發(fā)布時間：2018-01-05 13:11

  本文關鍵詞：PVDF壓力測量特性與水下爆炸近場多孔金屬夾芯板動力響應的研究　出處：《中國科學技術大學》2015年博士論文　論文類型：學位論文

  更多相關文章： PVDF壓電薄膜 壓力測量 水下爆炸 多孔金屬夾芯板 動力響應 光滑粒子法

【摘要】：多孔金屬材料夾芯結構具有超輕質(zhì)、高比強度、高比剛度、良好的耗能效率等物理和力學特性,近年來被廣泛應用于工程防護、航空航天、建筑和海洋工程等領域,在各種服役環(huán)境中發(fā)揮良好的工程作用,而有關多孔金屬夾芯結構在準靜態(tài)和動態(tài)載荷下的力學行為問題也由此成為學術研究的重點之一。由于多孔金屬夾芯結構組成方式的多樣性和受到載荷的復雜性,這一課題仍有大量問題需要解決。目前,有關多孔金屬夾芯結構在沖擊或爆炸等強動載荷作用下的力學行為研究多局限于空中加載條件下,然而該復合結構作為一種具有優(yōu)異物理特性和力學性能的工程結構,可在海洋防護和艦船工業(yè)中得到廣泛應用,而目前有關多孔金屬夾芯結構在水下爆炸載荷作用下的力學行為及其失效機理的研究較為少見。此外,以PVDF壓電薄膜為敏感元件的壓力傳感器在爆炸腫擊壓力測量中被廣泛地使用,相比于其他測壓敏感元件,壓電薄膜具有壓電常數(shù)大、頻響寬、信噪比高、便于加工、成本低廉等優(yōu)點。以其為敏感元件制作的薄膜式壓力計,便于布設在結構層間或表面進行壓力測試又不干擾結構響應。然而,其靈敏度系數(shù)不穩(wěn)定性及其應用技術方面仍然存在諸多問題,尤其是利用PVDF壓力計測量水下爆炸試驗中結構流固界面壓力時,仍然存在測試技術上的難點。因此,本文針對典型的蜂窩鋁夾芯板進行水下爆炸實驗,研究其抗水下爆炸性能及動態(tài)力學行為。為測試水下爆炸中流固界面上的加載壓力,特對夾芯式PVDF壓力計不同條件下的界面壓力測量特性進行研究與總結。 通過SHPB實驗裝置對自制夾芯式PVDF壓力計進行一系列的標定試驗,發(fā)現(xiàn)壓力計制作工藝引起的傳感器內(nèi)部不平整和壓桿端部接觸質(zhì)量是導致其力計靈敏度系數(shù)不穩(wěn)定的主要原因,包括引線覆壓區(qū)域的應力集中效應、剪切效應和標定實驗中壓桿端部與壓力計接觸時敏感元件實際受力面積的不確定性。針對壓力計厚度和實驗桿端接觸情況改進后,得到擬合靈敏度系數(shù)K=24.7pC/N。由此可知,PVDF壓力的標定和使用過程中,需要考慮壓力計的實際受力狀況。為此,針對不同情況下結構表面(固-固界面和流固界面)爆炸壓力的測量進行試驗研究,從壓力計橫向效應、界面的接觸情況和界面兩側介質(zhì)屬性的差異性三個方面分析了不同介質(zhì)交界面上PVDF壓力計的壓力測量特性,其中界面兩側介質(zhì)屬性差異性又主要體現(xiàn)在二者波阻抗和可壓縮性的差異性。然后為拓展PVDF壓力計在水下爆炸壓力測試中的應用,以壓電薄膜為敏感元件設計并制作一種PVDF型水下爆炸壓力傳感器,該傳感器基本能夠滿足近場水下爆炸壓力測試要求,通過水下標定實驗可知其靈敏度系數(shù)K=13.84pC/N,進一步證明PVDF壓力計的靈敏度系數(shù)應根據(jù)其實際使用條件進行標定。 針對鋁板-蜂窩鋁-鋁板夾芯結構進行近場水下爆炸實驗,并通過一系列對比實驗研究各設計參數(shù)對結構響應和次生沖擊波的影響規(guī)律。結果分析中,同時以結構背板最大塑性變形和背部次生沖擊波強度來衡量不同配置的復合結構的抗水下爆炸性能,并對水下爆炸載荷作用下的結構變形／失效模式進行了分析總結。結果表明：在保證芯層配置和加載條件相同的條件下,增大面板厚度可以有效降低結構背板最大塑性變形并同時降低次生沖擊波強度；當結構面板厚度和加載條件相同時,增大芯層的高度可以有效降低結構背板最大變形,同時能夠增大沖擊波的衰減行程從而降低背部次生沖擊波的強度；增大鋁箔厚度意味著增加芯層的相對密度,雖然能夠提高芯層壓縮過程中吸收的能量從而降低結構背板最大變形,但同時會增大背部次生沖擊波的強度；芯層孔邊長為單變量因素時,結構最大變形與其并不成單調(diào)關系。相同芯層高度和鋁箔厚度前提下,增大孔邊長度能夠提高芯層壓縮的容易程度以便吸收更多的能量從而降低背板的變形幅度,但是當芯層孔邊長度過大時,芯層極易過早地被壓縮至密實化,使得過多的能量傳遞到背板從而產(chǎn)生更大的變形。總結可知,芯層的密度是影響結構背部次生沖擊波強度的主要因素,而結構的能量吸收過程和動態(tài)響應則與芯層的設計參數(shù)相關。