Composite delamination modelling using a multi-layered solid element

This paper focuses on the latest development of a solid hexahedron element for composite delamination analysis. The 8-node solid is derived from a 20-node hexahedron. It is transformed into two physical independent 4-node shell elements according to the propagation of delamination process within the element.     

Determining buckling strain energy release rate through indentation-induced delamination

An oscillating indentation load was applied to delaminate a diamond-like-carbon film from a silicon substrate. After delamination occurred, a two-stage behavior was exhibited in the load-depth results; then, a three-stage behavior was exhibited after buckling occurred due to a long enough delamination length. After removing the indentation load, the debonding film was single-buckled and suspended over the substrate; thus, the delamination length was obtained via the residual profile. Through analysis of the deflection of the buckled film, the buckling strain energy release rate was evaluated.     

Energy absorption properties of multi-layered corrugated paperboard in various ambient humidities

This paper develops a mathematical model to depict the energy absorption properties of multi-layered corrugated paperboard (MLCP) in various ambient humidities. It is a piecewise function to model the energy absorptions corresponding to three deformation stages of MLCP (elastic stage, plateau stage and densification stage) separately. Simple formulas are derived for each stage which relating the energy absorption capacity of MLCP to the thickness-to-flute pitch ratio (_tc/λ$t_c/\lambda$) of corrugated-core cell, the mechanical properties of corrugated medium tested under a controlled atmosphere [23 °C and 50% relative humidity (RH)], and the RH. The theoretical energy absorption curves are then compared with experimental ones and good agreements are achieved for MLCP with wide range ratios of _tc/λ$t_c/\lambda$ in various ambient humidities. Results of this research can be applied in the optimum design and material selection of cushioning packaging with multi-layered corrugated paperboard.     

The heating of materials by a concentrated energy flux under volume absorption

An analysis is represented for the process of heating a massive body by concentrated energy flux with volume absorption taken into account. The boundaries of applicability are determined for models of surface and volume absorption. The temperature fields are computed and simple analytical dependences are obtained for the temperature at the center of the heating spot.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 59, No. 5, pp. 846–849, November, 1990.     

Flow advancement through multi-layered preform with sandwich structure

A new analytic model which can predict location of flow front in the multi-layered preform is proposed. The model includes the contribution of transverse flow between adjacent layers to entire flow through the preform. It is shown that the difference between flow fronts of neighboring layers become constant after sufficient time elapses. To verify the analytic results, numerical flow simulation and experiments are carried out. It is found that when the transverse permeabilities are relatively low, the analytic model underestimates the transverse flow when compared with numerical results. The reason is that the analytic model assumes that the transverse flow occurs only in the flow front region. In this study, effective permeability is analytically calculated and compared with the average permeability which is obtained by applying a simple rule of mixture.     

A critical plane-based fracture criterion for mixed-mode delamination in composite materials

A new critical plane-based mixed-mode delamination failure criterion is proposed in this study. First, many existing models are reviewed and their capability to handle the mixed-mode fracture of general anisotropic materials are discussed. Following this, a previously developed critical plane approach is extended to analyze the interfacial fracture of composite materials by considering the anisotropic fracture resistance under mixed-mode loadings. Next, comparison with extensive experimental data available in the literature is performed to demonstrate the validity of the proposed criterion. A general good agreement is observed between the model's predictions and experimental observations. Finally, some conclusions and future work are drawn based on the proposed study.     

Finite element simulation of delamination growth in composite materials using LS-DYNA

In this paper, a modified adaptive cohesive element is presented. The new elements are developed and implemented in LS-DYNA, as a user defined material subroutine (UMAT), to stabilize the finite element simulations of delamination propagation in composite laminates under transverse loads. In this model, a pre-softening zone is proposed ahead of the existing softening zone. In this pre-softening zone, the initial stiffness and the interface strength are gradually decreased. The onset displacement corresponding to the onset damage is not changed in the proposed model. In addition, the critical energy release rate of the materials is kept constant. Moreover, the constitutive equation of the new cohesive model is developed to be dependent on the opening velocity of the displacement jump. The traction based model includes a cohesive zone viscosity parameter (η) to vary the degree of rate dependence and to adjust the maximum traction. The numerical simulation results of DCB in Mode-I is presented to illustrate the validity of the new model. It is shown that the proposed model brings stable simulations, overcoming the numerical instability and can be widely used in quasi-static, dynamic and impact problems.     

Influence of heterogeneity on fracture behavior in multi-layered materials subjected to thermo-mechanical loading

Based on the heterogeneous characteristics of materials at mesoscopic level, the stress state and fracture behavior in multi-layered materials are numerically investigated by using RFPA^2D, a numerical code incorporated with thermo-mechanical-damage (TMD) model. We conduct this research through two logical steps. Firstly, we investigate the stress states between two adjacent fractures for a typical three-layer model. Our results show that the critical value of fracture spacing to layer thickness ratio is about 0.9 which is gently lower that of value in latest publications. Secondly, we use the same three-layer model without pre-assigned fractures. An isothermal loading is applied on the model until the state of fracture saturation is achieved. In the stage of initiation, fractures are formed one after another; in the stage of infilling, new fractures are created sequentially between the earlier formed fractures; in the stage of saturation, the formed fractures are spaced so closely that no more new fractures can be filled even with decreasing the temperature. Numerical study show that both the fracture pattern and the critical value of fracture spacing to layer thickness ratio is strongly dependent on the heterogeneous characteristics of the central layer materials. For the cases with a relatively homogeneous central layer, more interface fractures occur and the interface delamination evidently influences the fracture saturation.     

