Sulla storia degli studi di frattura in Italia

History of studies of fracture is inherently intermingled with the history of technology developments. In the beginning very little was written about. We must credit Leonardo and Galileo as the first ones that wrote about the problem and on how to measure and foresee rupture loads. Later, nineteenth century italian scientists distinguished themselves in attempting to establish material laws and multiple stresses rupture criteria. A review of the works of past centuries italian scientists is presented, along with a critical comparison with the work of other past european scientists

The way the mistery of the Mattei's case was solved

Enrico Mattei, the President of the Italian oil conglomerate, ENI, was about to land in Milan Linate Airport on October 27, 1962 when his airplane crashed on the ground due to a then unexplained accident. The investigation, reopened more than 30 years later, implied complete re-examining of the theories on macroscopic and lattice deformations under high velocity waves emanating from a small charge explosion.Various macro- and micro-structural changes are induced by an explosion and by the resulting shear stresses in metals exposed to it. At the microstructural level multiple slip bands or mechanical twins, induced from the pressure wave caused by an explosion, can be observed. The occurrence of either ones depend on the type of metal, the pressure and the strain rate. The temperature wave may also cause surface alterations. Different situations regarding stainless steels, aluminium, copper and gold alloys are analysed.Calculations to evaluate which deformation mechanism is eligible for different FCC metals and alloys are reported. Results of field explosion experiments are incorporated into the evaluation of microstructural signs possibly induced on metal targets by an unknown explosive event.Revisited theories were applied to the Mattei forensic case, reaching the conclusion that the aircraft had fallen following an on board small charge explosion

Sulla storia degli studi di frattura in Italia

History of studies of fracture is inherently intermingled with the history of technology developments. In the beginning very little was written about. We must credit Leonardo and Galileo as the first ones that wrote about the problem and on how to measure and foresee rupture loads. Later, nineteenth century italian scientists distinguished themselves in attempting to establish material laws and multiple stresses rupture criteria. A review of the works of past centuries italian scientists is presented, along with a critical comparison with the work of other past european scientists

Fatigue crack growth in inhomogeneous steel components

Massive low-alloy high-strength steel components often exhibit microstructure variations from surface to core due to decreasing cooling rates when moving towards the interior. Since different steel constituents exhibit different fatigue crack growth (FCG) behaviors, both the overall and local FCG rates are expected to be influenced by the microstructural change that in turn affects the crack shape. The case of slack-quenched components with simple geometries, having a surface flaw, and subjected to constant-force-amplitude tensile fatigue, is first examined theoretically. The microstructural variations are hypothesized by considering low-alloy steel hardenabilities and medium quench severities; thereafter, the FCG is computed by considering (during each integration step) the stress intensity factor amplitude and the FCG behavior of different points of the crack front, the pointwise FCG properties being determined by the local steel constituents fractions. Simulation results are compared with experimental evidences from a recent failure in a 90 mm diameter low-alloy steel connection rod of a 2460 kW naval diesel generato

Brittle Materials and Stress Concentrations: are they able to withstand?

AbstractThe combination of brittleness in materials and stress concentrations may lead to premature fracture of structural components. To improve the modelling capability more and more sophisticated methods have to be employed. To the purpose a Finite Fracture Mechanics (FFM) criterion based on the contemporaneous fulfilment of a stress requirement and the energy balance has been proposed in the literature. This coupled approach is here refined and applied to investigate brittle fracture in rounded V-notched samples under mode I loading. The failure FFM condition is expressed by a system of two equations in two unknowns: the critical crack advance and the apparent generalized fracture toughness (i.e., the failure load). The refined criterion is validated by its implementation with various experimental data, available in the literature, related to ceramic, metallic, and plastic brittle materials

Fracture behavior in Cu46.5Zr46.5Al7 and Cu46.5Zr41.5Al7Y5 bulk metallic glasses

The interplay between chemical composition, plastic behavior, and fracture modes of Cu46.5Zr46.5Al7 and Cu46.5Zr41.5Al7Y5 bulk metallic glasses (BMGs) was investigated by compression tests and fracture surfaces analyses. The aim was to explore the possibility of coupling physical, chemical, and hardness properties, with adequate macroscopic compressive plasticity. Cylindrical test samples, having a height-to-diameter ratio equal to 2, were machined and ground from as-cast bars and were tested in compression between lubricated plates, the displacement being measured by a clip-gage inserted between the plates. Y free BMG engineering stress-strain curves show a plastic behavior consisting of successive sudden stress drops and linear reloading segments. A detailed analysis of these features was performed to yield a correlation between the plastic deformation steps and the released elastic energy associated with each serratio

Comparison of Ni-Cr and Co-based alloys for fuel injectors

Presentazione orale al convegno TMS 2011 - 140th Annual Meeting & Exhibition, svoltosi a San Diego, USA, dal 27/02/2011 al 03/03/201

Advanced high-strength steels for car-body manufacturing

Presentazione oral