1,721,026 research outputs found
Estimation of the dissipative heat sources related to the total energy input of a cfrp composite by using the second amplitude harmonic of the thermal signal
Full text linkTheories for predicting the fatigue behaviour of composite laminates often make strong assumptions on the damage mechanisms that strongly depend on the designed laminate lay-up. In this regard, several physical and empirical models were proposed in the literature that generally require experimental validations. The experimental techniques, such as thermography, also provide useful tools for monitoring the behaviour of the specific material so, that they can be used to support the study of the damage mechanisms of materials. In this research, the second amplitude harmonic of the thermal signal has been investigated and used to assess the relationship with the total energy input in order to estimate the fatigue strength of the material. A thermal index was assessed by monitoring the constant amplitude tests (S/N curve) that were performed on a quasi-isotropic carbon fibre reinforced polymer (CFRP) laminate obtained by the automated fibre placement process. The obtained results demonstrated the capability of the second amplitude harmonic of the thermal signal to describe and monitor the fatigue damage
Analisi del limite di fatica di un acciaio C45 attraverso lo studio dei parametri legati alle sorgenti dissipative
No full textLe tecniche e gli strumenti attualmente disponibili per determinare il limite di fatica dei materiali risultano avere tempi e costi elevati. Nell’ottica di risparmiare tempi e costi della campagna sperimentale, la termografia rappresenta un valido supporto per le attività di caratterizzazione meccanica dei componenti. Suddetta tecnica, infatti, può essere adottata per caratterizzare il comportamento a fatica dei materiali attraverso il rilevamento delle sorgenti termiche che si sviluppano nel materiale quando viene sottoposto a carico ciclico. In questo lavoro si propone si propone una metodologia di analisi dei dati che consente di analizzare le componenti del segnale termico legate a sorgenti termoelastiche e dissipative. Si mostra inoltre un’affidabile procedura di analisi dei dati che permette di stimare l’inizio del danneggiamento del materiale ‘filtrando’ tutte le componenti termiche ad esso non correlate.The techniques present in literature for assessing the endurance limit of materials, involve expensive and long lasting experimental campaign due to remarkable number of specimen being tested. To avoid a time-consuming mechanical characterisation, Infrared Thermography allows to a rapid evaluation of material fatigue behaviour by monitoring the temperature of the intrinsic heat sources. However, the evaluation of heat sources requires a suitable data analysis for filtering out all the noisy heat sources not related to damage phenomena. In this work, the strong points of thermography are shown capable of a rapid fatigue damage assessment of C45 steel and a robust data analysis
Mechanical behaviour of stainless steels under dynamic loading: An investigation with thermal methods
Full text linkStainless steels are the most exploited materials due to their high mechanical strength and versatility in producing different alloys. Although there is great interest in these materials, mechanical characterisation, in particular fatigue characterisation, requires the application of several standardised procedures involving expensive and time-consuming experimental campaigns. As a matter of fact, the use of Standard Test Methods does not rely on a physical approach, since they are based on a statistical evaluation of the fatigue limit with a fixed probabilistic confidence. In this regard, Infra-Red thermography, the well-known, non-destructive technique, allows for the development of an approach based on evaluation of dissipative sources. In this work, an approach based on a simple analysis of a single thermographic sequence has been presented, which is capable of providing two indices of the damage processes occurring in material: the phase shift of thermoelastic signal φ and the amplitude of thermal signal at twice the loading frequency, S2. These thermal indices can provide synergetic information about the mechanical (fatigue and fracture) behaviour of austenitic AISI 316L and martensitic X4 Cr Ni Mo 16-5-1; since they are related to different thermal effects that produce damage phenomena. In particular, the use of φ and S2 allows for estimation of the fatigue limit of stainless steels at loading ratio R = 0.5 in agreement with the applied Standard methods. Within Fracture Mechanics tests, both indices demonstrate the capacity to localize the plastic zone and determine the position of the crack tip. Finally, it will be shown that the value of the thermoelastic phase signal can be correlated with the mechanical behaviour of the specific material (austenitic or martensitic)
Potenzialità dell'approccio basato sull'analisi del segnale termico per la caratterizzazione rapida di materiali ad alta diffusività
No full text
Potenzialità dell'approccio basato sull'analisi del segnale termico per la caratterizzazione rapida di materiali ad alta diffusività
No full textCaratterizzazione a fatica con tecnica termografica di giunti Friction Stir Welding in AA5754-H111
No full textA new procedure for fatigue life prediction of CFRP relying on the first amplitude harmonic of the temperature signal
No full textThe use of thermal indexes assessed by monitoring rapid fatigue tests with infrared detectors as reliable damage parameters to reconstruct S/N curve is a topic still presenting open points. First of all, the selection of the proper thermal index representing damage is a topic to be explored and also the relationship between the damage from rapid stepwise test and constant amplitude test is another a point of discussion. In the present work, we deal with such an issue by investigating the First Amplitude Harmonic (FAH) of thermal signal related to thermoelastic phenomena and dissipative effects too. It has been demonstrated that FAH is related to stiffness degradation and stress induced effects. Moreover, it provides a local analysis of the specific effect related to the material fatigue damage without artifacts. The results show that due to relationship between stiffness degradation and FAH, and specific material properties it is possible to reconstruct S/N curve by carrying out just one constant amplitude test and stepwise rapid tests. Moreover, the capability of temperature FAH to study fatigue behaviour and detect damage during any loading procedure, are also presented
- …