對實驗后的樣本進行結構變形／失效分析,發(fā)現(xiàn)近場水下爆炸作用下,結構的前面板變形較為復雜,當面板越薄、承受爆炸沖量越大時,面板失效形式越復雜,往往呈現(xiàn)出中心區(qū)域的局部失效、周邊區(qū)域的花瓣形褶皺失效以及整個迎爆面的塑性大變形：對于背板而言,所有背板均產(chǎn)生球冠形塑性大變形；芯層則首先呈現(xiàn)出與背板相吻合的彎曲變形和自上而下的漸進壓縮形態(tài),壓縮高度自中心向外逐漸降低,邊界處由于固支約束會形成一圈剪切破壞區(qū),當芯層被完全壓實時,可能出現(xiàn)孔外穿透、芯層拉伸斷裂等失效形態(tài)。最后,通過對等質(zhì)量的實體板對比實驗可知,蜂窩鋁夾芯板抵抗變形能力大于等質(zhì)量的實體板,而且復合結構對于降低背部次生沖擊波強度的效果更為明顯,蜂窩鋁夾芯結構的抗水下爆炸性能明顯優(yōu)于等質(zhì)量實體結構。 通過應變測量研究水下爆炸作用下前后面板的動態(tài)行為,然后進行對應的空中爆炸實驗,對比分析水下和空中爆炸載荷下蜂窩鋁夾芯板變形失效模式的差異性。結果表明：結構響應初期前面板中心區(qū)域的應變?yōu)閺澗刂鲗?中心向外區(qū)域彎矩主導過程較短而轉(zhuǎn)為面內(nèi)拉力主導的變形和失效,靠近邊界處面板由于固支邊界而表現(xiàn)出明顯的彎矩效應,前面板中心和邊界區(qū)域比中間區(qū)域應變受彎矩影響大。背板中心區(qū)域和邊界處的應變?yōu)閺澗睾兔鎯?nèi)拉力疊加作用,中間區(qū)域則主要為面內(nèi)拉力產(chǎn)生的正應變。面板應變信號初始時刻都有明顯的對應于沖擊波的沖擊應變,且對于相同芯層配置的結構而言,面板強度越低沖擊應變越明顯；沖擊應變之后面板均開始出現(xiàn)彎矩主導的應變信號,即對于強度較弱的結構,Fleck描述的三階段解耦模型相對保守。相同藥量和爆心距離條件下,水下爆炸作用下的結構失效主要以整體塑性大變形和芯層的漸進壓縮為主,而空中爆炸時結構則以面板中心區(qū)域的花瓣形撕裂和芯層的橫向破壞為主,即同藥量和爆心距時,近場空中爆炸對結構的毀傷程度和范圍大于水下爆炸。近場空中和水下爆炸載荷作用機理的差異性導致其毀傷模態(tài)的不同,其差異性可從沖擊波和流固耦合過程兩個方面解釋：一方面,一般情況下空氣中沖擊波速度較低,空氣沖擊波和爆炸產(chǎn)物的作用具有較強的局部性和瞬態(tài)性,因此結構易產(chǎn)生局部失效甚至破壞；另一方面,水下爆炸沖擊波和氣泡載荷能量相當,但二者作用時間尺度差別大,因此水下爆炸時結構受到的能量和沖量的傳遞過程較為分散,結構更趨向于產(chǎn)生整體變形。 基于上述實驗研究結果,應用非線性有限元程序LS-DYNA對水下爆炸載荷下蜂窩鋁夾芯結構的動態(tài)行為進行數(shù)值模擬研究,分析了水下爆炸載荷作用和結構響應過程,探討了夾芯結構各組件之間的能量傳遞和吸收規(guī)律。以六面體單元劃分的實體芯層模型計算中,分別考察面板厚度、芯層密度和高度三個關鍵參數(shù)對結構變形和各組件間能量吸收的影響規(guī)律,結果表明計算得到的三個關鍵參數(shù)對背板中心撓度的影響規(guī)律與實驗結果較為一致；通過結構各組件能量耗散分析發(fā)現(xiàn)增大面板厚度會降低結構吸收的總能量和芯層吸收能量在總能量中的比例；隨著芯層高度的增大,結構吸收的總能量降低,可以提高結構抗變形能力和芯層吸收能量的百分比；提高芯層密度會減小結構吸收的總能量,但可以提高芯層能量占總能量的比重。采用殼單元劃分的蜂窩模型可以較為清晰地描述芯層在變形過程中的漸進屈曲、密實化、塑性大變形和蜂窩面外壓縮等失效模式。分析認為面外屈曲壓潰和彎矩導致的孔壁轉(zhuǎn)動可能是導致芯層和背板層間失效的主要原因�？偨Y可知,抗爆炸／沖擊的結構在設計關鍵參數(shù)時,需要同時考慮結構的抗變形能力、衰減沖擊波的性能和各組件的能量吸收能力三個要素。
[Abstract]:Sandwich structure of porous metal materials with ultra lightweight, high specific strength, high specific stiffness, energy efficiency and other physical and good mechanical properties, has been widely used in engineering protection, aerospace, construction and marine engineering and other fields, in a variety of service play good role in environmental