颗粒材料对冲击载荷缓冲特性的离散元分析

发布时间：2018-04-10 19:05

本文选题：颗粒材料 + 离散元方法　；参考：《大连理工大学》2015年硕士论文

【摘要】：颗粒物质是自然界中存在最多的物质之一。它与人们的生活密切相关,并在工农业、航空航天、交通运输、建筑工程、自然灾害等各领域均得到良好地应用。颗粒物质不仅兼具流体与固体的性质,通常还会表现出更加复杂的力学性质,其中之一就是快速耗能特性。当颗粒物质承受外载荷作用时,会产生强烈的挤压和碰撞,使系统能量得到快速有效地衰减,从而对外载荷起到良好的缓冲作用。因此,颗粒物质通常被用来作为作减振吸能的优选材料。针对颗粒物质的缓冲特性,本文采用离散元方法,结合Hertz接触理论,建立了冲击物对颗粒材料的冲击模型,旨在揭示颗粒材料缓冲特性的内在作用机理以及其主要影响因素,并在此基础上进行深入的研究。本文工作将会对减振技术的提升具有指导意义,为颗粒材料的工程应用提供理论基础。首先,本文采用球形颗粒单元建立了颗粒材料的冲击模型。分析冲击物在不同颗粒层厚度下的运动规律及底板的受力特性,探讨了颗粒层厚度、表面摩擦系数以及初始排列密集度对颗粒材料缓冲性的影响,并从力链结构和能量变化的角度分析其内在作用机理,揭示了力链结构、能量耗散与颗粒物质缓冲性之间的关系。其次,文章分别建立了散体颗粒材料和粘结颗粒在随机排列和规则排列方式下的冲击模型,对冲击物和底板进行动力分析。研究了粘结强度对颗粒材料缓冲特性的影响和底板分布力的变化规律,并从细观角度展现了点载荷向分布载荷转化的过程。揭示了颗粒系统的缓冲特性与颗粒粘结强度、颗粒自由滑移度之间的关系,同时说明了排列方式对颗粒力链结构的决定性作用。最后,结合真实的冲击环境,介绍了冲击响应谱理论及其时域合成算法,选用合适的基本波形将冲击响应谱合成时域激励信号。将时域信号作为激励条件,采用离散元方法建立了粘结颗粒材料在时域激励作用下的冲击模型,计算不同排列方式下冲击物及底板的力学响应,并分析弹性模量对其缓冲特性的影响。结果表明,粘结颗粒材料能够通过降低振动频率和振幅从而对时域冲击激励起到衰减作用,并且衰减程度受排列方式和弹性模量的影响。
[Abstract]:It is closely related to people's life and has been well applied in the fields of industry and agriculture, aerospace, transportation, construction engineering, natural disasters and so on.Granular matter not only has the properties of fluid and solid, but also shows more complex mechanical properties, one of which is fast energy dissipation.When the particle material is subjected to external load, it will produce strong squeezing and collision, so that the energy of the system will be rapidly and effectively attenuated, thus the external load will play a good role in buffering.Therefore, particulate matter is usually used as an optimal material for vibration and energy absorption.Aiming at the buffer characteristics of granular materials, the impact model of impact materials on granular materials is established by using discrete element method and Hertz contact theory. The purpose of this paper is to reveal the internal mechanism of buffer properties of granular materials and its main influencing factors.And on the basis of this in-depth study.The work in this paper will be of guiding significance to the improvement of vibration absorption technology and provide a theoretical basis for the engineering application of granular materials.Firstly, the impact model of granular material is established by using spherical particle element.The effects of particle thickness, surface friction coefficient and initial arrangement density on the cushioning properties of granular material are discussed by analyzing the motion law of impact material under different particle layer thickness and the mechanical characteristics of the bottom plate, and the effects of particle thickness, surface friction coefficient and initial arrangement density on the buffer properties of granular material are discussed.From the point of view of force chain structure and energy change, the internal action mechanism is analyzed, and the relationship between force chain structure, energy dissipation and buffer property of granular material is revealed.Secondly, the impact models of granular materials and bonded particles in random arrangement and regular arrangement are established, and the dynamic analysis of impact material and bottom plate is carried out.The influence of bond strength on the buffer characteristics of granular materials and the variation of the distribution force of the bottom plate are studied, and the process of transformation from point load to distributed load is shown from the view of meso.The relationship between the buffer characteristics of the particle system and the particle bond strength and the free slip degree of the particles is revealed, and the decisive effect of the arrangement mode on the structure of the particle force chain is also explained.Finally, combined with the real impact environment, the theory of impulse response spectrum and its time-domain synthesis algorithm are introduced.The time domain signal is taken as the excitation condition and the discrete element method is used to establish the impact model of the bonded particle material under the time domain excitation. The mechanical responses of the impact material and the bottom plate under different arrangement are calculated.The influence of elastic modulus on its buffer property is analyzed.The results show that the bonded granular material can attenuate the shock excitation in time domain by reducing the vibration frequency and amplitude, and the attenuation degree is affected by the arrangement mode and elastic modulus.
【学位授予单位】：大连理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TB383.4

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