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Penetration of a rigid circular needle into soft target solids is studied combining closed-form solution based on linear elastic fracture mechanics, FEM simulations and experiments. The results provide a manageable tool to assess safety of soft materials against puncturing.

Auxetics are materials characterized by a negative Poisson’s ratio (NPR), an uncommon mechanical behavior corresponding to a transversal deformation tendency opposite to the traditional materials. Here we present the first example of a 3D synthetic molecular auxetic polymer, obtained by embedding a conformationally expandable cavitand as crosslinker into a rigid polymer of intrinsic microporosity (PIM). The rigidity and microporosity of the polymeric matrix are pivotal to maximize the expansion effect of the cavitand that, under mechanical stress, can assume two different conformations: a compact vase one and an extended kite form. The auxetic behavior and the corresponding NPR of the proposed material is predicted by a specific micromechanical model that considers the cavitand volume expansion ratio, the fraction of the cavitand crosslinker in the polymer, and the mechanical characteristics of the polymer backbone. The reversible auxetic behavior of the material is experimentally verified via Digital Image Correlation technique (DIC) performed during the mechanical tests on films obtained by blending the auxetic crosslinked polymer with pristine PIM. Two specific control experiments prove that the mechanically driven conformational expansion of the cavitand crosslinker is the sole responsible of the observed NPR of the polymer.

Liquid crystalline elastomers (LCEs) represent a promising class of responsive polymers whose physical properties are peculiar to both fluids and solids. Thanks to their microscale structure made of elongated rigid molecules (mesogens)—characterized by their capability to reversibly switch from an isotropic to an ordered state—LCEs exhibit a number of remarkable physical effects, such as self-deformation and mechanical actuation triggered by external stimuli. Efficient and physics-based modelling, aimed at designing and optimizing LCE-based devices (such as artificial muscles, deployable structures, soft actuators, etc.), is a fundamental tool to quantitatively describe their mechanical behaviour in real applications. In the present study, we illustrate the multi-physics modelling of light-driven deformation of LCEs, based on the photo-thermal energy conversion. The role played by the light diffusion and heat transfer within the medium is considered and their effect on the obtainable actuation is studied through numerical simulations based on the multi-physics theory developed.

Photopolymerization is an advanced technology to trigger free radical polymerization in a liquid monomer solution through light-induced curing, during which mechanical properties of the material are significantly transformed. Widely used in additive manufacturing, parts fabricated with this technique display precisions up to the nanoscale; however, the performance of final components is not only affected by the raw material but also by the specific setup employed during the printing process. In this paper, we develop a multiphysics model to predict the mechanical properties of the photo-cured components, by taking into account the process parameters involved in the considered additive manufacturing technology. In the approach proposed, the main chemical, physical, and mechanical aspects of photopolymerization are modelled and implemented in a finite element framework. Specifically, the kinetics of light diffusion from a moving source and chain formation in the liquid monomer is coupled to a statistical approach to describe the mechanical properties as a function of the degree of cure. Several parametric examples are provided, in order to quantify the effects of the printing settings on the spatial distribution of the final properties in the component. The proposed approach provides a tool to predict the mechanical features of additively manufactured parts, which designers can adopt to optimize the desired characteristics of the products.

Nowadays, hydrogeological instability is a very critical issue because of its impact on population, infrastructures and economic and productive sectors. This makes essential to use advanced and reliable defense technologies, which are able to guarantee high performance and reliability. Flexible and permeable structures are ideal for stopping natural phenomena like debris flow, thanks to their high deformation capacity and their water permeability. This study presents some results obtained from laboratory tests related to the impact of a simulated debris flow against a scaled physical model of the barrier. A granular flow composed of aggregates of known size particle was released in a channel with variable inclination and known length and height. Using this experimental setup, several tests were carried out by varying the inclination of the channel and the geometry of the barrier. The results obtained were correlated with data deriving from a simplified analytical model; the comparison between the measured and calculated values made possible to assess the good prediction capability of the model, providing a simple and innovative tool to design and assess the safety of deformable protection barriers.

Stimulus responsive elastomers are advanced engineered materials that perform desired functionalities when triggered by external stimuli. Liquid crystal elastomers (LCEs) are one important example that exhibit reversible actuation when cycled above and below their nematic-to-isotropic transition temperature. Here, we propose a micromechanical-based model that is centered on the evolution of the chain distribution tensor of the LCE network. Our model, framed within the statistical model of the chain network, enables a mesoscale description of their mechanical response under an external thermal stimulus. We compare the model to prior experimental observations of the bending response of 3D printed LCE elements with controlled director alignment.

