压杆应变式压力传感器在爆炸冲击波载荷测试中的应用

在容器内实施化学爆炸时，容器内壁上冲击波载荷的确定是进行爆炸容器结构动力响应分析、安全评估和工程设计的基础。获得比较准确、可靠的爆炸容器内壁上作用载荷的时间历程及分布情况，对研究结构动力响应意义重大。文章采用压杆应变式压力传感器来测量爆炸冲击波载荷，这种传感器解决了普通传感器在高频压力脉冲下频响低且容易损坏等问题。压杆应变式压力传感器为一细长弹性杆，爆炸冲击波作用在杆的一端，在杆中激发一维弹性应力波，通过测量杆上适当位置处的应变，利用一维弹性应力波理论可以计算出作用在杆端的爆炸冲击载荷。文章根据一维弹性波理论，设计了满足所需频响、上升时间、持续作用时间等参数要求的压杆应变式压力传感器，其材料为高强度钢，采用动态应变放大器和数据采集仪组成测量系统。通过实验，获得了比较完整的容器内壁上冲击波载荷曲线，测量结果的重复性和一致性很好。经分析表明，压杆应变式压力传感器能准确地测得容器内壁上冲击波荷载的幅值和比较完整的曲线，对爆炸冲击波载荷测试来说，是一种比较准确可靠的传感器。     

波在考虑热载荷和转动惯量效应的非线性大变形多层压电层合壳内的传播研究

研究了非线性大变形、层合壳的铺设形式、转动惯量及热载荷效应对波在压电层合壳中传播的影响。首先利用Hamilton最小势能变分原理推导了波在大变形压电层合壳内传播的非线性动力学平衡方程;通过求解方程特征值得到了波传播特征曲线;数值算例表明波在压电层合壳内传播与壳体大变形、转动惯量以及热载荷有关,并与线性小变形理论(Cooper-Naghdi壳体理论)进行了比较。     

复合壳体抗水下爆炸作用机理研究

结合应力波在介质界面的反射透射机理以及应力波的衰减规律对复合壳体抗水下爆炸冲击作用进行了研究,找出了影响应力波衰减的显著因子,并提出了"匹配系数"的概念,为设计具有最佳防护效果的复合壳体提供了理论依据.     

纤维增强攻坚战斗部在混凝土中爆炸威力试验研究

为考核纤维增强攻坚战斗部在混凝土中的爆炸毁伤效应,对裸装药、复合材料壳体、钢壳体装药在混凝土靶中的爆炸破坏效应进行了对比试验研究。试验结果表明,同样装药情况下,裸装药爆炸产生的破坏区域大于复合壳体及钢壳体装药;复合材料壳体装药在阻抗匹配方面要比钢壳体装药好,更利于爆炸冲击波的传播;同样装药情况下,复合材料壳体装药爆炸对靶体爆炸驱动有效能量大于钢壳体装药。     

波传播法求解低频激励下水中加端板圆柱壳的振动

采用波传播法研究了低频下水中壳体的振动与响应。水中壳体由有限长加流体载荷的圆柱壳和两端的圆形端板组成,其中外部流体载荷用无限长模型进行近似处理。为了模拟推动系统的激励及船体上某一点激励,分别考虑了不同位置的轴向载荷和径向载荷,讨论了单个周向模态下的位移在总位移中的比重。主要研究了4种载荷,即作用在端板中心的轴对称载荷、作用在端板与圆柱连接处的轴向载荷、作用在连接处的径向载荷和作用在壳体中间的径向载荷,比较得出了轴对称和非轴对称、同一点不同方向载荷、同一方向不同位置载荷的响应位移的不同。此外,还研究了两端端板对不同载荷下水中壳体响应的影响,得出了端板主要抑制了壳体的较高阶模态下径向位移的结论。解析法结果与有限元法结果进行了比较,验证了该方法的正确性。     

复合壳体对炸药抗破片冲击起爆影响研究

主要针对复合壳体对炸药抗破片冲击起爆的防护问题,基于仿真和实验结果可行性校验基础上,开展了不同复合壳体对炸药层内压力峰值、能量变化等影响特性研究。通过不同中间层复合壳体方案的对比可知,低波阻抗复合壳体(钢-聚脲树脂-钢)可使炸药层压力峰值大幅下降为单一钢壳体的36%;结果同时表明中间层材料比强度越高,抗破片侵彻和吸能性能越强;改变复合壳体排列顺序,将聚脲树脂作为壳体内衬时,炸药层峰值压力仅为单一钢壳体的30%,传入炸药层的能量比单一钢壳体降低近一个数量级;当复合壳体厚度与单一钢壳体相同时,钢-聚脲树脂复合壳体中炸药的峰值压力降为单一钢壳体的64%,传入炸药层的能量减少约一半。由此可见复合壳体显著降低了破片作用下炸药层的峰值压力和传入炸药的能量,可有效提高炸药抗破片冲击起爆的能力。研究结果可为复合壳体用于炸药抗冲击起爆的设计与分析提供重要参考。     

