Keywords

1 Introduction

Wheeled tactical vehicles, as fast maneuvering platforms and multi-purpose combat platforms, play an important role in the modern ground battlefield, and their battlefield safety has always been a focus of attention due to the huge amount of equipment and the complex environment of use [1]. In current research on active safety in vehicle collisions, seat belts can reduce occupant injuries [2]. According to the National Highway Traffic Safety Administration (NHTSA), seat belt use can reduce fatal injuries by nearly 45%, and severe injuries by 67% [3]. Data analysis of Crashworthiness Data System (CDS) shows that the head and chest are the most common areas causing serious injuries during vehicle crashes, and compared to common two-point and three-point seat belts, four-point and five-point seat belts can provide restraints in different orientations to better restrain the occupant in the seat, thus improving occupant safety. According to the literature [4] under 400N preload force makes the seat belt 93% effective for occupant safety. At this stage, there are experimental studies on collision are mostly concentrated in the field of civil vehicles, literature [5] on the use of seat belt pre-tensioners to analyze, expanding the scope of research on seat belt pre-tensioners and load limiters; literature [6] Liu Xin et al. will be the position of the seat belt hanging point, elongation and initial strain as a design variable for the optimization of the seat belt restraining system, fast and effective to obtain the optimal matching parameters of the seat belt restraining system to ensure the safety of automobile occupants; literature [7] on the impact of special vehicle seat belt form on space safety, mainly to study the application of multi-point seat belts in the explosion impact environment. In this paper, the seat belt restraint system under the collision conditions of wheeled tactical vehicles is studied, and the damage to the driver’s seat occupant is verified by comparing the test and simulation results to verify the accuracy of the simulation model. According to the simulation restraint system select the appropriate form of seat belt, to select the best restraint program.

2 Establishment and Analysis of the Whole Vehicle Model

2.1 Finite Element Modeling

The 3D model of the wheeled tactical vehicle is simplified, after which the mesh is divided using HyperMesh software for pre-processing. The body is mainly sheet metal parts, using two-dimensional shell cells for simulation, the cell size of the model division according to the size of the impact of the components on the calculation of the working conditions, the model cell size of this paper is 10–20 mm, the shape of the quadrilateral and triangular-based, the minimum side of the mesh is >5 mm, the cell warping degree is <15°, the triangle cell internal angle to be in the range of 20°–120°, the quadrilateral cell maximum/minimum angle to be in the range of 35°–145°, the cell Jacobian is >0.65, etc. The collision process mainly relies on the plastic deformation of the material to absorb energy, so the body parts are mostly simulated by MAT24, the bolts are simulated by RBE2 and BEAM, and the welds are simulated by rigid and weld cells. The vehicle model consists of 1,826,899 nodes and 1,855,398 grid cells. The finite element model of the whole vehicle is shown in Fig. 1.

Fig. 1
A 3-D model of a vehicle has differently colored components and structures. Some components are blurred.

Vehicle finite element model

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The Hybrid III 50% dummy model was used for the test. Before the simulation, the dummy was placed in the appropriate position of the seat, and the seat belt was built to adjust the dummy’s sitting posture and foot placement. The seat belt in contact with the dummy is divided by a two-dimensional grid, and the rest of the seat belt is divided by a one-dimensional cell, as shown in Fig. 2.

Fig. 2
An illustration of a driver restraint system in a car has a dummy seated in the driver’s seat with key components labeled as the B-Post slipring, retractor, seatbelt anchor, and seatbelt buckle.

Driver restraint system

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2.2 Simulation of the Two-Vehicle Collision

Since there is no current collision standard for military vehicles, refer to the civilian vehicle collision standard while considering the later experimental verification of the situation, set the initial speed of the vehicle collision *INITIA_VELOCITY_GENERATION for 50 km/h to hit another stationary vehicle lateral B-pillar. At the same time, the two vehicles will be given the vertical direction of the gravitational acceleration g = 9.8 m/s2, and the vehicle and the ground kinetic friction factor is set to 0.3, the basic situation is shown in Fig. 3.

Fig. 3
An illustration of a simulation model of a vehicle. On the left, a vehicle is in the initial static state. On the right, the vehicle is in motion, with an initial velocity of 50 kilometers per hour.

Simulation model illustration

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2.3 Simulation Results and Test Verification

To verify the accuracy of the whole vehicle collision test model, two protective assault vehicles were selected by the finite element model test for a real vehicle collision. One of the vehicles, code F2135, collided with another static parked vehicle, code S819, at a speed of 50 km/h, as shown in in Fig. 4. The Hybrid III 50% male test dummy was placed at the driver’s position of the collision vehicle. A Hybrid III 50% male test dummy was placed at the driver’s position of the collision vehicle, and accelerometers were placed at the B-pillar and the center of mass of the vehicle, which were consistent with the simulation model as shown in Fig. 5. The accuracy of the simulation model was verified by comparing the vehicle’s B-pillar and center-of-mass X-direction accelerations, as well as the injury responses of the dummy’s head, chest, and left and right thighs.

Fig. 4
A photograph of a collision test between two military vehicles. One vehicle’s front end is colliding with the side of the other.

Crash test chart of two vehicles

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Fig. 5
A photograph exhibits an inside view of a vehicle with a dummy in the driver's seat. The interior is equipped with various mechanical components.

Accelerometer and driver’s seat dummy

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According to the results of the actual collision as shown in Fig. 6, the injury response of the occupants under the whole vehicle collision is obtained to be more consistent with the occupant response in the simulation, and according to the peak response of the acceleration at the center of mass and the B-pillar of the vehicle and the time of emergence comparison, there is a high degree of similarity, which indicates that the vehicle collision simulation model has a high degree of accuracy. Under the rigid impact, the X-direction maximum acceleration at the center of mass position in the vehicle is 29.15 g during the actual collision, and the X-direction maximum acceleration at the center of mass position in the simulation is 26.36 g, which is easy to cause impact injuries to the occupants.

