本文選題：梯度多胞金屬　切入點(diǎn)：犧牲層　出處：《中國(guó)科學(xué)技術(shù)大學(xué)》2017年碩士論文　論文類型：學(xué)位論文

【摘要】：梯度多胞金屬材料由于其可設(shè)計(jì)性受到廣泛關(guān)注,引入密度梯度可望獲得更加優(yōu)異的抗爆炸、抗沖擊性能,在工程防護(hù)領(lǐng)域有著廣闊的應(yīng)用前景。多胞犧牲層是一種多胞材料夾芯復(fù)合結(jié)構(gòu),通過(guò)多胞材料的壓潰行為大量地吸收爆炸/沖擊能量。已有多胞犧牲層抗沖擊行為的研究中,多采用形式簡(jiǎn)單的剛性-理想塑性-鎖定(R-PP-L)沖擊波模型來(lái)表征多胞材料的動(dòng)態(tài)壓潰行為,其與實(shí)際的應(yīng)力-應(yīng)變曲線還存在較大的差異。此外,在梯度多胞材料的能量吸收和消波性能優(yōu)越性的問(wèn)題上尚有爭(zhēng)議。本文運(yùn)用一維非線性塑性沖擊波模型和細(xì)觀有限元模型研究密度梯度多胞犧牲層的抗爆炸性能。通過(guò)量綱分析方法得出影響臨界厚度的主導(dǎo)因素。針對(duì)臨界厚度偏于保守的設(shè)計(jì),發(fā)展了考慮反射波二次加載的分析方法,有效減小芯層厚度以提高多胞金屬材料的利用率�；诼薀o(wú)關(guān)的、剛性-塑性硬化(R-PH)模型,建立了描述沖擊波在梯度多胞犧牲層中傳播的控制方程,得到了密度線性分布的梯度多胞金屬在指數(shù)型爆炸脈沖下的響應(yīng)特性。多胞犧牲層的臨界厚度為爆炸能量恰好被吸收時(shí)的芯層最小厚度,在工程上是一個(gè)重要的設(shè)計(jì)指標(biāo)。分析了臨界厚度與載荷強(qiáng)度、覆蓋層質(zhì)量、多胞材料的密度梯度等參數(shù)之間的關(guān)系,給出了以臨界厚度和支撐端應(yīng)力峰值為指標(biāo)的密度梯度設(shè)計(jì)圖。結(jié)果表明,吸收同等強(qiáng)度的爆炸載荷,正梯度犧牲層需要的厚度小于負(fù)梯度犧牲層。通過(guò)增大梯度參數(shù)值,正梯度能夠有效地降低芯層厚度,但是會(huì)帶來(lái)更大的支撐端應(yīng)力峰值;實(shí)現(xiàn)應(yīng)力峰值最小,均勻密度和負(fù)梯度是較理想的選擇。本文還進(jìn)一步給出了特定的支撐端應(yīng)力峰值下,負(fù)梯度犧牲層臨界厚度與相關(guān)參數(shù)的設(shè)計(jì)圖。通過(guò)量綱分析的方法,建立梯度多胞犧牲層無(wú)量綱臨界厚度與三個(gè)無(wú)量綱參數(shù)之間的關(guān)系,利用控制變量法給出了無(wú)量綱臨界厚度的經(jīng)驗(yàn)公式,并且滿足一定的精度要求。分析結(jié)果表明,沖擊增強(qiáng)因子的平方根S01/2是影響無(wú)量綱臨界厚度的主導(dǎo)因素,密度梯度參數(shù)對(duì)其影響相對(duì)較小,進(jìn)而給出臨界厚度的一階近似解。動(dòng)態(tài)加載下,多胞材料的壓實(shí)應(yīng)變對(duì)沖擊速度具有依賴性,依據(jù)沖擊波衰減設(shè)計(jì)出的犧牲層臨界厚度偏于保守。研究了反射波在有初始變形的正梯度多胞金屬中的傳播規(guī)律,數(shù)值求解得到犧牲層響應(yīng)特性。結(jié)果顯示,在支撐端應(yīng)力不超過(guò)被保護(hù)許可應(yīng)力的前提下,進(jìn)一步縮短芯層厚度使得反射波后方的應(yīng)變從0.4增加到0.7附近,提高了材料的利用率。最后,采用二維Voronoi技術(shù)構(gòu)建了梯度多胞金屬的細(xì)觀有限元模型,檢驗(yàn)了一維非線性塑性沖擊波模型的抗爆炸分析的有效性。
[Abstract]:Gradient polycellular metal materials have attracted extensive attention due to their designability. The introduction of density gradient is expected to achieve better explosion and impact resistance. It has a wide application prospect in the field of engineering protection. The polycellular sacrificial layer is a kind of polycellular material sandwich composite structure, which absorbs the explosion / impact energy greatly through the crushing behavior of the polycellular material, and has been studied in the research of the impact resistance of the sacrificial layer. A simple rigid-ideal plastic locked R-PP-L shock wave model is used to characterize the dynamic collapsing behavior of polycellular materials, which is quite different from the actual stress-strain curves. The superiority of energy absorption and wave dissipation of gradient polycell materials is controversial. In this paper, the explosion resistance of density gradient polycell sacrificial layer is studied by using one-dimensional nonlinear plastic shock wave model and mesoscopic finite element model. . the main factors influencing critical thickness are obtained by dimensional analysis. For the conservative design of critical thickness, An analytical method considering the secondary loading of reflected wave is developed to reduce the thickness of core layer effectively to improve the utilization ratio of polymetallic materials. Based on the rate-independent rigid plastic hardening R-PHmodel, A governing equation describing the propagation of shock waves in gradient sacrificial layers is established. The response characteristics of gradient polycellular metal with linear density distribution under exponential explosion pulse are obtained. The critical thickness of the sacrificial layer is the minimum thickness of the core layer when the explosion energy is exactly absorbed. It is an important design index in engineering. The relationship between critical thickness and load strength, mass of overlay, density gradient of polycell material is analyzed. The density gradient design diagram with the index of critical thickness and peak stress at the support end is given. The results show that the thickness of the positive gradient sacrificial layer is smaller than that of the negative gradient sacrificial layer by increasing the gradient parameter value. The positive gradient can effectively reduce the thickness of the core layer, but it will bring greater stress peak at the support end, and the minimum stress peak value, the uniform density and the negative gradient are the ideal choices. The relationship between the dimensionless critical thickness of gradient polycell sacrificial layer and three dimensionless parameters is established by dimensional analysis. The empirical formula of dimensionless critical thickness is given by using the control variable method, and the accuracy requirement is satisfied. The analysis results show that the square root S01 / 2 of the impact enhancement factor is the dominant factor affecting the dimensionless critical thickness. The density gradient parameter has relatively little effect on it, and then gives the first order approximate solution of the critical thickness. Under dynamic loading, the compaction strain of the polycellular material is dependent on the impact velocity. The critical thickness of the sacrificial layer designed according to the attenuation of shock wave is conservative. The propagation law of the reflected wave in the positive gradient polymetallic with initial deformation is studied. The response characteristics of the sacrificial layer are obtained by numerical solution. Under the condition that the stress at the support end does not exceed the protected allowable stress, further shortening the thickness of the core layer causes the strain behind the reflection wave to increase from 0.4 to around 0.7, which improves the material utilization ratio. The mesoscale finite element model of gradient polycell metals was constructed by using two-dimensional Voronoi technique, and the effectiveness of the one-dimensional nonlinear plastic shock wave model was tested.
【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】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：TG139

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