Gruppo Italiano Frattura (IGF)
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A coupled interface-body nonlocal damage model for the analysis of FRP strengthening detachment from cohesive material
No full textIn the present work, a new model of the FRP-concrete or masonry interface, which accounts for the coupling occurring between the degradation of the cohesive material and the FRP detachment, is presented; in particular, a coupled interface-body nonlocal damage model is proposed. A nonlocal damage and plasticity model is developed for the quasi-brittle material. For the interface, a model which accounts for the mode I, mode II and mixed mode of damage and for the unilateral contact and friction effects is developed. Two different ways of performing the coupling between the body damage and the interface damage are proposed and compared. Some numerical applications are carried out in order to assess the performances of the proposed model in reproducing the mechanical behavior of the masonry elements strengthened with external FRP reinforcements
Recent developments in multi-parametric three-dimensional stress field representation in plates weakened by cracks and notches
No full textThe paper deals with the three-dimensional nature and the multi-parametric representation of thestress field ahead of cracks and notches of different shape. Finite thickness plates are considered, underdifferent loading conditions. Under certain hypotheses, the three-dimensional governing equations of elasticitycan be reduced to a system where a bi-harmonic equation and a harmonic equation have to be simultaneouslysatisfied. The former provides the solution of the corresponding plane notch problem, the latter provides thesolution of the corresponding out-of-plane shear notch problem. The analytical frame is applied to somenotched and cracked geometries and its degree of accuracy is discussed comparing theoretical results andnumerical data from 3D FE models
Tsunami numerical modeling and mitigation
No full textThe numerical modeling and wave theory are used in tsunami mitigation analysis. It is assumed seaforest is simulating offshore structure submitted to wave loads. The sea forest acts simulate break waves inconservation of coastal territory and facility installed over there. The result reveal that mathematical modelingand numerical simulation can be used to understand tsunami ability in design and urban construction, theresearch indicates reduction of water deep by sea forest resulted in reducing geometry and all wave ability
A review of thermographic techniques for damage investigation in composites
No full textThe aim of this work is a review of scientific results in the literature, related to the application ofthermographic techniques to composite materials. Thermography is the analysis of the surface temperature of abody by infrared rays detection via a thermal-camera. The use of this technique is mainly based on themodification of the surface temperature of a material, when it is stimulated by means of a thermal or mechanicalexternal source. The presence of defects, in fact, induces a localized variation in its temperature distribution and,then, the measured values of the surface temperature can be used to localize and evaluate the dimensions andthe evolution of defects. In the past, many applications of thermography were proposed on homogeneousmaterials, but only recently this technique has also been extended to composites. In this work severalapplications of thermography to fibres reinforced plastics are presented. Thermographic measurements areperformed on the surface of the specimens, while undergoing static and dynamic tensile loading. The jointanalysis of thermal and mechanical data allows one to assess the damage evolution and to study the damagephenomenon from both mechanical and energetic viewpoints. In particular, one of the main issues is to obtaininformation about the fatigue behaviour of composite materials, by following an approach successfully appliedto homogenous materials. This approach is based on the application of infrared thermography on specimenssubjected to static or stepwise dynamic loadings and on the definition of a damage stress, ?D, that is correlatedto the fatigue strength of the material. A wide series of experimental fatigue tests has been carried out to verifyif the value of the damage stress, ?D, is correlated with the fatigue strength of the material. The agreementbetween the different values is good, showing the reliability of the presented thermographic techniques, to thestudy of composite damage and their fatigue behaviour
Crack propagation mechanism and life prediction for very-highcycle fatigue of a structural steel in different environmental medias
No full textThe influence of environmental medias on crack propagation of a structural steel at high and veryhigh-cycle fatigue (VHCF) regimes is investigated based on the fatigue tests performed in air, water and 3.5%NaCl aqueous solution. Crack propagation mechanisms due to different crack driving forces are investigated interms of fracture mechanics. A model is proposed to study the relationship between fatigue life, applied stressand material property in different environmental medias, which reflects the variation of fatigue life with theapplied stress, grain size, inclusion size and material yield stress in high cycle and VHCF regimes. The modelprediction is in good agreement with experimental observations
