Research On Dynamic Mechanical Properties Of Articular Cartilage

Knee joint is the most complex joint and can be injured easily.In people’ entire life,the use of the knee is very frequent,and knee cartilage plays an important role in the knee movement.Knee cartilage located between two ends of the bones inside knee joint.It facilitates joint movement and protects joints,reducing the movement injury to the bone,which is equivalent of installing protective sleeve in the two bone ends of joint.In the event of a sudden intense exercise,the probability of collision damage and friction damage of knee cartilage is large.Dynamic characteristics of the knee joint cartilage is an important mechanics index to the normal operation of knee joint function,it’s also of great significance to set up the knee joint cartilage damage simulation model for studying knee cartilage damage mechanism.Compared to mechanical properties of articular cartilage under quasi-static loading,its dynamic mechanical properties are poorly understood,mainly because of the difficulty in testing dynamic behavior of soft materials,especially biological materials of human tissues under impact loadings.With regard to the difficulty,we have proposed a set of accurate Split Hopkinson Pressure Bars(SHPB)experimental techniques to test dynamic properties of articular cartilage.Using the techniques,we have obtained dynamic compression stress-strain curves of articular cartilage.Further,This thesis firstly developed a viscoelastic constitutive model based on "Zhu-Wang －Tang" constitutive model(referred ZWT equation)to describe the behavior of articular cartilage under quasi-static loadings or high strain-rate loadings.Material properties have a relationship with the physical location,and have little to do with the species.Due to the difficulty of obtaining human knee cartilage and it has similarities with porcine knee cartilage in the material constitutive and parameter properties,we can use porcine knee cartilage instead of human knee cartilage to study the dynamic characteristics of the knee cartilage.In this paper,articular cartilage at the knee joint of fresh pig hind legs was selected as the research object,and the quasi-static compression test was carried out by electronic universal material testing machine.Experimental results show that articular cartilage has obvious viscoelastic properties and strain-rate dependence.Based on traditional Hopkinson pressure bar,for the soft material such as porcine knee cartilage’s two major problems in dynamic mechanics performance,which includes the stress can’t be balance on both ends of the specimen and the transmission signal is too weak,we put forward the corresponding improvement measures.Porcine knee cartilage’s dynamic stress-strain curves at strain rate of 500s-1,1000s-1,2000s-1,2700s-1,and 3500s-1 are obtained by the experiment,investigating the influence of strain rate on dynamic properties of porcine knee cartilage.Biochemistry of articular cartilage in different age was measured in the study,The dynamic stress-strain curves at the strain rate of 3500s-1 of knee joint cartilage of three different ages were obtained according to the Hopkinson pressure bar experiment,investigating the influence of biochemistry of articular cartilage in different age on dynamic properties of porcine knee cartilage.The study established the porcine knee cartilage dynamic constitutive model related to strain rate in consideration of damage evolution based on ZWT equation,providing a reference for the study of the mechanism of the human knee cartilage damage and an assessment of articular cartilage injury repair.