Mechanical Properties And Intrinsic Modeling Of Adipose-muscle Composite Tissue

With the continued development of the modern automobile industry as well as road traffic construction,private car ownership in China has maintained a fairly high level,reaching 280 million vehicles by the end of 2020.At the same time,the overall traffic situation in the country remains grim,with the average number of traffic accidents reaching over 200,000 per year,more than 60,000 fatalities and more than one billion yuan of direct property damage,making traffic safety an urgent need for in-depth study.In the current state of research,occupant crash injury guidelines and occupant protection devices in the field of automotive safety have been developed primarily based on the 50th percentile dummy model.With the significant increase in the proportion of obese people in recent years,it is worth exploring whether occupant injury criteria and protective devices based on standard body types are still applicable to obese occupants.In addition,deep pressure sores(DPS),which are part of deep tissue injury(DTI),are a life-threatening,expensive to treat and common complication that causes necrosis of the skin,subcutaneous adipose tissue and transverse muscle meatus,often in bedridden,wheelchair-bound patients,and in most cases requires surgical excision to remove the necrotic tissue.The stress-strain distribution within the deep tissue leading to DPS generation is also a hot topic of research.The study of the performance of adipose-muscle composite tissues can not only theoretically and effectively predict the force situation of the human body in road traffic accidents when subjected to impact,thus promoting the updating of human injury protection equipment in road traffic accidents,improving the level of collision injury protection for obese people,realizing the optimization of active and passive safety equipment for automobiles,and improving the mechanism of the cause of injury to the injured or deceased in forensic identification.It can also help us in clinical medicine to understand the prevention and treatment of deep pressure sores(DPS)and provide a mechanical reference for the development of bionic materials for use with adipose or muscle-based materials.In this paper,the mechanical properties of adipose muscle composite tissues were investigated by means of an indentation test method similar to in vivo loading,based on the current state of research at home and abroad as well as the microstructure and mechanical properties of the experimental materials,and the contents and findings of the study are summarised as follows.(1)The extent to which the radius of the spherical indenter affects the mechanical properties of the indentation response of adipose-muscle composite tissue was investigated.It was found that,with the radius of the spherical indenter as the only experimental variable,indenter size had a significant effect on the indentation mechanical properties of the adipose-muscle composite tissue.The experimental results show that the radius of the indenter is proportional to the peak load,the larger the radius of the spherical indenter,the higher the peak load.The radius of the indenter is inversely proportional to the shear modulus,the larger the radius of the indenter,the smaller the measured shear modulus.(2)Study of the effect of muscle fibre orientation on the mechanical properties of adipose muscle composite tissue.It was found that with muscle fibre orientation as the only experimental variable,the mechanical response of the composite tissue indentation experiments was almost identical along muscle fibre orientation versus vertical muscle fibre orientation,with no significant effect of muscle fibre orientation on the composite tissue indentation mechanical experiments.(3)To investigate the effect of loading rate on the properties of adipose muscle composite tissue and to explore the sensitivity of the indentation mechanical response of the composite tissue to the loading rate.It was found that in the composite tissue indentation experiments,with the loading rate as the only experimental variable,the measured shear modulus tended to increase with increasing loading rate,the greater the loading rate the greater the corresponding shear modulus.The short-acting shear modulus increment(ΔG_S)was greater than the long-acting shear modulus increment(ΔG_L),i.eΔG_S＞ΔG_L.(4)To investigate the differences in the mechanical response of indentation tests between adipose and adipose-muscle composite tissues.It was found that with specimen type as the primary experimental variable and loading rate as the secondary experimental variable,there was a significant difference in the indentation test mechanical response between adipose tissue and adipose-muscle composite tissue.Under the same loading rate,the overall performance parameters of the adipose-muscle composite tissue were smaller than those of the adipose tissue.For different loading rates,both composite and single adipose tissue performance parameters were proportional to the loading rate.(5)To investigate the decay pattern of the mechanical properties of adipose muscle composite tissue after repeated loading.It was found that,with the number of loading times as the only experimental variable,the mechanical properties of the composite tissue continued to decay with increasing loading times,and the shear modulus showed a decreasing trend,but the trend slowed down significantly.The short-acting shear modulus(G_S)decay value was significantly greater than the long-acting shear modulus(G_L)value,i.e (?).The viscoelastic contribution ratio c(%)showed a decreasing trend,which increased faster with the superposition of loading times.(6)Study of viscoelastic instrinsic models.Based on the three principles of mathematical modelling convenience,experimental fit and visual friendliness,and the category of viscoelastic propriety models,Zener,DM and GM models were selected to fit curves to the shear modulus relaxation functions of indentation experiments on fatty muscle composite tissues.The fitting results were evaluated under the three principle criteria to select the most suitable viscoelastic model to characterize the composite tissue.The results showed that the Zener model>DM model>GM model in terms of mathematical modelling convenience,the DM model=GM model>Zener model in terms of visual friendliness,and the DM model=GM model>Zener model in terms of experimental fit.On balance,the DM model was more suitable for characterising the viscoelastic properties of the adipose muscle composite tissue compared to the Zener and GM models.