Curved glazed facades of buildings are often realized by cold bending of flat plates. This paper is devoted to experimental tests under static loading on the geometrically non-linear anticlastic bending of aluminium plates, whose constituent material is used as a phantom material to mimic the elastic mechanical behaviour of glass. The 3D displacement field of the plates is reconstructed through the use of the DIC (Digital Image Correlation) technique and several numerical FE analyses are performed to simulate the experimental results. A critical value, corresponding to a configuration of the plate where a change in its curvature sign occurs, of the applied displacement at the plate corner is determined. The results are discussed in terms of critical applied displacement against the plate thickness for different plate sizes. It is shown that the critical displacements are almost independent on the plate size, but linearly depend on the plate thickness.

In cutting soft elastic materials, friction is often the most relevant term of the total applied force, and techniques to minimise the required effort involve the restraint of frictional dissipation. It is well known from practical experience that cutting is made much easier if performed with a combination of slicing and pushing. A slice-push effect, known to reduce the cutting force, can be introduced by skewing the blade with respect to the travelling direction of the blade itself. The observed drop of the required force is connected to the competing dissipative contributions, with frictional dissipation being reduced at larger inclination angles. This study reports the results of several cutting tests on soft elastomeric plates, in which we have recorded the experimental force-displacement curves during the insertion of sharp stainless-steel blades. An energy-based model is employed to discern the different contributions to the measured force in the various stages of the cutting process, with particular focus on the steady state initiated after full penetration of the blade. The effects of the inclination angle of the blade are discussed with respect to the steady state force obtained from the experiments.

Active structural systems and materials, typically used to develop sensors or actuators, are those capable of responding to external stimuli with some physical detectable reactions. The triggering stimuli can be of various nature, ranging from temperature, pH, light, mechanical stress, etc. In this context, responsive materials have the capability to react at the molecular level, showing some changes in their microstructure that can be detected and measured at the meso- or macro-scale level. This ability can be obtained in polymers and polymer-like materials through the introduction in their network of switchable molecules, characterized by two geometrically distinct stable states, where the switch from one to the other can be seen as an instability phenomenon. In this research, we present a continuum mechanical model, developed starting from the micromechanics of the polymer network joined to molecules whose switching instability is induced by mechanical or chemical actions. The theoretical framework is presented by considering the general case of poly-disperse polymers and some final examples are given and discussed. The proposed model can be used as a tool for the development and design of smart responsive systems, applicable across a wide range of length scales.

Highly deformable materials (elastomers, gels, biological tissues, etc.) are ubiquitous in nature as well as in technology. The understanding of their flaw sensitivity is crucial to ensure a desired safety level. Fracture failure in soft materials usually occurs after the development of an uncommon crack path because of the non-classical near-tip stress field and the viscous effects. In a neo-Hookean material, the true opening stress singularity along the crack path (evaluated normal to the crack line) is of the order , while it is of the order ahead of the crack tip, promoting the appearance of a crack tip splitting leading to a tortuous crack. In the present paper, experimental tests concerning the fracture behavior of highly deformable thin sheets under tension are discussed, and the observed crack paths are interpreted according to the crack tip stress field arising for large deformations. The study reveals that higher strain rates facilitate the development of a simple Mode I crack path, while lower strain rates induce a mixed Mode in the first crack propagation stage, leading to the formation of new crack tips. The above described behavior seems to not be affected by the initial crack size.

The paper presents the results of experimental fatigue tests performed on welded S355 specimens subjected to combined bending and torsion loading. In order to analyse how the fillet joints shape and the load ratio affect the crack growth, we selected two kinds of fillet shape: concave and convex, and two load ratios, namely R = -1, 0. Rectangular specimens with stress concentrators in the form of the external two-sided blunt notches and fillet welded joint were tested. The test results were compared to experiments conducted on solid specimens without welds.

The description of a problem related to an evolving interface or a strong discontinuity requires to solve partial differential equations on a moving domain, whose evolution is unknown. Standard computational methods tackle this class of problems by adapting the discretized domain to the evolving interface, and that creates severe difficulties especially when the interface undergoes topological changes. The problem becomes even more awkward when the involved domain changes such as in mechanical problems characterized by large deformations. In this context, the phase-field approach allows us to easily reformulate the problem through the use of a continuous field variable, identifying the evolving interface (i.e. the crack in fracture problems), without the need to update the domain discretization. According to the variational theory of fracture, the crack grows by following a path that ensures that the total energy of the system is always minimized. In the present paper, we take advantage of such an approach for the description of fracture in highly deformable materials, such as the so-called elastomers. Starting from a statistical physics-based micromechanical model which employs the distribution function of the polymer’s chains, we develop herein a phase-field approach to study the fracture occurring in this class of materials undergoing large deformations. Such a phase-field approach is finally applied to the solution of crack problems in elastomers.

