半晶态高分子材料微尺度粘弹性力学行为研究

发布时间：2018-03-11 12:51

本文选题：高分子　切入点：粘弹性　出处：《太原理工大学》2016年博士论文　论文类型：学位论文

【摘要】：高分子材料的粘弹性力学特性是其工程设计与应用的重要基础与依据,随着其在微纳结构中的广泛应用,发展具有高分辨率的力学性能测试方法表征其微纳尺度下的相关粘弹性力学行为具有重要的现实意义。本文以半晶态高分子材料Polyamide 12(PA12)为研究对象,采用仪器化微/纳米压入测试系统对其进行原位测试,基于压入过程所得加载段、保载段和卸载段的测试结果,从细观角度系统研究了PA12的粘弹性力学行为,并将微压入蠕变与宏观蠕变的测试结果进行了对比分析。具体研究内容与结果如下:(1)采用微压入载荷控制法和应变率控制法(结合连续刚度测量技术,CSM)研究了加载速率及应变率对PA12加载过程载荷位移响应的影响。结果表明,加载过程中加载指数m是与材料硬度相关的参数,m2表明压入时材料发生软化,而m2则表明发生硬化;恒载荷速率加载时特征应变率与载荷速率无关,而与加载指数成反比。由于塑性变形区晶体相位错和非晶相热激活的混合变形机理,PA12在恒载荷速率加载时表现为软化,而通过应变率控制加载且应变率小于0.2 s-1时材料则表现为硬化。基于弹性接触理论计算卸载初始段卸载刚度的方法不再有效,研究通过接触硬度反推其表观卸载刚度的结果显示卸载刚度及弹性模量随卸载速率的增加而减小。(2)为消除卸载初始段“鼻子”现象所引起的弹性模量值的过高测量,基于弹性接触理论提出一种不受加载条件影响的弹性模量计算方法。结果表明,通过给定的蠕变校正因子定义式,弹性模量值不再受卸载速率与保载时间的影响且计算过程明显简化;随着保载时间和卸载速率的提高,蠕变校正因子趋近于1,经蠕变校正后的弹性模量值为一稳定值。(3)针对阶跃加载、斜坡加载和应变率加载三种加载方式作用后保载段的测试结果,采用唯象流变学模型分析了压入蠕变段的粘弹性响应。结果表明,阶跃加载后保载时,不同载荷条件下所得蠕变柔量及延迟谱基本相同,表现为线性粘弹性特征;而对于斜坡加载,加载段材料的结构松弛使得低速率预加载后保载所得蠕变柔量增大,同时随着预加载速率的降低,延迟谱峰强减弱且代表小分子运动的延迟峰消失;对于应变率加载后保载段的蠕变响应,随着加载应变率的减小,延迟峰峰强将显著减弱直至完全消失。(4)为表征不同载荷压入保载时粘弹性材料的蠕变响应,基于二次力学单元构建了一种描述蠕变变形过程的唯象学粘弹性模型。结果表明该模型可有效预测几何自相似尖锐压头压入保载段蠕变响应的全过程,蠕变位移和蠕变位移速率均与保载载荷的平方根成正比,而蠕变应变率则与保载载荷无关。(5)针对宏观与微观蠕变参量之间的跨尺度关联问题,分别采用常规压缩和柱形压头压入进行蠕变测试,并与阶跃加载后微压入保载段的粘弹性参数进行对比分析。结果表明,宏观蠕变试验中PA12表现出明显的非线性粘弹性特征,而微压入试验所得蠕变柔量和延迟时间谱峰强低于宏观试验,同时微压入延迟时间谱线上缺少代表大分子激活运动的延迟峰而宏观蠕变试验则缺少代表小分子激活运动的延迟峰。
[Abstract]:The viscoelastic mechanical properties of polymer materials is an important foundation for the design and application of the project, with its wide application in micro nano structure, characterization of mechanical properties test method with high resolution development has important practical significance to the related viscoelastic behavior of micro nano scale. In this paper, the semi crystalline polymer materials Polyamide 12 (PA12) as the research object, using the instrument of micro / nano indentation test system for in situ test, indentation process from loading section based on test results of loading and unloading section section, from the microscopic view of the viscoelastic behavior of PA12, and the test results of micro indentation creep with the macroscopic creep are analyzed. The specific research contents and results are as follows: (1) adopting micro indentation load control method and strain rate control method (with the continuous stiffness measurement technology, CSM) on the loading speed The rate and the effect of strain rate on the load displacement response of the PA12 loading process. The results show that the load index in the process of loading m parameters related to the hardness of the material, M2 shows that when pressing material softening, while M2 indicates a hardening; constant loading rate loading characteristics of strain rate and load rate, but inversely with the loading index. Due to the mixing of plastic deformation zone in crystalline phase and amorphous phase. The thermally activated deformation mechanism, PA12 in constant loading rate showed softening, and strain rate control by loading and the strain rate is less than 0.2 S-1 when the material is hard. The elastic contact theory calculation method of the initial period just uninstall is no longer valid based on the research, through contact with the apparent hardness of backstepping unloading stiffness results show unloading stiffness and elastic modulus decreases with the increase of unloading rate. (2) to eliminate the initial period of "unloading nose" phenomenon High measuring elastic modulus caused by the value of the contact put forward a kind of elastic modulus is not affected by loading conditions influence the calculation method based on the elastic theory. The results show that the creep correction factor given by the definition of elastic modulus, no unloading rate and impact load time and the calculation process was simplified; with holding time and the unloading rate is increased, the creep correction factor tends to 1, the modulus of elasticity creep values corrected for a stable value. (3) according to the step loading, ramp loading and strain rate loading three loading modes after the load test results of the phenomenological analysis of indentation viscoelastic creep segment the rheological response model. The results show that the step loading after loading, the creep compliance under different loading conditions and delay spectrum is basically the same as the linear viscoelastic characteristics; while for ramp loading, loading section material. The relaxation makes low rate after holding the pre loading creep compliance increases, and with the decrease of pre loading rate, delay and delay the peak peak intensity weakened, on behalf of small molecular motion disappears; response to creep strain rate loading after the holding period, with the decrease of strain rate, the peak will delay significantly. Until it completely disappeared. (4) the creep viscoelastic material response to characterize different load loading, two mechanical unit builds a process of creep deformation description phenomenological viscoelastic model. Based on the results show that the model can effectively predict the geometry of self similar process of sharp indentation load response. Creep, creep displacement and creep displacement rate and holding load is proportional to the square root, and the creep strain rate and holding load. (5) according to the multi-scale correlation problem between macroscopic and microscopic creep parameters, divided Don't use conventional compression and creep test of cylindrical indenter, and step loading after the micro pressure into the viscoelastic parameters of holding section were analyzed. The results show that the PA12 macro creep test shows the nonlinear viscoelastic characteristics, and micro indentation tests of the creep compliance and delay time the spectral peak intensity below the macro and micro indentation test, time delay lines represent the lack of movement and delayed peak molecular activation is the lack of macro creep tests on behalf of small molecules to activate the movement of the delayed peak.

【学位授予单位】：太原理工大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：O343

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