Mechanism Of Long Life Fatigue Failure Of Polyurethane Materials For Cardiac Pacemaker Conductors

This paper focuses on the practical application of pacemaker leads in clinical practice.Through experiments,the macroscopic long-life fatigue strength and crack propagation rate of pacemaker leads are obtained.Combined with failure analysis at the micrometer scale,the influence mechanism of the microstructure of Thermoplastic Polyurethane(TPU)materials composed of leads on the long-life fatigue strength and crack propagation behavior of Thermoplastic Polyurethane materials is deeply explored,based on this,a relationship model between local material fatigue characteristics and the overall macroscopic fatigue life of polyurethane is established.In this study,two types of polyurethane materials: TPU(80A)and TPU(55D)for pacing lead wrapping were mainly tested for basic mechanical properties and high-cycle fatigue,and their fatigue life was evaluated,revealed the fatigue failure mechanism of polyurethane materials during fatigue service.The crack growth rate and cumulative damage are discussed through fracture mechanics and Damage mechanics.Basic mechanical tests were conducted on thermoplastic polyurethane(80A)and(55D)through uniaxial tensile testing to obtain their stress-strain curves and Digital image correlation(DIC)strain field changes.The cyclic fatigue resistance of the two types of thermoplastic polyurethane was evaluated.The study showed that the tensile strength of thermoplastic polyurethane(80A)was about 32 MPa,and the strain amplitude was about700%.The tensile strength of thermoplastic polyurethane(55D)is about 70 MPa,and the strain amplitude is about 300%.Thermoplastic polyurethane(80A)has stronger plastic deformation ability than thermoplastic polyurethane(55D),and the strain of polyurethane is first concentrated in the middle part of the notch morphology during the stretching process,accumulating and gradually moving towards both ends along the stretching direction.At the same stress level,the cyclic deformation capacity of TPU(80A)is higher than that of TPU(55D).The deformation rate of TPU(80A)is also higher than that of TPU(55D).The hysteresis curve also indicates that TPU(55D)has better resistance to plastic deformation than TPU(80A).The main purpose of polyurethane high cycle fatigue test is to analyze the fatigue failure of TPU(80A)and TPU(55D)plate materials under tensile tensile load control test(frequency=5Hz,stress ratio=0.1),and consider the changes of hydrogen bond content in the material.The results indicate that the polyurethane material continuously consumes energy during the cyclic creep process and undergoes three stages of changes in the structural direction of the hard and soft segments.Infrared spectroscopy studies show that an increase in fatigue life will lead to more physical cross-linking,resulting in a decrease in hydrogen bond content and an increase in microphase separation,leading to the occurrence of fatigue fracture.In addition,scanning electron microscopy and Three-dimensional Confocal analysis that TPU(80A)cracks originate from the aggregation of micropores on the surface of the material,while TPU(55D)fatigue cracks originate from microcracks directly generated under cyclic loading.Both TPU(80A)and TPU(55D)are accompanied by molecular chain slip during the cycling process,and the slow crack propagation propagates along a direction of approximately 45°with the applied load,and the propagation rate gradually increases during its crack propagation process.