Gruppo Italiano Frattura (IGF)
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Liquefaction mathematical analysis for improvement structures stability
No full textThe stability of any structure is possible if foundation is appropriately designed. The Bandar abbas is the largest and most important port of Iran, with high seismicity and occurring strong earthquakes in this territory, the soil mechanical properties of different parts of city have been selected as the subject of current research. The data relating to the design of foundation for improvement of structure at different layer of subsoil have been collected and, accordingly, soil mechanical properties have been evaluated. The results of laboratory experiments can be used for evaluation of geotechnical characteristics of urban area for development a region with high level of structural stability. Ultimately, a new method for calculation of liquefaction force is suggested. It is applicable for improving geotechnical and structure codes and also for reanalysis of structure stability of previously constructed buildings
Investigation of crack propagation in single optical fiber composite with thermal influence by finite element method
No full textTwo parallel comparative ‘Conventional Method and Computer Simulation using ANSYS software’for prediction of crack growth and its behavior in optical fiber are studied and presented in this work.Corresponding finite element analysis was performed to determine the evolution of stress and strain states. Themethod is developed and combined with the modified J-integral theory to deal with this problem. The effects ofcrack length, temperature and mechanical forces are investigated by Finite Element Method in the crackedbody. The conditions where the Mode I stress intensity factor motivate fracture occurrence is investigated andvariations of the different cases are discussed. The most deleterious situation is found to be that wherein theentire model reaches rupture at some stage. The accuracy of the method is investigated through comparison ofnumerical results with computerized simulation using commercial ANSYS software
Multiscale approach to description of deformation and fracture of brittle media with hierarchical porous structure on the basis of movable cellular automaton method
No full textAn approach to multiscale description of deformation and fracture of brittle porous materials onthe basis of movable cellular automaton method was proposed. The material characterized by pore sizedistribution function having two maxima was considered. The core of the proposed approach consists infinding the automaton effective response function by means of direct numerical simulation of representativevolume of the porous material. A hierarchical two-scale model of mechanical behavior of ceramics undercompression and shear loading was developed. Zirconia based ceramics with pore size greater than the averagegrain size was considered. At the first scale of the model only small pores (corresponding to the first maximumof the pore size distribution function) were taking into account explicitly (by removing automata from the initialstructure). The representative volume and effective elastic properties of the porous material at this scale wereevaluated. At the second scale of the model, big pores were taking into account explicitly, the parameters of thematrix corresponded to the ones determined at the first scale. Simulation results showed that the proposedmultiscale model allows qualitatively and quantitatively correct describing of deformation and fracture of brittlematerial with hierarchical porous structure
The theory of critical distances applied to problems in fracture andfatigue of bone
No full textThe theory of critical distances (TCD) has been applied to predict notch-based fracture and fatigue in a wide range of materials and components. The present paper describes a series of projects in which we applied this approach to human bone. Using experimental data from the literature, combined with finite element analysis, we showed that the TCD was able to predict the effect of notches and holes on the strength of bone failing in brittle fracture due to monotonic loading, in different loading regimes. Bone also displays short crack effects, leading to R-curve data for both fracture toughness and fatigue crack propagation thresholds; we showed that the TCD could predict this data. This analysis raised a number of questions for discussion, such as the significance of the L value itself in this and other materials. Finally, we applied the TCD to a practical problem in orthopaedic surgery: the management of bone defects, showing that predictions could be made which would enable surgeons to decide on whether a bone graft material would be needed to repair a defect, and to specify what mechanical properties this material should have
Influence of mean stress on the fatigue strength of ASTM A743 CA6NM alloy steel
