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Alcune considerazioni sull’implementazione numerica del modello di anneggiamento di Lemaitre-Bonora
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Analisi di sensibilità di un algoritmo di identificazione di una legge plastica a partire dalla correlazione digitale di immagini
No full textIn this work is presented the sensitivity analysis of a plastic flow identification algoritm from full
field measurements obtained by digital image correlation. Starting from an exact solution, an artificial
controlled noise at different levels is added to kinematic full field measurements to evaluate the
thrustworthiness threshold level of the considered algoritm
Sensitivity analysis of test signal with respect to the transducers position in ultrasonic NDT testing
No full textThe state of the art of non-destructive acoustic tests provides information on the type of
transducers and on the number of tests to be conducted in order to obtain satisfactory mappings
on the surfaces of the elements under test, to trace shape and size of defects, both in Test Method
for Transparency (with emitter and received transducer arranged in corresponding points on
two opposite surfaces) either by using Tomographic Methods. The main problem in this type of analysis is related to the strong attenuation of the signals in reception, which often have amplitudes of the same order of magnitude of noise. For this reason, in this work we use cross-correlation between emitted chirp signal and the relative received signal, that allows to assess significant amplitudes. For this paper one refers to tests using Test Method for Transparency applied on a grid of points. The aim of this work is to assess how the relative position between the transducers and
the defects affect the accuracy of the results obtained. To implement this study, we use
orthogonal chirp signals. The study is performed using a specimen of steel of dimensions
(34×135×8) mm3 with three defects consisting of holes of 1 mm diameter with different depth.
To do the simulations we used the commercial finite element software COMSOL in the
frequency domain. In a second phase experimental verifications will be made to verify the obtained results and to tune the model. The instrumentation is as follows: function generator NI PXIe-6251 (NI PXI- 1042 chassis), TiePie Arbitrary Wave Form Generator, Handyscope HS5 and Krautkramer SEB 10 KF-3 @10MHz double probes
Identificazione dei parametri di danneggiamento attraversi misure globali ed analisi agli elementi finiti
No full textThe standard methodology for the identification of the parameters of CDM models is long and
difficult both from the numerical and experimental viewpoints. Indeed, even the simpler models
require specific tests (a series of ramps) and significant post-processing. In this work we propose an
inverse calibration approach based on a simple tensile test. In fact, most CDM models imply a
coupling between the damage and the true-stress true-strain curve. Thus by minimizing an error
functional it is possible to solve the inverse problem
Comparing Two Damage Models Under Shear Stress
No full textRecently, a new macro-mechanical model for ductile damage was presented by Wierzbicki, Xue et al., trying to address the role assumed by Lode angle and pressure sensitivity. The new model requires several experimental tests to identify all its parameters, but should outperform the "standard" formulations at high triaxiality levels. In this work a comparison between the Lemaitre's Continuous Damage Mechanics model and the Wierzbicki's one is proposed. After calibration of both models, the displacement field measured using the Digital Image Correlation technique in a large shear test case is compared with results of Finite Element simulations obtained using the two damage models considered. Results are not conclusive but show that the new damage model is quite accurateas rupture criterion, but damage evolution history deviates to some extent from the experimentally observed behavior
A Combined Optical-ultrasonic Approach to Investigate Mechanical Properties and Damage of Pultruded Materials
No full textInvestigating maritime accidents that involve dangerous goods using hierarchical clustering
Full text linkAlthough the important progress in terms of safety and technological advances, maritime
accidents remain a critical issue in merchant shipping. A high number of accidents continue to occur
every year, with negative consequences both in economic and environmental terms (with often
disastrous and lasting environmental impacts for marine ecosystems) and in the loss of human life.
Understanding the maritime accidents phenomenon is expedient to giving shipping practitioners a focus for tailored interventions aimed at enhancing maritime safety. Using hierarchical clustering methods, this paper analyses historical data relating to maritime accidents to highlight the potential causal relationships that can describe homogeneous groups of accidents. The study explores a database consisting of 1,079 marine accidents that occurred worldwide in the 2009-2019 decade. Accident data is taken from the International Maritime Organization (IMO) database. After illustrating a description of the data set, a non-supervised hierarchical clustering analysis is applied to identify accident patterns, thus helping to better describe the phenomenon and identify potential causal relations that repeat in various accidents. A significant distinction emerges between the accidents that occur for technical reasons and those where human factors (stress, fatigue, situation awareness, decision-making, communication, etc.) play a prevalent role. Afterwards, the clustering analysis is applied to a sub-set of accidents (153 accidents) involving ships carrying dangerous goods (gases, oils, explosives, etc.). The results of the analysis point out the role of the human factor as the prevalent (or contributing) cause of the marine accidents related to work operations. Conversely, fires and explosions, which are by far the most frequent accidents involving ships carrying dangerous goods, are mainly caused by technical problems
Confronto numerico sperimentale fra due modelli di danneggiamento duttile
No full textThe present paper wants to analyse two different models describing the damage process for ductile materials.
Between a large number of different approach, the Lemaitre-Bonora model and the Wierzbicki-Xue one were chosen for the comparison.
The analysis were made using the FE code MSC.Marc with customized usersubroutines to implement these two damage approaches.
The main intent is to show that, under severe load conditions, the importance of considering the Lode angle parameter and the influence of the hydrostatic pressure is a key factor to obtain more accuracy results
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