Papers by Keyword: Composite Laminate

Abstract: This paper presents an efficient finite element modeling technique for stiffened composite shells having different stiffening arrangements. The laminated shell skin is modeled with a triangular degenerated curved shell element having 3 corner nodes and 3 mid-side nodes. An efficient curved beam element compatible with the shell element is developed for the modeling of stiffeners which may have different lamination schemes. The formulation of the 3 nod degenerated beam element may be considered as one of the major contributions. The deformation of the beam element is completely defined in terms of the degrees of freedom of shell elements and it does not require any additional degrees of freedom. As the usual formulation of degenerated beam elements overestimates their torsional rigidity, a torsion correction factor is introduced for different lamination schemes. Numerical examples are solved by the proposed finite element technique to assess its performance.

Abstract: Designing light-weight high-performance materials which can sustain high impulsive loadings is of great interest to marine applications. In this study, a finite element fluid-structure interaction model is developed to understand the deformation and failure mechanisms of both monolithic and sandwich composite panels. Fiber (E-glass fiber) and matrix (vinylester resin) damage and degradation in individual unidirectional composite laminas are modeled with Hashin’s model. The delamination between laminas is modeled by developing a strain rate sensitive cohesive law. The deformation of the core (H250 PVC foam) in sandwich panels is modelled as a crushable foam plasticity model with volumetric hardening and strain rate sensitivity as well. The deformation history, fiber/matrix damage patterns in laminas, and inter-lamina delamination in both monolithic and sandwich composite panels are identified and compared with the experimental observations. The model suggests that the foam plays an important role in improving the performance of the sandwich panels by suppressing the transmitted impulsive acting on the back-sheets.

Abstract: An improved Memetic algorithm is applied in this article. Mathematical model is proposed to optimize the laminate strength. The composites laminate strength optimization system with local operator library and rule operator library has been developed by the object-oriented programming with C++. The local operator has contributed to increase the convergence rate and the rule operators have contributed to implement practical design aspects in optimization of laminated composite plates. A numerical example demonstrates the validity of optimization model and practical applicability of the improved Memetic algorithm; hence, exhibiting the improvement of the method in tackling the stacking sequence.

Abstract: A hand lay-up and vacuum bagging method was used in this study to fabricate glass fiber/epoxy laminated composites and carbon fiber/epoxy composite laminates with multi-walled carbon nanotube (MWCNT). The density, flexural properties, and burning rate of the laminated composites incorporated with different concentration of MWCNT (0.5, 1.0, and 1.5 vol%) were investigated and analyzed. Trend in the density, flexural and burning rate of glass fiber composite laminates were compared to those of carbon fiber composite laminates. Effect of MWCNT concentration on glass fiber composites properties varies from carbon fiber composite laminates. Incorporation of 0.5vol% of MWCNT has increased flexural strength by 54.4% compared to 5-ply glass fiber composite laminates. Nonetheless addition of 1vol% of MWCNT has only increased flexural strength by 34% compared to 5-ply carbon fiber laminated composites. Incorporation of MWCNT has successfully reduced the burning rate of the glass fiber composites as well as the carbon fiber laminated composites.

Abstract: Present paper studied the improvement of the fracture toughness under mixed mode loading obtained by using carbon nanotubes reinforcement in fiber glass mats/ epoxy laminates. Mixed-mode bending tests were performed considering different loading ratios G_II/G_I. Laminates were manufactured using the epoxy resin Biresin® CR120 reinforced with fiber glass triaxial mats ETXT 450 and multiwalled carbon nanotubes with 98% of carbon. It was observed that the total fracture toughness increases linearly with the mode II loading component and that linear mixed-mode fracture criteria reproduces the GI versus GII relationship. The incorporation of small quantity, up to 0.5%, of carbon nanotubes into matrix improves significantly mixed-mode fracture toughness.

Abstract: Based on the Upper Bound Theory, a Simplified Engineering Approach is Presented to Determine the Ultimate Strength of a pin-Loaded Composite Laminate in this Papaer. According to the Upper Bound Theory, the Displacement Rate in a Given Ply is Divided into Two Zones: the Moving Zone and the Static Zone. the Applied Load Q that Associated with Displacement must be Less than the Maximum Resistance of the Laminate. in this Paper we have Discussed the Failure Region, Failure Type of each Ply and Simplified the Tsai-Wu Failure Criterion. Experiments of Single-Bolt Double-Lap Joints have been Conduncted According to ASTM D5961 Test Standard. Finally, we can Observe that the Engineering Approach is in Good Agreement with the Test Results.

Abstract: A viable solution to the ever-demanding weight-saving target in aerospace industry is the replacement of conventional engineering alloys with composite materials in primary structures. A major concern to the effective use of composite laminates is the substantial reduction in the compressive strength when the contact force has exceeded the delamination threshold load (DTL). This paper focuses on the study of the contact behavior of composite laminates under quasi-static indentation (QSI) forces. The effect of damage initiation and growth on contact behavior has been investigated via detailed assessment of the relation between the indentation force and the dent depth. Different phases corresponding to undamaged, local damage, global damage, and final failure of the laminate have been identified. A modification to the classical Hertz contact law has been proposed to account for the matrix material resistance to plastic deformation.

Abstract: The effects of thickness on the impact damage of composite laminates were discussed in this paper. Impact tests for the composite laminates with the size of 600 mm×700 mm with three different thicknesses were subjected to impact energy levels from 5 J to 40 J. The crater depth and matrix length were investigated according to different energy levels and different thicknesses. The impact damage was evaluated by visual inspection, three-dimensional microscope. The experimental results reveal that the crater depth and the crack length increase with the increasing impact energy. The thickness had the negative effects on the impact damage of the specimens at the same impact energy.

Abstract: A progressive damage model (PDM) composed by 3D FEM, Hashin and Ye failure criteria and Changs degradation rules was established to deeply understand the failure of a new material system CCF300/5428 under low velocity impact. User defined subroutines were developed and embedded into the general FEA software package to carry out the failure analysis. Numerical simulations provide more information about the failure of composite laminates under low velocity impact, including initial damage status, damage propagation and final failure status. The history of the impact point displacement and various damage patterns were detailed studied.

Abstract: The low-velocity impact and residual compressive failure processes of composite laminate were investigated by the acoustic emission (AE) technique in this paper. The AE energy, amplitude, and the peak frequency were analyzed. At the same time, combining with the load-displacement curve varying feature, the compressive fracture processes were divided into different stages to deeply understand the damaged mechanisms of the composites. Results reveal that the behavior of AE parameters described well the fracture process of the composites.