1,720,980 research outputs found
Biomechanical analysis of the ligaments of the hindfoot: constitutive formulation and parameters identification for numerical modelling
No full textThe biomechanical behaviour of the hindfoot ligaments is investigated by means of a combined experimental and computational approach. To interpret the typical features of ligaments mechanical response, as anisotropic configuration, geometric non-linearity, non-linear elasticity and time-dependent behaviour, a specific fiber reinforced visco-hyperelastic model is provided. In order to define the constitutive parameters, analytical and numerical models that interpret tensile tests are defined. Model and experimental results are compared by a cost function, whose minimization leads to the optimal set of parameters. In detail the analytical method offers a preliminary set of constitutive parameters. Numerical models that consider the complex histo-morphometric configuration of samples are defined and numerical analyses that interpret the experimental conditions are performed. The analyses assume several sets of constitutive parameters, which are estimated starting from the preliminary set. The minimization of the discrepancy between numerical and experimental results entails the definition of a reliable set of parameters. Once constitutive parameters are evaluated, the biomechanical behaviour of the ligaments of the hindfoot is evaluated in several physiological conditions such as dorsiflexion, plantarflexion and inversion of the foot. This work offers the possibility to interpret and analyse the ankle joint trauma such as the ligaments rupture.Lo studio del comportamento biomeccanico dei legamenti del retro piede ha richiesto un approccio fortemente integrato di tipo computazionale e sperimentale. Al fine di analizzare aspetti tipici della risposta meccanica dei legamenti, come la non linearità per geometria e materiale, la configurazione anisotropa e la dipendenza dal tempo è stato utilizzato un modello visco-iperelastico fibro-rinforzato. La valutazione dei parametri costitutivi ha richiesto lo sviluppo di modelli analitici e numerici capaci di interpretare prove di trazione monoassiale, eseguite su campioni costituiti dal legamento e dalla coppia di ossa congiungenti il legamento stesso. I risultati di modello ed i risultati sperimentali sono stati confrontati attraverso una funzione costo, la cui minimizzazione ha portato alla definizione dei parametri oggetto dello studio. In dettaglio, attraverso l’utilizzo di un modello analitico, è stato possibile definire per ciascun legamento un primo set di parametri. Al fine di interpretare correttamente le reali caratteristiche isto-morfometriche dei tessuti, sono stati sviluppati modelli numerici rappresentativi i campioni sperimentali. Le analisi numeriche sono state eseguite per differenti sets di parametri costitutivi definiti a partire dal set preliminare. La minimizzazione delle discrepanza tra i risultati di modello numerico ed i risultati sperimentali ha condotto alla definizione dei parametri ottimali. Una volta definiti i parametri costitutivi di ciascun legamento, si è andati a studiare il loro comportamento biomeccanico in differenti condizioni fisiologiche: dorsiflessione, plantar-flessione ed inversione del piede. Il lavoro presentato fornisce le basi per la valutazione della funzionalità biomeccanica del retro piede in seguito alla rottura dei legamenti della caviglia
Biomechanical behaviour of ankle ligaments: constitutive formulation and numerical modelling
No full textThe present work is aimed at the definition of a constitutive formulation of ankle ligaments and of a procedure for the constitutive parameters evaluation, for the biomechanical analysis by means of numerical models. To interpret the typical features of ligaments mechanical response, as anisotropic configuration, geometric non-linearity, non-linear elasticity and time-dependent behaviour, a specific fibre-reinforced visco-hyperelastic model is provided. The identification of constitutive parameters is performed by a stochastic-deterministic procedure that minimizes the discrepancy between experimental and computational results. A preliminary evaluation of parameters is performed by analytical models in order to define reference values. Afterwards, solid models are developed to consider the complex histo-morphometric configuration of samples as basis for the definition of numerical models. The results obtained are adopted for upgrading parameters values by comparison with specific mechanical tests. Assuming the new parameters set, the final numerical results are compared with the overall set of experimental data, to assess the reliability and efficacy of the analysis developed for the interpretation of the mechanical response of ankle ligaments
Parameters identification in constitutive models for soft tissues mechanics
No full textIn the framework of the formulation of constitutive models for soft biological tissues an important challenge pertains to the parameters evaluation. Complex constitutive models are adopted for a phenomenological description of the biomechanical response, charac-terised by anisotropy, material non-linearity, almost-incompressibility and large strain and displacement. The present work describes a procedure for estimating the constitu-tive parameters to be adopted, by fitting predicted model results with specific experi-mental data. The approach provides an inverse analysis that uses the stress-strain history given by experimental data and attempts to estimate the parameter values that would yield the best fit for the constitutive model. This action is performed using an optimiza-tion procedure based on a specific algorithm formulated by coupling stochastic and a deterministic techniques. A solution is presented with regard to the periodontal ligament and oesophageal tissues. The reference to different soft biological tissues points out the ability of the approach to properly interpret different configurations and responses. The accuracy and completeness of experimental data influences reliability and completeness of solution. Result validation is performed by comparison of the experimental data and model results
Investigation of the biomechanical behaviour of hindfoot ligaments
No full textThe aim of this work is to provide a computational tool for the mechanical characterization of the hindfoot ligaments. The investigation is performed by a coupled numerical and experimental approach. For this purpose, a numerical model that represents the complex structural configuration of the hindfoot and the typical features of the mechanical behaviour of the ligament tissue is developed. The geometrical analysis of the anatomical site is performed starting from the processing of computed tomography and magnetic resonance images. Accounting for morphometric measurements, the virtual solid model provides an averaged configuration of the hindfoot structure. In order to specify the mechanical behaviour of the ligament tissue, a fibre-reinforced visco-hyperelastic model is adopted. The formulation accounts for the anisotropic configuration, geometric non-linearity, non-linear elasticity and time-dependent phenomena. Numerical analyses are performed to evaluate the biological tissues and structure mechanics with regard to physiological boundary conditions, accounting for dorsiflexion and plantarflexion movements. In order to evaluate the reliability of the numerical model developed, the experimental data are compared with the numerical results. The numerical results are in agreement with the range of values obtained by experimental test confirming the accuracy of the procedure adopted
