Concept.

<p>The classical fibre dissipates during fracture its cumulated strain energy, thus displaying a toughness modulus of (the factor 2 must be replaced by an other number for nonlinear elastic fibres). In contrast, a fibre with a slider, e.g. knot, can dissipate much more energy, thanks to a sliding friction force. The upper limit of the toughness in this case is constituted by the product of a force just below the breaking force and a displacement equal to the entire fibre length l, thus reaching a toughness modulus of . Accordingly, a huge () previously “hidden” toughness naturally emerges.</p

World toughness record (work in progress, with a zylon microfiber we have already achieved a toughness modulus of 1400 J/g starting from its intrinsic value of 20 J/g - preliminary results reported in the ERC proposal “Knotough”).

<p>Force vs displacement curve of Endumax fibres with (samples 2,3,4) or without a slider (sample 4). The pristine fibre has a toughness modulus of 44 J/g. The introduction of the slider dramatically changes the scenario: a long plastic-like plateau clearly emerges thanks the presence of the slider and allows the dissipation of a huge amount of energy, approaching an unprecedented toughness modulus of 1070 J/g (other two tests, leading to 988 and 1025 J/g are shown). The specific strength and thus maximal achievable toughness is for this fibre of about 1600 J/g (see stress peak in the figure).</p

Proof of concept.

<p>Specific force-displacement or stress-strain curves of knotted and unknotted Dyneema fibres (the number of knots is depicted for each curve; with mass per unit length, given in MPa*cm³/g or, equivalently, in J/g; test parameters are dx/dt = 2 mm/min, l₀ = 10 mm, l = 100 mm, μ = 0.0361 g/m). The appearance with the knot of the hidden toughness, the plastic-like plateau absent in the constitutive law of the unknotted fibre (27 J/g), is evident. For 1 and 2 coils the knot unties (peculiar mechanism) and stress goes to zero, then the fibres extends, deforms and fractures at the pristine fibre strength, with an increment in the toughness of up to 722% (2 coils, 195 J/g). For 3 coils the dissipated energy is further increased up to a maximal value of 320 J/g, corresponding to a toughness increment of 1185%. For 4 coils, premature failure leads to a reduction in both toughness and failure strain. The total hidden toughness is given by the specific strength, thus for this fibre it is close to 1000 J/g.</p

専賣ト戰後財政

We study the ballistic properties of two-dimensional (2D) materials upon the hypervelocity impacts of C₆₀ fullerene molecules combining ab initio density functional tight binding and finite element simulations. The critical penetration energy of monolayer membranes is determined using graphene and the 2D allotrope of boron nitride as case studies. Furthermore, the energy absorption scaling laws with a variable number of layers and interlayer spacing are investigated, for homogeneous or hybrid configurations (alternated stacking of graphene and boron nitride). At the nanolevel, a synergistic interaction between the layers emerges, not observed at the micro- and macro-scale for graphene armors. This size-scale transition in the impact behavior toward higher dimensional scales is rationalized in terms of scaling of the damaged volume and material strength. An optimal number of layers, between 5 and 10, emerges demonstrating that few-layered 2D material armors possess impact strength even higher than their monolayer counterparts. These results provide fundamental understanding for the design of ultralightweight multilayer armors using enhanced 2D material-based nanocomposites

The maximum strength of different types of (mainly spider) silks.

<p>The maximum strength of different types of (mainly spider) silks.</p

Finite Element Modelling details from Multilayer stag beetle elytra perform better under external loading via non-symmetric bending properties

Insect cuticle has drawn a lot of attention from engineers because of its multifunctional role in the life of insects. Some of these cuticles have an optimal combination of lightweight and good mechanical properties, and have inspired the design of composites with novel microstructures. Among these, beetle elytra have been explored extensively for their multilayered structure, multifunctional roles and mechanical properties. In this study, we investigated the bending properties of elytra by simulating their natural loading condition and comparing it with other loading configurations. Further, we examined the properties of its constitutive bulk layers to understand the contribution of each one to the overall mechanical behaviour. Our results showed that elytra are graded, multilayered composite structures that perform better in natural loading direction in terms of both flexural modulus and strength which is likely an adaptation to withstand loads encountered in the habitat. Experiments are supported by analytical calculations and finite-element method modelling, which highlighted the additional role of the relatively stiff external exocuticle and of the flexible thin bottom layer, in enhancing flexural mechanical properties. Such studies contribute to the knowledge of the mechanical behaviour of this natural composite material and to the development of novel bioinspired multifunctional composites and for optimized armours

Figure S5 from Multilayer stag beetle elytra perform better under external loading via non-symmetric bending properties

FEM images showing the von-Mises stress distribution (unit of measure GPa) in the wing and the beetle body under a concentrated load of 0.5 N .A) real structure with void, B) elytra with no void

Figure S4 from Multilayer stag beetle elytra perform better under external loading via non-symmetric bending properties

Comparison of bending FEM curves obtained with three different set of interface properties (τ_lim = 1/2 σ_lim) and the experimental curves. The results suggest optimal interface strength (τ_lim = 5.5 MPa) in the elytra

FESEM characterization of the silk stalk at different magnifications.

<p>FESEM characterization of the silk stalk at different magnifications.</p

FESEM characterization of the stalk cut with FIB: (a, b, c) at an eye angle of 52°, (d) from the top.

<p>FESEM characterization of the stalk cut with FIB: (a, b, c) at an eye angle of 52°, (d) from the top.</p