Crash-testing rivets

August 07, 2014

Steel, aluminum, magnesium, fiber-reinforced plastics: cars are built from a wide array of materials today. These have to be connected with each other reliably. To wit: even if the joints become loose in a crash, passengers must face no greater risk of injury than before. Manufacturers use their welding equipment for cars made entirely of steel. However, if you want to combine steel together with aluminum, for example, or steel with plastic materials, then conventional welding techniques are entirely unsuited, plain and simple. Automakers therefore resort to mechanical connections instead, such as rivets.

Very often, connections are the weak points: in a crash, they are typically the first thing to fail. And since a car has about 3,000 to 5,000 joints, manufacturers strive to minimize this risk. This is why automakers use simulations to verify if the various connection points sustain these stresses in an accident. Yet how stable are they in the first place? In many cases, the calculations can clearly predict how the individual joining points will perform, but not for every type of strain, though. If the joined components become bent (experts refer to this as a "flexural load" or "bending load"), then the simulations are quite often off the mark. For example, such computations could ascribe a greater load capacity than the rivets can actually bear under real emergency conditions. This uncertainy is something automakers greatly wish to eliminate.

Realistic projections through a new model

Researchers at the Fraunhofer Institute for Mechanics of Materials IWM in Freiburg - working together with their colleagues from the Laboratory for Material and Joining Technology LWF in Paderborn, and the Association for the Advancement of Applied Computer Science GFaI in Berlin - have essentially eliminated this drawback now, at least in the simulations."We have further engineered a model that allows us to forecast rivet performance more reliably - both with slow and fast bending loads, as well as with pull and shear forces that emerge when the joined components become shifted, relative to each other," explains Dr. Silke Sommer, Group Manager at IWM. For this purpose, researchers produced individual "sample components" from a variety of materials, connected them with rivets, and then applied stress. They bent them in a variety of directions, and pulled them and pushed them at varying speeds. They then integrated the performance of the rivet points into the mathematical equations."These equations contain various parameters - to account for the different materials and their densities, for instance," Sommer says. The researchers at IWM and LWF studied about 15 different combinations of materials. Based on these data, their colleagues at GFaI prepared projections for other similar material and density combinations.

If car manufacturers now want to calculate how the rivets perform in the event of an accident, then as a rule, they simulate the crash first. What forces appear at which points on the car? If these data are known, then the engineers can determine - for each rivet - whether it could withstand the strains at precisely this point or in that position. The model is finished and automakers can already use it, and therefore make their cars even safer than before.
-end-


Fraunhofer-Gesellschaft

Related Steel Articles from Brightsurf:

How soft hair deforms the sharpest steel blades
Why do the edges of a steel razor dull from cutting far softer materials?

HKU super steel project attains major breakthrough
The Super Steel project led by Professor Huang Mingxin at the Department of Mechanical Engineering of the University of Hong Kong (HKU), with collaborators at the Lawrence Berkeley National Lab (LBNL), has made important breakthrough in its new super D&P steel (produced using a new deformed and partitioned method) to greatly enhance its fracture resistance while maintaining super strong in strength for advanced industrial applications.

Making stronger concrete with 'sewage-enhanced' steel slag
Researchers examined whether steel slag that had been used to treat wastewater could then be recycled as an aggregate material for concrete.

Buildings can become a global CO2 sink if made out of wood instead of cement and steel
A material revolution replacing cement and steel in urban construction by wood can have double benefits for climate stabilization.

Finding out the factors that most influence the steel corrosion in reinforced concrete
This process causes structures to deteriorate internally and can even cause buildings to collapse.

Corrosion resistance of steel bars in concrete when mixed with aerobic microorganisms
Dissolved oxygen in pore solution is often a controlling factor determining the rate of the corrosion process of steel bars in concrete.

Scientists invented how to improve steel properties by 100 times
Scientists from Tomsk Polytechnic University developed a new method of ion implantation that dramatically expands the application of the alloying process in the industry.

C. difficile resists hospital disinfectant, persists on hospital gowns, stainless steel
Surgical gowns and stainless steel remained contaminated with the pathogen Clostridium difficile even after being treated with the recommended disinfectant.

30 shades of steel: Scientists develop 'cheat sheet' for the creation of new steels
Researchers from the National University of Science and Technology 'MISIS' developed a database that will help create new grades of steels.

Metal foam stops .50 caliber rounds as well as steel -- at less than half the weight
Researchers have demonstrated that vehicle armor using composite metal foam (CMF) can stop ball and armor-piercing .50 caliber rounds as well as conventional steel armor, even though it weighs less than half as much.

Read More: Steel News and Steel Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.