Mechanical Characterization And Modeling Of Energy Storage Materials,magnetic Guidewires,and Dressings For Cardiac Medicine

The performance of the pacemaker’s high energy storage density material directly determines its longevity;the cardiac interventional magnetic guidewire can be controlled to move under the drive of an external magnetic field,providing efficient lesion localization for cardiac bypass,cardiomyopathy ablation and other surgical operations;high toughness,fatigue-resistant polymers provide reliable dressings for hemostasis,drug delivery,and device loading on cardiac surfaces.The above-mentioned energy storage materials,magnetic guidewires and polymer dressings for cardiac medical treatment face a series of important mechanical problems during the development process.This thesis mainly uses experimental methods,theoretical models and numerical methods to develop efficient characterization of the mechanical properties of energy storage electrode materials during cyclic charge and discharge processes,to expand the workspace of the magnetic guidewire with optimal designs,and to reveal the microstructural toughening mechanism in low-hysteresis polymer networks.Firstly,based on the substrate curvature measurement technique and the Stoney formula describing the stress-curvature relationship,a photometric platform for in-situ curvature measurement of lithium battery thin-film electrodes was independently built up,and the in-situ stress evolution characterization of thin-film electrode materials during charging and discharging was realized.Since the Stoney formula coupling the mechanochemical-elastic constitutive relation during the electrode charge and discharge process may lead to the wrong prediction that the elastic modulus of the thin-film electrode exhibits a negative value,the modified Stoney formula is developed to reasonably describe the variation of elastic modulus with lithium concentration during electrochemical cycles in pure silicon electrodes and composite sulfur electrode films.Secondly,propose a design method to the workspace of magnetic guidewires based on regulating the distribution of hard magnetic particles.The influence of the distribution of hard magnetic particles in the polymer matrix on the deflection deformation of the magnetic guidewire was studied by using the deflection deformation model of the heterogeneous magnetic guidewire,and the workspace of five commercial permanent magnet embedded magnetic guidewires was calculated.By combining the deflection deformation model of the magnetic guidewire and the genetic algorithm optimization simulation,an optimal arrangement scheme of magnetic particles is proposed to maximize the workspace of the magnetic guidewire robot.The pulsed magnetic field was used to make the arrangement of NdFeB particles in the uncured composite material.Several kinds of composite hardmagnetic elastica with different arrangements of magnetic particles were obtained by orienting and arranging them in the matrix.Experiments confirmed that the magnetic guidewire with optimal distribution of magnetic particles can obtain a workspace 2.1 times that of the state-of-art of similar materials.Thirdly,by using A-B type tetra-arm polyethylene glycol(PEG)hydrogels to construct an ideal polymer network with precisely controlled defects,this thesis investigated the fracture and fatigue of the ideal polymer network with controllable dangling defects density.This thesis validates that the fracture toughness of an ideal polymer network with no defects or low-density dangling chain defects is approximately equal to the fatigue threshold experimentally,and its fracture toughness does not show a significant loading rate dependence.By using polyacrylamide hydrogel as a model material of low-hysteresis entangled polymer network,its fracture energy and fatigue threshold were characterized,furthermore,the toughening mechanism in low hysteresis polymers network relying on the pullout of molecular chains and misplacement failure near the crack tip was proposed.By decoupling the fracture toughness of polyacrylamide-alginate double network hydrogel,this thesis proposed an extreme toughening model that can quantitatively describe the toughening effects of near-crack tip dissipation and bulk dissipation.It is found that the classical volume dissipation toughening model will significantly underestimate the fracture toughness of such polymers.