本文關(guān)鍵詞：梯度多胞金屬的實(shí)驗(yàn)研究、多尺度分析和耐撞性設(shè)計(jì)　出處：《中國(guó)科學(xué)技術(shù)大學(xué)》2017年博士論文　論文類型：學(xué)位論文

  更多相關(guān)文章： 梯度多胞金屬 力學(xué)實(shí)驗(yàn) 沖擊波模型 材料參數(shù) 三維Voronoi模型 有限元方法 耐撞性設(shè)計(jì)

【摘要】：梯度多胞金屬繼承了均勻多胞金屬優(yōu)異的力學(xué)性能,具有良好的抗沖擊能力和吸能效果,且由于包含密度的變化,具有很強(qiáng)的可設(shè)計(jì)性,受到了越來(lái)越多的關(guān)注。梯度多胞金屬通�？梢苑譃檫B續(xù)密度梯度多胞金屬和層級(jí)密度梯度多胞金屬。由于制造技術(shù)的限制,目前大部分實(shí)驗(yàn)研究選用的試樣為層級(jí)密度梯度多胞金屬,即用具有不同密度的均勻多胞金屬熱壓或粘接而成,無(wú)法準(zhǔn)確描述梯度多胞金屬的力學(xué)行為。研究人員轉(zhuǎn)而采用理論分析或有限元分析,如基于沖擊波模型的理論分析和基于Voronoi技術(shù)的有限元分析。此外,研究人員還對(duì)梯度多胞金屬進(jìn)行了耐撞性設(shè)計(jì)研究,但大都是在一系列的密度分布組合或不同的密度梯度中篩選耐撞性能較好的密度分布,并沒(méi)有充分利用梯度多胞金屬的可設(shè)計(jì)性。本文主要基于Voronoi技術(shù)發(fā)展了梯度多胞金屬的三維細(xì)觀模型,用以更加準(zhǔn)確地開展梯度多胞金屬的有限元分析,并且率先提出了基于沖擊波模型反向設(shè)計(jì)梯度分布的耐撞性設(shè)計(jì)方法,以期實(shí)現(xiàn)吸能材料從傳統(tǒng)的被動(dòng)選擇過(guò)渡到主動(dòng)設(shè)計(jì)。用實(shí)驗(yàn)方法考察了梯度泡沫鋁的基本力學(xué)性能。由于難以按照特定密度分布制造閉孔連續(xù)梯度多胞金屬,先用間接測(cè)量的方法估算出選用的梯度泡沫鋁試樣的密度分布,采用線性擬合得到密度分布的近似表達(dá)式,并開展梯度泡沫鋁的準(zhǔn)靜態(tài)單軸壓縮實(shí)驗(yàn)。在實(shí)驗(yàn)中發(fā)現(xiàn)了試樣由胞元較大的一端開始漸近壓潰的現(xiàn)象。根據(jù)這一現(xiàn)象通過(guò)建立理論模型推導(dǎo)了壓縮載荷-位移關(guān)系,并用剛性-理想塑性-鎖定(R-PP-L)模型近似材料的應(yīng)力-應(yīng)變關(guān)系,對(duì)實(shí)驗(yàn)數(shù)據(jù)進(jìn)行了擬合,得到了 R-PP-L模型的力學(xué)參數(shù)。然后,用改造過(guò)的霍普金森壓桿開展了梯度泡沫鋁的動(dòng)態(tài)實(shí)驗(yàn),結(jié)合文獻(xiàn)中提出的"雙應(yīng)變片"測(cè)量法,通過(guò)計(jì)算得到了試樣支撐端的反力;利用高速攝影機(jī)和數(shù)字圖像相關(guān)技術(shù)求得子彈的速度歷史曲線,發(fā)現(xiàn)4組實(shí)驗(yàn)的結(jié)果吻合得較好。基于應(yīng)力波理論,建立了質(zhì)量塊撞擊梯度多胞桿的沖擊波模型,考察了密度梯度對(duì)梯度多胞金屬抗沖擊特性的影響�？紤]一系列具有相同平均密度、不同密度梯度且密度分布線性增加的梯度多胞金屬桿,推導(dǎo)出了質(zhì)量塊沖擊下質(zhì)量塊的速度和波陣面位置對(duì)時(shí)間的微分方程組,并采用R-PP-L模型的材料參數(shù),利用經(jīng)典龍格-庫(kù)塔法對(duì)微分方程組進(jìn)行數(shù)值積分求解。結(jié)果表明,密度梯度對(duì)梯度多胞金屬試樣的沖擊響應(yīng)有著很大的影響,并發(fā)現(xiàn)存在質(zhì)量塊的減速歷史振蕩非常小的情形,且此時(shí)最大減速度的值最小。對(duì)比理論分析的結(jié)果與實(shí)驗(yàn)結(jié)果,發(fā)現(xiàn)在沖擊過(guò)程的前期,理論和實(shí)驗(yàn)的結(jié)果吻合得非常好;隨著速度的下降,實(shí)驗(yàn)得到的支撐端反力明顯大于理論分析結(jié)果,而質(zhì)量塊的速度下降比理論分析結(jié)果更快。推測(cè)其主要原因是R-PP-L模型對(duì)于材料特性的模擬較為簡(jiǎn)化,并未考慮材料的硬化,且壓實(shí)應(yīng)變是固定的,影響了理論分析的結(jié)果。基于三維Voronoi技術(shù)發(fā)展了梯度多胞材料的細(xì)觀模型并開展力學(xué)行為的研究�；谧儼叽绶ê腿SVoronoi技術(shù),構(gòu)造了一系列具有相同平均密度且密度分布為線性的梯度多胞試樣,并通過(guò)驗(yàn)證胞元的相對(duì)密度和統(tǒng)一修正壁厚的方法得到具有準(zhǔn)確密度分布的三維Voronoi模型。然后利用ABAQUS/Explicit軟件進(jìn)行有限元分析,考察梯度多胞結(jié)構(gòu)在準(zhǔn)靜態(tài)壓縮下的力學(xué)行為和動(dòng)態(tài)沖擊下的抗沖擊特性和吸能效果。發(fā)現(xiàn)梯度多胞試樣在準(zhǔn)靜態(tài)壓縮下存在應(yīng)變持續(xù)增加應(yīng)力逐漸增加的階段,這不同于均勻多胞試樣的平臺(tái)段,從變形圖上可以觀察到由一端開始逐漸壓潰的現(xiàn)象。在動(dòng)態(tài)沖擊下,觀察到密度梯度對(duì)梯度多胞金屬的動(dòng)態(tài)力學(xué)性能同樣有著很大的影響,當(dāng)梯度多胞金屬密度大的一端靠近支撐端時(shí)可以更好地保護(hù)撞擊物,而密度小的一端靠近支撐端時(shí)對(duì)于支撐端處的結(jié)構(gòu)有很好的保護(hù)作用。從能量吸收的角度看,密度梯度對(duì)梯度多胞金屬的能量吸收同樣存在較大的影響。提出了根據(jù)耐撞性要求反向設(shè)計(jì)梯度多胞材料的密度梯度的方法。基于沖擊載荷的歷史曲線,應(yīng)用非線性塑性沖擊波模型,反向推導(dǎo)出了梯度多胞桿的密度分布,并考察沖擊力歷史為線性變化的耐撞性情形,得到了當(dāng)沖擊力歷史分別為恒定、線性增加和線性減少時(shí)的密度分布表達(dá)式。根據(jù)理論分析結(jié)果設(shè)計(jì)出的三種密度分布,構(gòu)建了相應(yīng)的三維細(xì)觀有限元模型,通過(guò)數(shù)值模擬驗(yàn)證反向設(shè)計(jì)得到的沖擊力響應(yīng)的結(jié)果。通過(guò)對(duì)比發(fā)現(xiàn),當(dāng)沖擊力歷史為恒定或線性增加時(shí),在有限元分析中梯度多胞桿的變形模式與假設(shè)的相同,得到的沖擊力歷史曲線與設(shè)定的值吻合得較好;當(dāng)沖擊力歷史為線性減少時(shí),沖擊過(guò)程中試樣兩端均發(fā)生了變形,這和理論分析中的假設(shè)沖突,兩者的結(jié)果也存在一定的差別。從變形圖樣中還發(fā)現(xiàn),初始的設(shè)計(jì)中梯度多胞桿靠近支撐端的一部分材料幾乎未發(fā)生壓潰,即設(shè)計(jì)是偏保守的。針對(duì)這樣的情況,提出了優(yōu)化設(shè)計(jì)的方法,即通過(guò)限制波陣面第一次到達(dá)支撐端時(shí)靠近支撐端處材料的波后應(yīng)變來(lái)縮短梯度多胞桿的長(zhǎng)度。所以,根據(jù)耐撞性反向設(shè)計(jì)梯度多胞材料的密度分布的設(shè)計(jì)方法能夠?qū)崿F(xiàn)。
