PVDF压力测量特性与水下爆炸近场多孔金属夹芯板动力响应的研究

发布时间：2018-01-05 13:11

本文关键词：PVDF压力测量特性与水下爆炸近场多孔金属夹芯板动力响应的研究　出处：《中国科学技术大学》2015年博士论文　论文类型：学位论文

【摘要】：多孔金属材料夹芯结构具有超轻质、高比强度、高比刚度、良好的耗能效率等物理和力学特性,近年来被广泛应用于工程防护、航空航天、建筑和海洋工程等领域,在各种服役环境中发挥良好的工程作用,而有关多孔金属夹芯结构在准静态和动态载荷下的力学行为问题也由此成为学术研究的重点之一。由于多孔金属夹芯结构组成方式的多样性和受到载荷的复杂性,这一课题仍有大量问题需要解决。目前,有关多孔金属夹芯结构在冲击或爆炸等强动载荷作用下的力学行为研究多局限于空中加载条件下,然而该复合结构作为一种具有优异物理特性和力学性能的工程结构,可在海洋防护和舰船工业中得到广泛应用,而目前有关多孔金属夹芯结构在水下爆炸载荷作用下的力学行为及其失效机理的研究较为少见。此外,以PVDF压电薄膜为敏感元件的压力传感器在爆炸肿击压力测量中被广泛地使用,相比于其他测压敏感元件,压电薄膜具有压电常数大、频响宽、信噪比高、便于加工、成本低廉等优点。以其为敏感元件制作的薄膜式压力计,便于布设在结构层间或表面进行压力测试又不干扰结构响应。然而,其灵敏度系数不稳定性及其应用技术方面仍然存在诸多问题,尤其是利用PVDF压力计测量水下爆炸试验中结构流固界面压力时,仍然存在测试技术上的难点。因此,本文针对典型的蜂窝铝夹芯板进行水下爆炸实验,研究其抗水下爆炸性能及动态力学行为。为测试水下爆炸中流固界面上的加载压力,特对夹芯式PVDF压力计不同条件下的界面压力测量特性进行研究与总结。通过SHPB实验装置对自制夹芯式PVDF压力计进行一系列的标定试验,发现压力计制作工艺引起的传感器内部不平整和压杆端部接触质量是导致其力计灵敏度系数不稳定的主要原因,包括引线覆压区域的应力集中效应、剪切效应和标定实验中压杆端部与压力计接触时敏感元件实际受力面积的不确定性。针对压力计厚度和实验杆端接触情况改进后,得到拟合灵敏度系数K=24.7pC/N。由此可知,PVDF压力的标定和使用过程中,需要考虑压力计的实际受力状况。为此,针对不同情况下结构表面(固-固界面和流固界面)爆炸压力的测量进行试验研究,从压力计横向效应、界面的接触情况和界面两侧介质属性的差异性三个方面分析了不同介质交界面上PVDF压力计的压力测量特性,其中界面两侧介质属性差异性又主要体现在二者波阻抗和可压缩性的差异性。然后为拓展PVDF压力计在水下爆炸压力测试中的应用,以压电薄膜为敏感元件设计并制作一种PVDF型水下爆炸压力传感器,该传感器基本能够满足近场水下爆炸压力测试要求,通过水下标定实验可知其灵敏度系数K=13.84pC/N,进一步证明PVDF压力计的灵敏度系数应根据其实际使用条件进行标定。针对铝板-蜂窝铝-铝板夹芯结构进行近场水下爆炸实验,并通过一系列对比实验研究各设计参数对结构响应和次生冲击波的影响规律。结果分析中,同时以结构背板最大塑性变形和背部次生冲击波强度来衡量不同配置的复合结构的抗水下爆炸性能,并对水下爆炸载荷作用下的结构变形／失效模式进行了分析总结。结果表明：在保证芯层配置和加载条件相同的条件下,增大面板厚度可以有效降低结构背板最大塑性变形并同时降低次生冲击波强度；当结构面板厚度和加载条件相同时,增大芯层的高度可以有效降低结构背板最大变形,同时能够增大冲击波的衰减行程从而降低背部次生冲击波的强度；增大铝箔厚度意味着增加芯层的相对密度,虽然能够提高芯层压缩过程中吸收的能量从而降低结构背板最大变形,但同时会增大背部次生冲击波的强度；芯层孔边长为单变量因素时,结构最大变形与其并不成单调关系。相同芯层高度和铝箔厚度前提下,增大孔边长度能够提高芯层压缩的容易程度以便吸收更多的能量从而降低背板的变形幅度,但是当芯层孔边长度过大时,芯层极易过早地被压缩至密实化,使得过多的能量传递到背板从而产生更大的变形。