D. SEMENSKI ET AL.: A CRACK GROWTH ANALYSIS IN CRITICAL STRUCTURAL COMPONENTS A CRACK GROWTH ANALYSIS IN CRITICAL STRUCTURAL COMPONENTS ANALIZA RASTI RAZPOKE V KRITI^NIH KOMPONENTAH NAPRAV Damir Semenski, @eljko Bo`i}, Hinko Wolf University of Zagreb, Faculty of Mechanical Engineering and Naval Architecture, Ivana Lu~i}a 5, HR-10000 Zagreb, Croatia damir.semenski fsb.hr Prejem rokopisa – received: 2006-05-17; sprejem za objavo – accepted for publication: 2006-07-18 Thesupervisingandhealthmonitoringofstructuresisanewfieldthathasbeenofincreasingimportancewithregardtocontrol durability, stability and safety as well as for estimating the life span of the structure. Crack growth is interesting for the proper evaluation of the reliability of structural parts. Different methods are used to record the actual situation in order to get reliable information about the on-site structure and structural elements. The experimental techniques in fracture mechanics are employedfordeterminingthestress-intensityfactors(SIFs)ofthecracksindeformedstructures.Aprocedureforthesimulation ofcrackpropagationformultiplecrackswasintroducedandSIFshavebeencalculatedbyusingthefinite-elementmethod.The crack growth of a single crack or a periodic array of cracks initiated at the stiffeners in a stiffened panel has been investigated. TheopticalmethodofcausticsisestablishedfortheapplicationtomechanicallyisotropicmaterialsthroughtheprocessofSIF’s evaluation and has advantageously improved applications with fiber-reinforced composites. Using high-speed photography and optical interferometric methods, we analyzed the phenomena of the dynamic failure process in composites and high-speed delamination. Valuable information gathered by the analysis of critical structural components should be important for making decisions about thestructuralrepairingorthehaltingofaplant’sproduction.Significantexamplesaretheanalysisofstructuresofthedeckofa ship,thejacketofagasandoilplatformandtheaeolianvibrationsinelectricaltransmissionlinesthatcancauseseveredamage or even the breakdown of the conductor due to material fatigue. Key words: caustics, CGS interferometry, risk assessment, FEM model, survey, aeolian vibrations Nadzor in ugotavljanje integritete konstrukcij je aktivnost z nara{~ujo~im pomenom zaradi kontrole trajnosti, stabilnosti in varnosti ter ugotavljanja preostale trajnostne dobe struktur. Raziskave rasti razpok so potrebne zaradi ocene zanesljivosti delov struktur. V uporabi so razli~ne metode za ugotavljanje stanja. Eksperimentalne metode mehanike loma se uporabljajo za dolo~anje faktorja intenzitete napetosti (SIFs) za razpoke v obremenjenih strukturah. Razvita je bila procedura za simulacijo propagacije razpoke v primeru ve~ razpok in izra~unana je bila SIFs uporabo metode kon~nih elementov. Raziskana je bila rast ene ali ve~ razpok, ki so nastale ob oja~itvah v oja~anem panelu. Opti~na metoda svetlobnih odsevov je bila razvita za uporabo pri mehansko izotropnih materialih z dolo~itvijo SIFs in prilagojena za uporabo pri vlaknatih kompozitih. Z uporabo fotografije z veliko hitrostjo in opti~no interferometrijo je bil analiziran pojav dinami~nega zloma kompozitov in hitre delaminacije. Podatki, zbrani z analizo kriti~nih komponent struktur, so temeljnega pomena pri odlo~itvah o popravilih ali ustavitvah proizvodnih naprav. Prikazani so primeri analize krova ladijske strukture, armatur plinskih in naftnih plo{~adi ter vibracije zaradi vetra pri elektri~nih daljnovodih, ki lahko povzro~ijo resno {kodo ali celo zlom zaradi utrujenosti materiala. Klju~ne besede: svetlobni odsevi, CGS-interferometrija, ocena rizika, FEM-model, pregled, svetlobne vibracije 1 INTRODUCTION Structurallifemanagementrequirestheintegrationof design and analysis, materials behavior and structural testing. Used properly, the defined procedures can prevent over-design and provide a balance between safety and costs. The results will serve to optimize machine parts and they will also enable advantageous functionality, decreasing of maintenance costs and improvements to the fatigue life. An improvement of the numerical and experimental methods will provide an observation of the damage process in the contact of two structural elements and the assessment of the reliability ofthepartsofthemechanicalsystem.Thiswillservefor betterendurance,stabilityandsecurityofthestructureas well as for a more reliable assessment of its life span. In recent years, substantial advances in the under- standing of the basic principles governing dynamic fracture, coupled with the development of new, relatively easy-to-use and verifiable computational methodologies have made it possible to utilize the concepts of dynamic fracture in a wide spectrum of very diverse applications. They are relevant to our rapidly developing technological world, such as accident prevention, manufacturing processes, and reliability in design. 2 AN ANALYSIS OF THE STRESS-INTENSITY FACTOR USING THE OPTICAL METHOD OF CAUSTICS A variety of modern optical interferometric methods, including the optical method of caustics, today provide the possibility of identifying and measuring the critical parameters governing the resistance of materials to both quasistatic and dynamic failure. Although existing MATERIALI IN TEHNOLOGIJE 40 (2006) 4 123 UDK 539.42:624 ISSN 1580-2949 Review article/Pregledni znanstveni ~lanek MTAEC9, 40(4)123(2006)