Oakland University is located a few minutes away from Chrysler’s corporate headquarters in Auburn Hills, MI. So, it’s appropriate that the school is home to the Fastening and Joining Research Institute (FAJRI), the only facility of its kind in the world.
“We pursue fundamental and applied research to develop and disseminate new technologies for the fastening and joining of metals, composites and polymers,” says Sayed Nassar, Ph.D., a mechanical engineering professor who serves as director of FAJRI. “[Our] objective is to enhance the reliability and safety of joints by advancing the science and technology of mechanical fastening, adhesive bonding, welding and riveting.
“Applications include automotive and aerospace bolted assemblies, adhesively bonded joints, and welded joints,” explains Nassar. “Special focus is assigned to multi-material lightweight applications for weight reduction and energy saving. [We also study] medical devices, such as [ways to stabilize] damaged human joints after spine, neck, knee or hip injuries.”
The Fastening and Joining Research Institute was created in 2003 through Congressional funding. According to Nassar, the federal government tasked the
organization with “finding ways to meet increased demand for the reliability and combat readiness of military vehicles, with trickle down civilian benefits in the automotive, energy and transportation sectors.”
Twenty faculty and students are currently active in FAJRI projects, which focus on developing advanced technologies that apply to threaded fasteners in bolted assemblies made of metals, composites, plastics and advanced polymers; adhesive bonding of laminated and fiber-reinforced composites; resistance welding of metals; and advanced riveting.
“Analytical, experimental and computer simulation techniques are used in the research,” says Nassar. “[For assembly line applications], we simultaneously consider the following [conditions] that are responsible for overall reliability and safety: Joint variables, such as materials, design, gaskets, tolerances, finish and heat treatment; fastener variables, such as coating, plating and manufacturing method; and assembly tool variables, such as type, capability, accuracy and repeatability.”
Other factors examined include process controls, such as torque-only, torque-angle, torque-to-yield, bolt stretch and elastic interaction; post-assembly loads, such as fatigue, service loads, gasket creep relaxation and vibration loosening; and environmental variables, such as corrosion, chemical, thermal and humidity.
FAJRI has worked with a variety of organizations in the past, including Chrysler, Cummins, Daimler, Deere, General Electric and the U.S. Army Tank Automotive Research and Development Engineering Center. In addition to solving assembly challenges, the organization has worked with nuclear power plants to address safety threats caused by joint leakage.
Nassar and his colleagues are currently working on a federally funded initiative focusing on the challenges of joining lightweight materials, such as aluminum, magnesium and carbon-fiber composites. They are assessing different joining methods in terms of the environmental condition effects on heat, humidity, static, dynamic load transfer capacity and joint durability.
FAJRI recently completed a study focusing on techniques for joining dissimilar materials. Using finite element analysis, they examined the pros and cons of using adhesive bonding, bolting and hybrid methods to create lap joints. The R&D effort focused on the strength and load transferring capacity of each assembly process.
Another recent project examined how to adapt highly repeatable aerospace bolt-tightening technology to automotive manufacturing. The real-time ultrasonic process uses high-frequency sound waves to estimate the amount of force a bolt provides to clamp two components together. Several hundred measurements per second permit feedback control to achieve consistent clamp force. According to Nassar, the process has the potential to reduce variation in clamping force from +/- 30 percent, through using torque as a measurement of clamp load, to as precise as 1 percent using the ultrasonic technique.