23 Feb 23 Feb 2017 – HIPEBA presents first results on the selection of high performance steels for Road Restraint Systems
The HIPEBA technical deliverable labelled as D2.2 has focused on i) complementing the information of D2.1 and ii) selecting the appropriate high performance steels for Road Restraint Systems (RRS).
The deliverable D2.2 complements the deliverable D2.1 by providing the results of a series of tests (not available during D2.1 due to some shipping delays) on materials behaviour under tensile, strain and formability stress.
In particular, the following tests were undertaken:
- Hopkinson Bar tests: to characterise the material behaviour at high strain rates.
- Result: No reason to adopt one type of steel or another in RRS due to their behaviour at high strain rates.
- Nakazima tests: to evaluate the formability of different steels.
- Result: S700 MC AND S960 MC steels more suitable for RRS.
- Dynamic tests: to measure the toughness –ability to absorb energy and deform without fracturing-.
- Result: when estimating toughness values from the area under the stress-strain curve, the highest value was calculated for S700 MC steel with slightly lower values for S355JR and S500 MC steels.
- Test of bolted unions: to find failures in the area of the union by searching for cracks and to compare the forces used for different steels.
- Result: The behaviour of the joints under longitudinal load is correct for all materials assessed.
- Three-point bending tests: entailing a test of 6 roll formed beams
- Result: S700 MC steel has higher elastic limit and much higher force is needed for its deformation.
- Coatings: to evaluate the types of protective coating and characterising the coating layer.
- Result: DP should be rejected for RRS because their service life is not ensured by any coating technology. However, this analysis opens the door to use the DP in the future to manufacture RRS when a technology capable to apply this coating on larger size elements becomes available
The second part of deliverable D2.2 establishes a ranking of the performance of the steel chosen based on the results from the tests, and taking into account the weighting criteria for material selection. The individual ranking is built according to each selected criteria: tensile tests, Charpy test, Nakazima test, welding analysis and price.
For the selection of the proper steels within the HIPEBA project, an overall analysis must be carried out. Hence a global value for each type of steel (see values in the following table), was estimated by adding the individual values from each criterion.
In the light of these first results, and once compared with the baseline steel taken as reference (S355), the steel grade with a better performance seems to be the D500, although only slightly (0.652 points against 0.622 points).
According to the results of the analysis carried out, the S960 steel grade performs worse (0.406 points against 0.622 points) when compared to the performance of the two ‘winner’ steels (S355 and D500). This lower rating is mainly due by their lower impact toughness and their high price.
The S700 steel comes into the picture halfway between D500 and S960 steel grades. This steel provides a lower rating than the D500 due to their performance according to the Charpy Impact Test (resistance to brittle failure and impact toughness).