Obiettivo
Development and validation of methods and procedures for reliability assessment and lifetime prediction ("best estimate" approach) by knowledge engineering and non invasive diagnostic techniques.
In tests on 1:5 scaled vessels, 2 fatigue cracks, nucleated and propagated in vessel A, have been studied during destructive examination of the vessel. The predicted crack growth rates have been compared with the actual crack growth history, experimentally determined via the examination of the fracture surfaces by optical and scanning electron microscope. The results show that the stress corrosion cracking (SCC) component produces a high crack growth rate; nevertheless, it is never dominant all over the crack front but affects small regions of it so that the environmental effect on the mean crack growth rate is limited. The observed crack growth rate is higher than the one predicted without accounting for SCC, but lower than the maximum crack growth rate expected by the environmentally assisted cracking (EAC) models.
Phase 1 of experimentation on pressurized thermal shocks has been completed: 1500 thermal shocks performed; 2 periodic inspections carried out (after 1000 and 1500 cycles respectively); relevant temperature and pressure data analysed for crack propagation prediction; no propagation has been either detected or predicted for the nozzle corner crack.
The basic structure has been designed of the knowledge based system backtracking and overviewing for structural safety (BOSS) conceived as an example of high level controller of a plant: management of the test rig operation, data analysis, safety and reliability evaluation. A prototype of the knowledge based system (KBS) reliability assessment for maintenance and inspection optimization (RAMINO) has been implemented, containing the basic knowledge to perform the reliability assessment of a structure starting from inspection data. A default base of data and knowledge has also been implemented to allow a conservative assessment when some information on the structure is not available.
The laser holographic interferometry technique has been successfully applied on graphite and epoxy composites for the det ection of impact induced damage and subsurface fabrication imperfections. A bench mark exercise on the application of acoustic emission as a damage monitoring technique on fibre reinforced, graphite epoxy composites has been started. Two new, high sensitivity interferometric sensors (one able to detect extremely weak temperature gradients in real time, the second acting as a nonlinear photorefractive crystal) have been realized during experimentation partly connected with exploratory research activity.
Progress to end 1991
Tests on 1:5 scaled vessels Two fatigue cracks, nucleated and propagated in vessel A, have been studied during destructive examination of the vessel. The predicted crack growth rates have been compared with the actual crack growth history, experimentally determined via the examination of the fracture surfaces by optical and scanning electron microscope. The results show that the Stress Corrosion Cracking (SCC) component produces a high crack growth rate; nevertheless, it is never dominant all over the crack front but affects small regions of it so that the environmental effect on the mean crack growth rate is limited. The observed crack growth rate is higher than the one predicted without accounting for SCC, but lower than the maximum crack growth rate expected by the Environmentally Assisted Cracking (EAC) models.
Pressurized Thermal Shocks
Phase 1 of experimentation has been completed: 1500 thermal shocks performed; two periodic inspections carried out (after 1000 and 1500 cycles respectively); relevant temperature and pressure data analysed for crack propagation prediction; no propagation has been either detected or predicted for the nozzle corner crack.
Phase 2, in which higher values are planned for the stress intensity factor at crack contour, is being started before the end of 1991.
The basic structure has been designed of the knowledge based system BOSS (Backtracking and overviewing for Structural Safety) conceived as an example og high level controller of a plant: management of the test rig operation, data analysis, safety and reliability evaluation.
Development of RAMINO (Reliability Assessment for Maintenance and Inspection Optimization) KBS. The related project (BRITE 2124) ended. A prototype of the knowledge based system (KBS) RAMINO has been implemented, containing the basic knowledge to perform the reliability assessment of a structure starting from inspection data. A "default base" of data and knowledge has also been implemented to allow a "conservative" assessment when some information on the very structure is not available.
NDE techniques
The laser holographic interferometry technique has been successfully applied on graphite-epoxy composites for the detection of impact induced damage and subsurface fabrication imperfections. A Bench Mark Exercise on the application of Acoustic Emission as a damage monitoring technique on fibre reinforced, graphite-epoxy composites has been started in the context of the EAMA (Acoustic Emission on Aeronautic Materials) group.
Two new, high sensitivity interferometric sensors (one able to detect extremely weak temperature gradients in real time, the second acting as a non-linear photorefractive crystal) have been realized during experimentation partly connected with exploratory research activity. Application for patents has been made.
Detailed description of work foreseen in 1992
NDE
The prenormative research will be prosecuted for the generation of norms and standards for the evaluation of the damage level on metals and on composite materials by the application of non destructive techniques: adiabatic thermal emission (microdamage), acoustic emission (micro and macrodamage), laser holographic interferometry (macro damage). Two types of materials will be invstigated: steel (fatigue and creep damage); composites: (tensile loading and fatigue). The development of new methods (mainly based on thermal emission and acoustic emission) will be pursued for the engineering characterization (behaviour under service conditions) of composite materials. The research on the fractal dimension of turbulent flow patterns will be ended.
Development of RAMINO KBS.
The RAMINO prototype will be analysed and checked carefully by the partners of the BRITE 2124 Consortium. Following the consequent results and suggestions, JRC will then modify and complete the KBS in order to allow its commercialisation.
A project for the "corroboration" of the knowledge based system will be prepared.
Tests on 1:5 scaled vessel
Studies will be performed on technical requirements and implications, timing and cost of two possible tests to be carried out on vessel B: one devoted to the investigation of the problem of fatigue crack initiation; the second focused on stress corrosion cracking at 300 degrees celsius. Each study will be carried out in collaboration with the company proposing the relevant test campaign. Possible organization of an "integrated project" with external laboratories and industries.
Short description of evolution of work in 1993
Prosecution of the research on damage assessment by non invasive methods. Corroboration/validation of expert systems for structural diagnostic.
Campo scientifico (EuroSciVoc)
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CORDIS classifica i progetti con EuroSciVoc, una tassonomia multilingue dei campi scientifici, attraverso un processo semi-automatico basato su tecniche NLP. Cfr.: Il Vocabolario Scientifico Europeo.
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Meccanismo di finanziamento
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Coordinatore
21020 Ispra
Italia
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