Super-Bridges Suspended Over Carbon Nanotube Cables

In this paper the new concept of super-bridges, i.e. kilometre-long bridges suspended over carbon nanotube cables, is introduced. The analysis shows that the use of realistic (thus defective) carbon nanotube bundles as suspension cables can enlarge the current limit main span by a factor of 3.Comment: 17 pages, 6 figures, 2 table

On the Strength of the Carbon Nanotube-Based Space Elevator Cable: From Nano- to Mega-Mechanics

In this paper different deterministic and statistical models, based on new quantized theories proposed by the author, are presented to estimate the strength of a real, thus defective, space elevator cable. The cable, of ~100 megameters in length, is composed by carbon nanotubes, ~100 nanometers long: thus, its design involves from the nano- to the mega-mechanics. The predicted strengths are extensively compared with the experiments and the atomistic simulations on carbon nanotubes available in the literature. All these approaches unequivocally suggest that the megacable strength will be reduced by a factor at least of ~70% with respect to the theoretical nanotube strength, today (erroneously) assumed in the cable design. The reason is the unavoidable presence of defects in a so huge cable. Preliminary in silicon tensile experiments confirm the same finding. The deduced strength reduction is sufficient to pose in doubt the effective realization of the space elevator, that if built as today designed will surely break (according to the s opinion). The mechanics of the cable is also revised and possibly damage sources discussed

Crackling noise in three-point bending of heterogeneous materials

We study the crackling noise emerging during single crack propagation in a specimen under three-point bending conditions. Computer simulations are carried out in the framework of a discrete element model where the specimen is discretized in terms of convex polygons and cohesive elements are represented by beams. Computer simulations revealed that fracture proceeds in bursts whose size and waiting time distributions have a power law functional form with an exponential cutoff. Controlling the degree of brittleness of the sample by the amount of disorder, we obtain a scaling form for the characteristic quantities of crackling noise of quasi-brittle materials. Analyzing the spatial structure of damage we show that ahead of the crack tip a process zone is formed as a random sequence of broken and intact mesoscopic elements. We characterize the statistics of the shrinking and expanding steps of the process zone and determine the damage profile in the vicinity of the crack tip.Comment: 11 pages, 15 figure

On unified crack propagation laws

The anomalous propagation of short cracks shows generally exponential fatigue crack growth but the dependence on stress range at high stress levels is not compatible with Paris’ law with exponent . Indeed, some authors have shown that the standard uncracked SN curve is obtained mostly from short crack propagation, assuming that the crack size a increases with the number of cycles N as where h is close to the exponent of the Basquin’s power law SN curve. We therefore propose a general equation for crack growth which for short cracks has the latter form, and for long cracks returns to the Paris’ law. We show generalized SN curves, generalized Kitagawa–Takahashi diagrams, and discuss the application to some experimental data. The problem of short cracks remains however controversial, as we discuss with reference to some examples

Evidence of friction reduction in laterally graded materials

In many biological structures, optimized mechanical properties are obtained through complex structural organization involvingmultiple constituents, functional grading and hierarchical organization. In the case of biological surfaces, the possibility to modifythe frictional and adhesive behaviour can also be achieved by exploiting a grading of the material properties. In this paper, we in-vestigate this possibility by considering the frictional sliding of elastic surfaces in the presence of a spatial variation of the Young’smodulus and the local friction coefficients. Using finite-element simulations and a two-dimensional spring-block model, we investi-gate how graded material properties affect the macroscopic frictional behaviour, in particular, static friction values and the transi-tion from static to dynamic friction. The results suggest that the graded material properties can be exploited to reduce static frictionwith respect to the corresponding non-graded material and to tune it to desired values, opening possibilities for the design of bio-inspired surfaces with tailor-made tribological propertie

Deep learning aided topology optimization of phononic crystals

In this work, a novel approach for the topology optimization of phononic crystals based on the replacement of the computationally demanding traditional solvers for the calculation of dispersion diagrams with a surrogate deep learning (DL) model is proposed. We show that our trained DL model is ultrafast in the prediction of the dispersion diagrams, and therefore can be efficiently used in the optimization framework

Materiali strutturali biologici e bioinspirati

I materiali sviluppati dall'uomo e utilizzati per applicazioni tecnologiche, in generale non sono multifunzionali, né tolleranti ai difetti, né auto-riparanti, né auto-pulenti, né gerarchici. Il contrario è vero per i materiali naturali, che manifestano queste proprietà nonostante siano "costruiti" usando un numero limitato di componenti di base estremamente comuni. Una comprensione approfondita del perché sia così potrebbe fornire la chiave per accelerare l'avvento di una nuova era basata su nuovi materiali.Questo è l'obiettivo della ricerca sui materiali bioispirati, che è in continua evoluzione e ha già fatto passi significativi verso questa meta