流体作用下正交各向异性圆锥壳的自由振动

给出了流体载荷作用下正交各向异性圆锥壳体的自由振动理论模型。通过波传播法和Galerkin法得到了流体载荷作用下截锥壳体自由振动的解。流体载荷作用下的锥壳被划分为好几段,并且每个小圆锥段被当作一个小圆柱段。通过确定每个小圆柱段的流体载荷,来确定锥壳的流体载荷。这样,作用在锥壳上的流体载荷逐段加载。流体载何以及没有流体载荷作用的各向同性和正交各向异性圆锥壳的数值结果被计算出来阐述求解过程的有效性。     

水下爆炸应力波在含声学覆盖层结构中的传播规律

 针对舰船的含声学覆盖层结构,对水下爆炸作用下应力波在该结构中的传播规律进行研究。采用二阶Godunov方法,建立水下爆炸应力波在多层介质中传播的计算模型,并与经典Taylor平板解析解进行对比验证;通过对不同工况下的应力波传播规律分析,获得边界条件、声学覆盖层厚度等参数对其影响规律,可为舰艇抗冲击设计、研究提供参考。     

织物/聚脲柔性复合材料抗爆性能研究进展

织物/聚脲柔性复合材料因轻质和优异的防爆性能而成为个体及公共建筑材料防爆领域的关键材料.本文阐述了爆炸载荷的传播机制及破坏机理,探讨了爆炸冲击载荷下织物/聚脲柔性复合材料的作用机制及吸能方式,总结了织物增强体和聚脲分别对防爆复合材料性能的影响;同时,在现有研究基础上指出了目前存在的问题并提出建议,为今后新型轻质高强织物/聚脲柔性复合材料的研究提供参考依据及前沿思路.     

含半椭圆表面裂纹圆柱壳体的三维热弹性动态断裂

研究了含轴向半椭圆表面裂纹的圆柱壳体在热应力与冲击载荷作用下的动态断裂情况,并应用所研制的三维动态断裂有限元程序进行了大规模的数值计算,确定了圆柱壳体的三维温度分布及热-力耦合下的动态应力强度因子,所得结果在一定程度上揭示了热-力作用下圆柱壳体的边界表面、裂纹面、物质惯性和弹性波的相互作用在结构动态断裂中的重要性。     

含随机参数的散粒体增量型内时本构关系

散粒体材料的力学性能具有较强的随机性,研究其对本构关系的影响很有必要。在散粒体增量型内时本构关系的基础上,考虑材料参数的随机性,利用小参数摄动法,分析了应力增量和材料参数的统计特征值之间的关系,探讨了各参数的随机性对应力的影响程度。首先推导了散粒体增量型内时本构关系的摄动表达式,然后对式中的各参数进行了确定,最后由材料参数的均值和方差得到了应力增量的均值和方差,并以一个算例验证了方法的可行性。     

Some observations on the regularizing field for gradient damage models

Summary Gradient enhanced material models can potentially preserve well-posedness of incremental boundary value problems also after the onset of strain softening. Gradient dependent constitutive relations are rooted in the assumption that some scalar or tensor field, which appears in the yield function, has to be enriched by adding a term involving its second-order gradient field. For gradient-dependent plasticity this term is universally accepted to be the equivalent plastic strain. For gradient-dependent damage models different choices have been presented in the literature. They all possess the desired regularization of the solution, but they are not identical as regards the structural response. In this paper the implications of the choice of the regularization field are discussed. As an example a plasticity-like damage material model is formulated. Finally, a well-known one-dimensional problem is solved analytically, and the results are compared with results obtained via other gradient approaches.     

Quasi-static analysis of multilayered domains with viscoelastic layer using incremental-layerwise finite element method

This paper presents a layerwise finite element formulation for quasi-static analysis of laminated structures with embedded viscoelastic material whose constitutive behavior is represented by the Prony series. To account the time dependence of the constitutive relations of linear viscoelastic materials, the incremental formulation in the temporal domain is used. This approach avoids the use of relaxation functions and mathematical transformations. A computer code based on the presented formulation has been developed to provide the numerical results. The high accuracy of the method is exhibited by comparing the results with existing solutions in the literature and also with those obtained using the ABAQUS software. Finally, and as an application of the presented formulation, the effects of time and load rate on the quasi-static structural response of asphalt concrete (AC) pavements are studied.     

