367 research outputs found
Fatigue crack propagation in a quasi one-dimensional elasto-plastic model
Fatigue crack advance induced by the application of cyclic quasistatic loads
is investigated both numerically and analytically using a lattice spring model.
The system has a quasi-one-dimensional geometry, and consists in two
symmetrical chains that are pulled apart, thus breaking springs which connect
them, and producing the advance of a crack. Quasistatic crack advance occurs as
a consequence of the plasticity included in the springs which form the chains,
and that implies a history dependent stress-strain curve for each spring. The
continuous limit of the model allows a detailed analytical treatment that gives
physical insight of the propagation mechanism. This simple model captures key
features that cause well known phenomenology in fatigue crack propagation, in
particular a Paris-like law of crack advance under cyclic loading, and the
overload retardation effect.Comment: To be published in the International Journal of Solids and Structure
A predictive model for the thermomechanical overstretching transition of double stranded DNA
By extending the classical Peyrard-Bishop model, we are able to obtain a
fully analytical description for the mechanical resistance of DNA under
stretching at variable values of temperature, number of base pairs and
intrachains and interchains bonds stiffness. In order to compare elasticity and
temperature effects, we first analyze the system in the zero temperature
mechanical limit, important to describe several experimental effects including
possible hysteresis. We then analyze temperature effects in the framework of
equilibrium statistical mechanics. In particular, we obtain an analytical
expression for the temperature dependent melting force and unzipping assigned
displacement in the thermodynamical limit, also depending on the relative
stability of intra vs inter molecular bonds. Such results coincide with the
purely mechanical model in the limit of zero temperature and with the
denaturation temperature that we obtain with the classical transfer integral
method. Based on our analytical results, explicit analysis of the phase
diagrams and cooperativity parameters are obtained, where also discreteness
effect can be accounted for. The obtained results are successfully applied in
reproducing the thermomechanical experimental melting of DNA and the response
of DNA hairpins. Due to its generality, the proposed approach can be extended
to other thermomechanically induced molecular melting phenomena
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