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Purpose -The purpose of the paper is to improve the calculability of a continuum damage failure model of composite laminates based on Tsai-Wu criteria. Design/methodology/approach -A technique based on viscous regularization, a characteristic element length and fracture energies of fiber and matrix are used in the model. Findings -The calculability of the material model is improved. The modified model can predict the behavior of composite structure better. Originality/value -The convergence problem and the mesh softening problem are main concern in the calculability of numerical model. In order to improve the convergence, a technique based on viscous regularization of damage variable is used. Meanwhile, characteristic element length and fracture energies of fiber and matrix are added into the damage constitutive equation to reduce the mesh sensitivity of numerical results. Finally, a laminated structure with damages is implemented using a User Material Subroutine in ABAQUS/Standard. Mesh sensitivity and value of viscosity are discussed.

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Abstract. Uniform silver nanowires (AgNWs) were synthesized by a simple chemical reduction method with a typical diameter of ~200 nm and a typical length of ~6 um, and poly(vinyl alcohol)(PVA) aqueous solution was used to prepare AgNWs/PVA film. This combination shows good nonlinear current-voltage(I-V) characteristic under relatively low applied voltage, the resistance of the film decreased strongly with increasing of the applied voltage, and the minimum value of resistance was 520Ω in the whole measurement. The quantum tunneling effect may be the main cause of the nonlinear I-V characteristic of the AgNWs/PVA. [13]. Some progress have been acquired in the study of electrically conductive properties of polymer matrix filling with metal filler, the percolation threshold of wire-like metal filler is lower than nanoparticle filler in the condition of obtaining the same conductivity [14], and wire-like filler with high aspect ratio filling polymer can be decreased than low aspect ratio filler [15]. In this way, the amount of filler can be reduced. Field-induced nonlinear electrically conductive characteristic was observed when the filler volume fraction is close to percolation threshold. Researchers have deserved to study the nonlinear conductive mechanism of composites for decades and proposed that quantum tunneling effect is the cause. Polley et al. proposed that electron "jump" across the gap, with an exponential dependence on gap [16]. Simmons proposed a generalized formula for the electric tunnel effect between similar electrodes separated by a thin insulating film [17]. Ping Sheng et al. suggested that nonlinear conductive mechanism is tunneling with potential-barrier modulation by thermal fluctuations [18]. Beek and Van Pul proposed that electron passage in these systems is due to tunneling, regarded as a special case of internal field emission [19]. Sadie I. White et al. suggested that resistive switching in silver nanowires composites may be the result of the field-induced formation of conducting silver filaments [20]. Nonlinear conductive polymer composites have broad application prospects in electromagnetic protection, integrated circuits, nonvolatile memory, and other fields [21,22]. IntroductionIn this paper, AgNWs were prepared with a typical diameter of ~200 nm and a typical length of ~6 um by simple chemical reduction method. As a important chemical material, poly(vinyl