鲜枣压缩及流变特性研究与仿真分析

发布时间：2018-03-20 06:36

本文选题：鲜枣　切入点：压缩特性　出处：《甘肃农业大学》2017年硕士论文　论文类型：学位论文

【摘要】：鲜枣属固体粘弹性农业物料,其在流通链各环节中难免会受到不同形式载荷作用(如挤压、碰撞、搓擦、振动等)而造成机械损伤。本研究为预测鲜枣在收获、贮运、加工等过程中的机械损伤及在特定状态(常变量、定载荷)下的机械响应,对甘肃省少雨干旱地区最有可能规模化种植的4种优良鲜食和加工兼用型枣品种进行整果压缩、应力松弛及蠕变试验研究。获得了5种工况下的试验曲线,阐明了各试验因素与结果间的相关关系。通过试验结果建立了鲜枣流变学模型及其本构方程,并运用有限元和虚拟样机的方法对压缩和应力松弛试验历程进行了数值模拟分析,拓宽了农业物料力学的研究范围。研究结果可为鲜枣包装、运输、加工、贮藏等环节的工程分析、品质评价及相关作业装备设计提供科学依据,并为深入了解鲜枣结构、改进鲜枣加工中的质量控制及减少枣果机械损伤提供理论依据。(1)对4种甘肃特产鲜枣(靖远小口大枣、临泽小枣、敦煌鸣山大枣、兰州坛坛枣)在5种加载速率下进行横向和纵向上的压缩力学特性试验研究。获得相应的力-变形曲线,得到各鲜枣品种的弹性模量、刚度、破坏能、破裂力及破裂相对变形量等力学参数。试验结果表明:各品种鲜枣横向受压时裂纹大多出现在枣果蒂部,纵向受压时裂纹出现在枣果经线的各个方向上,且开裂形态相对一致;横向压缩破裂力范围227.52-342.8N,纵向压缩时破裂力范围276.82-383.17N;鲜枣品种对弹性模量具有极显著影响,受压方向和加载速率对弹性模量的影响不显著;鲜枣横向压缩时,破裂力与弹性模量、破坏能呈极显著正相关(p0.01),而破坏能与弹性模量、破裂相对变形量呈显著正相关(0.01p0.05);纵向压缩时,破裂力与破裂相对变形量、破坏能呈极显著正相关,与弹性模量呈极显著负相关(p0.01),而弹性模量与破坏能、破裂相对变形量呈显著负相关,破坏能与破裂相对变形量呈显著正相关(0.01p0.05)。运用有限元法模拟鲜枣在横纵两方向的压缩力学试验过程,结果显示:鲜枣受压时,应力应变主要集中在加载点附近,这与试验结果鲜枣在压头加载处破裂一致;力-变形曲线试验值与仿真值最大偏差为11.4%。表明可以利用有限元法来模拟研究鲜枣的力学进程,拓宽了生物力学的研究方法。(2)对4种甘肃特产鲜枣在2种压缩位移(2mm、3mm)下进行横向和纵向应力松弛特性试验研究。获得应力松弛特性曲线,并选取适当的松弛数学模型,通过SPSS数据统计分析软件拟合出相应的松弛特性参数。试验结果表明:各品种枣样都具有明显的应力松弛现象,松弛应力在松弛初始时迅速衰减,直至平衡应力后趋于稳定;纵向压缩时松弛应力任意时刻都大于横向,且鲜枣的变形量越大,其最大松弛应力越大,任意时刻的松弛应力也越大,最终的平衡应力越大;鲜枣的应力松弛模型可用广义Maxwell五元件模型进行很好的模拟,相关系数达0.99以上;鲜枣品种、常变形量和加载方向对衰变弹性模量E1、E2呈极显著影响(p0.01),不同鲜枣品种对平衡弹性模量E0影响显著(0.01p0.05);E0与E1、E2呈极显著正相关(0.01p0.05),E1、E2之间呈极显著正相关(p0.01),粘性系数?2与E1、E2、E0都呈极显著正相关(0.01p0.05)。运用流变学模型,从动力学的角度模拟分析鲜枣流变过程,比较应力-时间曲线试验值与模拟值,最大偏差为4.7%,表明可以利用虚拟样机的方法来模拟研究鲜枣的流变进程,为生物力学的研究提供了新的思路。(3)对4种甘肃特产鲜枣在2种定载荷(85N、115N)下进行横向和纵向上蠕变特性试验研究。获得相应的蠕变特性曲线,选取蠕变数学模型拟合出相应的蠕变特性参数,分析不同鲜枣品种及不同加载力下的蠕变特性,通过对整果模型参数分析,获得鲜枣蠕变特性参数间的相关关系,试验结果表明:各鲜枣品种在受定载荷作用时,变形-时间关系曲线的变化趋势相同,且横向蠕变变形量大于纵向蠕变的变形量;横向压缩时,定载荷下鸣山大枣蠕变初始变形量最大(115N时为4.85mm,85N时为3.6mm),临泽小枣最小,曲线最低(115N时为4.16mm,85N时为3.0mm);定载荷越大,变形量越大;Burgers模型能够很好的模拟鲜枣的蠕变特性,SPSS拟合系数达0.99以上。鲜枣品种和加载方向对瞬时弹性E1具有极显著影响(p0.01),各因素对延迟弹性系数E2的影响均不显著。鲜枣品种、加载方向以及定载荷对?1、?2、T的影响均不显著(p0.05)。瞬时弹性系数E1与延迟弹性系数E2呈极显著正相关(p0.01)。瞬时粘性系数?1与弹性系数E1、E2呈显著负相关(0.01p0.05)。延迟时间与T与弹性系数E1、E2呈负相关,与粘性系数?1、?2呈正相关,但均不显著。
[Abstract]:Fresh jujube is solid viscoelastic material in all aspects of agriculture, circulation chain will be influenced by the effect of different load (such as extrusion, collision, rubbing vibration, etc.) caused by mechanical damage. This study for the prediction of fresh jujube in the harvest, storage, processing and other mechanical damage in the process and in particular state (often variable and constant load) under mechanical response, 4 excellent fresh and processing and jujube varieties in Gansu Province, lack of rain and drought area is most likely the large-scale planting of whole fruit compression, experimental study on stress relaxation and creep. The 5 conditions of the test curve, expounds the relationship the test factors and between the results. Through the test results of fresh jujube rheological model and the constitutive equation is established, and by using the finite element method and the virtual prototype of the compression and stress relaxation test process was simulated and analyzed, broaden the research of agricultural material mechanics Range. The research results