Technical – Side Pole Crash Developing Objective Targets APAC-21-153

Vijay Neve1* , Kedar Joshi1 , Pratap Daphal1 ,

1Integrated safety center, ERC, Tata Motors Limited, Pune *Corresponding author: vijay.neve@tatamotors.com

Side Pole Crash – Developing

Objective Targets – APAC-21-153

1. Introduction

Vehicle crashworthiness is defined as a measure of ability of a vehicle structure to protect the occupants in crash events. Crashworthiness is a measure of vehicle’s structural ability to plastically deform and yet maintain a sufficient survival space for occupants in crashes involving reasonable deceleration loads. The goal of crashworthiness design is to achieve an optimized vehicle structure that can absorb crash energy by controlled vehicle deformation while maintaining adequate space so that the residual crash energy can be managed by restraint systems to minimize crash loads transfer to occupants (1). Crashworthiness measurement of any vehicle is governed by different safety regulations across different countries depending on the markets where the vehicle is intended to be sold. Apart from the regulatory requirements, consumer group protocols like NCAP, IIHS etc. also measure the crashworthiness of the vehicles. The assessment is primarily based on occupant injuries and with different crash dummy types. For any vehicle, depending on the market where it is to be launched, vehicle level safety targets are defined at initial vehicle development phase by the vehicle manufacturer. The vehicle safety targets are cascaded to structural targets which influences abd constrain the vehicle structural development

2. Side Pole Crash critical design parameters for controlling occupant injuries

In real world scenario, some of the side crashes involve a vehicle travelling sideways into roadside objects such as trees or poles. Often this is the result of loss of control on the part of the driver, owing to over speeding, misjudgment of a corner or because of a skid in slippery conditions. In such accidents the nature of loading on the vehicle is localized which results in significant structural deformations. To set the structural targets for such complex and high severity crash condition, very detailed understanding of occupant injury mechanics has to be developed by considering effect of different parameters on occupant injury performances. The paper describes the effect of below mentioned parameters on occupant injury performance in Side Pole crash test. ➢ Peak Structural intrusions ➢ Occupant package space – occupant to interior trims space For structure performance target setting, the effect of the parameter has been evaluated for its contribution in occupant injury performance. The side pole test used is a perpendicular side pole crash at 29 kmph (NCAP) using simulations is being described. To evaluate and decide on structure targets for side pole crash, sensitivity study of each of the parameters was carried out digitally to evaluate effect on occupant rib deflection.

2.1 Peak structure intrusion

To study the effect of peak structure intrusions, two digital models of same vehicle were used. model A “Baseline vehicle design” and model B “Model A with Stiff structure with addition of reinforcements to reduce peak structure intrusions”. Figure 1 shows structure intrusions in lateral direction at center of the pole at thorax mid-level for Model A and B. The structure intrusions in model B are significantly lower as compared to Model A.

Occupant simulations were carried out with two models keeping same restraints and collision parameters. The rib deflection curve for Model A and B are shown in Figure 2. Model A and Model B have significant difference in structure intrusions however, there is not a significant difference observed in terms of rib deflection. The peak structure intrusions take place at a later in time than the peak injuries. Based on this observation the peak structure intrusions do not have significant influence on occupant injury performance.

2.2 Occupant package space

Effect of lateral clearance between the dummy and B-pillar or Door on rib deflection is studied in this section. Different occupant simulations were carried out to study the effect of “occupant package space” on rib deflection performance. All other parameters are maintained same for performing this study.