Investigation of the mechanical behaviour of the foot skin
No full textBackground/purpose: The aim of this work was to provide computational tools for the characterization of the actual mechanical behaviour of foot skin, accounting for results from experimental testing and histological investigation. Such results show the typical features of skin mechanics, such as anisotropic configuration, almost incompressible behaviour, material and geometrical non linearity. The anisotropic behaviour is mainly determined by the distribution of collagen fibres along specific directions, usually identified as cleavage lines. Methods: To evaluate the biomechanical response of foot skin, a refined numerical model of the foot is developed. The overall mechanical behaviour of the skin is interpreted by a fibre-reinforced hyperelastic constitutive model and the orientation of the cleavage lines is implemented by a specific procedure. Numerical analyses that interpret typical loading conditions of the foot are performed. The influence of fibres orientation and distribution on skin mechanics is outlined also by a comparison with results using an isotropic scheme. Results: A specific constitutive formulation is provided to characterize the mechanical behaviour of foot skin. The formulation is applied within a numerical model of the foot to investigate the skin functionality during typical foot movements. Numerical analyses developed accounting for the actual anisotropic configuration of the skin show lower maximum principal stress fields than results from isotropic analyses. Conclusion: The developed computational models provide reliable tools for the investigation of foot tissues functionality. Furthermore, the comparison between numerical results from anisotropic and isotropic models shows the optimal configuration of foot skin
Investigation of the mechanical behaviour of the plantar soft tissue during gait cycle: Experimental and numerical activities
No full textThe aim of this work is to investigate the mechanical response of the plantar soft tissue from the heel strike to the midstance, developing both experimental and numerical activities. Using force plates and motion tracking system, the dynamic and kinematic data of 10 subjects are evaluated. The average kinematics data obtained from the experimental tests are assumed as boundary and loading conditions for the computational analyses. A three-dimensional virtual solid model of the foot is developed from the analysis of Digital Imaging and Communications in Medicine images from computed tomography and magnetic resonance. Constitutive formulations that interpret the mechanical response of the biological tissues are defined. Because of the major role of plantar soft tissue in the proposed analysis, a specific visco-hyperelastic constitutive formulation is provided considering the typical features of the tissue mechanics. The three-dimensional numerical model permits to evaluate the capability of the plantar soft tissue to redistribute the deformations, especially during the midstance, and to define quantitative aspects related to the energy absorption. The numerical results highlight the stress distribution from the heel strike to the midstance. The values of stress and strain reached are more intensive during the midstance, when there is a single support of the foot
Biomechanical behaviour of heel pad tissues: constitutive formulation and analysis
No full textThe peculiar structure of heel pad is considered with regard to its biomechanical function as a dumping and pressure resistant cushion. According to a honeycomb configuration, heel pad tissue is organized as dense strands of fibrous tissue, characterized by circular or cone-shaped septa. The septa bound chambers filled with fat cells. The chambers are reinforced by further transverse and diagonal fibers. The fibrous tissue strands are firmly attached to the underface of the calcaneum and extending to the subcutaneous tissues. The structural configuration of heel pad, as a network of fibrous components binding fat cells, entails the capability to withstand impacts and prolonged pressure loads.
A specific visco-hyperelastic constitutive model is developed taking into account the typical features of heel pad tissue mechanical response, as large displacements and strains, almost incompressible behavior, non linear stress-strain relationship and time-dependent effects. Preliminarily, constitutive parameters are evaluated using a comparative analysis of model results and data from in vitro mechanical tests, according to stochastic-deterministic optimisation procedures. In order to interpret the mechanical response of heel pad living tissues, which is deeply influenced by interaction and connection with surrounding tissues and structures, constitutive parameters must be updated by considering data from specific additional experimental tests. Analytical and numerical models are provided to interpret the different experimental situations. Good agreement is achieved between experimental data and model results, confirming the mechanical coherence between the proposed constitutive formulation and heel pad tissues mechanics
Analysis of heel pad tissues mechanics at the heel strike in bare and shod conditions
Get PDFA combined experimental and numerical approach is used to investigate the interaction phenomena
occurring between foot and footwear during the heel strike phase of the gait. Two force platforms are
utilised to evaluate the ground reaction forces of a subject in bare and shod walking. The reaction forces
obtained from the experimental tests are assumed as loading conditions for the numerical analyses using
three dimensional models of the heel region and of the running shoe. The heel pad region, as fat and skin
tissues, is described by visco-hyperelastic and fibre-reinforced hyperelastic formulations respectively and
bone region by a linear orthotropic formulation. Different elastomeric foams are considered with regard to
the outsole, the midsole and the insole layers. The mechanical properties are described by a hyperfoam
formulation. The evaluation of the mechanical behaviour of the heel pad tissues at the heel strike in
bare and shod conditions is performed considering different combinations of materials for midsole and
insole layers. Results allow for the definition of the influence of different material characteristics on the
mechanical response of the heel pad region, in particular showing the compressive stress differentiation
in the bare and shod conditions
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