【作者】 刘朋；

【导师】 林洁琼；

【作者基本信息】 长春工业大学 ， 机械工程， 2020， 硕士

【摘要】 力学超材料(Mechanical metamaterials)是通过人工结构形成的复合物,具有天然材料所不具备的异常性质,可以实现某些奇异功能或比同类功能器件在性能上更为优越的新功能器件。被广泛的应用于航空航天、生物支架、微电子、光学、声学、电磁学等领域。常用的力学超材料加工方法有双光子聚合技术、直接激光烧结技术、熔体静电纺丝技术、纳米压印技术等。其中,双光子聚合(Two-Photon Polymerization,TPP)加工因其具有能够加工任意高分辨率复杂三维微纳结构的能力,是加工力学超材料最有潜力的技术之一。然而在双光子聚合加工过程中涉及到光敏材料的交联固化,从而导致加工结构的收缩现象,致使三维微纳结构的精度降低甚至功能性丧失。但目前针对双光子聚合加工过程中结构收缩及补偿问题的研究还很少。因此,开展双光子聚合加工过程中收缩特性及补偿方法的研究具有重要的意义。本文围绕力学超材料双光子聚合加工及收缩特性的补偿开展了以下研究。(1)通过经典牛顿力学原理,基于Ormocer光刻胶单体合成的步骤,提出一种随机多分子建模的方法建立光刻胶的分子模型,使建立的模型更符合实际的光刻胶结构。通过分子动力学模拟光刻胶的交联,分析出结构在交联过程中详细的能量变化以及聚合前后封装结构在尺寸上的变化,证明了双光子聚合加工过程中因交联反应而产生的收缩现象,并且通过对聚合后光刻胶模型与玻璃基底之间的动力学分析,揭示了光刻胶与玻璃基底之间的粘附力是由81.55%的范德华力和18.45%的静电力组成。(2)根据Maxwell原理设计一种面心立方体结构的力学超材料,并通过对相同相对密度下面心立方体结构和八面体桁架结构的抗压性对比分析,证明了面心立方体结构的抗压性更强。通过对不同相对密度下面心立方体结构杨氏模量进行分析,揭示了随着密度的改变,超材料力学性能的变化,为设计超轻、超强、超韧的面心立方体超材料提供理论依据。另外通过对空心面心立方体结构进行屈曲分析,揭示了结构最先发生屈曲的部位是节点处,为结构设计时优化结构的强度提供参考。(3)通过对双光子聚合加工过程中加工参数的分析,揭示了扫描速度和激光功率对加工精度的影响。通过有限元建模对光刻胶固化过程中的收缩应力分析,揭示了在光刻胶固化收缩过程中应力的变化,同时分析表面粘附力对加工结构的收缩性影响,通过对比交联固化前后结构的尺寸变化,建立了收缩补偿模型。更多还原

【Abstract】 Mechanical metamaterials are composites formed by artificial structures,which have unusual properties not possessed by natural materials,and can realize some strange functions or new functional devices with superior performance than similar functional devices.It is widely used in aerospace,biological scaffolds,microelectronics,optics,acoustics,electromagnetics and other fields.The commonly used mechanical metamaterial processing methods are two-photon polymerization technology,direct laser sintering technology,melt electrospinning technology,nano-imprint printing technology,etc.Among them,two-photon polymerization processing is one of the most potential technologies for processing mechanical metamaterials because of its ability to process arbitrary high-resolution complex three-dimensional micro-nano structures.However,in the process of two-photon polymerization,the cross-linking solidification of photosensitive materials is involved,which leads to the shrinkage of the processed structure,resulting in the reduction of the accuracy or even the loss of the functionality of the three-dimensional micro-nano structure.However,there are few researches on the structure shrinkage and compensation in the process of two-photon polymerization.Therefore,it is of great significance to study the shrinkage characteristics and compensation methods in the process of two-photon polymerization.In this paper,the following research has been carried out on mechanical metamaterial two-photon polymerization processing and shrinkage compensation.(1)Based on the classical Newton mechanics principle and Ormocer photoresist monomer synthesis steps,a random multi-molecular modeling method is proposed to establish the molecular model of photoresist,which makes the established model more in line with the actual photoresist structure.Through molecular dynamics simulation of photoresist crosslinking,the detailed energy changes of the structure in the crosslinking process and the size changes of the package structure before and after polymerization are analyzed,and the shrinkage phenomenon caused by crosslinking reaction in the two-photon polymerization process is proved.Through dynamic analysis of the polymerized photoresist model and the glass substrate,it is revealed that the interaction between the photoresist and the glass substrate is composed of 81.55% Van der Waals force and 18.45% electrostatic force.(2)According to Maxwell’s principle,a mechanical metamaterial with a face-centered cubic structure is designed.Through the comparative analysis of the compression resistance of the face-centered cubic structure and the octahedral truss structure under the same relative density,it is proved that the face-centered cubic structure has stronger compression resistance.Through the analysis of Young’s modulus of the core cube structure under different relative densities,the change of the mechanical properties of the metamaterial with the change of density is revealed,which provides a theoretical basis for the design of ultra-light,ultra-strong and ultra-tough surface-core cube metamaterial.In addition,through buckling analysis of hollow face-centered cube structure,it is revealed that the first buckling part of the structure is the joint,which provides reference for optimizing the strength of the structure during structural design.(3)Through the analysis of processing parameters in the two-photon polymerization process,the influence of scanning speed and laser power on processing accuracy is revealed.Through finite element modeling,the shrinkage stress in the curing process of photoresist is analyzed,and the change of stress in the curing process of photoresist is revealed.At the same time,the influence of surface adhesion on the shrinkage of processed structure is analyzed.By comparing the size change of structure before and after crosslinking and curing,a shrinkage compensation model is established.更多还原