Figure 1. Structure intrusion of Model A and B

ABSTRACT

Side pole crash is one of the most stringent loadcases for vehicle structural development. Due to its localized nature of loading, concentrated localized deformations are observed on the vehicle structure. Developing the vehicle structure for structural integrity and occupant injuries with such local deformation is a challenge. The vehicle structure development is done based on the cascaded structure level targets, which are set based on benchmarking studies, learnings and experience. The structure target setting based on benchmarking will not always be effective as the occupant injury performance depends on many vehicle specific aspects such as occupant package, occupant position with respect to B-pillar, interior packaging and local component stiffness etc. To set the structural targets, CAE based studies were carried out for side pole crashes to evaluate the effect of different parameters affecting occupant injury performance. The paper evaluates the sensitivity of different parameters on occupant injuries and process to set the structure targets for achieving the desired occupant injury performance. The structural targets set using the process are validated with physical side pole test. KEYWORDS: Side pole crash; structural targets

Parameter Variation (mm) Seat Centerline to Trim at Shoulder -30 , -15 , +15 , +30 Seat Centerline to Trim at Thorax -30 , -15 , +15 , +30 Seat Centerline at Trim to Abdomen -30 , -15 , +15 , +30 Seat Centerline to Trim at Pelvis -30 , -15 , +15 , +30

Figure 4. Rib deflection comparison

The comparison of occupant injuries with change in lateral clearance between seat to B pillar trim is shown in Figure 4. The Rib deflection is observed to be very sensitive to lateral clearances. It is clearly observed that the rib deflection is decreasing with increase in the distance between dummy and trims i.e. when more space available for occupant energy absorption. As the occupant space has significant impact on occupant injuries, this aspect is studied further in detail. In side pole crash, the occupant lateral space available for dummy movement can be divided in two phases. Phase 1 – Upto first 20 ms i.e. till the time airbag is fired and gets fully deployed. In this phase occupant starts moving towards door trim and the movement depends on global deceleration of vehicle. Phase 2 – Occupant Energy absorption phase. In this phase occupant interacts with the side airbags. The side airbag absorbs the occupant energy in this phase thereby controlling the occupant injuries. Figure 5 shows the movement of dummy in phase 1 and phase 2.

It is clear that the occupant space consumed in phase 1 is not playing any role in occupant energy absorption. In order to effectively utilize the initial occupant space the dummy movement in the first phase should be minimized. This will ensure in higher space for occupant energy management. To understand the occupant displacement in first phase, the effect of deceleration of vehicle during first 20 ms is studied. For this study, three models of same vehicle with different stiffness was analyzed viz. Baseline structure, stiff structure and very stiff structure. Figure 6 shows the structural intrusions comparison for these three structures. Deceleration levels for all these three models measured at non struck side B pillar bottom is shown in Figure 7. From comparison, it is seen that the stiffer structure shows higher deceleration levels and vice versa.

It was observed that the injury parameters are higher with stiffer structure. Refer Figure 8 for Rib deflection comparison. Higher deceleration of the vehicle during first 20msec resulted in higher occupant displacement and early interaction with deploying airbag. This is causing higher initial peak in occupant injury.

Therefore, Deceleration of vehicle during first 20 ms is to be controlled to minimize the occupant displacement towards door and B-pillar.

Figure 5. Thorax and Pelvis Displacement from analysis Figure 6. Comparison of lateral structure intrusion

Figure 7. Deceleration levels measured at non struck side B pillar bottom

Figure 8. Mid rib deflection comparison

3. Physical Validation – Test Results

The findings of this study are physically validated in the side pole crash test. Number of digital iterations are carried out to define the package space requirements for targeted occupant injuries. The deceleration levels are maintained as per the learnings from the study. The structure intrusions are observed to be on higher side and no modifications are done for improvement. With all these considerations, vehicle prototype was built for physical test. Physical testing was carried out and the occupant injuries were found to be within the target limit. With this, the findings from the study on occupant space, deceleration levels and structural intrusions are verified.

Figure 9. Residual Deformation measurement at different levels

Figure 10. Occupant Injury in Side Pole crash test

4. Conclusion

Based on above analysis it is clear that the peak structure intrusion does not play significant role for occupant injury performance in side pole crash. The occupant space is a very critical design parameter that should be considered for controlling the occupant injuries in side pole crash. Sensitivity studies should be carried out in initial phase of product development to define the occupant space targets based on performance requirements. The vehicle deceleration in phase 1 is important for effectively utilizing the available occupant space. This aspect should be considered while designing the vehicle for side pole crash.

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