Evaluation of thor dummy kinematics in front impacts

Vehicle safety design is one of the most important parameter to protect occupants in traffic accidents. Every passing day, number of vehicles are increasing enormously due to rapid increase of population. What does increased population means? Increase in population means that more transportation is needed. Therefore, risk of occupant injuries in traffic accidents should be decreased and controlled. The Insurance Institute for Highway Safety (IIHS) administration investigates traffic accidents according to vehicle type, impact type, and involved number of vehicles in crashes. Recent reports show that approximately half of both single and multiple crashes happen in front impact direction. Side impact crashes follows front impact ones, and mostly occur in multiple vehicle crashes. Another report by the IIHS describe occupant deaths according to vehicle types. In passenger vehicles, occupant deaths are decreased by approximately 40% in recent decades. This result shows that crashworthiness of vehicles is improved from 1975 to 2015. On the other side, occupant deaths occurring in pick-up trucks and sport utility vehicles (SUV) are 80% lower than those occurring in passenger vehicles. This is one of the reasons why SUV vehicles are more popular in nowadays. Safety organizations and car manufacturers investigate performance of restraint systems. Airbags and belts are main research areas for passive safety systems. Airbag vent optimizations and belt load limiter levels are checked for complexity reduction or getting better performance from dummy in safety performance tests. The National Highway Traffic Safety Administration (NHTSA) works on new dummy which is called Test device for Human Occupant Restraint (THOR) and new test protocol. THOR dummy is improved to get more realistic kinematic and injury predictions than the Hybrid III dummy. Also, NHTSA proposed to use THOR dummy in full frontal test and new oblique tests in driver side. In full frontal case, 5% Hybrid III dummy will be used in passenger side and THOR dummy will be used as a passenger in oblique crash test mode. Also, acceptance limits are changed with THOR dummy in new test protocol. Main difference between THOR and Hybrid III dummy is the chest deflection measurement methodology. Chest deflection is measured from 4 points in THOR dummy instead of 1 point when compared with the hybrid version. These 4 points represent humans 4th and 8th ribs. Finally, studies show that THOR dummy has similar kinematic and outputs as humans. Vehicle manufacturers design their vehicles according to customer needs. Ergonomic design, interior/exterior design and some engineering characteristics such as aerodynamic characteristics, durability performance and safety performance define overall vehicle identity. First conceptual works start with body structure design which is evaluated according to NVH, durability and safety targets. Before vehicles arrive to the customer, all vehicles are checked by government rules which are called regulations. Therefore, boundary conditions of vehicle designs are defined by regulation targets. Regulations are not only assessments but they are mandatory. Also, special organizations perform tests to evaluate vehicle performance such as the New Car Assessment (NCAP) organization. According to NCAP tests, vehicles are tested in 2 main sections which are front and side impacts to measure injury values from passengers and drivers. Briefly, vehicle engineering design can be classified as an input for tests and dummy injury values can be classified as an output of assessments. To protect occupant, vehicle acceleration and intrusion values are very critical. After final decision of vehicle structure design, vehicle interior and restraint system play a key role for occupant protection. In this study, assessments are completed via computer software program. Vehicle is modeled with hyper crash program and finite element model of THOR dummy is used in driver side. Before starting occupant analysis, correlated vehicle model is used. Chest acceleration of dummy and shoulder belt forces are checked for correlation level for the entire model. Evaluation of THOR dummy chest deflection values in front impacts is selected as a main focus of study. The reason for this can be explained by the major difference between THOR and the Hybrid III dummy. Chest deflections are measured at four points and rotations of sensors are included for calculation in THOR dummy assessments. In Hybrid III dummy, chest deflection is measured at one point and rotation is not included. These improvements in THOR dummy make kinematics of dummy more important. Given these updates, the restraint parts with THOR dummy need to be teste again. In new proposed US-NCAP test, limits are defined for every point of measured chest deflections. Therefore, restraint parameters are changed to achieve minimum chest deflection values for each point. Load limiter of belt is changed, and 6 different belts are created for iterations. Secondly, belt width is increased to 75 mm from 50 mm for more equal load distribution. Third, D-ring position is checked, and it is moved in x and z directions for optimum position. As a fourth iteration, buckle position of belt is moved in its own direction. 4-point belt usage is tested as a final iteration of belt system. Additionally, knee airbag and stiffness change of driver airbag is checked for evaluations. The results of the iterations are reported for the left upper, right upper, left lower and right lower chest deflection values. Decreasing load limiter levels helps to reduce chest deflections values. But different improvements are observed in 4 areas of measurement. Maximum improvement which is around 18 % is observed with lowest load limiter. But decreasing load limiter level increases the head accelerations. Therefore, optimum design should be selected for chest and Head Injury Criteria (HIC) values. Increasing belt width helps to reduce chest deflections in left upper and right lower areas approximately 7 %. Left upper and right lower sensors are under belt routing position. Thus, increasing belt width helps to distribute loads equally. On the other iterations moving D-ring rearward of vehicle and upper direction helps to reduce chest deflection. Limits of d-ring's position is defined with B pillar width of vehicle. Positioning d-ring in forward and lower direction causes slippage of belt over the shoulder. Positioning d-ring in rearward and upper direction avoids slippage of belt and chest deflection values are decrease with equally positioned belt. Same improvement is observed with using 4-point belt in assessments. No improvement is observed with airbag iterations and this result can be proof of main contribution of controlling chest deflection is belt. Finally, belt and airbag iterations are checked with THOR dummy in full frontal impact. In this study, iterations are completed without changing any vehicle structure parts. This means, same crash pulse is used for all design iterations. In best case, 14% decrease in left upper, 6% decrease in right upper, 9% decrease in left lower and 29% decrease in right lower sensor are observed. In best case, the restraint systems are belt D, 75mm width, buckle is in 30 mm forward in its own direction and D-ring is moved 50 mm in x and z directions. For further studies, passenger side can be studied with restraint iterations. Also, new oblique crash mode can be assessed with THOR dummy for new injury criteria.