Multiscale modeling of impact on heterogeneous viscoelastic solids containing evolving microcracks

Multiscale computational techniques play a major role in solving problems related to viscoelastic composites due to the complexities inherent to these materials. In this paper, a numerical procedure for multiscale modeling of impact on heterogeneous viscoelastic solids containing evolving microcracks is proposed in which the (global scale) homogenized viscoelastic incremental constitutive equations have the same form as the local‐scale viscoelastic incremental constitutive equations, but the homogenized tangent constitutive tensor and the homogenized incremental history‐dependent stress tensor at the global scale depend on the amount of damage accumulated at the local scale. Furthermore, the developed technique allows the computation of the full anisotropic incremental constitutive tensor of viscoelastic solids containing evolving cracks (and other kinds of heterogeneities) by solving the micromechanical problem only once at each material point and each time step. The procedure is basically developed by relating the local‐scale displacement field to the global‐scale strain tensor and using first‐order homogenization techniques. The finite element formulation is developed and some example problems are presented in order to verify the approach and demonstrate the model capabilities. Copyright © 2009 John Wiley & Sons, Ltd.     

A constitutive model for unsaturated soils: thermomechanical and computational aspects

This paper first presents a complete formulation of a constitutive model that deals with the irreversible behaviour of unsaturated soils under various loading and drying/wetting conditions. A standard form of incremental stress-strain relations is derived. The constitutive model is then cast into the thermodynamical theories and verified using the thermomechanical principles. It is shown that hydraulic hysteresis does not contribute to the plastic dissipation, though it contributes to the plastic work. All plastic work associated with a plastic increment of the degree of saturation is stored and can be recovered in a reversed plastic increment of saturation. The incremental constitutive equations are also reformulated for implementation in finite element codes where displacements and pore pressures are primary unknowns. Qualitative predictions of the constitutive model show that incorporating two suction related yield surfaces and non-associated flow rules into the Barcelona Basic Model opens a full range of possibilities in modelling unsaturated soil behaviour.     

A new asymptotic model of flexible composite shells of a regular structure

A new model of a flexible composite shell of a regular structure is obtained within the framework of the nonlinear membrane theory. The fundamental relations which describe the geometry and deformation of a thin shell on the basis of the geometrically nonlinear theory are used. It is assumed that the shell is made of an inhomogeneous composite material of a periodic structure, i.e. the midsurface consists of a large number of piecewise-homogeneous unit cells, whose dimensions are small in comparison with the characteristic tangential dimensions of the shell. Using the two-scale asymptotic homogenization technique, a system of nonlinear constitutive equations is obtained and a formulation is given of local problems on a unit cell, from whose solution the effective stiffnesses of the shell are determined. The general theory is applied to the derivation of the constitutive relations of the high-modulus reinforced flexible shells.     

Modelling of creep in continuous RC beams under high levels of sustained loading

A nonlinear theoretical model is developed in this paper for the long-term analysis of continuous reinforced concrete beams. The model accounts for creep, cracking, nonlinear behaviour in compression, shrinkage, aging, yielding of the reinforcement. The constitutive relations follow the modified principle of superposition, which are presented in the form of nonlinear rheological generalized Maxwell models with strain and time dependent springs and dashpots that account for material nonlinearity and aging of the concrete. The governing equations are presented in an incremental form, and are solved through a step-by-step algorithm in time along with the numerical shooting method for the solution along the beam. An iterative procedure is implemented at each time step for the determination of the rigidities and the creep strains. The capabilities of the model are demonstrated through numerical examples. The results show that creep and shrinkage have various influences on the structural response, and they may decrease the load carrying capacity and the factor of safety of continuous reinforced concrete beams with time.     

A control volume approach to a shock front propagating in laminated hyperelastic media

Finite amplitude shock wave front propagating in laminated semi-infinite bodies made of hyperelastic materials is analyzed using the concept of a control volume. The shock front is generated by an impulsive load which is applied to the one end of the semi-infinite body, and propagates steadily in the direction of the lamination. A control volume is therein defined to contain and move with the shock front and a set of steady-state conservation equations is written as in the case of a flow problem. These equations are solved with the aid of the material constitutive relations and the appropriate geometrical and boundary conditions. An illustrative problem of a semi-infinite plate is solved in detail, using rubber-like materials of the Neo-Hookean type. The numerical results for this problem are depicted in graphs, which display a marked non-linear shock Hugoniot relation.     

Elastoplasticity theory for porous materials

A continuum theory is derived for the modeling of elastoplastic work-hardening porous materials. The theory provides a set of constitutive relations which, using the properties of the inelastic matrix, determines by an incremental procedure the overall response of the porous solid to various types of loading. In the elastic region, effective elastic moduli of the porous material are obtained. Comparison with theoretical and experimental results are given.