Tony R. Laituri

Predictions of AIS3+ Thoracic Risks for Belted Occupants in Full-Engagement, Real-World Frontal Impacts: Sensitivity to Various Theoretical Risk Curves

A new, AlS3+ thoracic risk equation based on chest deflection was derived and assessed for drivers subjected to concentrated (belt-like) loading. The new risk equation was derived from analysis of an existing database of post mortem human subjects in controlled, laboratory sled tests. Binary logistic regression analysis was performed on a subset of the data, namely, 25th-75th percentile men (by weight) from 36-65 years old whose thoracic deformation patterns were due to concentrated (belt-like) loading. Other subsets of data had insufficient size to conduct the analysis. The resulting thoracic risk equation was adjusted to predict the AlS3+ thoracic risks for average-aged occupants in frontal crashes (i.e., 30 years old). Biomechanical scaling was used to derive the corresponding relationships for the small female and large male dummies. The new thoracic risk equations and three other sets of existing equations were evaluated as predictors of real-world crash outcomes. Specifically, thoracic risks associated with belt-only drivers in 1985-1997 model year passenger cars were derived via the four different sets of equations. Comparisons were made from two standpoints: (1) point estimates for 48 km/h potentially barrier-like frontal crashes and (2) aggregate risk estimates derived from simulations of full-engagement, non-rollover, tow-away frontal crashes through 56 km/h. In both cases, the new risk equation agreed with field results. Moreover, an existing thoracic risk equation with a commonly held assumption was shown to significantly overstate observed thoracic field risks.

Considerations of "Combined Probability of Injury" in the next-generation USA frontal NCAP.

Objective: The numerical basis for assigning star ratings in the next-generation USA New Car Assessment Program (NCAP) for frontal impacts was assessed. That basis, the Combined Probability of Injury, or CPI, is the probability of an occupant sustaining an injury to any of the specified body regions. For an NCAP test, a CPI value is computed by (a) using risk curves to convert body-region responses from a test dummy into body-region risks and (b) using a theoretical, overarching CPI equation to convert those separate body-region risks into a single CPI value. Though the general concept of applying a CPI equation to assign star ratings has existed since 1994, there will be numerous changes to the 2011 frontal NCAP: there will be two additional body regions (n = 4 vs. 2), the injury probabilities will be evaluated for lower-severity (more likely) injury levels, and some of the occupant responses will change. These changes could yield more disperse CPIs that could yield more disperse ratings. However, the reasons for this increased dispersion should be consistent with real-world findings. Related assessments were the topic of this two-part study, focused on drivers. Methods: In Part 1, the CPI equation was assessed without applying risk curves. Specifically, field injury probabilities for the four body regions were used as inputs to the CPI equation, and the resulting equation-produced CPIs were compared with the field CPIs. In Part 2, subject to analyses of test dummy responses from recent NCAP tests, the effect of risk curve choice on CPIs was assessed. Specifically, dispersion statistics were compared for CPIs based on various underlying risk curves applied to data from 2001–2005 model year vehicles (n = 183). Results and Conclusions: From Part 1, the theoretical CPI equation for four body regions demonstrated acceptable fidelity when provided field injury rates (R2= 0.92), with the equation-based CPIs being approximately 12 percent lower than those of ideal correlation. From Part 2, the 2011 NCAP protocol (i.e., application of a four-body-region CPI equation whose inputs were from risk curves) generally increased both the CPIs and their dispersion relative to the current NCAP protocol. However, the CPIs generally increased due to an emphasis on neck injury—an emphasis not observed in real-world crashes. Subject to alternative risk curves for the neck and chest, again there was increased dispersion of the CPIs, but the unrealistic emphasis on the neck was eliminated. However, risk estimates for the knee/thigh/hip (KTH) for NCAP-type events remained understated and did not fall within the confidence bands of the field data. Accordingly, KTH risk estimation is an area for future research.

