树脂基纳米复合材料力学行为及增强机理研究
发布时间：2018-07-14 16:19
【摘要】：纳米复合材料由于其优良的综合性能,特别是其性能的可设计性被广泛应用于航空航天、国防、交通和体育等领域。纳米颗粒具有颗粒尺寸小、比表面积大、表面能高、表面原子所占比例大等特点,以及其特有的宏观量子隧道效应,使得纳米复合材料在力热光电等领域的研究方兴未艾,比如在力学方面,由于纳米颗粒表面效应带来的增强效应使得纳米颗粒增韧复合材料得到了深入而广泛的研究。但是国内外关于纳米复合材料在动态力学性能方面的研究工作开展较少,对纳米颗粒的增强机理认识还不够全面。因此对不同物理性质的纳米颗粒开展相关研究,以期对颗粒增强机理有更深入的认识,这对颗粒增强复合材料的设计与应用具有重要的意义。本文基于分离式Hopkinson杆实验技术,系统地研究了基体环氧树脂以及分别由纳米SiO2和纳米橡胶颗粒增强的环氧树脂基复合材料压缩力学性能测试。对影响Hopkinson压杆实验精度的各因素进行了系统分析,得到了材料的力学行为与应变率、颗粒性能和颗粒含量的相关性;通过有限元分析软件建立复合材料的unit cell模型,对复合材料中颗粒作用机理进行了分析研究;根据环氧树脂类材料的力学响应,建立了含有8个参数的本构关系。论文所取得的主要结论为:(1)通过对Hopkinson压杆加载试样过程的解析分析表明:对于本文研究的环氧树脂类材料,即使施加于试样中的应力没有完全达到平衡,只要加载时间超过两个特征时间,根据三波法计算出的试样应力应变曲线也是足够精确。若以弹性模量的精确度为标准,计算的误差在5%之内。通过优化设计加载波,提出了一组优化应力波构型的解析解。对于线弹性材料试样在小应变加载下,满足该方程的应力波可以在两个特征时间之后,实现试样内应力平衡和恒定应变率加载,相应的有限元模拟和基于脆性砂石材料的试验也证实了该方程的准确性和可行性。(2)在复合材料动态弹性模量测试精度研究中,发现压痕效应、试样和杆不完全接触是材料动态弹性模量测不准的两大因素。对于金属类高弹性模量材料,通过有限元分析得知常规尺寸的试样和压杆端面间严重的压痕效应导致弹性模量测量误差远大于5%。当采用转接头和长试样时可以将测试误差降低,相应有限元分析证实了该方案的可行性。而对于聚合物类低弹性模量材料,可以通过增大试样直径以避免较大的压痕效应,通过采用本文开发的竖直Hopkinson杆加载技术,改善试样和杆端面的接触状态,实现了聚合物材料动态弹性模量的精确测量。(3)通过对环氧树脂材料进行一系列压缩试验发现:环氧树脂材料力学变形能否完全恢复的临界载荷大于材料的弹性极限,其数值非常接近峰值应力。对环氧树脂材料在峰值应力处变形机理进行研究,推断出可能的变形机理:当施加于材料中的载荷达到峰值应力时,材料内部分子链三维网状结构中交联点开始断裂破坏,随之启动了应变软化的变形过程,由这些分子链链段运动造成的形变是不能自主恢复的。(4)通过对刚性颗粒SiO2增强复合材料的峰值应力和相应的应变率敏感性分析研究发现:该颗粒增强效应不明显。基于unit cell模型数值模拟结果表明:刚性颗粒增强效果依赖于基体材料的本构特征,即受制于基体环氧树脂材料峰值应力后的应变软化率。进一步的模拟研究发现:当软化率低到一定程度时,即使添加刚性颗粒,其增强效果也可以为负,即减弱了复合材料的力学性能。通过对柔性橡胶颗粒增强复合材料的峰值应力和相应的应变率敏感性研究发现:虽然橡胶颗粒减弱了材料的峰值应力,但是颗粒在大变形下的应变硬化阶段的增强效果显著。Unit cell模型模拟发现:在大变形下,由于橡胶颗粒的不可压缩性,颗粒表现为具有刚性颗粒的增强效果。(5)基于环氧树脂材料的力学响应特征,提出了一种本构方程,该方程由Maxwell模型、Weibull模型和指数函数组成。模型采用8个参数,可以较好地反映环氧树脂类材料的峰值应力以及应变软化、平台应力和应变硬化等三大特征,并且容易拓展表征以此为基体的颗粒增强复合材料的力学响应。
[Abstract]:Nanocomposites have been widely used in aerospace, national defense, transportation and sports, due to their excellent comprehensive properties, especially their performance. Nano particles have small particle size, large surface area, high surface energy, large proportion of surface atoms, and its unique macroscopic quantum tunneling effect. The research of rice composite materials in the field of force and photoelectricity is in the ascendant. For example, in the mechanical aspect, the enhancement effect caused by the surface effect of nano particles makes the Nano Particles Toughened composites have been extensively studied. However, the research work on the dynamic mechanical properties of nanocomposites at home and abroad is less. The understanding of the enhancement mechanism of nano particles is not fully understood. Therefore, it is of great significance for the design and application of particle reinforced composites to carry out the related research on the nanoparticles with different physical properties, which is of great significance for the design and application of particle reinforced composites. Based on the separation type Hopkinson rod experiment technology, this paper systematically studies the base. The compressive mechanical properties of epoxy resin and epoxy resin matrix composites reinforced by nano SiO2 and nano rubber particles were tested. The factors affecting the experimental precision of Hopkinson pressure bar were systematically analyzed. The mechanical behavior and strain rate, the correlation of particle properties and particle content were obtained, and the finite element analysis was used. The unit cell model of composite material is established and the mechanism of particle action in the composite is analyzed and studied. According to the mechanical response of the epoxy resin material, the constitutive relation with 8 parameters is established. The main conclusions obtained in this paper are as follows: (1) the analytical analysis of the loading sample process of the Hopkinson pressure bar shows that: The stress and strain curves calculated by the three wave method are accurate enough that the stress and strain curves calculated according to the three wave method are accurate, if the loading time is more than two