On the determination of constitutive parametersin a hyperelastic model for a soft tissue

The aim of this paper is to study a model of hyperelastic materials and itsapplications into soft tissue mechanics. In particular, we first determine an unbounded domain of the constitutive parameters of the model making our smoothstrain energy function to be polyconvex and hence satisfying the Legendre–Hadamard condition. Thus, physically reasonable material behaviour are described by our model with these parameters and a plently of tissues can betreated. Furthermore, we localize bounded subsets of constitutive parameters in fixed physical and very general bounds and then introduce a family of descrete stress–strain curves. Whence, various classes of tissues are characterized. Ourgeneral approach is based on a detailed analytical study of the first Piola–Kirchhoff stress tensor through its dependence on the invariants and on the constitutive parameters. The uniqueness of parameters for one tissue is discussed by introducing the notion of manifold of constitutive parameters, whichis locally represented by possibly different physical quantities. The advantage of our study is that we show a possible way to improve of the usual approachesshown in the literature which are mainly based on the minimization of a costfunction as the difference between experimental and model results

marker tracking for local strain measurement in mechanical testing of biomedical materials

Local strain measurement is one of the key aspects in tensile tests of biomedical materials and biological tissues, especially if aimed at developing appropriate constitutive formulations to describe mechanical behavior. The measurement of strain as the ratio between the current and the initial length of the sample can be coupled with markers recognition via non-contact video extensometer for characterizing the local mechanical behavior. A crucial point in video extensometer measurement is the selection of the most appropriate markers and technique of their application on the sample surface. This work promotes understanding the effect of markers on material mechanical response. Different solutions were taken into account, as paint markers, namely a commercial lacquer and an acrylic paint, or physical markers attached with the use of adhesives, i.e. cyanoacrylate or medical spray band. Tensile tests revealed that markers can modify the mechanical response of the tested materials, inducing a local stiffening of the samples. The use of cyanoacrylate, as marker adhesive, affects not only the local but also the overall mechanical response, at least for the sample size considered in this work. These effects are more pronounced with higher material compliance. Based on these results, caution is recommended with the use of cyanoacrylate for attaching markers on biomedical polymers

Dental biomechanics / edited by Arturo N. Natali.

Includes bibliographical references and index.xvii, 271 pages

REALIZZAZIONE DI COMPONENTI PER IMPLANTOLOGIA DENTALE

Nell\u2019ambito dell\u2019implantologia dentale vengono diffusamente impiegati componenti realizzati in titanio. Il presente articolo illustra lo studio, realizzato mediante la simulazione numerica del processo, della produzione di barre in titanio per l\u2019accoppiamento di impianti endossei. Dette componenti protesiche vengono realizzate utilizzando processi di colata, con dispositivi e macchine di concezione innovativa. L\u2019impiego delle tecniche di analisi numerica, sia per la simulazione del processo produttivo che per lo studio del comportamento biomeccanico, risulta estremamente vantaggioso in termini tecnologici e operativi, costituendo un efficace strumento di conoscenza. L\u2019analisi numerica conduce infatti ad un miglioramento degli standard qualitativi di questa tipologia di componenti, rendendoli adeguati al delicato impiego per il quale sono concepiti, in considerazione anche delle specifiche esigenze cliniche

NUMERICAL ANALYSIS OF TITANIUM CAST DEVICES FOR DENTAL IMPLANTOLOGY

The present work pertains to a numerical investigation of the casting process of titanium devices adopted for dental implantology. The analysis of the titanium framework that connects different abutments, in a multi-implant configuration, is performed evaluating the characteristics of the material that depend on the manufacturing procedure. The connecting bar is obtained by a foundry process that is controlled through a numerical simulation by using a control volume technique. This analysis leads to the possibility to have detailed information on the process and control of the quality of the microstructure of the material produced that proves to be highly beneficial for defining mechanical properties. On the basis of the results obtained, a subsequent stress analysis can be performed, addressed to highlight critical conditions. Functional response of the whole bar-implant framework is studied by means of a numerical model, based on the geometric element method. This technique is particularly suited for describing complex morphology of the implant site. The present approach addresses a higher quality definition of the reliability of the device used in dental practice and represents a valuable tool in assisting optimisation procedures pertaining to manufacturing. In fact, the improvement of titanium devices is intended not only with regard to their mechanical performances, but also to requirements pertaining to manufacturing and clinical practice