总结可知,芯层的密度是影响结构背部次生冲击波强度的主要因素,而结构的能量吸收过程和动态响应则与芯层的设计参数相关。对实验后的样本进行结构变形／失效分析,发现近场水下爆炸作用下,结构的前面板变形较为复杂,当面板越薄、承受爆炸冲量越大时,面板失效形式越复杂,往往呈现出中心区域的局部失效、周边区域的花瓣形褶皱失效以及整个迎爆面的塑性大变形：对于背板而言,所有背板均产生球冠形塑性大变形；芯层则首先呈现出与背板相吻合的弯曲变形和自上而下的渐进压缩形态,压缩高度自中心向外逐渐降低,边界处由于固支约束会形成一圈剪切破坏区,当芯层被完全压实时,可能出现孔外穿透、芯层拉伸断裂等失效形态。最后,通过对等质量的实体板对比实验可知,蜂窝铝夹芯板抵抗变形能力大于等质量的实体板,而且复合结构对于降低背部次生冲击波强度的效果更为明显,蜂窝铝夹芯结构的抗水下爆炸性能明显优于等质量实体结构。通过应变测量研究水下爆炸作用下前后面板的动态行为,然后进行对应的空中爆炸实验,对比分析水下和空中爆炸载荷下蜂窝铝夹芯板变形失效模式的差异性。结果表明：结构响应初期前面板中心区域的应变为弯矩主导,中心向外区域弯矩主导过程较短而转为面内拉力主导的变形和失效,靠近边界处面板由于固支边界而表现出明显的弯矩效应,前面板中心和边界区域比中间区域应变受弯矩影响大。背板中心区域和边界处的应变为弯矩和面内拉力叠加作用,中间区域则主要为面内拉力产生的正应变。面板应变信号初始时刻都有明显的对应于冲击波的冲击应变,且对于相同芯层配置的结构而言,面板强度越低冲击应变越明显；冲击应变之后面板均开始出现弯矩主导的应变信号,即对于强度较弱的结构,Fleck描述的三阶段解耦模型相对保守。相同药量和爆心距离条件下,水下爆炸作用下的结构失效主要以整体塑性大变形和芯层的渐进压缩为主,而空中爆炸时结构则以面板中心区域的花瓣形撕裂和芯层的横向破坏为主,即同药量和爆心距时,近场空中爆炸对结构的毁伤程度和范围大于水下爆炸。近场空中和水下爆炸载荷作用机理的差异性导致其毁伤模态的不同,其差异性可从冲击波和流固耦合过程两个方面解释：一方面,一般情况下空气中冲击波速度较低,空气冲击波和爆炸产物的作用具有较强的局部性和瞬态性,因此结构易产生局部失效甚至破坏；另一方面,水下爆炸冲击波和气泡载荷能量相当,但二者作用时间尺度差别大,因此水下爆炸时结构受到的能量和冲量的传递过程较为分散,结构更趋向于产生整体变形。基于上述实验研究结果,应用非线性有限元程序LS-DYNA对水下爆炸载荷下蜂窝铝夹芯结构的动态行为进行数值模拟研究,分析了水下爆炸载荷作用和结构响应过程,探讨了夹芯结构各组件之间的能量传递和吸收规律。以六面体单元划分的实体芯层模型计算中,分别考察面板厚度、芯层密度和高度三个关键参数对结构变形和各组件间能量吸收的影响规律,结果表明计算得到的三个关键参数对背板中心挠度的影响规律与实验结果较为一致；通过结构各组件能量耗散分析发现增大面板厚度会降低结构吸收的总能量和芯层吸收能量在总能量中的比例；随着芯层高度的增大,结构吸收的总能量降低,可以提高结构抗变形能力和芯层吸收能量的百分比；提高芯层密度会减小结构吸收的总能量,但可以提高芯层能量占总能量的比重。采用壳单元划分的蜂窝模型可以较为清晰地描述芯层在变形过程中的渐进屈曲、密实化、塑性大变形和蜂窝面外压缩等失效模式。分析认为面外屈曲压溃和弯矩导致的孔壁转动可能是导致芯层和背板层间失效的主要原因。总结可知,抗爆炸／冲击的结构在设计关键参数时,需要同时考虑结构的抗变形能力、衰减冲击波的性能和各组件的能量吸收能力三个要素。
[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.

【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TB383.4

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