Fig. 6
Six graphs titled head resultant acceleration, chest X-displacement, femur-left force, femur-right force, centroid X-acceleration, and B-pillar X-acceleration have fluctuating curves for test curve and simulation curve.

Comparison plot of test simulation response

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The change of system energy during the collision process is shown in Fig. 7, the system energy is gradually converted from the initial kinetic energy of the vehicle to the internal energy generated during the collision process. When the hourglass energy is <5% of the total energy can be considered that the simulation model is credible [8]. Fig. 8 shows the change in the ratio of the hourglass energy to the total energy during the collision process, the maximum is 1.7%, which is <5%.

Fig. 7
A graph of energy versus time plots 2 curves. Kinetic energy, (0.00, 620), (0.10, 350), (0.20, 330). Internal energy, (0.00, 0), (0.10, 220), (0.20, 225). Total energy, (0.00, 625), (0.10, 630), (0.20, 630). Hourglass energy, (0.00, 10), (0.10, 12), (0.20, 15). Values are estimated.

Model energy changes during the collision

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Fig. 8
A graph of the hourglass energy slash total energy versus time plots an increasing trend curve for hourglass energy over total energy. (0.00, 0.00), (0.10, 0.012), (0.15, 0,015), and (0.20, 0.016). Values are estimated.

Model hourglass energy to total energy ratio during the collision

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2.4 Criteria for Evaluating Occupant Injury

In order to comprehensively evaluate the overall performance of the restraint system, the weighted injury criterion WIC [9] (Weighted Injury Criterion) is used to evaluate the occupant injury,

$$ WIC = 0.6\frac{HIC}{{1000}} + 0.35\left( {\frac{{C_{3ms} }}{60} + \frac{D}{75}} \right){ /}2 + 0.05\left( {\frac{{F_{FL} + F_{FR} }}{20.0}} \right) $$

The lower the WIC value, the better the protection performance. Among them, HIC is the comprehensive performance index of the head, and the limit value of this index is 1000; \({C}_{3ms}\) is the 3 ms acceleration value of the chest (unit G), and the limit value of the acceleration is 60G; D is the compression volume of the chest (unit mm), and the limit value of the compression volume is 75 mm; \({F}_{FL}\) and \({F}_{FR}\) are the axial force of the left and right thighs (unit kN), and the limit value of the axial force is 10 kN.

3 Study on the Effect of Different Seat Belt Styles on Driver Protection

To improve the spatial safety of the occupants, the pre-tensioned seat belts, which are primarily used in current civilian vehicles, as well as the four-point and five-point seat belts will be investigated for their effects on the occupant’s limb motion response and injury. Occupant injury results as shown in Table 1 are obtained after simulation model validation.

Table 1 Restraint effects of different forms of seat belts
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Based on the simulation results, it was obtained that an increase in the preload of the seat belt decreases the head injury of the dummy with a decrease in HIC by 3.9%, and an increase in the preload using the retractor increases the tension of the seat belt, resulting in an increase in the amount of compression in the chest of the dummy as well as an increase in the axial force in the right leg in the vicinity of the belt buckle, which increases by 0.5 and 3.9%, respectively. The four-point harness was more effective in reducing the head HIC value, the cumulative 3 ms synthetic acceleration of the chest, and the chest compression by 4.6 and 60.3%, respectively, compared to the three-point harness. Five-point seat belts have better restraint effects, mainly in the lower body, the actual wearing process is more cumbersome, which is not conducive to the vehicle occupants to deal with unexpected situations. For multi-point seat belts to increase the pre-tensioning, two pre-tensioning devices need to be added, the cost is higher, and at present most single pre-tensioning force-limiting seat belts are mainly used [10]. To comprehensively evaluate the effect of different forms of seat belts, the occupant injury numerical analysis, to establish a comprehensive performance evaluation of different seat belts on the occupant injury, the value of the safety coefficient varies from 0 to 1, the larger the value of the better the safety and protection performance [11], of which

$$ \begin{aligned} {\text{safety coefficient}} = \frac{{{\text{Standard}}\;{\text{Injury}}\;{\text{Threshold}} - {\text{Maximum}}\;{\text{Simulation}}\;{\text{Test}}\;{\text{Value}}}}{{{\text{Standard}}\;{\text{Injury}}\;{\text{Threshold}}}} \times 100\% \end{aligned} $$

According to Fig. 9 multipoint seat belts have a better restraining effect, after that, the occupant protection in different installation situations is further investigated.

Fig. 9
A radar chart ranging from 0.50 to 1.00 plots H I C, chest X-displacement, femur-right force, femur-left force, and C 3 m s and has data for three-point seatbelt, four-point seatbelt, and five-point seatbelt.

Occupant restraint safety factor curve

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4 Conclusion

In this paper, a 50 km/h frontal collision driver seat occupant damage verification was completed for a certain type of wheeled tactical vehicle, and based on the simulation results, the occupant damage study was carried out by increasing the preload force and multi-point seat belt. Based on the simulation results, the following conclusions were obtained: Multi-point seat belts have better crash safety constraints for the occupants of this type of particular vehicle, especially for the upper body constraints of the occupants, which can be selected according to the actual four-point or five-point full belts inside the special vehicle. In the case of the same form of seat belt, the use of the roll-up pre-tensioning force has less impact on the dummy injury, and only increases the upper body part of the occupant’s restraint, but will correspondingly increase the probability of injury to the occupant’s chest.