The paper presents a procedure of the determination of the fatigue energy characteristic diagram by using a controlled strain energy parameter which can be an alternative to the well-known stress and strain fatigue curves description of structural materials. The work contains the results of fatigue tests carried out in accordance with the procedure shown in the paper. Obtained test results were presented on diagrams and critically discussed.

Abstract Additive manufacturing (AM) is a broad definition of various techniques to produce layer-by-layer objects made of different materials. In this paper, a comprehensive review of laser-based technologies for polymers, including powder bed fusion processes [e.g. selective laser sintering (SLS)] and vat photopolymerisation [e.g. stereolithography (SLA)], is presented, where both the techniques employ a laser source to either melt or cure a raw polymeric material. The aim of the review is twofold: (1) to present the principal theoretical models adopted in the literature to simulate the complex physical phenomena involved in the transformation of the raw material into AM objects and (2) to discuss the influence of process parameters on the physical final properties of the printed objects and in turn on their mechanical performance. The models being presented simulate: the thermal problem along with the thermally activated bonding through sintering of the polymeric powder in SLS; the binding induced by the curing mechanisms of light-induced polymerisation of the liquid material in SLA. Key physical variables in AM objects, such as porosity and degree of cure in SLS and SLA respectively, are discussed in relation to the manufacturing process parameters, as well as to the mechanical resistance and deformability of the objects themselves. Graphic abstract

Responsive materials, often obtained by designing the molecular structure of polymers or gels, are able to respond with detectable physical changes to external stimuli of various nature, ranging from chemical (such as pH), temperature, light radiation, magnetic field, mechanical stress, etc. In this paper we propose a micromechanical model, rooted in the statistical approach to the network conformation of polymeric materials, to predict the mechanical response of polymers with embedded responsive molecules. The model makes use of the so-called chains distribution function, aimed at providing the current state of the network’s chains. A univocal relation between the distribution function and the mechanical state of the material is established, so the knowledge of the evolution of such a function with the applied deformation or other external stimuli allows to get the macroscopic response of the material. Finally, the case of responsive molecules inserted into the network as crosslinkers is considered. The responsiveness of the molecules is assumed to depend either on the mechanical and/or chemical stimuli coming from the external environment. The cases involving molecules sensible to chemical stimuli, always imply the presence of a solvent carrying the triggering chemical agent, and thus require to consider the swelling phenomenon induced by the fluid absorbed by the polymer network. The theoretical framework of the micromechanical model is illustrated and some examples are finally presented and discussed.

An experimental campaign has been carried out with the aim of providing an insight into the fracture processes occurring during the cutting of different types of polymers, with features ranging from typically brittle to soft hyperelastic behaviour. The steady state of cutting is investigated using a sharp thin blade, and tracking the insertion force versus the penetration displacement. For soft, highly-deformable polymers, the influence of large deformations at the crack tip is also taken into account, through full-field finite strain maps obtained by means of digital image correlation. In brittle polymers, the influence of the cutting tool sharpness is discussed with respect to the onset of crack propagation, through a comparison with a simplified analytical model, and numerical finite element analyses. The results suggest that the propagation of the cut clearly depends on the tool sharpness, and for a class of brittle polymers it appears that this may happen as a stable fracture process, with the distance between the blade and the crack tip remaining constant during propagation. On the contrary, soft polymers appear to be much less sensible to the tool profile, and it is the large deformation that ultimately determines the fracture behaviour when the crack tip is reached by the blade.

The macroscopic mechanical response of polymers can be traced down to the microscale physics of the network by using a statistical approach for the description of the configuration state of the polymer chains. In this paper we present a micromechanical model to capture the macroscopic behavior of polymers by tracking the evolution of a distribution function describing chain configurations, more specifically the statistics of the end-to-end distance on the network chains. Damage, manifested in the softening and hysteresis under cyclic loading, is accounted for through the scission of chains, whose occurrence is evaluated on the basis of the probability of failure, also settled in the configuration space. The proposed micromechanical model can easily accommodate also the mechanics of dynamic network with reversible cross-links, thereby providing a general and physics-based approach to the study of polymers and polymer-like materials.

