Damage tolerance assessment of composite sandwich panels with localised damage

Abstract

Damage tolerance assessment of composite sandwich panels with localised damage. Composites Science And Technology AbstractThe work described herein is part of a larger context in which the effect of damage in sandwich composite structures for marine applications has been investigated. The overall aim of this effort has been twofold: to develop and verify existing damage assessment models to be used to assess the effect of damage on marine sandwich structures, and to develop a damage assessment scheme to be used by shipyards, ship owners and navies. More specifically, this paper presents a sub-set of this overall effort looking at impact and indentation damage and its effect on the load carrying capacity of state-of-the-art carbon composite sandwich panels for marine applications. Damage types are modelled based on physical observations from tests. Testing is then performed on different scales in order to validate the models. The overall aim is to use such models to produce information that can be used for decision-making at two levels. The first is to evaluate the damage tolerance of ship structural components and thus to calculate the size and extent of damage that a component can have without risk of growth or failure at ultimate local or global loads on the entire ship. The second is to have information at hand to decide if, and when, a structural part needs to be repaired if damage has been detected. A scheme developed for this purpose is presented herein. Finally the paper will briefly describe a common framework for damage assessment in composite sandwich structures. Herein, models are used in conjunction with the design specifics and functional requirements to create a scheme for repair decisions.

Damage Tolerance of Naval Sandwich Panels

“…In a similar study, reported in [2], indentation damage was studied on sandwich panels with carbon/vinylester face sheets on a 50 mm Divinycell core material. The damage geometry in this case has the features of that in Figs.6a and 7a, i.e.…”

“…As seen herein, the dent growth is very rapid just before failure and the panel fail by compressive failure of the face sheet laminate. The same type of panels was used to study two types of impact damages, one resulting from a blunt impactor and one form a sharp [2,35,36]. These are shown in Fig.16.…”

“…The panel utilization factor, U p , is defined as the ratio between the ratio of the maximum load applied to the damaged panel under extreme load to the maximum allowable value of that load for the undamaged panel. The utilization factors U s is defined the same way but for the global load acting on the whole structure [1,2].…”

“…It will be completed with a summary of a suggested damage tolerance assessment scheme as outlined in [1] and [2].…”

Remote inspection system for impact damage in large composite structure

“…The current approach adopted by most of the aerospace industry is to over-design composite structures so that they can tolerate the existence of BVID [4] (more serious impact damage is assumed to be detectable during routine visual inspections between flights). Consequently, there is a real opportunity for reducing the weight of composite aircraft by developing an efficient method of detecting BVID between flights.…”