engineering, and the mechanical behavior of porous metal sandwich structure in quasi-static and dynamic loads which have become one of the focus of academic research. Because of the complexity of porous metal sandwich structure diversity and load, this topic is still a lot of problems need to be solved. At present, the porous metal sandwich structures under impact or explosion dynamic mechanical behavior of the load. The limited to air loading conditions, however, the composite structure is a kind of excellent physical properties and mechanical properties of engineering structures in ocean protection and Widely used in shipbuilding industry, and the current research on porous metal sandwich structure under water mechanics of explosion load behavior and failure mechanism is relatively rare. In addition, the PVDF piezoelectric film is widely used for pressure sensor pressure in the explosion swelling measurement, compared to other pressure sensitive element. The piezoelectric film has a large piezoelectric constant, wide frequency response, high signal-to-noise ratio, easy processing, low cost and other advantages. The film type pressure sensitive element production, convenient layout and pressure test in the structure layer or surface does not disturb the response of the structure. However, there are still many problems in its instability and its application the sensitivity coefficient, especially solid interface pressure structure blast test flow meter under the water pressure by PVDF, there are still difficulties in testing technology. Therefore, this paper. The underwater honeycomb sandwich panels were subjected to underwater explosion experiments to study their underwater explosion performance and dynamic mechanical behavior. In order to test the loading pressure on the fluid solid interface during underwater explosion, the characteristics of the interface pressure measurement of sandwich PVDF pressure gauge under different conditions were studied and summarized.
