Damage Analysis of Aluminum Structure Repaired with A Composite Patch

The interest in the application of high strength aluminum alloy in marine structures has been increasing in recent years due to its high strength-weight ratio and excellent corrosion resistance. However, those marine grade aluminum alloy unavoidably experience fatigue and stress corrosion cracking during their service life. Developing a reliable repair method is essential to address the damage problems. The composite patch has been demonstrated as a promising method to repair the damaged or reinforce the under-designed aluminum structures. This research focuses on creating a comprehensive understanding of damage mechanisms involved in the composite patch repaired structures. The compact tension testing of aluminum, four-point bend and fracture testing of composite repaired structures are employed to investigate the yielding and cracking in aluminum, fiber breakage, matrix cracking and delamination in the composite patch, and disbond of the bond line. The validated, high-fidelity 3D finite elements are developed to simulate those damage mechanisms. The sensitivity analysis coupling with the finite element simulations is then performed to study the effects of different damage modes and their interactions on the ability of the composite to restore the load capability of repaired structures. The most and least important factors affecting different damage modes are identified to reduce the design space, which enables the improvement of the design efficiency of the composite patch

Computational Methods for Failure Analysis and Life Prediction

This conference publication contains the presentations and discussions from the joint UVA/NASA Workshop on Computational Methods for Failure Analysis and Life Prediction held at NASA Langley Research Center 14-15 Oct. 1992. The presentations focused on damage failure and life predictions of polymer-matrix composite structures. They covered some of the research activities at NASA Langley, NASA Lewis, Southwest Research Institute, industry, and universities. Both airframes and propulsion systems were considered

Effect of delamination on the fatigue life of GFRP: A thermographic and numerical study

Delamination is the major failure mechanism in composite laminates and eventually leads to material failure. An early-detection and a better understanding of this phenomenon, through non-destructive assessment, can provide a proper in situ repair and allow a better evaluation of its effects on residual strength of lightweight structural components. Here we adopt a joint numerical-experimental approach to study the effect of delamination on the fatigue life of glass/epoxy composites. To identify and monitor the evolution of the delamination during loading, we carried out stepwise cyclic tests coupled with IR-thermography on both undamaged and artificially-damaged samples. The outcome of the tests shows that IR-thermography is able to identify a threshold stress, named damage stress ?D, which is correlated to the damage initiation and the fatigue performance of the composite. Additionally, we performed FE-simulations, implementing the delamination by cohesive elements. Such models, calibrated on the basis of the experimental fatigue results, can provide a tool to assess the effect of parameters, such as the delamination size and location and composite stacking sequence, on the residual strength and fatigue life of the composite material

Ninth DOD/NASA/FAA Conference on Fibrous Composites in Structural Design, volume 1

This publication contains the proceedings of the Ninth DOD/NASA/FAA conference on Fibrous Composites in structural Design. Presentations were made in the following areas of composite structural design: perspectives in composites; design methodology; design applications; design criteria; supporting technology; damage tolerance; and manufacturing

Advanced Approaches Applied to Materials Development and Design Predictions

This thematic issue on advanced simulation tools applied to materials development and design predictions gathers selected extended papers related to power generation systems, presented at the XIX International Colloquium on Mechanical Fatigue of Metals (ICMFM XIX), organized at University of Porto, Portugal, in 2018. In this issue, the limits of the current generation of materials are explored, which are continuously being reached according to the frontier of hostile environments, whether in the aerospace, nuclear, or petrochemistry industry, or in the design of gas turbines where efficiency of energy production and transformation demands increased temperatures and pressures. Thus, advanced methods and applications for theoretical, numerical, and experimental contributions that address these issues on failure mechanism modeling and simulation of materials are covered. As the Guest Editors, we would like to thank all the authors who submitted papers to this Special Issue. All the papers published were peer-reviewed by experts in the field whose comments helped to improve the quality of the edition. We also would like to thank the Editorial Board of Materials for their assistance in managing this Special Issue

Statistical estimation of strain energy release rate of delaminated composites

An improved two-sublaminate model based on first-order shear deformation theory is implemented in a general-purpose finite element software (ANSYS) to study delaminated composite plates. Double cantilever beam and end-notched flexure models of unidirectional and multidirectional composite plates with mid-plane and offset delaminations are analyzed. The total strain energy release rate and the mode-I, mode-II and mode-III components are evaluated using a plate-theory-based crack-closure technique.;The effects of variation of material properties, ply thickness, fiber orientation, coefficient of friction between the crack surfaces, finite element mesh density and virtual crack-closure length and applied load on the mixed-mode strain energy release rates are studied using Monte Carlo simulations. The statistics and trends are analyzed and quantified using sensitivity plots and scatter plots. Anderson-Darling goodness-of-fit tests are performed on the results to fit them to a two-parameter Weibull, normal or log-normal distribution and the statistically-based design values are calculated. Three-dimensional contour plots are also generated to study the overall variation in the strain energy release rate distribution along the delamination front.;In the case of double cantilever beam specimens, the ply thickness has a significant influence on the total and average strain energy release rate. Fiber misalignment controls the amount of mode-II and mode-III components observed. The maximum and minimum values are also highly dependent on the virtual crack-closure length. For unidirectional end-notched flexure models, sliding friction effects are found to be negligible and occur only adjacent to the supports. For the symmetric and unsymmetric end-notched flexure models studied, the energy loss due to sliding friction controls the total strain energy release rate for friction coefficients greater than 0.16 and 0.24, respectively

Advances in Fatigue and Fracture Testing and Modelling

Advances in Fatigue and Fracture Testing and Modelling explores various aspects related to fatigue and fracture in metallic and non-metallic materials in terms of mechanical testing and numerical modelling. The book provides results of research work conducted by experts worldwide. It discusses fatigue failure of materials and presents possible numerical solutions. It also presents predictive models and finite element (FE) activities to illustrate the behaviour of materials in real-life conditions