A Study On Occupant Injury In Offset Impact Of A Coach

As an important carrier of road transportation,coaches’collision safety is related to the safety of people’s lives and orderly development of social economy.In recent years,there have been frequent accidents caused by frontal collisions of coaches and the social impact is severe.Among the frontal collision accidents of coaches,the most frequent type of collisions are frontal offset collisions,but there are few researches on occupant injury and occupant protection of coaches offset collisions in China.It is very significant to carry out the research on occupant injury in coaches offset collision and helpful to reduce the crash casualty rate of coaches.In this paper,the occupant motion response and injury under different overlapping rates,different positions and different constraints are explored by offset collision simulation experiments.The optimization of occupant restraint system is carried out according to the dangerous working conditions and the optimization can provide some reference for the improvement of coach structure and occupant restraint system.In this paper,a 6120 coach is taken as the research object,conducts offset collision simulation tests with different overlap rates（20%,30%,40%,50%,60%）and the results of vehicle motion response,body frame deformation,B-pillar acceleration and vehicle impact energy response are analyzed.The results show that the deflection degree and the deformation degree of the front part of body decrease with the increase of the overlap rate,the impact load of the body increases with the increase of the overlap rate and the lateral impact load of the body is the largest when the overlap rate is 20%and 30%.In order to take into account the calculation accuracy and efficiency,the coupling model of the passenger-vehicle system is established by multi-rigid-body-finite element coupling method.The acceleration wave at the seat fixed point in the offset impact is introduced to carry out the crash simulation test of the dummy.According to the test results,the kinematic response and damage of the dummy in different positions and different overlapping rates under the constraint conditions are compared and analyzed.The results show that the three-point seat belt has a significant effect on limiting the displacement of the dummy’s chest and head and the risk of occupant injury is relatively small;under the two-point seat belt constraint,the risk of occupant injury on the collision side with different overlap rate is generally higher than that on the non-collision side,and the risk of occupant injury on the front row is generally higher than that on the rear row;under the 50%overlap impact condition,the risk of occupant injury on the collision side of the second row is the highest.Aiming at the 50%overlap offset impact condition,the single factor method was used to study the dummy injury factors influenced by coach seat back,cushion and seat belt.The result shows that the backside foam stiffness ratio coefficient is about 1.5,the seat distance is below800mm,the seat backrest angle is about 100 degrees,and the seat belt stiffness ratio coefficient is less than 1,which can reduce the overall injury risk of occupants.To reduce the risk of head and chest injury under 50%overlap offset crash condition,Seat distance,back foam stiffness,cushion friction and belt stiffness were taken as design variables by sensitivity analysis.30 groups of test samples were collected according to the Latin hypercube design and the corresponding Kriging agent model was established.Taking the minimum HIC value of the dummy head and the minimum C_3ms value of the chest as the optimization objective and the multi-objective optimization of occupant restraint system was carried out.After optimization,the seat distance is 736mm,the backside foam stiffness ratio coefficient is 1.55,the seat belt stiffness ratio coefficient is 0.81,the cushion friction coefficient is 0.362.After optimization,under the different overlap rate offset collision condition,the dummy’s head and chest injury descend obviously,the dummy comprehensive damage reduces by 15%.The optimization effect is remarkable.