arXiv subjects

Frederic Lechenault

Publications and source records attributed to Frederic Lechenault.

9 recordsLinked to original sources

arXiv2026

Hollow Needle Puncture Mechanics for Biopsy Sampling

Biopsy sampling relies on hollow needles that puncture soft tissues by propagating and opening a cylindrical crack, yet the mechanics governing this coring process remain only partially understood. Motivated by this gap, we develop a simple, energy based model for puncture by blunt hollow needles, grounded in brittle fracture mechanics and extended to include frictional interactions at the needle tissue interface. The model describes puncture as the competition between the fracture energy and the elastic energy. This energetic balance is controlled by the interplay among needle geometry (radius and wall thickness), material properties (toughness and elastic modulus), and interfacial parameters (adhesion and friction). This model provides semi-analytical predictions for five key quantities: core size, frictionless force, frictional force slope, critical insertion depth, and critical insertion force. Model predictions are validated against experiments, demonstrating that friction significantly improves force estimation and alters the puncture regime. These results offer quantitative insight into the mechanics of tissue coring and force generation during biopsy, providing a predictive foundation for needle design, sampling performance, and real time control in robotic biopsy and needle insertion systems.

cond-mat.soft↗

arXiv2022

Soft coring: how to get a clarinet out of a flute?

Cutting mozzarella with a dull blade results in poorly shaped slices: the process occurs in a configuration so deformed as to yield unexpectedly curved surfaces. We study the rich morphogenetics arising from such process through the example of coring: when a thin cylindrical hollow punch is pushed into a soft elastomer, the extracted core is "clarinet-shaped", reaching diameters far smaller than those of the tool. With contributions from fracture mechanics and large strain theory, we build a simple yet quantitative understanding of the observed shapes, revealing the crucial role of friction.

cond-mat.soft↗

arXiv2017

Roughness of oxide glass subcritical fracture surfaces

An original setup combining a very stable loading stage, an atomic force microscope and an environmental chamber, allows to obtain very stable sub-critical fracture propagation in oxide glasses under controlled environment, and subsequently to finely characterize the nanometric roughness properties of the crack surfaces. The analysis of the surface roughness is conducted both in terms of the classical root mean square roughness to compare with the literature, and in terms of more physically adequate indicators related to the self-affine nature of the fracture surfaces. Due to the comparable nanometric scale of the surface roughness, the AFM tip size and the instrumental noise, a special care is devoted to the statistical evaluation of the metrologic properties. The 2 roughness amplitude of several oxide glasses was shown to decrease as a function of the stress intensity factor, to be quite insensitive to the relative humidity and to increase with the degree of heterogeneity of the glass. The results are discussed in terms of several modeling arguments concerning the coupling between crack propagation, material's heterogeneity, crack tip plastic deformation and water diffusion at the crack tip. A synthetic new model is presented combining the predictions of a model by Wiederhorn et al. [1] on the effect of the material's heterogeneity on the crack tip stresses with the self-affine nature of the fracture surfaces.

cond-mat.soft↗

arXiv2016

Geometry and design of origami bellows with tunable response

Origami folded cylinders (origami bellows) have found increasingly sophisticated applications in space flight and medicine. In spite of this interest, a general understanding of the mechanics of an origami folded cylinder has been elusive. With a newly developed set of geometrical tools, we have found an analytic solution for all possible cylindrical rigid-face states of both Miura-ori and triangular tessellations. Although an idealized bellows in both of these families may have two allowed rigid-face configurations over a well-defined region, the corresponding physical device, limited by nonzero material thickness and forced to balance hinge and plate-bending energy, often cannot stably maintain a stowed configuration. We have identified the parameters that control this emergent bistability, and have demonstrated the ability to design and fabricate bellows with tunable deployability.

cond-mat.soft↗

arXiv2014

The mechanical response of a creased sheet

We investigate the mechanics of thin sheets decorated by non-interacting creases. The system considered here consists in parallel folds connected by elastic panels. We show that the mechanical response of the creased structure is twofold, depending both on the bending deformation of the panels and the hinge-like intrinsic response of the crease. We show that a characteristic length scale, defined by the ratio of bending to hinge energies, governs whether the structure's response consists in angle opening or panel bending when a small load is applied. The existence of this length scale is a building block for future works on origami mechanics

cond-mat.mtrl-sci↗

arXiv2010

Local origins of volume fraction fluctuations in dense granular materials

Fluctuations of the local volume fraction within granular materials have previously been observed to decrease as the system approaches jamming. We experimentally examine the role of boundary conditions and inter-particle friction $μ$ on this relationship for a dense granular material of bidisperse particles driven under either constant volume or constant pressure. Using a radical Voronoï tessellation, we find the variance of the local volume fraction $ϕ$ monotonically decreases as the system becomes more dense, independent of boundary condition and $μ$. We examine the universality and origins of this trend using experiments and the recent granocentric model \cite{Clusel-2009-GMR,Corwin-2010-MRP}, modified to draw particle locations from an arbitrary distribution ${\cal P}(s)$ of neighbor distances $s$. The mean and variance of the observed ${\cal P}(s)$ are described by a single length scale controlled by $\bar ϕ$. Through the granocentric model, we observe that diverse functional forms of ${\cal P}(s)$ all produce the trend of decreasing fluctuations, but only the experimentally-observed ${\cal P}(s)$ provides quantitative agreement with the measured $ϕ$ fluctuations. Thus, we find that both ${\cal P}(s)$ and ${\cal P}(ϕ)$ encode similar information about the ensemble of observed packings, and are connected to each other by the local granocentric model.

cond-mat.soft↗

arXiv2010

Universal shapes formed by two interacting cracks

We investigate the origins of the widely-observed "en passant" crack pattern which forms through interactions between two approaching cracks. A rectangular elastic plate is notched on each long side and then subjected to quasistatic uniaxial strain from the short side. The two cracks propagate along approximately straight paths until they pass each other, after which they curve and release a lenticular fragment. We find that for materials with diverse mechanical properties, the shape of this fragment has an aspect ratio of 2:1, with the length scale set by the initial crack offset $s$ and the time scale set by the ratio of $s$ to the pulling velocity. The cracks have a universal square root shape which we understand using a simple geometric model of the crack-crack interaction.

cond-mat.mtrl-sci↗

arXiv2009

An experimental test of volume-equilibration between granular systems

Understanding granular and other athermal systems requires the identification of state variables which consistently predict their bulk properties. A promising approach has been to draw on the techniques of equilibrium statistical mechanics, but to consider alternate conserved quantities in place of energy. The Edwards ensemble, based on volume conservation, provides a temperaturelike intensive parameter called compactivity. We present experiments which demonstrate the failure of compactivity to equilibrate (via volume-exchange) between a pair of externally-agitated granular subsystems with different material properties. Nonetheless, we identify a material-independent relationship between the mean and fluctuations of the local packing fraction which forms the basis for an equation of state. This relationship defines an intensive parameter that decouples from the volume statistics.

cond-mat.stat-mech↗

arXiv2006

Void statistics and compactivity measurement in an experimental granular pile

We investigate experimentally the statistics of the free volume inside bidimensional granular packings, for two different kinds of grains and two levels of compaction. With the aim to gain new insight into the statistical description of granular media, we measure the free volume distribution in clusters of increasing size. Our main result is that the logarithm of the free volume distribution scales in a nonextensive way with the cluster size, while still enabling the extraction of two intensive parameters. We discuss the interpretation of these parameters, and the consequences of the nonextensivity on the possible measurements of Edwards' ''compactivity''.

cond-mat.stat-mech↗