Design and experimental analysis for a new configuration of a safety barrier destined to absorb the impact energy.

Jiga, Gabriel ; Vlasceanu, Daniel ; Nutu, Emil 等

1. INTRODUCTION

Because important progress should be done in order to decrease the traffic accidents (especially those with serious injuries), an important role comes to researchers from the automotive industry. (Bayton, et al., 2007)

The impact energy produced during the collision with a safety barrier has to be absorbed by a deformable material able to dissipate this energy by deformation. Starting from these considerations one concludes that the application of rubber cushions on some barrier regions with a high injuriousness degree should contribute to impact attenuation as effect of the collision between the car and the safety barrier.

In the last years, parallel to a continuous development of numerical calculus systems, specialized software programs were developed for the simulation and analysis of the impact behavior of these structures. These codes are used by all automotive manufacturers for the simulation of the collision tests as well as for other tests linked to the passive safety.

The structure modeling at impact type loading represents one of the most complex and difficult demands for the structural analyst, involving the modeling of dynamic action, material properties, eventual car--barrier interaction and sensitivity influence of material high strain speeds.

2. EXPERIMENTAL ANALYSIS

2.1 Preparation and testing of specimens for the determination of strain-stress characteristics

The testing of the specimens has been achieved in conformity with the SR ISO37 Standard, which is identical to ISO 37/1994 International Standard--hard rubber or thermoplastic--determination of stress-strain characteristics at tensile tests (ASTM, 2001).

For the determination of tensile strength, dumb bells specimens were used, according to the standard presented above. The geometry of the specimens is presented in fig.1.

The standardized thickness of the middle part of the specimen must be 2 [+ or -] 0,2 mm, and the length of the specimen L was considered to be 25 [+ or -] 0,5 mm. The samples have been protected against all external influences (light, heat, humidity).

[FIGURE 1 OMITTED]

Three different variants were proposed to be tested. From a qualitative point of view, all the variants had as basic elastomer the styrene-butadiene rubber (SBR), reinforced with different materials able to induce different properties, a special accent on the elastic behavior it is being put on (Ren & Vesenjak, 2005).

The compositions for the three variants of rubber are presented below.

--First variant: blend of rubber with 30 PHR powder, 200 PHR regenerated rubber and 20 PHR filler;

--Second variant: blend of rubber with 150 PHR powder, 100 PHR regenerated rubber without filler;

--Third variant: blend of rubber with 100 PHR regenerated rubber and 100 PHR filler;

The rest of materials specific for the rubber composition are protective, cure and plastification agents.

The fundamental characteristics for the three variants are listed in Table 1.

2. 2 The experimental stand for impact simulation

Following the analysis of a series of safety barriers existent on our national roads, one could observe that their performances have not been improved during the last decades, being considered too stiff and consequently leading to inacceptable decelerations during impact.

It is necessary to introduce new technical solutions in order to obtain the new safety barriers with greater possibilities to absorb energy during impact. One of these solutions may be to attach some modular elements manufactured from rubber, which could diminish the impact effects during collision.

For designing certain safety barriers in accordance with Union European Standards, one has to take into account some aspects regarding damping characteristics of different types of rubber, which should be applied on the safety barriers surface.

Results of researches regarding static and dynamic mechanical behavior of safety barriers components are presented (Jiga, et al., 2007).

In figures, 2 and 3 are presented the actual and the improved solution of a safety barrier where a rubber strip has been applied, in the middle of a span, in order to increase the absorption of energy.

[FIGURE 2 OMITTED]

[FIGURE 3 OMITTED]

As an evaluation criterion for the experimental researches, the static and dynamic strains were considered. The tests were made in order to build up a safety barrier prototype for its future use in our country (Bratu, et al., 2007).

The modular components of composite rubber, having different thicknesses were made by S.C. Arteca S.A. This material was chosen because of its low cost fabrication.

The experimental tests were made on a stand that allowed fixation of the safety barrier at its ends, control of falling height of the impactor and measurement of displacement in the impact point. The displacements were determined using the strain gauge technique. A Spider 8800 bridge having eight channels and a data acquisition card was used for displacements measurement during the impact tests, which were collected from a displacement cell.

Three different configurations for safety barriers were tested:

a) safety barrier plated with 10 mm thick rubber;

b) safety barrier plated with 20 mm thick rubber;

c) non-plated safety barrier.

The safety barrier was fixed in both ends and the impact took place in its center (Figure 4).

[FIGURE 4 OMITTED]

[FIGURE 5 OMITTED]

3. RESULTS

The data presented in table 2 showed that the impact force corresponding to the 3 m falling height in case of non-plated safety barrier is 26% and 36% greater than the ones corresponding to the safety barrier plated with 10 mm and 20 mm thick rubber respectively.

Between the two plated barriers, an increase of impact damping with 8% can be obtained in case of safety barrier plated with 20 mm thick rubber.

The displacement at the time of impact in the case of 20 mm thick plated safety barrier is 9% smaller than the 10 mm thick plated one.

4. CONCLUSIONS

A method for evaluation of the material deterioration consists in determination of the amount of energy dissipated in the material during impact. The experimental results showed that a considerable amount of impact energy is absorbed by the composite rubber layer.

5. AKNOWLEDGEMENTS

This research was supported by AMCSIT Politehnica through the research project CEEX 211/2006 ELMOSTPRO. The financial support is gratefully acknowledged.

6. REFERENCES

American Society for Testing and Materials (ASTM), (2001), Standard specification for sheet steel, zinc coated or zinc--iron alloy-coated by the hot dip process. Pennsylvania: ASTM International;

Bayton, D.A.F., Jones, T.B., Fourlaris, G. (2007), Analysis of a safety barrier connection joint post-testing, Materials and Design, April, p.1-7.

Bratu, P., Jiga, G., Vlasceanu, D., (2007), "Methods for the analysis of dynamic performance of composite modular systems attached to safety barriers", A.S.T.R.--The Academic Days, November 28-30.

Jiga, G., Vlasceanu, D., Baciu, F., (2007) Analysis of a roll over protective structure using the finite element method, The 18th International DAAAM Symposium, ISSN 1726-9679, Croatia.

Ren, Z., Vesenjak, M., (2005), Computational and experimental crash analysis of the road safety barrier. Eng Failure Analalysis;12(6), p.963-73.

Tab. 1 Elastic and mechanical characteristics

 Ultimate Tensile
 Fracture tensile Young
Variant Hardness strength strain modulus

 [[degrees]ShA] [Mpa] [%] [Mpa]

 1 70-71 900 420 200
 2 78-79 380 150 220
 3 68-70 550 220 240

Tab. 2--The results for tested samples

 [DELTA]t [delta]
Case H [m] v [m/s] [s] din [mm] F [N]

 a 1 14.91 0.014 12.06 25039.45
 2 21.52 0.016 16.73 31078.7
 3 26.35 0.015 22.32 42422.04

 b 1 15.22 0.016 10.54 21953.04
 2 21.52 0.017 15.89 29160.3
 3 26.35 0.016 20.48 39412.46

 c 1 15.37 0.018 13.80 19812.93
 2 21.52 0.012 15.31 42158.46
 3 26.35 0.012 25.33 53496.13

 F*[DELTA]t
Case H [m] [Ns]

 a 1 351.83
 2 507.83
 3 621.96

 b 1 359.09
 2 507.83
 3 621.96

 c 1 362.66
 2 507.83
 3 621.96