[Abstract]:The gradient of cellular metal inherits the uniform mechanical properties of cellular metal excellent, good shock resistance and energy absorption effect, and because of the changes of density, can be well designed, has attracted more and more attention. The gradient of cellular metal can usually be divided into continuous density gradient and the level of cellular metal the density gradient of cellular metal manufacturing technology. Due to restrictions, most of the current sample experimental study was used in hierarchical cellular metal density gradient, i.e. with different density uniformity of cellular metal or hot pressing bonding, cannot accurately describe the mechanical behavior of cellular metal gradient. The researchers turn by theoretical analysis and finite element analysis based on the model, such as shock wave theory analysis and finite element analysis based on Voronoi technology. In addition, the researchers also conducted crashworthiness studies to design gradient of cellular metal, but are Screening of Crashworthiness density distribution of good performance in density distribution or a combination of a series of different density gradient, and can not make full use of the design gradient of cellular metal. This paper is mainly based on the Voronoi technology development model of three-dimensional meso gradient of cellular metal, used to accurately carry out gradient of cellular metal the finite element analysis, and proposed based on shock wave model of reverse design gradient distribution crashworthiness design method, in order to achieve the energy absorbing material from passive to active. The transition from the traditional design of the basic mechanical properties of aluminum foams were investigated by experimental method. According to the specific density distribution due to the continuous gradient of cellular manufacturing cell the metal, first with the indirect measurement method to estimate the density gradient distribution of aluminum foam specimen of the linear fitting is used to get approximate expressions for the density distribution, and carry out the global gradient Foam aluminum the quasi-static uniaxial compression experiment. The sample cell by the end of larger asymptotic collapse phenomenon began in the experiment. According to this phenomenon by establishing the theoretical model of compression load displacement relationship, and rigid - perfectly plastic locking (R-PP-L) model to approximate the material stress strain relationship, fit the experimental data, the mechanical parameters of the R-PP-L model. Then, Hopkinson pressure bar with a modified to carry out the dynamic experimental gradient of aluminum foam, combined with the proposed "double gauge" method, obtained by calculating the force supporting sample end; the speed of history curve image correlation technique to obtain the bullet speed camera and digital, found 4 sets of experimental results agree well. Based on the stress wave theory, established the impact mass impact gradient cellular rod wave model, effects of density gradient on the ladder Effect of cellular metal impact properties. Consider a series with the same average density, different density gradient and density gradient distribution of linear increase of cellular metal rod, deduced the mass under the impact of mass velocity and wave front position of time differential equations, and the material parameters of the R-PP-L model numerical solution of differential equations by using Runge Kutta method. The results show that has great influence on the shock response of density gradient gradient of cellular metal specimen, and found that there are very small oscillation situation deceleration history of mass, and the maximum velocity is the lowest. Compared with the results of theoretical analysis with the experimental results, found early in the impact process, the theoretical and experimental results agree well with the speed of decline; the support end force is significantly greater than the result of theoretical analysis, and quality Liangkuai