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B.3.21.1 Impact Attenuator Testing

B.3.21.1 IA Test Method.doc
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B.21.1 Impact Attenuator Test Method Question # 1: According to the rule B.3.21.1, the team must submit test data to show that their Impact Attenuator, when mounted on the front of a vehicle with a total mass of 300 kgs (661 lbs) and run into a solid, non-yielding impact barrier with a velocity of impact of 7.0 metres/second (23.0 ft/sec), would give an average deceleration of the vehicle not to exceed 20 g’s with a peak deceleration less or equal to 40 g’s. To simulate such a scenario, I would need to attach a 300kg mass to my impact attenuator and raise it to a height that is derived from the conservation of energy. Due to the lack of facilities, I am unable to raise it to this required height. To overcome this, I would like to drop a heavier mass from a lower height. Is this acceptable? Answer # 1: We purposely do not specify how a team must test their Impact Attenuator because different universities have different levels of facilities and capabilities. How you test your Impact Attenuator is up to you. The better your test methodology, the easier it will be to convince those grading your report that you deserve a high grade. Question # 2: I have a question regarding the Impact Attenuator Testing method. Does the test have to be a 661lb object striking a solid barrier or can it be a smaller weight with a higher velocity? Answer # 2: The 2009 Rules do not specify how the test data should or should not be acquired. They do not even require that the test be a dynamic test. That is up to the teams to decide. However, a strong case could be made for stating that energy is energy, and that for a dynamic test, a smaller mass at a higher velocity is equivalent! Question # 3: Can we use a press to simulate the impact attenuator test? Answer # 3: The Rules do not specify what form of test you must use. We left it open because of the different levels of equipment that universities have. There are many test methods available to you and it is up to each team to select one appropriate to your test equipment and resources. Just make sure you clearly explain your test method and supporting calculations to relate it back to the design requirements. Yes, a steady state crush test with a press can be used for your impact attenuator testing. Question # 4: Rule 3.21.1 states the impact attenuator has to be designed for a total mass of 300 kgs (661 lbs). Can we scale down the test for the actual test we perform? In other words, can we test half the mass with half of the crush area? We feel this would be safer and more practical, especially if we have to go through many iterations of design if our current one fails. Answer # 4: The mass and velocity specified in the rules are to set the design requirements for the impact attenuator. They are not intended to specify the only test method for evaluating your design. You are free to modify the mass and velocity as long as you achieve the required energy level. Also, you are not required to conduct a dynamic impact test. A steady state crush test could be conducted on your impact attenuator. There are many test methods available to you and it is up to each team to select one appropriate to their test equipment and resources. Just make sure you clearly explain your test method and supporting calculations to relate it back to the design requirements. However, although the Rules do not specify that the tests for the IA Data Report MUST be done on full size test pieces, the Rules Committee intended that to be the case, and Rules B.3.21.3 and B.3.21.4 imply that tests on full size pieces are required. Also, the consensus of those who grade the Impact Attenuator Reports is that scaling down the size of systems such as Impact Attenuators is extremely difficult to obtain accurate results. This is because there are many factors involved that cannot be scaled correctly. It is especially so with composites. To quote one of the reviewers: “Scaled model testing is too complicated, and with composites even more so to capture the right failure modes in scale.” And from another grader: “In my experience, it is very difficult to relate results from a scaled assembly test to full size assemblies unless EVERY aspect of the design is scaled (fasteners, bond lines, etc.) due to complicated failure modes in an assembly. I would give a team a lower grade if they tested a scaled-down IA assembly and did not provide a very convincing explanation of their correlation methods.” Therefore, as we have not been specific in the Rules, scaled-down testing of the Impact Attenuator is not prohibited. However, teams that do not run tests on full scale IA’s will need to justify in their report, that the scaling has been done correctly, and will be graded accordingly.”

Keywords:

B.3.21, B.3.21.1, IA data, IA method, IA testing, impact attenuator