Kinematic response of seated male volunteers in various reclined postures on a sled subjected to a braking pulse.

Vehicle occupants expect greater postural flexibility with the introduction of highly automated vehicles, such as reclined postures. Experiments have been conducted with post mortem human subjects to study the risk of injury under impact conditions in reclined postures. However, the influence of the pre-crash phase on the kinematics in reclined postures has not yet been thoroughly studied. The aim of the present study is to investigate human responses under low g braking conditions focusing on different backrest angles in a generic sled environment. Three 50th percentile male volunteers were recruited to participate in a sled experiment. Each of them was subjected to a total of fourteen trials under a braking pulse with a maximum acceleration of 0.7 g for 700 ms. Different sitting postures were investigated: from 23° to 45°, 60° and 75° backrest tilt with respect to the vertical axis. In addition, two different seat pan tilt angles were considered: a 16° tilt angle for 23°, 45° and 60° backrest inclination and a 36° tilt angle for 60° and 75° backrest inclination. Measurements of volunteer kinematics, muscle activation and interaction forces between the volunteers and the sled, among others, were acquired. Initial results show a significant reduction in maximum forward head displacement from the upright to the reclined postures (p < 0.02), with the exception of the 45° reclined posture. However, no significant difference in maximum head displacement was found between the different reclined postures (p > 0.1). Seat pan tilt angle did significantly influence forward head excursion when considering the same seatback inclination (p < 0.01). It is of great importance to investigate occupant kinematics during the pre-crash phase to understand its influence on the potential injuries that may occur with a reclined posture in the event of a collision.

Subcutaneous adipose tissue thickness around the ASIS area for human body models in reclined positions.

OBJECTIVE: Subcutaneous adipose tissue (SAT) thickness above the anterior superior iliac spine (ASIS) influences belt fit of a vehicle occupant. To improve finite element (FE) human body models and their application assessing future seating positions in cars, there is a need for more detailed data. METHODS: Anthropometric input data were used to statistically model a lower limit of the SAT thickness in the area around the ASIS (at the ASIS or in the groin) extracted from 102 postmortem computed tomography (pmCT) data sets (56 males and 46 females). Additionally, 2 pmCT scans of 1 male individual in both supine and sitting conditions were used to estimate change in SAT thickness by position. RESULTS: Distributions and locations of minimum values for SAT thickness were derived for males and females. Sex, age, and body mass index (BMI) remained in a linear regression model for the minimum SAT thickness in the ASIS area. Thirty-seven percent of the variance in the SAT distribution of the sample can be explained by these input variables. The individual with data in supine and sitting positions showed an SAT thickness value above the ASIS 6 times higher in the sitting position than in the supine position. CONCLUSIONS: Individual factors influence SAT thickness around the ASIS in addition to BMI, sex, and age. The presented values need to be regarded as a lower limit of SAT thickness, because in 63% the minimum was found in the groin area and the measurements were performed in a supine position. The increase in SAT thickness in a sitting position compared to supine seen in the case example shows the need for further data acquisition to establish a transfer function interpolating between both positions. The SAT thickness minimum values in the ASIS area shown in this study can provide valuable input for soft tissue modeling in human body models with the aim to analyze seat belt fit and to computationally assess lap belt and occupant interaction sensitivity to SAT tissue thickness under load. This might be crucial in reclined sitting positions in automated driving.

Comparison of Upper Neck Loading in Young Adult and Elderly Volunteers During Low Speed Frontal Impacts.

