ATA'S "THE EXPERT" NEWSLETTER - ISSUE OF MAY 2021



In this Issue:

ATA Staff Says Goodbye to a Legend

Race Car Impact Attenuator Testing

3D Photographic Reconstruction Process

This Issue's Toolbox Feature - Marine/Boating

































ATA STAFF SAYS GOODBYE TO A TRUE LEGEND





We at ATA were saddened to hear of the passing of a friend and work associate, three-time Indianapolis 500 winner Bobby Unser. He was a legendary figure in his chosen profession and an inspiring man to those he crossed paths with.

Amongst his post-racing career activities, Mr. Unser was a consultant and testifying expert in cases that covered a wide range of vehicular incidents and performance evaluations. On one hand, while just lending his name and presence as a racing legend to our investigations gave ATA enhanced credibility; it was his intuitive feel for how to execute and consistently perform complicated testing scenarios that always made working with him a special treat.

Mr. Unser’s work with ATA occurred over several decades and involved vehicle handling, vehicle dynamics, driver reactions, vehicle braking and tire testing. His advice and assistance with testing preparation and analysis was always invaluable.



So, we say goodbye to a good friend, a great champion and a valued business colleague. You will be missed, but not forgotten!








BACK TO TOP
















COLLEGE RACE CAR IMPACT ATTENUATOR TESTING




This spring, ATA Associates helped a team of five University of Houston students test two race car impact attenuators as the capstone project for their senior year of study in mechanical engineering. ATA provided facilities, instrumentation, and expertise in tests comparing a standard, commercially produced attenuator, and a novel attenuator designed and built by the students. Each attenuator had the form of a truncated pyramid with a volume of about one cubic foot – the commercial attenuator was made of plastic foam; the students’ design was made of aluminum honeycomb.

The students contacted ATA in the fall of 2020 with their request for assistance and a set of objective attenuator testing and performance criteria formulated by the Society of Automotive Engineers (SAE) to guide the project. Although the students’ design and testing efforts were primarily aimed at fulfilling academic requirements for graduation, if it tested successfully, their novel attenuator design would also be eligible to be incorporated into the university’s Formula SAE race car which was being built for entry into a national collegiate race coming up this summer. (More information on the University of Houston’s racing efforts can be found at: https:www.uhcougarracing.com).

As the students’ attenuator was taking shape in early 2021, ATA staff members worked to devise a means for releasing a mass of 661 lbs. from a drop-height of 8.2 feet to generate the specific impact energy prescribed by the SAE criteria. That task proved to be more challenging than it seemed at first, but it was eventually accomplished using a steel barrel, filled with lead and sand, sliding on vertical pipes as guide rails. ATA personnel were also responsible for selecting accelerometers from ATA’s inventory of electronic gear to measure decelerations in the tests – just one of several measures of attenuator performance specified in the SAE criteria. Although these tasks were consistent with ATA’s many years of corporate experience in vehicle crash testing and analysis, the project was, nevertheless, a genuine learning opportunity for individual ATA staff members as well as for the students. The project also provided a good opportunity to test cameras capable of recording high frame rate video (960 fps) which had been added to ATA’s arsenal of test equipment in late 2020.

The tests of the attenuators produced a mix of surprising results. The commercial attenuator and the students’ experimental attenuator both produced decelerations which exceeded 70 g. The actual peak deceleration was not captured in either test, because the “gain” of the accelerometer amplifiers had been set too high. The SAE test criteria seemed to imply that a commercial attenuator would generate a deceleration of no more than about 50 g, so in the pre-test instrumentation set-up and calibration, a gain setting that could capture decelerations up to 70 g was thought to be a judicious choice.

Although the high gain settings cropped off the top-most parts of the deceleration signatures for both attenuators, that cropping did not hide an unexpectedly high level of complexity in both signatures. The strip chart recordings of accelerometer output showed that irregular progressive crushing of the attenuators generated large magnitude, high frequency variations in both deceleration traces. Similarities in the complexity of the deceleration traces, however, belied any similarity in the effectiveness of the two attenuators. High frame rate video recordings showed that the commercial attenuator experienced a large, but almost completely reversible, deformation during the impact which effectively prevented intrusion of the attenuator into its steel mounting frame. In contrast, the students’ attenuator was much stiffer in its impact response, which resulted in an unacceptable level of intrusion of the attenuator into its steel mounting frame which represented the occupied part of the car.

The intrusion of the student attenuator constituted a “failure” of the experimental design according to the SAE criteria and precluded it from being incorporated in the university’s race car, but it did not equate to a failing grade for the project. The students, though surprised and disappointed, were able to accept the tests result philosophically and seemed to embrace the cliched fact that life’s best lessons usually come from our failures, not our successes.


BACK TO TOP






















3D PHOTOGRAPHIC RECONSTRUCTION PROCESS



In the beginning, there were photographs… or at least most incident reconstructions begin with photographs. ATA has received photographs from clients, and we continuously ask the question, “Why did they take so few pictures of the incident scene or vehicles?” We encourage clients to be as thorough as possible in taking photographs. Take photos from all angles and views, from different distances, and then take video as well. Hopefully, at the end of this article you will have an appreciation of why that is so important.

Many facets of the accident reconstruction process are directly affected by the number of photographs available; particularly when using photogrammetry to build 3D models. The more pictures that can be utilized, the easier the process is and the greater the chances for an excellent final product. Image 1 is a 3D point cloud model of an incident truck. It keeps all dimensional characteristics of the actual truck and is ready to be put into the reconstruction software to recreate the incident. The model was created using over 200 pictures. We recommend taking at least 200 pictures of each incident vehicle and at least 300 photos of a given site. Using less than 100 pictures means there is only a 50% chance of success in rendering a useful model and the quality could be limited by lack of photographic coverage.


Image 1 and 2: 3-D Point Cloud Model of Incident Truck (1: Exterior View; 2: Interior View)

Now that we have a high quality3D rendering of the incident truck, we begin the process of printing a 3D model. The 3D point cloud model is then transformed into a file format that is ready to be uploaded to a 3D printer. Models have multiple purposes for helping clients and a jury to understand the case facts. This rendering process begins and ends with photographic coverage.




Image 3 and 4: 3-D Model of Incident Truck (3: Exterior View; 4: Interior View)


BACK TO TOP
























Over 49 years ago, ATA’s original focus was on investigating boating and marine incidents, as well as studying boating safety issues. We have been involved with advanced level water craft testing and have been working maritime/shipping cases for decades.

To find out more about ATA’s history and experience in this field, visit:

ATA Toolbox - Boating/Marine.


BACK TO TOP