1,720,981 research outputs found
A predictive micromechanically-based model for damage and permanent deformations in copolymer sutures
No full textAn effective description of the mechanical behavior of biodegradable copolymers suture threads requires the analysis of their response under cyclic loading and the prediction of the fundamental damage and residual stretches effects. In this paper we propose a micromechanically-based model adopting a new form of Worm Like Chain free energy for the copolymer chains, which takes care of the insurgence of residual stretches on the basis of a rigorous statistical mechanics result. Under the affinity hypothesis we subsequently derive the macroscopic response of the material. The obtained model has a clear physical interpretation and depends on a small number of parameters, which can be fitted by a simple uniaxial test. The effectiveness of the theoretical results has then been verified by performing cyclic tests on Monocryl® monofilament sutures and showing the ability of the model in predicting with high accuracy the history dependence, the damage and permanent deformations in the obtained response
Tunable shear stiffness in a metamaterial sheet
No full textIn this paper a metamaterial sheet constituted by a periodic pattern of square tensegrity cells (T-bar) subjected to a uniform equibiaxial pressure is studied. In particular, a minimal mass lattice is analytical determined by imposing stability and material failure conditions. Interestingly, the shear stiffness of this optimized lattice is very small in comparison to the other moduli and exhibits a linear dependence on the applied load. This behavior suggests the interesting possibility of tailoring new materials with force tunable shear modulus
Damage, Self-Healing, and Hysteresis in Spider Silks
No full textAbstractIn this article, we propose a microstructure-based continuum model to describe the material behavior of spider silks. We suppose that the material is composed of a soft fraction with entropic elasticity and a hard, damageable fraction. The hard fraction models the presence of stiffer, crystal-rich, oriented regions and accounts for the effect of softening induced by the breaking of hydrogen bonds. To describe the observed presence of crystals with different size, composition, and orientation, this hard fraction is modeled as a distribution of materials with variable properties. The soft fraction describes the remaining regions of amorphous material and is here modeled as a wormlike chain. During stretching, we consider the effect of bond-breaking as a transition from the hard- to the soft-material phase. As we demonstrate, a crucial effect of bond-breaking that accompanies the softening of the material is an increase in contour length associated with chains unraveling. The model describes also the self-healing properties of the material by assuming partial bond reconnection upon unloading. Despite its simplicity, the proposed mechanical system reproduces the main experimental effects observed in cyclic loading of spider silks. Moreover, our approach is amenable to two- or three-dimensional extensions and may prove to be a useful tool in the field of microstructure optimization for bioinspired materials
Multiscale innovative materials and structures (MIMS)
No full text: Increasing attention is growing towards advanced multiscale metamaterials and nanostructures, due to recent developments in nanoscience and nanotechnology [...]
Damage, self-healing and hysterisis in spider silk
No full textIn this article, we propose a microstructure-based continuum model to describe the material behavior of spider silks. We suppose that the material is composed of a soft fraction with entropic elasticity and a hard, damageable fraction. The hard fraction models the presence of stiffer, crystal-rich, oriented regions and accounts for the effect of softening induced by the breaking of hydrogen bonds. To describe the observed presence of crystals with different size, composition, and orientation, this hard fraction is modeled as a distribution of materials with variable properties. The soft fraction describes the remaining regions of amorphous material and is here modeled as a wormlike chain. During stretching, we consider the effect of bond-breaking as a transition from the hard- to the soft-material phase. As we demonstrate, a crucial effect of bond-breaking that accompanies the softening of the material is an increase in contour length associated with chains unraveling. The model describes also the self-healing properties of the material by assuming partial bond reconnection upon unloading. Despite its simplicity, the proposed mechanical system reproduces the main experimental effects observed in cyclic loading of spider silks. Moreover, our approach is amenable to two- or three-dimensional extensions and may prove to be a useful tool in the field of microstructure optimization for bioinspired materials
Residential housing at beginning of XX century: Study of material, technological and structural features for its conservation
No full textThe research faces the study of the specificity of material, technological and structural features of residential housing of first decades of XX century referring to mixed structure buildings, whose particularity is determined by progressive combined use of "modern" elements and materials with "traditional" techniques and construction technologies.
It is a "new" building typology, whose experimental and innovative attitude has produced, in the time and in the continuity of its use, a series of specific problems connected with its conservation.
The study, getting started from social-economical and historical-cultural themes which determined development of new technologies, underlines the process of material-technical-technological-structural evolution generated by gradual introduction of new materials and substitution in a first time of single elements of building, then of entire parts and finally of the entire masonry box.
In this way the research examines constructive conception of mixed structure building, its progressive transformation and typological-technological-structural features of single elements and/or subsystems, highlighting potential "points of crisis" which characterize decay processes specific of define construction "type".
Such organised knowledge represents first stage of a vaster study aimed to determine physical, technical-technological and codes related decay processes and to define criteria for maintenance, conservation and codes complying of this building heritage
Morphological optimization of tensegrity-type metamaterials
Get PDFWe analyze the problem of mass and morphological optimization for metamaterials with tensegrity-type cells. Our approach is based on both local and global instability analyses. As a meaningful prototypical example we tassellate a compressed slab into periodic patterns of triangular, square and hexagonal cells
- …
