Quasi-static methods to evaluate seat strength in rear impacts

OBJECTIVE

Various methods have been used in the past 50 years to apply Quasi-static load to a seat in the rear direction and measure seat performance in rear impacts. This study compared five of the most-common test procedures to evaluate seats. In addition, occupant mass and center of gravity are discussed as important characteristics of rear loading of seats.

METHOD

Data was collected and analyzed from five different seat pull tests, including FMVSS 207, modified FMVSS 207, QST, body block and FRED II. Test data included peak force, moment and angle at peak moment. Occupant loading height of was determined using body segment weights and position in the forward (x) and vertical (z) directions based on anthropometry data.

RESULTS

Some of the inherent differences in the tests are shown by comparing data with the same seat structure. The QST and FRED II use a lower height of loading than FMVSS 207. The QST and FRED II peak moment and force did not coincide with the same seatback angle as in FMVSS 207 and body block testing. Center of gravity height varies depending on whether the whole body or only the upper torso is considered. For the 50th male, it is 171.5 mm (6.8") with the whole body and 246.7 mm (9.7") with the upper torso.

CONCLUSION

Results from different tests cannot be readily compared because of different loading conditions, including body shape and height of load about the H-point, which can cause the seat structure to respond differently.

Evaluation of the vibration attenuation properties of an air-inflated cushion with two different heavy machinery seats in multi-axis vibration environments including jolts

Seats and cushions can attenuate whole-body vibration (WBV) exposures and minimize health risks for heavy machine operators. We successfully developed neural network (NN) algorithms to identify the vibration attenuation properties for four different seating conditions (seat/cushion combinations), and implemented each of the NN models to predict the equivalent daily exposure A(8) values for various vehicles in the forestry and mining environments. We also evaluated the performance of the new prototype No-Jolt™ air-inflated cushion and the original cushion of each seat with jolt exposures. We observed that the air cushion significantly improved the vibration attenuation properties of the seat that initially had good performance, but not for the seat that had relatively poor vibration attenuation properties. In addition, operator's anthropometrics and sex influenced the performance of the air-inflated cushion when the vibration environment included jolt exposures.

Predicting the transmissibility of a suspension seat

Measurements of the stiffness and the damping of an air suspension seat were made. The seat was loaded with either a person or an equivalent rigid mass, and the effect of the following variables was investigated: duration; vibration magnitude; load on-the seat; seat adjustment. The results obtained with a rigid mass were used in conjunction with previous measurements of the apparent mass of the body and the apparent mass of the legs, to predict the transmissibility of the seat with a person. Good agreement was obtained between measured and predicted seat transmissibilities.