While pH-driven interconversion of tetraquinoxaline cavitands (QxCav) from vase to kite conformation has been extensively studied both in solution and at interfaces, cavitands behavior in solid matrices is still unexplored. Therefore, the synthesis of a new class of quinoxaline cavitand based copolymers is here reported; a soluble linear poly(butyl methacrylate) (PBMA) and an insoluble cross-linked polydimethylsiloxane (PDMS), ensuring a convenient incorporation of the switchable unit, were chosen as polymer matrices. Conformational studies, performed both in solution and at the solid state, confirmed the retention of vase → kite switching behavior when moving from monomeric units to polymeric structures.

Electroactive polymers with time-dependent behavior are considered in the present paper by way of a new physics-based micromechanical model; such viscoelastic response is described by the internal evolution of the polymer network, providing a new viewpoint on the stress relaxation occurring in elastomers. The main peculiarity of such internally rearranging materials is their capacity to locally reset their reference stress-free state, leading to a mechanical behavior that relaxes out (eases off) an induced stress state and that can thus be assimilated to a sort of internal self-healing process. Such high deformability and recoverability displayed by dynamically cross-linked polymers can be conveniently exploited when they are coupled in electromechanical problems; the deformation induced by an electric field can be easily tuned by the intensity of the electric field itself and the obtained shape can be maintained without any electric influence once the material microstructure has rearranged after a sufficient curing time. In the present paper, both features of the polymeric material, that is, internal remodeling and electromechanical coupled response, are considered and a theoretical framework is established to simulate representative boundary value problems.

Active materials are those capable of giving some physical reaction under external stimuli coming from the environment such as temperature, pH, light, mechanical stress, etc. Reactive polymeric materials can be obtained through the introduction of switchable molecules in their network, i.e. molecules having two distinct stable conformations: if properly linked to the hosting polymer chains, the switching from one state to the other can promote a mechanical reaction of the material, detectable at the macroscale, and thus enables us to tune the response according to a desired functionality. In the present paper, the main aspects of the mechanical behavior of polymeric materials with embedded switchable molecules—properly linked to the polymer's chains—are presented and discussed. Starting from the micro mechanisms occurring in such active material, a continuum model is developed, providing a straightforward implementation in computational approaches. Finally, some experimental outcomes related to a switchable molecules (known as quinoxaline cavitands) added to an elastomeric PDMS under chemical stimuli, are presented and quantitatively discussed through the use of the developed mechanical framework.

In the present paper, an experimental campaign is carried out with reference to the steady state propagation of an existing cut in polymeric plates, ranging from glassy to soft polymers. The steady state propagation is investigated by considering a commercial cutting tool under different insertion velocities of the blade. Full-field finite strain maps are experimentally recorded by means of digital image correlation technique, along with the recording of the insertion force vs displacement curve. It is shown that the cutting resistance is dependent on the fracture toughness of the target material and on the sharpness of the cutting tool. Different scenarios of steady state cut propagation are observed if either a relatively blunt or a relatively sharp blade penetrates in the material. Alternative blade sharpness parameters can be used to discriminate the different conditions of cut propagation observed in the experiments. A theoretical interpretation of the experimental outcomes is provided. (Less)

The safety level in advanced load bearing applications can be enhanced if the material would be able to detect the in-service deformation, allowing a real time evaluation of the reliability state of the components. Polymeric materials can be used to get such a functionality through the insertion of so-called mechanophore units, whose main property is to chemically respond to mechanical stimuli. In the present paper, a micromechanical approach is developed to model the response of polymers containing reporting units, whose activation is triggered by the deformation of the underneath network or by a chemical stimulus. The model, through an Arrhenius-like equilibrium reaction law, provides a quantitative evaluation of the fraction of stress-activated molecules. Moreover, if the mechanophore activation involves also a change in their geometrical conformation, it influences the network deformation and the corresponding mechanical effects must be also accounted for. The formulated micromechanical model is presented and implemented in a FE code in order to simulate structural elements made of a self-diagnostic material. In particular, we consider the fluorescence-based strain detection of pre-cracked elements made of polymers with supramolecular complexes cross-linked to the polymer’s chains; the fluorescence intensity is assumed to be proportional to the volume fraction of the activated units, thus enabling to quantify the associated material’s strain value.

