Papers by Keyword: Composite Damage

Abstract: Stiffened panels are widely used in aerospace, naval architecture, and bridge construction industries, where compressive loading often leads to critical buckling and structural failure. This study investigates the buckling and damage behavior of curved stiffened panels made from hybrid composite materials under uniaxial compressive loading. Numerical simulations use finite element analysis in Ansys, incorporating the Hashin damage model to predict failure mechanisms. Key parameters analyzed include fiber orientation of the skin and stiffener, cutout diameter, and the impact of titanium foil reinforcement. Results show that fiber orientation significantly influences the panels' critical buckling and damage loads. Panels with skin laminates of [45/90/-45/0]4s demonstrate higher stability than [+45/-45]4s laminates. Additionally, larger cutouts enhance critical buckling loads for both metallic and composite panels. Reinforcing stiffeners with titanium foil at the outermost layers of the composite panels substantially improves buckling and damage performance, providing higher stability and load-bearing capacity than aluminum or composite panels alone. These findings offer valuable insights for optimizing the design of hybrid composite panels in structural applications.

Abstract: A comprehensive continuum damage mechanics model [1] had been developed to capture the detailed behaviour of a composite structure under a crushing load. This paper explores some of the difficulties encountered in the implementation of this model and their mitigation. The use of reduced integration element and a strain softening model both negatively affect the accuracy and stability of the simulation. Damage localisation effects demanded an accurate measure of characteristic length. A robust algorithm for determining the characteristic length was implemented. Testing showed that this algorithm produced marked improvements over the use of the default characteristic length provided by Abaqus. Zero-energy or hourglass modes, in reduced integration elements, led to reduced resistance to bending. This was compounded by the strain softening model, which led to the formation of elements with little resistance to deformation that could invert if left unchecked. It was shown, through benchmark testing, that by deleting elements with excess distortions and controlling the mesh using inbuilt distortion/hourglass controls, these issues can be alleviated. These techniques contributed significantly to the viability and usability of the damage model.

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: A study on the use of modal parameter analysis for damage detection of structures made of composites is conducted. The damage-induced variations of modal parameters are investigated both numerically and experimentally. An appropriate finite element model is proposed to analyze the dynamic characteristics of different types of structures made of composites, such as honeycomb sandwich plates and multi-layer composite plates, with internal cracks and delamination. The numerical results are in good agreement with experimental results available in the literature. Natural frequencies, modal displacements, strains and energy are analyzed for the determination of damage severity and location. Vibration measurements are carried out using piezoelectric patch actuators and sensors for comparison and verification of the FEM model proposed in this study. Energy spectrum for wavelet packets decomposition of structural dynamic responses is used to highlight the features of damaged samples. The mechanism of mode-dependent energy dissipation of composite plates due to delamination is revealed for the first time. Experimental results clearly show the dependence of changes of modal parameters on damage size and location. The results obtained in this study show that the measured modal damping change combined with the computed modal strain energy distribution can be used to determine the location of delamination in composite structures. Both numerical and experimental findings in this study are significant to the establishment of guideline for size and location identification of damage in composite structures.