2011年7月農(nóng)業(yè)機(jī)械學(xué)報(bào)第42卷第7期土壤直剪試驗(yàn)的動(dòng)力學(xué)仿真楊望1蔡敢為2楊堅(jiān)2(1.廣西大學(xué)土木建筑工程學(xué)院,南寧530004;2.廣西大學(xué)機(jī)械工程學(xué)院,南寧530004)【摘要】采用 ANSYS/LS-DYNA仿真軟件,利用 Lagrange和SPH相結(jié)合的方法及修正的Mohr- Coulomb屈服準(zhǔn)則,建立土壤直剪系統(tǒng)可視化仿真模型,進(jìn)行4種土壤直剪動(dòng)力學(xué)仿真試驗(yàn),通過(guò)回歸分析建立了土壤剪切強(qiáng)度與剪切速度的數(shù)學(xué)模型,研究了土壤剪切破壞過(guò)程及剪切速度對(duì)剪切強(qiáng)度的影響規(guī)律及機(jī)理。結(jié)果表明,土壤剪切速度大,剪切強(qiáng)度大,剪切模量小時(shí),剪切強(qiáng)度與剪切速度呈三次方關(guān)系,剪切模量大時(shí),剪切強(qiáng)度與剪切速度成對(duì)數(shù)關(guān)系;土壤剪切模量對(duì)剪切強(qiáng)度影響大,剪切模量大,剪切強(qiáng)度大關(guān)鍵詞:土壤直剪剪切強(qiáng)度剪切速度機(jī)理動(dòng)力學(xué)仿真中圖分類號(hào):S152.9文獻(xiàn)標(biāo)識(shí)碼:A文章編號(hào):1000-1298(2011)0700906Dynamics Simulation of Direct Shear TestYang Wang Cai GanweiYa(1. College of Civil Engineering and Architecture, Guangxi University, Nanning 530004, China2. College of Mechanical Engineering, Guangxi University, Nanning 530004, China)AbstractThe direct shear system dynamics simulation model was developed on the basis of theMohr-Coulomb yield criterion by using ANSYS/LS-DYNA and a combination of lagrarsmoothed particle hydrodynamics( SPH). The dynamics simulation experiments of direct shekinds of soil have been carried out. The mathematic models of soil shear strength and shearing speed wereestablished by regression analysis. The research on soil shear failure process and the influence law andmechanism of shearing speed on shear strength was done. The results showed that with shearing speecincreasing, shear strength increased. Third-order relationship exits between shear strength and shearingspeed with small shear modulus. Logarithm relationship exits between shear strength and shearing speedwith large shear modulus. The effect of shear modulus on shear strength is large. The large shear strengthis with large shear modulusKey words Soil, Direct shear, Shear strength, Shearing speed, Mechanism, Dynamics simulation引言采用 ANSYS/LS-DYNA顯式動(dòng)力學(xué)仿真軟件建立直剪試驗(yàn)動(dòng)力學(xué)可視化仿真模型,進(jìn)行動(dòng)力學(xué)仿真剪切速度對(duì)土壤剪切強(qiáng)度的影響一直是土壤耕在細(xì)觀上研究土壤直剪斷裂機(jī)理,以期為挖拔式塊作機(jī)被硏究的熱點(diǎn),國(guó)內(nèi)外對(duì)其在宏觀尺度上進(jìn)行根拔起速度模型的研究、木薯收獲機(jī)械和其他土壤了較多的研究,得到了一些相關(guān)的數(shù)學(xué)模型及結(jié)耕作機(jī)械的設(shè)計(jì)提供參考。論口,但采用動(dòng)力學(xué)可視化仿真技術(shù),在微觀上研究土壤直剪斷裂的動(dòng)力學(xué)過(guò)程及對(duì)影響剪切強(qiáng)度的1土壤直剪仿真模型速度因素進(jìn)行研究鮮見(jiàn)報(bào)道。為探明直剪斷裂的動(dòng)1.1幾何模型力學(xué)過(guò)程及剪切速度對(duì)剪切強(qiáng)度的影響機(jī)理,本文根據(jù)陌和亦擴(kuò)制式直剪儀工作原中國(guó)煤化工收稿日期:2010-10-22修回日期:2010-12-15CNMHG·國(guó)家自然科學(xué)基金資助項(xiàng)目(51065003)和廣西科技創(chuàng)新能力與條件建設(shè)項(xiàng)目(y-007-055015)作者簡(jiǎn)介:楊望,博士生,主要從事甘蔗和木薯收獲機(jī)械動(dòng)力學(xué)仿真及性能優(yōu)化研究,E-mail:yanghe@163.com通訊作者:楊堅(jiān),教授,主要從事農(nóng)業(yè)機(jī)械設(shè)計(jì)及性能優(yōu)化研究,E-mlil:yangokok@gxu,edu.cn第7期楊望等:土壤直剪試驗(yàn)的動(dòng)力學(xué)仿真理,為了減少仿真計(jì)算時(shí)間,對(duì)直剪仿真試驗(yàn)裝置進(jìn)沒(méi)有網(wǎng)格畸變,能有效處理大變形問(wèn)題,模擬連續(xù)體行簡(jiǎn)化,其結(jié)構(gòu)簡(jiǎn)圖如圖1所示。建模時(shí),取土壤長(zhǎng)結(jié)構(gòu)的破碎、固體的層裂和脆性斷裂等現(xiàn)象。SPH100m,寬10mm,高200mm,上、下盒高度均為的基礎(chǔ)是插值理論,在SPH中任一宏觀變量(如密100mm,盒壁厚取10mm,為了與土壤耕作條件相度、壓力和溫度等)能方便地借助于一組無(wú)序點(diǎn)上近,上盒不封頂。的值表示成積分插值計(jì)算得到,各質(zhì)點(diǎn)相互作用借助插值函數(shù)來(lái)描述,利用插值函數(shù)給出量場(chǎng)在一點(diǎn)處的核心估計(jì)值,將連續(xù)介質(zhì)力學(xué)的守恒定律由微分方程形式轉(zhuǎn)換成積分形式,進(jìn)而轉(zhuǎn)換成求和。SPH方法中,質(zhì)點(diǎn)近似函數(shù)定義為mx)=()W(x-y,h)y(2)圖1直剪仿真試驗(yàn)裝置結(jié)構(gòu)簡(jiǎn)圖其中W(x,h)=、h"(x)Fig 1 Structural diagram of direct shear test1.上盒2.土壤3.下盒式中n—空間維數(shù)a(x)——輔助函數(shù)h——光滑長(zhǎng)度,隨時(shí)間和空間變化1.2材料模型W(x,h)是尖峰函數(shù),如圖2所示。SPH中最常用的土壤模型:參照文獻(xiàn)[8],本文采用MAT147光滑核是三次B樣條,定義為MAT_FHWA_SOIL)作為土壤材料模型,該模型考慮了應(yīng)變率效應(yīng)、孔隙比及孔隙水壓力的影響,其服32+3n(lal≤1)從修正的Mhr- Coulomb屈服準(zhǔn)則,修正后Mohra(a)=C×{1Coulomb屈服表面表達(dá)式為(1