| Knee articular cartilage is an important tissue covering the surface of the joint,and it is easily damaged due to its large and frequent load.Due to its special structure,it is difficult to self-repair after injury,and effective treatment has become a difficult problem to be solved in clinical practice.One of the important reasons is that the mechanical properties of cartilage will change greatly after injury.In this paper,the mechanical behavior of defect cartilage was studied from both cyclic loading and impact loading,and its mechanical response under various loads was obtained.From the mechanical point of view,it provides a reference for the study of cartilage damage mechanism and defect repair.In this paper,the ratcheting behavior of defect cartilage was studied experimentally.In this experiment,the distal femoral cartilage samples of adult pig femurs were used to perform triangular wave cyclic loading of different parameters of different defect depth cartilage samples.In combination with non-contact digital image technology,ratchet strain in different layers of cartilage is obtained.The experiment found that with the increase of the number of cycles of loading,the ratcheting strain of the cartilage layer showed a sharp increase first,then slowly increased and stabilized,and the ratcheting strain value from the shallow layer to the deep layer gradually decreased.The response of each layer to the number of cycles is different.The shallow layer increases the strain faster in 50 cycles,the strain increases faster in the middle layer in 100 cycles,and the strain increases faster in the deep layer in 75 cycles.In addition to the hysteresis of the mid-region response,the shallow and deep ratchet strain is positively correlated with the stress amplitude and defect depth,and negatively correlated with the loading rate.In this paper,ABAQUS software was used to establish a two-dimensional bone-cartilage model with different defect types.The model considered the relationship between material parameters and fiber distribution state with cartilage depth.The shape of the notch was set to rectangle,100 ° trapezoid,80° trapezoid and half.Round.The validity of the model is proved by the comparison between numerical simulation and experimental results.Based on the model,dynamic sinusoidal loading was used to study the effects of initial defect shape and notch depth on the stress and strain of cartilage and the evolution of damage.The study found that under impact loading,the shear strain of the cartilage layer increased sharply with the increase of the initial defect depth.However,the defect depth has almost no significant effect on the principal strain of each layer,which is quite different from the response under cyclic loading.Regardless of its initial defect shape,the defect cartilage will have a large stress concentration near the notch,and the stress concentration near the defect edge is the most obvious under the notch,while the central position stress immediately below the notch is small,showing a "U" type distribution with high and low intermediate ends.Under the impact,the basic performance of matrixand fiber damage is similar,but the fiber damage is slightly ahead of the matrix,and the damage evolution has a greater correlation with the initial notch shape.The defect cross section is rectangular and semi-circular,which appears from the bottom corner of the notch to the middle of the middle layer,and the notch begins to spread to the left and right sides.However,the trapezoidal cross section is mainly extended downward until the deep zone of the cartilage.According to the research in this paper,there is a big difference in mechanical properties between the defect cartilage and the normal cartilage under cyclic loading or impact loading.Remind people to pay more attention to cartilage health,and provide a certain reference for clinical repair of damaged cartilage. |
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