Impact damage can degrade the flexural strength of composite sandwich structures by over 50% due to a loss of skin support inducing localized skin buckling. Various self-healing methodologies have been applied to laminated composites but the concept of delivering a healing agent from a remote reservoir to a region of damage via a vascular network offers the potential for a robust and replenishable system housed in the core of a sandwich structure. In this pilot study a vascular sandwich structure that appears as a conventional sandwich composite has been developed and tested. The network has been shown to have negligible influence on the innate static mechanical properties of the host panel. Infiltration of the vascular network with a pre-mixed epoxy resin system after impact damage demonstrated a complete recovery of flexural failure mode and load. Infiltration with the same resin system from separate unmixed networks, where self-healing is initiated autonomously via mixing within the damage, has also been shown to fully recover undamaged failure load when both networks are successfully breached.

https://iopscience.iop.org/article/10.1088/0964-1726/16/4/031/pdf

Self-healing composite sandwich structures

Self-healing sandwich panels: Restoration of compressive strength after impact

http://kth.diva-portal.org/smash/get/diva2:333204/FULLTEXT01

Damage tolerance assessment of composite sandwich panels with localised damage

This work examines the performance of composite panels when subjected to underwater impulsive loads. The scaled fluid-structure experimental methodology developed by Espinosa and co-workers was emp ...

Failure mechanisms in composite panels subjected to underwater impulsive loads

The main concept currently in use in wind energy involves horizontal-axis wind turbines with blades of fiber composite materials. This turbine concept is expected to remain as the major provider of wind power in the foreseeable future. However, turbine sizes are increasing, and installation offshore means that wind turbines will be exposed to more demanding environmental conditions. Many challenges are posed by the use of fiber composites in increasingly large blades and increasingly hostile environments. Among these are achieving adequate stiffness to prevent excessive blade deflection, preventing buckling failure, ensuring adequate fatigue life under variable wind loading combined with gravitational loading, and minimizing the occurrence and consequences of production defects. A major challenge is to develop cost-effective ways to ensure that production defects do not cause unacceptable reductions in equipment strength and lifetime, given that inspection of large wind power structures is often problematic.

/pdf/materials-challenges-in-present-and-future-wind-energy-21c7jv5et9.pdf

Materials Challenges In Present and Future Wind Energy

Wrinkle defects may reduce the compressive strength of a face laminate for in-plane loading applied perpendicularly to the line of the wrinkle. To be able to decide whether a repair is needed, it is necessary to know the magnitude of the strength reduction for a given wrinkle geometry. In the studies reported here, the influence of wrinkle defects on the in-plane compressive strength of quasi-isotropic carbon fiber reinforced plastic (CFRP) laminates used in PVC foam-cored sandwich panels has been investigated by three approaches: testing of sandwich beam specimens in four-point bending, testing of sandwich panels with in-plane compression, and finite element simulation. Wrinkles involving different numbers of plies have been considered. Two different sandwich lay-ups typical of deck and hull bottom panels in naval ships have been included.

The Effect of Face Sheet Wrinkle Defects on the Strength of FRP Sandwich Structures

This paper describes experimental and numerical techniques to study the structural design of double lap shear joints that are based on thick-adherend steel/steel and steel/composite, with epoxy adhesive. A standard practical fabrication method was used to produce specimens of various dimensions and materials. These specimens consist of 10 mm steel inner adherend and various outer adherend materials including composite and steel of various thicknesses and overlaps. The composite is largely based on carbon fibre-reinforced plastic. The specimens were tested under monotonic tensile loading and the results showed that joint strength depends largely on materials combination and overlap length. The testing also included the use of an advanced imaging system to determine failure initiation and propagation. Two-dimensional finite element analysis (FEA) stress models were applied and showed the importance of modelling the composite layers adjacent to the adhesive bondline in order to account for the critical local...

Fabrication, testing and analysis of steel/composite DLS adhesive joints

Assessment of frp sandwich structures for marine applications

The paper describes a methodology for determining theinfluence of both production defects and in-servicedamage on the performance of composite sandwichpanels in ship structures, and for deciding whether,when and where replacement or repair is needed Theapproach is based on quantitative modelling of the respectivedefect and damage types

/pdf/the-influence-of-defects-and-damage-on-the-strength-of-1kwhd6n5v2.pdf

Brian Hayman

Papers

Damage tolerance assessment of composite sandwich panels with localised damage

The Effect of Face Sheet Wrinkle Defects on the Strength of FRP Sandwich Structures

Fabrication, testing and analysis of steel/composite DLS adhesive joints

Assessment of frp sandwich structures for marine applications

The Influence of Defects and Damage on the Strength of FRPSandwich Panels for Naval Ships