Quantum mechanics is one of the theoretical foundations of modern physics. It is the science that studies the laws governing the motion of microscopic particles. It has enabled people to move from the macroscopic level to the microscopic level of the material world, and has revolutionized our understanding of the structure of matter and its interactions. It has laid the foundation for modern fundamental theoretical research, including atomic physics, nuclear physics, molecular biology, and nonlinear optics.
Timken, a leading global bearing manufacturer, applies quantum mechanics research methods to bearing development.
Timken researchers Vikram Bedekar (left) and Rohit Voothaluru are working to improve bearing manufacturing processes by using neutrons on HFIR's HB-2B.
At the U.S. Department of Energy's Oak Ridge National Laboratory (ORNL), researchers at Timken hope to find ways to extend bearing life by using neutron scattering technology to better understand how internal residual stress generated during manufacturing affects bearing life.
Bearings are manufactured with high precision, small tolerances, and perfect fit, resulting in a long design life under extreme loads and long-term use and operation. Bearing performance is particularly important in safety-critical fields such as aerospace and mining. Although residual stress represents a small internal elastic deformation within the material structure, it can significantly impact the lifespan and reliability of bearings.
"Residual stress is primarily generated by the manufacturing process," says Vikram Bedekar, a materials expert at Timken. "All production processes, including molding and high-temperature processing, generate residual stress. If the stress is too high, the part will deform, and may even become so warped that it is unusable or unrecoverable."
Generally, bearing manufacturing begins with forming a ring from steel. Next, a lathe is used to obtain the required dimensions. Bedka explains that up to this point, this part is still "green," meaning it's still soft and unusable. Subsequent heat treatment hardens the material. Finally, a lathe or grinding machine is used to remove excess material to complete the part.
Large Timken® bearings are commonly used in industrial applications. Because neutrons have strong penetrating power, they can penetrate deeper into the metal than similar methods, such as X-rays. Residual stress in each bearing stems from asynchrony in the manufacturing process. (Image credit: ORNL/GenevieveMartin)
Because of their strong penetrating power, neutrons can provide researchers with unique information about the atomic structure of materials. Previously, researchers used laboratory X-rays to inspect bearings, but they could only probe a thickness of 200 micrometers inside the bearing. Neutrons allow them to observe the entire bearing much deeper.
“Standard X-ray intensity is insufficient to completely penetrate a section. Neutrons are the only way to see the entire interior,” Bedekar said.
Using the Neutron Residual Stress Mapping Facility (NRSF2) HB-2B at ORNL's High Flux Isotope Reactor (HFIR), researchers were able to map the different internal stresses generated at each step of the manufacturing process. The neutron data allowed them to observe how the stress state of the bearing changed with each iteration. The researchers said they chose NRSF2 because of its unique capabilities suited to this type of experiment.
"We were looking for ways to utilize residual stress maps," said Rohit Voothaluru, a product development specialist at Timken. "We came to NRSF2 because we felt we could get a general idea of the situation for similar samples and see the residual stress."
The team stated that they intend to use residual stress mapping data to improve the computational model in order to enhance internal stress prediction and optimize manufacturing processes.
Bedekar stated, "Ultimately, we can adjust the machining process or residual stress based on the performance of different bearings."
“We have a computational model today that can provide qualitative direction. However, to build a more fundamental, quantitative model based on actual physical processes, while also capturing real-time subsurface residual strain, requires extensive empirical validation. We hope to validate our model and take it to a new level,” Voothaluru said.
HFIR is the U.S. Department of Energy's Office of Science User Facilities. UT-Battelle manages ORNL for the Department of Energy's Office of Science. The Office of Science is the largest single supporter of basic research in the U.S. physical sciences and is working to address some of the most pressing challenges of our time.
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