Cervical pain and injuries are a major health problem globally. Existing neck injury criteria are based on experimental studies that included sled tests performed with volunteers, post-mortem human surrogates and animals. However, none of these studies have addressed the differences between young adults and elderly volunteers to date. Thus, this work analyzed the estimated axial and shear forces, and the bending moment at the craniocervical junction of nine young volunteers (18-30 years old) and four elderly volunteers (>65 years old) in a low-speed frontal deceleration. Since the calculation of these loads required the use of the mass and moment of inertia of the volunteers' heads, this study proposed new methods to estimate the inertial properties of the head of the volunteers based on external measurements that reduced the error of previously published methods. The estimated mean peak axial force (Fz) was -164.38 ± 35.04 N in the young group and -170.62 ± 49.82 N in the elderly group. The average maximum shear force (Fx) was -224.42 ± 54.39 N and -232.41 ± 19.23 N in the young and elderly group, respectively. Last, the estimated peak bending moment (My) was 13.63 ± 1.09 Nm in the young group and 14.81 ± 1.36 Nm in the elderly group. The neck loads experienced by the elderly group were within the highest values in the present study. Nevertheless, for the group of volunteers included in this study, no substantial differences with age were observed.

Feasibility study of a safe sled environment for reclined frontal deceleration tests with human volunteers.

Objective: The goal of the study was to assess the feasibility of a safe crash environment for volunteer tests in reclined seating positions. An iterative multimodal approach was chosen, consisting of full-body human body model (HBM) simulations, anthropomorphic test device (ATD) physical testing, and volunteer testing.Methods: To estimate a noninjurious deceleration pulse, the iterative inclination of the seat was supported through HBM simulations and physical ATD testing. One male volunteer was exposed to 5 low-speed frontal sled impacts with stepwise reclined seat angles. The volunteer was restrained with a non-pretensioned 3-point seat belt. All procedures were approved by the relevant ethics boards.Results: Volunteer sled tests in 3 different seat configurations were performed with one volunteer at noninjurious deceleration levels. Inclination of the seat and the absence of a footrest resulted in elevated axial seat reaction forces and almost pure translational motion of the human body.Conclusions: A maximum speed of 7.1 km/h and peak deceleration of 3.0 g was found to be a safe pulse for volunteer testing in frontal impacts with a rigid reclined seat. Larger soft tissue deformations were observed when reclined, possibly associated with higher shear loads within the soft tissue. Preliminary results highlight trade-offs between the degree of seat angulation, friction force, and restraint capability of a 3-point seat belt, thus causing forward translation and/or axial spinal compression of the occupant that may need to be addressed in the future.

Chest injuries of elderly postmortem human surrogates (PMHSs) under seat belt and airbag loading in frontal sled impacts: Comparison to matching THOR tests.

OBJECTIVE: The goal of the study was to develop experimental chest loading conditions that would cause up to Abbreviated Injury Scale (AIS) 2 chest injuries in elderly occupants in moderate-speed frontal crashes. The new set of experimental data was also intended to be used in the benchmark of existing thoracic injury criteria in lower-speed collision conditions. METHODS: Six male elderly (age >63) postmortem human subjects (PMHS) were exposed to a 35 km/h (nominal) frontal sled impact. The test fixture consisted of a rigid seat, rigid footrest, and cable seat back. Two restraint conditions (A and B) were compared. Occupants were restrained by a force-limited (2.5 kN [A] and 2 kN [B]) seat belt and a preinflated (16 kPa [A] and 11 kPa [B]; airbag). Condition B also incorporated increased seat friction. Matching sled tests were carried out with the THOR-M dummy. Infra-red telescoping rod for the assessment of chest compression (IRTRACC) readings were used to compute chest injury risk. PMHSs were exposed to a posttest injury assessment. Tests were carried out in 2 stages, using the outcome of the first one combined with a parametric study using the THUMS model to adjust the test conditions in the second. All procedures were approved by the relevant ethics board. RESULTS: Restraint condition A resulted in an unexpected high number of rib fractures (fx; 10, 14, 15 fx). Under condition B, the adjustment of the relative airbag/occupant position combined with a lower airbag pressure and lower seat belt load limit resulted in a reduced pelvic excursion (85 vs. 110 mm), increased torso pitch and a substantially lower number of rib fractures (1, 0, 4 fx) as intended. CONCLUSIONS: The predicted risk of rib fractures provided by the THOR dummy using the Cmax and PC Score injury criteria were lower than the actual injuries observed in the PMHS tests (especially in restraint condition A). However, the THOR dummy was capable of discriminating between the 2 restraint scenarios. Similar results were obtained in the parametric study with the THUMS model.