characteristic times. An analytical solution for the optimization of the stress wave configuration is presented. For the linear elastic material specimen under small strain loading, the stress wave satisfies the stress balance and the constant strain rate loading after two characteristic time. The corresponding finite element simulation and the experiment based on the brittle sand material also confirm the accuracy of the equation. (2) in the study of the testing precision of dynamic modulus of elasticity of composite materials, it is found that the indentation effect and the incomplete contact between the specimen and the rod are the two factors of the uncertainty of the dynamic modulus of elasticity of the material. For the high elastic modulus material of the metal class, the serious indentation effect between the specimen and the end face of the pressure rod is found by the finite element analysis. The measurement error of the modulus of elasticity is much greater than that of 5%. when the test error can be reduced when the connecting head and the long sample are used. The corresponding finite element analysis confirms the feasibility of the scheme. For the polymer with low modulus of elasticity, the diameter of the sample can be increased to avoid the larger indentation effect, and the vertical Hopkinson developed in this paper is adopted. The rod loading technique improves the contact state of the specimen and rod end face and realizes the accurate measurement of the dynamic elastic modulus of the polymer material. (3) through a series of compression tests on the epoxy resin material, it is found that the critical load of the complete recovery of the mechanical deformation of the epoxy resin material is larger than the elastic limit of the material, and its value is very close to the peak value. Force. The deformation mechanism of epoxy resin material at peak stress is studied, and the possible deformation mechanism is deduced. When the load in the material is reached to peak stress, the crosslinking point in the three-dimensional network structure of the internal molecular chain of the material begins to break and destroy, and then the deformation process of the strain softening is started, which is made by the movement of these chain segments. The deformation can not be recovered independently. (4) through the analysis of the peak stress and the corresponding strain rate sensitivity of the rigid particle reinforced SiO2 reinforced composite, it is found that the enhancement effect of the particle is not obvious. The results of the unit cell model numerical simulation show that the reinforcement effect of rigid particles depends on the constitutive characteristics of the matrix material, that is, it is restrained. The strain softening rate after the peak stress of the matrix epoxy resin is further studied. It is found that when the softening rate is low to a certain extent, even adding rigid particles, the reinforcement effect can be negative, that is, the mechanical properties of the composites are weakened. The peak stress and corresponding strain of the composites are strengthened by the flexible rubber particles. The rate sensitivity study found that although the rubber particles weakened the peak stress of the material, the enhancement effect of the particle in the strain hardening stage under large deformation was significant.Unit cell model simulation found that, under the large deformation, the particles showed an enhanced effect with rigid particles due to the incompressibility of the rubber particles. (5) based on epoxy resin material A constitutive equation is proposed, which consists of Maxwell model, Weibull model and exponential function. The model can well reflect the peak stress and strain softening of epoxy resin, the stress and strain hardening of the epoxy resin materials, and it is easy to expand the characterization by 8 parameters. The mechanical response of the particle reinforced composite.