Liquid crystal elastomers (LCEs) exhibit some remarkable physical properties, such as the reversible large mechanical deformation induced by proper environmental stimuli of different nature, such as the thermal stimulus, allowing their use as soft actuators. The unique features displayed by LCE are originated from their anisotropic microstructure characterized by the preferential orientation of the mesogen molecules embedded in the polymer network. An open issue in the design of LCEs is how to control their actuation effectiveness: the amount of mesogens molecules, how they are linked to the network, the nematic order degree, the cross-link density are some controllable parameters whose spatial distribution, in general, cannot be tuned except for the last one. In this paper, we develop a theoretical micromechanical-based framework to model and explore the effect of the network cross-link density on the mechanical actuation of LCE elements. In this context, the light-induced polymerization (photopolymerization) for obtaining the elastomers’ cross-linked network is of particular interest, being suitable for precisely tuning the cross-link density distribution within the material. This technology enables to obtain a molecular-scale architected LCEs, allowing the optimal design of the obtainable actuation. The possibility to properly set the cross-link density arrangement within the smart structural element (LCE microstructure design and optimization), represents an intriguing way to create molecular-scale engineered LCE elements having a material microstructure encoding the desired actuation capabilities.

The photopolymerization process used for the production of additively manufactured polymers employed in advanced applications, enables obtaining objects spanning a large dimensional scale thanks to the molecular size achievable by the solidification process. In fact, the photopolymerization is based on the physical-chemical network cross-linking mechanism taking place at the nanoscale. Since the starting raw material is a liquid resin that progressively becomes solid upon the irradiation by a suitable light source, the mechanical properties – and so the corresponding mechanical response of the final printed structural material – heavily depend on the degree and distribution of the polymerization induced in the material itself. In the present study, starting from the governing equations of the light-induced polymerization process, we determine the chain density formed within the solid domain. Then, the mechanical response of photopolymerized elements obtained with different photopolymerization parameters is investigated. Moreover, the microstructure optimization of polymeric elements in relation to the achievement of the desired mechanical response with the least energy spent in the polymer's formation, is studied. Finally, some interesting considerations related to the modeling of the photopolymerization process are outlined.

Highly deformable materials, such as elastomers and gels, can withstand very large deformation without failure, and this response is usually insensitive to the presence of macroscopic defects. These polymer-based materials, different from the traditional ones which are usually characterized by an enthalpic elasticity, show a mechanical response which is governed by the state of internal entropy of their molecular network. If fracture energy is large, the noticeable ability of soft materials to rearrange their network at the microscale, to display large deformation and to dissipate energy thanks to their viscoelasticity, allows the minimization of the local detrimental effect of existing flaws. In the present paper, the mechanical behavior of silicone-based edge cracked plates with different crack sizes and severity of the intrinsic flaws embedded in the material is examined by taking into account the time-dependent effects. Experimental and theoretical aspects are discussed to explain the defect tolerance of such materials. The detrimental effect of intrinsic voids is quantified, and the beneficial effect due to strain at low rates is analysed. The critical distance is related to the ultimate stretch value, the quality of the material, and the crack size.

Elastomeric polymers usually show a very low elastic modulus entailing a soft behaviour and a very high deformation capability. This macroscopic behaviour is determined by their microstructure which is characterized by a complex and entangled network of very long linear chains jointed together in some points called cross-links. Because of such a peculiar microstructure, the mechanical response (often time-dependent) of elastomeric polymers to external loads or deformations cannot be described by the classical theories developed for standard materials – such as the ones whose response depends on their crystalline structure (e.g. metal, ceramics, etc.) – since such polymers usually neglect entropic-related effects that are fundamental in highly deformable amorphous materials. In the present paper, the response of elastomeric plates containing a central crack under a tensile strain applied at various rates is experimentally analyzed giving particular emphasis on the observations of the full-field strain maps determined by means of some digital image correlation techniques. Some relaxation tests are performed, and the defect sensitivity of the material is discussed in relation to the applied deformation rate.

We present a physics-based theoretical framework to describe the transient mechanical response of polymers undergoing finite deformation. For this, a statistical description of the polymer network is provided by a distribution function that is allowed to evolve in time due to a combination of deformation and chain reconfiguration enabled by transient cross-links. After presenting the evolution law for the chain distribution function, we show that, using classical thermodynamics, one can determine how the entropy, elastic energy and true stress evolve in terms of the network configuration. In particular, we introduce the concept of distribution tensor, which enables a clean transition between the network statistics, its continuum representation and the macroscopic polymer response. In the context of Gaussian statistics, it is further shown that this tensor follows its own evolution law, enabling a simple handling of visco-elastic rubbers. The model degenerates to classical rubber elasticity when cross-links are permanent, while the case of viscous fluids is recovered for fast cross-link kinetics. The generality of the framework as well as its relevance to modeling a number of important dissipative processes occurring in polymers using a continuum approach are also discussed.

