Synaptic | product engineering

Il crash test e la legge di Murphy: Che cosa hanno in comune?

Concerning the #CrashTest story, one cannot fail to mention the scientist and engineer Edward Aloysius Murphy, the very one from the aforementioned ironic #Floyd's Laws.

His most famous phrase "If there are two or more ways to do something, and one of those ways can lead to a catastrophe, then someone will do it that way" (which later became The Second Murphy Law) was uttered in the 1950s during the very safety tests that Dr. John Paul Stapp, a US AIR FORCE physician, decided to do on himself to assess the effect of high stresses on the body while operating the new jet planes of the time.

Let's see what history tells us....

Already after World War II, the first tests were carried out on anesthetized animals, corpses and human volunteers. John Paul Stapp decided to study firsthand the effects of acceleration and deceleration, typical of the new jet aircraft of the time, on the human physique. With his team of engineers, he built a sled equipped with an aircraft thruster that enabled it to reach a speed of 1000km/h in just 5s and then stop in less than 1.5s. For this reason he has been called "the fastest man in the world." During sled tests, Dr. Stapp was able to reach accelerations of 40g, with devastating results to say the least: fractures of the neck and numerous ribs and detachment of the retina. His studies have served to significantly improve safety in aviation and transportation in general.

This is where scientist and engineer Edward Aloysius Murphy, a soldier in the United States Army Air Corps who was in charge of the technical team that was responsible for organizing the tests, comes in. At that time, the reliability of experimental testing was not what it is today, nor was it expected to be. Particularly unreliable was the assembly of the sensors by the technicians, who often made mistakes in the way they were assembled, rendering the test performed essentially useless. This led Murphy to pronounce, "If there are two or more ways of doing something, and one of those ways can lead to a catastrophe, then someone will do it that way." Later, Colonel Stapp declared, "We do all of our work in consideration to the Murhpy's law" (Source: The Fastest Man on Earth Why Everything You Know About Murphy's Law is Wrong by Nick T. Spark).

Image taken from (CC BY-NC-ND 2.0)

Image taken from (CC BY-NC-ND 2.0)


The evolution of the Crash Test

But then what do Murphy's laws have to do with crash-testing? Although the field in which Stapp and Murphy worked may seem very distant, their work significantly influenced many areas, including automotive safety.

A lot of progress has been made in the field of safety since then, thanks in part to Crash Tests, which have varied the approach criterion. We have gone from the first geometric approach where the passive safety of a vehicle was associated only with maintaining the structural integrity of its passenger compartment, to one of type biomechanical, linked to the health of the driver and passengers.

While the former was focused on the vehicle and not the person and was completely disconnected from the limits of human tolerance following blunt trauma, later, using biomechanical criteria, the focus shifted to verifying that the stresses experienced by the occupants were below the limits of human tolerance in the event of an accident.

Biomechanics is the subject that studies the application of the principles of mechanics to biological systems and, in particular, analyzes the behavior of physiological structures when subjected to static or dynamic stresses. Specifically, impact biomechanics analyzes injuries that can occur during traffic accidents and the related mechanisms that cause them (forces and accelerations acting on various parts of the body). The biomechanical approach thus offers a much more comprehensive concept of safety, understood as crashworthiness, or impact resistance: the goal is the mitigation of injuries to a vehicle occupant caused by an impact against an external obstacle or another vehicle.

Over the years, #Crashworthinessanalysis has evolved, and from just crash tests carried out at the end of the design of new vehicles, when there are now limited possibilities to intervene, we have moved on to introduce advanced simulation techniques directly in the study phase-a type of analysis where crash tests are reproduced virtually. We are talking about Explicit Nonlinear Simulation , an analysis that allows us to analyze the behavior of each individual component during a crash-how it deforms, when it collapses, how it interacts with other components. This is a totally different point of view than crash testing done in the lab where the analysis of the results only allows us to see the outcomes of the impact and where the control of what happens during the impact is limited by the number and position mode of the sensors and cameras (and thanks to Murphy we know how that might turn out...). Not to mention that with virtual simulation it is possible to evaluate the influence of new structural solutions in a relatively short time by limiting the production of prototypes or mockups that will by necessity be scrapped after testing.

As virtual crash testing evolves, there will be increasing savings in both time and cost of product design and implementation, with ever higher vehicle quality.

Does a future of extremely safe vehicles await us? It is difficult to arrive at 100 percent reliability of a transportation vehicle; too many unforeseen factors can still intervene.

What is certain is that today the virtual approach has become indispensable, an approach that charts the path to increasingly predictive design. We engineers must learn to support companies in their design by intervening more and more in the preliminary stages, even already in the conception and feasibility analysis of a project. Only in this way will we be able, together, to combine innovation with safety, economy with quality.