Cetim Cobra Software

When security comes firstHumans have been using screwed joints for thousands of years. These devices have been a part of our daily lives for so long that we tend to forget how important they are. Cutting-edge technologiesScrewed joints have evolved considerably since the days when bolts and screws were manufactured manually, and when customers could only choose very basic products. Recently, companies like Nord-Lock Group have considerably improved the bolted joint technology by inventing, for example, locking systems.

In addition, the focus has increasingly shifted to the actual analysis of joints. “In the past, people used to decide upon a certain size of fastener based on their experience alone, and, fingers crossed, it would work,” explains Bill Eccles, the mechanical engineer behind Bolt Science having more than 20 years of specialized experience in bolted joint technology. “Nowadays, people focus more on analysis and making sure things work before products are built and sent out into the market.”The tightening systems have also evolved a great deal. The multi-jackbolt tensioners (MJT) of the Superbolt tightening system encapsulate innovative technology for tightening bolts and stud bolts. New- generation hydraulic tensioners facilitate and improve tightening since they do not generate any torsional stress, which means no reaction arm and no adverse lateral effect. Multiple screws are tightened simultaneously and the assembly remains flat. New global R&D centerTo consolidate its expertise, Nord-Lock Group opened a research and development (R&D) technical center in 2011.

Based near Lyon, France, this global center sets out to support application engineers working in the field throughout the world to help customers conduct thousands of tests and checks. The center performs advanced calculations, characterizations and trials with partner laboratories such as the CETIM (Technical Center for Mechanical Industries).

The lab is equipped with measuring instruments, in particular the Junker test, considered the most rigorous vibration test for threaded joints.“In our laboratory, we carry out vibration, torque and preload tests, explains Zouhair Chaib, Nord-Lock Group’s R&D center manager and a technical expert in secure joints. “We can also test the behavior of systems, for example to ensure that the proposed solution will work properly and be reliable. The Junker test allows us to measure the stress states and the deformation of joints subjected to alternating transverse movements under the screw head or under the nut.”The R&D Center uses Cetim Cobra software, a solution for designing and calculating pre-loaded screwed and bolted joints, which has been the calculation standard for many years in various mechanical sectors.

Understanding, capitalizing, validating“During the design phase, we use the solution to gain insight into certain phenomena and to validate internal business rules,” says Chaib. “Parametric studies serve to analyze various scenarios and thus deduce simplified models which we make available to other technical centers throughout the world. This furthers our support mission since sales engineers have neither the time nor the resources to carry out complex calculations. It also helps to capitalize on the company’s technical expertise.”Simcenter also helps investigate failure situations. “We are sometimes confronted with complex breakage cases, in particular for multi-fastener joints,” Chaib explains.“Weaknesses in screwed joints generally have two main sources: spontaneous loosening caused by vibrations and dynamic loading effects, and slackening caused by preload loss as a result of settling and relaxation.

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To propose effective repair solutions, the process that led to the failure must be understood. For this purpose, we need to imagine the most likely scenario possible. This means defining different possible cases, then simulating them virtually to determine the most viable scenario.”Nord-Lock Group uses Simcenter 3D as an alternative to physical testing. “For some applications, physically testing a joint is quite simply not feasible,” Chaib says. This is the case both with giant structures and very small structures. Here, we turn to digital technology.”Nord-Lock Group’s plans for the future include custom application development using the NX application programming interface. “In the future, we plan to use NX Open to develop business tools that integrate Nord-Lock Group’s design rules, and then to make them available to sales engineers on tablets,” says Chaib.