can be used for fresh jujube processing, packaging, transportation, storage and other aspects of the project analysis, and provide scientific basis for quality evaluation and the related work equipment design, and to understand the deep structure of fresh jujube, jujube improvement in processing quality control and provide a theoretical basis for reducing the mechanical fruit damage (1) of 4. Gansu specialty jujube (Jingyuan small jujube, Linze jujube, Dunhuang Lanzhou Mingshan big jujube, jujube jar) were on the transverse and vertical compression test study on mechanical characteristics of the 5 kinds of loading rate. To obtain the corresponding force deformation curve, elastic modulus, the fresh jujube varieties are stiffness, damage, rupture rupture force and relative deformation and other mechanical parameters. The experimental results showed that all the varieties of fresh jujube transverse compression crack occurs mostly in the jujube fruit stalk, longitudinal compression crack in each direction warp fruit, and cracking form relatively uniform transverse compression; Rupture force range of 227.52-342.8N, longitudinal compression rupture stress range 276.82-383.17N; fresh jujube varieties had significant effects on the elastic modulus, compression direction and loading rate on the elastic modulus is not significant; fresh jujube lateral compression, rupture force and elastic modulus, failure energy were positively correlated (P0.01), and the destruction of energy and the elastic modulus of rupture, relative deformation was positively correlated (0.01p0.05); longitudinal compression, rupture force and rupture relative deformation, failure was significantly positive correlation, and negative correlation with elastic modulus (P0.01), while the elastic modulus and failure, rupture of relative deformation was significantly negatively related to failure can the relative deformation and rupture were positively correlated (0.01p0.05). The simulation of fresh jujube in the transverse and longitudinal direction of two by using the finite element method of mechanical testing, results showed that the fresh jujube is pressed, the stress and strain are mainly concentrated in the loading point In this, and the test results of fresh jujube rupture in head loading site; and simulation values of maximum deviation of 11.4%. showed that mechanical process can simulation of fresh jujube using the finite element method of curve deformation test force, broaden the research methods of biomechanics. (2) of the 4 Gansu specialty in 2 kinds of fresh jujube the compression displacement (2mm, 3mm) under horizontal and vertical experimental study on stress relaxation characteristics. The stress relaxation curve, and select the relaxation of a suitable mathematical model, through the SPSS data analysis software fitted relaxation properties of the corresponding parameters. The test results show: all varieties of jujube samples have obvious stress relaxation the stress relaxation phenomenon, decay rapidly in the initial relaxation, until balance stress tends to be stable; longitudinal compression stress relaxation at any time