No full textThe objective of this work is to evaluate the effects of mean stress on the fatigue behavior of ASTM A743 CA6NM alloy steel. It is used in several hydrogenator turbine components. In order to achieve it, 33 specimens were experimentally evaluated under axial loads with stress ratio of - 1 and more 60 specimens were tested under stress ratio 0, 1/3 and 2/3. Based on the obtained results it was possible to determine parameters that describe the fatigue behavior of the evaluated material, obtain its S-N curves, its endurance limit and its scatter bands. In the assessment of the mean stress effects of fatigue life, Goodman, Gerber, Walker and Kwofie’s relations were tested in order to evaluate the validity of the use of such rules for the tested material. According to the obtained results it was possible to verify that Goodman and Gerber’s relations do not model correctly the reduction effect fatigue life and presented high scatter. The predictions of Walker and Kwofie’s relation are consistent and the Walker’s relation presented smaller scatter than Kwofie’s relation. Walker’s relation makes it possible to evaluate in a consistent way the effect of the presence of mean stresses on fatigue strength
Crack propagation in micro-chevron-test samples of direct bonded silicon-silicon wafers
No full textWafer bonding describes all technologies for joining two or more substrates directly or using certain intermediate layers. Current investigations are focused on so-called low temperature bonding as a special direct bonding technology. It is carried out without intermediate layers and at temperatures below 400 °C. In addition to the wafer materials, the toughness of the bonded interface also depends on the bonding process itself. It can vary for different pre-treatments. Furthermore, an increase of the annealing temperature leads to a higher toughness of the bonded interface.
The fracture toughness is a suitable value to describe the damage behaviour of the bonded interface. Based on a micro-chevron-specimen, the fracture toughness can be determined either numerically or by combining numerical analysis with experimental measurement of the maximum force.
The maximum force is measured during a micro-chevron-test using a Mode I loading. The minimum of the stress intensity coefficient can be determined by a FE-simulation only. One possibility to estimate the stress intensity coefficient is the compliance method. The compliance of the whole specimen increases with a growing crack. The stress intensity coefficient can be directly derived from the simulated compliance and the crack length itself.
The paper is focused on the micro-chevron-test for direct bonded silicon-silicon wafers. Additional to the estimation of dimensionless stress intensity coefficient as a function of geometry, the influence of different pre-treatments and annealing temperatures on the measured maximum force are analysed and discussed
A dimensional analysis approach to fatigue in quasi-brittle materials
No full textIn this study, a generalized Barenblatt and Botvina dimensional analysis approach to fatigue crack growth is proposed in order to highlight and explain the deviations from the classical power-law equations used to characterize the fatigue behaviour of quasi-brittle materials. According to this theoretical approach, the microstructural-size (related to the volumetric content of fibres in fibre-reinforced concrete), the crack-size, and the size-scale effects on the Paris’ law and the Wöhler equation are presented within a unified mathematical framework. Relevant experimental results taken from the literature are used to confirm the theoretical trends and to determine the values of the incomplete self-similarity exponents. All these information are expected to be useful for the design of experiments, since the role of the different dimensionless numbers governing the phenomenon of fatigue is herein elucidated
Behaviour of a speargun with a novel muzzle Comportamento di un fucile subacqueo con testata innovativa
No full textThe paper presents the results of a numerical and experimental investigation performed on a barrelof a speargun equipped with two kinds of muzzle. In particular, a standard muzzle for speargun (having anelastic propulsion) has been compared with an innovative one called ‘roller’. This new muzzle is equipped withtwo rollers and special bands. The rubber bands, fixed at the lower side of the barrel, run through the rollersand are engaged in suitable seats of the shaft. These bands are, therefore, longer than the traditional ones and,consequently, with equal force applied by the diver, the roller speargun has a longer range. Thanks to theparticular geometry of the new muzzle, one of the front constraints of the elastic bands is moved to the lowerpart of the barrel or the handle.As a consequence, the scheme of the loads applied on the speargun remarkably changes passing from a standardmuzzle to a roller one. All that has a great influence on the level of deformation of the barrel and, consequently,on the accuracy of the shot. Because of the low velocity of the spear (if compared with the firearms), in fact, theaccuracy of the shoot if strongly influenced by the barrel bending due to the forces applied by means of theelastic bands..