Structural scale decomposition of energy release rates for delamination propagation

A kinematic based decomposition of energy release rates for structural scale delamination propagation is established for a general class of 1-D propagation in both curved and flat composite structures. The energy release rates, and the associated decomposition, allow for geometric nonlinearities, are self consistent, and are compatible with typical thin structure models employed in the analysis of composite structures. The energy release rates are expressed explicitly in terms of the curvatures and membrane strains (forces) of the sublaminates at the delamination edge, are independent of the particular loading of the structure, and allow for simple computation, application, evaluation and comparison of the critical delamination energy (toughness) based on simple experiments. The decomposition established herein is applied to several limiting cases to check proper convergence and is then applied to several selected examples.     

Application of the energy release rate approach for delamination growth in Glare

Fatigue crack growth in a fibre metal laminate such as Glare is accompanied by delamination growth at the interface between the aluminium and glass fibre/adhesive layers. To incorporate this delamination growth in crack growth prediction methods, the energy release rate approach is applied to describe the delamination growth rate. Tests were performed to determine the relationship between the delamination growth rate and the calculated energy release rate.     

Interface cracks in composite orthotropic materials and their delamination via global shape optimization

Based on the linear theory of elasticity a model describing two, in-plane deformation identical, homogeneous orthotropic materials coupled at an interface with the angle of 2β between their vertical planes of elastic symmetry and with a crack at the interface is studied. The model under consideration is spatial, and it does not split into independent isotropic/orthotropic in-plane and anti-plane models, which are treated here as the limit case of , respectively. The well-posedness of mathematical formulation of the problem is provided by variational methods. Applying a global optimization for the total potential energy with respect to one shape parameter of the crack length, a model for the quasi-static delamination is proposed and compared with the Griffith fracture criterion . Numerical experiments for the composite material with a plane interface crack of the fracture mode-1, mode-2, and mode-3 are presented and analyzed with respect to the half-angle β of coupling and length of the crack.     

Effect of delamination face overlapping on strain energy release rate calculations

The strain energy release rate is often used as a fracture mechanics parameter to describe delamination propagation and onset in composites, and is conveniently evaluated using finite element analysis. A common problem encountered in analysis is overlapping (interpenetration) of the delamination faces if these faces are not constrained. This paper examines the effect of overlapping on strain energy release rate calculated using the virtual crack closure method in conjunction with 3-dimensional anisotropic finite element analysis. A bilinear gap element was used between the delamination faces to prevent these faces from overlapping. Three problems were studied: (1) laminates with an embedded crack and embedded delaminations; (2) laminates with free edge delaminations; and (3) end-notched flexure specimens. The results of this investigation indicated that overlapping has a significant effect on the component values of G_I and G_II as well as on the total strain energy release rate. It was also found that end effects can create non-uniform energy release rates along the crack front in edge delamination problems due to twisting of the sublaminate with unsymmetrical lay-up, so that 3-dimensional finite element analysis is required.     

Evaluation of energy release rate-based approaches for predicting delamination growth in laminated composites

A variety of energy release rate-based approaches are evaluated for their accuracy in predicting delamination growth in unidirectional and multidirectional laminated composites. To this end, a large number of unidirectional and multidirectional laminates were tested in different bending and tension configurations. In all cases, the critical energy release rate was determined from the tests in the most accurate way possible, such as by compliance calibration or the area method of data reduction. The mode mix from the tests, however, was determined by a variety of different approaches. These data were then examined to determine whether any of the approaches yielded the result that toughness was a single-valued function of mode mix. That is, for an approach to have accurate predictive capabilities, different test geometries that are predicted to be at the same mode mix must display the same toughness. It was found that variously proposed singular field-based mode mix definitions, such as the =0 approach or basing energy release rate components on a finite amount of crack extension, had relatively poor predictive capabilities. Conversely, an approach that used a previously developed crack tip element analysis and which decomposed the total energy release rate into non-classical components was found to have excellent predictive capabilities. It is postulated that this approach is more appropriate for many present-day laminated composites.     

Complementary doping of van der Waals materials through controlled intercalation for monolithically integrated electronics

Nano Research - Doping control has been a key challenge for electronic applications of van der Waals materials. Here, we demonstrate complementary doping of black phosphorus using controlled ionic...     

Bifurcation analysis of absorption and reflection effects in electromagnetic wave absorbing composites with multi-layered structure

Static bifurcation of electromagnetic wave transmission differential equation for multilayered structural composite materials has been studied to explain the transformation effect of absorption and reflection. Experimental result is given to illustrate the absorption and reflection transformation caused by variation of inherent impedance of the composite.     

Improving the fracture energy of carbon fibre-reinforced plastics by delamination promoters

The effect of delamination promoters on the Charpy impact energy and other mechanical properties of carbon fibre-reinforced plastic has been studied. These delamination promoters consist of thin sheets of metallic or organic materials which make the multiple splitting of samples at the time of impact, a process involving a greater energy absorption, much easier.     

复合材料结构的能量吸收

针对缠绕成型的 [± 75 ]n玻璃纤维 /聚酯和 [0 /± 75 ]n玻璃纤维 /环氧树脂圆柱管的轴向与非轴向压缩失效行为及能量吸收特性进行了研究 (轴压的倾斜角度变化范围 0～ 2 5°) ,分析了复合材料圆柱管的宏观破坏模式和能量吸收机理 ,比较了轴向与非轴向载荷下能量吸收的特点 .研究表明 :复合材料圆柱管在偏轴角度下其压缩损伤过程可分为 3个阶段 ,即初始引发阶段、稳态渐进阶段以及压实或失稳阶段 ;圆柱管的压缩行为和吸能能力主要取决于偏轴压缩角度和载荷位移历程