The homemade sandwich type PVDF pressure gauge calibration test was made through a series of SHPB experimental device, pressure gauge sensor manufacturing process that caused by uneven and rod end contact quality is the main cause of its force sensitivity coefficient of instability, including lead overburden pressure in the area of stress concentration effect and shear effect the calibration experiment and the end of the pressure rod contact pressure gauge when the actual stress sensitive element area of uncertainty. According to the experimental pressure gauge thickness and rod end contact situation improved, fitting the sensitivity coefficient K=24.7pC/N. of the calibration and use of PVDF pressure, the need to consider the actual stress condition of pressure gauge. Therefore, according to the the surface structure under different conditions (solid solid interface and liquid-solid interface) experimental study on measurement of explosion pressure gauge, the transverse effect from pressure, contact and both sides of the interface dielectric interface Three aspects of quality attribute analysis on the difference of pressure measurement interface PVDF pressure gauge of different media, especially the difference of both sides of the interface properties of the medium is mainly reflected in the difference of wave impedance and compressibility of two. Then in the underwater explosion pressure measurement test plan for the application to expand PVDF pressure. Piezoelectric thin film pressure sensor for sensitive elements for design and a PVDF type underwater explosion, the sensor can basically meet the requirements of pressure test of near field underwater explosion, the underwater calibration experiment shows the sensitivity coefficient of K=13.84pC/N, further proved that the sensitivity coefficient of PVDF pressure gauge should be calibrated according to the actual conditions of use.
The aluminum - aluminum honeycomb sandwich structure - plate experiments near field underwater explosion, and through a series of experiments on various design parameters on the structural response and the impact of the secondary wave. The results of the analysis, at the same time to maximize the structure distortion and the back of the secondary shock wave to measure the intensity of different configurations of composite structure the anti explosion performance of underwater, underwater explosion load, deformation and failure mode were analyzed. The results showed that: in ensuring the core layer configuration and loading under the same conditions, increasing the thickness of the panel structure can effectively reduce the back the maximum plastic deformation and decrease the strength of the secondary shock wave when the structure; panel thickness and loading conditions are the same, increasing the height of the core layer can effectively reduce the maximum deformation of the structure at the same time can increase travel back, attenuation of shock wave and reduce back The secondary shock wave strength; increase the thickness of the aluminum foil means to increase the relative density of the core layer, the core layer can improve the compression process of the absorption of energy in order to reduce the maximum deformation of the structure back, but at the same time will increase the intensity of shock wave in the secondary back; the core layer hole length of single variable factors, the maximum deformation of structure and is not monotone the relationship between the same core. The height and thickness of aluminum under the premise of increasing hole length can improve the degree of compression of the core layer easy to absorb more energy so as to reduce the deformation amplitude back, but when the core hole length is too large, the core layer can easily be prematurely compressed to densification, making too much energy transfer to the backplane resulting in greater deformation. The summary, the core layer density is the main factors affect the structure of the back of secondary shock wave intensity, and the structure of the energy absorption process and dynamic response and The design parameters of the core layer. Failure analysis of deformation / structure of experimental samples after, found that near field underwater explosion, the front panel deformation of the structure is relatively complex, when the panel is thin, under explosion impulse is large, the panel failure forms more complex, often showing a local regional center of the failure of petals shaped fold surrounding area as well as the failure of blasting surface plastic deformation for backplane, produce spherical large plastic deformation are all back; the core layer is consistent with the first show back bending deformation and top-down progressive compression, compression height decreased gradually outward from the center, at the boundary due to solid a constraint will form a circle shear failure zone, when the core layer is fully compacted, possible hole penetration, failure form of core layer tensile fracture. Finally, through the entity board on the quality of the equivalence ratio, Honeycomb aluminum sandwich panels are more resistant to deformation than those of equal mass. Moreover, the composite structure has more obvious effect on reducing the secondary shock wave strength of the back, and the underwater explosion performance of honeycomb aluminum sandwich structure is better than that of the equal mass solid structure.