is greater than the horizontal, and the deformation of fresh jujube is bigger, the maximum stress relaxation is bigger, at any time loose The relaxation of stress is large, the final balance of greater stress; well simulate the stress relaxation model can be generalized Maxwell five element model of fresh jujube, the correlation coefficient is above 0.99; fresh jujube varieties, often deformation and loading direction on the decay modulus E1, E2 had significant effect (P0.01) effect of different varieties of fresh jujube, balance the elastic modulus of E0 significantly (0.01p0.05); E0 and E1, E2 had significantly positive correlation (0.01p0.05), E1, had a significantly positive correlation between E2 (P0.01), the viscosity coefficient of? 2 and E1, E2, E0 were positively correlated (0.01p0.05). With the rheological model, analysis of fresh jujube rheological process from the angle of dynamics simulation, comparing the stress time curve of test value and simulation value, the maximum deviation is 4.7%, the rheological process shows that method can use virtual prototyping to simulate study of fresh jujube, provides a new idea for the research of Biomechanics (3) of 4. A specialty of Gansu jujube In 2 kinds of loads (85N, 115N) experimental study on transverse and longitudinal creep properties were obtained. The creep curve corresponding to the selected creep mathematics model fitting creep parameters, analysis of the creep characteristics of different fresh jujube varieties and different loading force, through the analysis of the whole fruit to obtain the relevant model parameters. The relationship between the creep parameters of fresh jujube, the test results showed that the fresh jujube varieties under constant load, the change trend of deformation time curve, deformation and lateral creep deformation is larger than the longitudinal creep; transverse compression, constant load creep deformation under initial Mingshan Dazao (115N for maximum 4.85mm, 85N 3.6mm), Linze jujube (115N minimum, the minimum curve for 4.16mm, 85N 3.0mm); constant load is larger, the greater the deformation; the Burgers model can simulate the creep characteristics of fresh jujube is very good, SPSS fitting coefficient More than 0.99 varieties of fresh jujube. And the loading direction has significant effect on the instantaneous elastic E1 (P0.01), the influences of various factors on the delayed elastic coefficient E2 were not significant. The fresh jujube varieties, loading direction and constant load of? 1, 2? T, the effect was not significant (P0.05). The instantaneous elastic system the number of E1 and delayed elastic coefficient E2 showed significant positive correlation (P0.01). The transient viscosity coefficient and the coefficient of elasticity of E1? 1, E2 showed a significant negative correlation (0.01p0.05). The delay time and the coefficient of elasticity of E1 and T, E2 was negatively correlated with the viscosity coefficient of 1? 2,? Positively correlated, but not significantly.

【学位授予单位】：甘肃农业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：S665.1

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