| | | | TORQUE X TENSION CASE STUDY | | | | ------TORSION ANGLE TECHNOLOGY------

First, I would like to thank Mr. Yaldiz and his colleagues at Norm Civata for the suggestion to post this case study here on LinkedIn. Thank you also Mr. Yaldiz, for getting authorization from upper management in your company for me to share such data. That will for sure help many of our Fastening & Joining Technology colleagues to have access to a whole new way of testing and validating bolted joints and create more efficient, less expensive and lighter assemblies that will benefit everyone…

In this Case Study, we demonstrate that accessing bolt clamp-load is no longer a hard task to achieve and that you no longer need to invest big money in sensors and testing devices and processes. Also, that you can access bolt clamp-load even remotely from joints already assembled, even is the joints are assembled thousands of miles away from you...

HOW IT STARTED:

On October 2017, Mr. Yaldiz contacted us to learn more about the referred technology after watching the video shown at the bottom of this article...

Obviously, due to my engineering background and over 20 years in this industry, I would never expect my simple explanations of the technology, to be taken at face value as they could, if delivered by Elan Musk, Ginni Rometty, Susan Wojcicki or any other big names in the tech world. For that matter, I then decided to take a different approach to answer Mr. Yaldiz’s questions and this approach was: to answer his questions on a summarized way, while offering a totally free trial! (Even knowing Mr. Yaldiz and I, are over 6,000 miles away from each other as he is based in Turkey while I'm in Michigan, USA.)

Mr. Yaldiz said he would accept the challenge and my next questions to him in order to determine if it would be possible for me to run this trial were:

1.    Do you have a way that you trust, to measure bolt clamp-load (strain-gauge, ultrasonic or load cell)?

2.    Do you have a electronic transducerized torque wrench or DC electric nut runners from where you can collect Torque-Angle traces in CSV format?

Once his answers were yes and yes, then I gave him the following tasks:

a.    Run a few samples to a certain target torque, while measuring the load with his own load-cell devices (He could not send or tell me the clamp-load results…).

b.    Once the joint was already assembled, he needed to set the nut runner to continue the tightening process and then collect the Torque-angle curves for that portion of the process in CSV file format.

c.     Run a few additional samples until the bolt fails (Ultimate torque) and give me either the curves, or simply the ultimate torque values.

d.    Send me the information of the joint along with the torque-angle curves collected in (b) and that’s all I would need…

THE TRIAL PROCESS:

Once we received Mr. Yaldiz’s files with the torque and angle points and also the joint data, we then imported these curves into our software and within 5 minutes (time necessary to make adjustments on the curves and intersection points), we already had the “preliminary results”, which had shown estimated assembling clamp-loads between 13.65 kN and 14.74 kN (at this point, we still didn't have the results that Mr. Yaldiz collected with his load cell device).

Along with these results, our software also gave us CoF (coefficients of friction) varying from 0.171 and 0.233 shown on the screen, and since I was not sure if the estimations I made for the thread friction coefficients were correct, I simply went then to the step II of this analysis...

On Step II, we now used the Torque to Fail results simply to validate if the chosen thread friction coefficients were accurate enough. This step, takes into consideration a few known physical characteristics and behaviors of any bolted joint, i.e.: property class and the yield factor (formula in the side), which represents the reduction on the amount of maximum clamp-load a fastener can sustain due to tension-torsion combined state. The higher the thread friction, the lower is the yield factor. The mathematics is somehow simple and you only need to use the thread friction coefficient you have chosen and input in this formula to find out what factor you need to multiply the minimum tensile strength of the bolt for. Once you have done it, you can then estimate with very good accuracy at which clamp-load range those bolt would have failed... Find below an example (extracted from report sent to Norm Civata):

• M8x1.25 Property class 10.9:............................. (1,040 N/mm2 tensile stress).
• Maximum load on tension only: ……….36.61 mm2 x 1,040 N/mm2 = 38,07 kN
• Estimated thread friction: …………………....................................….. 0.09 to 0.14
• True K factors using the above formula and estimated thread friction coefficients:
• For μG 0.14 and μG 0.09, Yield Factors are: 0.847 & 0.908, the corrected Max Clamp-loads achievable at failure would then be between: 32.25 kN and 34.57 kN.
• According to the Torque to Failure results, we had values on an average of 37.5Nm. With T = F.D.K, we should expect CoFs of: (K = 0.145) at Fmax = 32,25 kN and (K = 0.136) for Fmax = 34.57kN

From the results shown here for "true CoF", it indicates that the first results reported by the software were generated using too high values of thread friction coefficients, otherwise, the K factors would have fallen in between 0.136 to 0.145, but instead, they were between 0.171 and 0.233 in the first results…

Now, going back to the software we accessed each sample and, individually adjusted down the thread friction coefficient inputs until the software returned CoF values for each sample within the calculated range 0.136 to 0.145. 

THE RESULTS (charts provided by Norm Civata):

Video demonstrating the TGiro System.

>>>>POSSIBLE APPLICATIONS FOR THIS TECHNOLOGY:<<<<

Joint relaxation studies | Torque-angle analysis | Fastener Testing | R&D | Definition of assembling parameters | Failure analysis & Diagnosis | Clamp-load analysis | Estimation of friction coefficients | Residual Torque Audit | Etc...

To learn more or to request your free trial, please go to www.pcltork.com