【学位授予单位】：西北工业大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TB33
本文编号：2122220
[Abstract]:Nanocomposites have been widely used in aerospace, national defense, transportation and sports, due to their excellent comprehensive properties, especially their performance. Nano particles have small particle size, large surface area, high surface energy, large proportion of surface atoms, and its unique macroscopic quantum tunneling effect. The research of rice composite materials in the field of force and photoelectricity is in the ascendant. For example, in the mechanical aspect, the enhancement effect caused by the surface effect of nano particles makes the Nano Particles Toughened composites have been extensively studied. However, the research work on the dynamic mechanical properties of nanocomposites at home and abroad is less. The understanding of the enhancement mechanism of nano particles is not fully understood. Therefore, it is of great significance for the design and application of particle reinforced composites to carry out the related research on the nanoparticles with different physical properties, which is of great significance for the design and application of particle reinforced composites. Based on the separation type Hopkinson rod experiment technology, this paper systematically studies the base. The compressive mechanical properties of epoxy resin and epoxy resin matrix composites reinforced by nano SiO2 and nano rubber particles were tested. The factors affecting the experimental precision of Hopkinson pressure bar were systematically analyzed. The mechanical behavior and strain rate, the correlation of particle properties and particle content were obtained, and the finite element analysis was used. The unit cell model of composite material is established and the mechanism of particle action in the composite is analyzed and studied. According to the mechanical response of the epoxy resin material, the constitutive relation with 8 parameters is established. The main conclusions obtained in this paper are as follows: (1) the analytical analysis of the loading sample process of the Hopkinson pressure bar shows that: The stress and strain curves calculated by the three wave method are accurate enough that the stress and strain curves calculated according to the three wave method are accurate, if the loading time is more than two characteristic times. An analytical solution for the optimization of the stress wave configuration is presented. For the linear elastic material specimen under small strain loading, the stress wave satisfies the stress balance and the constant strain rate loading after two characteristic time. The corresponding finite element simulation and the experiment based on the brittle sand material also confirm the accuracy of the equation. (2) in the study of the testing precision of dynamic modulus of elasticity of composite materials, it is found that the indentation effect and the incomplete contact between the specimen and the rod are the two factors of the uncertainty of the dynamic modulus of elasticity of the material. For the high elastic modulus material of the metal class, the serious indentation effect between the specimen and the end face of the pressure rod is found by the finite element analysis. The measurement error of the modulus of elasticity is much greater than that of 5%. when the test error can be reduced when the connecting head and the long sample are used. The corresponding finite element analysis confirms the feasibility of the scheme. For the polymer with low modulus of elasticity, the diameter of the sample can be increased to avoid the larger indentation effect, and the vertical Hopkinson developed in this paper is adopted. The rod loading technique improves the contact state of the specimen and rod end face and realizes the accurate measurement of the dynamic elastic modulus of the polymer material. (3) through a series of compression tests on the epoxy resin material, it is found that the critical load of the complete recovery of the mechanical deformation of the epoxy resin material is larger than the elastic limit of the material, and its value is very close to the peak value. Force. The deformation mechanism of epoxy resin material at peak stress is studied, and the possible deformation mechanism is deduced. When the load in the material is reached to peak stress, the crosslinking point in the three-dimensional network structure of the internal molecular chain of the material begins to break and destroy, and then the deformation process of the strain softening is started, which is made by the movement of these chain segments. The deformation can not be recovered independently. (4) through the analysis of the peak stress and the corresponding strain rate sensitivity of the rigid particle reinforced SiO2 reinforced composite, it is found that the enhancement effect of the particle is not obvious. The results of the unit cell model numerical simulation show that the reinforcement effect of rigid particles depends on the constitutive characteristics of the matrix material, that is, it is restrained. The strain softening rate after the peak stress of the matrix epoxy resin is further studied. It is found that when the softening rate is low to a certain extent, even adding rigid particles, the reinforcement effect can be negative, that is, the mechanical properties of the composites are weakened. The peak stress and corresponding strain of the composites are strengthened by the flexible rubber particles. The rate sensitivity study found that although the rubber particles weakened the peak stress of the material, the enhancement effect of the particle in the strain hardening stage under large deformation was significant.Unit cell model simulation found that, under the large deformation, the particles showed an enhanced effect with rigid particles due to the incompressibility of the rubber particles. (5) based on epoxy resin material A constitutive equation is proposed, which consists of Maxwell model, Weibull model and exponential function. The model can well reflect the peak stress and strain softening of epoxy resin, the stress and strain hardening of the epoxy resin materials, and it is easy to expand the characterization by 8 parameters. The mechanical response of the particle reinforced composite.
【学位授予单位】：西北工业大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TB33
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