521 research outputs found
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
Dynamic Quantized Fracture Mechanics
A new quantum action-based theory, Dynamic Quantized Fracture Mechanics
(DQFM), is presented that modifies continuum-based dynamic fracture mechanics.
The crack propagation is assumed as quantized in both space and time. The
static limit case corresponds to Quantized Fracture Mechanics (QFM), that we
have recently developed to predict the strength of nanostructures
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
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 Parisâ 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 Basquinâs 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 Parisâ law. We show generalized SN curves, generalized KitagawaâTakahashi 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
The multiple V-shaped double peeling of elastic thin films from elastic soft substrates
M. P. is supported by the European Commission H2020 under Graphene Flagship Core 1 No. 696656 (WP14 âPolymer compositesâ) and FET Proactive âNeurofibresâ Grant No. 732344
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