Parametric studies of the translational head injury model

In the past two decades , the concept of using mechanical lumped­ parameter model to simulate human head impact responses was introduced and later developed into injury criteria by many researchers ( 1 8 ) . One of these models , proposed and later modified by Stalnaker , e t . al . (1 , 4) , will be studied in details in this paper . Originally in 197 1 , a model with two masses , one spring , and one damper (as shown in Figure 1 ) was used in con­ j unction with the Mean Strain Criterion (MSC) to predict human head responses in the lateral ( leftright) direction ( 1 , 6) . The model responses agreed well with experimental impedance , F/V( s ) , at the resonant point ; however , the agreement was not observed at the antiresonant point . Later in 1981 , a new lumped-parameter model composed of two masses , one spring, and two dampers was introduced ( 4 , 5 ) . This new model is shown in Figure 2 . The model is essentially an extension of the original MSC lumped-parameter model with an additional damper in series to the model spring element . The New Mean Strain Criterion (NMSC) and later a more complete injury critirion called the Translational Energy Criterion (TEC) was developed from this new improved lumped-parameter model , now called the Translational Head Injury Model (THIM) . The impedance predicted by the new model agreed very well with the observed experimental data at both the resonant and the antiresonant points . In addition, this model was designed in four directions : anterior-posterior (AP , or front-back) , posterior-anterior (P-A, or backfront) , left-right (L­ R) , and finally , superiorinferior ( S I , or top-bottom) instead of j ust one direction as in the case for the MSC . The theoretical predictions of the TEC for human and primate head injuries also agreed very well with the AIS scale and experimental skull fracture data ( 10 ) . This new lumped-parameter model can be used to predict the head impedance responses for both human and primates or any impact responses with a similar shaped impedance curve . Different parametric values of the lumped elements must be adjusted to modify the model responses to fit the experimen­ tal results for each case separately . Several sets of primates and human head data were used to generate different sets of parametric values for different models in several impact directions . And as noted earlier , com­ parison of the theoretical predications and experimental data f or the head responses show very good agreements . Thus it may be concluded that this new lumped parameter model are very versatile and fairly convenient to use in the analysis and evaluation of head impact responses . In this paper , a detailed parametric study on this new lumped­ parameter model is conducted . The influences of the adjustments of the lumped elements on the natural frequencies (w ' s ) and the damping ratios n ( r ' s) of the resonant and the antiresonant peaks are evaluated. The effects