡胶中的防老化效能

本文介绍防老剂AW－P在天然胶和丁苯腔中的应用情况。通过与含4010和4010NA试样进行热氧老化和臭氧老化性能对比实验,结果表明AW－P具有良好的抗臭氧老化性能;而老化龟裂现象与含4010NA的试样相似,但比含4010的试样好;抗热氧老化性能则比含4010和4010NA的试样稍差.     

初始光氧老化对极端工况下天然橡胶复合材料磨耗行为的影响

采用布鲁克摩擦磨损试验机考察了光氧老化对NR/炭黑复合材料在极端工况(高速、高载荷、高温)下磨耗行为的影响.结果 表明,在实验范围内,经历初始光氧老化的试样与未老化试样在磨耗行为及机理方面较为类似,但初始光氧老化导致试样的表面变硬、耐磨性增加、磨损体积降低,磨耗会破坏试样表层初始光氧老化后形成的分子结构和交联结构.     

橡胶的疲劳老化与防护

橡胶的疲劳老化是指在交变应力或应变作用下使橡胶的物理机械性能逐渐变坏,以致最后丧失使用价值的现象。橡胶的疲劳老化除取决于应力外,还受其结构及所处的环境因素如温度、氧、臭氧及其它环境介质等的影响。     

盐雾老化对风电叶片用环氧树脂性能的影响

采用差示扫描量热(Differential Scanning Calorimetry,简称DSC)、红外光谱(Fourier transform infrared spectroscopy,简称FTIR)、静态力学性能测试等分析方法对复合材料风电叶片用环氧树脂浇铸体老化前后的性能进行分析,通过对比盐雾老化前后树脂浇铸体的玻璃化转变温度(Glass transition temperature,简称Tg)和力学性能,研究了环氧树脂浇铸体的老化机理。结果表明,树脂浇铸体的Tg随着老化时间的增加呈现先上升后下降的趋势,老化20天时Tg由未老化前的55℃升高到62℃,20天后开始下降,到50天时下降为51℃,比未老化的下降了4℃。随着老化时间的增加,树脂浇铸体力学强度和模量均呈下降趋势,50天盐雾老化后树脂浇铸体的弯曲强度和拉伸强度分别下降了13%和12%,而弹性模量和弯曲模量分别下降了16%和9%。     

Analysis of zirconia mechanical properties after application of a protocol to simulate clinical aging

In order to test the effects of hydrothermal and clinically related aging on zirconia, monolithic disc-shaped samples were milled, sintered and polished from two high translucency zirconia , 3 mol % (HT) and 5 mol % (XT). Samples were divided into three groups: non-aged: control (CT); hydrothermal aging (HA - autoclave aging for 12.5 h at 134 °C, 2 bar); in vitro clinically-related aging (CRA - chewing simulation for 1.2 million cycles followed by 50,000 thermocycles and acidic exposure in HCl, pH 1.2, for 15 h). Mechanical properties (flexural strength, fatigue, hardness and elastic modulus) were analyzed and compared using the analysis of variance (at a level of 5% significance). In vitro clinically-related aging significantly decreased fatigue strength of XT zirconia with no effects on HT zirconia. Surface hardness and elastic modulus were not affected (p = 0.591 and 0.392 respectively). Hydrothermal aging increased fatigue strength for both materials and decreased the surface hardness and modulus of HT zirconia (p ≤ 0.001). Hydrothermal aging and in vitro clinically-related aging have different effects on the mechanical properties of zirconia , when used to simulate five years of clinical service.     

加速紫外老化对聚乙烯薄膜力学性能的影响

介绍了聚乙烯(PE)薄膜老化机理,并对PE薄膜进行了人工加速紫外光老化试验。分析了老化时间对PE薄膜力学性能的影响。结果表明:紫外光的照射使PE的化学键发生交联和断裂反应,其中断裂反应占主导,使聚合物分子量减小,物理性能下降;PE薄膜的拉伸强度、断裂伸长率和弹性模量随老化时间的延长而降低;PE薄膜抵抗破坏的能力在老化60 h以上会急剧下降,而此时弹性模量的变化趋势变得平缓,断裂伸长率与老化时间近似成线性关系递减。     

Effects of water contents and postcuring conditions on Bis‐GMA/TEGDMA dental restorative composite resins

