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111.
采用前文高聚物长时标力学行为的研究[1~3.7]所推导出的高聚物蠕变柔量(D)与推迟时间系数(β)、特征时间(t0)之间的定量关系式和t0与应力(σ)的关系式,分析了PVC在不同拉伸和剪切应力水平下的蠕变数据,得到了β和t0值,并验证了t0与σ成线性关系,提出了从不同拉伸和剪切应力水平下短时标蠕变测试来预测高聚物长时标尺寸稳定性和使用寿命方法,具有重要学术意义和使用价值. 相似文献
112.
Dynamic mechanical measurements were conducted for several kinds of ultra–high-strength polyethylene fibers with different methyl branch contents. As is the case with conventional polyethylene materials, UHSPE fibers also exhibit α, β, and γ-relaxation dispersions. Each relaxation process is the function of both the tensile moduli and the branch contents of UHSPE fibers. It was also found that the γ-process of UHSPE fibers is dominated mainly by the localized molecular motion in the crystalline part, such as a dislocation mode of crystallite defects, which is very sensitive to the branching content. From the time and temperature superposition of the frequency dispersion experiments, it was found that activation energies for both the α2-process and α3-process increase proportionally to the methyl branch content, while the α1-process is not so affected by the branch content. This result shows that the incorporated branch sites in the crystalline part effectively hinder the chain-to-chain slippage; meanwhile, they have not hindered the slippage at the grain boundary so far, which also enables us to explain the creep improvement of UHSPE fibers through branch incorporation with the same mechanism. © 1994 John Wiley & Sons, Inc. 相似文献
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Studies have been made of the creep behavior of oriented (15:1) polyethylenes containing 0.4 and 1.3 butyl branches per 1000 C atoms. Increasing the branch concentration reduces significantly the creep strain and the equilibrium strain rate. The data have been fitted to an established model comprising two thermally activated processes in parallel, relating to the amorphous network at low stress, and the crystal phase at high stress. Analysis based on this model indicates the similarity between branching, entanglements, and crosslinks on the creep response. The creep behavior of electron-beam-irradiated materials shows that increasing the branch concentration makes the polyethylene more susceptible to mainchain scission, indicated by increased creep flow rates at higher stress, consistent with previous rubber elasticity studies. Irradiation in an acetylene atmosphere with low (< 1 Mrad) doses is shown to reduce the creep rates at all accessible stresses, and this attributed to an increase in crosslinking compared with scission. © 1994 John Wiley & Sons, Inc. 相似文献
115.
研究了DD3单晶高温合晶在疲劳-蠕变复合作用下的材料形变特点,分析了DD3单晶在不同的交变应力和平均应力的组合下材料的动态变形曲线特点,建立了在930℃此单晶的疲劳-蠕变交互作用变形类的断裂特征图。研究发现DD3单晶合金断裂特征图F区具有较宽的应力范围,而C区则具有相对较窄的应力范围。这表明DD3单晶合金具有相对较强的抗蠕变能力和相对较弱的抗疲劳能力。 相似文献
116.
A method based on rational approximations is presented to interpolate the data from sinusoidal experiments in linear viscoelasticity. Bounds to the corresponding dynamical function and a discrete approximation to the spectrum are established. From this approximation the related viscoelastic functions can be computed. The method is checked by considering two theoretical models of physical interest and a satisfactory accuracy is achieved. 相似文献
117.
稳态奥氏体合金的氢致软化 总被引:1,自引:0,他引:1
本文通过拉伸、室温蠕变及透射电镜观察,研究了稳态奥氏体合金的氢致软化现 象。确认稳态奥氏体合金中存在氢致软化,充氢改变位错组态和氢的运动是产生氢致软 化的原因之一。 相似文献
118.
为了认识不同含水状态下碎裂板岩的蠕变特性,利用Instron全数控电液伺服力学试验机对贵州黔东南地区隧道洞口的碎裂板岩进行单轴压缩蠕变试验,研究其自然风干、不完全饱和和饱和试样的蠕变特性。实验研究结果表明:(1)碎裂板岩蠕变过程主要包括衰减蠕变和稳态蠕变过程,超过一定应力后,在极短的时间内破坏,因此可由广义开尔文模型描述其蠕变过程;(2)自然风干试样蠕变破坏应力为66.2 MPa,为自然风干试样瞬时单轴抗压强度的71.7%,不完全饱和试样蠕变破坏应力为56.1 MPa,饱和试样蠕变破坏应力为38.2 MPa;(3)不完全饱和试样的最大蠕变应变为自然风干试样的2.7倍,而饱和试样的最大蠕变应变值是自然风干试样的4.3倍。 相似文献
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120.
Abstract A review is presented of a very general aspect of the response of all metals subjected to displacive irradiation. This aspect is referred to as «persistence» and describes the tendency of both radiation-induced microstructural evolution and the associated changes in material properties or dimensional stability to evolve to saturation states that resist further change upon continued irradiation. It is shown that new persistent states can develop on a longer time frame associated with the late-term loss of existing microstructural components or the gain of new components, especially when transmutation and/or segregation occurs. The persistent states are often dependent on the irradiation conditions, and if these are changed, the material usually adjusts to form the persistent state characteristic of the new conditions, with the memory of the former state often lost, and sometimes leaving no visible record of the former state in the new microstructure. Depending on the microstructural components involved, the transition toward the new persistent state can occur quickly or very slowly. 相似文献