本文選題：超高速 + 混凝土本構模型�。� 參考：《湘潭大學》2017年碩士論文

【摘要】：在2~4 km/s速度范圍內,具備一定長徑比的實心金屬桿(動能桿)依靠自身具有的巨大動能,以直接撞擊目標的方式,在撞擊過程中形成強度高、持時長、指向性強的沖擊波,從而貫穿或摧毀目標并最終形成數(shù)倍彈徑口徑的彈坑。表面的彈坑和深層的彈洞是超高速鎢動能桿正撞擊混凝土的主要兩種毀傷模式。但是目前對2~4 km/s速度范圍內的兩種毀傷模式研究較少,而成坑特性決定著輻射出來的波的基本參數(shù),反映能量分配的份額,是揭示介質壓實破碎特性、地沖擊特性和毀傷機理的關鍵因素。因此,探究超高速動能桿撞擊混凝土成坑規(guī)律是首當其沖的關鍵科學問題。而現(xiàn)有的混凝土本構均不能較好地同時模擬這兩種現(xiàn)象。因此,針對超高速鎢動能桿正撞擊混凝土在數(shù)值模擬上的問題,本文完成了如下幾個方面的工作:(1)在現(xiàn)有混凝土本構模型基礎上,引入塑性功損耗定義損傷,模擬混凝土在加載過程中的軟化階段,并考慮了壓縮損傷對拉伸損傷的強化效果;引入塑性體積應變,解決了等向拉伸損傷問題;考慮到不同的受力情況和動態(tài)響應下屈服面的變化,引入羅德角和應變率強化因子對其進行修正。(2)通過Fortran語言編寫子程序將修正混凝土本構模型嵌入LS-DYNA有限元程序進行二次開發(fā)。采用單個單元測試了本構模型的力學性能,主要包括混凝土在外載為單軸、雙軸和三軸拉壓的力學行為。結果表明,本文的修正混凝土本構模型可以比較好地刻畫混凝土的屈服,損傷和應變率行為。(3)利用修正混凝土動態(tài)本構模型對超高速鎢動能桿正撞擊混凝土的過程進行了數(shù)值模擬,很好地重現(xiàn)了超高速正撞擊混凝土靶板后的缺陷形貌,其中包括:表面徑向裂紋、環(huán)向裂紋、彈坑和層裂。分析了一系列撞擊速度下,靶板彈坑直徑、侵徹深度和動能桿余長隨撞擊速度的變化關系,模擬結果與實驗吻合較好,驗證了模型的合理性。通過模擬在不同撞擊速度下,不同質量和不同長徑比動能桿撞擊混凝土靶板過程,得到成坑規(guī)律為:當采用相同動能桿撞擊時,侵深隨著撞擊速度先增后減,彈坑直徑隨撞擊速度的增加而增加;當采用相同橫截面、不同質量的情況下,彈坑直徑存在一個最大值平臺,侵深卻一直增加;當質量一定,橫截面變化情況下,彈坑直徑存在一個最大值,侵深卻一直增加。研究結果可為超高速鎢動能桿正撞擊混凝土靶板過程的特性分析提供理論基礎,為超高速動能桿設計提供參考。
[Abstract]:In the range of 2 ~ 4 km/s velocity, the solid metal rod (kinetic energy rod) with a certain aspect ratio depends on its own huge kinetic energy. In the way of directly impacting the target, the shock wave with high intensity, long duration and strong directivity is formed during the impact process.Thus penetrating or destroying the target and eventually forming multiple caliber craters.Surface craters and deep bullet holes are the two main damage modes in which the hypervelocity tungsten kinetic energy rod is striking the concrete.However, there are few studies on the two damage modes in the range of 2 ~ 4 km/s velocity, and the characteristics of the pits determine the basic parameters of the radiated waves, which reflect the share of the energy distribution and reveal the compaction and fracture characteristics of the medium.The key factors of ground impact characteristics and damage mechanism.Therefore, it is the most important scientific problem to explore the law of crater formation when hypervelocity kinetic energy rod hits concrete.However, the existing concrete constitutive models can not simulate these two phenomena well at the same time.Therefore, in order to solve the problem of direct impact of ultra-high speed tungsten kinetic energy rods on concrete, the following work has been done in this paper: 1) on the basis of existing constitutive models of concrete, plastic loss is introduced to define damage.The softening stage of concrete under loading is simulated, and the strengthening effect of compression damage on tensile damage is considered, and the problem of isotropic tensile damage is solved by introducing plastic volume strain.Taking into account the variation of the yield surface under different forces and dynamic responses,The modified concrete constitutive model is modified by introducing Luo De angle and strain rate strengthening factor. (2) the modified concrete constitutive model is embedded in the LS-DYNA finite element program for secondary development by Fortran language.The mechanical properties of the constitutive model including uniaxial biaxial and triaxial tensile and compression behaviors of concrete under external loading were tested by a single unit.The results show that the modified concrete constitutive model can describe the yield of concrete well.The damage and strain rate behavior of concrete is simulated by using the modified dynamic constitutive model of concrete.These include: surface radial cracks, toroidal cracks, craters and spallation.The relationship between the crater diameter, penetration depth and residual length of kinetic energy rod under a series of impact velocities is analyzed. The simulation results are in good agreement with the experimental results, and the rationality of the model is verified.By simulating the impact process of kinetic energy rod with different mass and ratio of length to diameter against concrete target at different impact velocities, the law of crater formation is obtained: when the same kinetic energy rod is used, the penetration depth increases first and then decreases with the impact velocity.The diameter of crater increases with the increase of impact velocity. Under the same cross section and different mass, the diameter of crater exists a maximum platform, but the depth of the crater increases. When the mass is constant, the cross-section changes.There is a maximum diameter of the crater, but the depth of the crater increases.The results can provide a theoretical basis for the analysis of the characteristics of the hypervelocity tungsten kinetic energy rod directly impacting the concrete target, and provide a reference for the design of the ultra-high velocity kinetic energy rod.
【學位授予單位】：湘潭大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TJ01;TU528.01

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本文編號：1763220