The dynamic behavior of underwater explosion under the front and rear panels of strain measurement, and then the air explosion experiments corresponding to the difference analysis of failure modes of aluminum honeycomb sandwich plate under water and air explosion load deformation are compared. The results show that: the structural response before early strain heart panel for the moment leading, the center outward bending moment the leading process is short to in-plane deformation and failure of the dominant force, close to the border because the panel clamped boundary and show bending effect obviously, the front panel center and the border area than the middle region. Effects of bending strain and strain back center area and the boundary for the moment and the surface tension of superposition effect the middle region is mainly positive in-plane tension. The initial strain signal panel has obvious impact strain corresponding to the shock wave, and for the same core layer The structure, the lower panel strength impact strain is more obvious; the impact of strain after the panel began leading the bending strain signal, the structure for weak intensity, the three phase decoupling model described by Fleck is relatively conservative. The same charge and blasting center distance under the condition of the structure subjected to underwater explosion failure mainly progressive compression the overall plastic deformation and the core layer, and the air blast when the structure is destroyed in the transverse panel in the center region of the petal shaped tear and core layer, namely the same charge and blasting center distance, near field air explosion on damage degree and range of structure than that of underwater explosion. The difference of load mechanism near field air and underwater explosion caused the damage mode is different, the difference can be from two aspects of shock wave and fluid solid coupling process: on the one hand, the general situation of air shock wave in low speed, The air shock wave and explosion effect of the product is local and transient stronger, so the structure is easy to produce local failure or damage; on the other hand, the underwater explosion shock wave and the bubble load energy, but the role of the two different time scales, so the underwater explosion energy transfer process by node structure and impulse the more dispersed structure tend to produce a deformation.
Based on the experimental results, the dynamic behavior of the application of nonlinear finite element program LS-DYNA on aluminum honeycomb sandwich structure under the underwater explosion load was studied by numerical simulation, analysis of the load and the structure response process of underwater explosion, probes into the sandwich structure of each component of energy transfer and absorption law. With solid core layer model divided hexahedron element in the calculation, respectively. The effect of panel thickness, structural deformation and influence rules between components of the energy absorption of the core density and height of three key parameters, the results show that the three key parameters calculated on the backplane center deflection and the impact of the experimental results are consistent; through the analysis of energy dissipation structure of each component that increases the panel the thickness will reduce the total energy absorption structure and core layer to absorb energy in the total energy ratio; with the increase of the height of the core layer, absorbing structure The total energy is reduced, the structure can improve the anti deformation capacity and energy absorption percentage of core layer; increasing the core density will reduce the total energy absorption structure, but can improve the core energy and total energy. The proportion of the honeycomb model shell elements can clearly describe the core layer in the deformation process of the progressive buckling, densification, plastic deformation and honeycomb compression failure mode. Analysis shows that the rotating wall buckling and bending moment caused by crushing was likely to cause the core layer and the backplane layer failure. The summary, structure of anti explosion / impact in the design of key parameters, taking into account the needs of the anti deformation capability of the structure, the three elements of attenuation of shock waves and the components of the energy absorption capacity.

【學位授予單位】：中國科學技術大學
【學位級別】：博士
【學位授予年份】：2015
【分類號】：TB383.4

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