decreased the rate of results than the theoretical analysis. The main reason is that faster simulation for material properties of the R-PP-L model is simplified, not considering the material strain hardening, and the compaction effect is fixed, the results of the theoretical analysis. Research on 3D Voronoi technology development of the mesoscopic model gradient of cellular materials and carry out mechanical behavior based on the variable cell size method and 3D Voronoi based technology, to construct a series with the same average density and density distribution of linear gradient cell samples, and got the 3D Voronoi model accurate density distribution through the validation of cellular relative density and uniform wall thickness correction method. Then using finite element analysis ABAQUS/Explicit software, anti shock characteristics of gradient cellular structures in the quasi-static compression and dynamic mechanical behavior under the impact and effect of energy absorption. Found cellular gradient The sample in the presence of increasing strain stress increasing stage under quasi static compression, which is different from the uniform cellular sample platform, observed by the end began to collapse from the phenomenon of deformation. In the dynamic map can be observed under the impact of density gradient also has great influence on the dynamic mechanical properties of gradient cellular metal, when the end of the gradient of cellular metal density near the end of the support can better protect the impactor and the end of low density near the end of the support structure supporting end has a good protective effect. From the perspective of energy absorption, density gradient on the gradient of cellular metal energy there are also greater absorption effect. Based on the crashworthiness requirement of density gradient reverse gradient design of cellular materials. The history curves of impact load based on the application of nonlinear plastic shock wave model, reverse thrust Density gradient of cellular rod is derived, and the effects of impact resistant situation impact history as a linear change, is obtained when the impact force history were constant, linear increase and linear decrease in density distribution expressions. According to the theoretical analysis of three kinds of density distribution results to design, construct the three-dimensional finite element model the corresponding micro, through numerical simulation verified the impact of reverse design response results. By comparison, when the impact force history to increase the constant or linear time, deformation model and hypothesis in the finite element analysis of cellular rod of the same gradient, the impact force history curve obtained with set values agree well when the impact force history; linear decrease, in the process of impact specimen are deformed, and this assumption conflict in theoretical analysis, the results also have certain difference. From the deformation pattern in the hair Now, the initial gradient in the design of cellular rod near the support end of a portion of the material had hardly been crushing, namely the design is conservative. In view of this situation, put forward the method of optimization design, which is close to the end of support material by limiting the wave front first arrived at the support end after strain wave shorten the gradient cellular rod length. Therefore, according to the design method of the density distribution of the crashworthiness design of reverse gradient cellular materials can be achieved.

【學(xué)位授予單位】：中國(guó)科學(xué)技術(shù)大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2017
【分類號(hào)】：TG146.21;TB383.4

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