Abstract
Using the slow-growth certification approach for damage tolerance of composite aircraft structures has the potential to reduce their weight. Applying this approach requires that damage growth is slow, stable, and predictable. However, currently available methods do not allow for sufficiently accurate predictions, due to knowledge gaps related to damage characterisation, prediction of damage growth, and prediction of final failure.This article highlights these knowledge gaps, discusses the limitations of the current state of the art and research approaches, and identifies possible ways forward.
Highlights
Another point to highlight regarding final failure is that a slow-growth analysis may have different needs when it comes to residual strength
The question is, up to what size can the damage be allowed to grow, such that the residual strength does not decrease below design limit load (DLL)? In other words, the question is not what is the critical load for a given damage, but rather, what is the critical damage size for a given load? Note that due to the complexity of damage in an impacted laminate, and the possibility of interaction between different damage modes, ’critical damage size’ in this context should be understood as referring to a certain delamination envelope, or a set of critical damage configurations, rather than a single length or area measure
Switching to a slow-growth damage management concept for CFRP structures with impact damage could offer weight benefits. Before this is possible, knowledge gaps need to be addressed in three areas
Summary
Impact damage in CFRP structures is currently managed using the ‘no-growth’ concept, meaning that damage is not allowed to gImropwacutnddaemr faagteigiuneCloFaRdiPngs.trTuhcitsurreesquisirceusrtrheanttslytremssaensaignedtheusminagtetrhiael‘anroe-kgerpowt bthel’ocwonthceepfat,timgueeanliimngit,thimatpdoasminaggaesiisgnniofitcaalnlot wweedightot pgeronwaltuyn. dAer‘sfalotiwgu-gerloowadthin’ gc.oTncheisptrewqouuirledsathllaotwstmreossreeseiffin cthieenmt sattreurciatul raarledkeespitgbnes,lobwutthseevfeartaigl ukenoliwmlietd, igmepgoaspisngneaesdigtnoifibecaandtdwreesisgehdt bpeefnoarletyt.hAis‘isslopwos-gsirbolwe.thT’hceosnecgeapptsweoxuisldt ianlltohwreme moraeineffiarceiaesn:t (s1tr)udcatumraagl edecshigarnasc,tbeuritsasetivoenr,a(l2k)nfoawtilgeudegedrgivaepns ndeeeladmtoinbateioanddgrreoswsethd abfetfeorreimthpiascits, apnodss(ib3l)e.fiTnahlesfaeilguarpesoefxiismt pinacttherdeelammaininataerse.aTs:h(e1)padpaemrahgieghclhigarhatcsteorpiseantiqoune, s(t2io)nfsatiagnudetdhreivsehnordtecloammiinngastioonf cgurorrwetnht raefsteeraricmhpiancat,dadnredss(i3n)gfitnhaelmf,aailnudresuogfgiemstpsaacvteednuleasmfionrafteustu. rTehreespeaaprcehr.highlights open questions and the shortcomings of current research in addressing them, and suggests avenues for future research. In current practice composite structures are designed and certified according to a ‘no-growth’ philosophy In this philosophy loads have to be kept below the fatigue threshold, even in the presence of damage, which imposes a weight penalty. This paper will highlight the open questions preventing adoption of slow growth damage management for fatigue after impact in composites and discuss why current research practices may not be helpful in addressing them. It will offer some perspectives for alternative research approaches to better address these knowledge gaps
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