Development of a Hybrid III 5th percentile facet dummy model

A MADYMO multibody model of the Hybrid III 5th percentile female dummy has been developed. Most attention is placed on modeling the thorax, pelvis- abdomen, head and neck. Those parts are modeled with facet surfaces and deformable bodies are used for the thorax. The remaining dummy parts are identical to an existing ellipsoid model. The facet component models have a more detailed geometry and are therefore more realistic than the ellipsoid model. The model enables accurate interaction with a FE lap belt, or seat, or airbag. The dummy model has been tested and validated using component tests and fully dummy tests. From the results, it can concluded that the model is an improved tool, which will give engineers more confidence concerning predictability. The model is slightly slower than the ellipsoid model, but still fast enough to perform parametric studies and optimizations

Variability of Hybrid III Clearance Dimensions Within the FMVSS 208 and NCAP Vehicle Test Fleets and the Effects of Clearance Dimensions on Dummy Impact Responses

The study aims to examine: 1) the extent of variability of occupant clearance dimensions in currently manufactured vehicles when the Hybrid III dummy is placed in driver and passenger seating positions in accordance with NCAP and FMVSS No. 208 test procedures, and 2) to explore if occupant clearance dimensions differ among several classes of vehicle sizes. The findings are compared with real world occupant clearance data reported by other researchers. The study also aims to explore if a relationship exists between dummy responses and clearance dimensions. This is done through statistical analysis of the data used in this study and through a computer model analysis created by the Ford Motor Company.

Finite-Element-Based Transfer Equations: Post-Mortem Human Subjects versus Hybrid III Test Dummy in Blunt Impact

In the present study, transfer equations relating the responses of post-mortem human subjects (PMHS) to the mid-sized male Hybrid III test dummy (HIII50) under matched, or nearly-identical, loading conditions were developed via math modeling. Specifically, validated finite element (FE) models of the Ford Human Body Model (FHBM) and the HIII50 were used to generate sets of matched cases (i.e., 256 frontal impact cases involving different impact speeds, severities, and PMHS age). Regression analyses were subsequently performed on the resulting age-dependent FHBM- and HIII50-based responses. This approach was conducted for five different body regions: head, neck, chest, femur, and tibia. All of the resulting regression equations, correlation coefficients, and response ratios (PHMS relative to HIII50) were consistent with the limited available test-based results. Language: en

Fracture Modeling Inputs for a Human Body Model via Inference from a Risk Curve: Application for Skull Fracture Potential

A three-step process was developed to estimate fracture criteria for a human body model. The process was illustrated via example wherein skull fracture criteria were estimated for the Ford Human Body Model (FHBM) - a finite element model of a mid-sized human male. The studied loading condition was anterior-to-posterior, blunt (circular/planar) cylinder impact to the frontal bone. In Step 1, a conditional reference risk curve was derived via statistical analysis of the tests involving fractures in a recently-reported dataset (Cormier et al. 2011a). Therein, Cormier et al. authors reported results for anterior-to-posterior dynamic loading of the frontal bone of rigidly-supported heads of male post mortem human subjects, and fracture forces were measured in 22 cases. In Step 2, the FHBM head was used to conduct some underlying model validations relative to the Cormier tests. The model-based Force-at-Peak Stress was found to approximate the test-based Fracture Force. In Step 3, models of Cormiers setup with assumed fracture criteria were made such that they produced the experimentally-observed spread of fracture forces. Moreover, iteration was conducted on the model-based stress and strain fracture criteria (viz., σult and eult). The outcomes were analyzed via the same statistical approach applied in Step 1, and subject to σult ≈ 125 MPa and eult ≈ 2.2%, the model-based risk curve nearly identically recovered the reference test-based risk curve (i.e., PFE-based ≈ 1.03 Preference and R2=0.99). Language: en

Further Validation of the Head in the Ford Human Body FE Model

The head in the Ford human body model (FHBM) was previously validated against impact test data involving post mortem human subjects (PMHS). The objective of the current study was to further validate the head model against more PMHS tests. The data included the following published tests: rigid bar impact to the forehead, zygoma, and maxilla (2.5–4.2 m/s), lateral pendulum impact (5.7 m/s), and front pendulum impact to the frontal bone, nasal bone, and maxilla (2.2 m/s). The responses from the model were compared to available published cadaveric response corridors and to various cadaveric responses. When compared to the cadaveric response corridors, the responses from the model were within those corridors. In addition, the model responses demonstrated acceptable fidelity with respect to the test data. The head injury criterion (HIC15 ), strain, and stress values from the model were also reported.Copyright