Dental restorative composite resins of the monomer bisphenol A glycerolate dimethacrylate (Bis‐GMA/TEGDMA; 50/50, mass ratio), with different initial water contents in monomer mixtures and subject to various postcuring conditions, were prepared. The effects of water contents and postcuring conditions on photopolymerization rate, degree of methacrylate double bond conversion, and mechanical properties (flexural strength and elastic modulus) were systematically investigated. Within the scope of this investigation, the initial water content was not found to significantly affect the mechanical properties of the photocured composite resins. Nevertheless, the addition of distilled water into the monomer mixture slightly increased the degree of methacrylate double bond conversion, and slightly slowed down the photocuring process, especially when the amount of water was oversaturated. Postcuring conditions of 37°C vapor or water aging increased the degree of methacrylate double bond conversion, but made the mechanical properties of the composite resins less desirable, especially under water‐aging conditions. Postcuring treatment of the composite resins in a 100°C vacuum (～ 27.9 KPa) oven for 1 day improved both the flexural strength and the elastic modulus by at least 30%, but the improvements quickly diminished upon subsequent 37°C water aging. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 492–502, 2004     

丁苯橡胶在热空气和海水中老化性能的比较

对丁苯橡胶在热空气和海水中进行了加速老化试验,比较了老化前后其性能的变化,得出了该橡胶的性能变化与老化时间的函数关系,并建立了100%定伸应力和撕裂强度与硬度的关联关系。结果表明,在整个老化期间,丁苯橡胶的100%定伸应力和硬度逐渐增大,撕裂强度逐渐减小。在相同的温度下,老化初期在海水中丁苯橡胶的性能变化比在空气中的快,而老化后期在空气中的性能变化比在海水中快。丁苯橡胶的100%定伸应力和撕裂强度与硬度呈线性关系,说明通过硬度的变化监测丁苯橡胶力学性能的变化是可行的。     

Time and temperature effects on the tensile yield properties of polypropylene

Tensile tests were made on polypropylene films as a function of aging temperature from 80 to 130°C at a strain rate of 5 cm min^-1. Polypropylene films aged at 60 and 100°C and at time intervals up to 180 min were also stretched at the same strain rate. The yield stress and initial modulus were found to be linear functions of temperature, extrapolating to a zero value close to the thermodynamic melting point of the polymer (170°C). The work of yield, the plastic and yield strains also decreased with increase in aging temperature but the elastic strain increased. The plastic strain, yield strain, yield stress, and initial modulus for the 60°C aged film had larger values than the corresponding values for the 100°C aged film at equivalent time intervals and all properties decreased with increasing log time of aging. These decreases in properties were explained in terms of decrease in the density (crystallinity) of aged PP films. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 625–633, 1997     

Effect of temperature and aging on the mechanical properties of concrete: Part I. Experimental results

This paper reports the results of curing temperature and aging on the strength and elastic modulus and the Part II paper suggests a prediction model based on these experimental results. Tests of 480 cylinders made of Types I, V, and V cement+fly ash concretes, cured in isothermal conditions of 10, 23, 35, and 50 °C and tested at the ages of 1, 3, 7, and 28 days are reported. According to the experimental results, concretes subjected to high temperatures at early ages attain higher early-age compressive and splitting tensile strengths but lower later-age compressive and splitting tensile strengths than concretes subjected to normal temperature. Even though the elastic modulus has the same tendency, the variation of elastic modulus with curing temperature is not so obvious as compressive strength. Based on the experimental result, the relationships among compressive strength, elastic modulus, and splitting tensile strength are analyzed, considering the effects of curing temperature, aging, and cement type.     

Effects of prior aging at 288°C in air and in argon environments on creep response of PMR‐15 neat resin

The creep behavior of PMR‐15 neat resin, a polyimide thermoset polymer, aged in air and in argon environments at 288°C for up to 1000 h was evaluated. Creep tests were performed at 288°C at creep stress levels of 10 and 20 MPa. Creep periods of at least 25‐h in duration were followed by 50‐h periods of recovery at zero stress. Prior isothermal aging increased the elastic modulus and significantly decreased the polymer's capacity to accumulate creep strain. The aging environment had little influence on creep and recovery behaviors. However, aging in air dramatically degraded the tensile strength of the material. Dynamic mechanical analysis revealed an increase in the glass transition temperature from ∼330°C to ∼336°C after 1000 h in argon or in air at 288°C. The rise in the glass transition temperature with aging time is attributed to an increase in the crosslink density of the PMR‐15 polyimide. Increase in the crosslink density due to aging in both air and argon environments is likely behind the changes in the elastic modulus and the decreased capacity for inelastic straining. A visibly damaged surface layer of ∼0.16 mm thickness was observed in specimens aged in air for 1000 h. Results indicate that the unoxidized core material governs the overall mechanical response, whereas the oxidized surface layer causes a decrease in tensile strength by acting as a crack initiation site and promoting early failures. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009