A method for developing biomechanical response corridors based on principal component analysis.

The standard method for specifying target responses for human surrogates, such as crash test dummies and human computational models, involves developing a corridor based on the distribution of a set of empirical mechanical responses. These responses are commonly normalized to account for the effects of subject body shape, size, and mass on impact response. Limitations of this method arise from the normalization techniques, which are based on the assumptions that human geometry linearly scales with size and in some cases, on simple mechanical models. To address these limitations, a new method was developed for corridor generation that applies principal component (PC) analysis to align response histories. Rather than use normalization techniques to account for the effects of subject size on impact response, linear regression models are used to model the relationship between PC features and subject characteristics. Corridors are generated using Monte Carlo simulation based on estimated distributions of PC features for each PC. This method is applied to pelvis impact force data from a recent series of lateral impact tests to develop corridor bounds for a group of signals associated with a particular subject size. Comparing to the two most common methods for response normalization, the corridors generated by the new method are narrower and better retain the features in signals that are related to subject size and body shape.

A point-wise normalization method for development of biofidelity response corridors.

An updated technique to develop biofidelity response corridors (BRCs) is presented. BRCs provide a representative range of time-dependent responses from multiple experimental tests of a parameter from multiple biological surrogates (often cadaveric). The study describes an approach for BRC development based on previous research, but that includes two key modifications for application to impact and accelerative loading. First, signal alignment conducted prior to calculation of the BRC considers only the loading portion of the signal, as opposed to the full time history. Second, a point-wise normalization (PWN) technique is introduced to calculate correlation coefficients between signals. The PWN equally weighs all time points within the loading portion of the signals and as such, bypasses aspects of the response that are not controlled by the experimentalist such as internal dynamics of the specimen, and interaction with surrounding structures. An application of the method is presented using previously-published thoracic loading data from 8 lateral sled PMHS tests conducted at 8.9m/s. Using this method, the mean signals showed a peak lateral load of 8.48kN and peak chest acceleration of 86.0g which were similar to previously-published research (8.93kN and 100.0g respectively). The peaks occurred at similar times in the current and previous studies, but were delayed an average of 2.1ms in the updated method. The mean time shifts calculated with the method ranged from 7.5% to 9.5% of the event. The method may be of use in traditional injury biomechanics studies and emerging work on non-horizontal accelerative loading.

Characterization of ovine utero-placental interface tensile failure.

Data on the strength of the utero-placental interface (UPI) would help improve understanding of the mechanisms of placental abruption (premature separation of the placenta from the uterus) during motor-vehicle crashes involving pregnant occupants. An ovine model was selected for study because like the human, its placenta has a villous attachment structure. Uteri with intact placentas were obtained from three sheep as by-products of another research study. The samples were harvested between 102 and 119 days of the 145-day gestational period. Rectangular specimens with areas measuring 15 mm × 5 mm were cut through the thickness of the placenta and uterus. Each subject provided eight samples, of which four were tested at a nominal strain rate of 0.10 strains/sec and the remainder was tested at a nominal strain rate of 1.0 strains/sec. Sutures were used to secure the uterine side of the specimens to the test fixture, while mechanical clamps were used to attach the placenta side. A FARO arm scanner recorded the initial geometry of the tissue, and a random dot pattern applied to the placenta and uterus tissue allowed visualization of displacement. For the structure of the UPI, mean tensile failure strain and standard deviations are 0.37 (0.11) and 0.37 (0.18) for the 0.10 and 1.0 strain rates, respectively (p-value = 0.970) while the associated failure stresses are 6.5 (1.37) and 15.0 (5.08) kPa, (p-value = 0.064). The results from sheep UPI testing provide the first estimate of the human UPI structural failure tolerance.

Development and Testing of a Prototype Pregnant Abdomen for the Small-Female Hybrid III ATD.

A new prototype pregnant abdomen for the Hybrid III small-female ATD is being developed and has been evaluated in a series of component and whole-dummy tests. The new abdomen uses a fluid-filled silicone-rubber bladder to represent the human uterus at 30-weeks gestation, and incorporates anthropometry based on measurements of pregnant women in an automotive driving posture. The response of the new pregnant abdomen to rigid-bar, belt, and close-proximity airbag loading closely matches the human cadaver response, which is thought to be representative to the response of the pregnant abdomen. In the current prototype, known as MAMA-2B (Maternal Anthropomorphic Measurement Apparatus, version 2B), the risk of adverse fetal outcome is determined by measuring the peak anterior pressure within the fluid-filled bladder. Peak internal bladder pressures measured in a series of sled-test simulations of frontal crashes of different severities and occupant-restraint conditions have been correlated to the likelihood of adverse fetal outcome based on risk curves developed from in-depth investigations of real-world crashes involving pregnant occupants. Compared to the original pregnant abdomen, the new prototype has improved geometry and improved impact response to a range of potential in-vehicle loading conditions, However, additional instrumentation development and more rigorous testing are needed before the MAMA-2B can be confidently used to assess restraint system performance with regard to reducing the likelihood of adverse fetal outcome in motor-vehicle crashes.