Elastomers display a mechanical behavior that is, both in the elastic as well as at the incipient failure, quite different from that of traditional materials. Their mechanical characteristics makes them attractive to a myriad of applications ranging from rubber, optical lenses to tissue engineering scaffolds. Their study is therefore fundamental for understanding and controlling their mechanical response, especially when it involves large deformation, viscous effects and damage nucleation around defects. In the present paper we consider the mechanical response up to final failure, of pre-cracked silicone sheets under different strain rates. A simple statistically-based theoretical model, combined with a failure criterion, is formulated to describe the observed complex mechanical response. The model is further implemented in a finite element model to provide comparison of the damage nucleation predicted by the model and those obtained from experimental tests.

The capability of materials to bear loads even in presence of defects like cracks, notches or generic geometric discontinuities is usually indicated as flaw tolerance, and is crucial in modern safety design of structural components. Such a tolerance capability can be remarkable in highly deformable materials (also called soft materials), usually much more pronounced than in conventional ones. The ability of highly deformable materials to undergo very large deformations before failure is mainly due to their noticeable rearrangement of the molecular network with a significant decrease of the internal entropic state. Neglecting such an entropic effect can lead to erroneous underestimations of the safety level against defect-driven failure. In the present research, the mechanics of highly deformable materials is discussed by examining silicone-based notched and cracked plates. Experimental, numerical and theoretical aspects of the involved phenomena are analyzed in order to provide an explanation of the mechanism of defect resistance in such a class of materials from a physics-based point-of-view.

The description of a problem involving the existence of an interface or of a strong discontinuity requires to solve partial differential equations on a moving domain, whose evolution is also unknown, leading to severe difficulties, especially when the interface undergoes topological changes. The solution becomes even more complex when the whole problem domain changes, such as in mechanical problems involving large deformations. In this context, the phase-field approach allows to easily reformulate the problem through the use of a continuous field variable mimicking the real physical discontinuity. In the present paper we take advantage of such an approach for the description of damage and failure of highly deformable strain rate-dependent materials, such as the elastomeric ones. By harnessing a statistical physics-based micromechanical model of the polymers chain network characterized by the capability to reorganize the distribution of its chain lengths in time, the behavior of a rate-dependent polymer can be simulated. The adopted physics-based approach, upscaled at the continuum level and combined with a phase-field approach, allows us to describe the damage and fracture occurring in this class of materials in the large deformations regime. Some examples are provided to demonstrate the reliability of the proposed model.

The safety assessment of short-fibre-reinforced (SFR) composites, commonly used in structural applications involving repeated loads, requires to evaluate the degrading phenomena taking place in the matrix and at the fibre–matrix interface. The mechanical behaviour under both static and cyclic loading can be simulated applying damage degradation to the matrix mechanical characteristics, and employing fracture mechanics concepts to examine the fibre–matrix detachment as a 3D growing crack with degrading interface properties. In the present paper, a micromechanical model for unidirectional or random SFR materials under fatigue is developed. Some applications related to SFR polymeric composites found in the literature are presented.

Defect tolerance is usually understood as the ability of a material to withstand an external load in the presence of a geometrical flaw. The case of a defect represented by a notch (i.e. a geometric discontinuity with finite curvature radius) can be described by the so-called stress (strain) concentration factor at the notch root and by the stress (strain) gradient in the vicinity of the notch root which is a preferential site for crack nucleation and propagation. Under static loads and within the elastic regime, notch effect in traditional structural materials is simply governed by the initial notch geometry. On the other hand, in highly deformable materials, such as soft matters (biological tissues, colloids, polymers, gels, foams, etc.), notch effect must be evaluated by considering large strain values arising around the notch, responsible for its blunting. In addition, when notches are contained in non-confined plate-like components, a sort of augmented notch blunting might occur as a consequence of local flexural instability of the material plate in the compressed zones. In the present paper, an experimental and theoretical study is discussed for a silicon sheet with different levels of notch severity. It is shown as the safety against notch concentration effect (that can reduce up to about 40–70%) can be greater than that in low deformable materials, and so notch blunting and plate's localized instability are beneficial contributions, leading to an increase of the element’s tensile strength.