Valutazione della capacità di rientro alla base di un elicottero in presenza di danno balistico ad un albero di trasmissione della linea rotore di coda
No full textNella progettazione di un elicottero militare, destinato ad operare a bassa quota e in ambienteostile, il danneggiamento di componenti critici, conseguente ad impatto balistico, riveste un ruolo primario nellavalutazione delle possibilità di sopravvivenza dell’intera macchina. In questo articolo è quindi proposto unostudio sperimentale, suddiviso in diverse fasi, riguardante la verifica della capacità di un elicottero di portare atermine una missione di rientro alla base a potenza ridotta e in presenza di danneggiamento balistico ad unalbero di trasmissione della linea rotore di coda.Il lavoro ha richiesto dapprima l’esecuzione, su esemplari del componente in esame, di prove sperimentali diimpatto balistico, condotte utilizzando un proiettile calibro 7.62 NATO. Successivamente su ciascun alberodanneggiato sono state eseguite prove torsionali statiche ed a fatica, il cui scopo è stato verificare la resistenzaresidua del componente all’applicazione di opportuni carichi rappresentativi delle sollecitazioni riscontratedurante la missione di rientro
Microstructural characterisation related to hot tearing of Al-Cu sand mould castings
No full textIn this paper, the hot tearing behaviour in Al-(4.8?6)%Cu sand mould castings was preliminary investigated by means of microstructural examination and image analysis. A dog-bone pattern was employed for the realisation of the castings and three Al-Cu alloys with different Cu and Si contents were used. The effects of the alloy composition and of different pouring temperatures on the hot tearing behaviour of the castings were evaluated. The quantity of the eutectic phase available during solidification is considered a very important parameter for the crack healing phenomenon, in fact the eutectic liquid flows into the hot tear areas and covers parts of the cracks. The hot tear paths and surfaces were observed by means of optical and scanning electron microscopes, which showed that the fracture surfaces were dominated by bridged grain boundaries and the presence of a liquid film, in particular at higher copper concentrations. Several samples were also drawn from the zones characterised by the maximum cross-section variation and the micrographs from the optical microscope were statistically analysed by means of commercially available image analysis software. The quantitative microstructural parameters of percentage, mean area and distribution of the eutectic phase were evaluated and correlated to the capacity of the eutectic liquid to heal open fractures caused by hot tearing for the examined alloys
Failure prediction of T-peel adhesive joints by different cohesive laws and modelling approaches
No full textIn this work, Cohesive Zone Modelling (CZM) was used to simulate failure of T-peel bonded joints with 1.5mm thick adherends, respectively, bonded toghether with Loctite Multibond 330 adhesive. The fracture toughness and load-opening behaviour recorded in previous experiments on bonded Double Cantilever Beam (DCB) specimens were taken as reference to calibrate CZM parameters. Two-dimensional models were analysed using the FE code ABAQUS. The failing interface was modeled with the cohesive elements available in this software. The influence of:
i) different cohesive law shapes,
ii) modeling the presence of the adhesive layer explicitly, was studied
Analysis of the influence of the anisotropy induced by cold rolling on duplex and super-austenitic stainless steels
No full textThis report contains the results obtained from the mechanical characterization tests carried out on
two different stainless steel (duplex 6%Ni, 22%Cr and super-austenitic 31%Ni, 28%Cr) used for the
manufacturing of pipes which are employed in the oil production.
The activity has been performed in order to evaluate the effects of anisotropy, induced by cold rolling, on the
mechanical characteristics of the investigated steels, measured in the three main directions.
Considering the small size of the component, the method and the specimens used for the tests were not the
standard one. The procedure carried out provided the strain measurement of the specimen during testing by
means of resistive strain gages, bonded on the specimens
On the relationship between J-integral and CTOD for CT and SENB specimens
No full textIn this investigation the relationship between J-integral and CTOD is studied considering a Compact Tensile (CT) and Single edge notched bend (SENB) specimens using finite element analysis. The magnitude of CTOD is estimated by 90o-intercept method and also by plastic hinge model. The results indicate that there exists a discrepancy in estimation of CTOD by 90o-intercept method and by plastic hinge model. The CTOD values obtained by both the methods are found to be linearly proportional to J-integral. The linear proportionality constant dn between CTOD and J is found to strongly depend on the method of estimation of CTOD, specimen geometry and a/W ratio of the specimens